Reprinted From The FOA Newsletter Section "Good Question!"
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Updated 11/21
Manufacturing
Guide?
Q: Is there a guide published by FOA that provides
insight as to the process of fiber optic manufacturing? It's
my understanding that the guide stresses quality and controls
to ensure performance and reduce product loss?
A: We do have a guide
for manufacturers. It is mostly aimed at communications
systems and components manufacture. Here
is a link to download it.
Reflectance
Q: What is the importance of reflectance and all the other numbers in installing and trouble shooting a fiber circuit?
A: Reflectance has always been a secondary issue to connection
loss but has some important issues that need consideration. There are
two basic issues with reflectance, affecting with the output of laser
transmitters and creating background &#;noise&#; in a fiber link.
Reflectance can interact with the laser chip itself, causing laser
transmitters nonlinearities or random fluctuations in the output. The
background noise is a secondary issue, but can be seen in ghosts in an
OTDR trace. The light bouncing back and forth in the fiber that causes
ghosts will be added to the signal at the receiver end, adding noise to
the actual signal. Both these effects are more significant on shorter
links, for example FTTH or LANs using PONs (passive optical networks).
We always recommend using APC (angled physical contact) connectors on
short SM links. And most short SM networks do use APC connectors.
FOA tries to stick to the definition that reflectance is the light
reflected from a connection but some others call it &#;return loss.&#;
Return loss has been defined generally as the combination of reflectance
and backscatter from the fiber, and that&#;s how OTDRs measure return
loss. Standards vary in the definition sometimes.
Here is a FOA Guide page on reflectance that gives the basics and
explains how it is tested.
https://foa.org/tech/ref/testing/test/reflectance.html
Electromagnetic Interference
Q: Is there and electromagnetic interference with optic cables?
A: The fiber is glass and the cable is plastic, neither of
which are affected by electromagnetic interference. There is a cable
used in electrical transmission lines called OPGW- optical power ground
wire - that has fiber inside a wire conducting high voltage - doesn&#;t
bother the fiber at all.
How Light travels In An Optical Fiber
Q: Is there a generalised ratio between
the length of an optic fibre and the length of the path actually taken
by a light pulse inside that fibre? If yes, do OTDRs factor in such
differences in any way? or they such sown the length of the actual path
of the light pulses?
A: Each optical fiber has an effective
independent of refraction. The index of refraction is the ratio of the
speed of light to the speed of light in the material: n=c/v where
n=index of refraction, c=speed of light in a vacuum and v=speed of light
in the fiber.
For an optical fiber, the manufacturer measures the index of refraction
which is usually in the range of 1.47. Corning SMF-28 singlemdoe fiber
for example is specified at 1. @ nm and 1. @ nm.
So if you use the equation above, the speed of light in SMF-28 fiber for
a nm pulse is c/n or 300,000 km/s divided by 1. = 204,500 km/s.
When an OTDR measures length, it actually measures the time its test
pulse takes to go to the end of the fiber and return, so the distance is
2X the actual fiber length. The distance is speed x time.
If a fiber is 1 km long and the speed is 204,500 km/s, the time
forlight to travel the 1km is 1/ = 0. seconds or about 5
milliseconds.
OTDR will measure that fiber as 10 ms becasue its pulse has to go both
ways, and it would calculate the length as i km, using that effective
index of refraction of 1..
Back to your original question, the index of refraction is the generalized number based on how light travels in the fiber.
Minimizing Latency
Q: Latency a term that is widely used today. If we manage to
make the light travel without interruption we will achieve that the
speed is perfect, but the equipment (router, OLT, firewall, etc)
generates a processing that takes some time, do you think that LATENCY 0
will be achieved?
A: The work on achieving minimal latency has been gong on for
decades, primarily driven by the computerized stock traders who rely on
microsecond trading. One recent project used an experimental fiber with a
hollow core becasue light travels 50% faster in the air than glass.
Most low latency networks try to use the longest fiber links possible
using submarine cable technology because the electronic switching takes
too much time. But most electronics require digital signal processing in
the transceivers which takes time, switches to the trading computers
takes time and while you can minimize it all, it can never reach &#;0&#;.
Wavelengths
Q: What is different between nm and nm
A: Those are the two wavelengths used with singlemode fiber.
They are used because they were two wavelengths that the fiber would be
singlemode (>nm) and wavelengths that it was easy to make solid
state lasers 40 years ago when they were introduced. Longer
wavelengths like nm have lower loss in the fibers so the
fibers for very long distance links are optimized for nm
Managing And Maintaining a Fiber Optic Cable Plant During Its Lifetime.
Q: Are there guides / recommendations for optic fibre cable
life cycle management? (outside plant) including rehabilitation /
replacement timelines together with factors that may alter those
timelines ( such as seismic activity, extreme weather, human
activity-induced fibre cuts etc) also including typical performance
deterioration over the life cycle, and the performance levels at which
replacement / rehabilitation happens. Or does it happen (and is it
normally expected) that operators replace entire sections of fibre (say
400 km) as part of routine maintenance?
A: There is a saying here in the US that in fiber optics &#;the most common cause of failure is &#;backhoe fade&#; in underground cables
and &#;target practice&#; for aerial cables.&#; In other words, damage
caused by humans. We know of many fiber optic cable plants that have
survived natural disasters like earthquakes - in fact there is a lot of
work today using regular cables used in communications to monitor for
seismic activity. Fire can be a problem in remote areas, but often it&#;s
because the poles are burned causing the cables to fall.
Over the years we have questioned cable manufacturers about the lifetime
of fiber optic cable. They don&#;t like to make definitive statements but
we have been told that based on the cables installed in the past that
40 years is a probable lifetime for most cables. There are certainly
cables in use today that are over 30 years old already. The glass fiber
is not a problem, it&#;s the protection from the cables that will
eventually fail. Installation techniques can have an effect on the
longevity. For example splice closures should be sealed properly to
prevent ingress of moisture or dirt. Cables should not be installed with
bends below the rated bend radius or with excess tension.
FOA has always told users that fiber optic cables do not need maintenance (https://foa.org/tech/ref/user/maintain.html),
a response to some people advocating periodic inspection and cleaning
of connections, for example. That&#;s just more likely to cause damage.
When an accidental break in a cable occurs, we have guidelines for restoration (https://foa.org/tech/ref/restoration/rest.html), and planning for restoration when building the cable plant is very important.
Someday you will certainly want to replace cables, often well before the
lifetime of the cable, but generally because you need more fiber or the
older fiber will not support the network speeds you want for upgrades.
Planning for more fiber by installing more cables can be eased by
installing spare underground ducts when first installing cables - here
in the US, we call this &#;Dig Once&#; (https://foa.org/tech/ref/OSP_Construction/Underground_Construction.html). Testing fibers for higher speeds is called "fiber Characterization&#; (https://foa.org/tech/ref/testing/test/CD_PMD.html) and is routinely done when speeds above 10G or certainly 100G are considered for older fibers.
Knowing that the lifetime of fiber optic cable plants are ~40
years, it makes sense to plan ahead for future applications, installing
lots of fibers, leaving lots of open duct space and choosing network
architectures that will not obstruct upgrades. See the article on
Netly's network above.
Transmitting Multiple Data Types
Q: How do you integrate fiber optic digital communications with other sensing and control systems and platforms?
A: Fiber optic networks generally have lots of bandwidth and
sensors and control systems generally do not require much bandwidth. The
mixing of data streams is generally done by multiplexing the data using
electronics on each end, but one can also do it with wavelength
division multiplexing.
Single Fiber DWDM
Q: Can you do bidirectional links on a single fiber with DWDM? (Dense Wavelength Division Multiplexing)?
A: A company Called Edge Optical Solutions sells
multiplexers for bi-directional DWDM on one fiber by using
adjacent wavelength channels for each direction. It is good to ~400km
with coherent transceivers but cannot use fiber amplifiers for
repeaters.
Identifying Users On A PON Network
Q: How or what testing tool or technique can I
use to verify whether there is a live customer w/ONT
working on any fiber i may select @ a splice
enclosure prior to getting further down the cable
and to the MST service terminal. All our
fibers have light on them leaving the CO so when we
go into a splice enclosure to pick a fiber to
connect a drop to, to service a home, they are
usually all lit up in that enclosure.
A: The simple answer for a tool or technique
that can tell you if a customer is connected on an
output of a PON splitter is &#;documentation.&#; If you
know where each fiber is connected going downstream.
Then the IT person who programs users into the
system can tell you if that fiber is connected to a
customer. There is a possibility that there is a
test solution. Have you ever heard of a &#;fiber
identifier&#;? It&#;s a gadget that can tell if there is
signal in a fiber and some can identify the
direction it comes from. What I don&#;t know if the
unit can somehow indicate bi-directional traffic.
Nobody we contacted seems to know either.
Slow
Internet After Conversion From DSL To FIber
Q:
A:
Minimum
Link Length
Q: I have a question regarding minimum fiber optic
distances for horizontal runs. Is there a minimum distance for
a horizontal fiber optic run? Any information regarding this
would be greatly appreciated. Thank you for you help!
A: The answer to your question is for the most part no,
there is no minimum distance for a fiber optic link. For
example, fiber is used in offices, data centers, etc.
sometimes connecting equipment on a single rack. And there are
many fiber optic links used on platforms - aircraft,
helicopters, ships, etc. - and in command posts.
Most of the Ethernet standards are based on a 2m minimum, but
also most are defined by a maximum length. For multimode
systems, the max length is mainly a bandwidth issue, so
shorter links are no problem.
For singlemode links, the bandwidth is not an issue, it&#;s the
power budget, limited by the transmitter power and receiver
sensitivity, translated into the loss of the cable plant. But
for receivers, often they have not only a minimum input power
limited by their baseline noise but also a maximum power they
can have before saturating and causing high bit error rates.
See &#;Power
Budget&#; on this page in the FOA Guide. So if a
singlemode link is short, the receiver can be overloaded so an
attenuator is used at the receiver.
There is a secondary problem with singlemode systems,
reflectance. Reflections from connections can cause problems
with both transmitters and receivers, a topic covered in the
link given above. The reflectance problem can be solved with
APC connectors.
The FOA
Guide has many pages on links, networks, reflectance,
testing, etc. that you may find helpful.
What
Is A Ring Network?
Q: If according to the TIA or ISO structured cabling
standards the fiber optic campus backbone must be
star-hierarchical type, how should a fiber optic "ring" be
built? to always ensure connectivity on a LAN?
A: A &#;ring&#; network consists of a series of links
connecting equipment (nodes) in series until the last one
connects back to the first. Since the links are communicate in
both directions, the network can still operate if any one
cabling link or equipment fails. Today, survivability is
usually ensured by using a &#;mesh&#; network; the architecture of
data centers, the Internet or phones. In addition to having a
series connection of nodes, there are other interconnections
that provide for multiple alternative paths. See Networks
in the FOA Guide.
Crossed
Connections
Q: If a FO connector is crossed connected i.e Rx
connected Rx and Tx to Tx at both end, will it works?
I know in theory it will not due to light circuits
arrangement, but is there SFP in the market can tolerate
that?
A: We do not know how a SFP could sense and change
polarity unless it had an optical switch inside the module. A
transmitter is a laser or LED and a receiver has a
photodetector. Unless one could have the devices change
function, changing polarity would be impossible.
FTTH
GPON
Q: Can you guide me some websites or pages where I can learn more about GPON Technology please?
A: FOA Guide has a big section on FTTH and OLANs using GPON technology. Follow those links, Also FOA has a new book, The FOA FTTH Handbook you can order from Amazon.
Cheating
On Link Length
Q: I have a fiber run for a camera starts at location A
to location B it is 467 feet. Location B jumpers through
to location C which is ft at location C. Transceivers
areSFPs ONLY GOOD UP TO ft, but this company only has a
multimode system. Is there something i can do to make this
work?
A: It might work as is, since electronics are usually
quoted with conservative specs and will work farther than
specified most of the time. If you have several SFPs, test the
output power to see if it exceeds specs and choose the 2 ones
with highest power. If that still doesn&#;t work, contact SFP
manufacturers for higher power units.
Errors
In A Data Link
Q: What is the significance of bit error, and what is
the acceptable rate for communications and submersible
vehicles?
A: On any data link, there is an acceptable amount of
error that can be tolerated. If it&#;s a digital voice link, a
BER 10E-6 (1 error in 1million bits) is acceptable without
affecting voice quality. If it&#;s a link to your bank, the
typical standard is a million times higher (10E-12). Link
protocols usually have ways to determine BER, like attaching a
checksum to the end of a data packet and having it checked at
the receiving end. If a error is suspected, the packet will be
discarded and retransmitted. Here is a tutorial
on BER and an explanation
of errors in a a fiber optic link.
GPON
Q What is normal Range for good power in an FTTH fiber?
A: The GPON specification for downstream power from the
OLT is OLT transmitter power should be 0 to +6dBm and link
attenuation in the range of 13 to 28dB, which says receiver
power the ONT must be a maximum of 13 dB less than +6dBm or
-7dBm and a minimum of 28 dB less than 0dBm or -28dBm, so -7
to -28dBm at the receiver.
Upstream, the similar calculation is ONT transmitter -4 to
+2dBm and the receive power at theOLT is -11 to
-32dBm.
See http://thefoa.org/tech/ref/appln/FTTH-PON.html for the
full specifications for GPON.
Reflective
Events Causing Transmission Problems
Q: I have a technical question about reflective events.
I recently assisted to troubleshoot an intermittent SM fiber
link for a customer. The cable was dug up a few years ago and
a fiber contractor has (fusion spiced) a different chunk of
cable into the link to repair it. When troubleshooting the
link, I checked the cable with the otdr. I found that each of
the 12 fibers had a reflective event at the fusion splice.
This was only at the splice tube closest to me. The other
fusion splices in the other tube were virtually invisible (as
they should be). I'm a little puzzled as to why there are
reflections at the fusion splices. I did a little research,
but couldn't come up with a good answer as to what is a
possible cause of the reflections. (The OTDR also showed a lot
of ghosting on every fiber tested) (in some cases it recorded
over 40 ghost events) Although I haven't been able to confirm
that there is high Bit error rate due to the transceiver not
providing these statistics, (except for 3 out of 10 pings
fail) I am suspecting that High reflectance is possibly the
cause of their unreliable fiber link.
A: Reflectance is a big problem in SM links,
especially short links. If you are seeing lots of ghosts, I
suspect the link is very short. Fusion splices can have
reflectance if the splicer is improperly set and the fusion is
incomplete or has bubbles. Those splices should have not only
have reflectance but higher loss. The solution is to open up
the closure, use a VFL to find the reflective events and redo
the splices.
POTS
over Fiber
Q: I would like to know if there is information on your
website that explains "POTS OVER FIBER"?
A: POTS - the acronym for &#;plain old service&#;
- is digitized to transmit over fiber. In the early days (late
70s and 80s) it was simply T-carrier with a fiber converter.
By the end of hte 80s it was ATM and SONET. More recently,
it&#;s all going to carrier Ethernet since 99%+ of the traffic
is data not voice or PONs (passive optical networks) for fiber
to the home.
Can I Build A GPON Network
With "Taps"?
Q: Can I build a GPON network where I do a drop to one
subscriber then continue to the next subscriber for another
drop and so on?
A: There have been examples of this type of &#;tap&#; drop
proposed, for example in rural areas for drops to
widespread subscribers on a longer network than is typical for
FTTH. It&#;s just a version of a cascaded splitter network. with
taps that just do a 2 way split. The taps used are typically
90/10 taps, where 10% of the power is tapped off for the drop.
There are some important issues to consider - Since you are
dropping 10% of the power at each tap, you are limited by how
many drops you can have. If you calculate the loss
budget - after the first tap, you have 90% power left less the
excess loss of the splitter (~0.3-0.5dB). The tap power is
down ~10.3 dB and the through power is down ~0.6 dB. At the
next tap, you use the same formula plus you add the loss
of the fiber to that tap and so on until you reach the GPON
limit. It&#;s a pretty complicated process to design, but
you can see that with these power losses you will not get a
large number of drops in a GPON network with 28dB max power
budget. We did a rough calculation and 20-24 drops may be
possible depending on the fiber lengths.
This network will probably be much more expensive and more
distance limited than simply running a cable with many fibers
and dropping fibers from that cable with midspan entry.
Couplers are expensive, fiber is cheap. We also do not know
the issues with the large differences in transmission times
between the first connections and the last ones, which depends
on the length of fiber in the systems. That may require some
programming at the OLT.
Do
We Need Repeaters For 30 Mile Link?
Q: I need to design a 30 mile (~50km) link. Will regeneration
like a fiber amplifier be necessary?
A: It depends on the comms equipment but I doubt you need
regeneration. 30 miles is 50km, only 10dB of loss for the
fiber at nm, maybe 10 splices at <0.1dB adds only 1dB
loss and another dB for connectors on each end. I think you
probably can find equipment that runs on 12dB loss budget.
That said, most new high speed systems (>10G) have 20km
versions then go to expensive long haul coherent systems. So
talk to the communications equipment manufacturers and see
what they say. If you do need a EDFA, they are not that
expensive but the site is expensive and requires power (+
backup). See if it&#;s possible to put the EDFA in the end
facilities to get enough power for the whole run.
Connecting WiFi Access Points In a Passive Optical LAN
Wireless Infrastructure
Fiber
Ports Or Media Converters?
Q: Should I Buy A Switch With Fiber Ports Or Use
Media Converters?
A: I&#;m assuming you
are thinking of using a switch with copper Ethernet ports and
a media converter instead of a switch with fiber ports. The
downside is that it adds complexity and increases the chance
of failure. My analogy is something my primary flight
instructor told me many years ago - multiengine planes are not
safer because having two engines doubles your chance of having
an engine failure. IBM still says that most network problems
are cabling problems. Using media converters adds more
electronics, more power supples and more cabling connections.
Passive
OLANs in Hotels And Resorts
Q: Are passive OLANs a good choice for hotels or
resorts?
A: Passive Optical
LANs are enterprise networks based on fiber to the home (FTTH)
technology not Ethernet over structured cabling. The FTTH
network is usually using GPON standard equipment over one
singlemode fiber with passive optical splitters that provides
basic Level 1 and 2 network functionality. This is not
Ethernet but carries Ethernet over the GPON protocols at 2.5G
downstream and 1.25G upstream.
Passive OLANs offer several advantages over conventional
Ethernet switches and structured cabling, including much less
cost (~50% capital expense and ~20% operating expense),
much lower space requirements (see the link to the library
photos below and note the two racks of equipment that support
drops), longer distance requirements (to 20km), easy
expansion (these are systems designed for hundreds of
thousands of users) and easy management (when you have
hundreds of thousands of users, that&#;s important.)
For hotels, convention centers and similar facilities, the
ease of upgrading to a passive OLAN is a big advantage - one
fiber goes from the computer room to a splitter where it can
serve 32 switches of 4 ports each. That&#;s right, one fiber can
support 128 users! It can support anything that a network can
- wireless access points, security cameras, secure entry
systems, VoIP phones or POTS phones - anything that will run
over a conventional network.
Duplex
Communications Over One Fiber
Q: Is true duplex over a single fiber possible, or is
more like a shared time-domain technique in a quasi-duplex
mode? I would guess that true duplex would lead to
interference problems.
A. Bidirectional links
are widely used - that&#;s how FTTH PONs work. They use
splitters to combine/split the signals and one wavelength
downstream and another upstream. See Fiber
Optic Datalinks and for FTTH FTTH
Architectures.
Rural FTTH
Q: What does A Rural FTTH Connection Cost?
A: That's a very complicated question, because "rural" has a lot
of meanings. Is it a small town where building a FTTH Network is easy or
remote users in Alaska? An interesting set of data was made available
this month from the US Department of Agriculture, announcing $700
million in grants and loans in the 4th round of the ReConnect Program https://lnkd.in/gFe9T4b7.
Fiber Optic Color Codes Reference Chart
Q: Has anyone made a fiber optic pocket reference chart that has cable
color orders, frequencies, or other commonly used info on it?
A: The FOA has a page on its Online Guide that covers color codes
(https://foa.org/tech/ColCodes.htm). It is the most popular page in the
FOA Guide! It works great with a smartphone.
Where
In The US Do Contractors Need Licenses For Fiber Optics?
NECA/NEIS
Good Technical Website For Installers
Markers Required For Underground Fiber Optic Cables?
Q: Are signs required for underground cables like fiber
optic cables? Are they required to have signage so people don&#;t dig them
up or damage them?
A: In the US the answer is NO. There is no Federal or State law
which requires marking anything other than hazardous liquids and gases.
It is purely a business decision or a moral decision to invest in
signs/markers to protect buried fiber. If a fiber gets cut it can
disrupt 911 service and all kinds of vital communication related to
hospitals, air traffic control, etc.
Distances Between Manholes
Q: What is the standard or max distance between manholes and handholes for fiber optic cable?
A: There are no hard rules, but the distances are determined by a
number of factors. In populated areas, the manholes or handholes would
be situated where you need drops line in front of a building or a
splitter pint for FTTH or conversion from underground to aerial or
underwater cables. From a viewpoint of how far you can go, it&#;s
determined by: 1. The length of cable on the reel (typically ~5km max,
maybe further for smaller cables, shorter for higher fiber count
cables. 2. The type of the duct, cable and method of installation
for underground. That includes the type of duct, lubricant used, the
number of corners passed, pulling equipment (pulled or blown) and
the tupe of cable - most limited to 600 pound tension. Cable
manufacturers and American Polywater (lubricants) are good sources of
information here. 3. Aerial cable can have quite long spans, esp. using
the moving reel method, which can be limited by the length on the spool.
Gloves
for Fiber Techs
Q:
I was wondering if as part of the safety rules, in addition to
glasses, if it is recommended to use gloves.
If that the case, would you recommend a specific type of
gloves.
A: FOA
emphasizes the need for safety glasses because of the problem
with fiber scraps flying around, especially when students in
class are learning to strip fibers. Proper safety glasses have
side shields that provide more protection than regular
eyeglasses. For eyeglass wearers, prescription safety glasses
are available at very reasonable costs that are much more
comfortable to wear than wearing safety glasses over the
user&#;s prescription eyeglasses.
We only recommend gloves when working with cables that have
sharp metallic armor in them or some heavy outside plant
cable. The metallic armor can cause serious cuts if one slips
when splitting or removing it. The gloves to use are the
kevlar gloves used to prevent cuts (they are also used for
chefs working with sharp knives.)
Once the cable is opened and you are dealing with buffer tubes
or bare fibers, gloves like the ones used for cables can make
the work difficult because gloved hands are clumsy. Tight
surgical rubber gloves might work for some, but still make
working with bare fiber difficult and provide limited
protection. There we recommend bare hands and being very
cautious.
Height
Of Aerial Fiber Optic Cables
Q:
Is there a code standard for how high from the ground a for a
fiber optic cable running through a residential yard? if yes,
please provide the standard or point me to the standard.
A:
If we go by NEC , the height is 8 feet,above roofs. with
this qualifier. No driveways just over grass. Art
/section 770.44 B. Also 800.44 A 4 states 12 inches between
electric service and Fiber optic cable. But service has to be
12 feet at house so I would say 11 feet above grass. If
driveway is there, Residential 15 feet for service,
electrical, so fiber at 14 feet.
Seal
End Of Cable
Q: For
aerial OSP cable, are there any problems with leaving the end
of the cable open or should it always be put into a closure of
some kind?
A: The
open end of the cable allows moisture to get into the cable
and can be a problem.
I see several scenarios here. If the cable is installed and
waiting for splicing, it could be a matter of time. If the
work is to be done soon - a week or two - leaving it open is
OK, but if the time is longer or you prefer being careful,
just seal the end of the cable by wrapping it with plastic
electrical tape. The end will be opened up for splicing;
about 2m of cable needs to be stripped to splice it, so a few
days exposure is OK, but long term we&#;d recommend a simple
tape seal, the way manufacturers do when shipping cable on a
reel.
Installing
Cable
Q: Below
are specs for an installation. We&#;ve never installed a Fiber
Optic run this long. Please see below questions and info.
-Fiber Optic cable to be used is a 24 strand Single Mode
application
-Length of run is m long
-Appears that all the Fiber is on one reel. However do you
recommend having some junction points on pedestals along the
way for testing-maintenance purposes or just one continuous
run if possible?
A: FOA
has lots of information to help answer your questions:
Re underground installation. See https://foa.org/tech/ref/OSP_Construction/Underground_Construction.html
and https://foa.org/tech/ref/OSP_Construction/Underground_Installation.html
in the FOA Guide.
There are other questions you need to ask:
Are there no intermediate connections or drops required? It&#;s
just one straight fiber run? You should be able to install it
continuously.
What is the installation type? Pulled in conduit or direct
burial?
If pulled in conduit and you can pull in one try, that&#;s best.
You should use a pulling capstan to limit tension, attached to
the cable with a breakaway swivel pulling eye and use
lubrication. Use the American Polywater guides (https://www.polywater.com/product/polywater-f-fiber-optic-pulling-lubricant/)
for choosing lubricant and decide if you need an intermediate
pull.
Direct burial is simple for a long run, just ensure you have
the proper equipment.
Preparing
Cable For Splicing
Q: Is
there any standard on the preparation length of strip jacket
upto the splice tray. Ideally its better to have a loop of
buffer before getting into the tray if ever the closure has
enough space for slack.. its also nice to put some hose to the
buffer to add on protection. So far, i don't see any standard
and can't support the remarks on what to follow. The practice
was to take note on macrobend and have enough length of fiber
to reach the machine.
A: There
is a lot of variation in the size, shape and design of splice
closures, so the length varies according to the closure and
trays. For loose tube cable, the length of buffer tube from
the entrance to the splice tray and the length of fiber needed
in the tray are given in the directions for that splice tray.
Similarly for ribbon cable, but the variations in ribbon cable
designs often requires special handling and sleeving for the
ribbons. Most manufacturers have specs available online.
Fiber Splicing Cost
Q: What is the standard of costing for fiber splicing and
terminations? Is it per core / per splice or per each cable end
irrespective of the number of cores?
A: That is a very hard question to answer, other than to say &#;it
depends. &#; The number of fibers is definitely a factor because each
fiber must be stripped, cleaned, cleaved and spliced then placed in the
splice tray.
It also depends on:
Lashing
Aerial Cable With Cable Ties?
Q: I am considering an electrical job installing fiber
optic aerially on a messenger cable.
I have seen the cable tie method of lashing the fiber to the
messenger. Would you recommend this method considering the
cost of a lashing machine for a single project and if so what
would be a good distance between ties for the proper support
of the fiber to the cable.
A: The normal way to attach an aerial cable to a
messenger is lashing the cable with stainless steel wire. If
you use cable ties, you would need ensure the cable doesn&#;t
droop and the cable ties are designed for outdoor use in the
sun over a long time (stainless steel ones are available). How
long is the span? If it&#;s more than 100 feet, I think I would
go with lashing. If you don&#;t have a lasher, you can rent one.
You will need a bucket truck anyway.
Cable
Installation Guidelines
Q: I am trying to find information on the
recommendations regarding fiber underground in conduit. I am
looking for industry specific verbiage on the cumulative turn
degrees before you need a handhole or manhole. I believe it is
180 degree cumulative but I can&#;t find it anywhere.
A: We&#;ve heard the 180 degree limit mentioned on some
conduit but not for fiber optics. For any fiber optic cable
pulling, the relevant issues are pulling tension and bend
radius.
We know of no specific standards or guidelines on conduit
bends for fiber optics. It has many factors, including conduit
size and type - there are many types, length of the pull,
radius of the bends, type of fiber optic cable and lubricants
used, if any. For the cable, there are thousands of fiber
optic cable designs that vary in diameter from ~3mm to ~30mm
depending on the type of cable and number of fibers, the
stiffness of the cable and the location and type of
stiffer/strength members and the method of installation -
pulling or blowing/jetting. And for locations as far North as
you are, temperature can be an issue as cable gets stiffer
when colder!
For any given installation, corners are generally accommodated
by handholes/manholes and pulling done from handhole to
handhole with figure-8ed cable pulling techniques to prevent
cable damage by excessive tension or bending.
FOA has a section of our Guide on OSP construction: Outside
Plant Fiber Optic Cable Plant Construction and in that
is a section on OSP
installation. For specific cables or conduit runs, we&#;d
suggest talking to the application engineers at cable
manufacturers who can give specific advice.
Construction
Near Underground Fiber
Q: What is the recommended distance for any new building
construction to build near underground fiber duct channel?
A: We do not know of any standards or codes related to
construction near fiber or other underground utilities. Common
sense dictates that one stay far enough away to prevent
accidental damage, so adding 5-6 meters(15-20ft) from the
areas of construction makes sense.
Pulling
Cable
Q: I&#;m having trouble finding much information on the
matter. What type of swivel should be used to pull fiber and
what would be the correct way to pull armored fiber.
A: Start on the FOA Guide here and go here for
types of swivel pulling eyes. with https://foa.org/tech/ref/OSP_Construction/Underground_Installation.html
and here are sources https://www.comstarsupply.com/cable-pulling/swivels.html
It&#;s not common to &#;pull&#; armored cable since it&#;s designed
for direct burial, but a kellums
grip on the jacket will generally work.
Communications
Cables on Utiity Poles
Q:
Is there a standard that service providers such as ISP, FTTH
or cable TV should follow when installing their cables on
existing electric poles. For necessary clearances etc. ?
A: The location of comms cables is in the
&#;Communications Space.&#; At the top of the pole is the &#;Supply
Space&#; for power conductors and between the two is a &#;Safety
Zone Space.&#; It is There are guidelines of various types,
mostly referring to NESC Rule 235. One of the best documents
on this is from Nashville
Electrical Service. This presentation
from Finley Engineering offers a good summary.
"Snowshoes" On Aerial Cable
Q: For
overhead installation, can snow shoes, or other service
loop devices, hold two separate cables?
A: Snowshoes are sized for
different cable sizes and types. Some snowshoes are big
enough for several cables, that&#;s no problems.
Fiber
and Power Sharing Conduit
Q: We are working on a project that has miles
of underground 7 cell innerduct conduit with existing fiber
already running through one of the cells. Is it possible to
run electrical conductors through the 2 of the other cells?
The conductors would be no larger than 1/0 AWG at 480V or
600V. Both the fiber and the electrical are being installed
for the same use.
A:We questioned several people in the electrical side
that also do fiber work. The opinion is that the electrical
may use the other ducts. If the fiber cable has conductive
members, e.g. armor, it must be properly grounded. And any
cables spliced in manholes need separation and marking. The
concern is over what happens with a dig up, but as long as the
electrical is turned off before restoration begins, there
should be no problem.
Fan-Out Kits Needed?
Q:I&#;m working on some MM fiber and am unsure if I need a fan out kit. Is there a way I can tell if I do?
A: Is it 250 micron or 900 micron buffer? Splicing or termination? Loose tube or tight buffer cable? Generally loose tube cable with 250 micron fiber needs no fan out kit for splicing - tubes go to splice tray and bare fibers are protected in the tray - but probably needs it to terminate if the fibers are exposed, for eample with SOCs - splice on connectors. Tight buffer - 900 micron fiber - does not need fan out kits.
Pull ADSS Cable In Ducts Underground?
Q: Our city is installing a 1.5 mile run, mostly
aerial and we want to use ADSS cable. There are two or three
road crossings where we want to go underground in conduit
installed by directional boring. Can the ADSS cable be
dead-ended, brought to the ground, figure-8ed and pulled
through conduit then continue the aerial installation?
A: The answer is yes this is not an issue and is done
all the time. It is standard procedure. (Thanks to Pat
Dobbins, FOA, the expert on ADSS cables.)
Microtrenching
Q: I recently read an article you wrote in April of
last year about micro trenching..Currently, I am employed
with an underground construction company. Something we have
never been involved with is micro trenching and would like
to possibly get some equipment and training scheduled in the
near future. In saying that, it has seemed to be almost
impossible to find numbers on the price per foot.
Essentially, I am asking if you have any resources to some
up with those numbers or models to maybe use for pricing
purposes.
A: Microtrenching is becoming another tool that
contractors are adopting because like directional boring is
is less disruptive than regular underground construction.
I&#;m working with one group that&#;s using microtrenching in CA
cities, installing microducts and a 288 fiber
about the size of a #2 pencil. Cost is difficult to
generalize other than &#;more than aerial and less than
trenching.&#; Cost is very dependent on where you are
working and what the local geography looks like. We know one
contractor who claimed to do 5 miles a day in rural
Washington at costs near that of aerial. It&#;s especially
good in areas with lots of base stone where trenching or
boring is near impossible or cluttered utilities downtown.
Here are a couple of pages on the FOA website about
microtrenching:
Outside
Plant Fiber Optic Cable Plant Construction
Underground
Cable Construction
Microtrenching
Ditch Witch sells equipment for trenching and trains users.
Condux has the equipment for blown cable and offers training
several times a year.
Microtrenching
Q: What is microtrenching?
A: Microtrenching is a technique for installing underground
fiber. It is done by sawing a groove in the road or sidewalk and
dropping a small (~1/2 inch or 13mm) plastic tube (duct) into the
groove and filling it up with material like the surface so it almost
disappears. The cable is &#;blown&#; into the duct with high pressure air -
actually the air floats the cable in the duct to reduce friction and the
cable is pushed into the duct.
Here are photos of a microtrenching installation in Toronto. Here is the explanation of microtrenching in the FOA Guide section on OSP Construction (about 3/4 down the page.)
We don&#;t think any of our schools teach this in the US but Triple Play does in South Africa.
In the US we recommend going to one of the companies that makes the construction equipment, primarily Ditch Witch.
Blasting
Near Fiber Optic Cables
Q:
Markers
For Underground Fiber Optic Cables
Q: I have a general question about above ground
markers for fiber optic cable in conduit. Is there a
recommended spacing for the markers? Is there a standard
to reference for this?
A: We asked some people who make them and they said the
guideline is &#;line of sight.&#; The rules for markers are
mainly what information needs to be on them. Of course we also
recommend adding marker tape about a foot above the conduit. I
was curious if there were any legal issues and I found this
interesting page from Cornell Law School: https://www.law.cornell.edu/cfr/text/49/192.707
So I might add to line of sight any crossings of
roadways, rail ways and some markers for bridge crossings.
We have a new section on the FOA Guide: Outside
Plant Fiber Optic Cable Plant Construction that may be
useful.
Terminate
All Fibers Or Just Some?
Q:We
are currently running fiber which will be 12/24, my question
is do we need to terminate every pair even if we aren't going
to be using them or is there an alternative?
A: No
you do not need to terminate all of them and leaving some bare
fibers is often done when there is no planned use for the
fibers or to save money. However, there are some other issues
to consider. You do need some spare fibers ready to use,
either in case of problems or for upgrades. For small fiber
counts, the cost of terminating them all at once will be
cheaper than having to come back to the site and doing it in
the future. The economics are quite different if you have 144
or more fibers, of course. If you leave bare fibers, be sure
to leave enough length to terminate or splice later - about a
meter for termination and 2m for splicing. And protect them
from damage so they can be used in the future.
Removing
Old Fiber
Q: I have several feet of old 62.5/125 armored
fiber optic trunks under a raised floor that I am
replacing/upgrading to 50u MM and SM trunks. Is there any
guidance on &#;Best Practices&#; to follow when cutting these
trunks into more manageable lengths for removal?
A:
Use a jaws-type cutter to cut the cable into reasonable
lengths and remove it. There should be no danger in cutting
the cable up as long as your workers only cut the right cable.
Raised floors often have large numbers of cables - often
including power cables - so its important to ensure the proper
cables are being cut an removed.
Re-routing
Old Fiber Optic Cables
Q; I have a questions about the re-routing of fiber
optic lines that have been in place for a number of
years. Is it a standard transaction in the fiber optic
business to have to re-route fiber that has been in service
for a long period of time. (e.g. >20 years) If
so, is there a best practice for removal from conduit for
re-rerouting?
A; There is no way we would recommend removing and
reinstalling 20-year old fiber cable. First of all, old cable
may be damaged in removal. Then cable and fiber technology has
improved over the years so you can get much better components
today at greatly lower prices. (One industry analyst I know
likes to say that fiber is cheaper than kite string and
fishing line!) Today&#;s cable designs allow for much smaller
cables with many more fibers (288 fibers in 9.7mm - just over
3/8&#;) and new conduit designs allow for more cables in a
conduit (microducts and cloth ducts) and easier installation -
blowing in cables and microtrenching are perfect for metro
areas.
More fibers, especially in a big city, is a must. Smart
cities, small cells, FTTH (fiber to the home), ITS
(intelligent traffic systems), V2X (vehicle to vehicle,
infrastructure, etc.) and many other services need lots of
fibers.
Our recommendation is to pull it out and dump it. Install new
ducts and the fiber you need (x10 maybe?) and have new ducts
for future use. Are you familiar with &#;Dig Once&#;?
Why A Figure 8 Cables?
Q: What is the reason for wrapping the cable in a figure
eight?
A: When you need to do an intermediate pull, you have
to pull the fiber and coil it on the ground. A simple coil
will put a twist in the cable. Figure-8 coils put in twists of
opposite directions on each side of the 8 making for no
overall twist in the cable. See How
To "Figure 8" Cable For Intermediate Pulls in the FOA
Online Guide.
Maintenance
of Fiber Networks
Q: Can you guide me how to prepare Optical Fiber
Cable Annual Maintenance Proposal?
A: Basically, the
network needs to be installed properly, fully tested and
everything carefully documented. Then no routine maintenance
is required. Most problems with fiber optic networks occurs
when techs are working with it, e.g. damaging cables or
getting connectors dirty when testing, so leaving it alone
is the best plan.
Electronic transmission equipment can be tested anytime to
ensure proper data transmission, but that does not involve
accessing the fiber.
We have several things which may be of help:
You Tube Video: FOA
Lecture 39 Maintaining Fiber Optic Networks
Web page: Maintenance
Getting
Old Cables Out Of Conduit
Q: How do you get old cables out of a conduit when
they are stuck?
A: Usually we are concerned about reducing friction
when pulling cables through conduit, but sometimes you need to
get them out. Here
is a page from American Polywater the leading lubricant
company with advice on the subject.
Designations For Fibers
Q: I'm currently working on a project involving optical fiber
with VMS signs, CCTV cameras and other ITS equipment. I was wondering if
there is a standard or a good practice which describe the typical
assignation for each optical fiber on a 6 fibers cable for
example? By that, I mean :
- fibers number 1 and 2 : VMS;
- fibers number 3 and 4 : CCTV;
- fibers number 5 and 6 : spares
A: There are several ways people assign polarity on duplex links.
The way you suggest is the most common I believe. Use the odd number
fibers to transmit in one direction, even number fibers to transmit in
the other direction and document the color codes.
Finding Buried Fiber Optic Cables
Q: We have a client that needs their private fiber located. We have
been on site and confirmed the lines were installed with no tracer wire
or conductive conduit/sheathing. Want to know if you had any
suggestions on how to locate or if there was specialized equipment that I
am aware of.
A: Interesting question on an important topic. The answer is a qualified
maybe. Ground penetrating radar (GPR) can sometimes spor fiber optic
cable, maybe more easily if it is in duct or conduit. It requires
someone with a lot of experince in GPR. There are companies around the
US with this capability. Then there is a new proposal using the sensing
capability of fiber with above ground vibrators. Nothing commercial is
available here as far as I know.
https://www.winlab.rutgers.edu/~hansiiii/papers/OECC__Liu.pdf
Depth To Bury Fiber Optic Cable
Q: What is the ideal depth to bury a fiber optic internet cable for home
use? What is the minimum depth to prevent injury to the cable?
A: Normally fiber optic cable is buried about 3 ft/1m deep, but with
drops to the home, in the subscriber&#;s yard, it&#;s considered acceptable
to go only ~1ft/30cm deep with a narrow trench to prevent damage to the
lawn. It&#;s important that th eowner know exactly where the cable is
however since they must be careful when digging near it to prevent
damage.
Grounding Armored Jumper Cables
Q: Do you need to bond/ground FTTH drop "jumpers" that ise an armored cable?
A: Yes, just like any other cable that has conductive elements. A
manufacturer of the cables Tinifiber seems to agree:
https://tinifiber.com/bonding-and-grounding-armored-fiber-cable/
I do not know of any fiber optic connectors that address this, unlike the RJ-45/modular 8-pin connectors for UTP copper.
Reuse Of Cable Being Removed From Service
Q: Is there ever a feasible reuse for used/older fiber optic cable?
Would some one be in the market for the FOC that is removed from
service? Lets say 20year old aerial cable ADSS?
A: We have been asked that question a lot. It often involves cheap
fiber on eBay or from surplus dealers. With the advances in fiber
technology and manufacturing, 20 or even 10-year old fiber is
essentially obsolete. Lots of service providers are replacing that fiber
with today&#;s higher performance fibers because networks are going from
the ~2 gigabit speeds then to terabit speeds today. We would never
recommend reusing fiber removed from service. You have no knowledge of
how it was installed originally and environmental conditions can be hard
on some types of cables. Besides, the cost of the cable is only 5-15%
of the project cost. Most of the cost is in the labor of installation so
the savings would be minimal and the risk high.
We have been telling people who have leftover cable from projects to
offer it to FOA schools. They are always in need of OSP cables.
"Mining" Cables In Data Centers (Cable Removal)
Q: Is there any documentation out there on best practices for data center cable mining? Any help would be greatly appreciated.
A: This has been a topic in premises cabling since first
proposed by NFPA for the NEC twenty years ago. FOA has gotten this
kind of question before for many different circumstances, but I must
admit that I know of no recommended procedures or standards for the
removal of abandoned cable.
Cable &#;mining&#; often refers to the removal of underfloor cable, may apply to cables in trays and is hard to get information online - search for &#;Cable mining&#; and you get links to sellers of cables designed to be installed in mines (coal, salt, minerals, etc.) underground!
The biggest problem with removing unused cables is identifying the cables to remove. Underlloor cables are particularly bad, it seems, since you have generations of abandoned cables, often poorly marked, sometimes mixed with power cables. With metallic cables, you can sometimes use an ancient tool, a &#;toner&#; to trace cables, With fiber you just have to be careful that you identify the cable before you cut.
Why We Warn You To Be Careful About Fiber Shards
Photo courtesy Brian Brandstetter, Mississauga Training Consultants1-844-440-
Fiber Optic Color Codes Reference Chart
Q: Has anyone made a fiber optic pocket reference chart that has cable
color orders, frequencies, or other commonly used info on it?
A: The FOA has a page on its Online Guide that covers color codes
(https://foa.org/tech/ColCodes.htm).
It is the most popular page in the
FOA Guide! It includes a print your own pocket color code chart and one
for your smartphone or tablet - works great with a smartphone.
Multimode
In Premises Cabling
Q:
I wonder when/if single mode fiber will start invading the
enterprise. There's a whole ecosystem, of course, in addition
to physical fiber cabling. Switches, server connections,
protocols, etc. But I'm wondering if you see the industry
moving towards some set of standards using single mode?
A: Today, singlemode transceivers are as cheap as
multimode for 10G and cheaper at higher speeds. Indoor cell
systems (DAS) use singlemode. FTTH PONs (passive optical
networks using singlemode) are being used for LANs because
they are cheaper too. Both technology and costs point to the
advantages of SM. Multimode is the historical design and it's
hard to change. But structured cabling standards (TIA-568, ISO
) include singlemode and POLs (passive optical
LANs.)
Storing Fiber Optic Cable On Reels
Q: is there a "standard" for how to store a fiber optic cable reel?
A: This is another detail that has not in my knowledge ever been
included in a standard. However manufacturers usually put a note on the
reel to keep it upright - standing on the edges of the spool sides, not
flat on one side of the spool. If the fiber is to be stored for a
period of time, it should be stored in a cool dry place and the ends
sealed with electrical tape.
(Photo storing cable on reel)
Midspan
Drop Cables
Q: I
am working on a project that has 5 sections, consisting of 5
miles each section, CCTV, detectors, DMS connected by 192
count fiber. We were directed to use the consultants
plans from the first section as a guide for uniformity for the
remaining contracts. The attached fiber detail shows a 4
fiber drop cable going to the ITS device. I was thinking
to take all 12 fibers to the device and back for
redundancy? Also, if we did use the 4 fiber drop cable,
I didn&#;t understand why they would splice the other 10 thru
cables and instead leave them intact? Is there a preferred
method for a drop cable to a device or just preferences?
A: We are not sure why they do it the way they do.
Perhaps the designer was not familiar with midspan access
which would preclude having to make the other splices. Using a
12 fiber drop cable would be more expensive and perhaps
unnecessary unless the device being connected is in a location
where a small cell site might be located. They may also have
uses for those other fibers that require a connection through
the drop point. We&#;d suggest to the designer that
midspan access might allow saving the 10 splices at each drop.
Fiber
Flexibility and Longevity
Q:
When I think of glass, I think of a material that is not
very flexible. If you try to bend most glass, it will break.
So it is rather remarkable that you can bend a fiber and
not crack it, even though the strands are quite thin. Perhaps
it's not a good idea to bend fiber too sharply? I was talking
to the people who maintain the fiber network at the university
here. They tell me they have a problem when fiber gets to be
about 15 years old, it will start to become brittle. If you
flex it, it will crack or break. Is this a common problem? How
long can fiber be expected to last before it becomes brittle?
Is fiber that is manufactured more recently have a longer
life-span?
A: Fiber is quite flexible. One demo I did when I taught
classes was to walk up to a large window and push on it,
telling everyone to watch the reflections to see how the glass
flexed. I can flex quite a lot. Like most materials, as it
gets smaller, it can bend more easily because the stress is
less across the cross sectional area. Consider a bar of steel
1&#; in diameter compared to a piano wire or banjo string. Most
things break because either they are overstressed or there is
some impurity in the material that focuses the stress and the
crack propagates from there. Ever cut glass? You scratch it
and stress it along the scratch line and its maps off - called
cleaving - where the stress concentrates along the induced
fault. Fiber is extremely low in impurities - a matter of how
it&#;s made from raw materials, not melted sand like most glass
- that&#;s part of what makes them have such low loss (efficient
transmission) and high strength. A glass fiber is much
stronger than steel of the same size. Corning
explains it here.
The brittleness of older fiber is due to the migration
of moisture up the cable into the glass. The H2O becomes the
OH radical which interacts with the glass to reduce its
strength. Most cable companies say their cable today protects
the fiber well enough that it should last 40 years, but where
fiber is terminated or spliced and exposed to the air, it can
get brittle and be hard to handle in 10 years or more. Older
fiber had shorter lifetimes simply because we learned to make
fiber coatings and cables better at sealing fiber from the
ambient atmosphere.
Fiber
Choice for LANs
Q: Many manufacturers or suppliers worldwide emphasize
the use of OM4 multimode optical fiber for the LAN. Does
single-mode fiber not provide greater bandwidth than
multimode? Do they imply that single mode optical fiber should
only be used for long distance applications and not in LAN
environments?
A: Multimode fiber is acceptable for LANs up to 10
gigabits/second and up to 550 meters depending on the type of
fiber and Ethernet version. See this
page for a complete list of network
specifications.Higher versions of multimode fiber OM2-OM3-OM4
have higher bandwidth capability. OM5 is a version of MO4 that
also supports wavelength division multiplexing with VCSEL
sources in the extended wavelength 850-950nm range. OM1 is a
earlier fiber with a different core size that has not been
designed into new systems for almost 20 years. LANs can use
singlemode fiber for all versions. Singlemode has longer
distance capability (up to 40km) and virtually infinite
bandwidth. See the singlemode specification in the link above.
Singlemode is also used in passive optical LANs that can be
much cheaper to build than conventional networks. See this
page for information on optical LANs (OLANs)
including passive OLANs based on FTTH GPON technology.
Fiber
Lifetime
Q: I am often ask how long the fiber we are deploying
today will last or be useable , I typically say something like
it will last at least 20 years and that no one really knows
how long it can be used. What is the oldest fiber
optic network or longish segment that is still in production
that you know of?
A: Current cables are probably good for 40 years or so.
Today there is some fiber being used by telcos from the late
s and lots form the late s and early s. Lots of
OPGW (optical power ground wire) is in use up to 30 years old.
Some of this old fiber is being used at 10Gb//s. But remember
that fiber from 20 or 30 years ago may have limitations on
bandwidth, since both chromatic and polarization mode
dispersion has been reduced in newer fibers for higher speed
networks. And spectral attenuation of older fibers may be
higher and have the water peak at nm that can affect
wavelength-division multiplexing systems. But the weak point
may not be the cable or fiber, but the splice and termination
points where bare fibers may be exposed to the elements. It's
not uncommon to find these fibers have become brittle and are
hard to work with. What we always tell people is if it&#;s
working, leave it alone. If you want to upgrade to higher bit
rate systems, use fiber characterization to determine if the
fibers are capable of use at higher speeds.
Cable
Bend Radius
Q:
We are working on project where we need to know
difference between short term and long term bend radius for
fiber optic cable?
A: The bend radius for cables is generally specified
under two conditions - under stress, e. g. when being pulled,
it is a radius 20 times the cable diameter. Relaxed, after
installation, it is a radius 10 times the cable diameter. The
relaxed specification, 10X, is considered a long term
specification. Some of the new high fiber count cables have
different specifications, sometimes 15X or 20X under either
condition. Check with the manufacturer for their specific
cable. See this
article on bend radius in the FOA Guide.
Old
Multimode Fiber
Q: We have old multimode fiber and we are still
connecting more equipment to it over greater distances and
need some way to insure the equipment will work.
A: I do not know of any simple formula for figuring
this out. Last time I remember such a formula from around
done for Gigabit Ethernet with VCSELs and the equation
reminded me of the quantum mechanics course I took in physics.
The problem is you have two bandwidth factors, modal
dispersion and chromatic dispersion. Modal dispersion is
highly dependent on mode fill, e.g. the metric &#;encircled
flux&#; was developed to define the mode fill of multimode fiber
with VCSEL sources for simulations to estimate bandwidth.
Chromatic dispersion is dependent on the fiber spec and the
spectral width of the source which is better with lasers and
LEDs.
What generally happens is the standards group developing the
network standard, especially IEEE 802.3 for Ethernet, runs the
numbers and specifies a maximum distance for the particular
network and its speed. FOA has a table of these specs here: Specifications
for fiber optic links and systems, including FTTx
105 Micron Fiber?
Q: I have a customer asking about 105um fiber. Does it exist? What is it basically used for? After FOA suggested a clarifying question to the customer: The
fiber is for Power over Fiber(PoF). The construction is 105um fiber
with 125um cladding. The question or assumption would be &#; The
termination would be the same as 50,62.5 or 8.3um with a 125um cladding?
A: The people who do laser surgery and power over fiber
use special step index fibers and SMA connectors. The power density can
be very high so the heat can build up in the cable. SMA connectors or
the metal ferrule swaged-on connectors are often used for their
all-metal construction with the ability to withstand heat and sometimes
the need to be drilled for special fiber diameters. Because of the high
power, the polish needs to be low reflectance, so we&#;d recommend using a
wet polish and end with a very fine polishing film - 0.3 microns or so.
Like polishing SM for DWDM.
Cleanliness is very important for these applications. I remember a call
from a doctor doing laser surgery who kept ruining cables because they
were dirty and the high power literally exploded the dirt and pitted the
ends. When that happens, sometimes they can be polished out but often
they are ruined. The same thing happened to the 120 inch telescope at
Lick Observatory when Joe Wampler tried using it to laser range to the
retroreflector Apollo 11 left on the moon. Exploding dust pitted the
aluminization on the mirror.
Replacing
OM1 MM Fiber
Q: We are an automation system integrator in South Africa. We
have a client that has multimode 62.5/125 fibre optic plant
wide. None of the runs between components are longer than 2km.
We intend to upgrade the technology from a proprietary
communication protocol to a standard ethernet protocol at 100
MHZ. The fibre to copper convertors we will be using are using
nm light source and have a Fibre Optic Link Budget of
12.8dB for 62.5/125 um and 9.8dB for 50/125 um. The client has
been advised to replace the multimode 62.5/125 with multimode
50/125 cabling and we need to know if this is really a
requirement.
A: Do you know how old the fiber is? It should be what we
called FDDI grade 62.5/125 fiber with a loss of ~1dB/km and a
bandwidth of 500MHz-km at nm. A 2km link should have a
loss of 2dB for the fiber and ~0.5dB/connection - well under
the power budget of the link. 100Mb/s Ethernet variants were
designed for 2km or more on this fiber. There is no reason to
upgrade at this time, 50/125 fiber would not be needed until
Gigabit Ethernet was desired.
Can A
Fiber Optic Cable
Catch "Fire"
Q: While working on a cut-over of a dwdm circuit
something has happened that I am now looking for an
explanation. A transmission fiber emitted "fire" on that same
fiber! We did not see any optical light we saw fire. About 5
cm of fiber burned and remained smoke. What phenomenon
occurred? Are the dwdm amplifiers so powerful enough to
generate fire? Unfortunately I could not get into the station
to take the model of the equipment.
A: We&#;ve heard of high power WDM systems exploding
dirt of the endface of fiber connectors and damaging them, but
this is a new one. We contacted several technical people in
fiber companies and found that this can happen if there was a
crack in the fiber in the cable near the connector or lots of
reflection perhaps caused by a very dirty connector that
allowed the very high power to heat the cable enough for
combustion. DWDM with many multiplexed signals and a fiber
amplifier creates a lot of power confined to a very small core
of the singlemode fiber. That power can ignite the acrylate
coating on the fiber.
What's
The Lifetime Of Fiber?
Q:
"The utility I work for has some FO cable installed,
some 20 years+ and I am wondering what is industry standard
for the useful life of a cable? This is from an asset
management point of view. I realize that FO cables can and do
last for decades, especially if the work on them is minimized
(ie. splicing for repair or relocation), but what would you
consider a good book value for useful life?"
A: Cable manufacturers have generally made fiber optic
cable for a lifetime of 20+ years and in the last decade or so
we&#;ve been told that 40 years is reasonable for a cable. But
that means the cable will retain its specifications for that
time frame. Networks, however, do not stand still. In the last
20 years, network speeds have increased by up to 100 times. In
the same time period, the fiber has been engineered to
accommodate longer and faster links. 20+ year old fiber was
installed when speeds were around 1Gb/s, where dispersion was
not an issue, nor was dense wavelength division multiplexing
(DWDM) being widely deployed. So if you are using fiber at
lower speeds, the current cables are probably fine. You might
have trouble splicing older fibers in closures because the
exposed fibers do tend to get brittle.
If you want to upgrade to faster speeds or DWDM, the older
fibers will need testing - we call if fiber characterization -
and here is a page in our FOA
Guide about it: Fiber
Characterization and Testing long haul networks (CD,
PMD, Spectral Attenuation)
Differences
In Fibers
Q: What is the difference between OM3 and OM4 type
fibers and G.654/G.655? They seem to be rated for the
same amount of GBs (10-400) and the only difference
seems to be the multi-mode nature of OM3/4 vs. the single mode
nature of G.654/655. Can they both be used in long haul
communications if laser optimized?
A:
OM3 and OM4 fibers are both 50/125 micron fiber but have
different bandwidth capability. OM3 is rated at MHz-km
while OM4 is rated MHz-km. OM4 is an evolution of OM3
where design and manufacture allow more bandwidth. More
bandwidth translates into slightly longer link lengths in
faster networks, ~1-10Gb/s. For example, Ethernet at 10Gb/s
will go 300m on OM# and 450m on OM4, which can be important if
it is being chosen for a enterprise network backbone.
The differences in G.654 and G.655 are more complicated. G.654
is singlemode fiber optimized for use at nm for long
distance use. G.655 is &#;non-zero dispersion shifted&#; fiber
tweaked for dense wavelength division multiplexing (DWDM) to
prevent secondary problems with high power and closely spaced
wavelengths of DWDM and fiber amplification. It&#;s the kind of
fiber used in long submarine cables.
Arsenic
Coated Cable?
Q: I was told a contractor installed arsenic
coated fiber optic cable because they didn&#;t want animals to
chew through it. Is this true?
A: Some cable has
chemicals put in the jacket to make it taste bad to rodents.
We have not found any one who claims to use arsenic, in fact,
we could find no references to what kinds of chemicals are
used.
Why
Do Cables "Go Bad"?
Q: It&#;s been my observation over ~15 years of
building and managing fiber channel storage area networks that
from time to time cables will fall out of transmission
spec. In terms of communicating with non-storage people,
they in essence, &#;go bad&#;. Other than possible damage
due to physical disruption of a cable, or contamination at the
connectors usually caused by a human being
unplugging/replacing, has it been your observation that MM
cables can &#;go bad&#;?
A: There are some
possible causes of problems over time. We know of connectors
that fail for several reasons.
Armored
Indoor Cable?
Q: Can I get an indoor armored 8 core fiber optic
cable?
A: Most cable
manufacturers make indoor armored cable using corrugated wrap
armor to protect cables from crushing loads from other cables
especially in under floor installations.
More
Than &#;Single&#; Mode?
Q: We're now using SM fibre so it looks like we
don't need mandrels in the Ref Lead at the Light Source.
The info I have is that we need to make a couple of air coils
35mm to 50mm in diameter. Why?
A: When you launch
from a pigtial laser source through a connector into a
reference cable, you do have several modes being propogated.
It usually takes 100m or so for the second or third order
modes to attenuate. So the coil causes them to be attenuated
by the stress enough to no longer be significant - it&#;s a mode
filter just like MM. If you do not do this, you will measure
higher loss in the fiber and at connections near the source.
Since most SM has traditionally been long distance, the effect
was small or ignorable, but with short links, it can be
significant.
Followup Q: But how do we explain multiple modes in Single
Mode fibre?
A: When you get the core of the fiber down to ~5-6 times the
wavelength of the light, it no longer acts like geometric
optics (like MM fiber). Some of the light can travel outside
the core (see the note on &#;waveguide
dispersion&#;here http://www.thefoa.org/tech/ref/testing/test/CD_PMD.html).
At launch, significant amounts of power are at higher angles
creating short lived modes that are highly attenuated.
Replacing OM1 MM Fiber
Q: We are an automation system integrator in South
Africa. We have a client that has multimode 62.5/125 fibre
optic plant wide. None of the runs between components are
longer than 2km. We intend to upgrade the technology from a
proprietary communication protocol to a standard ethernet
protocol at 100 MHZ. The fibre to copper convertors we will be
using are using nm light source and have a Fibre Optic
Link Budget of 12.8dB for 62.5/125 um and 9.8dB for
50/125 um. The client has been advised to replace the
multimode 62.5/125 with multimode 50/125 cabling and we need
to know if this is really a requirement.
A: Do you know how
old the fiber is? It should be what we called FDDI grade
62.5/125 fiber with a loss of ~1dB/km and a bandwidth of
500MHz-km at nm. A 2km link should have a loss of 2dB for
the fiber and ~0.5dB/connection - well under the power budget
of the link. 100Mb/s Ethernet variants were designed for 2km
or more on this fiber. There is no reason to upgrade at this
time, 50/125 fiber would not be needed until Gigabit Ethernet
was desired.
Old
Fiber
Q: We are looking at a company&#;s fiber network which
has been laid at various points in time over numerous
years. In this process, we are trying to identify the
changes that were made to either/both the glass fiber and the
cladding. Are there different generations of what was
industry standard in creating the fiber? For example,
are you able to identify the difference in a fiber that was
laid in versus one laid today? Was the cladding the
same size/thickness etc. in as it is today or has this
been modified/improved upon over the years? In all, we
are trying to find what modifications have been over the years
and how this may improve the life of the network and its
capabilities.
A: This is a common
problem today. Many network operators are evaluating their
fiber networks for upgrades, hampered by the fact that few are
properly documented. Below is a timeline that should answer
your questions. What many network owners are doing now is
testing their cable plants - a process called Fiber
Characterization. There are contractors who do
this service.
Fiber Tech Timeline
How
to Clean POF (plastic optical fiber)
Q: I
heard that plastic fibres such as PMMA can suffer damage from
cleaning from an alcohol solution. Are there alternate
cleaning solutions available for these types of fibres."
A: You can use a 10/90
mix of isopropyl alcohol/water. Typically use with a
lint free swab. (from out POF consultants)
Older
Fiber?
Q: I have some 62.5 mm and sm inside fiber plant
over 20 years old. When is a good time to upgrade?
A: When you need to or
have to. If it's working OK, there is no need to upgrade!
We recently got this from a student with field experience taking a fiber optic class:""The instructors are telling us that we are stripping the cladding from the core when prepping to cleave MM and SM fiber. I learned from Lenny Lightwave years ago, this is not correct. I do not want to embarrass them, but I don't want my fellow techs to look foolish when we graduate from this course."
I'll share with you our answer to this student in a moment, but first it seems important to understand where this misinformation comes from. We did an image search on the Internet for drawings of optical fiber. Here is what we found:
MM Splice-on Connector On Singlemode Cable
Q: I encountered a situation where a MM
mechanical connector was used on a SM fiber and passed on an OTDR test.
The client and I are interested in understanding how these connectors
could have passed?
A: The joint between a multimode and
singlemode fiber should have vrey high loss, ~17-20 dB, depending on the
mode fill of the MM fiber. However the short length of the MM fiber,
~10mm, might not be enough to cause the modes to fill in the short fiber
in the connector, resulting in relatively low loss.
Eric Pearson, one of the most knowledgeable people on connectors
expressed this idea then tested it with 100m singlemode connected to a
second singlemode cable. The second singlemode cable has an OM3 LC
unicam connector, An EXFO ftb-400 OTDR indicates a 2.09 dB drop. That is
way too much to pass a test but nowhere near the loss that could be
expected from the MM/SM joint. See the OTDR trace below.
Connector Mating
Adapter Loss
Q: When looking in data sheets on duplex
adapters, it&#;s telling me that it has a Insertion
Loss of about 0,2dB. Is that common? Only thought it
was the connector that had a loss.
A: Technically,
a single connector or mating adapter does not have
any loss. It&#;s not &#;connector loss&#; but &#;connection
loss&#; defined as the insertion loss when two
connectors are mated, and for most connectors that
requires a 3rd component, a mating adapter to align
the ferrules. (Some connectors like MPOs have their
own alignment mechanism so the mating adapter merely
holds the two connectors - one with pins and one
with holes - together.)
The connector manufacturer&#;s specification for
&#;Connector loss&#; is the loss of their connector
mating to a reference connector with a mating
adapter. Connectors are graded in ISO/IEC standards,
but not TIA, and the best connectors are ~0.2dB loss
when mated to another of the same grade.
If a mating adapter manufacturer is quoting loss,
one assumes they mean their adapter with two of the
best connectors will have a connection loss of
0.2dB.
Mating adapters for 2.5mm ferrule connectors - FC,
SC and ST - have a split sleeve alignment bushing
that is the critical element. They have been made
with molded glass-filled plastic, phosphor bronze
and ceramic. In our opinion/experience, the plastic
ones are only good for multimode fiber and wear out
in ~10 insertions, discoloring connector ferrules
and leaving dust scraped off the plastic on the
ferrule ends. The metal ones are good for SM or MM
and hundreds of insertions, but they tend to wear
and leave marks on the ceramic ferrules. The ceramic
ones are recommended for SM and for testing as they
work best and last practically forever.
Maximum Fusion Splice Loss
Q: We have set 0.4 dB as our max for all losses per splice
and my counterparts argue that customer quality will not suffer with a
1.0db-1.5db loss at a splice. What do you think?
A: We would argue that the issue with high loss splices is more
one of reliability. Most fusion splices of singlemode fiber are 0.05 to
0.1 dB A splice that has more than ~0.2dB loss probably has some
inclusion (dirt that got on the fiber after cleaving) or an air bubble
with means the splice is deficient in strength and may fail over time.
If the network is operating at high power with WDM and fiber amplifiers,
the inclusions or bubbles may produce heat which can cause failures. At
very high speeds or using coherent communications over long lengths, it
might affect dispersion.
Loss
For APC vs UPC Connectors
Q:
I was wondering if there will be a standard connector loss for
a UPC connector and a different lower value for an APC
connector.. ex. upc has 0.5dB while APC is 0.3dB.
I would like to make all connectors uniform on a new network
infra to avoid mismatch and causing any possible damage on the
equipment when APC will be plugged into to a flat.
A: There is really no statistical difference between
APC and UPC connector loss. The lower reflectance of the APC
actually reduces loss since the reflectance represents a
factor in connection loss, This issue of connector grades has
been discussed at international standards committees for
years. ISO/IEC wants to have grades of connectors, rated for
connector loss in ranges from 0.1 to 1dB, but I do not think
it&#;s standardized. I recommend using 0.3-0.5dB for loss
budgets, where in OSP networks it matters little, since there
are only a few connections and fiber and splice loss is a
larger factor.
Keeping UPC and APC connectors straight is easy - APCs are
Green, UPCs are blue. Everybody just needs to be taught that!
Fusion
Splice-On Connectors (SOCs) (From an FOA Instructor)
Q: A
question came up from one of our students regarding splice on
connectors. Is there a TIA or other standards body that
addresses this issue? We are used to the 0.75 dB loss for a
mated pair, however, when this mated pair has two fusion
splices that terminate the connector, is there a
recommendation?
One could make the argument that it does not make any
difference as the other alternative is splicing a pigtail for
termination of a cable. This pigtail splice is normally
included in the link loss budget calculation. So
similarly, with a splice on connector it is the same as
splicing on a pigtail.
A: There are no specific TIA or IEC specs that address
these splice-on connectors or pigtails. If you used TIA
numbers and included the splice and connector it would be
1.05dB - 0.75dB for the connection and 0.3dB for the splice,
that&#;s mated to a factory adhesive/polish
connector. Or if it were two similar connectors,
1.35dB.
Everybody, including the people in TIA standards groups, know
those numbers are too high for most single ferrule connectors.
They keep them at 0.75dB for prepolished/splice connectors (w/
mechanical splices) and array connectors (MPOs) which have
somewhat unpredictable performance. Internationally, IEC has
created grades of connectors from ~0.3 to over 1dB. The newer
mechanical splice connector kits now use the Chinese copied
cleavers which are super - at least the few we have tested -
and the connectors are now much lower loss and consistent.
SOCs (fusion splice-on connectors) are spec&#;ed as the total
termination and are generally just as good as the typical
adhesive polish connector - 0.5dB is plenty of margin for a
those mated to a factory adhesive/polish connector.
Spliced on pigtails are generally considered a termination and
the splice is not broken out - like a long SOC. But I cannot
guarantee everybody thinks that way. But a fusion splice is
typically <0.1dB anyway.
APC or
UPC?
Q: Can my otdr test upc connectors? Can I test
this distribution without problems?
A: APC and UPC connectors are not compatible. APCs are
green, UPCs are blue. See https://foa.org/tech/ColCodes.htm To
test UPC connectors you would need a launch cable that is UPC
on the OTDR end and APC to to mate to an APC connectors. But
if I look behind these green APC mating adapters, I seem to
see blue connectors - blue is UPC not APC. (add photo)
PON
Troubleshooting
Q: I have question about DBM IN GPON system with
splitter 1:64. I spliced 2 fiber from splitter to customer
going through 4 splicing points and when I measured the loss
at the end (customer) the #2 fiber was fine but the #1
fiber was down 12 dB. I checked the fiber with OTDR without
splitter and it looks fine. What you think is the problem?
A: You need to test the splitter itself to make sure
all ports are good.
Q:
A customer said he said he would test 100 foot pigtails with
OTDR. I question that practice and think OLTS Tier 1 and
microscope test for defects,
Splice
Loss
Q:
We are installing 216 fiber aerial cable for 12km with 2
splicing points. We use 3 different fusion machines and they
report that all splices are 0.00db. But when we check using
OTDR we get above 0.04db. The question is how can we get below
0.04db splicing loss?
A: The loss results from both fusion splicers and
OTDRs are estimates, with considerable uncertainty. The
splicing machines estimate based on the optical images of the
fibers. The OTDR estimates loss based on fiber backscatter and
may give significant differences depending on the direction of
test. The differences you quote are within the uncertainty of
the two instruments.
APC
Connectors
Q: Why NOT make the use of APC connectors the new
standard for all adds, moves and changes to any campus, MDU or
similar application using single mode cable?
A: There is absolutely no reason not to use APC
connectors other than the cost is slightly higher and one must
be careful if they are used in a cable plant that also has PC
or UPC connectors because they are incompatible. We recommend
them all the time for short links like data centers, passive
optical LANs and FTTH where runs of singlemode fiber are
short. In fact they are very common in these networks today.
Cleaning
Connector Protective Caps
Q:How do you clean LC Fiber Optic end caps (the cap that
covers the cleaned fiber cable)? Is there a tool for that?
A: We assume you are talking about the small plastic
protective caps on the connector ferrule. There is a joke in
the industry that goes &#;there&#;s a reason they call them "dust
caps&#;&#; they&#;re often full of dust.&#; The problem is these are
plastic molded parts that are made by the billions for various
purposes - some just fit fiber optic connectors. They come out
of the molding machine and are dumped in barrels. No provision
is made to keep them clean, plus they will have some mold
release chemicals inside them that can attract or hold dust.
Even static electricity is a problem.
We know no way to clean them nor to keep them clean. We
recommend using them to protect the connector ferrule - in
fact we&#;re trying to get people to call them &#;protective caps&#;
- but after they are removed and before use (connecting to
another cable or a transceiver or testing them) they need
inspection and cleaning.
See these pages in the FOA Guide: Microscope
Inspection And Cleaning of Fiber Optic Connectors
Cleaning
Fiber Optic Connections
Directional Splice Loss
Q:
I have a customer that is splicing a fiber distribution hub to
their fiber plant. The fiber distribution hub utilizes
100FT long fiber stubs of SMF G.657.A1 and the fiber plant
uses SMF G.654.D. The project has a contract fusion
splice passing spec of 0.2dB loss, averaged bi-directional and
also a one-way <0.3dB loss (either direction)
specification; using an OTDR for measurements.
From my research, if the splices OTDR&#;s test results for the 2
directions are -0.2dB / +0.6 (average of +0.2), the network is
not actually seeing a +0.6dB loss; but this is how the OTDR
interprets the backscatter information&#; the OTDR being
somewhat confused due to the bend insensitive fiber
characteristics.
A: Correct - the directional differences are due to the
mode field diameter variations in the two fibers. G.654
is a large MFD fiber, ~12.5microns, compared to ~9 microns for
G.657.A fiber. The OTDR measures based on backscatter which
will be very different for the two fibers.
Connector
Mating Adapters
Q: I am looking for a standard that describes the value
of parameters (IL, RL) and class (if we can talk about class)
for FO mating adapters.
A: Mating adapters are part of the connection but like
each connector they only contribute to the total loss of the
connection and cannot be separated from the other two when
talking about loss. They can be specified by mechanical
dimensions and materials. For example on 2.5mm ferrule
connectors (SC, ST, FC and the obsolete FDDI and ESCON duplex
connectors) the mating adapters have had alignment sleeves
made of molded glass-filled thermoplastic, phosphor-bronze and
ceramic. The plastic ones are cheap but wear out quickly - 10
insertions will leave plastic dust all over the mating
connectors. Phosphor-bronze mating adapters last longer -
maybe 500 cycles. The ceramic sleeve ones last almost
indefinitely. We know this because we were in the test
equipment business for 20 years (we started FOTEC in and
sold it to Fluke in ) and we tested these mating adapters
for longevity with reference test cables used in insertion
loss testing. We had many calls from techs with problems
caused by the adapters with plastic sleeves. So the way we
know the mating adapters are graded is by alignment sleeve
materials.
APC
Connectors
Q: With a fiber optic pathway that has multiple
patching points...if the end user requires APC connections,
isn't it only important to have those angled connectors at the
end/equipment connections with UPC being acceptable throughout
the middle part of the link?
A:
Reflectance at the connection is the issue, of
course.
Reflectance near a transmitter can affect the laser
transmitter causing nonlinearities or noise in the device.
That&#;s always been a major concern.
The second issue is reflectance causing background noise in
the link. If you have ever seen a ghost on an OTDR, you have
seen a reflectance at a connection that is bouncing back and
forth in the fiber and is of high enough amplitude that you
can see it at the source. Of course if it reflects back and
forth in the fiber link, it will also show up at the receiver
end, becoming noise and/or distorting the receiver pulses. In
a bidirectional single-fiber network like a PON, it affects
receivers at both ends.
Some refer to this as multipath interference. It is being
studied by international standards groups but nothing has been
published on it as far as I know.
We are familiar with a link that was ~1km of SM fiber with
hand-polished ST connectors at several connections. The link
had acceptable loss for all the fibers in the cable but none
would work with electronics. Replacing the connectors with
fusion spliced pigtails cleared the problem up immediately.
Was the problem
With that background, I would answer you question this way.
APC connections at each end of the link will effectively stop
any reflectance issues going back and forth in the whole link.
Using UPC or PC connectors in the link with reflectance better
than -40dB are unlikely to cause problems. (Keep them clean of
course since dirty connectors show high reflectance.) If the
links are very short (<1km), the fiber will not attenuate
any reflectance substantially, so short SM links (FTTH and
passive OLANS for example) often use APC connectors
everywhere.
And a final practical issue - mixing APCs and PC connectors is
very bad, perhaps damaging the surfaces. If you do mix them in
a link, you must train personnel how to handle them. If you
have patch panels with PCs and equipment with APCs, for
example, you have to ensure the patch cords are color coded
properly (blue = PC, green = APC) and everybody knows not to
mix them
Connector
Loss At Patch Panel
Q: If I have two SC connections in a cabinet eg one
incoming cable jumperd to an out going cable. Should I be
looking for a loss of no more than .75db across the two of
them as per TIA-568
A:
TIA 568 has included a connector loss of 0.75dB for decades.
Even the committee is aware that this is a bogus number for
most connectors but they leave it in because the manufacturers
of MPO connectors need it to comply with the standard.
SC connections should be ~0.2-0.3dB if the connectors are good
and properly cleaned. Now in the patch panel you describe,
each of the two connections should be in that range for a
total loss of 0.2-0.6dB. TIA would allow 0.75dB for each
connection or 1.5dB total.
Differences
Between Singlemode or Multimode Connector Mating Adapters
Q: What is the difference between singlemode and
multimode bulkhead/adapters (mating adapters). My
understanding is you cannot use the singlemode with the
multimode and visa versa.
A: There are 3 types of adapters - rated for SM or MM
- based on the alignment sleeve material.
-Plastic (glass filled thermoplastic) alignment sleeves are
cheap, not very precise and wear quickly (you can see ceramic
ferrules get dirty using them) - only good for multimode and
one or two insertions - not recommended
-Metal (phosphor bronze) alignment sleeves are better with
good alignment but still wear some - OK for MM, some are rated
for singlemode (check before you buy), and are OK for most
uses but will wear out if used for repetitive testing
-Ceramic alignment sleeves are the best and most expensive.
They are very precise in alignment and last for a long time.
Recommended for all singlemode and all testing purposes.
Don&#;t use MM adapters for SM but SM adapters are OK for MM.
Polishing
Films
Q: Are there different grades (micron)
polishing films/papers for multimode and single mode fiber
cables in ODF termination ? If yes, What are the grades
polishing papers for multimode 50/125 um and 62.5/125 um
fibers.
A: The polishing of
MM and SM fiber is indeed different. Both start with an &#;air
polish&#; with 12micron alumina polishing film to remove the
protruding fiber. Then the polishing continues on a soft
polishing pad (3mm 80 durometer rubber).
MM uses a 3micron alumina polishing film polished dry then a
final 0.3micron alumina film polish. See
http://www.thefoa.org/tech/ref/termination/ConnHints.html
SM is usually done with a wet polish using as special
polishing slurry and diamond polishing film. The diamond film
will polish both the ferrule and the fiber to get the best end
finish. See http://www.thefoa.org/tech/ref/termination/sm.html
There are even more pages of information on the FOA Guide at http://www.thefoa.org/tech/ref/contents.html#Components
MPO
Connector Loss
Q: Is there a current standard, for maximum allowable
loss, for MPO fiber connectors? If so&#; what is the standard #
from EIA/TIA? (Was it amended in 568B, since they were
introduced?) Would it be similar to standard connectors @
0.75dB Max allowable loss?
A: The MPO is covered
under the TIA 568 standard. All fiber optic connectors are the
same - 0.75dB.
There are discussions being held at TIA and ISO/IEC on using a
different method of specification, statistical in nature, that
says X% would be less than YdB in several stages from 0.1-0.2
to over 1dB, but it&#;s led to some headed discussions.
MPOs for MM are probably no less than 0.5dB and SM are near
the 0.75dB mark. At least the SM ones are APC (usual 8
degrees, but still a flat polish).
I&#;ve recently learned that MPOs are polished for fiber
protrusion to try to get fiber contact, but the evenness along
the line of fibers is harder to control.
image from SUMIX
showing protruding fibers in MPO connector
Fusion Splicing Regular And Bend-Insensitive
Singlemode Fiber
Q: Would fusion splicing
single mode bend insensitive to standard fiber with
same core cause a numerical aperture mismatch? We
are seeing loss but it&#;s hard to tell from what.
Going from a drop to BI inside cabling. Any
direction is appreciated!
A: There is a lot of
controversy in this area and has been for some time.
The issue is mode field diameter(MFD)
differences between regular and bend-insensitive
(BI) fiber caused by the low index trenches around
the core that are used to limit bend insensitivity.
Some (maybe most) manufacturers make BI SMF to match
MFD of their regular SMF, since a common use is
splicing BI SMF pigtails onto regular SMF. With so
much BI SMF fiber being used in microcables and high
fiber count cables, the opposite situation could be
an issue also.
Another factor at play here is the fusion splicing
program. The different structures of the fiber may
need special programming in the fusion splicer to
get heat and feed right for the two different
fibers.
FOA hopes to have some independent data on this
topic soon. FOA Master Instructor Joe Botha has done
tests before on splicing dissimilar fibers when BI
fiber first became available (read the
report here) and has planned a
more extensive set of tests to update that data for
more recent fibers soon.
Fusion
Splicing Live Fibers
Q: Is it safe to fusion splice a live fiber, or is
there a chance that
the light from the arc will damage the detectors in the
modules at the end (20km-rated SM for us).
A: I have never heard
of this being a problem. The amount of light coupled into the
fiber from the splicing would be very small compared to a
properly coupled laser. When a cable is broken you might be
splicing the fibers that are live without knowing which are
live and not caring. On your newer splicers this is not a
problem. On the older splicers with the LID system you would
have to reduce the power to get a good splice which they would
do by putting a bend in the Fiber.
Maximum Fusion Splice Loss
Q: We have set 0.4 dB as our max for all losses per splice
and my counterparts argue that customer quality will not suffer with a
1.0db-1.5db loss at a splice. What do you think?
A: We would argue that the issue with high loss splices is more
one of reliability. Most fusion splices of singlemode fiber are 0.05 to
0.1 dB A splice that has more than ~0.2dB loss probably has some
inclusion (dirt that got on the fiber after cleaving) or an air bubble
with means the splice is deficient in strength and may fail over time.
If the network is operating at high power with WDM and fiber amplifiers,
the inclusions or bubbles may produce heat which can cause failures. At
very high speeds or using coherent communications over long lengths, it
might affect dispersion.
Testing
Connectors (From A Patchcord Maker)
Q:
A:
The description on our Guide is here: http://www.thefoa.org/tech/ref/testing/test/conntest.html
"Connector
Loss" or "Connection Loss"
Q: I have always counted the loss of a connector as
.75 dB (568B-3) and 1.5 for a mated pair. Is that correct?
A: While the industry
always says "connector" loss, it is actually "connection"
loss. As we explain in the page on termination and splicing (http://www.thefoa.org/tech/ref/basic/term.html)
When we say "connector" loss, we really mean "connection" loss
- the loss of a mated pair of connectors, expressed in "dB."
Thus, testing connectors requires mating them to reference
connectors which must be high quality connectors themselves to
not adversely affect the measured loss when mated to an
unknown connector. This is an important point often not fully
explained. In order to measure the loss of the
connectors you must mate them to a similar, known good,
connector. When a connector being tested is mated to several
different connectors, it may have different losses, because
those losses are dependent on the reference connector it is
mated to."
The TIA spec of 0.75dB is for a mated pair of connectors. If
you have been passing connectors tested @ 1.5dB loss....you
may have some very bad connectors in your cabling!
Fiber Splicing Cost
Q: What is the standard of costing for fiber splicing and
terminations? Is it per core / per splice or per each cable end
irrespective of the number of cores?
A: That is a very hard question to answer, other than to say &#;it
depends. &#; The number of fibers is definitely a factor because each
fiber must be stripped, cleaned, cleaved and spliced then placed in the
splice tray.
It also depends on:
Mating Mismatched Connectors
Q: I have a question during OTDR Testing... The interface
port of the OTDR is SC-APC so i have also a launch cable with SC-APC
connectors, end to end. the fiber cable plant that i need to test has a
patch panel connector of LC-UPC.. can i use a hybrid adapter to connect
my launch cable to the patch panel? if this is allowed, what will be the
formula for calculating the connector loss.. note: the adapter has an
insertion loss of <0.3dB
A: You need to use a hybrid adapter cable with a LC/UPC
connector on one end to connect to the cable plant under test and a
connector to connect to your usual launch cable - and that cable needs
to be longer than the dead zone of the OTDR so the connection to the
cable plant can be separated and not affected by the connection on the
other end to your normal launch cable. Alternatively, you can have a
hybrid launch cable with SC/APC on the OTDR end and LC/UPC on the cable
plant end.
You cannot use a hybrid mating adapter. The angled SC/APC connector
cannot be mated to a UPC connector. Anyway th ehybrid SCLC mating
adapters are not a good idea becasue of the difference in the diameter
of the ferrules.
Maintaining Fusion Splicers
Q: What are the best practices for the preventative maintenance of splicers, cleavers, and thermal strippers.
A: Because of the large number of manufacturers and variety of
models and applications, The FOA generally tells people to follow the
manufacturer&#;s directions for use and be especially careful about
keeping the splicer unit, cleaver and stripping tools clean, then having
it serviced regularly by the manufacturer or an authorized service
facility.
Splicing Dissimilar FIbers
Q: Recently I came across a new problem while splicing optical fiber
cable. Splicing of 2 Fujikura fibers was done but loss was
observed. Initially, we felt that it is due to splicing but upon
resplicing the loss was still the same i.e. 0.3db at the splice point.
Both the cables were checked again and observed that both cables were
from different manufacturers. My question is that if different
manufacturer's cables are spliced, will it give loss? Note: Both fibers
were Fujikura but had different IOR.
A: The difference in IOR tells the reason. The loss at the joint
between the two fibers when measured by an OTDR depends on the optical
characteristics of the fibers. A difference in the fibers IOR and
backscatter coefficient will cause the loss measurement to be affected.
In one direction it measures too high, in the other direction too low or
even shows a gain. That&#;s why some measwurements are called gainers. If
you measure it in the opposite direction you should see low loss or a
gain. It&#;s explained here in the OTDR page on the FOA Guide https://foa.org/tech/ref/testing/OTDR/OTDR.html in the section &#;OTDR Measurement Uncertainty.&#;
Basic
Tests For Fiber Optic Cable Plants
Q: I
A:
Fiber optic testing does have a hierarchy of tests.
Is A "Flashlight Test" Adequate?
Q:
I contracted a firm to install an OM3 of 200 meters. On one end I have an SFP SX ,on the other a SX converter from optical to UTP. We made pings but they never reached, and I didn&#;t see the laser at the extreme of the fiber. They promised me to send me the certification they supposely made ,though they assured me the fiber is ok, because WITH A FLASHLIGHT THEY SENT WHITE LIGHT FROM ONE SIDE TO THE OTHER AND IT WAS VISIBLE. I saw the light too, and I thought the culprit was my switch or my SFP. I want to know: is this a good demonstration that the fiber is ok?A:
A visual continuity test is not adequate - your eye is not calibrated! The power of the lamp is unimportant as each eye&#;s sensitivity is different. And your eye probably cannot see the light from a 850nm VCSEL source - most people&#;s eyes are not sensitive at that infrared wavelength. The installer should have tested the link with a light source and power meter (http://www.thefoa.org/tech/ref/testing/test/OFSTP-14.html) and given you the loss in dB. The connectors should also be inspected with a microscope to ensure proper polishing and cleanliness (http://www.thefoa.org/tech/ref/testing/test/scope.html). If the SFP output is -6dBm, what is the power at the receiver? base-SX is supposed to work with 4.5dB loss (see http://www.thefoa.org/tech/Linkspec.htm). The fiber loss should be ~0.6 dB, so you must have >4dB connector losses! That says bad installation! The SX link should work over 200m if the fiber has been properly installed.
Microscope
Magnification (11/13)
Q:
Calibration of Fiber Optic Power Meters
Q:
However, these meters have a menu item that allows you to calibrate them
yourself. We've calibrated all the ones we tested to match our
calibrated instruments and after that they work OK.
Interestingly, they show loss as negative dB, which is how we think it
should be. Some large, famous manufacturers manipulated the standards to
make loss a positive number, so if you measure gain, it is considered a
fault.
Differences in OTDR Traces
Q: What causes the differences in otdr traces for fibre cores that are in the same cable?
A: Several things can cause the fibers in a cable to have differences in their OTDR traces:
Differences in fiber from different production batches including fiber that may come from different preforms.
Differences in stress on the fiber caused by inconsistent cable design and manufacture
Of course differences in splices including stress on fibers in a splice
closure and terminations including stress on fibers in racks and panels.
Test Source Variations
Q: When we plug in the patch cable to use as a reference
to get ready for our insertion loss test, our power meter gives us
different readings each time we plug in and unplug the cable. Is
this normal?
A: If you plug a reference cable into a source, it is likely
to have some variation in coupling each time so the power out of the
cable is different. Once you plug the cable into the source and a
reference set with the meter, you should not remove the cable until you
finish testing.
Test Source Modulation Options
Q: Our light source user&#;s manual listed the following:
&#;In the actual project, it is necessary to load the audio carrier in the
optical signal to identify the optical fiber. The equipment contains
three carrier frequencies, which are 270Hz, 1KHZ, and 2KHz.&#; Can you
tell me if I need to be concerned about setting this to a certain value?
A: Sources often have an option to modulate the source for
use with another instrument called a &#;fiber identifier.&#; Then it offers
the output as DC or CW (a steady unvarying signal) or modulated at
270HZ,1 or 2 kHz. When testing loss the DC or CW setting should be used.
850 LED Test Source
A: Multimode fibers should be tested with an LED. Lasers have several problems in multimode fiber that may cause untrustworthy readings. The problem is that LEDs are no longer used for transmission systems; every MM system now uses VCSEL transmitters, a surface emitting laser. As a result most LEDs at 850nm for MM have gone out of production. Two engineers I know who have been looking for them say there is now only a few sources and the price is much higher that of a few years ago. We've been buying used test sources on eBay for training.
Optical Power Of FTTH Signals
Q:
Documenting Fiber Optic Cable Plants
Q:
Documenting Test Results
Maintaining
Dark Fiber
Q:
Identifying
Users On A PON Network
Q:
Microscope
Power For Connector Inspection
Q:
esting
Cable Before Installation
Testing
Cable Before Installation
Testing OM2/3/4 Multimode Fiber
Mismatched Fiber Losses
Reflectance
And Return Loss
Q:
Reflectance Testing Expanded Beam Connectors
Q:
LC/SC/ST
-----------to------------- MIL-DTL-
Or
MIL-DTL- -------to----------
MIL-DTL-
A:
Testing
At 820 or 850nm
Q:
OTDR AutoTest
Q:
A:
VFL for 10km?
Q: I have 10 kilometers of singlemode cable installed that was not labeled. It has been suggested that we shoot a VFL down the fiber and label it. I am having trouble finding a VFL that will shoot this far. Any ideas?Testing
PON Meters And Sources
Q:
A:
There is no requirement for having a PON to test the meters. I would check it against a meter you trust to testHigh
Loss At nm?
Q:
A:
That wavelength is the center wavelength of the OH+ water peak, so you are seeing the extra attenuation there. Older fibers will have attenuation of 2-3 dB/km at that wavelength but new &#;low water peak&#; fibers will be <1dB/km. See &#;Low Water Peak Fibers&#; here http://www.thefoa.org/tech/ref/OSP/fiber.htmlBi-Directional
OTDR Testing
Q:
A:
For more information, please visit Metallic Flexible Conduit.
Yes, you should use the same test set from each end but this way - take a trace, disconnect the OTDR from the launch cable and go to the far end of the receive cable and connect it there to take the second trace. The usual way people do bi-directional tests is to disconnect the launch cable and take it to the far end and shoot back up, often not using a receive cable at all, figuring they get the far end connector on the second test. But when you disconnect the launch cable (and/or the receive cable) you lose the connection you want to test in the other direction! As for using the same OTDR, every OTDR is different and the results you get may be significantly different, esp. if they are not calibrated recently - and few OTDRs are ever calibrated.Calibrating
An OLTS
Q:
A:
Any optical loss test set needs to be calibrated for &#;0dB&#; whenever anything changes - the launch cable - source output - or even every few tests to ensure the connector is clean and undamaged - plus they wear out. See 5 different Ways To Test Fiber Optic Cables.Insertion
Loss
Q:
A:
Insertion loss was the term originally used for the loss of a connector tested by a manufacturer. They would set up a source and length of fiber connected to a meter, measure power, insert a pair of connectors and measure the loss. Since it was an inserted connection, it became known as insertion loss.Using
Hybrid 2.5-1.25mm Connector Mating Adapters
Q.
A:
We do not recommend them for most uses, especially testing, as they can be highly unreliable. Reserve them for emergencies and use hybrid patch cords instead.
Test MM Fiber @ nm?
Q:
What is your opinion about the need for testing at nm on OM3 and OM4 fiber especially now that bend insensitive multimode fiber is taking over?
A:
Another Way Of Expressing dB?
FTTH Network Loss
Testing FTTH Networks
Q:
OTDR Questions
Testing
Bare Fibers With OTDR
Q:
A:
I assume you mean you need to test with a bare fiber on the OPGW. For testing bare fiber, use a splice, not a connector. Have a long pigtail on the OTDR as a launch cable, long enough for the test pulse to settle, say 100-500m, then use a splice for a temporary connection. You can fusion splice the fibers then cut the splice out or use a removable splice like the Corning Camsplice (http://catalog.corning.com/opcomm/en-US/catalog/ProductDetails.aspx?cid=&pid=&vid=)
OTDRs
- Launch Cables And Range
Fiber Backscatter Coefficient
Q:
Negative Loss?
Q:
A:
OTDR Setup
Q: What are good OTDR settings for a 300-500m fibers? We&#;re using a 1.5 m launch cable and sometimes got (-) loss,
FOA consistently makes the point that the most
important part of a network design or installation is the documentation.
It tell the installers what to build and records their test results. It
helps troubleshoot faults if a cable plant problem arises and
restoration becomes necessary.
Documentation is also a big help when testing with
an OTDR, as two technical inquiries this month showed. One concerned
the testing of a cable still on the reel before installation. In this
case, just knowing the exact length of the cable or fiber would be
helpful.
Here is the first trace sent to FOA:
There was nothing wrong with the fiber.
The second trace was for a longer fiber, still a cable on a reel before installation:
The question was why was there a "gainer" in the middle of the fiber.
The trace sent to FOA showed a noisy trace with a "gainer" at around
feet. Again there seems to be no problem with the fiber, but the
OTDR setup caused the noisy trace and that "gainer" was because the
noise exceeded the threshold for events set in the OTDR. Redoing the
trace with a longer test pulse or longer integration time should reduce
to noise. In this case, just knowing the fiber was continuous with no
splices tells you a gainer (caused by the joint between two different
fibers) was not the cause of the event. And looking at the noise on the
fiber says the OTDR is either not properly set up or defective.
I
have 4 questions about OTDRs:
Q:
A:
Q:
Q:
"Connector Loss" or "Connection Loss"
Q: I
have always counted the loss of a connector as .75 dB (568B-3) and 1.5 for a mated pair. Is that correct?A:
While the industry always says "connector" loss, it is actually "connection" loss. As we explain in the page on termination and splicing (http://www.thefoa.org/tech/ref/basic/term.html) When we say "connector" loss, we really mean "connection" loss - the loss of a mated pair of connectors, expressed in "dB." Thus, testing connectors requires mating them to reference connectors which must be high quality connectors themselves to not adversely affect the measured loss when mated to an unknown connector. This is an important point often not fully explained. In order to measure the loss of the connectors you must mate them to a similar, known good, connector. When a connector being tested is mated to several different connectors, it may have different losses, because those losses are dependent on the reference connector it is mated to."
Are
FOA Videos and Web Up To Date?
Math
of Fiber Optics
Q:
Have An Old Cell Phonet? Use it to test for infrared light in fiber optics. See the video on
1&#; How much does a fiber drop cable cost?
Typically, the price per fiber optic cable ranges from $30 to $, depending on the type and quantity of fibers: G657A1/G657A2/G652D/OM2/OM3/OM4/OM5, jacket material PVC/LSZH/PE, length, and Structural design and other factors affect the pricing of drop cables.
2&#;Will fiber optic cables be damaged?
Fiber optic cables are often classified as fragile, just like glass. Of course, the fiber is glass. The glass fibers in fiber optic cables are fragile, and while fiber optic cables are designed to protect the fibers, they are more prone to damage than copper wire. The most common damage is fiber breakage, which is difficult to detect. However, fibers can also break due to excessive tension during pulling or breaking.
Fiber optic cables are usually damaged in one of two ways:
&#; Prefabricated fiber optic cables may damage the connectors if excessive tension is applied during installation. This can happen when long fiber optic cables are passed through tight conduits or ducts or when fiber optic cables get stuck.
&#; The fiber optic cable was cut or broken during operation and needed to be re-spliced to reconnect.
3&#;How do I know if my fiber cable is damaged?
If you can see a lot of red lights, the connector is terrible and should be replaced. The connector is good if you look at the other end and only see the light from the fiber. It's not good if the whole ferrule is glowing. The OTDR can determine if the connector is damaged if the cable is long enough.
4&#; How to Choose Fiber Optic Cables based on Bend Radius?
The bend radius of the fiber optic cable is critical for installation. Factors that affect the minimum radius of a fiber optic cable include outer jacket thickness, material ductility, and core diameter.
To protect the integrity and performance of the cable, we cannot bend it beyond its allowable radius. In general, if bend radius is a concern, bend-insensitive fiber is recommended,
allowing easy cable management and reducing signal loss and cable damage when the cable is bent or twisted. Below is the bend radius chart.
Fiber Cable Type
Minimum Bend Radius
G652D
30mm
G657A1
10mm
G657A2
7.5mm
B3
5.0mm
5&#;How to test fiber optic cable?
Send the light signal into the cable. When doing this, look carefully at the other end of the cable. If the light is detected in the core, it means the fiber is not broken, and your cable is fit for use.
6&#; How often do fiber cables need to be replaced?
For about 30 years, for properly installed fiber cables, the probability of failure in such a time frame is about 1 in 100,000.
By comparison, the chance of human intervention (such as digging) damaging the fiber is about 1 in 1,000 over the same time. Therefore, under acceptable conditions, a high-quality fiber with good technology and careful installation should be very reliable - as long as it is not disturbed.
7&#;Will cold weather affect fiber optic cables?
When the temperature drops below zero and the water freezes, ice forms around the fibers - which causes the fibers to deform and bend. This then reduces the signal through the fiber, at least reducing the bandwidth but most likely stopping data transmission altogether.
8&#; Which of the following problems will cause the loss of the signal ?
The most common causes of fiber failures:
&#; Fiber breakage due to physical stress or excessive bending
&#; Insufficient transmit power
&#; Excessive signal loss due to long cable spans
&#; Contaminated connectors can cause excessive signal loss
&#; Excessive signal loss due to connector or connector failure
&#; Excessive signal loss due to connectors or too many connectors
&#; Incorrect connection of fiber to patch panel or splice tray
Usually, if the connection fails completely, it's because the cable is broken. However, if the connection is intermittent, there are several possible reasons:
&#; Cable attenuation may be too high due to poor quality connectors or too many connectors.
&#; Dust, fingerprints, scratches, and moisture can contaminate connectors.
&#; Transmitter strength is low.
&#; Poor connections in the wiring closet.
9&#; How deep is the cable buried?
Cable Depth: The depth to which buried cables can be placed will vary depending on local conditions, such as "freeze lines" (the depth to which the ground freezes each year). It is recommended to bury fiber optic cables to a deep/coverage of at least 30 inches (77 cm).
10&#; How to find buried optic al cable s ?
The best way to locate a fiber optic cable is to insert the cable pole into the conduit, then use an EMI locating device to connect directly to the cable pole and track the signal, which, if done correctly, can provide a very accurate location.
11&#; Can metal detector s find optic al cable s ?
As we all know, the cost of damaging live fiber optic cables is high. They usually carry a hefty load of communications. It is imperative to find their exact location. Unfortunately, they are challenging to locate with ground scans. They're not metal and can't use steel with a cable locator. The good news is that they are usually bundled together and may have external layers. Sometimes, they are easier to spot using ground-penetrating radar scans, cable locators, or even metal detectors.
12&#;What is the function of the buffer tube in the optical cable?
Buffer tubes are used in fiber optic cables to protect fibers from signal interference and environmental factors, as they are commonly used in outdoor applications. Buffer tubes also block water, which is especially important for 5G applications because they are used outdoors and are often exposed to rain and snow. If water gets into the cable and freezes, it can expand inside the cable and damage the fiber.
13&#;How are fiber optic cables spliced together?
Types of Splicing
There are two splicing methods, mechanical or fusion. Both ways offer much lower insertion loss than fiber optic connectors.
Mechanical splicing
Optical cable mechanical splicing is an alternative technique that does not require a fusion splicer.
Mechanical splices are splices of two or more optical fibers that align and place the components that keep the fibers aligned by using an index matching fluid.
Mechanical splicing uses minor mechanical splicing approximately 6 cm in length and about 1 cm in diameter to permanently connect two fibers. This precisely aligns the two bare fibers and then mechanically secures them.
Snap-on covers, adhesive covers, or both are used to secure the splice permanently.
The fibers are not permanently connected but are joined together so that light can pass from one to the other. (insertion loss <0.5dB)
Splice loss is typically 0.3dB. But fiber mechanical splicing introduces higher reflections than fusion splicing methods.
The optical cable mechanical splice is small, easy to use, and convenient for a quick repair or permanent installation. They have permanent and re-enterable types.
Optical cable mechanical splices are available for single-mode or multi-mode fiber.
Fusion splicing
Fusion splicing is more expensive than mechanical splicing but lasts longer. The fusion splicing method fuses the cores with less attenuation. (insertion loss <0.1dB)
During the fusion splicing process, a dedicated fusion splicer is used to precisely align the two fiber ends, and then the glass ends are "fused" or "welded" together using an electric arc or heat.
This creates a transparent, non-reflective, and continuous connection between fibers, enabling low-loss optical transmission. (Typical loss: 0.1 dB)
The fusion splicer performs optical fiber fusion in two steps.
1. Precise alignment of the two fibers
2. Create a slight arc to melt the fibers and weld them together
In addition to the typically lower splice loss of 0.1dB, the benefits of splice include fewer back reflections.
14&#;What is the acceptable splice loss in optical fiber
Typical insertion loss for single-mode mechanical connectors ranges from 0.05 to 0.2 dB. Fiber splicing is one of the most widely used permanent methods of connecting optical fibers.
15&#; What is the difference between external fiber cable and i ndoor fiber cable ?
Indoor cables&#;
Fiber cables can be divided into indoor and outdoor according to different use environments.
The indoor optical cable is a kind of optical cable formed by optical fiber (optical transmission carrier) through a specific process. It mainly consists of optical fibers (glass filaments as thin as hair), plastic protective sheaths, and plastic casings.
There is no gold, silver, copper, or aluminum in the optical cable, and it generally has no recycling value.
The indoor optical cable is a kind of communication line that is formed by a certain number of optical fibers in a certain way, and some are wrapped with a sheath or an outer sheath to realize optical signal transmission.
Indoor fiber optic cables have low tensile strength and poor protection but are more portable and economical. Indoor optical cables are mainly used for building wiring connections between network equipment.
Characteristics of indoor optical cable&#;
Indoor optical cables have low tensile strength and a poorer protective layer, but they are relatively light and more economical. The indoor optical cable is mainly suitable for horizontal wiring and backbone subsystems. Outdoor optical cables have higher tensile strength and a thicker protective layer and are generally packaged with armor. Outdoor optical cables are primarily used in building complex subsystems and can be used on the occasions such as outdoor burial, pipeline, overhead and underwater laying, and other events.
Outdoor Fiber Cable&#;
Outdoor optical cables are optical cables for outdoor use. The comparison is the indoor optical cable. Outdoor optical cables are communication lines used for optical signal transmission.
A certain number of optical fibers form a cable core in a certain way, with an inner jacket and an outer jacket.
F
eatures of the outdoor optical cable :
It mainly consists of optical fibers (glass filaments as thin as hair), plastic protective sheaths, and plastic casings. There is no gold, silver, copper, or aluminum in the optical cable, and it generally has no recycling value. Outdoor optical cables have higher tensile strength and thicker protective layers and are usually armored (that is, covered with metal skin). Outdoor fiber optic cables are mainly used for interconnection between buildings and remote networks.
Contact us to discuss your requirements of Non-metallic Conduits. Our experienced sales team can help you identify the options that best suit your needs.