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The 2018-2019 Fiber Optic Update

Every year is another busy year for fiber optics. New technology, components, applications and usually a few surprises. On this page we've gathered some of the more important stories for the year, stories covering topics that FOA believes every tech needs to know. Many of these articles are from the FOA monthly newsletter, which you can subscribe to here.

We also recommend the FOA "Fiber FAQs" page with tech questions from customers originally printed in the FOA Newsletter. We had lots of interesting questions in 2018.

This page is part of a Fiber U Tech Update Course.

FOA Guide

Got questions? Try the FOA Guide and use the site search.


Optical Loss: Are You Positive It’s Positive?

A recent post on a company’s blog and article on the CI&M website discussed the topic of the polarity (meaning “+” or “-“ numbers) of measurements of optical loss, claiming loss was a positive number. The implication was that some people failed fourth grade math and did not understand positive and negative numbers. The claim is that insertion loss is always a positive number. Is that right?

Well the real problem is that to understand this you need to understand logarithms and that’s Algebra II*, way beyond fourth grade addition and subtraction. You see dB is defined as a logarithmic function:

dB equation

With logarithms, if the ratio of measured power to reference power is greater than 1, e.g. measured power is more than reference power, the log is positive. If the ratio of measured power to reference power is less than 1, e.g. measured power is more than reference power, the log is negative. If the ratio is 1, the log is 0.

Since the logarithm for optical power ratio is base 10 and then multiplied by 10, each change of 10 in the ratio of the measured and reference power becomes a change of 10dB. E.g. +10 dB is a factor of 10 (10 times log10 10 which is 1), +20dB is a factor of 100  (10 times log10 100 which is 2), +30dB a factor of 1000  (10 times log10 1000 which is 3)and so on. Negative dB means division, so -10 dB means a factor of 1/10th  (10 times log10 0.1 which is -1), -20dB a factor of 1/100th  (10 times log10 0.01 which is -2) and so on. 0 dB means the measured power to reference power ratio is 1 – they are equal.

Let’s try a graphic explanation of this equation. Take a look at this “semi-log” graph (logarithmic on the x axis and linear on the y axis) of dBm vs optical power in the range commonly used for fiber optics and calculated with our equation above. Remember 0 dBm means all power is referenced to 1 milliwatt optical power.

dB to watts

As you move to the right, power increases and the value in dBm gets more positive – that would be gain. So from 1mw to 10mw, we see a gain from 0dBm to +10dBm or 10dB, a positive change.

As you move to the left, to lower optical power, as would be loss, the dBm value gets more negative. From 1mw to 100microwatts (that’s 1/10mw), we go from 0dBm to -10dBm, or -10dB; that negative change indicating a loss of 10dB.

That shows gain is positive dB and loss is negative dB. Now we’re getting to the fourth grade math.*

How about an example? Let’s say we decide to test a singlemode cable plant. We start with a laser source and launch cable which we measure our reference level for loss with a power meter to have an output of 0dBm. That’s 1 milliwatt of power, about the normal output of a fiber optic laser. After we attach the cable plant to test and a receive cable to our power meter, we measure 3dB loss.

What power did we measure? The power must be lower, of course, since we have loss, and 3dB is approximately a factor of 2, so the power the meter measured is 1mw divided by 2 = 1/2milliwatt or 0.5mw. Since our power meter is measuring in dBm, it will read minus 3dBm (-3 dBm), since lower optical power is always more negative. If it read +3dBm, the power measured would be 2mw and that would be a gain from our reference (0dBm) which we know is incorrect – passive cable plants are not fiber amplifiers.

Here is the graphical version of this loss test:

 dB loss or gain

And then there is this short movie on the FOA Guide page explaining dB showing how a power meter shows loss when a cable is stressed to induce loss:

dB on a power meter

As the fiber is stressed, inducing loss, the power level goes from -20.0 dBm to --22.3 dBm.That's a more negative number.

No question – loss means a more negative power reading in dB and a negative number in dB indicates loss.**

But if you are a manufacturer of fiber optic test instruments that offers optical power meters and sources to test loss, why would this confuse you? 

Perhaps we should blame accounting.

Suppose you have a company that has $1million in sales and $900,000 in expenses. What’s the profit? It’s $1,000,000 - $900,000 = $100,000. That’s a profit, right?

But suppose your company has $1million in sales and $1,100,000 in expenses. What’s the bottom line? It’s $1,000,000 - $1,100,000 =  - $100,000. Wait a minute, that is a negative number – that’s not a profit, it’s a loss.

So in accounting, profits are positive numbers and losses are negative numbers when we do the math, but when we talk about loss, we don’t say we have a loss of “-$100,000,” we just have we have a loss of $100,000. Then we’ll put that number in parentheses when we publish our P&L like this ($100,000) and hope it doesn’t get noticed by investors, but you know it will.

Loss and gain in fiber optic measurements are similar. If you are using a separate source and power meter, loss will be a negative number and gain will be a positive number. But because of convention, we sometimes drop the signs when we report the values because loss always means the optical power measurement was negative and gain means the optical power measurement was positive. But maybe that’s not what the convention has evolved to.

Optical loss test sets (OLTS) aren’t designed to measure and display optical power, just loss. The actual power measured is lost in the algorithms used for calculating loss based on the “0dB” reference power and the measured loss. Long ago, most OLTS measured loss and displayed it as a negative number, but some companies who got into the fiber optic test equipment business from other test businesses arbitrarily decided to display loss as a positive number, and today most OLTS do show loss as a positive number. But when the instrument sees a gain, which it can do if improperly used, it therefore displays a negative number, which can be very confusing to a trained fiber tech who understands fiber optic power and loss measurements.

OTDRs do the same thing. I looked at traces from a half-dozen OTDRs and all showed loss as a positive number and gain as a negative number. And yes, when you have a gainer in one direction, they show it as a negative number. Telling them that is wrong will fall on deaf ears, I’m afraid.

The same article/blog post goes on to discuss optical return loss and reflectance, which has similar issues but they get it more or less right, which is confusing. Why can they understand that more negative numbers for reflectance means lower power in the reflectance but claim the opposite for insertion loss?

The “less right” is that with most OTDRs reflectance of an event and optical return loss (ORL) are not the same thing. ORL is the summation of all reflectance events and fiber backscatter from the entire length of fiber.

And, please, please stop saying “back reflection;” a reflection always goes back toward the source so the term is redundant and was dropped from fiber optics years ago.

*So the problem is not simply fourth grade math, it also involves a bit of convention and tradition and marketing. And it requires understanding logarithms that create the negative number of loss. That’s more like Algebra II or 7th grade math, and here is a good tutorial from Kahn Academy on that:

And more basic, here is a tutorial on adding and subtracting negative numbers

** If you want to calculate this yourself, FOA has a XLS spreadsheet you can download that will calculate the equations for optical power for you.

The FOA has an explanation of dB on our online Guide and a couple of graphics that illustrate what happens with loss.

What's That Fiber?

Regular and BI MMF

A reader sent FOA these microscope photos of two MM (multimode) fibers, asking what was the difference with the one on the right. It is a bend-insensitive fiber and compared to the regular graded-index MM fiber you readily notice the index "trench" around the core that reflects light lost in stress bends right back into the core. You can read more about bend-insensitive fiber in the FOA Guide.

Blasting Near Fiber Optic Cables

Last month we ran a Q&A question about blasting near fiber optic cables. Bill Graham, FOA Board Member and long-time instructor in Canada, tells us that he suggests a more conservative approach. This is what he has taught in his classes:

Blasting and Fiber Optic Cables

Two situations:
1.)    Aerial on poles or towers
2.)    Buried in ground


Blasting near fiber optic cables
Blasting close to poles with fiber optic cables can depend on the soil between the blasting area and the pole.  For example:  In parts of Ontario there are large areas of solid granite. The pole is generally bracketed to the rock. (Some areas have started drilling the rock) there is a solid connection from the blast hole to the pole, up the pole onto the bracket and to the Fiber Optic cable, which they seem to forget is glass.

Blasting near fiber optic cables

We recommend the following:
1.)    Cover the aerial cable with Big O (4” perforated drain pipe slit along the length) as shown in the photo above. This protects only from flying rock.
2.)    Removing the cable from the pole clamp and hanging it from the bracket with a  Bungie strap.

Blasting near fiber optic cables

Blasting locations are carefully engineered… however, if the crew wants to get home early on Friday and they double up on the blasting the damage risk increases substantially. ( The red cups in the photo are blast holes.) Most companies are wary  enough not to guarantee “no glass damage”. This area is almost all solid granite.

Cables Buried Underground:
Regardless of Kinder Morgan’s recommendation, I suggest 5-6 meters separation is not adequate and  should be at least 12 to 15 meters.

The Perils Of 2-Cable Referencing

This month FOA received an inquiry about fluctuations in insertion loss testing. The installer was using a two cable reference method where you attach one reference cable to the source, another to the meter and connect them to set the "0dB" reference. The 2-cable reference method is allowed by most insertion loss testing standards, along with the 1- and 3- cable reference methods, although each gives a different loss value.

When a 1-cable reference is used, one sets a reference value at the output of the launch cable and measures the total loss. With a 2-cable reference, a connection between the launch and receive reference cables is included in making the reference, so the loss value measured will be lower by the amount of that connection loss. The 3-cable reference includes two connection losses so the loss will be lower still.

two cable reference
The other problem with the two cable reference is the uncertainty added by including the connection between the two reference cables when setting the
"0dB" reference.Unless you carefully inspect and clean the two connectors and check the loss of that connection before setting the "0dB" reference, you add a large amount of uncertainty to measurements of loss. The best way to use a 2-cable reference is to set up the source and reference cable (with inspected and cleaned connectors), measure the output of the launch cable, attach the receive cable (with inspected and cleaned connectors) and measure the loss of the connection before setting the "0dB" reference. If the connection loss is not less than 0.5dB, you have connectors that should not be used for testing other cables. Find better reference cables.

Unfortunately, one reason the two cable reference is often used is the connectors on the cables or cable plant being tested are not compatible with the connectors on the test equipment, so you must use hybrid launch and receive cables. Then you can only reference the cable when connected to each other. In that case, you are stuck with the 2-cable reference and should expect higher measurement uncertainty. Experiments have shown that the uncertainty with a 1-cable reference is around +/-0.05dB while the 2-cable has an uncertainty of around +/-0.2 to 0.25dB caused by the mating connection between the two reference cables. Those experiments also showed the uncertainty of the 3-cable reference was not significantly larger than the 2-cable reference.

When possible, use a 1-cable reference. When you must use the 2- or 3-cable reference, inspect and clean all connectors carefully before making connections for the reference or test.

Troubleshooting With A VFLFibers Damaged In Splice Trays

Is this a trend? Twice in one week, we have inquiries from readers with problems and both were traced to fibers cracked when inserted in splice trays. The photo below shows one of them illuminated with a VFL. This was the same issue we found in the first field trial of a VFL more than 30 years ago that led to its popularity in field troubleshooting.

Broken fiber found with visual fault locator
Photo courtesy Alan Kojima.

They've ALL Got It All Wrong - And They Confuse A Lot Of People - YOU CANNOT STRIP THE CLADDING OFF GLASS FIBER!!!

We recently got this email 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:

bad fiber drawings

EVERY fiber drawing we found on the Internet search with one exception (which we will show in a second) showed the same thing - the core of the fiber separate -sticking out of the cladding and the cladding sticking out of the primary buffer coating. Those drawings are not all from websites that you might expect some technical inaccuracies, several were from fiber or other fiber optic component manufacturers and one was from a company specializing in highly technical fiber research equipment.

The only drawing we found that does not show the core separate from the cladding was
- really! - on the FOA Guide page on optical fiber.

correct fiber drawing

No wonder everyone is confused. Practically every drawing shows the core and cladding being separate elements in an optical fiber.

So how did FOA help this student explain the facts to his instructors? We thought about talking about how fiber is manufactured by drawing fiber from a solid glass preform with the same index profile as the final fiber. But we figured a simpler way to explain the fiber core and cladding is one solid piece of glass was to look at a completed connector or a fusion splice.

We started with a video microscope view of the end of a connector being inspected for cleaning.

fiber view - core/clad

Here you can see the fiber in the ceramic ferrule. The hole of the connector is ~125 microns diameter (usually a micron or two bigger to allow the fiber to fit in the ferrule with some adhesive easily.) The illuminated core shows how the cladding traps light in the core but carries little or no light itself. This does not look like the cladding was stripped, does it?

Here is the same view with a singlemode fiber at higher magnification.

Fiber view - SM

And no connector ferrules have 50, 62.5 or 9 micron holes so that just the core would fit in the ferrule, do they?

What about stripping fiber for fusion splicing. Here is the view of fiber in an EasySplicer ready to splice.

Fusion splice - core/clad

What do you see in the EasySplicer screen? Isn't that the core in the middle and the cladding around it? In fact, isn't this a "cladding alignment" splicer?

We rest our case. If that's not sufficient to convince everyone that you do not strip the cladding when preparing fiber for termination or splicing, we're not sure what is.

Special Request: To everyone in the fiber optic industry who has a website with a drawing on it that shows the core of optical fiber separate from the cladding, can you please change the drawing or at the very least add a few words to tell readers that in glass optical fiber the core and cladding are all part of one strand of glass and when you strip fiber, you strip the primary buffer coating down to the 125 micron OD of the cladding?

Are Manufacturers Beginning To Realize That It's Time To Go Singlemode?

Back 40 years ago when I (JH) was being introduced to optical fiber technology by the scientists at Bell Labs in Murray Hill, NJ who were developing it, they gave me a glimpse of the future technologies. At the time, the installed fiber links were based on 850nm Fabry-Perot lasers (VCSEL technology was 20 years in the future) and multimode fiber (62.5/125 micron was their standard then, later replaced with higher bandwidth 50/125 fiber for the early long distance links.)

But the future would be dominated by singlemode fiber, they assured me. These scientists, many of whom had worked on the Bell Labs projects associated with millimeter wave transmission in the 1960s, explained that multimode fiber had the same problem as mm RF waveguides - noise and bandwidth limits caused by multimoding. To realize the potential of optical fiber, it was necessary to move transmission to singlemode fiber.

The transfer from multimode to singlemode fiber was not simple. At first, there were attempts to make 850nm singlemode fiber. The problem was the core needed to be ~4-5 microns diameter, a problem since the technology to make optical fiber with precise geometry did not exist then, nor was there technology to make connectors precisely enough. Some of that fiber was made, and is still being made, but it's use is mainly for sensors like fiber gyros, and in the 1990s for use in measuring mode fill in multimode fiber using the CPR (coupled power ratio) technique. Furthermore, moving the wavelength of transmission to longer wavelengths in the infrared allowed larger core sizes (~8-10 microns) where the loss of the fiber is much lower as well as easier manufacture of the components.

All the necessary technologies came together in the early 1980s. Lasers were developed and mass produced at 1310nm (built on assembly and test equipment supplied to AT&T by my company Fotec.) Singlemode fiber was successfully engineered and manufactured by AT&T, Corning and others. The final breakthrough came from Japan, where NTT and Kyocera developed the ceramic ferrule connector that had the precision to mate singlemode fiber reliably. Other techniques like fusion splicing worked just fine with the new fiber.

We can probably say the turnaround to SM fiber started at one meeting, the KMI Newport Conference in the Fall of 1984. The technical lead of MCI presented a paper that stated MCI was abandoning digital microwave transmission, their transmission system of choice at that point, for singlemode fiber. After their talk, attendees, representing practically component and system manufacturer plus many users, ran for the pay phones (remember pay phones? this was before cell phones) in the hotel lobby to call their offices with the news.

From that point, the industry never looked back - telecom was all based on singlemode. Speeds increased, wavelength division multiplexing (WDM) increased fiber utilization. Fibers got installed under the seas and inside power lines. Now everything, including wireless, depends on those fibers.

But the data people who were just getting started connecting PCs on LANs, stayed with multimode. They could use cheaper LED sources with the multimode fiber for their slower systems (10Mb/s) over shorter links (<2km.) Longer links than about 500m used 1300nm LEDs rather than the 850nm LEDs because of the lower attenuation of the fiber (~1dB/km @ 1300 vs ~3dB/km @ 850nm.) When LANs got to 100Mb/s, fiber was re-engineered for higher bandwidth for 1300nm bandwidth to get the longer length links.

That was a stable technology for the entire 1990s. But when gigabit Ethernet was introduced, LED sources were no longer usable; they run out of bandwidth at a few hundred Mb/s. Fortunately inexpensive VCSEL lasers were developed that had the ability to be modulated at gigabit speeds, and have been upgraded for 10 and 25 Gb/s over the years. But VCSEL technology only works at 850nm, limiting its use to multimode fiber. And the introduction of VCSELs led to a return to the older fiber with a 50/125 micron core that had been optimized for lasers when it was used for the original telecom systems in the early 1980s.

VCSELs and multimode fiber have had a long run - 20 years now. Speeds have increased from 1 to 10 gigabits/second. Fiber has been engineered to have higher bandwidth, from OM2 to OM3 and OM4, and even to allow short wavelength division multiplexing (SWDM) with VCSELs in the range of 850-950nm.

But that run may be ending. We may see some use of MM fiber at 25 Mb/s, but that's just a small step up from 10 Gb/s. To get to the next big step, 100 Gb/s requires making a difficult choice: use parallel transmission over 8 or 20 multimode fibers, use the new VCSEL WDM over a pair of multimode fibers or use well-developed SM WDM over a pair of singlemode fiber singlemode fiber. The masses of multimode fiber needed for parallel transmission is a complicated solution and generally requires using prefab cable assemblies with array connectors. The transceiver industry has shown limited interest in SWDM and OM5 fiber is expensive. The SM WDM solution has been the choice of data centers who are using 100G and working their way toward 200, 400G and 1T - one terabit/s.

While high speeds have definitely migrated to singlemode, it's also become a viable choice for LANs. The passive optical network technology developed for fiber to the home (FTTH) has been successfully been adapted to LANs and has become the choice of many large LANs over the last 5 years. Adopting a passive optical LAN (OLAN) requires abandoning the 25+ year old structured cabling model, a tough choice for those who grew up in the "Cat 5" era. But a passive OLAN uses much less fiber, simplified electronics and typically costs half as much to build and maybe a quarter as much to operate. It's a no-brainer for large LANs as early adopters like government facilities discovered first and is now being implemented in hotels, hospitals, campuses, etc. While it's good for LANs, it's also compatible with wireless, both WiFi and cellular for indoor use.

Fiber techs who have worked with multimode in premises cabling often claim singlemode is much harder to install. Maybe that was true a decade ago, but the technology developed for outside plant and FTTH, especially multi-dwelling units and data centers has changed all that. Bend-insensitive fiber allows the cables to be made much smaller (microcables) and the same for ducts. Microducts allow fiber to the "blown in" more quickly. Splice on connectors (SOCs) and low cost fusion splicers solve the termination problem. This will cause techs to invest in some new gear and get some training, but the payback is there. And finally the last complaint about electronics cost is going away; transceivers are getting cheaper because of the higher volume, especially in data centers.

We've been saying this for decades, but now we're seeing others ask the same question. The impetus for this article was the announcement of two webinars - one by premises cabling stalwarts Leviton and Fluke Networks called "The Road To Singlemode" and one by the TIA FOTC called "Implementing next-gen PON technologies over existing fiber infrastructure."

Maybe it's time. But don't hold your breath. Like Cat 5, multimode will not "go gentle into that good night..." Dylan Thomas.

How about structured cabling? Last month we discussed a new version of Ethernet over a new single-pair UTP cable. Recently, Belden, a cable manufacturer, posted an interesting article titled "Single-Pair Ethernet Standards: Is Structured Cabling Dead? It includes the statement "With the advancement of networking protocols and applications, and the growth and evolution of IoT, we are seeing the end of the structured cabling world we’ve known so well for the past 30 years."

See also the article below on fiber types in data centers.

ED: In the article below on faster Ethernet standards, we've highlighted the fiber types to emphasize the dominance of SM fiber. Note that 6 of the 7 use singlemode fiber and 4 of the 7 use WDM over 2 fiber links.

200/400G Ethernet Approved

Last December, the Ethernet committee approved a new standard, IEEE Std 802.3bs-2017: 200 Gb/s and 400 Gb/s Ethernet with seven variations.

200GBASE-DR4: 200 Gb/s transmission over four lanes (8 fibers total) of singlemode optical fiber cabling with reach up to at least 500 m

200GBASE-FR4: 200 Gb/s transmission over a 4 wavelength division multiplexed (WDM) lane (i.e. 2 fibers total) of singlemode optical fiber cabling with reach up to at least 2 km

200GBASE-LR4: 200 Gb/s transmission over a 4 wavelength division multiplexed (WDM) lane (i.e. 2 fibers total) of singlemode optical fiber cabling with reach up to at least 10 km

400GBASE-SR16: 400 Gb/s transmission over sixteen lanes (i.e. 32 fibers total) of multimode optical fiber cabling with reach up to at least 100 m

400GBASE-DR4: 400 Gb/s transmission over four lanes (i.e. 8 fibers total) of singlemode optical fiber cabling with reach up to at least 500 m

400GBASE-FR8: 400 Gb/s transmission over an 8 wavelength division multiplexed (WDM) lane (i.e. 2 fibers total) of singlemode optical fiber cabling with reach up to at least 2 km

400GBASE-LR8: 400 Gb/s transmission over an 8 wavelength division multiplexed (WDM) lane (i.e. 2 fibers total) of singlemode optical fiber cabling with reach up to at least 10 km

An MPO-16 plug and receptacle is required to support the 32-fiber 400GBASE-SR16 multimode application. The MPO-16 plug is designed with an offset key to prevent accidental mating with a standard MPO/MTP receptacle. All 2-fiber applications may be supported with a 2‑fiber LC singlemode interface and all 8-fiber applications may be supported with standard MPO/MTP receptacles.

This graphic shows how many "outlaw" Ethernet versions there are:

Ethernet speeds

100G SWDM4 is for VCSEL WDM on OM5 fiber.  100GBase-ZR is a tech marvel using special modulation and coherent technology like long haul telecom. As you can see from the list above, the 400G standards are now approved along with some 200G not listed here. Remember our quote (above) from Bob Metcalfe, co inventor of Ethernet: 
"The wonderful thing about standards is we have so many to choose from."

What does Bend-Insensitive Fiber Look Like?

While researching the answers to the question above, we talked to Phil Irwin at Panduit. He mentioned that you could see the structure of BI fiber and sent along this photo:
Bend-insensitive fiber photo    BI fiber structure
At the left, you can see the gray area surrounding the core, shown in the drawing in the right as the yellow depressed cladding region.

If you want to try to see it yourself, it's not easy. Phil tells us that OFS fiber is the easiest to see, Corning a bit more difficult. You need a good video microscope. You may need to vary the lighting and illuminate the core with low level light.

If you try it and it works for you, send us your results.

How "Fast" Is Fiber?

We've probably all heard the comment that fiber optics sends signals at the speed of light. But have you ever thought about what that speed really is? The speed of light most people think about is C = speed of light in a vacuum = 300,000 km/s = 186,000 miles/sec. But in glass, the speed is reduced by about 1/3 caused by the material in the glass. The light is slowed down and the amount is defined as the index of refraction of the glass. V= speed of light in a fiber = c/index of refraction of fiber (~1.46) = 205,000 km/s or 127,000 miles/sec. So in glass, the "speed of light" is about 2/3 C, the speed of light in a vacuum.

One of the FOA instructors sent us this question:  "I work with at Washington Univ with an engineer who works for an electrical utility. He asked a question about the speed of signal transmission over fiber optics, single mode, at top of towers. They need signal to be sent in 18 millisecs for relays to function properly. Is there a problem over a distance of 150 miles?"

Electrical transmission lines

Let’s do a calculation:

C = speed of light in a vacuum = 300,000 km/s = 186,000 miles/sec
V= speed of light in a fiber = c/index of refraction of fiber (~1.46) = 205,000 km/s or 127,000 miles/sec
150 miles / 127,000 miles/sec = 0.00118 seconds or ~1.2 milliseconds

Another way to look at it is 127,000 miles/sec X 0.018 seconds (18ms) = 2,286 miles

So the fiber transit time is not an issue. The electronics conversion times might be larger than that.

I used to explain to classes that light travels about this fast:

300,000 km / sec
300 km / millisecond
0.3km /microsecond or 300m / microsecond
0.3 m per nanosecond - so in a billionth of a second, light travels about 30cm or 12 inches

Since it travels slower by the ration of the index of refraction, 1.46, that becomes about 20cm or 8 inches per nanosecond.

That is useful to know since an OTDR pulse 10ns wide translates to about 200cm or 2 m pr 80 inches (6 feet and 8 inches), giving you an idea of the pulse width in distance in the fiber or an idea of the best resolution of the OTDR with that pulse width. 

What Does A FTTH ONT Look Like Today?


That's all there is to the ONT that goes into the home. The arrow points to the 1310 TX/1490 RX transceiver for SC-APC connectors.


Here are several technologies that have continued growing in importance in the fiber optic marketplace  -  components that every tech needs to learn about and become familiar with their use.

High Fiber Count Cables

We ran this first in the March 2019 FOA Newsletter with updates in May and June. We received some feedback and have been talking to people in the industry also. We even have samples  to photograph. We thought we'd share some of what we've been told and see if others agree. Feel free to comment!

June 2019

High Fiber Count Cables

We've had a continuing feature on high fiber count cables in the FOA Newsletter and we now have some interesting photos to show you. Corning generously sent FOA some samples of 1728 and 3456 "RocketRibbonTM" cable. We took some photos and must admit that these cables are fascinating updates on the traditional fiber optic cables.

high fiber count cable

Here are Corning RocketRibbon 1728 fiber (bottom) and 3456 fiber (top) cables. To get an idea of these cables size, look at this photo:


The 3456 fiber cable is 32mm diameter, 1.3 inches. The 1728 fiber cable is 25mm, 1 inch diameter.

These are cables made from conventional "hard" ribbons, not the "flexible" ribbons used on some cable designs. As a result of using hard ribbons, the fibers are arranged in regular patterns to get high density.


These are the tubes of ribbons from these cables. Each of those tubes of ribbons has the equivalent of 24 ribbons of 12 fibers each (actually 8 X 12 fibers and 8 by 24 fibers stacked up) for 288 fibers total. The 1728 fiber cable has 6 tubes and a center foam spacer, with 144 ribbons total. The 3456 fiber version has 12 tubes and no spacers, 288 fiber ribbons total.

What amazes us is the density of fibers.


We calculated the "fiber density" of this 3456 fiber cable based on 200 micron buffered fibers and determined that 54% of the cable is fiber. Compare that to a typical 144 fiber loose tube cable, which is about 14% fiber or a 144 fiber microcable which is about 36% fiber.

Looking at the end of this cable reminded us of nothing so much as this PR photo from AT&T from their intro of fiber in 1976:


Not the fiber, the dense cable of copper pairs!

Of course the cable is much lighter than copper but much heaver than you are used to with fiber - it weighs 752 kg/km or about 1/2 pound per foot. And it's stiff. Very stiff. The minimum bend radius is 15 times the cable diameter or 480mm (~19 inches), about a meter or yard in diameter.

As we noted in the photo above, Ian Gordon Fudge of FIBERDK taught some data center techs how to handle a 1728 fiber Sumitomo cable with a slotted core. Ian sent FOA this photo to illustrate the number of fibers in the cable he was using for training. Impressive!

Fiber DK

Here is the slotted core that separates the flexible fiber ribbons
in the Sumitomo cable:

slotted core

More on high fiber count cables and our continuing coverage

March 2019

FOA has recently gotten several inquires about the new high fiber count cables - 1728, 3456 or even 6,912 fibers. Like this one from Prysmian with 1728 fibers:

Prysmian 1728 fibers

These cables use bend-insensitive fibers to allow high density of fibers without worrying about crushing loads affecting attenuation. Most also use fibers with 200 micron buffer coatings instead of 250
micron buffer coatings to allow even higher density. Many, or even most, use ribbons of fiber, either the conventional hard ribbons or the newer flexible ribbons, since, as we show below, the time to splice even a 1728 fiber cable is extremely long unless ribbon splicing is used.

High Fiber Count Cables may not be for everyone. Maybe only for a very few. A single cable that has as many fibers as 12-144 fiber cables (1728 fibers) in a cable with a diameter of only twice that of a conventional 144 fiber cable can present challenges.
  • First of all, the cost - it's high. You do not want to waste cable at this price. Engineering the cable length precisely will save lots of money.And it's worse for higher fiber counts.
  • Likewise, making mistakes when preparing the cable for termination can be expensive.
  • The cable may require special preparation procedures to separate fibers for termination. Most use new methods of identifying cables and bundles.
  • Besides skill, the tech working with high fiber count cables needs lots of patience.
  • Splicing multiple cables at a joint can get complicated keeping all fibers straight.
  • These cables will generally use 200 micron buffered fiber and often a flexible ribbon instead of a typical rigid ribbon structure to reduce fiber sizes. This may complicate splicing as the methodology to splice the flexible fibers and splice 200 micron fibers to regular 250 micron fibers is a work in progress.
  • Splicing 200 to 250 micron fibers may be easier with the flexible ribbon designs which make it easier to spread fibers to the same spacing.
  • We've heard the splicing time for flexible ribbons is about 50-100% longer than that of conventional rigid ribbons. So if you use that table below, you may need to increase your ribbon splicing estimates when working with flexible ribbons.

We've been looking for directions on how to deal with high fiber count cables. Several contractors tell us ribbon splicing is the way to go, and most of these cables now use a version of the new ribbon types that are flexible. We've  put together this table from some articles on splicing ribbons:
ribbon splicing

Is that realistic? We've heard the flexible ribbons may take
50-100% longer than conventional ribbons due to the need to carefully arrange and handle fibers.

Here's links to some of the information we've been reading and watching online:
Corning sticks with solid ribbons in high density cables.
Corning ribbon splice closure for 1728 fibers.
Directions from Corning on ultra high-density cabinets
Designing a high fiber count cable with flexible ribbons - SEI.
Fujikura (Japan) Highest density Optical Fiber Cable.
OFS Presentation on 200micron buffer, bend insensitive, high fiber count cables.
Ribbonizing 250 micron loose tube fibers for splicing, AFL Fujikura. (video).  (Written instructions too.)
Splicing AFL "SpiderWeb ribbon cable.
Ribbonizing 250 micron loose tube fibers for splicing, Sumitomo. (video).  
Procedures for ribbonizing and de-ribbonizing fibers.  (Telonix)
Some things you need to know about splicing 200micron buffered fibers.

Some things you need to know about the new ribbon cables (Prysmian)

These current links to news may disappear over time.

New Connectors

We're seeing some interesting new connectors being introduced. 3M announced a multifiber array connector using expanded beam technology and several new ideas of making a duplex connector smaller.

3M Expanded Beam Connector
3M Expanded Beam connector 3M

Details are sketchy but from the video on the 3M website, the connection is made by a small plastic fixture that is shown by the arrow in the top photo. The plastic seems to turn the beam 90 degrees so the connection is made when two pieces overlap., in the direction of the arrow in the lower photo. The connectors are hermaphroditic - that is two identical connectors can mate. There are models for singlemode and multimode fibers and you can stack the connection modules to handle up to 144 fibers. We understand this was not part of the 3M fiber optic product line recently acquired by Corning. 3M Expanded Beam Connector.  

For more information on expanded beam connectors, see the FOA Newsletter for October 2018 that discusses the R&M QXB, another multifiber expanded beam connector announced last Fall. 

In the FOA Newsletter for January 2018, we featured the SENKO CS connector, a miniature duplex connector using two 1.25mm ferrules, but much smaller than a duplex LC. The CS is sell on its way to becoming standardized with a FOCIS (fiber optic connector intermateabliity standard), but on the SENKO web page, there is another new connector, the SN, that makes the SC look huge! The big difference is the vertical format that allows stacking connectors very close. That can allow transceivers to have more channels, a big plus for data centers. Here is more information on the SENKO CS and SN connectors.


Comparison of SENKO CS (L) and SN (R) connectors with duplex LC.

US Conec MXC and MDC Connectors
The R&M and 3M expanded beam multifiber connectors reminded us that US Conec introduced the
MXC connector over 5 years ago, using similar technology for up to 64 fibers per connector. The MXC is on the US Conec website, but seems to be aimed at board level connections, not far off its original purpose as a connector for silicon photonic circuits. But when we checked the US Conec website, there was a connector name we dis not recognize, the MDC. The MDC (below) is a vertical format duplex connector using 1.25mm ferrules that looks similar to the SENKO SN above. Here is information on the US Conec MDC duplex connector.

US Conec MDC connectorUS Conec

Its All About The Data Center
Just like the high fiber count cables discussed above, the CS, SN and MDC connectors are aimed at high density cabling and transceivers for data centers. All three are specified for the new QSFP-DD pluggable transceiver multi-source agreement.

Micros: Microcables, Microducts and Microtrenching

Corning MiniXtend cable

144 fiber Corning MiniXtend cable is smaller than a pencil

MIcrocables, microducts and microtrenching - three technologies that have more in common than the prefix "micro" are gaining in acceptance along with blown cable, the obvious method of installation using them. Smaller is always better when it comes to crowded ducts, especially in cities where duct congestion is a problem in practically every city we have contact with.

With the demand for more fiber for smart cities services like small cells and smart traffic signals, not to mention a ton of other smart cities services, installing more cables in current ducts - without digging up streets - is a major interest. Sometimes it's possible to install microducts in current ducts with a cable and blow in a new microcable. Sometimes it's worth it to pull an older cable out and install a new microduct that will accommodate 6 cables, making room for future expansion. The makers of the fabric ducts, Maxcell, can even show you how to remove the ducts in conduit without disturbing the current cables and pull in fabric ducts to install more cable.

Comparison of MaxCell ducts to rigid plastic duct

If you have to trench, microtrenching is probably the best choice for cities and suburbs. Rather than digging wide trenches or using directional boring (remember the story about the contractor in Nashville, TN using boring to install fiber who punctured 7 water mains in 6 months?), microtrenching is cheaper, faster and much less disruptive.

All of this implies that contractors are willing to invest in new machinery and training, sometimes an optimistic assumption. Microtrenching machines and cable blowing machines are available for rent, but personnel must be trained in the design of networks using these technologies and operating the actual machinery in the field. That's still a considerable investment.

Splice-On Connectors

Terminating with SC SOC in EasySplicer

Termination has been seeing greater acceptance of the SOC - splice-on connector - using fusion splicers. It's popularity started in data centers for singlemode fiber where the number of connections is very large so the cost of a fusion splicer is readily amortized and the speed of making connections is the real cost advantage. The performance of SOCs is much better than prepolished/splice (mechanical splice) connectors simply because of the superiority of a fusion splice and the cost of the SOCs are much less since they do not have the complex mechanical splice in the connector.

We have used SOCs in training and the techs take to them readily. In classes you can combine splicing and termination in one session. The cost of fusion splicers has been dropping to near the cost of a prepolished/splice (mechanical splice) connector kit so the financial decision to use SOCs is easier to make.

Fiber For Wireless

WiFi, DAS or Small Cell?

Nothing provides perspective better than looking at something as an outsider. Especially an outsider who's just trying to understand something instead of an insider trying to perform successfully as an insider. That's how we feel about wireless communications. If you say "wireless" to an IT or LAN person, they think WiFi. But to a telecom person they think cellular. FOA's involvement is based on trying to understand the infrastructure to support wireless, OSP or premises, WiFi or cellular, tower site or small cell.

We're basically outsiders on the technology looking at the infrastructure to support them. Recently we've been trying to understand the technologies, markets and applications for both to better include the two technologies in our training and certification programs.

The initial question we had dealt with distinguishing DAS (distributed antenna systems for cellular) and small cells (also cellular). In most ways they seem to be very similar, except perhaps DAS is indoors and small cells outdoors.

We've started to interview insiders in both technologies to try to understand how they work and why we should have both. Right off, we found that there appears to be a general lack of technical understanding about the other from almost everybody we talk to who works with one of them. And we're talking real basics - what frequencies are used, protocols, coverage, bandwidth, etc. etc. etc. Even the jargon is different, but that's not unexpected. So we've tried to consolidate information on the three different premises wireless technologies appropriate for general usage. Over time we expect to refine this comparison with more data and user feedback. (got any? send it to us)

Based on the current evaluation, WiFi is essential to premises spaces and because of the ubiquity of WiFi, it is inexpensive. However, WiFi connections for cellular mobile devices appears to have not yet been refined sufficiently to provide reliable coverage for cellular voice, but data is good and video, maybe. Given the cost structure of data plans, using cellular for video can be very expensive but WiFi is preferable since it is only limited by bandwidth.

The choice between small cell and DAS in premises spaces is simple - small cells are generally single carrier connections and that is too limiting for most users. DAS is similar technology but has the advantage of offering multiple service providers. If better cellular service is desired indoors and WiFi connections for cellular calls is unreliable, a DAS is the best solution.

Small cells appear to be a good solution for better cellular service outdoors in metropolitan areas but the capital costs for building systems is quite high - Deloitte, you might remember from an earlier FOA Newsletter, forecast a cost of over $200 billion. It makes one wonder if the carriers can make that investment while simultaneously investing in 5G.

Premises Wireless
WiFi DAS (Cellular)
Small Cell (Cellular)
Connects to: PCs, tablets, phones, many other devices Phones, tablets, some other devices Phones, tablets, some other devices
Usage Free, sponsored Paid Paid
Origin Private, LAN Public, telco Public, telco
Frequency Ranges Unlicensed
2.5GHz (802.11n, 14 - 40MHz channels, 3 max non-overlapping)
5GHz (802.11ac or 802.11n, 24 -  80 MHz channels, 23 max non-overlapping)(more bandwidth, less range)
3G:  850, 1700, 1900, 2100 MHz
4G/LTE:  600, 700, 850, 1700, 1900, 2100, 2300, 2500 MHz
CBRS (Citizens band Radio Service, shared, unlicensed): 3600 MHz, 20MHz channels,
5G: Eur: 24-27GHz, US: 37-48GHz, 71-74GHz
3G:  850, 1700, 1900, 2100 MHz
4G/LTE:  600, 700, 850, 1700, 1900, 2100, 2300, 2500 MHz
CBRS (Citizens band Radio Service, shared, unlicensed): 3600 MHz,
20MHz channels,
5G: Eur: 24-27GHz, US: 37-48GHz, 71-74GHz
Connects to: Internet Multiple telco carriers Single telco carrier
Mobility Log in to each new private system required, limited handoffs between WiFi systems or WiFi and cellular
Seamless handoffs Seamless handoffs subject to coverage
BYOD (bring your own device) OK OK Depends on service provider device connects to
Optimized for Data 3G: voice
4G/LTE/5G: data
3G: voice
4G/LTE/5G: data
Data: Max data rate: 802.11n: ~35-300Mb/s
802.11ac: ~400Mb/s - 7 Gb/s (MIMO)
4G/LTE: ~100Mb/s
5G: ~Gb/s (proposed)
4G/LTE: ~100Mb/s
5G: ~Gb/s (proposed)
Voice VoIP: good
Cellular on WiFi: not optimal, depends on device/carrier/implementation
Good with proper coverage Good with proper coverage
Video Good 4G/LTE: marginal, expensive
5G: Good (proposed), cost?
4G/LTE: marginal, expensive
5G: Good (proposed), cost?
Cabling (typical)
Fiber backbone to Cat 5, POE
Fiber, sometimes Cat 5
Fiber, sometimes Cat 5
Best for data on PCs, tablets, smartphones, good for VoIP systems, marginal on cellular devices
Best for cellular devices since can cover all service providers, not optimal for high throughput data (today, future 5G ?)
Good for cellular devices but can cover only one service provider, not optimal for high throughput data (today, future 5G ?)

What We Learned From Visiting A Wireless Conference

FOA recently attended the WIA's Connect(X) conference in Charlotte, NC. This was the first wireless show we'd attended in over a year and the topics of conversation were similar to last year - 5G topped the list. We attended several tech sessions and our takeaway from one was the answer to an attendees question to a speaker: "When can we expect a standard for 5G." The answer was revealing: "5G is not a standard, 5G is a goal."

If you search the web for cellular standards, you will probably end up at a Wikipedia page called "Comparison of Mobile Phone Standards." It's an interesting history of the development of cellular systems. Nothing on that page refers to 5G, but there is a page on 5G that starts off saying "This article is about proposed next generation telecommunication standard. 5th-Generation Wireless Systems (abbreviated 5G) is a marketing term."

Generally we don't recommend using Wikipedia for technical information because it is too often edited for commercial bias, (that's why we created the FOA Guide,)  but in this case the candor is refreshing.

Zinwave  Ericsson DAS

As we toured the trade show exhibits, we did see something new, this "Standalone Small Cell" from Zinwave. What's notable, is that like a similar device we saw last year from Ericsson that saw at the IWCE wireless meeting and we reported on in the June 2017 FOA newsletter, it looks similar to a WiFi wireless access point including Gigabit Ethernet interfaces to standard Category-rated copper cabling. DAS, it seems is migrating to operating off Cat 6/Cat 6A in a structured cabling system. Since most offices need both cellular (small cell or DAS) and WiFi, this makes sense.

When we tried to find a link to this Zinwave device on the company website and could not find it, we found something even more interesting on a page called "Cellular As A Service": Unfortunately, carriers are no longer spending on in-building commercial cellular coverage in the way they used to. That means building owners—whether they are in commercial real estate, healthcare, hospitality, or the enterprise—are now having to find and fund the solution themselves, and it’s not easy. It’s difficult to budget for the kind of capital outlay needed to deploy an in-building connectivity solution.

This may indicate a movement to make indoor cellular more accessible using small cells replacing DAS. We've been told that DAS is a declining market because most of the large public areas like sports arenas and convention centers have been done. Enterprise DAS has not been as big but if small cells on LANs, similar to WiFi, becomes cost effective - and at least one person told us it would be - then we are looking at a change in enterprise networks.

Wireless At FOA: This addition of cellular wireless to WiFi and of course the usual fiber or copper Ethernet connectivity expected of a corporate network is something we've seen before, and it's the reason FOA expanded it's course offerings and certifications to include a general "Fiber For Wireless" programs. We now offer a free
"Fiber For Wireless" program on Fiber U, a curriculum for our schools to teach, and of course a page on the FOA Guide.

Recommended Reading: "Revealing Underlying Wi-Fi Problems with Ultrafast Broadband" by Adtran, a provider of equipment for networks.

Recommended Watching: A YouTube video on how the Mexican city San Miguel Allende installed a small cell/DAS system in a historic city. La ciudad de San MIguel de Allende se pone a la vanguardia en telecomunicaciones, al contar con un sistema de antenas distribuido conectado por fibra óptica. (In Spanish with English subtitles)

Nanotrenching Failure In Louisville, KY

Google FIber tried a new way to install cable in Louisville, KY, that turned out to be a very expensive failure. Nanotrenching is what some call very shallow trenching for installing fiber optic cable - see the photo below - and filling with rubber cement. It did not work.

Google Fiber ending service in Louisville

Chris Otts, WDRB Louisville,
Feb 7, 2019

LOUISVILLE, Ky. (WDRB) – Google Fiber is leaving Louisville only about a year after it began offering its superfast Internet service to a few neighborhoods, citing problems with the method it used to build the network through shallow trenches in city streets.

The shut off will happen April 15, said Google Fiber, a unit of Silicon Valley tech giant Alphabet, in a blog post Thursday.

Google Fiber has served about a dozen cities, and Louisville is the first it has abandoned."

Shortly after Google announced Louisville as a possible location in 2015, the Metro Council passed a utility pole ordinance at Google’s behest, then spent $382,328 on outside lawyers to defend the ordinance in lawsuits from AT&T and the cable company now called Spectrum.

Mayor Greg Fischer said in early 2016 that Louisville’s landing Google Fiber was “huge signal to the world.”

Louisville’s public works department allowed Google Fiber to try a new approach to running fiber – cutting shallow trenches into the pavement of city streets to bury cables.

It led to a lot of problems, including sealant that popped out of the trenches and snaked over the roadways.


Louisville street,
Copyright 2019 WDRB Media. Reproduced with permission.

It feels like you are using us for a science-fair experiment,” Greg Winn, an architect who lives on Boulevard Napolean, told Google Fiber representatives during a Belknap Neighborhood Association meeting last year. “…Our streets look awful.”

Google Fiber would go on to fill in the trenches with asphalt, what company executives said was like filling a 60-mile long pothole.

Google Fiber never ended up using the utility pole law -- a policy called One Touch Make Ready -- that Louisville passed at its behest, as the company only buried its wires instead of attaching them to poles.

A public relations representative for Google Fiber said no one was available for an interview.

In written responses, the spokesman said Google Fiber initially chose not to use the utility pole access because of "uncertainty" about whether the ordinance would hold up. Now that it has cut trenches in the streets, the company has no desire to start over.

Even using (One Touch Make Ready), we’d need to start from scratch, and that’s just not feasible as a business decision," the spokesman said.

FOA: Be sure to watch the video from WDRB.

Copyright 2019 WDRB Media. Reproduced with permission.

Telecom "Pole Wars"

New Battles In The "Pole Wars"

pole wars

You may remember the FOA Newsletter of July 2016 when we first reported on the battles raging over attaching new fiber optic cables to utility poles. The incumbents were trying to restrict access to their poles to try to stop or at least slow down the encroachment of newcomers wanting to build fiber networks, especially FTTH.

We've covered other skirmishes in the Pole Wars including the victory from the newcomers when several cities passed a "one-touch make-ready" (OMTR) ordinance (FOA NL 9-16) to ease the entrance of newcomers to the market after the incumbent dragged their feet on making ready poles for the newcomer. The battles were fierce as incumbents sent in battalions of lawyers to fight the OMTR ordinances in cities.

But now a couple of years later, the same companies that fought OMTR in cities are took the battle to the national level and convinced the new, big business friendly FCC to pass a national OMTR regulation. (See article below from last month.) Why the change of sides on this front? Simple, the big guys wanted access to those same poles - and every pole with a street light on it - for their small cell sites.

But the big guys did not stop there, they also asked for - and got - a nationwide maximum rate of $270 that cities can charge for small cell installations on public poles. Furthermore, the FCC decreed that the cities must respond to permit requests in less than 60 to 90 days, depending on the type of installation. And, If the cities charge more than $270 or take longer than 60 - 90 days they are subject to litigation.

“There has never been a federal decision to price-regulate the way local governments provide access to their own property,” said Blair Levin, a fellow at the Brookings Institution who served as chief of staff to Reed Hundt, the Clinton-era chairman of the FCC. “That’s an extreme step.”

Cities are reacting negatively to this intrusion on their sovereignty also. Not only is the FCC meddling in what cities see as their affairs, they note the idea of a nationwide fee of $270 is not realistic. Companies in Seattle can pay up to $1800 per pole annually. In Manhattan it can go as high as $5100. Comparing this to rural costs is irrelevant as the issue is where to cite small cells in cities.

According to an article in the LA Times*, the city of LA said that the break-even point for small cell facilities is $800 per installation. But in exchange for amenities such as free Wi-Fi in Skid Row and at recreation centers, $400,000 of scholarship money, and launching an innovation center in the city, L.A. is charging Verizon just $175 per device per year for 10 years for up to 1,000 installations, plus the cost of electricity. It is estimated that the city of LA will need 8-10,000 small cells for coverage.

The FCC says the new rule will save money for telecommunications companies, which will redirect those funds to deploy 5G service to less-connected rural areas. Haven't we hears promises like that before? And isn't it interesting how companies can switch sides of an issue like OTMR when it goes from being an advantage for others to being an advantage for them.

Stay tuned for the next battles in "The Pole Wars."

*If you read the article in the LA Times about LA and 5G  you will find the current common misconception that all small cells are 5G and current field trials are using 5G mobile devices. Not so. Small cells are being installed for current 4G/LTE mobile devices because 1) there is no standard for 5G - "it's a goal, not a standard" as one speaker said at a conference earlier this year and 2) there are no 5G mobile devices. Here's how one wireless website described a phone introduced as the first 5G smartphone:

"The world’s first 5G smartphone just launched and we all missed it mainly because there are no 5G networks to begin with. You’d have no way of actually taking advantage of 5G features just because your device supports the new standard. Also, the new Android phone, as it is now, can’t do 5G for another reason. It doesn’t technically have a 5G modem inside, which will be a problem when 5G launches."

FCC Adopts One Touch Make Ready (OTMR) Rules For Utility Poles

On August 3, The US Federal Communications Communications Commission adopted a new rule that allows "one-touch make-ready" (OTMR) for the attachment of new aerial cables to utility poles. From the FCC explanation of the rule, "the new attacher (sic) may opt to perform all work to prepare a pole for a new attachment. OTMR should accelerate broadband deployment and reduce costs by allowing the party with the strongest incentive to prepare the pole to efficiently perform the work itself."

You may remember that FOA has reported on the "Pole Wars" for several years. Battles over making poles available and/or ready for additional cable installation has been slowing broadband installations for years and now threatens upgrading cellular service to small cells and 5G in many areas.

Is OTMR A Good Idea?

OTMR has the potential to speed deployment of new communications networks if handled properly. However, one hopes the installers doing OTMR know what they are doing. We've heard so many horror stories about botched installations, cut fiber and power cables, punctured water mains and gas lines done by inept contractors that we just hope this doesn't cause even more trouble.

For example, here is a pole in the LA area where small cells are being installed. Can just any contractor handle OTMR on this pole?

Pole wars

Data Centers

Data Center Connections - 40G Looks Obsolete Already


Which Fiber For Data Centers?

From The Leviton Blog:

The Market Has Spoken: OM4 (MMF), OS2 (SMF) Leave No Place for Unproven OM5 (MMF)

Typically, industry standards and associations set the stage for the next-generation of cabling and infrastructure that support network communications. But there are instances when the market decides to take a different route. This is currently the case with the recently standardized OM5 fiber. Even though TIA developed a standard for OM5 (TIA-492AAAE), this new fiber type very likely won’t see wide industry adoption because there is no current or planned application that requires it.

Due to new transceiver launches, coupled with customer perception of their needs and network requirements, the market is ignoring the new, unproven OM5 cable and sticking with proven solutions like OM4 and single-mode fiber.

This trend is supported by a recent Leviton poll that found a significant jump in OS2 single-mode, compared to surveys from previous years.


Some of the follow-up comments from the Leviton survey included responses about OM5:

“I do not believe that OM5 offers a real advantage, it’s mainly a marketing ploy by manufacturers.” — IT manager at a global financial company

“OM5 isn’t needed. There is no real place for it between OM4 and OS2.” — communications consultant

Thanks to CI&M for bringing this to our attention.

Fiber Optic Testing

Test Sources For Multimode Fiber Testing

One of our schools recently asked up for recommendations on test sources for multimode fiber, wondering if the sources should be a LED or laser. Multimode test sources are always LEDs and these sources should be always used with a mode conditioner, usually a mandrel wrap. See here. This is how all standards for testing multimode fiber require test sources.

Years ago, as systems got faster and LEDs were too slow at speeds above a few hundred Mb/s. Fortunately 850nm VCSELs were invented to provide the solution for faster transmitters. But VCSELs were not good for test sources. They had variable mode fill and modal noise, so testers continued using LEDs for test sources, but with mode conditioners like the mandrel wrap that filtered out higher order modes to simulate the mode fill of an ideal VCSEL

The bigger issue with MM fiber is whether to test at both 850 and 1300nm. In the past, we did both because there were systems that used 1300nm LEDs or Fabry-Perot lasers for sources because the fiber attenuation was lower at 1300nm than 850nm. As network speeds increased to 1Gb/s and above, bandwidth became the limiting factor for distance, not attenuation.  VCSELs only worked at 850nm and all systems in MM basically have been switched to 850nm VCSELs.

We also used to test at both wavelengths because if a fiber was stressed, the bending losses were higher at 1300nm, so you could determine if a fiber had problems with stress. But since MM fiber has all gone to bend-insensitive fiber, that no longer works and the need or reason to test at 1300nm went away. It has not been purged from all standards yet however.

To complicate things, standards say that you should not use bend-insensitive fiber for test cables (launch or receiver reference cables) because they modify modal distribution, but it’s a moot point - practically all MM fiber is bend-insensitive so you have no choice but to use it. And most links will have BI to BI connections that should be tested. But we checked with some technical contacts and there are no specifications for BI fiber mandrels as mode conditioners.

Best solution - 850 LED with a mode conditioner on non-BI fiber.

A Conversation About Fiber And Testing

Recently an extended conversation between Eric Pearson and Jim Hayes, both FOA founders, covered the issues of testing fibers at multiple wavelengths. We've summarized the conversation here because there is some very interesting and useful information in it.

March 2018 update: Here is a OTDR trace from EXFO Eric uses in one of his books to illustrate bend sensitivity of fiber and different wavelengths:

OTDR bend sensitivity

And our conversation from February 2018:

EP: Testing multimode fiber at both wavelengths (850 and 1300nm) has been recommended to evaluate the presence of stress. If EF (encircled flux) testing fills the 30µ center of the core and 1300 nm testing fills the entire core, is it possible that this difference in core fill would indicate stress, even though there is no stress?

JH: There are definitions for EF testing at 1300nm for multimode with similar mode fill requirements included in various standards documents that cover EF so there should be no difference in stress loss due to mode fill. However, you need a 1300nm EF source.  But using 1300 nm for finding stress loss may be irrelevant since the majority of multimode fiber today is bend-insensitive (BI) fiber. That's becoming true for more singlemode fiber also, as BI SM fiber is used in microcables, spider ribbons and other new cable types.

EP: Is there any reason to test multimode at both 850 and 1300 nm then? How about SM at both 1310 and 1550?

JH: The issue of dropping 1300nm testing of MM fiber has been discussed in standards committees for years. Since the advent of the cheap VCSEL - which of course is only feasible at 850nm - there is practically no use of MM fiber at 1300nm and no real reason to test at that wavelength. But just try to remove something from a standard - it's just about impossible!

The issue of SM fiber at 1310 and 1550nm is different. Today most SM fiber is probably used at both 1310 and around 1550nm with DWDM systems and PONs, so testing at both wavelengths is necessary. Much of the testing of SM fiber for stress is done by OTDRs at 1625nm anyway, but I do not know how that is affected by BI fiber structures.

The whole topic of testing MM fiber skirts the BI fiber issues. Controlling mode distribution in BI fiber is problematic. Those 20-25mm mandrels you used for regular MMF don't work with BI fiber. It takes a mandrel ~6mm to produce the same mode filtering as a 20-25mm mandrel, but then the BI fiber structure simply refills the higher order modes. Creating EF in BI fiber is questionable. Standards have recommended against using BI fibers for reference cables (because it produces higher losses than mode-filtered regular fiber) but you are probably testing cable plants with BI fibers. Finding non-BI fiber patchcords to use for reference cables is difficult since most MM fiber is BI. Some manufacturers have made nothing but BI fiber for nearly a decade!

Historical Footnote 1: As an example of how long this issue has been discussed, look at these two clips from Corning AEN-131 from 2009.

fiber testing

fiber testing

Historical Footnote 2: While searching for this ap note (we found it in our own files where we had downloaded it in 2010), we found another interesting Corning ap note, AN3060, March 2014, on OTDR testing of SM fiber fusion splices.

What interested us was this graph, showing OTDR loss measurement differences depending on direction and mode field diameter differences.

OTDR errors with MFD

We remembered another graph similar to this that we (JH) created 30 years ago. You can tell its age by the crudeness of the computer generated graph from Lotus 123, an early spreadsheet program.

OTDR errors with MFD

This data was taken with some early singlemode fibers and an early OTDR from a sample of Spectran SM fiber spliced to Corning fibers. The work was done for Spectran to show their fibers could be spliced to Corning fibers. We obtained the data from a contact at Spectran specifically to analyze for directional loss differences and show why "gainers" happened. This graph was one of two graphs that showed the reason - gainers were caused by backscatter differences in fiber of differing mode field diameters (MFD.)

Out of curiosity we overlaid a red line showing the modern Corning data and the similarity is obvious. The scattering is much less because fibers today are much more consistent (Corning's largest MFD difference was 0.3 microns and the 1980s fiber MFD varied up to 0.8 microns, a combination of actual fiber variations and the greater errors in measurements then) and modern OTDR data is undoubtedly more consistent too.

In our analysis of the data, we also had data on the attenuation coefficient of the fiber, so we looked at another relationship that we thought would be useful - loss difference vs the difference in fiber attenuation coefficient.

OTDR errors

Within the limitations of the data, it's obvious that the directional difference in splice loss is also related to the difference in the attenuation coefficient of the fiber. We found this very interesting because most techs running OTDR tests do not have data on MFD but they can easily measure the attenuation coefficient of the two fibers being spliced. With these early fibers, a difference in fiber attenuation of 0.1dB/km would indicate a loss difference of around 0.4dB. Looking at the difference in fiber attenuation could provide an indication of the potential error of the OTDR loss measurement.

OTDRs could easily calculate this - the data is imbedded in the LSA splice loss measurement. Perhaps if someone would repeat the Corning test with modern fibers and duplicate the graph above to show the relationship of
difference in the attenuation coefficient to the difference in splice loss and it looked better - like the Corning data on modern fibers - the OTDR manufacturers might incorporate this and provide a better single-ended splice loss test.

Nitpicking: The Corning graph has a series of black dots labeled "Actual Splice Loss." In the paper they refer to them as "
bi-directional averaged (actual) splice loss values." While that is a commonly accepted fact, technically it's inaccurate. It is really an average splice loss for the two directions, because if you measure the actual loss of a splice between two fibers in each direction, you will find the difference in MFD will cause real differences in loss in each direction. Measuring it is non-trivial, however, and the difference is small with small MFD differences. We go into this in the new FOA book on testing.

Things You Learn While Training

Recently we were training instructors at a new FOA approved school. Only FOA has a program to train and certify instructors because we believe the instructor is key to any school offering a quality training program. Thee guys were experienced teachers, just not in fiber optics, so we were focused on fiber knowledge and skills. One of the instructors was originally trained at MIT where they not only provide quality education but instill in graduates a very strong curiosity! Thus we spent the time delving into several topics in great depth and the discussions led to some unique ways of explaining some of these topics. We made copious notes and took photos of the boards covered with diagrams to capture this information.

class whiteboard
One of our boards filled with notes

We decided it would be worthwhile to share these topics with our readers and we'll archive these into the FOA Guide in the near future.

Let us know what you think about these explanations - we'll make them discussions on LinkedIn so you can comment.

Key: Question means we were asked to elaborate on the topic. Comment is a comment from the instructors that led to more discussion. Note: That's one of our comments.

Power Budgets, Loss Budgets, Setting A "0dB" Reference And Modal Distribution

Not only was this topic a long discussion with our new instructors but it's a common question asked of the FOA - we received two inquiries on loss budgets in the last month alone. The confusion starts with the difference between a power budget and a loss budget, so we'll start there. and we'll include the points where we were stopped to explain things.

What's The Difference Between Power Budget And Loss Budget?
A power budget is the amount of loss the link electronics can tolerate - transmitter to receiver. The link loss budget is the estimated loss of the fiber optic cable plant including the loss of the fiber, splices and connections.

Consider this diagram:
Fiber optic loss budgets
At the top is a fiber optic link with a transmitter connected to. a cable plant with a patchcord. The cable plant has 1 intermediate connection and 1 splice plus, of course, "connectors" on each end which become "connections" when the transmitter and receiver patchcords are connected. At the receiver end, a patchcord connects the cable plant to the receiver.

Question: A connector is the hardware attached to the end of a fiber which allows it ti be connected to another fiber or a transmitter or receiver. When two connectors are mated to join two fibers, usually requiring a mating adapter, it is called a connection.

Below the drawing of the fiber optic link is a graph of the power in the link over the length of the link.  The vertical scale (Y) is optical power at the distance from the transmitter shown in the horizontal (X) scale. As optical signal from the transmitter travels down the fiber, the fiber attenuation and losses in connections and splice reduces the power as shown in the green graph of the power.

Comment: That looks like an OTDR trace. Of course it does. The OTDR sends a test pulse down the fiber and backscatter allows the OTDR to convert that into a snapshot of what happens to a pulse going down the fiber. The power in the test pulse is diminished by the attenuation of the fiber and the loss in connectors and splices. In our drawing, we don't see reflectance peaks but that additional loss is included in the loss of the connector.

On the left side of the graph, we show the power coupled from the transmitter into its patchcord, measured at point #1 and the attenuated signal at the end of the patchcord connected to the receiver shown at point #2. We also show the receiver sensitivity, the minimum power required for the transmitter and receiver to send error-free data.

The difference between the transmitter output and the receiver sensitivity is the Power Budget. Expressed in dB, the power budget is the amount of loss the link can tolerate and still work properly -
to send error-free data.

The difference between the
transmitter output (point #1) and the receiver power at its input (point #2) is the actual loss of the cable plant experienced by the fiber optic data link.

Comment: That sounds like what was called "insertion loss" with a test source and power meter. Exactly! Replace "transmitter" with test source, "receiver" with power meter and "patchcords" with reference test cables and you have the diagram for insertion loss testing which we do on every cable.

The loss of the cable plant is what we estimate when we calculate a "Link Loss Budget" for the cable plant, adding up losses due to fiber attenuation, splice losses and connector losses. And sometimes we add splitters or other passive devices.

Power Budget  For A Link

Question: How is the power budget determined? Well, you test the link under operating conditions and insert loss while watching the data transmission quality. The test setup is like this:

Measuring fiber optic link power budget
Connect the transmitter and receiver with patchcords to a variable attenuator. Increase attenuation until you see the link has a high bit-error rate (BER  for digital links) or poor signal-to-noise ratio (SNR for analog links). By measuring the output of the transmitter patchcord (point #1) and the output of the receiver patchcord (point #2), you can determine the maximum loss of the link  and the maximum power the receiver can

From this test you can generate a graph that looks like this:
fiber optic BER
A receiver must have enough power to have a low BER (or high SNR, the inverse of BER) but not so much it overloads and signal distortion affects transmission. We show it as a function of receiver power here but knowing transmitter output, this curve can be translated to loss - you need low enough loss in the cable plant to have good transmission but with low loss the receiver may overload, so you add an attenuator at the receiver to get the loss up to an acceptable level.

You must realize that not all transmitters have the same power output nor do receivers have the same sensitivity, so you test several (often many) to get an idea of the variability of the devices. Depending on the point of view of the manufacturer, you generally error on the conservative side so that your likelihood of providing a customer with a pair of devices that do not work is low. It's easier that way.


Furthermore, if your link uses multimode fiber at high bit rates, there will be dispersion. Dispersion spreads out the pulses, causing a power penalty. That's why high speed Ethernet at 10G has a loss budget of 2dB while the power budget calculated from transmitter and receiver specifications is about 6dB.

Note: We've talked about measuring power. Fiber optic power meters have inputs for attaching fiber optic connectors and detectors designed to capture all the light coming out of the fiber. This connection is considered a "no loss" connection. In reality, we do not capture all the light from the fiber because there is a glass window on the detector and that window and the detector are slightly reflective. However the coupling is very consistent and when we calibrated the meter, we calibrate with a fiber optic cable under the same conditions. Thus, what we measure of the light by presenting a connector to the power meter is both consistent and calibrated (as long as you choose the proper calibration wavelength, of course.)

Fiber optic power meter detector

But what about connections from the transmitter to the patchcord and the connection of the patchcord to the receiver? We can't measure those connections because we do not have access to the actual devices the fiber is coupling to to know what the connection loss is. Therefore our measurement convention is to measure them coupled to a patchcord. We simply have to ensure we have good patchcords. A patchcord that is low loss connected to another patchcord should be low loss connected to a transmitter or receiver port.

The connection to the receiver is also unknowable. All we can do is measure the output of the cable that we connect to the receiver when testing the power budget of the link. Whatever the connection loss is becomes irrelevant, but it is included in testing of the receiver and the link.

Comment: Stan Hendryx, the MIT graduate in our class, became so interested in the notion of measuring in dB that he researched to topic and sent us a treatise on dB that includes this history:

"In 1924, engineers at Bell Telephone Laboratories adopted the logarithm to define a unit for signal loss in telephone lines, the transmission unit (TU). The TU replaced the earlier standard unit, miles of standard cable (MSC), which had been in place since the introduction of telephone cable in 1896. 1 MSC corresponded to the loss of signal power over 1 mile of standard cable. Standard cable was defined as having a resistance of 88 ohms and capacitance of 0.054 microfarads per mile. 1 MSC equals 1.056 TU. The loss factor in TU was ten times the base-10 logarithm of the ratio of the output power to the input power.
In 1928, Bell Telephone Laboratories renamed the transmission unit (TU) the decibel (dB)."
You can read Stan's paper here.

Question: If we measure the transmitter output and receiver input that way, what does that mean for calculating the loss budget or measuring insertion loss?

Once we understand the way we measure (and calibrate) power as the output of a fiber optic cable connected to a power meter, these two topics make more sense.

Refer to the first diagram of the fiber link and the power in the link. Note we measure transmitter power at point #1 on the graph, the power we use as the output of the transmitter, the reference power for insertion loss measurements or the power for the calculation of the power budget. We measure that power before the connection to the cable plant so the transmitter power is attenuated by that first connector on the cable plan. Therefore that first connector must be included in the calculation of the loss budget of the cable plant.

At the receiver end, the receiver patchcord connects to the installed cable plant and suffers connection loss before it is connected to the receiver. Thus that connection should be included in the link loss budget also.

So when calculating a link loss budget, include the connectors on both ends of the cable plant.

Note: When you do an insertion loss test, you use a meter and source and two reference cables - launch and receive. They substitute for the link cable pllant patchcords and you make measurements just like you would in testing the link power budget. Your insertion loss test will also include both connections.

One, Two, Three Cable 0dB Reference

Question: This looks like the 1-cable reference method for insertion loss testing. What happens when you use the 2-cable or 3-cable reference method? And why would you use those other methods anyway?

One common misunderstanding is why you use the two or three cable reference methods (see below) for insertion loss testing.

insertion loss test reference
Some people think it's related to how you want to perform the test, but the reason is much more a matter of practicality. It all depends on the connectors on the cable plant you are testing and the connector interfaces on your test equipment. And some history.

The 1-cable method has always been the method of choice because it does not require compensating for the connections in the reference cables when setting the "0dB" reference. It's like we discussed measuring transmitter power above. You measure the output of the launch reference cable, connect it to the cable plant under test, launch power through that first connection and measure the loss of all losses in the cable plant. The meter connects to the cable plant at the far end with a receive reference cable, and when the meter makes it's measurement it includes the connection of the receive reference cable. Thus both connections on each end of the cable plant are measured, Just like the actual link will work in operation. No corrections are needed.

But suppose you have a LC cable plant and your instruments have SC connector interfaces? Or suppose 35 years ago, you test set had SMA connectors and you needed to test a cable plant with Biconics. (Don't know those connectors? Look them up here.) You can use hybrid reference cables with SMA connections on one end for your instruments and Biconics on the other end to mate with the cable plant. Use a biconic mating adapter to set your reference - including that connection - and make measurements remembering - or ignoring - that your reference value included one unknown connection.

Or suppose you are trying to test connectors that do not match the connections on your instruments nor do they mate with each other because they are gendered - male/female or plug/jack? Hybrid reference cables won't help here, so you go to a "cable substitution" test. Set up your instruments with hybrid cables and set your reference with a third cable that is a short version of the cable plant you want to test. Since most cable plants using plug/jack connectors (like a MPO prefab cable plant or multipin military connectors) have the permanently installed cable plant end in connectors of the same gender (MPO jacks are connectors with pins), you will have your instruments with similar cables and the reference cable will have the opposite styles of connectors to mate with them.

Note: All three methods are approved in most standards and at least the 1-cable or 3-cable methods are approved in all standards we're aware of.

Note: Just remember that you will make measurements that yield different loss values depending on the reference method you use.

Question: If you use a 2-cable method don't you just reference out one of the connectors on the end of the cable plant you are testing, and if
you use a 3-cable method don't you just reference out both of the connectors on the end of the cable plant you are testing? No! Each connection is different. If you include one or two connections in your reference setting, you will reduce the loss by one or two unknown connection losses - it has nothing to do with the final insertion loss measurement which includes all connection losses from the ends of the cable plant. Here is an example by Fluke that shows the variation based on standard connection loss values.

Multimode Fiber
One thing that confuses people is how multimode fiber works. We discussed total internal reflection in fiber and how graded index multimode fiber was made in layers, so it works like this (from the FOA Guide on Fiber):


To help visualize the layers in the fiber, we like to show a Fresnel lens, a "flat" lens made from annular rings of glass that approximate a regular lens. These lenses are used in lighthouse lights like this one:

Lighthouse lens  lens

A Fresnel lens like this one used in a lighthouse is a flat lens made of segments of a regular lens.

Multimode Loss With A Mandrel Wrap, Testing The Effect In Class

When we got to the slide in the lecture about multimode mode conditioning for testing, we got into a discussion about how to do mode conditioning. One of the instructors had read about using a "mandrel wrap" on the launch cable so we spent some time discussing it. First we covered  the reason why mode power distribution makes a difference.

Here is a slide showing testing with a fully filled fiber and one where the higher order modes have been stripped off to simulate the fiber with a typical VCSEL source.

Modal effect on fiber optic connector loss

The industry has always known about the effects of modal distribution and has created metrics to measure and standardize it for testing multimode fiber. The methods included MPD (mode power distribution), CPR (coupled power ratio) and the latest, EF (Encircled Flux.) 

In class, the instructors had each made at least one good connector in our termination lab (we were using the most basic technique, heat-cured epoxy and polishing) so we decided to test their connectors with and without a mandrel wrap mode conditioner to see if it made a difference.

mandrel wrap

After adding the mandrel wrap to the launch cable, we tested the LED test source using a HOML (higher order mode loss) test as described in the page on EFWith the mandrel wrap, the power was reduced by ~0.6dB, so we left the mandrel on for our testing.

Adding the mandrel wrap certainly did make a difference. Connections tested single-ended without the mandrel wrap at ~0.6dB loss were measured at ~0.2dB with the mandrel wrap. That's how much difference modal conditioning can make on a single connection.

Think about that the next time you are testing multimode fiber!

That's all our notes from this instructor training session. Hope you found them interesting!


Bad Advice

Our inbox recently had a message with this thought:

"It is time for spring cleaning, and we don't mean just at home. Contaminated fiber end faces remain the number one cause of fiber related problems and test failures. With more stringent loss budgets, higher data speeds and new multifiber connectors, proactively inspecting and cleaning will help you ensure network uptime, performance, and reliability. Despite "everyone" knowing this, fiber contamination and cleaning generates a lot of failed test results."

Well, experience tells us that "proactively inspecting and cleaning" can generate a lot of damage to operating fiber optic networks.

Inspection and cleaning should be done whenever a fiber optic connection is opened or made, of course. But the act of opening the connection exposes it to airborne dirt and the possibility of damage if the tech is not experienced in proper cleaning. Fiber optic connections are well sealed and if they are clean when connected, they will not get dirty sitting there. Fiber optic connections do not accumulate unseen dirt like under your bed or sofa, requiring periodic cleaning, as implied in this email.

Clean 'em, inspect 'em to ensure proper cleaning, connect 'em and LEAVE THEM ALONE!!!

And, duh, remember to put dust caps on connectors AND receptacles on patch panels when no connections are made

Was this perhaps another early April Fools' this one we ran several years ago about the wrong way to clean connectors:

Connector cleaning - NOT!

Why You Clean Connectors Before You Make Connections

Brian Teague of Microcare/Sticklers send us this series of photos showing what happens when you make connections with dirty connectors. It speak for itself!

Dirt on fiber optic connectors

Wet-Dry Cleaning With a Mechanical Connector Cleaner

Brian Teague of Microcare/Sticklers, the cleaning experts, offers this trick.

W-D clean

Here's a simple and easy to use 3 step process that will significantly improving the cleaning performance of your mechanical fibre optic connector click cleaners. The cleaning fluid will break the end face contamination and create the dissipative medium for eliminating static charges that pull in dust onto the connector's end face.

Why You Need To Protect Cables From Water

fiber growth
Fiber Growth
These are photos of some indoor/outdoor cable that suffered water ingress from a cable cut. In a few months the cable grew these calcium deposits on the end of the cable. We discussed this with several cabling companies and they have seen it before. Basically the cable grows "stalactities" on  the end.

How To Backfill A Trench For Underground Construction

backfill a trench

Here's the answer to a question we've gotten. Where did we find the answer? In the new FOA Guide section on OSP Construction developed using Joe Botha's OSP Construction Guide which is published by the FOA. Joe's book covers underground and aerial installation from a construction point of view, covering material after the FOA's design material and before you get into the FOA's information on splicing, termination and testing.

The 2019 update of the FOA Reference Guide To Outside Plant Fiber Optics contains this and lots of other new material on OSP construction.

Safety On The Job

bucket truck job  

Safety is the most important part of any job. Installers need to understand the safety issues to be safe. An excellent guide to analyzing job hazards is from OSHA, the US Occupational Safety and Health Administration. Here is a link to their guide for job hazard analysis.

Why We Warn You To Be Careful About Fiber Shards

Fiber in Finger

Photo courtesy  Brian Brandstetter,  Mississauga Training Consultants

Power Over Ethernet (PoE) And Counterfeit Cable

PoE Efficiency Superior Essex Comparison Of Cable Efficiency

This graph showed up in an interesting white paper on PoE from Superior Essex, LeGrand and Fluke. You might remember we did an analysis of PoE power efficiency in the November FOA Newsletter article "PoE Analysis From The Ethernet Alliance (With Our Analysis). This graph has some data we did not consider - the efficiency of counterfeit cable that uses copper-clad aluminum conductors instead of pure copper. The inefficiency of this cable means that more than half the power will be lost in transmission - not only inefficient but dangerous as the power lost is converted to heat. Considering that the samples of counterfeit cable that we have tested use flammable insulation and jackets, that could be a very hazardous application!

Recent conversations with people involved with adding PoE applications to the US National Electric Code bring up a further problem. The IEEE did not register "PoE" as a trademark so it's being used to describe applications like daisy-chained lighting and cables longer than the 100m limit of Ethernet. This makes the safety considerations even more important - and scary.

FOA is researching PoE as part of our CPCT certification and have created a FOA Guide page on PoE which we will be updating regularly.

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