Fiber Optics Tutorials

8/6/2019 Fiber Optics Tutorials

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FIBER OPTICS

THE BASICS OF FIBER OPTIC CABLE

a Tutorial

BRIEF OVER VIEW OF FIBER OPTIC CABLE ADVANTAGES OVER COPPER:

SPEED: Fiber optic networks operate at high speeds - up into the gigabits BANDWIDTH: large carrying capacity DISTANCE: Signals can be transmitted further without needing to be "refreshed" orstrengthened. RESISTANCE: Greater resistance to electromagnetic noise such as radios, motors orother nearby cables. MAINTENANCE: Fiber optic cables costs much less to maintain.

In recent years it has become apparent that fiber-optics are steadily replacing copperwire as an appropriate means of communication signal transmission. They span thelong distances between local phone systems as well as providing the backbone formany network systems. Other system users include cable television services, universitycampuses, office buildings, industrial plants, and electric utility companies.

A fiber-optic system is similar to the copper wire system that fiber-optics is replacing.The difference is that fiber-optics use light pulses to transmit information down fiberlines instead of using electronic pulses to transmit information down copper lines.Looking at the components in a fiber-optic chain will give a better understanding of howthe system works in conjunction with wire based systems.

At one end of the system is a transmitter. This is the place of origin for informationcoming on to fiber-optic lines. The transmitter accepts coded electronic pulseinformation coming from copper wire. It then processes and translates that informationinto equivalently coded light pulses. A light-emitting diode (LED) or an injection-laserdiode (ILD) can be used for generating the light pulses. Using a lens, the light pulsesare funneled into the fiber-optic medium where they travel down the cable. The light(near infrared) is most often 850nm for shorter distances and 1,300nm for longer


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distances on Multi-mode fiber and 1300nm for single-mode fiber and 1,500nm is usedfor for longer distances.

Think of a fiber cable in terms of very long cardboard roll (from the inside roll of papertowel) that is coated with a mirror on the inside.

If you shine a flashlight in one end you can see light come out at the far end - even if it'sbeen bent around a corner.

Light pulses move easily down the fiber-optic line because of a principle known as totalinternal reflection. "This principle of total internal reflection states that when the angle ofincidence exceeds a critical value, light cannot get out of the glass; instead, the lightbounces back in. When this principle is applied to the construction of the fiber-opticstrand, it is possible to transmit information down fiber lines in the form of light pulses.The core must a very clear and pure material for the light or in most cases near infraredlight (850nm, 1300nm and 1500nm). The core can be Plastic (used for very shortdistances) but most are made from glass. Glass optical fibers are almost always made

from pure silica, but some other materials, such as fluorozirconate, fluoroaluminate, andchalcogenide glasses, are used for longer-wavelength infrared applications.

There are three types of fiber optic cable commonly used: single mode, multimode andplastic optical fiber (POF).

Transparent glass or plastic fibers which allow light to be guided from one end to theother with minimal loss.


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Fiber optic cable functions as a "light guide," guiding the light introduced at one end ofthe cable through to the other end. The light source can either be a light-emitting diode(LED)) or a laser.

The light source is pulsed on and off, and a light-sensitive receiver on the other end ofthe cable converts the pulses back into the digital ones and zeros of the original signal.

Even laser light shining through a fiber optic cable is subject to loss of strength,primarily through dispersion and scattering of the light, within the cable itself. The fasterthe laser fluctuates, the greater the risk of dispersion. Light strengtheners, calledrepeaters, may be necessary to refresh the signal in certain applications.

While fiber optic cable itself has become cheaper over time - a equivalent length ofcopper cable cost less per foot but not in capacity. Fiber optic cable connectors and theequipment needed to install them are still more expensive than their coppercounterparts.

Single Mode cable is a single stand (most applications use 2 fibers) of glass fiber witha diameter of 8.3 to 10 microns that has one mode of transmission. Single Mode Fiberwith a relatively narrow diameter, through which only one mode will propagate typically1310 or 1550nm. Carries higher bandwidth than multimode fiber, but requires a lightsource with a narrow spectral width. Synonyms mono-mode optical fiber, single-modefiber, single-mode optical waveguide, uni-mode fiber.

Single Modem fiber is used in many applications where data is sent at multi-frequency(WDM Wave-Division-Multiplexing) so only one cable is needed - (single-mode on onesingle fiber)

Single-mode fiber gives you a higher transmission rate and up to 50 times moredistance than multimode, but it also costs more. Single-mode fiber has a much smallercore than multimode. The small core and single light-wave virtually eliminate anydistortion that could result from overlapping light pulses, providing the least signalattenuation and the highest transmission speeds of any fiber cable type.


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Single-mode optical fiber is an optical fiber in which only the lowest order bound modecan propagate at the wavelength of interest typically 1300 to 1320nm.

jump tosingle mode fiberpage

Multi-Mode cable has a little bit bigger diameter, with a common diameters in the 50-to-100 micron range for the light carry component (in the US the most common size is62.5um). Most applications in which Multi-mode fiber is used, 2 fibers are used (WDM isnot normally used on multi-mode fiber). POF is a newer plastic-based cable whichpromises performance similar to glass cable on very short runs, but at a lower cost.

Multimode fiber gives you high bandwidth at high speeds (10 to 100MBS - Gigabit to275m to 2km) over medium distances. Light waves are dispersed into numerous paths,or modes, as they travel through the cable's core typically 850 or 1300nm. Typicalmultimode fiber core diameters are 50, 62.5, and 100 micrometers. However, in longcable runs (greater than 3000 feet [914.4 meters), multiple paths of light can causesignal distortion at the receiving end, resulting in an unclear and incomplete datatransmission so designers now call for single mode fiber in new applications usingGigabit and beyond.


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The use of fiber-optics was generally not available until 1970 when Corning GlassWorks was able to produce a fiber with a loss of 20 dB/km. It was recognized thatoptical fiber would be feasible for telecommunication transmission only if glass could bedeveloped so pure that attenuation would be 20dB/km or less. That is, 1% of the lightwould remain after traveling 1 km. Today's optical fiber attenuation ranges from0.5dB/km to 1000dB/km depending on the optical fiber used. Attenuation limits arebased on intended application.

The applications of optical fiber communications have increased at a rapid rate, sincethe first commercial installation of a fiber-optic system in 1977. Telephone companiesbegan early on, replacing their old copper wire systems with optical fiber lines. Today'stelephone companies use optical fiber throughout their system as the backbonearchitecture and as the long-distance connection between city phone systems.

Cable television companies have also began integrating fiber-optics into their cablesystems. The trunk lines that connect central offices have generally been replaced withoptical fiber. Some providers have begun experimenting with fiber to the curb using afiber/coaxial hybrid. Such a hybrid allows for the integration of fiber and coaxial at aneighborhood location. This location, called a node, would provide the optical receiver


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that converts the light impulses back to electronic signals. The signals could then be fedto individual homes via coaxial cable.

Local Area Networks (LAN) is a collective group of computers, or computer systems,connected to each other allowing for shared program software or data bases. Colleges,

universities, office buildings, and industrial plants, just to name a few, all make use ofoptical fiber within their LAN systems.

Power companies are an emerging group that have begun to utilize fiber-optics in theircommunication systems. Most power utilities already have fiber-optic communicationsystems in use for monitoring their power grid systems.

jump toIllustrated Fiber Optic Glossarypages

Fiber

by John MacChesney - Fellow at Bell Laboratories, Lucent Technologies

Some 10 billion digital bits can be transmitted per second along an optical fiber link in acommercial network, enough to carry tens of thousands of telephone calls. Hair-thinfibers consist of two concentric layers of high-purity silica glass the core and thecladding, which are enclosed by a protective sheath. Light rays modulated into digital

pulses with a laser or a light-emitting diode move along the core without penetrating thecladding.

The light stays confined to the core because the cladding has a lower refractive indexa measure of its ability to bend light. Refinements in optical fibers, along with thedevelopment of new lasers and diodes, may one day allow commercial fiber-opticnetworks to carry trillions of bits of data per second.

Total internal refection confines light within optical fibers (similar to looking down a

mirror made in the shape of a long paper towel tube). Because the cladding has a lowerrefractive index, light rays reflect back into the core if they encounter the cladding at ashallow angle (red lines). A ray that exceeds a certain "critical" angle escapes from thefiber (yellow line).


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STEP-INDEX MULTIMODE FIBER has a large core, up to 100 microns in diameter. Asa result, some of the light rays that make up the digital pulse may travel a direct route,whereas others zigzag as they bounce off the cladding. These alternative pathwayscause the different groupings of light rays, referred to as modes, to arrive separately ata receiving point. The pulse, an aggregate of different modes, begins to spread out,losing its well-defined shape. The need to leave spacing between pulses to prevent

overlapping limits bandwidth that is, the amount of information that can be sent.Consequently, this type of fiber is best suited for transmission over short distances, inan endoscope, for instance.

GRADED-INDEX MULTIMODE FIBER contains a core in which the refractive indexdiminishes gradually from the center axis out toward the cladding. The higher refractiveindex at the center makes the light rays moving down the axis advance more slowlythan those near the cladding. Also, rather than zigzagging off the cladding, light in thecore curves helically because of the graded index, reducing its travel distance. Theshortened path and the higher speed allow light at the periphery to arrive at a receiverat about the same time as the slow but straight rays in the core axis. The result: a digitalpulse suffers less dispersion.

SINGLE-MODE FIBER has a narrow core (eight microns or less), and the index ofrefraction between the core and the cladding changes less than it does for multimodefibers. Light thus travels parallel to the axis, creating little pulse dispersion. Telephoneand cable television networks install millions of kilometers of this fiber every year.


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BASIC CABLE DESIGN

1 - Two basic cable designs are:

Loose-tube cable, used in the majority of outside-plant installations in North America,and tight-buffered cable, primarily used inside buildings.

The modular design of loose-tube cables typically holds up to 12 fibers per buffer tubewith a maximum per cable fiber count of more than 200 fibers. Loose-tube cables canbe all-dielectric or optionally armored. The modular buffer-tube design permits easydrop-off of groups of fibers at intermediate points, without interfering with otherprotected buffer tubes being routed to other locations. The loose-tube design also helpsin the identification and administration of fibers in the system.

Single-fiber tight-buffered cables are used as pigtails, patch cords and jumpers to

terminate loose-tube cables directly into opto-electronic transmitters, receivers andother active and passive components.

Multi-fiber tight-buffered cables also are available and are used primarily for alternativerouting and handling flexibility and ease within buildings.

2 - Loose-Tube Cable

In a loose-tube cable design, color-coded plastic buffer tubes house and protect opticalfibers. A gel filling compound impedes water penetration. Excess fiber length (relative tobuffer tube length) insulates fibers from stresses of installation and environmental

loading. Buffer tubes are stranded around a dielectric or steel central member, whichserves as an anti-buckling element.

The cable core, typically uses aramid yarn, as the primary tensile strength member. Theouter polyethylene jacket is extruded over the core. If armoring is required, a corrugatedsteel tape is formed around a single jacketed cable with an additional jacket extrudedover the armor.


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Loose-tube cables typically are used for outside-plant installation in aerial, duct anddirect-buried applications.

3 - Tight-Buffered Cable

With tight-buffered cable designs, the buffering material is in direct contact with thefiber. This design is suited for "jumper cables" which connect outside plant cables toterminal equipment, and also for linking various devices in a premises network.

Multi-fiber, tight-buffered cables often are used for intra-building, risers, general buildingand plenum applications.

The tight-buffered design provides a rugged cable structure to protect individual fibersduring handling, routing and connectorization. Yarn strength members keep the tensile

load away from the fiber.

As with loose-tube cables, optical specifications for tight-buffered cables also shouldinclude the maximum performance of all fibers over the operating temperature rangeand life of the cable. Averages should not be acceptable.

Connector Types


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Gruber Industries

cable connectors

here are some common fiber cable types

Distribution Cable

Distribution Cable (compact building cable) packages individual 900m buffered fiberreducing size and cost when compared to breakout cable. The connectors may be

installed directly on the 900m buffered fiber at the breakout box location. The space


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saving (OFNR) rated cable may be installed where ever breakout cable is used. FIS will

connectorize directly onto 900m fiber or will build up ends to a 3mm jacketed fiberbefore the connectors are installed.

Indoor/Outdoor Tight Buffer

FIS now offers indoor/outdoor rated tight buffer cables in Riser and Plenum rated

versions. These cables are flexible, easy to handle and simple to install. Since they donot use gel, the connectors can be terminated directly onto the fiber without difficult to

use breakout kits. This provides an easy and overall less expensive installation.(Temperature rating -40C to +85C).

Indoor/Outdoor Breakout Cable

FIS indoor/outdoor rated breakout style cables are easy to install and simple to terminate

without the need for fanout kits. These rugged and durable cables are OFNR rated sothey can be used indoors, while also having a -40c to +85c operating temperature range

and the benefits of fungus, water and UV protection making them perfect for outdoorapplications. They come standard with 2.5mm sub units and they are available in plenum

rated versions.

Corning Cable Systems Freedm LST Cables

Corning Cable Systems FREEDM LST cables are OFNR-rated, UV-resistant, fully

waterblocked indoor/outdoor cables. This innovative DRY cable with water blocking


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technology eliminates the need for traditional flooding compound, providing more

efficient and craft-friendly cable preparation. Available in 62.5m, 50m, Singlemodeand hybrid versions.

Krone Indoor Outdoor Dry Loose Tube Cable

KRONEs innovative line of indoor/outdoor loose tube cables are designed to meet allthe rigors of the outside plant environment, and the necessary fire ratings to be installed

inside the building. These cables eliminate the gel filler of traditional loose tube stylecables with super absorbent polymers.

Loose Tube Cable

Loose tube cable is designed to endure outside temperatures and high moisture

conditions. The fibers are loosely packaged in gel filled buffer tubes to repel water.Recommended for use between buildings that are unprotected from outside elements.

Loose tube cable is restricted from inside building use, typically allowing entry not toexceed 50 feet (check your local codes).

Aerial Cable/Self-Supporting


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Aerial cable provides ease of installation and reduces time and cost. Figure 8 cable can

easily be separated between the fiber and the messenger. Temperature range ( -55C to+85C)

Hybrid & Composite Cable

Hybrid cables offer the same great benefits as our standard indoor/outdoor cables, withthe convenience of installing multimode and singlemode fibers all in one pull. Our

composite cables offer optical fiber along with solid 14 gauge wires suitable for avariety of uses including power, grounding and other electronic controls.

Armored Cable

Armored cable can be used for rodent protection in direct burial if required. This cable is

non-gel filled and can also be used in aerial applications. The armor can be removedleaving the inner cable suitable for any indoor/outdoor use. (Temperature rating -40C to

+85C)

Low Smoke Zero Halogen (LSZH)

Low Smoke Zero Halogen cables are offered as as alternative for halogen freeapplications. Less toxic and slower to ignite, they are a good choice for many

international installations. We offer them in many styles as well as simplex, duplex and1.6mm designs. This cable is riser rated and contains no flooding gel, which makes the

need for a separate point of termination unnecessary. Since splicing is eliminated,

termination hardware and labor times are reduced, saving you time and money. Thiscable may be run through risers directly to a convenient network hub or splicing closetfor interconnection.


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What's the best way to terminate fiber optic cable? That depends on theapplication, cost considerations and your own personal preferences.The following connector comparisons can make the decision easier.

Epoxy & Polish

Epoxy & polish style connectors were the original fiber optic connectors.They still represent the largest segment of connectors, in both quantityused and variety available. Practically every style of connector isavailable including ST, SC, FC, LC, D4, SMA, MU, and MTRJ.

Advantages include:

Very robust. This connector style is based on tried and truetechnology, and can withstand the greatest environmental andmechanical stress when compared to the other connector technologies. This style of connector accepts the widest assortment of cable jacket

diameters. Most connectors of this group have versions to fit onto900um buffered fiber, and up to 3.0mm jacketed fiber. Versions are. available that hold from 1 to 24 fibers in a singleconnector.

Installation Time: There is an initial setup time for the field technicianwho must prepare a workstation with polishing equipment and anepoxy-curing oven. The termination time for one connector is about 25minutes due to the time needed to heat cure the epoxy. Average timeper connector in a large batch can be as low as 5 or 6 minutes. Fastercuring epoxies such as anaerobic epoxy can reduce the installationtime, but fast cure epoxies are not suitable for all connectors.

Skill Level: These connectors, while not difficult to install, do require themost supervised skills training, especially for polishing. They are bestsuited for the high-volume installer or assembly house with a trainedand stable work force.

Costs: Least expensive connectors to purchase, in many cases being30 to 50 percent cheaper than other termination style connectors.However, factor in the cost of epoxy curing and ferrule polishingequipment, and their associated consumables.

Pre-Loaded Epoxy or No-Epoxy & Polish

There are two main categories of no-epoxy & polish connectors. Thefirst are connectors that are pre-loaded with a measured amount ofepoxy. These connectors reduce the skill level needed to install aconnector but they don't significantly reduce the time or equipmentneed-ed. The second category of connectors uses no epoxy at all.


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Usually they use an internal crimp mechanism to stabilize the fiber.These connectors reduce both the skill level needed and installationtime. ST, SC, and FC connector styles are available. Advantagesinclude:

Epoxy injection is not required. No scraped connectors due to epoxy over-fill. Reduced equipment requirements for some versions.

Installation Time: Both versions have short setup time, with pre-loadedepoxy connectors having a slightly longer setup. Due to curing time, thepre-loaded epoxy connectors require the same amount of installationtime as standard connectors, 25 minutes for 1 connector, 5-6 minutesaverage for a batch. Connectors that use the internal crimp methodinstall in 2 minutes or less.

Skill Level: Skill requirements are reduced because the crimpmechanism is easier to master than using epoxy. They providemaximum flexibility with one technology and a balance between skilland cost.

Costs: Moderately more expensive to purchase than a standardconnector. Equipment cost is equal to or less than that of standardconnectors. Consumable cost is reduced to polish film and cleaningsup-plies. Cost benefits derive from reduced training requirements andfast installation time.

No-Epoxy & No-Polish

Easiest and fastest connectors to install; well suited for contractors whocannot cost-justify the training and supervision required for standardconnectors. Good solution for fast field restorations. ST, SC, FC, LC,and MTRJ connector styles are available. Advantages include: No setup time required. Lowest installation time per connector. Limited training required. Little or no consumables costs.

Installation Time: Almost zero. Its less than 1 minute regardless ofnumber of connectors.

Skill level: Requires minimal training, making this type of connector idealfor installation companies with a high turnover rate of installers and/orthat do limited amounts of optical-fiber terminations.

Costs: Generally the most expensive style connector to purchase, since


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some of the labor (polishing) is done in the factory. Also, one or twofairly expensive installation tools may be required. However, it may stillbe less expensive on a cost-per-installed-connector basis due to lowerlabor cost.

jump toCalculating fiber loss and distance

jump torelated fiber optic equipment pages

jump to Telebyte Fiber tutorial pages

(very good write up)

2. The Fiber Optic Data Communications Link For the Premises Environment2.1 The Fiber Optic data Communications Link, End-to-End2.2 Fiber Optic Cable

2.3 Transmitter2.4 Receiver

2.5 Connectors2.6 Splicing

2.7 Analyzing Performance of a Link

jump to The Complete Telebyte Fiber tutorialpages

y jump to In-depth - very technical - Fiber optic write upy jump to The Belden Cable Company's Fiber tutorialy jump to Fiber 101 by Corning Incorporateda good animated

Tutorial

y jump to WDM basics (Wavelength Division Multiplexing)URLy jump to DWDM basics (Dense Wavelength Division Multiplexing)

URL

y jump to Fiber Optics Training Provider

also view

y http://en.wikipedia.org/wiki/Optical_fibero The Fiber Optic Association


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o FOA color code for connectorso Lennie Lightwave's Guide To Fiber Opticso "Fibers", article in RP Photonics' Encyclopedia of Laser

Physics and Technologyo How Fiber Optics are made In videoo

"Fibre optic technologies", Mercury Communications Ltd,August 1992.o "Photonics & the future of fiber", Mercury Communications

Ltd, March 1993

ARC Electronics800-926-0226

[email protected]

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Fiber Optic Testing

After the cables are installed and terminated, it's time for testing. For every fiber

optic cable plant, you will need to test for continuity, end-to-end loss and then

troubleshoot the problems. If it's a long outside plant cable with intermediate

splices, you will probably want to verify the individual splices with an OTDR also,

since that's the only way to make sure that each one is good. If you are the network

user, you will also be interested in testing power, as power is the measurement that

tells you whether the system is operating properly.

You'll need a few special tools and instruments to test fiber optics. See Jargon in the

beginning of Lennie's Guide to see a description of each instrument.

Getting Started


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Cat 5E & 6 Tutorial

All About CAT 6A

How to Make Cat 5E /

Patch Cable

How to Make Category

Patch Cable

Installing Cat 5E/6E

Shielded Modular Plug

Even if you're an experienced installer, make sure you remember these things.

1. Have the right tools and test equipment for the job. You will need:

1. Source and power meter, optical loss test set or test kit with proper equipment

adapters for the cable plant you are testing.2. Reference test cables that match the cables to be tested and mating adapters,

including hybrids if needed.

3. Fiber Tracer or Visual Fault Locator.

4. Cleaning materials - lint free cleaning wipes and pure alcohol.

5. OTDR and launch cable for outside plant jobs.

2. Know how to use your test equipment

Before you start, get together all your tools and make sure they are all working

properly and you and your installers know how to use them. It's hard to get the job

done when you have to call the manufacturer from the job site on your cell phone to

ask for help. Try all your equipment in the office before you take it into the field.

Use it to test every one of your reference test jumper cables in both directions using

the single-ended loss test to make sure they are all good. If your power meter has

internal memory to record data be sure you know how to use this also. You can

often customize these reports to your specific needs - figure all this out before you

go it the field - it could save you time and on installations, time is money!

3. Know the network you're testing...

This is an important part of the documentation process we discussed earlier. Make

sure you have cable layouts for every fiber you have to test. Prepare a spreadsheet

of all the cables and fibers before you go in the field and print a copy for recordingyour test data. You may record all your test data either by hand or if your meter has

a memory feature, it will keep test results in on-board memory that can be printed

or transferred to a computer when you return to the office.

A note on using a fiber optic source eye safety...

Fiber optic sources, including test equipment, are generally too low in power to

cause any eye damage, but it's still a good idea to check connectors with a power

meter before looking into it. Some telco DWDM and CATV systems have very high

power and they could be harmful, so better safe than sorry.

Fiber optic testing includes three basic tests that we will cover separately:

Visual inspection for continuity or connector checking, Loss testing, and

Network Testing.

Visual Inspection


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How to Terminate Cat 6

Shielded Jacks

How to Wire Phone Jack

Fiber Optic Tutorial

Fiber Optic Jargon

Fiber Optic Basics

Fiber Optic Fiber

Fiber Optic Cable

Fiber Termination

Fiber Optic Network

Fiber Optic Estimating

Fiber Optic Testing

Fiber Optic Training

Fiber Optic Glossary

Mode Conditioning

Pulling Fiber Optic &

Communication Cables

Designing Conduit Runs

Visual Tracing

Continuity checking makes certain the fibers are not broken and to trace a path of a

fiber from one end to another through many connections. Use a visible light "fiber

optic tracer" or "pocket visual fault locator". It looks like a flashlight or a pen-like

instrument with a lightbulb or LED soure that mates to a fiber optic connector.Attach a cable to test to the visual tracer and look at the other end to see the light

transmitted through the core of the fiber. If there is no light at the end, go back to

intermediate connections to find the bad section of the cable.

A good example of how it can save time and money is testing fiber on a reel before

you pull it to make sure it hasn't been damaged during shipment. Look for visible

signs of damage (like cracked or broken reels, kinks in the cable, etc.) . For testing,

visual tracers help also identify the next fiber to be tested for loss with the test kit.

When connecting cables at patch panels, use the visual tracer to make sure each

connection is the right two fibers! And to make certain the proper fibers are

connected to the transmitter and receiver, use the visual tracer in place of the

transmitter and your eye instead of the receiver (remember that fiber optic links

work in the infrared so you can't see anything anyway.)

Visual Fault Location

A higher power version of the tracer uses a laser that can also find faults. The red

laser light is powerful enough to show breaks in fibers or high loss connectors. You

can actually see the loss of the bright red light even through many yellow or orange

simplex cable jackets except black or gray jackets. You can also use this gadget to

optimize mechanical splices or prepolished-splice type fiber optic connectors. In

fact- don't even think of doing one of those connectors without one no other

method will assure you of high yield with them.

Visual Connector Inspection

Fiber optic microscopes are used to inspect connectors to check the quality of the

termination procedure and diagnose problems. A well made connector will have a

smooth , polished, scratch free finish and the fiber will not show any signs of cracks,

chips or areas where the fiber is either protruding from the end of the ferrule or

pulling back into it.

The magnification for viewing connectors can be 30 to 400 power but it is best to

use a medium magnification. The best microscopes allow you to inspect the

connector from several angles, either by tilting the connector or having angle

illumination to get the best picture of what's going on. Check to make sure the

microscope has an easy-to-use adapter to attach the connectors of interest to the

microscope.

And remember to check that no power is present in the cable before you look at it in

a microscope protect your eyes!

Optical Power - Power or Loss? ("Absolute" vs. "Relative")


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Practically every measurement in fiber optics refers to optical power. The power

output of a transmitter or the input to receiver are "absolute" optical power

measurements, that is, you measure the actual value of the power. Loss is a

"relative" power measurement, the difference between the power coupled into a

component like a cable or a connector and the power that is transmitted through it.

This difference is what we call optical loss and defines the performance of a cable,

connector, splice, etc.

Measuring power

Power in a fiber optic system is like voltage in an electrical circuit - it's what makes

things happen! It's important to have enough power, but not too much. Too little

power and the receiver may not be able to distinguish the signal from noise; too

much power overloads the receiver and causes errors too.

Measuring power requires only a power meter

(most come with a screw-on adapter that

matches the connector being tested) and a littlehelp from the network electronics to turn on the

transmitter. Remember when you measure

power, the meter must be set to the proper

range (usually dBm, sometimes microwatts, but

never "dB" that's a relative power range used

only for testing loss!) and the proper wavelengths

matching the source being used. Refer to the

instructions that come with the test equipment

for setup and measurement instructions (and

don't wait until you get to the job site to try the

equipment)!

To measure power, attach the meter to the cable that has the output you want to

measure. That can be at the receiver to measure receiver power, or to a reference

test cable (tested and known to be good) that is attached to the transmitter, acting

as the "source", to measure transmitter power. Turn on the transmitter/source and

note the power the meter measures. Compare it to the specified power for the

system and make sure it's enough power but not too much.

Testing loss

Loss testing is the difference between the power coupled into the cable at the

transmitter end and what comes out at the receiver end. Testing for loss requires

measuring the optical power lost in a cable (including connectors ,splices, etc.) witha fiber optic source and power meter by mating the cable being tested to known

good reference cable.

In addition to our power meter, we will need a test source. The test source should

match the type of source (LED or laser) and wavelength (850, 1300, 1550 nm).

Again, read the instructions that come with the unit carefully.

We also need one or two reference cables, depending on the test we wish to


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perform. The accuracy of the measurement we make will depend on the quality of

your reference cables. Always test your reference cables by the single ended

method shown below to make sure they're good before you start testing other

cables!

Next we need to set our reference power for loss our "0 dB" value. Correct setting

of the launch power is critical to making good loss measurements!

Clean your connectors and set up

your equipment like this:

Turn on the source and select the wavelength

you want for the loss test. Turn on the meter,

select the "dBm" or "dB" range and select the

wavelength you want for the loss test. Measure

the power at the meter. This is your reference

power level for all loss measurements. If your

meter has a "zero" function, set this as your "0"

reference.

Some reference books and manuals show setting

the reference power for loss using both a launch

and receive cable mated with a mating adapter.

This method is acceptable for some tests, but will reduce the loss you measure by

the amount of loss between your reference cables when you set your "0dB loss"

reference. Also, if either the launch or receive cable is bad, setting the reference

with both cables hides the fact. Then you could begin testing with bad launch cables

making all your loss measurements wrong. EIA/TIA 568 calls for a single cable

reference, while OFSTP-14 allows either method.

Testing Loss

There are two methods that are used to measure

loss, which we call "single-ended loss" and

"double-ended loss". Single-ended loss uses only

the launch cable, while double-ended loss uses a

receive cable attached to the meter also.

Single-ended loss is measured by mating the

cable you want to test to the reference launch

cable and measuring the power out the far end

with the meter. When you do this you measure 1.

the loss of the connector mated to the launch

cable and 2. the loss of any fiber, splices or other

connectors in the cable you are testing. This

method is described in FOTP-171 and is shown in

the drawing. Reverse the cable to test the connector on the other end.

In a double-ended loss test, you attach the cable to test between two reference


23/37

cables, one attached to the source and one to the meter. This way, you measure

two connectors' loses, one on each end, plus the loss of all the cable or cables in

between. This is the method specified in OFSTP-14, the test for loss in an installed

cable plant.

What Loss Should You Get When

Testing Cables?

While it is difficult to generalize, here are some

guidelines:

- For each connector, figure 0.5 dB loss (0.7

max)

- For each splice, figure 0.2 dB

- For multimode fiber, the loss is about 3 dB per

km for 850 nm sources, 1 dB per km for 1300

nm. This roughly translates into a loss of 0.1 dB

per 100 feet for 850 nm, 0.1 dB per 300 feet for

1300 nm.

- For singlemode fiber, the loss is about 0.5 dB

per km for 1300 nm sources, 0.4 dB per km for 1550 nm.

This roughly translates into a loss of 0.1 dB per 600 feet for 1300 nm, 0.1 dB per

750 feet for 1300 nm. So for the loss of a cable plant, calculate the approximate

loss as:

(0.5 dB X # connectors) + (0.2 dB x # splices) + fiber loss on the total

length of cable

Troubleshooting Hints:

If you have high loss in a cable, make sure to reverse it and test in the opposite

direction using the single-ended method. Since the single ended test only tests the

connector on one end, you can isolate a bad connector - it's the one at the launch

cable end (mated to the launch cable) on the test when you measure high loss.

High loss in the double ended test should be isolated by retesting single-ended and

reversing the direction of test to see if the end connector is bad. If the loss is the

same, you need to either test each segment separately to isolate the bad segment

or, if it is long enough, use an OTDR.

If you see no light through the cable (very high loss - only darkness when tested

with your visual tracer), it's probably one of the connectors, and you have few

options. The best one is to isolate the problem cable, cut the connector of one end

(flip a coin to choose) and hope it was the bad one (well, you have a 50-50 chance!)

OTDRTesting


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As we mentioned earlier, OTDRs are always used on OSP cables to verify the loss of

each splice. But they are also used as troubleshooting tools. Let's look at how an

OTDR works and see how it can help testing and troubleshooting.

How OTDRs Work

Unlike sources and power meters which measure the loss of the fiber optic cable

plant directly, the OTDR works indirectly. The source and meter duplicate the

transmitter and receiver of the fiber optic transmission link, so the measurement

correlates well with actual system loss.

The OTDR, however, uses backscattered light of the fiber to imply loss. The OTDR

works like RADAR, sending a high power laser light pulse down the fiber and looking

for return signals from backscattered light in the fiber itself or reflected light from

connector or splice interfaces.

At any point in time, the light the OTDR sees is the light scattered from the pulse

passing through a region of the fiber. Only a small amount of light is scattered backtoward the OTDR, but with sensitive receivers and signal averaging, it is possible to

make measurements over relatively long distances. Since it is possible to calibrate

the speed of the pulse as it passes down the fiber, the OTDR can measure time,

calculate the pulse position in the fiber and correlate what it sees in backscattered

light with an actual location in the fiber. Thus it can create a display of the amount

of backscattered light at any point in the fiber.

Since the pulse is attenuated in the fiber as it passes along the fiber and suffers loss

in connectors and splices, the amount of power in the test pulse decreases as it

passes along the fiber in the cable plant under test. Thus the portion of the light

being backscattered will be reduced accordingly, producing a picture of the actual

loss occurring in the fiber. Some calculations are necessary to convert this

information into a display, since the process occurs twice, once going out from the

OTDR and once on the return path from the scattering at the test pulse.


25/37

There is a lot of information in an OTDR display. The slope of the fiber trace shows

the attenuation coefficient of the fiber and is calibrated in dB/km by the OTDR. In

order to measure fiber attenuation, you need a fairly long length of fiber with no

distortions on either end from the OTDR resolution or overloading due to large

reflections. If the fiber looks nonlinear at either end, especially near a reflective

event like a connector, avoid that section when measuring loss.

Connectors and splices are called "events" in OTDR jargon. Both should show a loss,

but connectors and mechanical splices will also show a reflective peak so you can

distinguish them from fusion splices. Also, the height of that peak will indicate the

amount of reflection at the event, unless it is so large that it saturates the OTDRreceiver. Then peak will have a flat top and tail on the far end, indicating the

receiver was overloaded. The width of the peak shows the distance resolution of the

OTDR, or how close it can detect events.

OTDRs can also detect problems in the cable caused during installation. If a fiber is

broken, it will show up as the end of the fiber much shorter than the cable or a high


26/37

loss splice at the wrong place. If excessive stress is placed on the cable due to

kinking or too tight a bend radius, it will look like a splice at the wrong location.

OTDRLimitations

The limited distance resolution of the OTDR makes it very hard to use in a LAN or

building environment where cables are usually only a few hundred meters long. The

OTDR has a great deal of difficulty resolving features in the short cables of a LAN

and is likely to show "ghosts" from reflections at connectors, more often than not

simply confusing the user.

Using The OTDR

When using an OTDR, there are a few cautions that will make testing easier and

more understandable. First always use a long launch cable, which allows the OTDR

to settle down after the initial pulse and provides a reference cable for testing thefirst connector on the cable. Always start with the OTDR set for the shortest pulse

width for best resolution and a range at least 2 times the length of the cable you are

testing. Make an initial trace and see how you need to change the parameters to get

better results.

Coming soon - our OTDR self-study course will teach you a lot more about how to

use OTDRs!

Restoration

The time may come when you have to troubleshoot and fix the cable plant. If you

have a critical application or lots of network cable, you should be ready to do it

yourself. Smaller networks can rely on a contractor. If you plan to do it yourself, you

need to have equipment ready (extra cables, mechanical splices, quick termination

connectors, etc., plus test equipment.) and someone who knows how to use it.

We cannot emphasize more strongly the need to have good documentation on the

cable plant. If you don't know where the cables go, how long they are or what they

tested for loss, you will be spinning you wheels from the get-go. And you need tools

to diagnose problems and fix them, and spares including a fusion splicer or some

mechanical splices and spare cables. In fact, when you install cable, save the

leftovers for restoration! And the first thing you must decide is if the problem is with

the cables or the equipment using it. A simple power meter can test sources for

output and receivers for input and a visual tracer will check for fiber continuity. Ifthe problem is in the cable plant, the OTDR is the next tool needed to locate the

fault.


27/37

Fiber Optic Patch

Cable Assemblies

Patch Cables, Mode

Conditioning, Pre-

Terminated Assemblies,

MTP Cables & Modules

Fiber Optic Test

Instruments

Test Kits, Power Meters,

Length Testers, Fault

Locators, Talk Sets, &

Connector Adapters

Fiber Optic Hardware

& Accessories

Termination Boxes,

Mating Sleeves, Bare

Fiber Adapters, & Optical

Attenuators

Jargo

n

Basic

s

Fibe

r

Cabl

e

Terminatio

n

Networ

k

Estimatin

g

Testin

g

Trainin

g

Glossar

y

NEXT

The information on this page is an original copyrighted article by

VDV Works LLC which has been authored and licensed to Atcom

Services, Inc.. We welcome you to link this page from your

website; however, copying this article in whole or in part is

strictly prohibited.

Disclaimer: We have provided this article as general installation advice

to our customers. We make no claims about the completeness or the

accuracy of the information as it may apply to an infinite amount of field

conditions. It is the responsibility of the person or persons using this

information to check with all concerned parties, owners and local

authorities, etc. before doing an installation. Users of this information

agree to hold Atcom Inc. harmless form liabilities of any kind relating to

the use of this information.


28/37

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Quick-Cat PRO System

Fiber Optic Cable, Hardware, etc.

Patch Cables Cat 5E & 6 (UTP/STP)

Cat 5E/6 Data & Voice Hardware

Cat 5E/6E/6A Bulk Cable

Tools & Testers

Technician's Tool Kits

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Rip-Tie Cable Ties

Racks, Brackets & Metal Products

Innerduct

Cisco Router Cables

Network Equipment

Labeling Tools & Acc.

Hi-Tech Home

Whats NEW

SALE ITEMS

Connectors

Tools

Tool Kits

Patch Cables

Pre-Terminated Assemblies

MTP Solution

Test Instruments


29/37

Termination Boxes

Mating Sleeves

Attenuators

Bare Fiber Adapters

Multimode

10-GiG Multimode

Singlemode

Mode Conditioning

Reference Cable Kits

ST to ST

ST to SC

SC to SC

MT-RJ to MT-RJ

MT-RJ to ST

MT-RJ to SC

LC to MT-RJ

LC to LC

LC to ST

LC to SC

LC to SC

LC to LC

SC to SC

ST to ST

ST to SC

SC to SC

LC to LC

LC to ST

LC to SC

MT-RJ to MT-RJ

MT-RJ to ST

MT-RJ to SC

MT-RJ to FC


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MT-RJ to LC

FC to FC

FC to ST

FC to SC

FC to LC

SC Equipment Side

LC Equipment Side

MT-RJ Equipment Side

SC to SC

SC to ST

SC to LC

SC to MT-RJ

LC to LC

LC to ST

LC to SC

LC to MT-RJ

MT-RJ to MT-RJ

MT-RJ to ST

MT-RJ to SC

MT-RJ to LC

Multimode

Singlemode

Indoor

Indoor/Outdoor

Indoor/Outdoor Interlock Armor

Outdoor

Outdoor with Messenger

Multimode

10-GiG Multimode

Singlemode

4 Strand

6 Strand


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12 Strand

24 Strand

4 Strand

6 Strand

12 Strand

24 Strand

4 Strand

6 Strand

12 Strand

24 Strand

Multimode

10-GiG Multimode

Singlemode

4 Strand

6 Strand

12 Strand

24 Strand

4 Strand

6 Strand

12 Strand

24 Strand

48 Strand

4 Strand

6 Strand

12 Strand

24 Strand

6 Strand Multimode

12 Strand Multimode

Multimode

Singlemode

4 Strand

6 Strand


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12 Strand

24 Strand

4 Strand

6 Strand

12 Strand

24 Strand

Multimode

Singlemode

4 Strand

6 Strand

12 Strand

24 Strand

4 Strand

6 Strand

12 Strand

24 Strand

MTP Cables

MTP Modules

Multimode

Singlemode

Test Kits

Power Meters

Reference Cable Kits

Length Testers

Fault Locators

Talk Sets

Meter Connector Adapters

Zoom OWL

WaveTester OWL

Micro OWL

Fiber OWL

Photonix LANLITE


33/37

Photonix TECHLITE

Multimode

Singlemode

Male to Female

In-line Fixed

In-line Variable

Singlemode

Multimode

Category 6

Category 6 Plenum

Category 6 Shielded

Category 6 Shielded Plenum

Category 6A Shielded

Category 6A Shielded Plenum

Category 5E

Category 5E Plenum

Category 5E Shielded

Category 5E Shielded Plenum

'110' to '110'

'110' to 'RJ-45'

Jacks & Accesories

Patch Panels

Bulk Cable

Cat 5E

Cat 6

Keystone

Wall Brackets

Cat 5E

Cat 6E

Cat 6A

Co-ax

Cat 5E


34/37

Cat 6E

Cat 6A

Co-ax

for Data & Voice

Technician's Tool Kits

for Coax & CATV

for Cable Installation

Collapsible Utility Carts

Suggested Telecom/Electrical

Hardside Cases

Sewn Cases

Pouches etc.

Wheeled Cases

Watertight Cases

Collapsible Utility Carts

Shippable Cases

Empty Cases

Polyethylene

Polypropylene

SUPER-SIZE

Soft-Molded

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Standard

Fire Retardant

Hinged Wall Brackets

Relay & Server Racks

Portable Data Cabinets/Racks

Wire Management Units

Wall Racks

Adapters, Fillers & Acc.

Data Cabinets

Equip. & Keyboard Shelves


35/37

Plenum

Riser

1-Inch Plenum

1.25-Inch Plenum

1-Inch Riser

1.25-Inch Riser

CAB 232/530

CAB-V35

CAB-449

CAB-X21

CAB-OCTAL

CAB-SS

CAB-GELX

Media Converters

Switches

Audio/Video

Fiber NIC Cards

UTP to Multimode Fiber

UTP to Singlemode Fiber

Gigabit

10BaseT

10/100BaseTX

Fiber Optic Modules

Gigabit

100BaseTX/100BaseFX

With Fiber Optic Slot

With SNMP & VLAN

ID PAL System

IDXPERT System

TLS2200 System

TLS PC Link System

ID PRO Plus System


36/37

ID PAL Labeling Tool

Labels & Accessories

IDXPERT Printer & Accessories

IDXPERT Labels

Datacom Application

Electrical Application

MRO/Facility/Safety

Printer & Accessories

Labels

Datacom Application


Industrial Application

Printer & Accessories

Labels

Datacom Application


Industrial Application

Accessories

Labels

Jacks & Accesories

Patch Panels

Cat 5E Cable

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Coax Tools & Connectors

Cat 5E

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Keystone

Wall Brackets


37/37

Documents

Fiber Optics Tutorials