What is Optical Fiber Cable

7/30/2019 What is Optical Fiber Cable

1/26

1

Faculty

Engineering

Report Title

Optical fiber

Module Code

ECE 532

Module Title

Optoelectronics

Instructor Name

DR.Waleed

TAs Name

Eng.Mohamed Said

Student ID

094815

Student Name

Yasmeen Maher


2/26

2

What is optical fiber cable :

An optical fiber is a glass or plastic fiber that carries light along its length. Fiber optics is the

overlap of applied science and engineering concerned with the design and application of Optical

fibers .Optical fiber are widely used in fiber optic communication , which permits transmission

over longer distance and at higher bandwidth (data rates) because light has high frequency than

any other form of radio signal than other forms of communication .Light is Kept in the core of the

optical fiber by total internal reflection. this causes the fiber to act as a waveguide. Fiber are

used instead of metal wires because signal travel along them with less loss, and they are also

immune to electromagnetic interference ,which is caused by thunderstorm .Fiber are also used

for illumination ,and are wrapped in bundles so they can be used to carry images ,thus allowing

viewing in tight spaces .Specially designed fiber are used for a variety of other applications

including sensors and fiber lasers.

Fiber:

Fiber is the medium to guide the light from the transmitter to the receiver.It is classified into two

types depending on the way the light is transmitted: 1)-multimode fiber 2)-signal mode fiber.

The two distinct types of fiber-optic strands are the single- (single path) and multimode (multiple paths).

The practical differences between these two cable types depend on the light source used to send light

down the fiber core

Multimode Fiber Single-Mode Fiber

62.5+ m in core diameter 8.3 m in core diameter

Generally uses cheap light-emittingdiode light source

Utilizes expensive laser light

Multiple paths used by light Light travels in a single path downthe core

Short distances, 5 miles

Power distributed in 100% of the fiber core and into the cladding Power in the center of the fiber core only


3/26

3

COMPONENTSFIBER OPTIC CABLE

In most applications, optical fiber must be protected from the environment using avariety ofdifferent cabling types based on the type of environment in which the fiber will be used.Cabling provides the fiber with protection from the elements, added tensile strength forpulling,rigidity for bending, and durability. In general, fiber optic cable can be separated into twotypes:indoor and outdoor.Indoor Cables: Simplex cablecontains a single fiber for one-way communication

Duplex cablecontains two fibers for two-way communication Multifiber cablecontains more than two fibers. Fibers are usually in pairs for duplexoperation. A ten-fiber cable permits five duplex circuits. Breakout cabletypically has several individual simplex cables inside an outer jacket.The outer jacket includes a zipcord to allow easy access Heavy-, light-, and plenum-duty and riser cable Heavy-duty cables have thicker jackets than light-duty cable, for rougher handling. Plenum cables are jacketed with low-smoke and fire-retardant materials. Riser cables run vertically between floors and must be engineered to prevent firesfrom spreading between floors.Outdoor Cables:

Outdoor cables must withstand harsher environmental conditions than indoor cables.Outdoorcables are used in applications such as: Overheadcables strung from telephone lines Direct burialcables placed directly in trenches Indirect burialcables placed in conduits Submarineunderwater cables, including transoceanic applicationsSketches of indoor and outdoor cables are shown in Figure


4/26

4

FIBER OPTIC SOURCESTwo basic light sources are used for fiber optics: laser diodes (LD) and light-emittingdiodes(LED). Each device has its own advantages and disadvantages as listed in Table

Table LED Versus LaserFiber optic sources must operate in the low-loss transmission windows of glass fiber.LEDs aretypically used at the 850-nm and 1310-nm transmission wavelengths, whereas lasersareprimarily used at 1310 nm and 1550 nm.LEDsare typically used in lower-data-rate, shorter-distance multimode systemsbecause of their


5/26

5

inherent bandwidth limitations and lower output power. They are used in applications inwhichdata rates are in the hundreds of megahertz as opposed to GHz data rates associatedwith lasers.Two basic structures for LEDs are used in fiber optic systems: surface-emittingand

edgeemittingas shown in Figure

In surface-emitting LEDs the radiation emanates from the surface. An example of this istheBurris diode as shown in Figure. LEDs typically have large numerical apertures, whichSource:

makes light coupling into single-mode fiber difficult due to the fibers small N.A. and core

diameter. For this reason LEDs are most often used with multimode fiber. LEDs areused inlower-data-rate, shorter-distance multimode systems because of their inherentbandwidthlimitations and lower output power. The output spectrum of a typical LED is about 40nm,which limits its performance because of severe chromatic dispersion. LEDs operate in amore


6/26

6

linear fashion than do laser diodes. This makes them more suitable for analogmodulation.Figure 8-22 shows a graph of typical output power versus drive current for LEDs andlaserdiodes. Notice that the LED has a more linear output power, which makes it more

suitable foranalog modulation. Often these devices are pigtailed, having a fiber attached during themanufacturing process. Some LEDs are available with connector-ready housings thatallow aconnectorized fiber to be directly attached. They are also relatively inexpensive. Typicalapplications are local area networks, closed-circuit TV, and transmitting information inareaswhere EMI may be a problem.

Laser diodes(LD) are used in applications in which longer distances and higher datarates arerequired. Because an LD has a much higher output power than an LED, it is capable oftransmitting information over longer distances. Consequently, and given the fact that theLD has

a much narrower spectral width, it can provide high-bandwidth communication over longdistances. The LDs smaller N.A. also allows it to be more effectively coupled withsingle-modefiber. The difficulty with LDs is that they are inherently nonlinear, which makes analogtransmission more difficult. They are also very sensitive to fluctuations in temperatureand drivecurrent, which causes their output wavelength to drift. In applications such aswavelengthdivisionmultiplexing in which several wavelengths are being transmitted down the same fiber,the stability of the source becomes critical. This usually requires complex circuitry andhigh-speed transmission using LDs typically outweigh the drawbacks and added

expense.Laser diodes can be divided into two generic types depending on the method ofconfinement ofthe lasing mode in the lateral direction. Gain-guidedlaser diodes work by controlling the width of the drive-current distribution;this limits the area in which lasing action can occur. Because of different confinementmechanisms in the lateral and vertical directions, the emitted wavefront from these


7/26

7

devices has a different curvature in the two perpendicular directions. This astigmatisminthe output beam is one of the unique properties of laser-diode sources. Gain-guidedinjection laser diodes usually emit multiple longitudinal modes and sometimes multipletransverse modes. The optical spectrum of these devices ranges up to about 2 nm in

width, thereby limiting their coherence length. Index-guidedlaser diodes use refractive index steps to confine the lasing mode in boththe transverse and vertical directions. Index guiding also generally leads to both singletransverse-mode and single longitudinal-mode behavior. Typical linewidths are on theorder of 0.01 nm. Index-guided lasers tend to have less difference between the twoperpendicular divergence angles than do gain-guided lasers.Single-frequencylaser diodes are another interesting member of the laser diode family.Thesedevices are now available to meet the requirements for high-bandwidth communication.Otheradvantages of these structures are lower threshold currents and lower power

requirements. Onevariety of this type of structure is the distributed-feedback (DFB) laser diode (Figure 8-23).With introduction of a corrugated structure into the cavity of the laser, only light of a veryspecific wavelength is diffracted and allowed to oscillate. This yields output wavelengthsthatare extremely narrowa characteristic required for DWDM systems in which manycloselyspaced wavelengths are transmitted through the same fiber. Distributed-feedback lasershavebeen developed to emit light at fiber optic communication wavelengths between 1300

nm and 1550 nm

FIBER OPTIC DETECTORSThe purpose of a fiber optic detector is to convert light emanating from the optical fiberbackinto an electrical signal. The choice of a fiber optic detector depends on several factorsincluding wavelength, responsivity, and speed or rise time. Figure 8-30 depicts thevarious typesof detectors and their spectral responses


8/26

8

that produces the light. Light striking the detector generates a small electrical currentthat isamplified by an external circuit. Absorbed photons excite electrons from the valenceband to theconduction band, resulting in the creation of an electron-hole pair. Under the influenceof a bias

voltage these carriers move through the material and induce a current in the externalcircuit. Foreach electron-hole pair created, the result is an electron flowing in the circuit. Typicalcurrentlevels are small and require some amplification as shown in Figure

The most commonly used photodetectors are the PIN and avalanche photodiodes(APD). Thematerial composition of the device determines the wavelength sensitivity. In general,silicondevices are used for detection in the visible portion of the spectrum; InGaAs crystal areused inthe near-infrared portion of the spectrum between 1000 nm and 1700 nm, and

germanium PINand APDs are used between 800 nm and 1500 nm. Table 8-5 gives some typicalphotodetectorcharacteristics:


9/26

9

Responsivitythe ratio of the electrical power to the detectors output optical powerQuantum efficiencythe ratio of the number of electrons generated by the detector tothenumber of photons incident on the detectorQuantum efficiency = (Number of electrons)/PhotonDark currentthe amount of current generated by the detector with no light applied.Darkcurrent increases about 10% for each temperature increase of 1C and is much more

prominent in Ge and InGaAs at longer wavelengths than in silicon at shorterwavelengths.Noise floorminimum detectable power that a detector can handle. The noise floor isrelated to the dark current since the dark current will set the lower limit.Noise floor = Noise (A)/Responsivity (A/W)Response timethe time required for the detector to respond to an optical input. Theresponse time is related to the bandwidth of the detector byBW = 0.35/trwhere tris the rise time of the device. The rise time is the time required for the detectortorise to a value equal to 63.2% of its final steady-state reading.

Noise equivalent power (NEP)at a given modulation frequency, wavelength, andnoisebandwidth, the incident radiant power that produces a signal-to-noise ratio ofoneat theoutput of the detector (Source: Electronic Industry AssociationEIA)

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 willprobably 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


10/26

10

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

Getting StartedEven 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 toyour 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 recording your 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...


11/26

11

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

Visual Tracing

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


12/26

12

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")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 lossand defines the performance of a cable, connector, splice, etc.

Measuring PowerPower 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 little help 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,


13/26

13

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 LossLoss 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.) with a

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 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 EquipmentLike This:Turn on the source and select the wavelength you want for

the loss test. Turn on the meter, select the "dBm" or "dB"


14/26

14

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 LossThere 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 measuringthe 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 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?


15/26

15

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 ofcable

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!)


16/26

16

OTDR TestingAs 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 WorkUnlike 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 back

toward 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, calculatethe 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.


17/26

17

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 OTDR

receiver. 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.


18/26

18

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 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.

OTDR LimitationsThe 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 OTDRWhen 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 the first 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 aninitial trace and see how you need to change the parameters to get better results.

RestorationThe 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 thecable 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


19/26

19

for input and a visual tracer will check for fiber continuity. If the problem is in the cable

plant, the OTDR is the next tool needed to locate the fault.

Siemens Company

Description

fiber-optic cable is used for transmitting signals with the help of electromagnetic waves

in the optical frequency range. Fiber-optic cables are recommended as an alternative to

copper cables wherever there is severe electromagnetic interference, the equipotential

bonding is to be saved, in open-air systems or where no electromagnetic radiation is

wanted.

To construct optical network structures, glass fiber optic cables are used for longer

paths, while plastic fiber optic cables are used for shorter paths. These plastic cablesuse light-conducting plastics such as polymer optic fiber (POF) or polymer cladded fiber

(PCF).

Detail

Different versions for different applications

Halogen-free version for use in buildings, trailing cable for the special case where

forced movement is required. Available pre-assembled

FO Standard Cable GP 50/125 (Type C)

FO Trailing Cable 50/125 (Type C)

FO Training Cable GP 50/125 (Type C)

FO Ground Cable 50/125 (Type C)

FO FRNC Cable 50/125 (Type B)


20/26

20

Features

Rugged design for industrial applications indoors and outdoors.

High immunity to noise thanks to insensitivity to electro-magnetic fields

Tap-proof due to lack of radiation from the cable

Silicon-free, therefore suitable for use in the automotive industry (e.g. in paintshops) Electrical isolation of PROFINET/Ethernet devices

Protection of the transmission route against electromagnetic interference

Certified for various applications, e.g for the American and Canadian market (UL listing

such as OFN/OFNG for fiber-optic cables or CM/CMG for copper cables)

PROFINET-compatible

RoHS conformity

Free from varnish-moistening substances

Benefits

Simple laying with pre-assembled cables, without grounding problems and very light

fiber-optic cables.

Various approvals

Communication Bandwidth

Many of the new technologies for advanced tieback systems like subsea processing

and multiphase pumping, either require or can benefit from improved controls support.

Why should many advanced systems be limited to a share of a 1200 baudcommunication line? Norsk Hydro a.s. have recently completed commissioning on the

Troll Pilot subsea separator. The separator control system handles a 1000 fold increase

in data transmission. At the same time, it operates in an environment which includes the

risk of EMI interference from the high-power supply umbilical to the MWatt re-injection

pump that resides on the separator manifold. The Troll Pilot program took the decision

at an early stage to use only fiber-optic communication.

A dual-redundant fiber-optic backbone runs from the surface control system through the

ISU (Integrated Service Umbilical), which includes the high voltage supply lines to the

re-injection pump, to the wet-mate fiber-optic connectors on the Umbilical Termination

Assembly (UTA). From the UTA, oil-filled jumper assemblies link to ROV installed wet-

mate, fiber-optic connectors on the individual control systems for the separator and the

water injection x-tree (see photo 1).


21/26


22/26

22

Single-mode optical communication provides very long distance unrepeated

communication. A long haul optical fiber communication system is one proposal for the

West Delta Deep Program offshore Egypt. The distance is mainly limited by optical

signal dispersion in the fiber and is bit rate dependent. At 200 Mbit/sec, single-mode

fiber can support an unrepeated transmission distance in excess of 100 km.

Using EDFA (Erbium Doped Fiber Amplifier) technology from the telecommunications

industry that provides passive amplification without conversion to an electrical signal,

and an appropriate choice of fiber, unrepeated distances of 200-300 km can be

achieved. These distances will support one of the long-term goals of the tieback

community;- tieback to shore.

CAPEX Reduction for Umbilical Manufacture and Installation

As step-out distances increase and installations get ever deeper, the costs associated

with ISUs grow in relation to the overall development capital expenditure. The unit

length manufacturing cost for an ISU is dependent on the cross-sectional construction

and the final diameter of the active elements drives the weight of armoring needed.

Therefore, any reduction in the dimension of the umbilical internals can lead to a

reduction in weight per unit length, which may lead to further cost reduction for

installation.

As a case study, the original installation plan for the BP Amoco Kings Peak field in the

deep-water GOM called for dual-redundant electrical communication with a 16 mile (25

km) ISU linking the Kings Peak gathering manifold with the production vessel proposed

for the King field. The water depth over most of the installation is in excess of 6,000 ft.

The original umbilical design included separate twisted shielded pair conductors to each

control module. The resultant ISU was too large to manufacture in one piece. This

Coupler

Erbium Doped Fiber

Fiber-optic

Weak Input

Signal

Fiber-optic Pump

Source

Amplified Fiber-

optic Signal


23/26

23

meant that the installation vessel specifications had to include a moon pool for launch

and recovery of the termination assemblies and the central splice enclosure. At this

point, the forecast development costs were becoming uneconomic, largely driven by the

cost of manufacture and installation of the ISU.

BP Amocos decision to replace the electrical communicat ion lines with optical fibers ina hermetically welded steel tube resulted in a reduction in cross-section and in the

amount of armoring needed. This led to a sufficient weight saving so that the ISU could

be fabricated in one length. The installation could now be carried out by a less costly

vessel as the moon pool was no longer a requirement.

Once the decision to use optical fiber communication was taken, an additional benefit

was realized. BP Amoco were able to implement a real time interrogation of the PES

SCRAMS system directly from the surface, simply by adding additional fibers in the

existing fiber tubes and placing additional optical modems in the Subsea Control

Modules. This decision did not affect the cross-section of the umbilical and the cost

impact was limited to a few cents per foot for each additional fiber.

EMI Noise Immunity To Support High-power Systems

Electrical communication is at risk of data corruption from electromagnetic noise, such

as that generated by high-voltage power lines and large electric motors. The growth in

interest in subsea single and multiphase pumps for pressure boost and water re-

injection, where extended step-outs require either assistance for fluid movement and/or

environmentally friendly disposal of produced water from a subsea separator, has led to

the development of a number of different pump/motor systems. Many of these motors

are electrically driven and at powers in the 2-5 MW range.

In order to supply these levels of power, low-loss, high-voltage transmission lines need

to be used. In addition, the motor control loop will often use a variable frequency power

supply to provide motor speed control. Under these conditions, the power conductors

and the motors become sources of high levels of electromagnetic interference.

Two options exist for electrical communication:

a) Shield the communication conductors from the noise source. This is costly interms of umbilical construction and is not always successful.


24/26

24

b) Run a separate communication cable. Again, this is costly in terms ofumbilical installation. The communication and power cables will need to beinstalled at least 1m apart. Difficulties may arise when trying to keep thecommunications cable shielded at the subsea termination.

Optical fiber is inherently noise immune. The fiber can be run in a stainless steel orcopper carrier tube in the same umbilical as the high-power conductors, with no risk ofdata corruption through EMI.

Subsea installations of high-power pumps, including the Troll Pilot water injection pumpand the Petrobras SBMS multiphase pump, have used all optical communication withwet-mate fiber-optic connectors and jumpers providing the modular installationnecessary for these large systems.

Sensors and Sensor Support

As tieback technology continues to increase its level of sophistication with theinstallation of complex subsea systems, ever more sophisticated sensors with real timedata access are needed as a fundamental component of any feedback loop controlsystem. No longer are subsea sensors needed to just monitor valve position. Todayssuite of sensors provide real time data on single and multiphase flow conditions,temperature and pressure, pipe erosion monitoring, level sensing, water cut, etc.

Optical fiber provides the high bandwidth communication backbone necessary for theimplementation and best use of many of these sensors. This can allow the sensorcontrol and diagnostic equipment to be located on the platform and have a number ofpassive sensor heads located in the extreme environment, either downhole or inside

pipe-work. In addition, optical fiber is itself capable of sensing many of themeasurements covered by the sensors listed above.

One sensor system already in place for a downhole pressure and temperaturemeasurement is the FOWM (Fiber-Optic Well Monitoring) gauge system used by Shellon ETAP (Eastern Trough Area Project). The ten high temperature wells on the threefields Skua, Egret and Heron that make up Shell ETAP were not suitable for electronicgauge technology with temperatures in excess of 160 C. The FOWM system usesdiscrete optical pressure and temperature sensors, interrogated over a single fiber foreach well set. A wet-mate, single channel, fiber-optic connector resides between the x-tree and tubing hanger, with additional wet-mate fiber-optic connectors and jumpers

linking the x-tree to the umbilical termination assembly. The umbilical is fabricated inthree sections linking each field and there are multi-circuit, wet-mate, fiber-opticconnectors and optical jumpers linking each umbilical section. The sensor interrogationand diagnostics equipment, including the lasers and drive electronics, reside on theplatform where easy servicing can be performed. Separate fibers link each well to theplatform with spare fibers to each UTA and available through protected spare wet-matefiber-optic connectors. The furthest well is >25 km from the Marnock platform, so the


25/26

25

sensor signal traverses a round trip to the sensor in excess of 50 km. All of the opticalsensors are read in real time and at the same time.

In its simplest form, optical fiber can be used as a distributed temperature sensorcapable of measuring 30 km lengths with 1m measurement spacing and a temperatureaccuracy of 0.1 C. This technology is proving very useful in pipeline monitoring andpipeline heating programs, and even has a successful history of downhole distributedtemperature measurement.

The addition of a Bragg Grating to the fiber converts that section of the fiber to a pointsensor where any external effect which causes a change in length of the fiber grating,i.e. temperature, pressure, strain, etc., can be detected. A Bragg grating is a section offiber encoded with a modulated transmission profile where the pitch on the modulationis equivalent to the optical signal wavelength passing through it. The grating istransparent to wavelengths that do not match the grating pitch. This allows gratings withdifferent pitches to be added in series to a length of fiber creating a series of pointsensors.

The sensor operates by having the parameter under test change the length of thegrating by a small amount, thereby changing the pitch of the grating and the wavelengthof a reflected signal. With a number of sensors in series on a fiber, they can all be readat the same time by illuminating the fiber with a white light source and monitoring(scanning) for the frequencies of the reflected signals.

There are a number of other discrete sensors that use optical measurement techniquesand can be interrogated over an optical fiber. One of the largest potential uses of opticalsensors is in high sensitivity passive geo-phones for use on the sea-floor or down-holein the well for continuous production draw-down monitoring

Bragg Grating Fiber

Optical wavelength matches the

grating pitch and is reflectedBG

Optical wavelength does not match the grating pitch and is transmitted

Input

Input

Return

Transmitted

1-BG


26/26

Documents

What is Optical Fiber Cable