Fiber Optic Communication Overview, Cable Construction, Laying & Splicing By OFC faculty, ALTTC,...

Fiber Optic

Communication Overview,

Cable

Construction,

Laying & Splicing

ByOFC faculty, ALTTC,

GZB.

OFC Faculty Optical Fiber Communication

CONTENTS

• HISTORY• ADVANTAGES • APPLICATIONS • FIBER OPTIC PRINCIPLE • WINDOWS OF OPERATION • FIBER CLASSIFICATION• FIBER PROPERTIES• STANDARD FIBER TYPES • A TYPICAL OPTICAL FIBER LINK• CURRENT TRENDS IN FIBER OPTIC COMMUNICATION

04/19/23


• 1790: Optical telegraph was devised by Claude Chappe.

• 1880: Alexander Grahem Bell invented the PHOTOPHONE.

• 1940’s: Optical guides with reflective coating to carry visible light.

• 1960:Invention of “LASER”-The first major break through in fiber optic technology. Unguided (non fiber) communication systems were developed after laser discovery.

• 1966 Onwards: Development of optical fibers by companies like Corning Glass (very high loss).

• IN 1970, Low loss fiber was developed and OFC system became practical. It was operated at wave-length around 820 nm and at attenuation of 1db/km.

• Now fibers with losses of only a fraction of 1 db/km are available (0.15-0.35 db/km).

“HISTORICAL PERSEPECTIVE”(1)

04/19/23


“HISTORICAL PERSEPECTIVE”(2)

04/19/23


• High information carrying capacity:A valid comparison would be on the basis of cost per meter per telephone channel, rather than just cost per meter.

• Resource plentiful:The basic materials are either silicon dioxide for glass fibers or transparent plastic which are plentiful

• Less attenuation:A typical fibre attenuation is 0.3 dB/km. Whereas a coaxial cable (RG-19/U) will attenuate a 100-Mz signal by 22.6 dB/km.

• Greater safety:Optic fibers glass/plastic, are insulators. No electric current flows through them.

ADVANTAGES OF FIBRE COMMUNICATIONS (1)

04/19/23


• Immunity to Radio Frequency Interference:Fibers have excellent rejection of radio-frequency interference (RFI) caused by radio and television stations, radar, and other electronics equipment.

• Immunity to Electromagnetic Interference:Fibers have excellent rejection of electromagnetic interference (EMI caused by natural phenomena such as lighting, sparking, etc).

• No cross-talk:The optic wave within the fiber is trapped and does not leaks out during transmission to interfere with signals in other fibers.

• Higher Security:fibers offer higher degree of security and privacy.


04/19/23


• Small size and light weight:typical optical cable has a fiber dia. of 125m, cable dia. 2.5 mm and weight of 6 kg/km in comparison a coaxial cable (RG-19/U) has a outer dia. Of 28.4 mm, and weight 1110 kg/km.

• Corrosion : Corrosion caused by water/chemicals is less severe for glass than for copper.

• Less temperature sensitive:Glass fibers can with stand extreme temperatures before deteriorating. Temperatures up to 800 C leave glass fiber unaffected.


04/19/23


• Telecommunications:Long-Distance Telecommunications. Inter-exchange junction.Fibre in the loop (FITL).

• Video Transmission:Television broadcast, cable television (CATV), remote monitoring, etc.

• Broadband Services:provisioning of broadband services, such as video request service, home study courses, medical facilities, train timetables, etc.

• High EMI areas:Can be laid along railway track, through power substations and can be suspended directly from power line towers, or poles.

• Military applications:• Non-communication fiber optic:

eg. fiber sensors.

APPLICATION OF FIBER OPTIC COMMUNICATIONS

04/19/23


Ray Theory:• A number of optic phenomena are adequately explained by

considering light as narrow rays.• The theory based on this approach is called geometrical optics.• These rays obey a few simple rules:1. In a vacuum, rays travel at a velocity of c =3x108m/s. In any other

medium, rays travel at a slower speed, given byv = c/n n =refractive index of the medium.

2. Rays travel straight paths, unless deflected by some change in medium.

3. If any power crosses the boundary, the transmitted ray direction is given by Snell’s law:

n1 sin Øi = n2 sin Ør

Optic review

04/19/23


INCIDENT RAYS 1REFLECTED RAYS

REFRACTED RAYS

1

1

3

2

2

3

n2¢r

¢i

PRINCIPAL OF TOTAL INTERNAL REFLECTION

n1 = 1.48n2 = 1.46

n1

04/19/23


THE OPTICAL FIBRE

Cladding

125 mCore 6-10 m

Refractive index

04/19/23


LIGHT PROPAGATION IN FIBRE

04/19/23


321

3

2

1

LIGHT PROPAGATION IN FIBRE

04/19/23


Air 1.0

Carbon dioxide 1.0

Water 1.33

Ethyl alcohol 1.36

Magnesium fluoride 1.38

Fused silica 1.46

Polymethyl methacrylate polymer 1.5

Glass 1.54

Sodium chloride 1.59

Zinc sulfide 2.3

Gallium arsenide 3.35 Silicon3.5

Indium gallium arsenide phoshide 3.51

Aluminium gallium arsenide 3.6

Germanium 4.0

INDEX OF REFRACTION MATERIALS

04/19/23


Wave Nature of Light :• Many light phenomena can be explained by realizing that light is

an electromagnetic wave having a very high oscillation frequencies.

• The wavelength of light beam: = v/f v = beam velocityf = its frequency.

Particle Nature of light :• Sometimes light behaves as though it is made up of very small

particles called photons. The energy of a single photon is:Wp = hf joulesh = 6.626 x 10-34 j x s is Planck’s constant..

f = frequency.

04/19/23

NATURE OF LIGHT


Visible wavelengths 0.4 m (red)

• Silica glass fiber attenuates light heavily in visible & UV regions.

• Glass fiber is relatively efficient in infrared region.

• Three window of operation are at 0.85, 1.3 and 1.55 m.

1015

1014

1013

1012

1011

1010

109

108

107

106

105

104

103

102

101

POWER

RADIO

MICROWAVE

ULTRAVIOLET

INFRARED

ELECTROMAGNETIC SPECTRUM

04/19/23


Basic Fibre• core with R.I., n1 is

supported by concentric cladding layer with R.I. n2.

• R.I. of core is greater than cladding (n1 > n2).

• The cladding layer is surrounded by one or more protective coating.

• Change in RI is achieved by selectively doping the glass perform.

CONSTRUCTION OF OPTICAL FIBER CABLE

CORE

CLADDING

04/19/23


• Cabling is done to protect the fiber during transportation, installation & operation.

• Cabling protects the optical fibers from mechanical damage and environmental degradation.

• It resembles conventional metal cables externally.• There are a variety of cable design available and irrespective of their

design ,fiber optic cables have the following parts in common :

• Buffer : to protect fiber from outside stress; materials used - nylon, or plastic.

• Strength member : to reduce stress due to pulling, shearing, and bending; materials used-textile fibers (kevlar), or steel.

• Cable filling compound: to prevent moisture intrusion and migration in the cable.

• Cable jacket : to protect the fiber against cut and abrasion; material used-polyethylene polyurethane, polyvinyl chloride or teflon.

CABLING OF OPTICAL FIBRE

04/19/23


Material Classification :• Liquid core fibre.• All fused-silica-glass fibre: have silica-core and silica-cladding.• Plastic-clad-silica (PCS) fibre: have silica core and plastic cladding.• All-plastic fibre : have both core and cladding made up of plastic.• Compound glass fibre such as fluride glass fibre.

Modal classification :• Similar to metallic wave guides, there are stable propagation states of

electromagnetic waves in an optical fibre called modes.• Fibers can be classified based on number of modes available for

propagation : Single-mode (SM) fibre Multi-mode (MM) fibre.

Classification based on refractive index profile :• Step index (SI) fibre.• Graded index (GRIN) fibre.

CLASSIFICATION OF OPTICAL FIBRE

04/19/23


2a

2a

2a 8 - 12 m

50 - 200m

50 m

C) Multi mode GRIN fiber

b) Multi mode step-index fiber

a) Single mode step-index fiber

CLASSIFICATION OF OPTICAL FIBRE

04/19/23


- 190 THz

OH- OH-

OH-

Cut - off wave length for single - mode fibre

- 50 THz

Att

enti

on (

db

/km

)

Wavelength (m.)0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7

0

1

2

3

4

5

First WindowSecond Window

Third Window

Fourth Window

WINDOW CONCEPT IN SPECTRUM OF OPTICAL FIBER

04/19/23


soil categorization : ( for depth of trench )(A) Rocky : Cable trench, where it is not possible to be dug

without blasting and/or chiseling. (B) Non Rocky : Other than ‘A’ above, soil mixed with stone and soft

rock.Pipes for cable layingAdvantage for using pipes :1.It gives mechanical protection 2.Pipes can be laid in advance so that the cable laying is faster (1) HDPE pipe 75 mm (diameter) length 5m. (approx 18 to 20’ ) (2) HDPE pipe 50 mm (diameter) length 5m. (approx 18 to 20’ ) (3) PLP pipe (40 mm. outer diameter ) length 1km/200m

LAYING OF CABLE

04/19/23


• Mow manual laying method is discouraged as it is expensive , time consuming and also due to safety consideration.

• Now for digging JCB machines are preferred.• Air blowing method by using Pressure machine is

used for cable laying.

04/19/23

LAYING OF CABLE


Measurement of cable depth Depth should be measured from the top of pipe.However it is acceptable, if it is less upto eightcms from the specified depth. (A)Cross country rout (normal soil):HDPE pipe or PLP pipe depth is 1.5 meter .

In rocky area minimum depth 0.9 m ( where digging more

then 1 meter above pipe is not possible due to anyObstruction etc) should be considered. However, all cables

having depth less then 1.2 meter should be protected by RCC/GI pipes

04/19/23

LAYING OF CABLE


(B) In built up area (city/town/urban area): (1) OF cable should be laid through exiting duct.

(2) GI pipe or RCC pipe at the entry of duct. (3) In non duct area it should be laid through HDPE

pipe/PLP pipe at depth of 1.5 meter using RCC/GI pipe for

protection.

(4) Depth in rocky soil may be consider as 0.9 to 1.0 meter

(C) On culvert/bridge over river and nallah: (1) At the depth of 1.5 meter. Pipe length should be extended upto 2 meters at both ends.

(2) This should be fixed along the parapet wall/bridge wall when

river or nalla is full of water through out year, through fixed GI pipe on wall at suitable height above the water level.

04/19/23


(D) Along rail bridge or crossing : Through HDPE pipe/PLP pipe protected by RCC or iron pipe as per the prescribed by railway authority.

(E)On road crossing : At a depth of 1.5 meter through HDP pipe enclosed in RCC pipe extended by 3.0 meter to the either side end of the road.

Indicators along route : (A) Route indicator At every 200 m route length, showing name of route & no of indicators. (B) Joint indicator :

At every joint (Splice), generally it is placed at every 2/4 Km(Drum length) (C) Branch (Root diversion) indicator:

Provided at route diversion or branching from the main root.

04/19/23


• There are several points in an optic system where losses occur.• These are: coupler, splices, connectors and the fiber itself.• Losses associated within the fiber classified as under:• Losses due to absorption: Even the purest glass will absorb heavily

within specific wavelength regions. Other major source of loss is impurities like, metal ions and OH ions.

• Losses due to scattering: caused due to localized variations in density, called Rayleigh scattering and the loss is:

L = 1.7(0.85/)4 dB/km is in micrometers

• Losses due to geometric effect: – micro-bending.– macro-bending.

LOSSES IN OPTICAL FIBER

04/19/23


• OTDR is used for measurement of splice loss/ fiber loss in a section.• Optical power meter is used to know total loss of terminated cable section.

GENERAL ANALYSIS OF OTDR PLOT

FRESNE REFLECTIONSLOSS

(db)

SPLICE

CONNECTOR

DISTANCE (KM)04/19/23


• Dispersion is spreading of the optical pulse as it travels down the length.• Dispersion limits the information carrying capacity of fibre.• Classified as : Material Disp, Waveguide Disp. & Modal Disp.,

• Material Dispersion:– R.I. varies with Wave length causing velocity variation.

d n2 z– Pulse spread : (t/L) = - C d2 = - M

• Waveguide Dispersion:– effective R.I. varies with wavelength for given film thickness (n eff =

c/vg) d n2 eff z

– Pulse spread : (t/L) = - C d2 = - M g • Modal Dispersion:

– pulse spreading caused by various modes.– Pulse spread:(t/L) = Ln1 2 /2c for GRIN fiber

• Total Dispersion = - (M + Mg ) L for SM fiber• = (modal disp.)2 + (mat. disp.)2 for MM fiber (as MG = 0).

DISPERSION IN FIBER

04/19/23


A basic comm. System consists of : a transmitter, a receiver, & a medium.

• Optical Transmitters:– convert electrical signals to optical.

• Optical Receivers:– convert optical signal to electrical.

• The basic elements in transmitters: Electronic interfaces, Electronics processing circuitry, Drive circuitry, light source, optical interfaces, output sensing and stabilization, Temperature sensing and control.

• The basic elements in an optical receiver: Detector, Amplifier, Decision circuits.

BASIC FIBRE OPTIC COMMUNICATIONS

Ligh t source

ELECTRICAL

SIGNAL

TRANSMITTER MEDIUM RECIEVER

Ligh t sansor

ELECTRICAL SIGNAL

04/19/23


• The device which actually converts electrical signals to its optical equipment.

• Most common light sources:– light-emitting diodes (LEDs) .– Light Amplification by Stimulated Emission of Radiation

(laser) diodes.• It is particularly required in lasers to maintain stable output power

by way of feedback mechanism.• Laser is very sensitive to temperature. Operating characteristics

of a semiconductor laser - notably threshold, current, output power, and wavelength change with temperature. Hence temperature sensing and control is required to maintain stable temperature.

OPTICAL SOURCES

04/19/23


• The detectors used in fibre optic communications are semiconductor photodiodes or photodetectors.

• It converts the received optical signal into electrical form.– Pin photodiode: cheaper, less temperature

sensitive, and requires lower reverse bias voltage.– Aavalanche photodiode (APD): used where

receiver is to detect lower power,

DETECTORS

04/19/23


• Power budget: for a link to be feasible.Source Transmitting Power - (coupling Loss to fibre + Connectors Losses + Fibre Loss + Splicing Loss Maintenance Margin) Receiver Sensitivity

• Rise time Budget: to check total link rise i.e. this time is to be within permissible limit.

SYSTEM DESIGN

04/19/23


SYSTEM CONSIDERATIONS * NUMBER OF CIRCUITS * TRANSMISSION DISTANCE

* UPGRADABILITY

Fibre Network Fiber Loss Topology Bandwidth

Sources * Wavelength * Line Width * Rise Time

Cable network* Route Loss* Route BW* Network Flexibility

LED LASER

PIN APD

Detectors* Responsivity* Dark Current* Gain

APD PIN

04/19/23


Thank You

04/19/23

Fiber Optic Communication Overview, Cable Construction, Laying & Splicing By OFC faculty, ALTTC,...

Documents

Transcript of Fiber Optic Communication Overview, Cable Construction, Laying & Splicing By OFC faculty, ALTTC,...