Fibre Optic Communication

8/10/2019 Fibre Optic Communication

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Over view of OFCommunication


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1790: OPTICAL TELEGRAPH DEVISED BY CLAUDE CHAPPE. 1880: ALEXANDER GRAHEM BELL INVENTED THE PHOTOPHONE.

1940s: OPTICAL GUIDES WITH REFLECTIVE COATING TO CARRYVISIBLE LIGHT.

1960: INVENTION OF LASER-THE FIRST MAJOR BREAKTHROUGH IN FIBER OPTIC TECHNOLOGY.

UNGUIDED (NON FIBER) COMMNS. SYSTEMS WERE DEVELOPEDAFTER LASER DISCOVERY.

1966 onwards: DEVELOPMENT OF OPTICL FIBERS BYCOMPANIES LIKE CORNING GLASS (VERY HIGH LOSS).

IN 1970, LOW LOSS FIBER WAS DEVELOPED AND FIBER OPTICALCOMMNS. SYSTEM BECAME PRACTICAL. IT WAS OPERATED AT

WAVE-LENGTH AROUND 820 nm AND ATTENUATION OF 1db/km. NOW FIBERS WITH LOSSES OF ONLY A FRACTION OF A db/km

ARE AVAILABLE (0.15-0.35 db/km).

HISTORICAL

PERSEPECTIVE(1)


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High information carrying capacity:A valid comparison would be on the basis of cost per meter pertelephone 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 coaxialcable (RG-19/U) will attenuate a 100-Mz signal by 22.6 dB/km.

Greater safety:

Optic fibers glass/plastic, are insulators. No electric currentflows through them.

ADVANTAGES OF FIBRE

COMMUNICATIONS (1)


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Immunity to RFI:

Fibers have excellent rejection of radio-frequency interference(RFI) caused by radio and television stations, radar, and otherelectronics equipment.

Immunity to EMI:

Fibres 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; none leaks out duringtransmission to interfere with signals in other fibers.

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

Advantages of fibre

communications(2)


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Small size and light weight:typical optical cable; fiber dia. 125m, cable dia. 2.5mm and weight 6 kg/km. A coaxial cable (RG-19/U),outer dia. 28.4 mm, and weight 1110 kg/km.

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

Less temperatures sensitive:

Glass fibers can with stand extreme temperaturesbefore deteriorating Temperatures up to 800 C leaveglass fiber unaffected.

Advantages of fibre communications

(3)


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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:

Along railway track, through power substations can be suspendeddirectly from power line towers, or poles.

Military applications:

Non-communication fiber optic:

eg.fiber sensors.

Application of fibre optic

communications


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ALTTC OFC faculty 7

Ray Theory:

A number of optic phenomena are adequately explained byconsidering 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 anyother medium, rays travel at a slower speed, given by

v = c/n n =refractive index of the medium.

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

3. If any power crosses the boundary, the transmitted ray directionis given by Snells law:

n1 sin i = n2 sin r

Optic review


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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


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The Optical Fibre

Cladding

125 mCore6-10 m

Refractive index


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Light Propagationin fibre


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Light Propagation in fibre


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321

3

2

1



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321

3

2

1



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Air 1.0

Carbon dioxide 1.0

Water 1.33

Ethyl alcohol 1.36

Magnesium fluoride 1.38

Fused silica 1.46Polymethyl methacrylate polymer 1.5

Glass 1.54

Sodium chloride 1.59

Zinc sulfide 2.3Gallium arsenide 3.35

Silicon 3.5

Indium gallium arsenide phoshide 3.51

Aluminium gallium arsenide 3.6

Germanium 4.0

Index of Refraction materials


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Wave Nature of Light :

Many light phenomena can be explained by realizing that light isan 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 were made up of very small

particles called photons. The energy of a single photon is:

Wp = hf joules

h = 6.626 x 10-34j x s is Plancks constant..

f = frequency.


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Visible wavelengths :

0.4 m (red) Silica glass fiber

attenuates light

heavily in visible &

UV regions.

Glass fiber isrelatively efficient in

infrared region.

Three window of

operation are at

0.85, 1.3 and 1.55m.

1015

1014

1013

1012

1011

1010

109

108

107

106

105

104

103102

101POWER

RADIO

MICROWAVE

ULTRAVIOLET

INFRARED

Electromagnetic Spectrum :


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Basic Fibre core with RI n1

supported byconcentriccladding layer withRI n2.

RI of core isgreater thancladding (n1 > n2).

The cladding layeris surrounded byone or moreprotective coating.

Change in RI isachieved byselectively dopingthe glass perform.

Construction of Optical Fibre

Cable

CORE

CLADDING


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

Cabling protects the optical fibres from mechanical damage andenvironmental degradation.

Resembles conventional metal cables externally.

There are a variety of cable design available and irrespective of their

design fibre optic cables have the following parts in common : Buffer : to protect fibre from outside stress; materials used - nylon, or

plastic.

Strength member ; to reduce stress due to pulling, shearing, andbending; materials used-textile fiibres (kevlar), or steel.

Cable filling compound: to prevent moisture intrusion and migrationin the cable.

Cable jacket : to protect the fibre against cut and abrasion; materialused-polyethylene polyurethane, polyvinyl chloride or teflon.

Cabling of Optical Fibre :

CLASSIFICATION OF OPTICAL


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Material Classification

Allfused-silica-glass fibre: have silica-core and silica-cladding.

Plasti-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 ofelectromagnetic 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)

Graded index (GRIN) fibre.

CLASSIFICATION OF OPTICAL

FIBRE


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2a

2a

2a 8 - 12 m 125 m

50 - 100m 125-400m

50 m 100-400m

C) Multi mode GRIN fiber

b) Multi mode step-index fiber

a) Single mode step-index fiber

Classification of Optical Fibre

Wi d C t i S t


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- 190 THz

OH- OH-

OH-

Cut - off wave lengthfor single - mode

fibre

- 50 THz

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 Window

Second Window

Third Window

Fourth Window

Window Concept in Spectrum

of Optical Fiber

L i f bl


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soil categorization : ( for depth of trench )

(A) Rocky : Cable trench, where can not be dug without blastingand/or chiseling.

(B) Non Rocky: Other than A above, soil mixed with stone and softrock.

Pipes for cable laying

Advantage 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


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Now manual laying method is discoursed due to expensive, time consuming and due to safety consideration.

Now for digging JCB machines are preferred.

Air blowing method by using Pressure machine is used

for cable laying.


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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 heavilywithin specific wavelength regions. Other major source of loss isimpurities 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/)4dB/km

is in micrometers

Losses due to geometric effect:

micro-bending.

macro-bending.

Losses in Optical Fiber


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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)

FRESNEL REFLECTIONSLOSS

(db)

SPLICECONNECTOR

DISTANCE (KM)


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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 temperaturesensing and control is required to maintain stable temperature.

Optical Sources


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The detectors used in fibre optic communications aresemiconductor photodiodes or photodetectors.

It converts the received optical signal into electrical

form.

Pin photodiode; cheaper, less temperaturesensitive, and requires lower reverse bias voltage.

Aavalanche photodiode APD); used where

receiver is to detect lower power,

DETECTORS


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Power budget: for a link to be feasible.Source Transmitting Power

Less

coupling Loss to fibre + Connectors Losses + Fibre Loss +Splicing Loss

Maintenance Margin Receiver Sensitivity

System Design

System Considerations


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System Considerations* number of circuits * Transmission Distance

* Upgradability

Sources* Wavelength

* Line Width

* Rise Time

Cable network

* Route Loss

* Route BW

* Network Flexibility

LED LASER

PIN APD

Fibre Network FiberLoss Topology Bandwidth

Detectors* Responsivity

* Dark Current

* Gain

APD PIN


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Thank You

Fibre Optic Communication

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