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OF Comm&s OFC Faculty 1

Optical Fiber Communication

andSystems

By

OFC FACULTYALTTC, Gzb.

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OF Comm&s OFC Faculty 2

CONTENTS

• Optical fiber concept &type• Fiber characteristics• Fiber classification• Optical communication advantages• Transmission windows• Transmission challenges

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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

Optical Principle(Internal reflection theory)

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INCIDENT RAYS 1REFLECTED RAYS

REFRACTED RAYS1

1

3

2

2

3

N2 cladding¢r

¢i

(Principle of total internal reflection)

n1 = 1.48n2 = 1.46

N1 core

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The Optical Fibre

Cladding

125 µmCore 6-10 µm

Refractive index

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321

3

2

1

Light propagation in fibre

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321

3

2

1

Light propagation in fibre

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Basic Fibre• core with RI n1

supported by concentric cladding layer with RI n2.

• RI 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 FIBRE CABLE

CORE

CLADDING

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

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

for propagation :- single-mode (SM) fiber.

- Multi-mode (MM) fiber.

Classification based on refractive index profile :• step index (SI)• Graded index (GRIN) fiber.

CLASSIFICATION OF OPTICAL FIBRE

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2a

2a

2a 8 - 12 µm 125 µm

50 - 200µm 125-400µm

50 µm 125-400µm

C) Multi mode GRIN fi ber

b) Multi mode step-index fiber

a) Single mode step-index fiber

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5

4

3

2

1

00.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7

~ 190 THz~ 50 THz

OH- OH-

First window

Second window

Third window

Fourth window

Fifth window

Wavelength (µm)

Window Concept in Spectrum

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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

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/λ)4 dB/kmλ is in micrometers

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

LOSSES IN FIBER ( Attenuation)

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Dispersion - Pulse Spreading

• Optical fibres that carry data consist of pulses of light energy following each other. The fibre has a limit as to how many pulses per second can be sent to it and be expected to emerge intact at the other end. This is known as pulse spreading which limits the Bandwidth of the fibre.

• The pulse sets of f down the f ibre with a square wave shape. As it travels along the f ibre, it progressively gets wider and the peak intensity decreases.

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SYNCHRONOUS :One master clock & all elements synchronies with

it.

DIGITAL:Information in binary.

HIERARCHY:

Set of bit rates in a hierarchical order .

WHAT IS S D H ?

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SDH is an ITU-T standard for a high capacity Telecom Network.

SDH is a synchronous digital transport system, aim to provide a simple, economical and flexible telecom infrastructure.

WHAT IS S D H ? (CONTD)

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PDH HIERARCHIES

EUROPE (Mbps)

565

140

34

8

2

USA (Mbps)

274

45

6

1.5

JAPAN (Mbps)

400

100

32

6

1.5

x4

x4

x4

x4

x6

x7

x4

x4

x4

x5

x3

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• Basis of today ’s high capacity network

LIMITATIONS OF PDH

• Non standard experiences:

• Network requirement

-Changing requirement

-Elaborate arrangement for dropping

-Three different hierarchies with diff erent signal formats and line encoding methods.

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BASIS OF TODAY’S NETWORK

DDF

LINE

DDF

DDF

DDF

DDF

DDF

• ELABORATE DROPPING ARRANGEMENT

MUX

MUX

MUX

MUX

MUX

MUX

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Simplification (ability to directly drop lower trib)

Can accommodate both existing and future signalsImproved service quality (through supervision )

Advanced N/W management and mtce capabilities.

N/w survivability

Dynamic N/W capacity management

Multi vendor networking (mid fibre meet)

SDH- ADVANTAGES

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SDH ACCOMMODATES EXISTING SIGNALS

C4

C3

C12

34M140M

8M34M

2M8M

64K2M

63

1

SDH

MUX

3

1

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SIGNAL HIERARCHY

SONET vs SDH BIT RATESSONET SDH

SynchronousTransport Signal

Bit RateMbps

SynchronousTransport Module

*Bit rates for higher order is n-times the lower order

Optical Carrier

STS-1STS-3STS-9STS-12STS-18STS-24STS--36STS-48STS-192

OC-1OC-3OC-9OC-12OC-18OC-24OC-36OC-48OC-192

51.84155.52466.56622.08933.121244.161866.242488.329953.28

----STM-1----STM-4---------STM-16STM-64

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STM-N AUG AU-4 VC-4

AU-3 VC-3

TUG-3 TU-3 VC-3

C-4

C-3

TUG-2 TU-2

TU-1

VC-2

VC-1 C-1

(GENERALIZED MULTIPLEXING STRUCTURE/ G.708)

C-2

MULTIPLEXING STRUCTURE

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STM-N AUG AU-4 VC-4

TUG-3 TU-3 VC-3

C-4

C-3

TUG-2

TU-1 VC-1 C-1

140Mbps

34Mbps

2Mbps

(Reduced Diagram For SDH-Multiplexing)

REDUCED MUX STRUCTURE

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DWDM BASICS

SINGLE FIBRE

SDH OPTICAL SIGNALS

NEW REQUIREMENTS:

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BLOCK SCHEMATIC

Tx RxMUX DEMUX

OFA WDM

WDM

λ2....

λ1

λ16

TRANSPONDERS

OPTICALSIGNALS.STM-1STM-4STM-16

ATMIP

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Wayside Optical Add/Drop Multiplexer

TM TM WDM MUX

WDM DEMUXλ2

λ 15

λ16

λ1

λλ1-4 5-8

OA

OA

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DIFFERENCES FROM OLD SYSTEM

• REGs• FIBRES REQUIREMENT• LASERS• TYPES OF COMPONENT S• CAPACITY• FIBRE TRANSMISSION BEHAVIOUR

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ADVANTAGES OF DWDM

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OPTICAL NETWORK ELEMENTS

TP

TP OA

OD

EM

UX

OM

UX

OADM OXC

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TRANSPONDER / TRANSLATOR / WAVELENGTH CONVERTOR

O/E E/OElectrical REGENERATION

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TRANSPONDERS• Converts broadband opt ical signals to a specific wavelength

via optical to electrical to optical conversion (O-E-O)• Used when Optical LTE (Line Termination Equipment) does

not have tight tolerance ITU optics• Performs 2R or 3R regeneration function• Receive Transponders perform reverse function

Low Cost IR/SR Optics

Wavelengths Converted

λ1

From OLTE To DWDM MuxOEO

OEO

OEO

λ2

λn

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Optical AmplifierAdvantages:

•Design simplicity &high reliability .•Fewer components and economical.•Very low noise level.•Ability to amplif y multiple wavelength signals in the operatingband.•No interchannel interference .

Careful design can remove the dispersion problems also.

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v EDF Amplifier Characterti cs

1. Highly Efficient

2. High gain

3. Low Noise figure.

4. Low Cost

Erbium Doped Fiber Amplifier (EDFA)

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Erbium Doped Fiber Amplifier

“Simple” device consisting of four parts:• Erbium-doped fiber• An optical pump• A coupler• An isolator to cut off backpropagating noise

Isolator Coupler IsolatorCoupler

Erbium-DopedFiber (10–50m)

PumpLaserPumpLaser

PumpLaserPumpLaser

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Optical Supervisory Channel - OSC

• OSC mainly carries order wire and network management information.

• signals at 1510 nm or 1480 nm• 2.048 Mb/s

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Optical Supervisory Channel(OSC)

Line Terminal Equipment In-line Amplifier

Tx λ1

Tx λ2

Tx λ3

Tx λ4

Tx λ5

Tx λ6

Tx λ7

Tx λ8

DAT

A IN

λ1

λ2

λ3

λ4

λ5

λ6

λ7

λ8

Rx

Rx

Rx

Rx

Rx

Rx

Rx

Rx

λ1

λ2

λ3

λ4

λ5

λ6

λ7

λ8

Line Terminal Equipment

Σ λ + λsupervisory

Tx λsup

System ControlProcessor

Rx Tx

OSC

Network Management Network Management

System ControlProcessor

Rx λsup

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NominalCentral ∨

(THz)

Central λ(nm)

NominalCentral ∨

(THz)

Central λ(nm)

NominalCentral ∨

(THz)

Central λ(nm)

196.1 1528.77 194.7 1539.77 193.3 1550.92

196.0 1529.55 194.6 1540.56 193.2 1551.72

195.9 1530.33 194.5 1541.35 193.1 1552.52

195.8 1531.12 194.4 1542.14 193.0 1553.33

195.7 1531.90 194.3 1542.92 192.9 1554.13

195.6 1532.68 194.2 1543.73 192.8 1554.94

195.5 1533.47 194.1 1544.53 192.7 1555.75

195.4 1534.25 194.0 1545.32 192.6 1556.55

195.3 1535.04 193.9 1546.12 192.5 1557.36

195.2 1535.82 193.8 1546.92 192.4 1558.17

195.1 1536.61 193.7 1547.72 192.3 1558.98

195.0 1537.40 193.6 1548.51 192.2 1559.79

194.9 1538.19 193.5 1549.32 192.1 1560.61

194.8 1539.77 193.4 1550.12

ITU –T G.692 Frequency Grid

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Thank You