Optical Fiber Systems

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Transcript of Optical Fiber Systems

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Optical Fiber Communication and SystemsBy OFC FACULTY ALTTC, Gzb.OF Comm&s OFC Faculty 1

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CONTENTSOptical fiber concept &type Fiber characteri stics Fiber classification Optical communication advantages Transmission windows Transmission challengesOF Comm&s OFC Faculty 2

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Optical Principle (Internal reflection theory)

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 by v = 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 i = n2 sin rOF Comm&s OFC Faculty 3

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(Principle of total internal reflection)

1 INCIDENT RAYS 1 2 N1 core 3

n1 = 1.48 n2 = 1.46 iREFLECTED RAYS

3 2

r N2 claddingOF Comm&s

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REFRACTED RAYSOFC Faculty

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The Optical FibreRefractive index

6-10 mm

Core

125 mm

Cladding

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Light propagation in fibre

1 2 3 3 2 1

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Light propagation in fibre

1 2 3 3 2 1

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CONSTRUCTION OF OPTICAL FIBRE CABLE

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.OF Comm&s OFC Faculty

CORE

CLADDING8

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CLASSIFICATION OF OPTICAL FIBRE

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.

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2a

8 - 12 mm 125 mm

a) Single mode step-index fiber

2a

50 - 200mm 125-400mm

b) Multi mode step-index fiber

2a

50 mm 125-400mm

C) Multi mode GRIN fi berOF Comm&s OFC Faculty 10

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Window Concept in Spectrum

5 4 3 2 1 0 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7Wavelength (mm) First window Second windowOF Third window Comm&s

~ 190 THz OH-

~ 50 THz OH -

Fourth window Fifth windowOFC Faculty 11

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LOSSES IN FIBER ( Attenuation)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/l)4 dB/km l is in micrometers Losses due to geometric effect:micro-bending. macro-bending.

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Dispersion - Pulse SpreadingOptical 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.OF Comm&s OFC Faculty 13

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WHAT IS

SDH ?

SYNCHRONOUS : One master clock & all elements synchronies with it. DIGITAL: Information in binary. HIERARCHY: Set of bit rates in a hierarchical order .

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WHAT IS S D H ? (CONTD)

SDH is an IT U-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.

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PDH HIERARCHIESUSA (Mbps) JAPAN (Mbps) 400 x4 100 x3 32 x5 6 x4 1.5

EUROPE (Mbps) 565 x4 140 x4 34 x4 8 x4 2

274 x6 45 x7 6 x4 1.5

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LIMITATIONS OF PDHNon standard experiences:-Three

different hierarchies with diff erent signal formats and line encoding methods. Basis of today s high capacity network -Elaborate arrangement for dropping Network requirement-Changing

requirementOF Comm&s OFC Faculty 17

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BASIS OF TODAY S NETWORK

M U X M U X M U X

LINE

M U X M U X

DDF DDF

DDF DDF

M U X

DDF ELABORATE DROPPING ARRANGEMENT

DDF

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SDH- ADVANTAGES

Simplification (ability to directly drop lower trib) Can accommodate both existing and future signals Improved 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)OF Comm&s OFC Faculty 19

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SDH ACCOMMODATES EXISTING SIGNALS

34M

140M

1

C43

8M

34M

C3

S D H M U X

2M

8M

6364K 2M

1

C12OFC Faculty 20

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SIGNAL HIERARCHYSONET vs SDH BIT RATES SONETOptical Carrier OC-1 OC-3 OC-9 OC-12 OC-18 OC-24 OC-36 OC-48 OC-192 Bit Rate Mbps 51.84 155.52 466.56 622.08 933.12 1244.16 1866.24 2488.32 9953.28

Synchronous Transport Signal STS-1 STS-3 STS-9 STS-12 STS-18 STS-24 STS--36 STS-48 STS-192*Bit

SDH

Synchronous Transport Module ---STM-1 ---STM-4 ------STM-16 STM-64

rates for higher order is n-times the lower orderOF Comm&s OFC Faculty 21

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MULTIPLEXING STRUCTUREAUG AU-4 VC-4 TUG-3 AU-3 VC-3 TUG-2 TU-2 TU-1 VC-2 VC-1 TU-3 VC-3 C-4

STM-N

C-3 C-2

C-1

(GENERALIZED MULTIPLEXING STRUCTURE/ G.708)OF Comm&s OFC Faculty 22

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REDUCED MUX STRUCTURE

STM-N

AUG AU-4 VC-4TUG-3

C-4 140Mbps TU-3 VC-3 C-3 TUG-2 TU-1 VC-1 C-1 2Mbps 34Mbps

(Reduced Diagram For SDH-Multiplexing)OF Comm&s OFC Faculty 23

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DWDM BASICSSINGLE FIBRE

SDH OPTICAL SIGNALS

NEW REQUIREMENTS:OF Comm&s OFC Faculty 24

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BLOCK SCHEMATICTxl1 l2. . . .

OPTICAL SIGNALS. STM-1 STM-4 STM-16 ATM IP

MUXW D M

DEMUX

Rx

OFA

l16

W D M

TRANSPONDERSOF Comm&s OFC Faculty 25

Wayside Optical Add/Drop MultiplexerBSNL

l1 l2 l 15 l

TM

WDM MUXO A

WDM DEMU XO A

TM

16

l

1-4

l 5-8

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DIFFERENCES FROM OLD SYSTEMREGs 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

OA

OADM

OXC

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ODEMUX29

TP

OMUX

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TRANSPONDER / TRANSLATOR / WAVELENGTH CONVERTOR

O/E

Electrical REGENERATION

E/O

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TRANSPONDERS

Converts broadband optical 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 functionOEO l1 l2

From OLTE

OEO ln OEO

To DWDM Mux

Low Cost OF Comm&s IR/SR Optics

Wavelengths OFC Faculty Converted

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Optical Amplifier

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

Careful design can remove the dispersion problems also.OF Comm&s OFC Faculty 32

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Erbium Doped Fiber Amplifier (EDFA)

v EDF Amplifier Characterti cs1. 2. 3. 4. Highly Efficient High gain Low Noise figure. Low CostOF Comm&s OFC Faculty 33

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Erbium Doped Fiber AmplifierIsolator Coupler Coupler Erbium-Doped Fiber (10 50m) Pump Laser Pump Laser Isolator

Simple device consisting of four parts: Erbium-doped fiber An optical pump A coupler OF Comm&s OFC Faculty An isolator to cut off backpropagating noise

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Optical Supervisory Channel - OSCOSC 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)In-line Amplifier Li