Prof. Anjan K Ghosh DAIICT

Overview  

•  Fiber optical networks – advantages •  Multiplexing – DWDM •  Main components: fibers, splitters, optical

amplifiers, gratings, add-drop multiplexers, cross-connects

•  Examples of WDM based optical networks

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Op-cal  Networks  

•  The foundation of global information superhighway

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Why  Fiber  Op-cs?  

•  “Unlimited” bandwidth – Light frequency ~1015 Hz, even 1% of it = 1013 Hz ~ 1

billion digital audio channels •  Very low loss (0.2 dB/km) •  Secure •  Not affected by EMI •  Abundant raw material •  Cost-effective

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Advantage  of  the  Bandwidth  

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Think of the speed. Suppose you were to download the entire Library of Congress of the USA onto your PC using a dial-up modem transferring data at a rate of 56 thousand bps. It would take about 82 years. A wireless connection going at 2 million bps would move the library in a little over two years. How long would a 3-trillion-bps fiber-optics connection take? 48 seconds. From: http://www.wonderquest.com/fiber-optics-internet.htm

The capacity of the “L band” of wavelength of a standard single-mode fiber

Is about 25 trillion bps.

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Op-cal  Fiber  Network  Between  Con-nents  

From:  hHp://networks.cs.ucdavis.edu/~zhuk/maps.html  

A  Fiber  Op-c  Network  in  India  

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From:  hHp://www.sintelsat.com/fibernetworks/FLAG.html  

Fiber  Op-c  Network  in  a  State  

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From:  hHp://www.iowanetworkservices.com/Provider/map_state.aspx  

Metropolitan  Area  Op-cal  Network  

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From: Text book by Ramaswamy and Sivarajan

Local  Area  Network  (LAN)  

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From: http://www.mysecurecyberspace.com/encyclopedia/index/local-area-network-lan.html

Passive  Op-cal  Network  (PON)  or  

Fiber  to  the  X  (FTTX)  

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A  Typical  Fiber  Op-c  Communica-on  Link  

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S.  Pachnicke,  Fiber-­‐Op-c  Transmission  Networks,  Springer-­‐Verlag  Berlin  Heidelberg  2012    

Growth  in  Fiber  Op-cs  and  Internet  Traffic  

1/25/12   Op-cal  Networks     13  

S.  Pachnicke,  Fiber-­‐Op-c  Transmission  Networks,  Springer-­‐Verlag  Berlin  Heidelberg  2012    

Growth  in  Fiber  Op-c  Network  Capacity  

1/25/12   Op-cal  Networks     14  

S.  Pachnicke,  Fiber-­‐Op-c  Transmission  Networks,  Springer-­‐Verlag  Berlin  Heidelberg  2012    

Fiber  Op-cs  &  Broadband  in  India  

•  Must grow 100 times •  Information and knowledge to people •  Enormous scope in future

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“India has plans to extend its fiber optic network to reach the village level to connect and push e-services to rural areas, according to a government official. In a Friday statement, Shri Kapil Sibal, India's minister of communication and information technology said the Telecom Commission has proposed to create the National Optical Fiber Network (NOFN) which will extend the country's existing fiber optic network from the district level to the village level, or gram panchayat level.” ZDNet Asia on July 25, 2011

Mul-plexing  

•  Combining signals from different sources together to best utilize a channel

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From: http://en.wikipedia.org/wiki/File:Multipexing_demultiplexing_scheme_en.svg

Mul-plexing  

•  Time •  Frequency •  Code •  Wavelength

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Time  Division  Mul-plexing  (TDM)  

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From: http://zone.ni.com/devzone/cda/ph/p/id/270

TDM  

1/25/12   Op-cal  Networks     19  

TI Channel between two Central Offices carry 24 different Digital voice channels (PCM) each of bit rate 64 kbps

From:http://zone.ni.com/devzone/cda/ph/p/id/270

Frequency  Division  Mul-plexing  

1/25/12   Optical Networks 20  

From:  hH

p://electriciantraining.tpub.com/14189/css/14189_105.htm

 

Voice  of  User  1  

Voice  of  User  2  

Power  Spectrum  

FDM  

1/25/12   Optical Networks 21  

From:  hHp://fmfi-­‐uk.hq.sk/Informa-ka/Distribuovane%20Systemy/knihy/ICN/ch2s4p2.htm  

FDM  

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From:  hHp://en.wikibooks.org/wiki/Communica-on_Systems/Frequency-­‐Division_Mul-plexing  

Wavelength  

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Wavelength  =  (phase  velocity  )/frequency  

Wavelength  of  Light  

•  Frequency of light ~ 1015 Hz •  Instead of frequency we use wavelength in

micrometers or nanometers in photonics •  Visible light wavelength ~ 400 nm to 700 nm •  In Fiber optic communication networks we use

infra-red light with wavelength in the range of 1300-1350 nm or 1500-1600 nm

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Electromagne-c  Spectrum  

From: http://www.sengpielaudio.com/calculator-wavelength.htm

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Wavelength  Division  Mul-plexing  (WDM)  

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From:http://www.fiber-optics.info/fiber_optic_glossary

Typical  Dense  WDM  (DWDM)  Spectrum  

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From: http://www.gare.co.uk/technology_watch/dwdm.htm

DWDM  

•  WDM is similar to that of FDM •  Each wavelength = carrier for one super-super-

jumbo FDM group

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DWDM  

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From: Ramaswamy and Sivarajan

Composite FDM, TDM or CDM Signal

A  DWDM  Op-cal  Network  

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Figure 1.5 A WDM wavelength-routing network, showing optical line terminals (OLTs), optical add/drop multiplexers (OADMs), and optical crossconnects (OXCs). The network provides lightpaths to its users, which are typically IP routers or SONET terminals.

From: Ramaswamy and Sivarajan

A  Typical  Op-cal  Fiber  

cladding

core refractive index

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Snell’s  Law  of  Refrac-on  

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Total  Internal  Reflec-on  (TIR)  

TIR critical angle

RI = n2 > n1

RI = n1

= sin-1 (n1/n2)

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TIR  in  an  Op-cal  Fiber  

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Materials  of  Op-cal  Fibers  

•  Silica /glass with doping •  Chalcogenide glass •  Halide glass •  Rare-earth doped glass •  Plastic •  Speciality material such as sapphire •  Photonic bandgap structure

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A  Typical  Fiber  Op-c  Long-­‐haul  Communica-on  System  

Electronic Signal source

Optical transmitter

Fiber Cable 1

Fiber Cable 2

Fiber Cable 3

Fiber Cable 4

Optoelectronic Repeater

Optical Receiver

Signal Destination

Splice

Splice

0 dBm -40 dBm 0 dBm

If loss = 5 dB/km then distance = 8 km If loss = 1 dB/km then distance = 40 km

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AHenua-on  in  Op-cal  Fiber  Links  

•  Absorption •  Scattering

– Molecules –  Impurities

•  Bending and deformation •  Joints

– Fiber to fiber •  Connectors (removable) •  Splices (non-removable)

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Absorp-on  Spectrum  of  Silica  Fibers  

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Dispersion  

•  Causes spreading and distortion of lightwave signal pulses –  Intersymbol interference – Reduced bandwidth availability

•  Measured as a parameter with units ps/(km-nm)

Z=0 Z = L

t t

Optical Fiber

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Dispersion  and  RMS  Pulse  Width  

•  Light spectral width = Δλ nm •  Length of fiber = L km •  Dispersion parameter = σ ps/(km-nm) •  Pulse spread: ps •  Original rms pulse width at source = τ0 ps •  Final rms pulse width

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Δτ =σ LΔλ

Dispersion  Reduces  Available  Signal  Bandwidth  

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Graded  Index  Fiber  for  Less  Modal  Dispersion  

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Material  +  Waveguide  =  Chroma-c  Dispersion  

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Material  +  Waveguide  Dispersion  

Engineer

Can be changed By altering RI Distribution in core and cladding

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Dispersion  Compensa-on  

•  Use a dispersion compensating fiber segment •  Equalization techniques (esp. for polarization

dispersion) •  Use Soliton-pulse based propagation

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Power  Division  in  an    Ideal  DC  

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P3 = aPi Pi

P4 = (1-a)Pi

0 < a < 1

Ideal P3+P4 = Pi No Extra Loss

8x8  star  coupler  made  with  2x2  DC  

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All  Op-cal  Amplifica-on  

•  Semiconductor Laser Amplifiers •  Er Doped Fiber Amplifiers (EDFAs)

Basic  Physics  of  EDFAs  

•  Pump laser is absorbed by Er atoms •  Er atoms in higher energy state •  When a signal photon @ 1550 nm comes excited Er loses energy

giving extra photons @ 1550 nm •  New photons may add up with signal photons in phase •  Number of signal photons increase (some extra noise too) •  Depends on pump laser power, Er doping level, length of Er doped

fiber …

Schema-c  of  an  EDFA  

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From: http://www.fiberoptics4sale.com/wordpress

Amplified  Spontaneous  Emission  

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Advantages  of  EDFAs  

•  Attenuation or loss is less important now •  Power is low – put an EDFA •  (No. of EDFAs depends on noise and bandwidth

tolerances)

Gain  Characteris-cs  of  EDFAs  

Gain  Satura-on  in  EDFAs  

A  WDM  Link  with  EDFAs  

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From: Ramaswamy and Sivarajan

Fiber  Bragg  Gra-ngs  

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From: Wikipedia

FBG  Reflec-on  Spectrum  

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From: Ramaswamy and Sivarajan

Wavelength  Add  Drop  Mul-plexing  

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From: Ramaswamy and Sivarajan

Wavelength  Add-­‐drop  Mul-plexer  

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From: United States Patent 6832018

Mirrors

Array of Optical Filters

Need  for  OADM  

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From: Ramaswamy and Sivarajan

Serial  and  Parallel  OADM  

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From: Ramaswamy and Sivarajan

2x2  Op-cal  Switch  

•  A directional coupler on an Electro-Optic substrate •  Apply external E field •  Change coupling

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Crossbar  Switch  with  2x2  

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From: Ramaswamy and Sivarajan

MEMS  based  Op-cal  Switch  

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Op-cal  Cross  Connect  

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From: Ramaswamy and Sivarajan

Fiber  Op-c  Network  with  WDM  

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From: DWDM – S. Kartalopoulos

Fiber  Op-c  Metro  Network  with  WDM  

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WDM  based  PON  

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Scope  of  Research  

•  Enormous •  Fiber Optics + Free space Optics another 50-60

years

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Research  in  DAIICT  

•  Optical communication and Networking •  Optical Sensors •  Sensor Networking with Optics

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Summary  

•  Fiber optical networks – advantages •  Multiplexing – DWDM •  Main components: fibers, splitters, optical

amplifiers, gratings, add-drop multiplexers, cross-connects

•  Examples of WDM based optical networks

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References  

•  Optical Networks – Ramaswamy and Sivarajan •  DWDM – S. Kartalopoulos

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