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Optical Networking Components:

Optical Networking Components: 5
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Dr.NeerajMittal,India,Teacher
Published Date:19-07-2017
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Optical Networking Components: Part I Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 1Overview  Couplers, Splitters, Isolators, Circulators  Filters, Gratings, Multiplexors  Optical Amplifiers, Regenerators  Light Sources, Tunable Lasers, Detectors  Modulators  Chapter 2 and 3 of Ramaswami/Sivarajan Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 2Couplers, Splitters Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 3Optical Couplers  Combines & splits signals  Wavelength independent or selective  Fabricated using waveguides in integrated optics  = coupling ratio  Power(Output1) =  Power(Input1)  Power(Output2) = (1-) Power(Input1)  Power splitter if =1/2: 3-dB coupler  Tap if  close to 1 -selective if  depends upon  (used in EDFAs) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 4Couplers (contd)  Light couples from one waveguide to a closely placed waveguide because the propagation mode overlaps the two waveguides  Identical waveguides = complete coupling and back periodically (“coupled mode theory”)  Conservation of energy constraint: Possible that electric fields at two outputs have same magnitude, but will be 90 deg out of phase Lossless combining is not possible Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 5Couplers (Contd) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 68-port Splitter Made by Cascading Y- Couplers Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 78x8 Star Coupler Power from all inputs equally split among outputs Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 8Isolators and Circulators  Extension of coupler concept  Non-reciprocal = will not work same way if inputs and outputs reversed  Isolator: allow transmission in one direction, but block all transmission (eg: reflection) in the other  Circulator: similar to isolator, but with multiple ports. Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 9Recall: Polarization • Polarization: Time course of the direction of the electric field vector - Linear, Elliptical, Circular, Non-polar • Polarization plays an important role in the interaction of light with matter - Amount of light reflected at the boundary between two materials - Light Absorption, Scattering, Rotation - Refractive index of anisotropic materials depends on polarization (Brewster’s law)Polarizing Filters Done using crystals called dichroics Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 11Rotating Polarizations Crystals called “Faraday Rotators” can rotate the polarization without loss Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 12Optical IsolatorPolarization-dependent Isolators Limitation: Requires a particular SOP for input light signal Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 14Polarization-independent Isolators SWP: Spatial Walk-off Polarizer (using birefringent crystals) Splits signal into orthogonally polarized components Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 15Multiplexers, Filters, Gratings Wavelength selection technologies… Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 16Applications  Wavelength (band) selection,  Static wavelength crossconnects (WXCs), OADMs  Equalization of gain  Filtering of noise  Ideas used in laser operation  Dispersion compensation modules Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 17Characteristics of Filters  Low insertion (input-to- output) loss  Loss independent of SOP: geometry of waveguides  Filter passband independent of temperature  Flat passbands  Sharp “skirts” on the passband & crosstalk rejection  Cost: integrated optic waveguide manufacture  Usually based upon interference or diffraction Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 18Gratings  Device using interference among optical signals from same source, but with diff. relative phase shifts (I.e. different path lengths)  Constructive interference at wavelength  and grating pitch, a, if asin( ) - sin( ) = m  i d  m = order of the grating Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 19Transmission vs Reflection Grating  Narrow slits (tx) vs narrow reflection surfaces (rx)  Majority of devices are latter type (rx)  Note: etalon is a device where multiple optical signals generated by repeated traversals of a single cavity Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 20