How to Measure and Manage for Optimal Performance Wajih Daab - PowerPoint PPT Presentation

Me Polarization in Fiber Optic Systems: How to Measure and Manage for Optimal Performance Wajih Daab Product Line Manager May 19th, 2020

Outline  Introduction to Polarization  Polarization Related Issues in Fiber Optic Systems  Methods for Measuring Polarization Parameters  Polarization Management Technologies  Polarization Mitigation Techniques  Summary

Fundamental Parameters of Light Waves    ( / ) c f Simple electric field representation of a light wave: Amplitude Frequency Phase (constant) Amplitude Amplitude Amplitude Time Time Time 3

Polarization is Also an Important Property Light Waves Polarization describes the oscillation direction of an electric field. A polarized wave may be expressed as a sum of two orthogonal waves    i A e x  x   E  i   A e y   y http://www.radartutorial.eu/06.antennas/pic/zirkulanim.gif via de.wikipedia.org 4

State of Polarization (SOP) Linearly Polarized Light Circularly Polarized Light Elliptically Polarized Light                  ( , ) cos( ) sin( ) ( , ) cos( ) sin( ) E z t x A t Kz y A t Kz E z t x A t Kz y A t Kz ( , ) cos( ) E z t x A t Kz , or 0 0 0 0 x y 0    (Left-Circularly Polarized), or ( , ) cos( ) , or E z t y A t Kz 0       E 0     ( , ) cos( ) sin( ) E 0 E z t x A t Kz y A t Kz ( , ) cos( ) E z t x A t Kz y 0 0 x 0 x   cos( ) y A t Kz (Right-Circularly Polarized) 0 y 5

State of Polarization (SOP) Linear and Circular polarization states are special cases of the generalized elliptical polarization states Note: If δ varies randomly with time, then the light is unpolarized 6

Poincare Sphere Presentation of Polarization Any SOP can be represented as a point on a sphere with spherical coordinates defined by the orientation angle Y and ellipticity angle c . In the Poincaré Sphere representation, the Cartesian coordinates of the point are the Stokes parameters S1, S2, and S3. RHC  x ( c = p /4,  = 0 ) L-45 LV ( c =0,  =3 p /4) c ( c =0,  = p /2) 2     S 1 0      c  2 S cos 2 cos 2     LH   1 S     c  S cos 2 sin 2 L45 ( c =0,  =0) 2     ( c =0,  = p /4) LHC c  S   sin 2  3 ( c =- p /4,  = 0 ) 7

Degree of Polarization (DOP) DOP is defined as the fraction of the power of the light signal that is polarized Polarization Filter DOP = 0: Unpolarized light  Natural light DOP < 1: Partially polarized light.  Reflected natural light, SLED, ASE… DOP = 1: 100% polarized light  Laser light DOP (instantaneous) = 1, <DOP> t ~ 0  Scrambled light 8

Outline  Introduction to Polarization  Polarization Related Issues in Fiber Optic Systems  Methods for Measuring Polarization Parameters  Polarization Management Technologies  Polarization Mitigation Techniques  Summary

Polarization is Time Varying in Fiber Systems Free space: Polarization does not change with time Fiber: Stresses, Temperature, imperfections → fiber birefringence variation Sources of fiber stress  Temperature (Slow)  Wind caused vibration (Fast)  Train induced acoustic vibration (Faster)  Lightning/ electromagnetic field (Ultra fast) 10

Polarization Related Issues in Fiber Optic Systems Polarization Dependent Loss (PDL)  Difference in maximum and minimum IL due to polarization effects as a function of wavelength.  Different polarization states suffer different attenuations   P   max, i   10 log PDL Component , dB i   P   min, i Polarization Mode Dispersion (PMD)  The difference in propagation time between fastest-travelling and the slowest-travelling polarization modes.  Sometimes called differential group delay (DGD).       ( ) ( ) d d   Component i i PMD ps   i d d max min DGD 11

Polarization Related Issues in Fiber Optic Systems Polarization Extinction Ratio (PER):  The ratio between the optical power in the principal linear polarization component and that in the orthogonal linear polarization component at the point of measurement (typically after propagating through a system) Slow Axis   P   slow , i   10 log Polarization PER dB , i   Maintaining P   fast , i Component Fast Axis Polarization Dependent Gain (PDG):  Difference in maximum and minimum Gain due to polarization effects  The stronger component may experience faster gain saturation P   out , , || G  , || P  in , , ||   G G      10 log PDG dB   G   || 12

Polarization Affects the Performance of Coherent Systems Fast changes in SOP, high PDL and PMD are limiting factors in high-speed transmission systems Polarization mainly affects the following polarization related functions in the receiver:  Polarization tracking and demultiplexing  Polarization Mode Dispersion (PMD) Compensation  Polarization Dependent Loss (PDL) Compensation/Mitigation R X T X T X processor QPSK DeMUX algorithm PBS 90 ° hybrid TL PBC DSP PMDC algorithm  SOP Variation QPSK TL PDLC algorithm  PDL Variation  PMD Variation 13

Optical Component and System Characterization is Essential Optical components and devices modify the light propagating through them Industry needs to know whether components meet spec Researchers are interested in evaluating / discovering the optical characteristics of devices Input Distinguishable Output Output error 14

Outline  Introduction to Polarization  Polarization Related Issues in Fiber Optic Systems  Methods for Measuring Polarization Parameters  Polarization Management Technologies  Polarization Mitigation Techniques  Summary

SOP Measurement Methods Real observables  Electrical field cannot be measured.  What can be measured is optical power Stokes Parameters method      S P P     1 2   o '     S P P P P  1 1 2 1 2     S P P               1 1 2 ' [ 2 ( )] S S S P P P P P P1           2 3 1 2 1 2 2 ( ) S P P P        2 3 1 2 '      [ 2 ( )]  S P P P P P     3 4 1 2 1 2    2 ( )  S P P P 3 4 1 2 P2 P3  /4 plate P4 Circular polarizer PSGA-101 POD-201 16

DOP Measurement Methods Polarimeter Polarization Scrambling Maximum/minimum Search Power  P P Power  max min DOP P Po, max  o,max P P Po, min max min P o, min Time Polarization Polarization Time 0 90 45 RHC Laser Electronics Polarization Polarization Polarization Scrambler Control Laser Electronics Scrambler Scrambler Scrambler Photodetector Polarizer Electronics Photodetector Polarizer Feedback     2 2 2 P P P P S S S   max min max min  1 2 3 DOP DOP DOP   P P P P S o max min max min POD-201 MPC-201 DOP-201 17

PER Measurement Methods Polarimeter Rotating Polarizer Distributed Polarization Cross-talk Power D Z B =L B D n A B P C D o,max L B P o, min Broadband Time Electronics Power in slow axis DUT Stress Stress DUT Light Source L C C’ B’ Rotating PM fiber Photodetector Power in fast axis Polarizer X-talk at B X-talk at C      P P P       fast max 10 . log 10 . log PER PER       P P   min fast PXA-1000 POD-201 ERM-202 18

PDL Measurement Methods Polarization scrambling (PDL only) Maximum/minimum search (PDL only) Power Power P o,max Po, max P Po, min o, min Time Time Polarization Polarization Polarization Polarization DUT Laser Electronics DUT Laser Electronics Scrambler Scrambler Scrambler Control Photodetector Feedback Photodetector     P P       max 10 . log max PDL 10 . log   PDL     P   P min min PDL-201 MPC-201 19