Williams Tutorial Updated 11 14
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Williams Tutorial Updated 11 14

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Fiber and component metrology for high-speed communications:What the manual doesn’t tell youPaul Williams, Paul Hale, and Tracy ClementNational Institute of Standards and TechnologyBoulder, Colorado1. Polarization-mode dispersion (Williams)2. Transmitter/receiver frequency response (Hale and Clement)1Part 1. Polarization-mode dispersionPMD measurement advice for folks with turnkey measurement systemsAssumptions:A basic understanding of PMDA PMD measurement systemAn understanding of the measurement techniquesAvoid measurement traps that give false results.2Steps to a good PMD measurement1. Perform measurement “calibration”2. Understand limitations imposed by measurement conditions3. Choose measurement parameters correctly4. Be aware of measurement uncertaintiesAssumption: measurement system works correctly3Review: PMD DefinitionsOutput PSP_General Case:(slow)Output PSP+Input PSP_ (fast)Input PSP+(slow)(fast)• Birefringence affects propagation velocity and output polarization state• PMD is characterized by two Principal States of Polarization (PSP)• PSPs are wavelength-independent (to first order)• Propagation along PSPs is the fastest/slowest possible• PMD is the phenomenon, DGD (∆τ) is the magnitudeDifferential group delay (DGD): ∆τ =τ −τfast slow4Review: Time domain PMD measurementlow-coherence interferometery (INT)broadband sourceDet.∆τ Time (ps)• “Width” of delay histogram gives mean DGD• Measures only mean DGD ...

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Fiber and component metrology for high-speed communications: What the manual doesnt tell you
1.
2.
Paul Williams, Paul Hale, and Tracy Clement National Institute of Standards and Technology Boulder, Colorado
Polarization-mode dispersion (Williams)
Transmitter/receiver frequency response (Hale and Clement)
1
Part 1. Polarization-mode dispersion
PMD measurement advice for folks with turnkey measurement systems
Assumptions: A basic understanding of PMD A PMD measurement system An understanding of the measurement techniques
Avoid measurement traps that give false results.
2
Steps to a good PMD measurement
1. Perform measurement calibration 2.Understandlimitationsimposedbymeasurement conditions 3.Choosemeasurementparameterscorrectly 4. Be aware of measurement uncertainties
Assumption:eremtnssyetmowmeasuyltcerrocskr
3
General Case:
Input PSP+ (fast)
pu _ In t PSP (slow)
Review: PMD Definitions
Output PSP _ (slow)
Output PSP+ (fast)
Birefringence affects propagation velocity and output polarization state PMD is characterized by two Prin cipal States of Polarization (PSP) PSPs are wavelength-independent (to first order) Propagation along PSPs is the fastest/slowest possible PMD is the phenomenon, DGD (∆τ) is the magnitude
Differential group delay (DGD):
=
fast
slow
4
broadband source
Review: Time domain PMD measurement low-coherence interferometery (INT)
∆τ
Width of delay histogram gives mean DGD Measures only mean DGD
Det.
Time (ps)
5
Poincaré sphere
S2(ω2)
Review: Frequency domain PMD measurements
S
S1(ω1)
(3-d representation of polarization state) Equator:linear polarization states Poles:left and right circular Elsewhere:elliptical
Measure transmitted polarization state of light - at two optical frequencies (ω1andω2) r d Sial Group τ=dω)DGD(ylaDDefeifntre Polarization-based DGD definition (ω= radian frequency)
Measures DGD(λ)
Jones Matrix Eigenanalysis (JME), Mueller matrix method (MMM), Poincaré sphere analysis (PSA)
6
Review: Polarization-mode coupling
Non-mode-coupled devices:
Simple birefringence (fast and slow eigenaxes independent of wavelength)
Examples: waveplates, single crystals, polarization maintaining fiber, typical components
Typical measurement results (non-mode-coupled)
Low Coherence Interferometry
Time (ps)
Polarimetric
Wavelength (nm)
1300
Fixed analyzer
1400 1500 160 Wavelength (nm)
0
1700
7
Mode-coupled devices:
Review: Polarization-mode coupling
Complex birefringence (collection of simple birefringent elements) Fast and slow eigenaxes are wavelength-dependent
Examples: Long fibers, multiple splices of polarization maintaining fiber, full systems
Typical measurement results (Mode-coupled) Low Coherence InterferometryPolarimetric
Time (ps)
0 .8 0 .7 .6 .5 .4 .3 .2 .1 0 1 4 6 0
1 4 8 0
1
5 0 0 1 5 2 0 1 5 4 0 W a v e le n g th (n m )
1 5 6 0
1 5 8 0
1300
Fixed analyzer
1400 1500 1600 Wavelength (nm)
1700
8
Artifact Selection Criteria: DGD approximates that of your DUT DGD can be predicted by other means Environmentally stable
Single birefringentcrystal
Polarization-maintaining fiber
PMD emulator
Calibration: Non-mode-coupled (measure a device of known DGD)
Predictable DGDτ=ngL ,L=thickness,ng= group birefringence c Beware of waveplate tilt, multiple reflections, and dispersion Maximum DGD limited (0.5 ps or so)
DGD predictable but less certain Beware of temperature coeff. (2-10x > quartz) Large DGD values possible
DGD predictable from geometry Beware of reflections and polarization extinction ratio Variable DGD possible
s p
9
Artifact Selection Criteria:  Mean DGD approximates that of your DUT  DGD(λ) looks typical Environmentally stable
DGD prediction difficult (lenses, alignment, adhesives,) 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
1480
1500
1520 1540 1560 Wavelength (nm) Multiple 35-plate stacks (identical preparation)
0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1
Calibration: Mode-coupled I
Stacked, misaligned crystals
x
x x x x xx Spliced PM fiber
x
x
wavelength shift with temperature
0 1460
Stack of 35 quartz plates
1480
1500
1520
1540
Wavelength (nm)
28 C 16.5 C
1560
1580
Beware:  Instability with fibe r lead reorientation (Non-polarimetric techniques) Disagreement between techniques
Calibration: Mode-coupled II
25 20 15 10 5
30 25 20 15 10 5 0 120 100 80 60 40 20 0
(FA)
(INT)
(Polarimetric)
∆τ (ps)
Simulation: 35 quartz plates, 200 nm measurement spectrum, 100 measurements
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