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 ...

Informations

• Publié par: Choon
• Nombre de lectures: 19
• Langue: English

Extrait

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.Understandlimitationsimposedby measurement conditions 3.Choosemeasurementparameterscorrectly 4. Be aware of measurement uncertainties

Assumption:eremtnssyetmowmeasuyltcerrocskr

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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

S 2 ( ω 2 )

Review: Frequency domain PMD measurements

∆ S

S 1 ( ω 1 ) 

(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 (ω 1 andω 2 ) r d S ial Group ∆τ= dω )DGD(ylaD D e feifntre Polarization-based DGD definition (ω= radian frequency)

Measures DGD(λ)

Jones Matrix Eigenanalysis (JME), Mueller matrix method (MMM), Poincaré sphere analysis (PSA)

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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 Interferometry Polarimetric

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 birefringent crystal

Polarization- maintaining fiber

PMD emulator

Calibration: Non-mode-coupled (measure a device of known DGD)

Predictable DGD ∆  τ  =  ∆  n  g  L  , L=thickness,∆n g = 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 x x 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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