PMD Compensation at Ultra-High Bit Rates or Optical Spectral - - PowerPoint PPT Presentation

PURDUE UNIVERSIT Y UL T RAFAST O PT IC S & O PT IC AL FIBER C O MMUNIC AT IO NS L A BO RAT O RY A.M. We ine r (O FC 2008)

Optical Spectral Processing / All-Order PMD Technology: Compensation, Sensing, Emulation

A.M. Weiner Purdue University amw@ecn.purdue.edu http://ece.www.ecn.purdue.edu/~amw Funding:

PMD Compensation at Ultra-High Bit Rates

• r

PURDUE UNIVERSIT Y UL T RAFAST O PT IC S & O PT IC AL FIBER C O MMUNIC AT IO NS L A BO RAT O RY A.M. We ine r (O FC 2008)

Outline

• Introduction to PMD (focus on all-order PMD)
• Optical spectral processing (pulse shaping etc.)
• Sub-ps pulse all-order PMD compensation experiments
• Extending to DWDM via hyperfine-resolution spectral dispersers
• Spectral polarization sensor (parallel sensing at under 1 ms)
• All-order PMD emulation (generation)

PURDUE UNIVERSIT Y UL T RAFAST O PT IC S & O PT IC AL FIBER C O MMUNIC AT IO NS L A BO RAT O RY A.M. We ine r (O FC 2008)

Polarization Mode Dispersion (PMD)

“Anatomy of a real fiber”

Poole and Nagel, in Optical Fiber Telecommunications IIIA, Academic Press (1997). See also Kogelnik, Jopson, and Nelson, in Optical Fiber Telecommunications IVB, Academic Press (2002).

Δτ For broadband inputs, random birefringences lead to wavelength- dependent polarization scrambling and wavelength- and polarization-dependent delays.

PURDUE UNIVERSIT Y UL T RAFAST O PT IC S & O PT IC AL FIBER C O MMUNIC AT IO NS L A BO RAT O RY A.M. We ine r (O FC 2008)

First Order PMD

Narrowband inputs

• Fiber characterized by two principal states of polarization (PSPs), in general elliptical
• For input light launched along a PSP, output SOP is constant to first order in ω
• Two PSPs have a differential group delay (DGD) – Maxwellian distribution
• Valid only for small DGD (compared to pulse width)

2 2 2

( ) ( ) / ( ) PSP ω = Ω ω Ω ω

• 2

2 3 1

( ) ( ) DGD θ ω = Ω ω ≈ ω − ω

• ˆ

ˆ

• ut
• ut

s s ∂ = Ω × ∂ω

• ŝ(ω1)

ŝ(ω2) ŝ(ω3) S3 S1 S2 Ω(ω2)

θ

Poincare sphere Poole and Giles, Opt. Lett. 13, 155 (1988)

Differential group delay (DGD)

1st Order PMD: Small distortion – Small bandwidth limit

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• M. Duelk and P. Winzer, IEEE 802. 3 High Speed Study Group, Nov. 2006

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• M. Duelk and P. Winzer, IEEE 802.3

High Speed Study Group, Nov. 2006

• Appropriate modulation format and FEC suggests impressive inroads against PMD
• For very speed systems or higher PMD fibers, PMD issues likely to remain important

PURDUE UNIVERSIT Y UL T RAFAST O PT IC S & O PT IC AL FIBER C O MMUNIC AT IO NS L A BO RAT O RY A.M. We ine r (O FC 2008)

Distorted input Polarization splitter Polarization controller Adjustable delay Polarization combiner Compensated

• utput

PMD Compensation

First-order optical compensator

• Applies only to small DGD
• less than a few tenths of pulse duration for RZ
• less than a few tenths of bit period for NRZ
• Already challenging in view of:
• time-dependent, random PMD variations
• requirements for low outage probability (e.g., <10-5)

Split into PSPs, delay, and recombine! (or similar)

• Electrical compensation
• Impairment resistant modulation format
• Optical compensation (bit-rate and format independent)

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Limitations to First Order PMD Approximation

The autocorrelation bandwidth of the PSP vectors is inversely proportional to the mean differential group delay.

Foschini, Jopson, Nelson, and Kogelnik, Journal of Lightwave Technology 17, 1560 (1999) Shtaif, Mecozzi, and Nagel, IEEE Phot. Tech. Lett. 12, 53 (2000).

0.64

PMD

B DGD

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All-Order PMD Effects

800 fs pulse distorted by PMD emulator with mean DGD ~ 5.5 ps

• Complicated frequency-dependent polarization scrambling
• Frequency- and polarization-dependent delays
• Will occur whenever the distortion approaches the pulse width or bit period
• H. Miao, et, Opt. Lett. 32, 2360 (2007)

PURDUE UNIVERSIT Y UL T RAFAST O PT IC S & O PT IC AL FIBER C O MMUNIC AT IO NS L A BO RAT O RY A.M. We ine r (O FC 2008)

All-Order Optical PMD Compensation

TX Link RX Compensator Controller Sensor

Complex frequency-dependent vector field All-order PMD (frequency-dependent complex transfer matrix)

• Spectral polarimetry?
• Frequency-dependent

delay or phase?

• Complexity?
• Requirements on TX?
• Generate frequency-dependent

inverse matrix?

• Operate on frequency-dependent

vector field?

• Compensator synthesis in the time-domain (digital filter approach)
• Compensator synthesis in the optical frequency domain

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Digital filter (time-domain) approach

All-Order Optical PMD Compensation

Cascaded all-pass filter elements – e.g., cascaded first-order compensator elements

C.K. Madsen, Opt. Lett. 25, 878 (2000)

Examples

• Cascaded polarization mode coupling in birefringent LiNbO3 – R. Noe, et al, Elec. Lett. 35, 652 (1999)

[Univ. Paderborn]

• Cascaded ring resonators in silica PLCs - C.K. Madsen, et al, JLT 22, 1041 (2004) [Lucent]

Challenges

• Large number of stages for all-order PMD
• Complexity of control problem grows with number of stages
• Compensation of various orders of PMD is coupled and must be considered simultaneously

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• Pulse shaping
• Dynamic spectral equalizers
• Dynamic wavelength processing

Parallel, Optical Spectral Processing

Spatial light modulator Control of phase, intensity, polarization … Frequency-by-frequency, independently, in parallel Spectral disperser Spectral combiner Broadband input

• Ultrashort pulse
• CW plus modulation
• Multiple wavelengths

Processed output

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Femtosecond Pulse Shaping

• Diverse applications: fiber communications, coherent quantum control,

few femtosecond pulse compression, nonlinear optical microscopy, RF photonics ...

Examples: Phase encoded O-CDMA waveform; square pulse

Fourier synthesis via parallel spatial/spectral modulation

A.M. Weiner, Rev. Sci. Instr. 71, 1929 (2000)

Weiner et al, Opt. Lett. 15, 326 (1990); IEEE JQE 28, 908 (1992)

Liquid crystal modulator (LCM) arrays:

• Originally phase-only, then independent

phase and intensity, now polarization

• Down to ~msec response, hundreds of pixels

Basic 4-f optical system, plus spectral masking:

• Long pulses (Nd:YAG), fixed mask:
• C. Froehly et al, Progress in Optics 20, 65 (1983)
• 100 fs pulses, fixed mask:

Weiner, Heritage, and Kirschner, JOSA B 5, 1563 (1988)

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“Pulse Shaping” in WDM: Intensity Control

Manipulation on a wavelength-by-wavelength basis No concern for phase or for coherence between channels

Ford et al, J. Lightwave Tech. 17, 904 (1999) [Lucent] Ford et al, IEEE JSTQE 10, 579 (2004) [Lucent]

Wavelength selective add-drop multiplexer (and wavelength selective switches) Spectral gain equalizer

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Programmable Fiber Dispersion Compensation Using a Pulse Shaper: Subpicosecond Pulses

• Coarse dispersion compensation using matched lengths of SMF and DCF
• Fine-tuning and higher-order dispersion compensation using a pulse shaper as a

programmable spectral phase equalizer

• Similar ideas apply to DWDM tunable dispersion compensation and

few femtosecond pulse compression.

Spectral phase equalizer

( ) ( )

−∂ψ ω τ ω = ∂ω

A.M. Weiner, U.S. patent 6,879,426

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Higher-Order Phase Equalization Using LCM

Input and output pulses from 3-km SMF-DCF-DSF link

Chang, Sardesai, and Weiner,

• Opt. Lett. 23, 283 (1998)

Input pulse Output pulse (with quadratic & cubic correction) Output pulse (without phase correction)

already compressed several hundred times

Applied phase

• No remaining distortion!

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460 fs transmission over 50 km SMF

• 10
• 5

5 10 15 20 Time (ps) Intensity cross-correlation (a.u.)

both second- and third-

• rder DC by pulse shaper

without DC by pulse shaper second-order DC by pulse shaper Phase (rad) 20 40 60 80 100 32 64 96 128 Pixel #

2π

π

(A) (B)

Commercial DCF module (as is) with spectral phase equalizer

• ~ 5 ns after SMF
• 13.9 ps after DCF
• 470 fs after quadratic/cubic phase equalization
• Z. Jiang, Leaird, and Weiner, Opt. Lett. 30, 1449 (2005)

Essentially distortion-free!

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“Pulse Shaping” in WDM: Dispersion Compensation Research

AWG pulse shaper and phase mask

Takenouchi, Goh and Ishii, OFC 2001 (NTT)

VIPA pulse shaper and curved mirror

Shirasaki and Cao, OFC 2001 (Fujitsu/Avanex) Sano et al, OFC 2003 (Sumitomo)

• Either colorless dispersion compensation or independent fine-tuning of different channels

AWG pulse shaper and deformable mirror

Neilson et al, JLT 22, 101 (2004) [Lucent]

Grating pulse shaper and MEMS deformable mirror array

( ) ( )

−∂ψ ω τ ω = ∂ω

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Frequency-Domain All-Order PMD Compensation (Principles and sub-ps pulse experiments)

A.M. Weiner, U.S. Patent application 20020060760 (May 23, 2002)

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An All-Order Compensation Scheme

(1) Distorted pulse: (2) Sense and correct full spectrally dependent state of polarization (3) Sense and compensate full spectral phase (generalized chromatic dispersion)

{ }

ˆ ( ) ( ) ( ) ˆ ( )

PMD

in

E a b ω ω ω ω = + E α β

{ }

( ) ( )exp ( ) ˆ

in

E j y ω ω ω = Ψ E ( ) ( ) ˆ

in

E y ω ω = E (1) (2) (3)

Distorted input

(vector field)

Equalize spectral phase Align

• utput

SOPs

State-of-polarization shaper Phase shaper Restored pulse

Scalar field

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All-Order PMD-Compensator Implementation

• Concatenated polarization and phase pulse shapers
• Wavelength-parallel polarimeter for control of polarization pulse shaper
• Ultrashort pulse measurement approach for control of phase shaper

(1542-1556nm) (~576 fs pulse width) (16-piece PM fiber) (7.6 dB insertion loss) (4.5 dB insertion loss) (Cross correlation with 72 fs reference pulse; or FROG)

New LCM configuration New sensor

• M. Akbulut, et al, Opt. Lett. 29, 1129 (2004); Opt. Lett. 30, 2691 (2005); OFC 2005 (post-deadline); JLT 24, 251 (2006)

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State-of-polarization (SOP) Control

• Rotate

ARBITRARY POLARIZATION STATE into a FIXED LINEAR STATE

• In an array in a pulse shaper

configuration, many frequency components can be SOP-rotated independently and in parallel

Birefringence axis

• f LCM First Layer

Birefringence axis

• f LCM Second Layer

LCM Second Layer Operation LCM First Layer Operation SOP for a single wavelength (OR a single LCM pixel) RHCP

• M. Akbulut, et al, Opt. Lett. 29, 1129 (2004)

Two liquid crystal layers, aligned at 90°/45°

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Phase and Partial Polarization Control

• Two LC layers successively rotate

SOP about 45o point

• Polarization rotation depends on arc

length (retardance) difference

• together with a polarizer, this gives

amplitude control (as in a spectral gain equalizer)

• Phase modulation depends on total

arc length (total retardance) Poincare sphere

Two liquid crystal layers, aligned at ±45°

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Pure Phase Control

Liquid crystal layers at 45

±

• Poincare sphere
• With equal retardances, rotations

by two LC layers are equal and

• pposite
• Output SOP = input SOP:

no polarization rotation (independent of input SOP)

• Phase modulation depends on total

arc length (independent of input SOP)

PURDUE UNIVERSIT Y UL T RAFAST O PT IC S & O PT IC AL FIBER C O MMUNIC AT IO NS L A BO RAT O RY A.M. We ine r (O FC 2008)

• Various ultrafast measurement techniques available
• Here we use the Gerchberg-Saxton algorithm
• Uses I(t), measured via cross-correlation, and power spectrum

Spectral Phase Retrieval: 1st method

( )

( )

j

I e β ω ω

( )

( )

j t

I t e α

( )

( )

j t

E t e α

( )

( )

j

E e β ω ω

Use initial guess to start algorithm

FFT -1 FFT

Apply intensity data Apply power spectrum

Typically 70-250 iterations

Apply phase to shaper Measure new intensity profile Improved pulse (Iterated G-S algorithm)

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600 fs input pulse through PMD emulator (16 section PM fiber, mean DGD ~1.3 ps)

PMD Distorted SOP Spectrum Corrected SOP Spectrum

• 8 -4 0 4 8

Time (ps)

• 8 -4 0 4 8

Time (ps)

• 8 -4 0 4 8

Time (ps)

• 8 -4 0 4 8

Time (ps)

Input Pulse (575.7 fs) PMD Distorted Pulse After SOP correction Recovered Pulse (630.8 fs)

All-Order Compensation Experiment (1)

• M. Akbulut, et al, Opt. Lett. 30, 2691 (2005); OFC 2005 (post-deadline); JLT 24, 251 ( 2006)

Frequency-dependent polarization correction adds frequency-dependent phase

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800 fs input pulse through PMD emulator (16 section PM fiber, mean DGD ~1.3 ps)

PMD Distorted SOP Spectrum Corrected SOP Spectrum

• 8 -4 0 4 8

Time (ps)

• 8 -4 0 4 8

Time (ps)

• 8 -4 0 4 8

Time (ps)

• 8 -4 0 4 8

Time (ps)

Input Pulse (791.8 fs) PMD Distorted Pulse After SOP correction Recovered Pulse (696.3 fs)

All-Order Compensation Experiment (2)

• M. Akbulut, et al, Opt. Lett. 30, 2691 (2005); OFC 2005 (post-deadline); JLT 24, 251 ( 2006)

Frequency-dependent polarization correction adds frequency-dependent phase

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• Second-Harmonic Generation (SHG) Frequency-Resolved Optical Gating (FROG)
• Two-dimensional data set
• Iterative retrieval (much more robust than G-S)
• Innovations: extremely high sensitivity using A-PPLN waveguides; polarization

insensitive measurement operation

• R. Trebino, “Frequency resolved optical gating”, KAP, 2000

2-D Spectrogram with respect to frequency and delay

Spectral Phase Retrieval: 2nd method

• H. Miao, et al, OFC 2007; Opt. Lett. 32, 424 ( 2007); Opt. Lett. 32, 874 ( 2007)

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22 nW coupled fundamental power, FROG error=0.007 600 fs pulse through PMD emulator with mean DGD ~1.4 ps) Measured pulse after SOP correction, but before phase correction.

Phase Sensing via FROG

Pulses measured after SOP correction, before phase correction

• H. Miao, et al, OFC 2007

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22 nW coupled fundamental power, FROG error=0.003 Measured pulse after SOP and phase correction 642 fs 600 fs pulse through PMD emulator with mean DGD ~1.4 ps)

Phase Sensing via FROG

Pulses measured after both SOP and phase correction

• H. Miao, et al, OFC 2007

Robust: comparable results in several different experiments

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All-Frequency PMD Compensator in Feedforward Scheme

• P. B. Phua, Hermann A. Haus, and E. P. Ippen

Phua, Haus, and Ippen, JLT 22, 1280 (2004)

Frequency- dependent PSP vector via Poincare arc method with polarization switching Isotropic dispersion compensation Rotate PSP vector to common direction Frequency-dependent DGD compensation Depiction of PSP vectors

• Proposal and analysis, with some suggestions for implementation
• Sensing via launch polarization switching; differentiation of spectral polarimetry data

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Wavelength-Parallel Jones Matrix Correction

( )

j

e

ψ ω

Chromatic dispersion ( ) ( ) ( ) ( )

* * f

U α ω β ω β ω α ω ⎡ ⎤ = ⎢ ⎥ − ⎣ ⎦

PMD part All-Order PMD Compensation Correcting Uf to a frequency-independent matrix

• Wavelength-parallel Jones matrix sensing
• Sensing via launch polarization switching and spectral polarimetry data

(no differentiation of polarimetry data)

• Wavelength-by-wavelength Jones matrix correction

Jones space: Full Jones matrix

( )

( )

( )

j f

T e U

ψ ω

ω ω =

( ) ( ) ( )

• ut

in

E T E ω ω ω =

• H. Miao, et, Opt. Lett. 32, 2360 (2007)

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Wavelength-Parallel Jones Matrix Sensing

Fast wavelength-parallel polarimeter for SOP sensing, ms responding time

• S. X. Wang, et al, JLT., vol. 24, 3982-3991, 2006

Uf Broadband Signal 0° Linear Input SOP Spectral Polarimeter Uf RHC Input SOP Spectral Polarimeter Broadband Signal

• H. Miao, et al. CLEO 2007
• Determines Jones matrix, not PSP vector
• Polarimetry data processed via standard matrix inversion (no differentiation) (+)
• Less susceptible to measurement noise, reduced demands on spectral resolution
• Switching between known polarizations, as in standard Jones matrix methods (-)

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Modified Wavelength-Parallel Jones Matrix Sensing

Select two output SOP spectra with angular separation closest to 90°(60°~120°) Calculate cross product of selected SOP spectra Associate one selected SOP spectrum, and cross-product spectrum, with 0°and 45°linear input SOP, respectively Matrix inversion gives U(ω)=Uf(ω)Uconst , where Uconst is an unimportant frequency- independent rotation matrix Compensating Uf(ω) constitutes all-order PMD compensation (plus simple frequency-independent polarization rotation)

Broadband Signal with frequency independent SOP

FLC FLC (0°, 45°) (45°, 90°) 4 SOPs

Uf Broadband Polarimeter

4 Output SOP Spectra

f const

U U U =

• H. Miao, et, Opt. Lett. 32, 2360 (2007)

Works for arbitrary input polarization

Processing algorithm

Ferroelectric liquid crystals (switchable wave plates)

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Jones Matrix Correction

* *

U α β β α ⎡ ⎤ = ⎢ ⎥ − ⎣ ⎦ cos sin sin cos

j j j j

e e U e e

φ ψ ψ φ

θ θ θ θ

− −

⎡ ⎤ = ⎢ ⎥ − ⎣ ⎦

Jones matrix of a 0°linear retarder

( ) ( ) ( ) ( )

3 1 2 2 1 3 1 2 2

exp exp cos sin exp exp sin cos j j j U j j j θ θ θ θ θ θ θ θ

−

− − ⎡ ⎤ ⎡ ⎤ − ⎡ ⎤ = ⎢ ⎥ ⎢ ⎥ ⎢ ⎥ − ⎣ ⎦ ⎣ ⎦ ⎣ ⎦

Jones matrix of a 0°linear retarder Jones matrix of a 45°linear retarder

Each frequency sensed and compensated independently ( ) ( )

1 2 3

2 4, , and 2 4 θ ϕ ψ π θ θ θ ϕ ψ π = + + = − = − −

with Jones matrix Jones matrix inverted 4-layer LCM configuration: 0° 45° 0°90°

( )

1 exp ( )

LCM

U j V θ ⎡ ⎤ = ⎢ ⎥ ⎣ ⎦

Compare matrix of a liquid crystal retarder (difference leads to extra isotropic phase; taken out with layers 3&4)

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Compensation Experiments

Custom 4-layer, 128-pixel liquid crystal modulator array Pixel spacing: 11.6 GHz

• H. Miao, et, Opt. Lett. 32, 2360 (2007)

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Experimental Results (Distorted SOP Spectra)

800 fs pulse distorted by PMD emulator with mean DGD ~ 5.5 ps

• H. Miao, et, Opt. Lett. 32, 2360 (2007)

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Distorted and Restored Pulses

826 fs 828 fs

Intensity cross-correlation measurements

• H. Miao, et, Opt. Lett. 32, 2360 (2007)

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Extension to Parameters Suitable For DWDM (e.g., 40 Gb/s systems)

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Hyperfine Resolution Wavelength Demux

Virtually Imaged Phased Array (VIPA)

λ1 λ2 λ3

VIPA Fiber Collimator Cylindrical Lens Virtual Source Array

• Introduced by Shirasaki, Opt. Lett. (1996)
• Offers high spectral resolution, as in a Fabry-Perot
• But acts as spectral disperer, with large spectral dispersion arising from multiple beam

interference in “side-entrance” etalon geometry

Why?

R r

k x τ θ ω ∂ ∂ ≈ ∂ ∂

Bor et al, Opt. Commun. 59, 229 (1985)

Angular dispersion is fundamentally linked to delay gradient across a beam.

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8-Channel Hyperfine Demux

(~700 MHz linewidth, ~3 GHz channel spacing, 50 GHz FSR)

VIPA Receiving Fiber Array (output) Collimator (input) Cylindrical Lens Cylindrical Lenses

Xiao and Weiner, IEEE PTL 17, 372 (2005)

VIPA spectral disperser

(Parts donated by )

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Programmable Hyperfine Resolution VIPA Pulse Shaper

Tunable Dispersion Compensation at 10 Gb/s over 240 km SMF

CYL

SLM + Mirror VIPA

λn λ1

CYL

Circulator Collimator B2B

G.-H. Lee, S. Xiao, and A.M. Weiner, OFC 2006 (paper OTHE5); IEEE PTL 18, 1819 (2006)

SMF 240km uncompensated Compensated (shaper only, no DCF) Uncompensated @ 20 km, 40 km

( ) ( )

−∂ψ ω τ ω = ∂ω

Apply quadratic phase

A.M. Weiner, U.S. patent 6,879,426

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PMD Compensation with VIPA Pulse Shaper

Collimator Cylindrical Lens 200 GHz VIPA Lens Flipper Mirror LCM Polarimeter PC Photo Detector & Sampling Scope FLC PMD Optical Pulses FLC

15 ps 1550.7 nm 50 MHz ~42 ps mean DGD 4-layer LCM 1.6 GHz/pixel

13.8 dB insertion loss

Jones matrix sensing and compensation, as before, but scaled to finer spectral resolution and larger time aperture

• H. Miao, et al, OFC 2008 (OThG2)

Pulse widths compatible with 40 Gb/s systems

PURDUE UNIVERSIT Y UL T RAFAST O PT IC S & O PT IC AL FIBER C O MMUNIC AT IO NS L A BO RAT O RY A.M. We ine r (O FC 2008)

Compensation Results

Initial pulse, FLC stable PMD distorted pulse FLC switching at 20 Hz PMD distorted pulse FLC switching at 2 kHz Restored pulse FLC switching at 2 kHz

Continues to work while input polarization is switching (enables continuous, real-time sensing)

• H. Miao, et al,

OFC 2008 (OThG2)

PURDUE UNIVERSIT Y UL T RAFAST O PT IC S & O PT IC AL FIBER C O MMUNIC AT IO NS L A BO RAT O RY A.M. We ine r (O FC 2008)

Wavelength-Parallel Polarimetry

Requirement to sense frequency-dependent polarization data in milliseconds!

A.M. Weiner and X. Wang, U.S. patent 7,116,419

PURDUE UNIVERSIT Y UL T RAFAST O PT IC S & O PT IC AL FIBER C O MMUNIC AT IO NS L A BO RAT O RY A.M. We ine r (O FC 2008)

Current Practice: Single-Channel Polarimetry

detector source adjustable wave-plates fixed polarizer To achieve frequency (wavelength) resolution: Multiple polarimeters (expensive)

• r

Frequency-swept measurements (slow) Example: serial configuration

PURDUE UNIVERSIT Y UL T RAFAST O PT IC S & O PT IC AL FIBER C O MMUNIC AT IO NS L A BO RAT O RY A.M. We ine r (O FC 2008)

Fast Wavelength-Parallel Polarization Sensor

FLC controller and data processing Broadband

• ptical source

InGasAs detector array Fast switching FLC retarders Polarizer (fixed) Spectral disperser (grating/lens) State 1 State 2 State 1 State 2

Configured for:

• 256 channels
• 0.4 nm (50 GHz) spacing
• < 3° polarization error
• < 1 ms read-out time

Wang et al, Opt. Lett. 29, 923 (2004); JLT 24, 3982 (2006)

PURDUE UNIVERSIT Y UL T RAFAST O PT IC S & O PT IC AL FIBER C O MMUNIC AT IO NS L A BO RAT O RY A.M. We ine r (O FC 2008)

High Resolution Spectral Polarimeter

• ~1GHz / pixel spacing
• ~1GHz 3dB resolution
• <1 ms read-out time
• < 3° polarization error

SOP string spectral SOP points

10 GHz WDM channel FLC switching λ/4 retarder pair polarizer 0° 50 GHz VIPA InGaAs line- scan camera lens

Live 10 Gb/s traffic in AT&T central office Laboratory tests showing tight correlation between SOP string length and PMD- induced power penalty

Now able to resolve polarization variations within 10 Gb/s channel

Wang, Weiner, Boroditsky and Brodsky, IEEE PTL 18, 1753 (2006); Wang, Weiner, Foo, Bownass, Moyer, O’Sullivan, Birk, and Borodistsky, JLT 24, 4120 (2006)

PURDUE UNIVERSIT Y UL T RAFAST O PT IC S & O PT IC AL FIBER C O MMUNIC AT IO NS L A BO RAT O RY A.M. We ine r (O FC 2008)

2D Fast Wavelength Parallel Polarization Sensor

Application to PMD sensing and compensation – Multiple λ’s in single instrument!

High resolution 2D configuration:

• 32.8 nm span
• 1500 channels
• 2.8 GHz channel spacing (<20 dB crosstalk)
• 5 ms read-out time (potential)

Grating dispersion direction VIPA direction

1520 nm 1552.8 nm Wang, Xiao, and Weiner, Opt. Express 13, 2005

2D wavelength demux

50 GHz

PURDUE UNIVERSIT Y UL T RAFAST O PT IC S & O PT IC AL FIBER C O MMUNIC AT IO NS L A BO RAT O RY A.M. We ine r (O FC 2008)

All-Order PMD Emulation (Generation)

PURDUE UNIVERSIT Y UL T RAFAST O PT IC S & O PT IC AL FIBER C O MMUNIC AT IO NS L A BO RAT O RY A.M. We ine r (O FC 2008)

Traditional PMD Emulators

• L. Yan, et. al., JLT, vol. 24, 3992-4005, 2006

Spectral Processor “PMD pulse shaper”

A new approach

Wang et al, IEEE PTL 19, 1203 (2007); Opt. Express 15, 2127 (2007); Miao et al, IEEE PTL, in press.

PURDUE UNIVERSIT Y UL T RAFAST O PT IC S & O PT IC AL FIBER C O MMUNIC AT IO NS L A BO RAT O RY A.M. We ine r (O FC 2008)

For SOP Sensing Generate 0°linear and RHC input SOP for PMD sensing Müller Matrix Method (MMM) is used for PMD characterization 4-layer LCM programmed according to target PMD (Jones matrix) profile

All-Order Emulation Experimental Setup

Miao et al, IEEE PTL, in press.

PURDUE UNIVERSIT Y UL T RAFAST O PT IC S & O PT IC AL FIBER C O MMUNIC AT IO NS L A BO RAT O RY A.M. We ine r (O FC 2008)

PSP

All-Order Emulation Experimental Results

Simple case: emulation of two concatenated fibers DGD

Miao et al, IEEE PTL, in press

All-order example: programmed according to computer generated target with 5 ps mean DGD target data target data

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Broadband source 200 GHz VIPA

cylindrical lens f=75mm f=500mm achromatic lens

Fast scope

1 2 3 (–12dB) 2-layer 128-element LCM + mirror

Independently programmable multi-channel DGD emulation

• Hyperfine resolution VIPA shaper
• Accommodates 4 WDM channels at 50 GHz spacing
• High-order DGD with fixed PSP (this example)

Frequency dependent DGD profiles CH1 CH2 CH3 CH4

Wang et al, IEEE PTL 19, 1203 (2007); Opt. Express 15, 2127 (2007)

PURDUE UNIVERSIT Y UL T RAFAST O PT IC S & O PT IC AL FIBER C O MMUNIC AT IO NS L A BO RAT O RY A.M. We ine r (O FC 2008)

Summary

Optical spectral processing applied to all-order PMD

• First reported all-order PMD compensation experiment (sub-ps pulses)
• Wavelength-parallel polarization sensor (parallel sensing at under 1 ms)
• All-order PMD generation
• Extension towards DWDM compatible implementations
• Future challenges, questions, opportunities
• Systems tests
• Endless all-order compensation
• Elucidation of compensation limits, outage probabilities
• 2D spectral disperser geometry with potential for compensation/

sensing/emulation of multiple DWDM channels within a single box

• H. Miao
• M. Akbulut
• X. Wang

Li Xu D.E. Leaird G.-H. Lee

• S. Xiao
• Z. Jiang

Purdue

• P. Miller and L. Mirkin (CRI)
• M. Boroditsky and M. Brodsky (AT&T)

C .Lin (Avanex)

• M. Fejer (Stanford)

Thanks to…