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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
Optical Spectral Processing /All-Order PMD Technology:
Compensation, Sensing, Emulation
A.M. Weiner
Purdue University
http://ece.www.ecn.purdue.edu/~amw
Funding:
PMD Compensation at Ultra-High Bit Ratesor
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 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)
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 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).
ΔτFor broadband inputs,random birefringences
lead to wavelength-
dependent polarization
scrambling and
wavelength- and
polarization-dependent
delays.
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 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
( ) ( ) DGDθ
ω = Ω ω ≈ω − ω
ˆˆout
out
ss
∂= Ω ×
∂ω
ŝ(ω1)ŝ(ω2)
ŝ(ω3)S3
S1
S2Ω(ω2)
θ
Poincaresphere
Poole and Giles, Opt. Lett. 13, 155 (1988)
Differential
group delay
(DGD)
1st Order PMD:
Small distortion –
Small bandwidth limit
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
M. Duelk and P. Winzer, IEEE 802. 3 High Speed Study Group, Nov. 2006
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
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
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
Distorted
input
Polarization
splitter
Polarization
controller
Adjustable
delay
Polarization
combiner
Compensated
output
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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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
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).
0.64PMD B
DGD
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
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)
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
All-Order Optical PMD Compensation
TX Link RXCompensator
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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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
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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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
-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
Spectraldisperser
Spectral
combiner
Broadband input- Ultrashort pulse
- CW plus modulation
- Multiple wavelengths
Processed output
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
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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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
“Pulse Shaping” in WDM: Intensity Control
Manipulation on a wavelength-by-wavelength basisNo 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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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
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 andfew femtosecond pulse compression.
Spectral phase equalizer
( )( )−∂ψ ω
τ ω =∂ω
A.M. Weiner, U.S. patent 6,879,426
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
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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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
460 fs transmission over 50 km SMF
-10 -5 0 5 10 15 20Time (ps)
I n t e n s i t y c r o s s - c o r r e l
a t i o n ( a . u . )
both second- and third-order DC by pulse shaper
without DCby pulse shaper
second-order DC
by pulse shaper
P h a s e (
r a d )
0
20
40
60
80
100
0 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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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
“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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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
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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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
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 bω ω ω ω = +E α β
( ) ( )exp ( ) ˆin E j yω ω ω = ΨE
( ) ( ) ˆin E yω ω =E
(1) (2) (3)
Distorted input(vector field)
Equalize
spectral
phase
Alignoutput
SOPs
State-of-polarizationshaper
Phase shaper
RestoredpulseScalar field
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
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 LCMconfiguration
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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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
State-of-polarization (SOP) Control
• Rotate
ARBITRARYPOLARIZATION STATE
into a
FIXED LINEAR STATE
• In an array in a pulse shaper configuration,many frequency components
can be SOP-rotatedindependently and in parallel
Birefringence axis
of LCM First Layer Birefringence axis
of 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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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
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 givesamplitude 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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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
Pure Phase Control
Liquid crystal layers at 45±
Poincare sphere
• With equal retardances, rotations
by two LC layers are equal and
opposite
• Output SOP = input SOP:
no polarization rotation
(independent of input SOP)
• Phase modulation depends on total
arc length (independent of input
SOP)
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 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 guessto 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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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
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 8Time (ps)
-8 -4 0 4 8Time (ps)
-8 -4 0 4 8Time (ps)
-8 -4 0 4 8Time (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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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
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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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
• 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 tofrequency 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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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
22 nW coupledfundamental 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 FROGPulses measured after SOP correction, before phase correction
H. Miao, et al, OFC 2007
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
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 FROGPulses measured after both SOP and phase correction
H. Miao, et al, OFC 2007
Robust: comparable results in several different experiments
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
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
Isotropicdispersion
compensation
Rotate PSP vector to common direction Frequency-dependentDGD 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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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
Wavelength-Parallel Jones Matrix Correction
( ) je
ψ ω
Chromatic
dispersion ( ) ( )
( ) ( )* * f U
α ω β ω
β ω α ω
⎡ ⎤= ⎢ ⎥−⎣ ⎦
PMD part
All-Order PMD
CompensationCorrecting 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 =( ) ( ) ( )out in E T E ω ω ω =
H. Miao, et, Opt. Lett. 32, 2360 (2007)
l h ll l i S i
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
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
BroadbandSignal
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 (-)
difi d l h ll l i S i
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
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 SOPFLC FLC
(0°, 45°) (45°, 90°)
4 SOPsUf
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)
Jones Matrix Correction
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
Jones Matrix Correction
* *U
α β
β α
⎡ ⎤= ⎢ ⎥−⎣ ⎦
cos sin
sin cos
j j
j j
e eU
e e
φ ψ
ψ φ
θ θ
θ θ − −
⎡ ⎤= ⎢ ⎥
−⎣ ⎦
Jones matrix of a
0°linear retarder
( )
( )
( )
( )3 12 21
3 12 2
exp 0 exp 0cos sin
0 exp 0 expsin cos
j j jU
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 32 4, , and 2 4θ ϕ ψ π θ θ θ ϕ ψ π = + + = − = − −with
Jones matrix
Jones matrix
inverted
4-layer LCM configuration: 0° 45° 0°90°( )
1 0
0 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)
Compensation Experiments
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
Compensation Experiments
Custom 4-layer, 128-pixel liquid crystal modulator array
Pixel spacing: 11.6 GHz
H. Miao, et, Opt. Lett. 32, 2360 (2007)
E i t l R lt (Di t t d SOP S t )
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
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)
Distorted and Restored Pulses
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
Distorted and Restored Pulses
826 fs
828 fs
Intensity cross-correlation measurements
H. Miao, et, Opt. Lett. 32, 2360 (2007)
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
Extension to Parameters Suitable For DWDM
(e.g., 40 Gb/s systems)
Hyperfine Resolution Wavelength Demux
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
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.
8-Channel Hyperfine Demux
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
8 Channel Hyperfine Demux(~700 MHz linewidth, ~3 GHz channel spacing, 50 GHz FSR)
VIPA
Receiving Fiber Array
(output)
Collimator
(input)
Cylindrical LensCylindrical Lenses
Xiao and Weiner, IEEE PTL 17, 372 (2005)
VIPA spectral disperser
(Parts donated by
)
Programmable Hyperfine Resolution VIPA Pulse Shaper
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
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 =
∂ωApply
quadratic
phase
A.M. Weiner, U.S. patent 6,879,426
PMD Compensation with VIPA Pulse Shaper
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
PMD Compensation with VIPA Pulse Shaper
Collimator
Cylindrical
Lens
200 GHzVIPA 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 DGD4-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
Compensation Results
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 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)
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 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
Current Practice: Single-Channel Polarimetry
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
g y
detector
source
adjustablewave-plates
fixed
polarizer
To achieve frequency (wavelength) resolution:
Multiple polarimeters (expensive)
or
Frequency-swept measurements (slow)
Example:
serial configuration
Fast Wavelength-Parallel Polarization Sensor
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
g
FLC controller
and data processing
Broadband
optical source
InGasAs
detector
array
Fast switchingFLC 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)
High Resolution Spectral Polarimeter
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 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
WDMchannel
FLCswitching
λ /4 retarder pair
polarizer
0°
50 GHz
VIPAInGaAs 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)
2D Fast Wavelength Parallel Polarization Sensor
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
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
V I P A d
i r e c t i o n
1520 nm 1552.8 nm
Wang, Xiao, and Weiner, Opt. Express 13, 2005
2D wavelength demux
50 GHz
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
All-Order PMD Emulation (Generation)
Traditional PMD Emulators
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
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.
All-Order Emulation Experimental Setup
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
F o
r S O P
S e n s i n g
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
Miao et al, IEEE PTL, in press.
All-Order Emulation Experimental Results
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
PSP
Simple case: emulation of
two concatenated fibers
DGD
Miao et al, IEEE PTL, in press
All-order example: programmedaccording to computer generated
target with 5 ps mean DGD
targetdata
target
data
Independently programmable multi-channel DGD emulation
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
Broadband source
200 GHz
VIPA
cylindricallens
f=75mmf=500mm
achromaticlensFast scope
12
3 ( – 1 2 d B ) 2-layer
128-elementLCM + mirror
- 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)
SummaryO i l l i li d ll d PMD
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PURDUE UNIVERSITY ULTRAFAST OPTICS & OPTICAL FIBER COMMUNICATIONS LABORATORY
A.M. Weiner (OFC 2008)
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. MiaoM. Akbulut
X. Wang
Li Xu
D.E. LeairdG.-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…