Transcript Optical Switch Fabrics: What is their value, and When will

Dynamic Spectral Equalizer
Joseph Ford, James Walker, David Neilson, Keith Goossen
References:
Ford, Walker, Goossen & Neilson, European Conference on Optical Communications 1999
Greywall, Busch & Walker, Sensors & Actuators A A72, 1999.
Ford, Walker, Greywall & Goossen, IEEE J. Lightwave Tech. 16, 1998
Goossen, Arney & Walker, IEEE Phot. Tech. Lett. 6, 1994
Dynamic gain equalization
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Equalizer
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Signals start out uniform…
Source power adjusted by fixed line-build-out attenuators
… but power divergence is inevitable
Spectral gain dependence in amplifiers is ~ 1 dB at best
Fixed wavelength add/drop creates divergence
Dynamic add/drop switching creates radical divergence
Gain saturation in amplifiers depletes weaker signals, and
Transmission nonlinearities limit maximum useful laser output power
Solution: Dynamic spectral equalization
Basic: 2 nm resolution over 35 nm passband, 0.5 sec response
(resolves amplifier cascade nonuniformity)
Fancy: 50 GHz resolution (0.2 nm) over 70 nm band, 10 usec response
(resolves wavelength add/drop dynamics)
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The “MARS” resonant MEMS modulator
MARS (Membrane Anti-Reflection Switch) analog optical modulator
l/4 Silicon Nitride “drumhead” suspended over a Silicon substrate
input
reflect
l/4 SiNx
PSG
Vdrive
Voltage Response
measured
Silicon
theory
0 < Vdrive < 30V
3l/4 < gap < l/2
transmit
Drive voltage (V)
Ford, Walker, Greywall & Goossen, IEEE J. Lightwave Tech. 16, 1998
Greywall, Busch & Walker, Sensors & Actuators A A72, 1999.
Goossen, Arney & Walker, IEEE Phot. Tech. Lett. 6, 1994
MARS equalizer device
Mechanically continuous membrane with segmented actuator electrodes
Voltage
Applied
Optical Window
Voltage
Applied
Reflection loss:
2.0 dB @ 0V,
27 dB @ 30V
electrodes
PSG
silicon substrate
Material: 200 nm Low-stress Silicon-rich nitride on 1150 nm PSG spacer
Membrane dimensions: 300 um x 1500 um (8x8 mm chip)
Actuators: 40 chrome-gold electrode pairs on a 32 micron pitch
Ford & Walker, IEEE Phot. Tech. Lett. 10, 1998
Free-space WDM package
I/O Fiber
(to circulator)
Micromechanical
Attenuator Array
Lens and l/4
f = 50mm
Grating in tip/tilt mount
600 lp/mm, 43o blaze angle
Gold-coated epoxy on Zerudur substrate
Electrical I/O
3.7 dB loss, 0.1 dB PDL
(incl. optical circulator)
100 nm spectral range
(5 mm active area)
Custom achromatic lens
(athermal lens & kovar mechanics)
Ford, Walker, Goossen & Neilson, European Conf. On Optical Commun.. 1999
Manual dynamic gain equalization filter
ASE power (dB, relative to input)
0
-10
Initial ASE (gain) spectra
11dB
-20
1dB
-30
Equalized ASE (gain) spectra
-40
-50
1520
1530
1540
1550
1560
1570
Wavelength (nm)
Performance: 6 dB uniform insertion loss, 0.1 dB PDL
< 0.1 ps polarization mode dispersion,
0.5 ps/nm chromatic dispersion
25 dB dynamic range over 40 nm spectrum
Ford & Walker, IEEE Phot. Tech. Lett. 10, 1998; Ford, Walker, Goossen & Neilson, European Conference on Optical Communications 1999
Computer-Controlled Equalizer Prototype
Control Algorithm
Users program power setpoints
Computer estimates drive voltages*
Feedback from OSA refines settings
Optical spectrum analyzer
Rack-mounted PC controller
DGEF & optical circulator
Equalizer response model:
Membrane displacement estimated by adding
Lorentzian-shaped features with crosscoupling;
Optical response computed analytically.
Ford, Walker, Goossen & Neilson, European Conference on Optical Communications 1999
Conventional Erbium fiber amplifier
input power, dBm (schematic)
Input power spectrum
Original “MONET” amplifier
-8
-18
-13
-23dBm/ch
dBm/chxx16
36ch
ch
0
2 gain stages
with DCF port
(7 dB fixed loss)
-10
-20
-30
1st stage
-40
1525
wavelength, nm
1565
Original amplifier design:
12 nm band & fixed input power
< 1 dB output power divergence
Extended operation?
Operating band to 30 nm
Input power range by 15 dB
-> 7 dB loss divergence
2nd stage
Output power spectrum
Automatically-equalized EDFA
input power, dBm (schematic)
Input power spectrum
Auto-equalized amplifier
-18
-13
-23 dBm/ch x 36 ch
OSA
0
-10
PC controller
DGEF
-20
-30
1st stage
1525
2nd stage
tap
-40
wavelength, nm
1565
Original amplifier design:
12 nm band & fixed input power
< 1 dB output power divergence
Extended operation:
operation?
Operating band to 30 nm
Input power range by 15 dB
Using
Add
equalizer
equalizer
atat
DCF
DCF
port
port:
Feedback
<
1 dB divergence
output tap into OSA
> 20 dB input power range
> 30 nm bandwidth
Algorithm convergence
MEMS dynamic gain equalizers now in production…
although not at Lucent or their spinoff Agere!
Note: Similar spectral equalizers except using Liquid Crystal attenuator arrays
available from Corning, JDS Uniphase, OptoGone, Avanex