Dynamic Spectral EqualizerJoseph Ford, James Walker, David Neilson, Keith Goossen

References: Ford, Walker, Goossen & Neilson, European Conference on Optical Communications 1999Greywall, Busch & Walker, Sensors & Actuators A A72, 1999.

Ford, Walker, Greywall & Goossen, IEEE J. Lightwave Tech. 16, 1998Goossen, Arney & Walker, IEEE Phot. Tech. Lett. 6, 1994

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… 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

… 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

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Dynamic gain equalization

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Signals start out uniform… Source power adjusted by fixed line-build-out attenuatorsSignals start out uniform… Source power adjusted by fixed line-build-out attenuators

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Equalizer

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Solution: Dynamic spectral equalizationSolution: Dynamic spectral equalization

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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)

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)

The “MARS” resonant MEMS modulatorMARS (Membrane Anti-Reflection Switch) analog optical modulator /4 Silicon Nitride “drumhead” suspended over a Silicon substrate

0 < Vdrive < 30V3/4 < gap < /2

input

/4 SiNx

Silicon

PSG

reflect

transmit

Vdrive

0 < Vdrive < 30V3/4 < gap < /2

input

/4 SiNx

Silicon

PSG

reflect

transmit

VdriveVoltage Response

theory

measured

Drive voltage (V)

Ford, Walker, Greywall & Goossen, IEEE J. Lightwave Tech. 16, 1998Greywall, Busch & Walker, Sensors & Actuators A A72, 1999.Goossen, Arney & Walker, IEEE Phot. Tech. Lett. 6, 1994

MARS equalizer device

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

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

VoltageApplied

silicon substrate

PSG

electrodes

Optical Window

VoltageApplied

Ford & Walker, IEEE Phot. Tech. Lett. 10, 1998

Reflection loss: 2.0 dB @ 0V, 27 dB @ 30V

Mechanically continuous membrane with segmented actuator electrodes

Free-space WDM package

Ford, Walker, Goossen & Neilson, European Conf. On Optical Commun.. 1999

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)

I/O Fiber(to circulator)

Electrical I/O

Lens and /4f = 50mm

MicromechanicalAttenuator Array

Grating in tip/tilt mount600 lp/mm, 43o blaze angle

Gold-coated epoxy on Zerudur substrate

Wavelength (nm)

AS

E p

ow

er (

dB

, rel

ativ

e to

inp

ut)

1520 1530 1540 1550 1560 1570

0

-10

-20

-30

-40

-50

Initial ASE (gain) spectra

Equalized ASE (gain) spectra

Manual dynamic gain equalization filter

Ford & Walker, IEEE Phot. Tech. Lett. 10, 1998; Ford, Walker, Goossen & Neilson, European Conference on Optical Communications 1999

1dB

11dB

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

Performance:

Computer-Controlled Equalizer Prototype

Control Algorithm Users program power setpoints Computer estimates drive voltages* Feedback from OSA refines settings

Ford, Walker, Goossen & Neilson, European Conference on Optical Communications 1999

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.

Original “MONET” amplifier

1st stage 2nd stage

Input power spectrum

1525 wavelength, nm

0

-10

-20

-30

-40

inp

ut

po

wer

, dB

m (

sch

emat

ic)

-13 dBm/ch x 36 ch-18 dBm/ch x 36 ch

1565

-8 dBm/ch x 16 ch

2 gain stageswith DCF port

(7 dB fixed loss)

Original amplifier design: 12 nm band & fixed input power < 1 dB output power divergence

1525 wavelength, nm

0

-10

-20

-30

-40

inp

ut

po

wer

, dB

m (

sch

emat

ic)

-13 dBm/ch x 36 ch-18 dBm/ch x 36 ch

1565

-13 dBm/ch x 36 ch

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

Output power spectrum

1525 wavelength, nm

0

-10

-20

-30

-40

inp

ut

po

wer

, dB

m (

sch

emat

ic)

1565

-18 dBm/ch x 36 ch-18 dBm/ch x 36 ch

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

1525

0

-10

-20

-30

-40

inp

ut

po

wer

, dB

m (

sch

emat

ic)

1565wavelength, nm

-23 dBm/ch x 36 ch

Conventional Erbium fiber amplifier

Auto-equalized amplifier

1st stage 2nd stage

DGEF

PC controller

OSA

tap

Input power spectrum

1525 wavelength, nm

0

-10

-20

-30

-40

inp

ut

po

wer

, dB

m (

sch

emat

ic)

-13 dBm/ch x 36 ch-18 dBm/ch x 36 ch

1565

-13 dBm/ch x 36 ch

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

Add equalizer at DCF port Feedback output tap into OSA

1525 wavelength, nm

0

-10

-20

-30

-40

inp

ut

po

wer

, dB

m (

sch

emat

ic)

1565

-18 dBm/ch x 36 ch-18 dBm/ch x 36 ch

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

Using equalizer at DCF port: < 1 dB divergence > 20 dB input power range > 30 nm bandwidth

1525

0

-10

-20

-30

-40

inp

ut

po

wer

, dB

m (

sch

emat

ic)

1565wavelength, nm

-23 dBm/ch x 36 ch

Automatically-equalized EDFA

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 arraysavailable from Corning, JDS Uniphase, OptoGone, Avanex