1. 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

2. I … 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 I Dynamic gain equalization I I Signals start out uniform… Source power adjusted by fixed line-build-out attenuators Signals start out uniform… Source power adjusted by fixed line-build-out attenuators I Equalizer I Solution: Dynamic spectral equalization I I 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)

3. The “MARS” resonant MEMS modulator MARS (Membrane Anti-Reflection Switch) analog optical modulator /4 Silicon Nitride “drumhead” suspended over a Silicon substrate 0 < V drive < 30V 3 /4 < gap < /2 input /4 SiN x Silicon PSG reflect transmit V drive 0 < V drive < 30V 3 /4 < gap < /2 input /4 SiN x Silicon PSG reflect transmit V drive Voltage Response theory measured 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

4. 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 Voltage Applied silicon substrate PSG electrodes Optical Window Voltage Applied Ford & Walker, IEEE Phot. Tech. Lett. 10, 1998 Reflection loss: 2.0 dB @ 0V, 27 dB @ 30V Mechanically continuous membrane with segmented actuator electrodes

5. 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 /4 f = 50mm Micromechanical Attenuator Array Grating in tip/tilt mount 600 lp/mm, 43 o blaze angle Gold-coated epoxy on Zerudur substrate

6. Wavelength (nm) ASE power (dB, relative to input) 152015301540155015601570 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:

7. 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.

8. Original “MONET” amplifier 1st stage2nd stage Input power spectrum 1525wavelength, nm 0 -10 -20 -30 -40 input power, dBm (schematic) -13 dBm/ch x 36 ch-18 dBm/ch x 36 ch 1565 -8 dBm/ch x 16 ch 2 gain stages with DCF port (7 dB fixed loss) Original amplifier design: 12 nm band & fixed input power < 1 dB output power divergence 1525wavelength, nm 0 -10 -20 -30 -40 input power, dBm (schematic) -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 1525wavelength, nm 0 -10 -20 -30 -40 input power, dBm (schematic) 1565 -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 input power, dBm (schematic) 1565wavelength, nm -23 dBm/ch x 36 ch Conventional Erbium fiber amplifier

9. Auto-equalized amplifier 1st stage2nd stage DGEF PC controller OSA tap Input power spectrum 1525wavelength, nm 0 -10 -20 -30 -40 input power, dBm (schematic) -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 1525wavelength, nm 0 -10 -20 -30 -40 input power, dBm (schematic) 1565 -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 input power, dBm (schematic) 1565wavelength, nm -23 dBm/ch x 36 ch Automatically-equalized EDFA Algorithm convergence

10. 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