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Dynamic Dispersion Compensator. Christi Madsen, James Walker, Joseph Ford, Keith Goossen, David Neilson, Gadi Lenz. References: "Micromechanical fiber-optic attenuator with 3 microsecond response"  

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Slide1 l.jpg

Dynamic Dispersion Compensator

Christi Madsen, James Walker, Joseph Ford, Keith Goossen, David Neilson, Gadi Lenz

References:

"Micromechanical fiber-optic attenuator with 3 microsecond response"  

J. Ford, J. Walker, D. Greywall and K. Goossen, IEEE J.of Lightwave Tech. 16(9), 1663-1670, September 1998

"A tunable dispersion compensating MEMS all-pass filter"   

Madsen, Walker, Ford. Goossen, Nielson, Lenz, IEEE Photonics Tech. Lett. 12(6), pp. 651-653, June 2000.


Chromatic dispersion in long distance telecom l.jpg

Fiber core index depends (slightly) on l

Any modulated signal has nonzero linewidth

Chromatic dispersion is the result:

Spread in arrival time after signal transmission

Fiber core index depends (slightly) on l

Any modulated signal has nonzero linewidth

Chromatic dispersion is the result:

Spread in arrival time after signal transmission

100 km

1 km

500 km

1500 km

Fiber spans are “dispersion compensated”

But residual dispersion at 3000 km D = 1050 ps/nm

V. Srikant (Corning) OFC 2001

DCF

DCF

DCF

DCF

DCF

Is that OK? Depends on data rate B and length L:

(relation for 1 dB power penalty; Tigye Li, Proc. IEEE, 1993)

B2DL ~ 105 ps/nm (Gb/s2)

MARGINAL

Cumulative dispersion budget:

1000 ps/nm @ 10 Gb/s

63 ps/nm @ 40 Gb/s

CRITICAL

Chromatic dispersion in long-distance telecom


Dynamic chromatic dispersion compensation l.jpg

Equalizer

Dispersion

Compensator

I

BER feedback

Uncompensated

Compensated

Dynamic chromatic dispersion compensation


Phase only all pass filter l.jpg

Gires-Tournois Interferometer

Periodic spectral phase response

L / 2

Round Trip Delay

Free Spectral Range

Phase-only “all-pass” filter

  • For a lossless filter, magnitude response = 1 (allpass!)

  • Periodic Gaussian dispersion feature (DCF requires linear chirp)

  • Approximately linear dispersion over a limited bandwidth

Madsen, Walker, Ford, Goossen & Lenz, ECOC 1999; see also recent IEEE LEOS article


Multi stage filter dispersion l.jpg

1

2

3

4

Increases passband width and total dispersion

Ripple = dev. from ideal linear response

Multi-stage Filter Dispersion

Madsen, Walker, Ford, Goossen & Lenz, ECOC 1999


The mars resonant mems modulator l.jpg

Voltage Response

measured

theory

input

input

reflect

reflect

Vdrive

l/4 SiNx

l/4 SiNx

PSG

PSG

Drive voltage (V)

Silicon

Silicon

transmit

transmit

0 < Vdrive < 30V

3l/4 < gap < l/2

0 < Vdrive < 30V

3l/4 < gap < l/2

Vdrive

The “MARS” resonant MEMS modulator

MARS (Membrane Anti-Reflection Switch) analog optical modulator

l/4 Silicon Nitride “drumhead” suspended over a Silicon substrate

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 all pass filter l.jpg

£

£

0

R

70%

L/2

2

=

r

R

100%Reflector

(dielectric enhanced gold mirror)

Tunable

Partial

Reflector

V

Substrate

MARS All-Pass Filter

Double polysilicon MEMS structure

(flat l response, no charging)

411 um thick Silicon (100 GHz FSR)

2 control parameters per stage:

MEMS voltage controls front mirror reflectivity (phase feature amplitude)

Substrate temperature controls free spectral range (phase feature location)

Madsen, Walker, Ford Goossen, Neilson & Lenz, IEEE Phot. Tech. Lett. 12, 2000


Fiber coupling package l.jpg

optical breadboard package

Vmirror

TTEC controller

input

d

$

D

f

f

output

ferrule

collimator

device

hermetic MEMS VOA package

Fiber-coupling package

Key optical package parameters

Lens focal length f = 3 mm

Fiber separation d = 125 um

Illuminated diameter D = 600 um

MEMS device diameter 1250 um

Substrate thickness t = 411 um

Package loss (mirror at device plane) 0.4 dB


Cavity round trip loss l.jpg

Awindow-Afeatures

Awindow

Scatter = ( )N

Cavity round-trip loss

Absorption = (e-aL)N

a = 10-4/cm

Reflection = (Rmirror)N

device

R = 98.5%

T = 99.3%

Shift = 10-0.434(NdT/nF)2

Dy = 5 / 600 um

Defocus = f(Nf)

package

fmembrane< 444 mm (20 um / pass)

Coupling = To

T = 93.3%


Single filter response l.jpg

1

Measured Phase & Amplitude

Wideband (30 nm) Transmission

Single filter response

Madsen, Walker, Ford Goossen, Neilson & Lenz, IEEE Phot. Tech. Lett. 12, 2000


2 stage dcf results l.jpg

Tuned for 50 GHz bandwidth and 100 GHz (0.8 nm) FSR

1

2

Negative

Positive

Madsen, Walker, Ford Goossen, Neilson & Lenz, IEEE Phot. Tech. Lett. 12, 2000

2-stage DCF results

Design: Dispersion goal = +/-104 ps/nm; predicted ripple of +/- 2.5 ps

Result: Set at +/- 102 ps/nm, yielded ripple of +/- 2.5 ps


2 stage dcf results continued l.jpg

2x dispersion for 30 GHz bandwidth and 100 GHz (0.8 nm) FSR

1

2

Madsen, Walker, Ford Goossen, Neilson & Lenz, IEEE Phot. Tech. Lett. 12, 2000

2-stage DCF results (continued)

200 ps/nm range, 1.5 ps ripple

(further improvement in loss uniformity required)


Slide13 l.jpg

Current status: Still R&D!

Optical performance (loss uniformity) needs to be improved

Control algorithms need more development

Dispersion compensation not critical until 40 Gb/s deployed


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