High-speed optical switching based on diffusive conduction in an opticalwaveguide with surface-normal optical control

V. A. Sabnis, H. V. Demir, M. B. Yairi, J. S. Harris, Jr., and D. A. B. Miller

Edward L. Ginzton Laboratory and Solid State and Photonics Laboratory,

Stanford University, 450 Via Palou, Stanford, California 94305

Journal of Applied Physics, Volume 95, 2258 (2004)

Presenter: F. Hakan Köklü

Outline Introduction Concept of diffusive conduction Device concept Theoretical results Experimental results Conclusions

Introduction All-optical information transfer schemes vs.

conventional optical-electronic-optical conversion A single p-i-n diode containing multiple quantum

wells performing wavelength conversion and optical regeneration at mW power levels

Two-dimensional scalability and integration with electronics

Quantum confined Stark effect Diffusive conduction High extinction ratio

Concept of Diffusive Conduction

2

20

, 0 exp/ 2M

rV r t V

w

2

, exp4M

rV r t V

t D t

2

0 1

42

w

D

dVD V

dt 2ÑDiffusion Equation:

(Ohm’s Law, Kirchoff’s Laws, Q=CV)

Initial Condition:

Solution:

RSQ = Resistance per squareCA = Capacitance per unit area

DR CSQ A

1

Device Concept Quantum confined

Stark effect Field screening Modulating the signal

output by control input Non-inverting optical

switching Wavelength

conversion Local capacitor

Device Concept

Diffusion equation in one dimension .

Solution:

where

for a switch having the local capacitor at the edge of the waveguide.

2

2

dx

VdD

dt

dV

1

2 )exp(12

)sin(4),(

mm

m tDm

xVtxV

L

mm 2

)12(

Device Concept

Theoretical Results

A simulation model in conjunction with empirically measured quantum well data is established.

Modulation bandwidths of tens of GHz.

Theoretical Results

Simulation of 10 Gb/s nonreturn-to-zero operation with a 2μm wide, 250μm long center bias point device

Rl = 16 Ohm/μm

Cl = 0.23 fF/μm

λcontrol = 822nm

λsignal = 864nm >10 dB signal extinction

ratio

Experimental Results

A 2μm wide, 300μm long device for single transverse mode operation for wavelengths longer than 860nm

Waveguide is designed to be a surface-illuminated photodetector between 814nm-833nm.

Quantum wells are engineered to have an absorption edge at 850nm.

Rl = 16 Ohm/μm, Cl = 0.23 fF/μm

λcontrol = 822nm, λsignal = 868nm A continuous-wave Ti-sapphire for signal beam and a

diode laser for control beam were used.

Experimental Results

Reverse biases greater than 5 V results in significant increase in absorption.

7.7 dB signal transmission change is observed with an incident control beam power of 7.8 mW and a reverse bias of 7 V.

Experimental Results At 2.5 GHz, wavelength-

converting optical modulation is demonstrated.

Distortions at the output signal beam due to mechanical instability

The ability to electrically enable or disable the device using bias voltage.

Conclusions

A wavelength-converting, surface-normal optically controlled, waveguide switch based on diffusive electrical conduction is demonstrated.

Possibility of tens of GHz optical switching with mW-level optical switching powers

Two dimensional scalability for high-density switching