1. High-speed optical switching based on diffusive conduction in an optical waveguide 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

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

3. 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

4. Concept of Diffusive Conduction Diffusion Equation: ( Ohm’s Law, Kirchoff’s Laws, Q=CV ) Initial Condition: Solution: R SQ = Resistance per square C A = Capacitance per unit area

5. Device Concept Quantum confined Stark effect Field screening Modulating the signal output by control input Non-inverting optical switching Wavelength conversion Local capacitor

6. Device Concept Diffusion equation in one dimension. Solution: where for a switch having the local capacitor at the edge of the waveguide.

7. Device Concept

8. Theoretical Results A simulation model in conjunction with empirically measured quantum well data is established. Modulation bandwidths of tens of GHz.

9. Theoretical Results Simulation of 10 Gb/s nonreturn-to-zero operation with a 2μm wide, 250μm long center bias point device R l = 16 Ohm/μm C l = 0.23 fF/μm λ control = 822nm λ signal = 864nm >10 dB signal extinction ratio

10. 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. R l = 16 Ohm/μm, C l = 0.23 fF/μm λ control = 822nm, λ signal = 868nm A continuous-wave Ti-sapphire for signal beam and a diode laser for control beam were used.

11. 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.

12. 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.

13. 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