GaAs-AlAs Monolithic Microresonator Arrays

Abstract

Miniaturization of optical logic devices has long been considered to be a key to minimizing their energy requirements but difficult to achieve1-4. We demonstrate a straightforward technique for fabricating arrays of GaAs/AlAs Fabry-Perot etalon devices (microresonators) as small as 1.5 μm in diameter. The growth of integrated GaAs-AlAs nonlinear etalons by molecular beam epitaxy5 (MBE) represents a tremendous advance over previous fabrication techniques6. From the sample of reference 5 we have formed close-packed arrays of monolithic "posts" or microresonators 1.5-5 μm across by ion-beam assisted etching7 and have performed optical NOR/OR gating experiments on them using picosecond pump and probe pulses. These microresonators represent a qualitative advance over the GaAs devices reported by Lee et al8. In that work pixels 9×9 μm square were formed in the active material only, and then sandwiched between dielectric mirrors in the usual way.6 Growth of integrated devices by epitaxial techniques such as MBE allows us to etch right through both mirrors and the active material. This is critical since in an optimized nonlinear etalon the dielectric mirrors comprise most of the total thickness. The lateral optical confinement in these waveguiding structures allows efficient operation with diameters as small as one can focus the light. Elimination of carrier diffusion9,10 out of the devices permits very close spacings. Reduction of energy requirements is expected due to the decreased volume of interaction. Finally, surface recombination8,11 on the sidewalls of the microresonators should produce fast relaxation times. Our experiments show reduced energy requirements (factor of >8), essentially uniform response over small arrays, practically no crosstalk with 3-μm center-center spacing, ~200 ps full recovery time, and thermal stability at 82 MHz operating frequency.