Low power response of all-optical crossbar networks in quantum well heterostructures

A new device configuration has been examined for its potential as a compact, all-optical modulator, operating at low input powers (~ 3 mW). This device utilizes the large optical nonlinearities of Al(x)Ga(1-x)As/GaAs multiple quantum well heterostructures to modulate a low power-guided wave test beam with an orthogonally propagating control beam. This configuration has the advantage of maximizing the packing density of nonlinear modulators having interaction lengths of only ~ 5 microm. Several modes of device operation are possible, including thermal modulation, optical limiting, bistable switching, and multiple-input logic. We present experimental results for the throughput of single and multiple waveguide beams, as well as for the operation of this device as a waveguide modulator array. A theoretical model is compared with the experimental results for input pulse lengths ranging from ~ 300 ns to 1 s and input powers up to ~ 3 mW. Several optical nonlinearities are experimentally observed, including an electronic nonlinearity and two thermal effects, which are classified as either local or global in origin, with time constants of ~ 30 ns, ~ 4 micros, and ~ 40 ms, respectively. For an optimized waveguide geometry, the intrinsic optical device described herein should be suitable for use in systems requiring fast, high-density waveguide arrays for optical computing and serial/parallel data-processing applications.