VCSEL Operational Requirements for Optoelectronic Neural Networks

摘要

In this paper we shall describe the design and successful operation of an optoelectronic Hopfield network demonstrator system. This demonstrator system, based around a free-space diffractive optical interconnect, was designed to perform a range of optimisation tasks, in particular those associated with the scheduling of packets through different switching topologies. Experimental optimisation of the neural network throughput, for both a crossbar and Banyan switch topology, allows the neural network parameters (e.g. neuron bias, neuron weighting) to be tuned to ensure optimal operation of the network for a particular switch topology. The weighted interconnections in this optoelectronic system are provided by a diffractive optical element/lens combination whilst the neurons are implemented electronically. The transition between the electronic and optical domains is handled by an 8x8 VCSEL array for the electronic-optic interface, and an 8x8 Si photodetector array for the optic-electronic interface. The VCSEL array, supplied by Avalon Photonics, is an oxide-confined near-infrared GaAs device capable of 250MHz modulation at a wavelength of 960nm. The diffractive optical interconnect is designed using simulated annealing optimization and fabricated using VLSI photolithography. Using these techniques it is possible to create interconnects with a total efficiency of ～70% and a uniformity of < 1%.