Compact Crossbar Switch For Optical Interconnects

Optical crossbar switches are used in a variety of applications: in optical computing, optical communications, and optical interconnects in computers. High speed optical crossbars have been demonstrated for the use in communications such as waveguide electro-optic switches in LiNbO3 [1], semiconductor quantum well modulators [2]. For applications in optical computing it is important to have very large switching arrays to utilize the massively parallel capability of optical signal processing. This has been achieved using spatial light modulators (SLM) which are available in large arrays, such as liquid crystal TVs and ferroelectric liquid crystal devices [3], and high speed, such as PLZT [4] or quantum well modulators [2]. Many systems based on SLMs utilize the vector-matrix multiplication configuration to realize crossbar networks, linear algebra operations, iterative vector-matrix multiplication, and optical neural networks. Crossbars based on this configuration, though suffer from fan-out losses, are very versitile, offer broadcasting capability needed in optical interconnects, and can easily form large array sizes. Most SLM based systems, which use bulk optics, lenslet arrays, and fiber optic couplers [5], are bulky and require tedious alignment. In this paper we describe a compact vector-matrix mulitplier in which waveguides with arrays of grating couplers are used to distribute and collect light signals.