Optoelectronic look-up table using VCSEL-based logic

Look-up tables, also known as truth tables, have been commonly used in several processing tasks, such as database operations, associative processing, residue arithmetic, cache memories, mathematical function modules, and instruction decoding. In its simplest form, a look-up table contains a list of values that must be compared against an input argument. If the input value is found among the table entries, a match signal is generated. Many variations of this scheme exist, such as input/output tabulation, multiple and/or partial matching capability, content addressable memories, and auto- and heteroassociative memories. The main function of searching the look-up table is a highly parallel process and must be completed, preferably, in a single step. The low computational requirements of the look-up operation, coupled with its large degree of parallelism and tabular representation of data, have led to several implementations of optical look-up table architectures. In this paper, we describe an optoelectronic look-up table configuration based on an array of exclusive-or gates implemented with heterostructure phototransistors (HPT) and vertical cavity surface emitting lasers (VCSEL)