1. Field of Invention
This invention relates to communication networks between computer processors and memories.
2. l Description of the Related Art
Computer architectures now commonly comprise a large number of processors executing programs concurrently. Such parallel computing architectures require a communication network between processors and between processors and memories. In parallel processing systems, it is desirable to allow many processors to send information to the processors and/or memories simultaneously.
The use of optics for the communication network is particularly effective, since optical systems can provide appropriate inherent parallelism, suitable bandwidths and low interaction between separate beams in a linear medium.
One of the most important optical communication networks utilizes the well known crossbar network. In particular, the crossbar network allows all processors and/or memories to be dynamically interconnected in an arbitrary permutation, without moving any existing interconnections.
Attention is now directed to FIG. 1 which exemplifies a "star" crossbar network 10 that utilizes opto-electronic detection components. The crossbar network 10 is disclosed in MacDonald et al, Electron Lett. 16 (1978) 402. The disclosure is incorporated herein by reference. The crossbar network 10 includes four transmitters, 12, 14, 16 and 18, each of which transmitters may be considered to be run by a processor. The transmitters provide input signals which are routed on optical fibers 20, 22, 24, and 26. The four separate inputs 20, 22, 24, 26, are in turn, fanned out four times and then made incident on 16 separate detectors 28. Each of the detectors 28 comprises a photodetector connected in series with a preamplifier, and each detector 28 provides the same electronic function, namely, to serve as a switching element. Briefly, each of the detectors 28 inputs light, and outputs an electrical signal on instruction from bias control circuitry (not shown). In operation, therefore, the crossbar network 10 functions to allow selection of a particular transmitted input signal for rebroadcast to a desired output (a memory or processor unit), shown in FIG. 1 as receivers 30, 32, 34, and 36. This rebroadcasting further requires a conversion of the electrical signals to optical signals by way of optical repeaters 38, 40, 42, 44, and transmission over a return fiber line.