With the introduction of communications theory and allied studies of random data and the engineers' increasing understanding of these fields the demand for wideband multichannel correlators is increasing rapidly (Ref. 1). Correlation techniques most commonly used today employ either dig-ital computers, coherent-optical correlators or an application of one of the nonlinear characteristics of semi-conductor devices. At present, however, no wholly satisfactory method of simulataneously correlating a large number of wide-band signals has been found; systems developed for this purpose suffer from one or more draw-backs, viz: phisical instability, slow operation, narrow bandwidth or lack of isolation between channels.
N.A. M. Mackay,
M. G. Dohler,
"A Fibre-Optics Matrix For A Multi-Channel Correlator", Proc. SPIE 0031, Fiber Optics Comes of Age III, (1 April 1973); doi: 10.1117/12.953580; https://doi.org/10.1117/12.953580