Broadband Adaptive Optoelectronic Discrete Time Signal Processor

Optical fibres can be used to provide delay up to tens of microseconds with high bandwidth, low loss and high linearity. In combination with signal weighting by controlled detection of intensity modulation optical signals and signal summation by photocurrent addition, analogue discrete time signal processors can be implemented with fibre delays. We have previously reported the implementation of a 16-tap finite impulse response (transversal) filter using this technique [1, 2]. Extending the concept to a two dimensional matrix of controlled photodetectors provides the inner product operation among a vector of broadband signals and the matrix of weights set by the photodetector array. We have proposed such a structure as a basic device for a broadband neural processor [3] and as a generalized signal processor [5] [6]. As an extension of work on broadband optoelectronic switching [7, 8] we have constructed such a processor. We report its performance in implementing FIR, IIR, and adaptive discrete time filters and show the effect of coupling of bandwidth to gain in the bias controlled MSM photodetectors and how it can be compensated. The possibility of using such a filter to equalize modal dispersion in multimode fibre is also investigated. An eightfold improvement in bandwidth-distance product is possible.