Blocks and Architecture for a Multichannel Fibre Optic Correlator

Abstract

There are two key operations implemented in a fibre optic correlator: the delay and the multiplication. This paper presents the choice of optical and microwave delays to optimise performance and cost and a comparative analysis of different ways to implement the multiplication blocks using the AND operation. The ANDing of 0.35 ns FWHM pulses was demonstrated experimentally using either very fast avalanche photodiodes with thresholding or a GaAs double gate MOSFET. Their relative performances are compared. For stationary signals, as an inexpensive way to expand the number of correlator channels by a factor of five, a five-step microwave switchable delay line was built and used. The ability to measure the correlation function of a 500 MHz sinusoidal signal is proved using double gate MOSFETS as AND gates, optical implementation for the delays longer than 5 ns and microwave implementation for the delays shorter than 5 ns.