Fiber Optic Recirculating Analog Delay Line

Single mode fibers appear to be attractive for delay line applications as their low loss and high bandwidth should lead to a large time-bandwidth product, which determines the information storage capacity of the delay line. We are interested in analog signal storage for a noncoherent radar application1 in which the optical delay line provides a time delay equal to the radar pulse repetition frequency, and radar returns are stored until they can be subtracted from the next incoming pulse. The pulse subtraction provides an indication of a moving target. Design considerations for the delay line are dynamic range, linearity, signal-to-noise ratio (SNR) and cancellation or signal-to-distortion ratio. By recirculating a 2 ns pulse around a 20 km single mode fiber five times, we obtain the equivalent of a 100 km or 0.5 msec delay and a time-bandwidth product of > 105.