Rayleigh backscattering in optical fiber recirculating delay lines

We derive the backscattering impulse response of a recirculating fiber delay line. The response consists of periodic discontinuities that occur at multiples of the loop transit time. The magnitude of each discontinuity is found to depend only on the coupling coefficient and the number of recirculations and is independent of both propagation loss and loop length. A graphical aid for describing the response of the system is also presented.