Optical delay lines

摘要

A method of applying a Doppler shift to an optical signal as it passes through an optical delay line comprises the step of progressively altering a property of the optical delay line during passage of the optical signal therethrough such that the time taken for the optical signal to pass therethrough is progressively lengthened or progressively shortened for successive portions of the optical signal. The optical delay line may comprise a stretchable optical fibre wound around a piezoelectric transducer 20 to which a sawtooth signal is applied to stretch and relax the fibre.