Multimode optical-fibre phase modulators and discriminators: I-theory

Low-moded optical fibres are very microphonic when guiding highly coherent light. Acoustic signals applied to the fibre cause phase modulation of the optical carrier. This phase modulation is then converted to a related amplitude modulation by a fibredyne (fibre-optic self-homodyne) detection process at the photodiode. A simple theory is presented which describes the causes and characteristics of three p.m. to a.m. discriminator effects in coherent multimode fibre systems. Possible applications for fibredyne systems include data highways and low-fidelity distributed microphones.