Fibredyne systems for passive or semipassive fibre-optic sensors

Fibredyne systems employ fibre-optic self-homodyne techniques for exploiting the microphonic nature of optical fibres when conveying highly coherent light. Any strain, pressure or temperature change applied to a fibre will cause phase modulation of the guided optical carrier. End reflections in single-mode and multimode optical fibres cause conversion of this phase modulation to amplitude modulation at the photodetector. We show how very simple passive and semi-passive fibre-optic sensors can be constructed using fibredyne detection of optical echoes.