Loss-compensation technique for fiber-optic sensors and its application to displacement measurements

This report describes a new type of intensity-modulating fiber-optic sensor which has high immunity to the effects of variations in the losses of the fiber-link. A variable-splitting-ratio transducer is used to differentially modulate the intensities of the light which it transmits and reflects. Using a four-fiber optical link, light is impinged onto the transducer from either direction, and in each case, the transmitted and reflected signals are measured. These four signals are then processed to remove the effects of the fiber and connector losses. Loss-compensated sensors of angular position and displacement are described, and their outputs are shown to be highly stable despite considerable variations in the transmissivities of the fiber-link components.