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

This paper describes a new type of fiber-optic sensor which has high immunity to the effects of variations in the fiber and connector losses. A beam-splitting transducer differentially modulates, as a function of the sensed parameter, the proportions of the incident 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 light are measured. These four signals are processed to remove the influence of the fiber and connector losses. A loss-compensated displacement sensor, which uses a schlieren-type transduction mechanism, is demonstrated. The experimental results show that this loss-compensation technique can stabilize the sensor output to a high degree despite considerable variations in the transmissivities of the fiber-link components.