ABSTRACT
This chapter presents a novel fiber-optic acoustic sensor consisting of two laser diodes and a fiber Sagnac interferometer. Two laser diodes operate under external optical injections, including self and mutual injections. In fiber-optic acoustic sensors, the fiber Sagnac interferometer can provide ideal sensing performances, in terms of the sensitivity and frequency response, to detect the faint, high-frequency, partial discharge-induced ultrasonic waves. The fiber Sagnac interferometer used in this sensor configuration is taken as a wide-band, reflectivityariable loop mirror. The experimental results demonstrate that the proposed sensing concept is practicable and the sensor has very high sensitivity and good frequency response property in detection of high-frequency and weak ultrasonic waves produced by the discharges. Compared to the traditional detection method used in the ordinary Sagnac sensor with a light source and a detector, this nonlinearity-based detection method can greatly enhance the sensitivity of the sensor system.
