Ultrasonic sensor employing two cascaded phase-shifted fiber Bragg gratings suitable for multiplexing.

An ultrasonic sensor based on two cascaded phase-shifted fiber Bragg gratings (PS-FBGs) is proposed and demonstrated. In place of an external cavity laser, a broadband amplified spontaneous emission light source is used to demonstrate multiplexing ability suitable for sensor networks. The system has a high sensitivity to ultrasonic waves generated by a PZT actuator placed 7.5 cm away from the PS-FBG, because of the steep slope in the center of the PS-FBG spectrum. A second advantage of the phase shift is to reduce the effective sensor length, leading to the achievement of broadband characteristics. A pencil lead break test was performed and all results are compared to a traditional PZT sensor.