Distributed optical fiber disturbance sensing system based on semiconductor laser with optical feedback and ring interferometer

A novel distributed optical fiber disturbance sensing system based on a feedback semiconductor laser and a fiber-ring as a self-mixing interferometer is proposed and demonstrated. When an external disturbance acts on the sensing fiber, a phase change in the light beam propagating in the fiber-ring will be induced, which in-turn is converted into an intensity modulation in the laser output through a feedback light interference in the laser and a nonlinear optical amplification by the laser. The sensor output signals can be obtained directly from the laser module equipped with an internal photodiode. The primary experiments were carried out and the results show that the RMS value of output electrical signal has a linear relation with the disturbance position, so this feature can be utilized as a means of localizing disturbances along the sensing fiber. The maximum location error obtained in our experiments is about 27 m within a 1-km long sensing fiber. Therefore, the proposed sensing system and location method are feasible. Moreover, the system is high in the sensitivity and simple in the structure as well as in signal processing.