Distributed optical fiber sensing system based on semiconductor lasers with mutual unbalanced double optical injection

A distributed optical fiber sensing system based on semiconductor lasers with mutual unbalanced double optical injection is proposed. Unequal lengths of the two injection paths enhance the nonlinear effect of the laser. The optical phase modulation caused by an external vibration acting on the sensing fiber is converted into the intensity modulation by the unbalanced double optical injection effect of the laser. Based on the synchronization effect of the mutually injected lasers, two waveform changes corresponding to the same external vibration emerge in the output signal of the system. The vibration position can be determined by the time difference between the two waveform changes. The period-one state of the system is employed to reduce the influence of optical phase noise and improve the sensing performance. The sensing system is modeled based on the rate equations of the mutually injected semiconductor lasers, and the working principle of the system is validated by numerical simulation. The location performance of the system is investigated experimentally. The average location error is less than 11 m on the 3.7 km-long sensing fiber. The experimental results show that the proposed system can work stably with a simple and accurate location method and does not require high coherence of the light source.