Study on a four-channel multi-longitudinal mode fiber-ring laser sensor array based on frequency division multiplexing

Combined with beat frequency demodulation technology, a four-channel multi-longitudinal mode fiber-ring laser (MMFRL) sensor array base on frequency division multiplexing (FDM) is proposed and experimentally investigated. The MMFRL sensor is formed using a fiber Bragg grating, a 3 dB coupler and a section of erbium-doped fiber. Because the different cavity lengths of the fiber laser have different frequency intervals, the beat signal for each sensor is addressed using FDM technology. The proposed sensor array is experimentally validated. The responses of the beat frequencies shift to the strain are −0.584 kHz/με@782.680 MHz and −0.890 kHz/με@1185.880 MHz, which are in good agreement with the theoretical expectations. By using multiplexing technology, the cost of each sensor was greatly decreased. This is a very promising technique for use in large scale monitoring fields.