Adaptive fiber-ring lasers based on an optical fiber Fabry–Perot cavity for high-frequency dynamic strain sensing

A fiber-optic Fabry-Perot (FP) interferometer integrated with an adaptive fiber-ring laser is configured as a switchable multi-wavelength fiber laser that can be utilized for ultrasound detection. Because the FP sensor acts as a wavelength filter and a reflector of the fiber-ring laser, the reflective spectrum of the FP sensor changes due to static/dynamic strains, and the wavelength of the laser output shifts accordingly, which is subsequently converted into a corresponding phase shift and demodulated by an unbalanced interferometer. By carefully controlling the polarization of the system, the lasing outputs with a side-mode suppression ratio higher than 30 dB can be obtained, and the lasing linewidth is much narrower than that of the spectrum of the FP sensor. The experiments show that the proposed sensing system has high sensitivity for ultrasound detection and can be adaptive to the low-frequency drifts due to environmental noise.