Research on Ultra-High Sensitivity Fiber-Optic Cascaded Fabry-Perot Resonator Optical Sensor Based on the Comb-Spectrum Vernier Effect

The fiber-optic cascaded Fabry-Perot (FP) cavity structure is a significant interferometric sensor configuration, offering superior spectral resolution compared to Mach-Zehnder type sensors. In response to the comb-spectrum characteristics of fiber-optic cascaded FP sensors, we propose a novel optical vernier processing method. This method calculates the peak positions of individual resonance peaks without the need to track the drift of envelope modulation curve peaks, as required by traditional optical vernier scale methods. Utilizing this approach, we have significantly enhanced the sensitivity of cascaded FP cavity sensors. The strain and temperature sensing tests achieved sensitivities of 4.76 pm/μϵ and 271.61 pm/°C, respectively, representing an increase of over 20 times compared to a single-stage cascaded FP cavity. More importantly, the Figure of Merit (FOM) for the cascaded FP cavity sensors can be improved by more than two orders of magnitude under the same sensitivity amplification factor, compared to traditional optical vernier technologies based on envelope curve recognition. This also effectively avoids potential errors that may arise during the fitting process of the envelope modulation curve. These advantages endow the cascaded FP cavity sensors with significant potential for application in the field of high-performance fiber-optic sensing.