High-Performance Optical Fiber Fabry-Perot Sensor Based on a Sawtooth Spectrum and Its Application in Acoustic Sensing

An optical fiber sensor based on Fabry-Perot (F-P) resonance with sawtooth spectral shape can break the mutual constraint of sensitivity and response range through simultaneously demodulating intensity variation of lasers working on the two asymmetric spectral lines. Here, theoretical solution and practical approach for obtaining the F-P resonance with a sawtooth spectrum have been proposed. The linear range and slope of the asymmetric spectrum are first calculated based on the proposed theoretical model, which regulates the spectral shape variation. Then, the composite film on fiber end face has been solved to fulfill the model parameters required for the sawtooth spectrum through reversely utilizing an equivalent interface approach, which has been theoretically and experimentally demonstrated by using a composite film of platinum and germanium (Pt/Ge) as the first reflective mirror and gold film as the second mirror. Finally, an optical fiber F-P sensor with sawtooth spectral characteristics is prepared for underwater acoustic sensing application, which demonstrates an average of 10-dB improvement in dynamic range at the frequency range of 20-800 Hz.