Dual Enhanced Fiber-Optic Microphone Using Sensitive Diaphragm-Free Transducer and Ultrahigh-Resolution Spectral Demodulation

Interferometric fiber-optic microphones (FOMs) with outstanding sensitivity are ideal method to detect weak acoustic signals. In this work, we demonstrated an ultrasensitive fiber-optic Michelson microphone with dual enhancement by using a diaphragm-free acoustic transducer and a high-resolution optical path difference (OPD) demodulation device. A cylindrical polyvinyl chloride (PVC) tube wrapped around by the optical fiber was employed as a transducer to enhance the responsivity to weak acoustic wave. A high-resolution spectrum demodulation-based white-light interferometer (WLI) was utilized to measure the variations of OPD. In theory, the FOM owns features to overcome defects of the conventional diaphragm-based or intensity demodulation method-based FOMs, such as quadrated point (Q-point) drifting and being sensitive to environmental interference. Experimental results showed that this FOM had an ultrahigh sensitivity of ~6800 nm/Pa at the resonance frequency of 1455 Hz. The sensitivity and the noise-limited minimum detectable sound pressure level (MDSPL) at 1000 Hz were calculated to be 315.3 nm/Pa and - 20.4 dB/Hz
^1/2
(1.9μ Pa/Hz
^1/2
), respectively.