A glass-diaphragm microphone was developed based on fiber-optic Fabry-Perot (FP) interferometry. The glass diaphragm was shaped into a wheel-like structure on a 150-μm-thick glass sheet by laser cutting, which consists of a glass disc connected to an outer glass ring by four identical glass beams. Such a structural diaphragm offers the microphone an open air chamber that reduces air damping and increases sensitivity and results in a cardioid direction pattern for the microphone response. The prepared microphone operates at 1550 nm wavelength, showing high stability in a range of temperature from 10 to 40 °C. The microphone has a resonance peak at 1152 Hz with a quality factor of 21, and its 3-dB cut-off frequency is 32 Hz. At normal incidence of 500 Hz sound, the pressure sensitivity of the microphone is 755 mV/Pa and the corresponding minimum detectable pressure is 251 μPa/Hz^1/2. In addition to the above characteristics of the microphone in air, a preliminary investigation reveals that the microphone can also work stably under water for a long time due to the combination of the open-chamber and fiber-optic structures, and it has a large signal-to-noise ratio in response to waterborne sounds. The microphone prepared in this work is simple, inexpensive, and electromagnetically robust, showing great potential for low-frequency acoustic detection in air and under water.

The bionic sound detector based on the principle of the Ormia ochracea fly’s coupled ears is a miniature directional microphone that is sensitive to the sound pressure gradient. In this work, a silicon micro-electro-mechanical system bionic diaphragm consisting of two interconnected wings is designed and prepared, and a fiber-optic Fabry-Pérot interferometric microphone is constructed using the bionic diaphragm, and the characteristics of this microphone are studied theoretically and experimentally. According to the simulation results, the bionic diaphragm has two vibration modes of rocking and bending, and the rocking-mode displacement amplitude at a given sound pressure depends on the frequency and the propagation direction of the incident sound wave, and the closer to the eigenfrequency of the rocking mode the sound frequency, the greater the amplitude is; the rocking-mode displacement amplitude changes with the propagation direction in the three-dimensional space, resulting in a spindle-shaped distribution, and the long axis of the spindle is parallel to the long axis of the diaphragm, implying that the microphone is most sensitive to the sound wave propagating along the long axis of the diaphragm. The rocking-mode resonance frequency of the fiber-optic bionic microphone is measured to be slightly smaller than the simulated value. The output signal amplitude of the microphone changes with the horizontal azimuth angle of the sound source, producing a figure-8 polar pattern. A linear relationship between the microphone response and the azimuth angle is obtained in a range of 0° – ±60°, and in this angle range the directional sensitivity of the microphone is 39.98 mV/(°).

A prototype optical bionic microphone with a dual-channel Mach–Zehnder interferometric (MZI) transducer was designed and prepared for the first time using a silicon diaphragm made by microelectromechanical system (MEMS) technology. The MEMS diaphragm mimicked the structure of the fly Ormia Ochracea’s coupling eardrum, consisting of two square wings connected through a neck that is anchored via the two torsional beams to the silicon pedestal. The vibrational displacement of each wing at its distal edge relative to the silicon pedestal is detected with one channel of the dual-channel MZI transducer. The diaphragm at rest is coplanar with the silicon pedestal, resulting in an initial phase difference of zero for each channel of the dual-channel MZI transducer and consequently offering the microphone strong temperature robustness. The two channels of the prototype microphone show good consistency in their responses to incident sound signals; they have the rocking and bending resonance frequencies of 482 Hz and 1911 Hz, and their pressure sensitivities at a lower frequency exhibit an “8”-shaped directional dependence. The comparison indicates that the dual-channel MZI transducer-based bionic microphone proposed in this work is advantageous over the Fabry–Perot interferometric transducer-based counterparts extensively reported.