Han Chunyang, Ding Hui, Li Baojin, Shi Lei, Xu Haodong
State Key Laboratory of Electrical Insulation and Power Equipment, School of Electrical Engineering, Xi'an Jiaotong University, Xi'an 710049, China.
Rev Sci Instrum. 2022 Apr 1;93(4):045001. doi: 10.1063/5.0084559.
The sensitive detection of sound waves is essential for a variety of applications. In this work, we propose a miniature diaphragm-free fiber-optic microphone based on a plano-concave optical micro-interferometer. A solid plano-concave micro-interferometer is formed at the end of a cleaved fiber by depositing a tiny volume of liquefied glass. Sound wave induced periodic variation of pressure can significantly modify the refractive index of the plano-concave glass due to the elasto-optic effect, and then, the phase difference between two interferometric beams will be remarkably changed accordingly. The interferometer finally converts the fluctuation of the phase difference into the change in the output optical power. Consequently, the sound wave can be demodulated by detecting the output power of the microphone. The experimental results show that the proposed microphone has the ability to detect sound waves in the whole audible range and almost omnidirectional. The noise-limited minimum detectable sound pressure is around 12 µPa/Hz. In addition, the human voice detection test shows that the performance of our microphone is competitive with the most advanced commercial device. The structure is stable without any movable mechanical parts, and the size is as small as 0.25 mm, which makes the proposed microphone an attractive alternative to the conventional one for sound wave detection.
声波的灵敏检测对于多种应用至关重要。在这项工作中，我们提出了一种基于平凹光学微干涉仪的微型无膜光纤麦克风。通过沉积少量液化玻璃，在劈开光纤的末端形成一个固态平凹微干涉仪。由于弹光效应，声波引起的压力周期性变化会显著改变平凹玻璃的折射率，进而相应地显著改变两干涉光束之间的相位差。干涉仪最终将相位差的波动转换为输出光功率的变化。因此，通过检测麦克风的输出功率可以解调声波。实验结果表明，所提出的麦克风能够在整个可听范围内检测声波，并且几乎是全向的。噪声限制下的最小可检测声压约为12 µPa/Hz。此外，人声检测测试表明，我们的麦克风性能与最先进的商用设备相当。该结构稳定，没有任何可移动的机械部件，尺寸小至0.25毫米，这使得所提出的麦克风成为传统声波检测麦克风的一个有吸引力的替代品。
