Objective Optical fiber microphones hold significant practical value in applications like mine safety monitoring and disaster relief, where they must maintain stable performance despite external environmental interference. Many researchers have proposed diverse design schemes for optical fiber microphones, significantly enhancing their sensitivity, minimum detectable sound pressure, and directional recognition capabilities. However, there is still a lack of comprehensive research on the accuracy of continuous speech detection and the robustness of optical fiber microphone systems. These performance metrics are particularly critical in fields such as mine safety and disaster response. In environments like mines or disaster zones, not only must microphones be highly sensitive to capture low frequency or faint sounds, but also maintain stable performance amidst temperature fluctuations and other environmental factors. Moreover, speech signals in these scenarios are often complex and varied, demanding microphone systems with advanced signal processing capabilities to accurately discern key speech information. Therefore, it is essential to conduct robustness research on optical fiber microphones. Methods In this paper, we propose a highly stable optical fiber microphone sensing system based on polarization low coherence interferometry. The microphone designed for voice detection comprises a polyphenylene sulfide sensitive diaphragm and an optical fiber end face, forming a cross- correlation sensing system with a birefringent crystal based on polarization low coherence interferometry. By extracting the DC component of the interference signal through a birefringent crystal of known length, we effectively compensate for external environmental factors, thereby achieving high stability.<br /> Results and Discussions To evaluate the frequency response characteristics of the experimental scheme, we test the optical fiber microphone across a frequency range of 0.02 to 20.00 kHz. The results, depicted in Fig. 2, demonstrate that the optical fiber microphone system effectively detects sound signals within this range, maintaining a signal-to-noise- to- noise ratio (SNR) consistently above 50 dB across all frequencies. To assess its capability in detecting speech signals, we test continuous distress voice signals from both female and male subjects, as shown in Fig. 3. These findings highlight the system's 's accurate capture and reproduction of voice signals over a wide frequency spectrum. Long speech signals are also compared with those captured by a reference microphone. Furthermore, the system's 's performance under initial cavity length drift conditions is examined, with the outcomes presented in Fig. 6. These experiments illustrate the optical fiber microphone's 's robust adaptability and stability in scenarios involving output light source attenuation and initial cavity length drift.<br /> Conclusions We introduce a highly stable optical fiber microphone sensing system based on polarization low coherence interferometry in this paper. The microphone includes a sensitive diaphragm made of polyphenylene sulfide material and an optical fiber end face, along with a cross- correlated sensing system formed by custom birefringent crystals on three paths at the rear end. By extracting the direct current component of the interference signal through a birefringent crystal of known length, the system effectively compensates for external environmental factors and other irrelevant interferences, thereby strengthening system stability. Experimental results demonstrate a signal-to-noise- to- noise ratio of over 50 dB across the 0.02 to 20.00 kHz frequency range for this optical fiber microphone sensing system. Further detection and analysis of voice signals from different genders are conducted, followed by comparative analysis with a standard microphone. The system is also simulated under conditions of external environmental interference, where the initial cavity length of the sensor drifted by 1.631 mu m and the system input power attenuated by 60%. Compared to unchanged conditions, the cumulative distances of the system's output voice signals are 0.29073 and 0.28154, respectively, showcasing the voice detection stability of this optical fiber microphone. Given these characteristics, the proposed optical fiber microphone sensing system holds significant application potential in disaster warning, rescue operations, and other scenarios requiring highly stable voice detection. It accurately captures crucial voice information in complex and dynamic environments, providing essential technical support for safety monitoring and emergency response in critical areas.
