Acoustic Wave Sensor Based on the Optical Fiber-Diaphragm Composite Structure

In this paper, an optical sensor based on the fiber-diaphragm composite structure is proposed for detecting low-frequency acoustic waves. The main structure of the proposed sensor is built up by an in-line Mach-Zehnder interferometer (MZI) and a round polyethylene terephthalate (PET) diaphragm. The inline MZI is fabricated based on the sandwich structure of multimode fiber (MMF)-six holes single core fiber (SHSCF)-MMF. The interference dip intensity of the MZI can change linearly with the curvature variation. If the curvature sensor is stuck closely along the diameter of the PET diaphragm, this fiber-diagram composite structure can detect low-frequency acoustic waves because the sound field information is modulated to the curvature of the sensor by the vibration of the PET diaphragm. Then, by demodulating the light intensity with a photodetector, the original acoustic information can be obtained in real-time. The experimental results show that a flat response to sound waves is achieved in the frequency range from 50 Hz to 3000 Hz.