Fabrication Of Cantilever Integrated Fiber Micro Cavity And Its Acoustic Sensing Properties

Acoustic wave sensing technique has been researched as the basic way of detection. With the detection field developing, the traditional acoustic sensor can’t meet the demands of the detection in sensitivity, environmental adaptability, size and power consumption. All-fiber acoustic sensor based on optical fiber sensing technology has been widely researched for the advantages of high sensitivity, small size, good environmental adaptability and anti electromagnetic interference. The reported optic acoustic sensors can be classified as types of optical intensity modulation, wavelength modulation and light phase modulation. Among these sensors, fiber Fabry-Pérot interferometers based on optical phase modulation attract more attention owing to their advantages in sensitivity, structure miniaturization and environmental adaptability.This paper aims to improve the sensitivity of the All-fiber acoustic sensor by integrating a fiber cantilever into the optical fiber micro cavity. The strain and acoustic wave sensing properties of the cantilever integrated fiber micro cavity was investigated theoretically and experimentally respectively. The main research contents are as follows.Firstly, a simple fiber tapering system was built and a high quality optical fiber cantilever was fabricated. The diameter of optical fiber cantilever can be control and the length can reached 1400 μm.Secondly, the sealed fiber micro cavities with different length were fabricated.Based on the optical fiber Fabry-Pérot interference model, we studied strain and acoustic modulation mechanisms of the common fiber micro cavity respectively with the divergence angle of the single-mode fiber. The effects of the cavity length on the strain and acoustic sensitivity were studied experimentally. The results show that the strain sensitivity of the sealed fiber micro cavity decreases with the increase of the cavity length. The acoustic sensitivity of the micro cavity can be adjusted periodicity by changing the cavity length slightly.Finally, the cantilever integrated fiber micro cavity was proposed and fabricated by integrating a optical fiber cantilever into the sealed fiber micro cavity.The sensitivity of the All-fiber acoustic sensor was improved by increasing the effective cavity length integrating a fiber cantilever into the optical fiber micro cavity. The effects of the interference length and the active length on the sensitivity of strain and sound pressure were investigated theoretically and experimentally. The strain sensitivity of the cantilever integrated fiber micro cavity is 16 times higher than that of common fiber micro cavity with the same interference length.Meanwhile, the acoustic sensitivity is improved 4 ~ 5 times higher when the frequency ranges from 200 Hz to 1000 Hz.