| Author: | Liu, Shangming |
| Title: | Optical fiber resonant acoustic sensors based on a 3D micro-printed ferrule-top ortho-planar spring optomechanical resonator |
| Advisors: | Zhang, A. Ping (EEE) |
| Degree: | M.Sc. |
| Year: | 2024 |
| Department: | Department of Electrical and Electronic Engineering |
| Pages: | 1 volume (various pagings) : color illustrations |
| Language: | English |
| Abstract: | Optical fiber sensors play a critical important role in many areas owing to their advantages such as compact size, lightweight, immunity to electromagnetic interference, remote sensing and multiplexing capabilities. One of the noteworthy optical fiber sensors is optical fiber acoustic sensors. Over the past few decades, many efforts have been made to develop high-performance optical fiber acoustic sensors with miniaturized size, high sensitivity, and low limit of detection. In this thesis, miniature optical fiber acoustic sensors based on a ferrule-top optomechanical resonators are designed and fabricated for measuring acoustic waves. Ortho-planar springs (OPSs) are introduced in the design of the sensor head to suspend a thin-film micro-disk reflector to form an optomechanical resonator with enhanced sensitivity. The structure of the ortho-planar springs is numerically analyzed using the finite element method (FEM) to reveal their displacement sensitivity and resonance modes. The ortho-planar spring suspended thin-film microdisk reflector and the end-face of optical fiber form an Fabry-Perot micro-interferometer, which enables the interferometric read-out of acoustic sensing signal. Notably, the large aspect ratio of the fiber-optic ferrule and the ultra-small size of its end surface impose challenges for conventional micro/nano-fabrication technologies. Therefore, a digital micromirror device (DMD)-based optical 3D micro-printing technology has been applied to fabricate the designed ortho-planar microstructures on the end-face of fiber-optic ferrule. With the use of SU-8 photoresist and the optimized 3D micro-printing processes, the ortho-planar spring-based optical fiber acoustic sensors have been well fabricated in the experiments. Moreover, the optical sensitivity and acoustic sensitivity of three optical fiber acoustic sensors based on different ortho-planar springs are experimentally tested and compared with simulation results. The noise equivalent pressure of the best fabricated optical fiber acoustic sensor is around 33.12 µPa/√Hz at the resonance frequency, and the mechanical quality factor of its fundamental vibration resonance is around 30. Such a small-size and high-sensitivity ortho-planar spring optical fiber acoustic offers significant potential for applications such as photoacoustic gas detection. |
| Rights: | All rights reserved |
| Access: | restricted access |
Files in This Item:
| File | Description | Size | Format | |
|---|---|---|---|---|
| 8495.pdf | For All Users (off-campus access for PolyU Staff & Students only) | 2.01 MB | Adobe PDF | View/Open |
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