| Author: | Yang, Zongru |
| Title: | Optical sensors with special fiber and novel structure |
| Advisors: | Yu, Changyuan (EEE) |
| Degree: | Ph.D. |
| Year: | 2024 |
| Subject: | Optical fiber detectors Fiber optics Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Electrical and Electronic Engineering |
| Pages: | xxvi, 160 pages : color illustrations |
| Language: | English |
| Abstract: | In the realm of optical sensing, fiber-optic sensors have emerged as a pivotal technology due to their flexibility, robustness, and compatibility with existing infrastructures. This thesis presents a comprehensive exploration of novel approaches to address key challenges in optical fiber sensing, spanning temperature cross-sensitivity mitigation, sensor miniaturization, concise fabrication, and sensitivity enhancement. Firstly, a pioneering optical fiber sensor employing the anti-resonant reflecting optical waveguide (ARROW)-hollow core Bragg fiber (HCBF) configuration is presented, enabling concurrent measurement of curvature and temperature. The four-layer Bragg framework of HCBF can enhance transmission spectra visibility. The meticulously crafted ARROW-HCBF design facilitates the identification of unique resonant dips, each distinctly responsive to variations in temperature and curvature. Employing a 2 × 2 matrix demodulation technique accomplishes simultaneous curvature and temperature measurement. Then, a dual Fabry-Pérot interferometer (FPI) configuration utilizing HCBF for gas pressure sensing is demonstrated. The combination of FPIs with varying optical path lengths (OPLs) creates a first harmonic Vernier effect (HVE), enhancing sensitivity. The low loss of HCBF permits longer cavity lengths, simplifying fabrication. Experimental results exhibit an ultra-high pressure sensitivity of 119.3 nm/MPa and minimal temperature crosstalk (0.074 kPa/°C), offering real-time monitoring capabilities through a simple, repeatable design. Subsequently, an innovative transverse force sensor using a Mach-Zehnder interferometer (MZI) based on ring core fiber (RCF) is proposed. This MZI combines coreless fiber (CLF) and the RCF segment with SMFs for cost-effective fabrication. Experimental results show a high force sensitivity of 4.109 nm/(N/mm) within the 0.26 N/mm to 1.5 N/mm range, with 0.9824 linearity. Temperature cross-sensitivity is systematically studied, demonstrating sensor resilience. The 2 × 2 matrix technique mitigates temperature effects, ensuring accurate force measurement. The MZI-based force sensor exhibits potential for practical applications in structural health monitoring and supercapacitor safety detection. Finally, a novel fiber-optic pressure sensor employing a chitosan-coated twin core side hole fiber (TCSHF) based structure is presented. By combining a Michelson interferometer (MI) with an FPI in a compact configuration, the sensor achieves an unprecedented pressure sensitivity of 589.41 nm/MPa and a temperature sensitivity of -0.47 nm/°C. The sensor’s dual-parameter measurement capability is enabled by the second HVE, with the internal envelope demodulation method ensuring accurate HVE envelope dip localization. The sensor’s stability over pressure cycles and time is demonstrated, emphasizing its potential for practical applications. The proposed sensor design offers a simplified yet highly effective approach to ultra-sensitive gas pressure and temperature sensing. |
| Rights: | All rights reserved |
| Access: | open access |
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