Author: Yuan, Weihao
Title: Optical communication and sensing devices based on specialty fibers assisted with novel materials
Advisors: Yu, Changyuan (EIE)
Degree: Ph.D.
Year: 2022
Subject: Optical communication
Optical fibers
Optical fiber detectors
Hong Kong Polytechnic University -- Dissertations
Department: Department of Electronic and Information Engineering
Pages: xxiv, 124 pages : color illustrations
Language: English
Abstract: In the thesis, we studied the various applications of novel structured fibers for optical communication and sensing devices. For the part of optical communication, the light modulators assisted with 2D materials are introduced. The mechanisms of graphene-based light modulation and modulators with different fiber structures are presented. Then the light modulator with down-tapered SMF structure assisted with graphene is proposed and demonstrated. The performances of the proposed and successfully fabricated light modulator are studied and improved, and the analysis of experimental results is included. The experimental results demonstrate a feasible method for all-optical light modulation with down-tapered fiber structure assisted with graphene nanoflakes. The measured response time is up to 0.4 ns, indicating the potential for optical signal processing with bandwidth of up to 2.5 GHz. The research will play a very important part in the optical communication system to simplify the optical components and realize all-fiber light modulation.
For the part of sensing devices, the fiber sensors are introduced including characteristics of fiber sensors, different sensing principles and various physical structures. The fiber sensors are constructed by different structures, such as mismatched single-mode fibers, ring-core fiber and hollow core Bragg fiber. Firstly, a mismatched fiber structure is successfully created and simulated that demonstrates its application for sensing temperature and humidity based on cladding modes modulation. With CNT attached to the fiber, the sensitivity of temperature detection in small ranges is enhanced from 0.24561 to 1.65282 dB/°C, and the humidity sensing becomes more reliable for real application. Secondly, the MZI fiber sensor based on SMF-NCF-RCF-SMF structure is successfully achieved. The experiments on temperature, RI and curvature sensing are conducted. Dual demodulation of temperature and RI is realized. The maximum sensitivity of temperature sensing is 69 pm/°C and that of RI sensing reaches 182.07 dB/RIU and -31.44 nm/RIU with the intensity and wavelength demodulation methods, respectively. The maximum sensitivity of curvature sensing is -3.68 nm/m-1 with the measurement range of 1.3856 to 3.6661 m-1. Based on the linear relationship between dip wavelength shift and the variation of temperature and curvature, these two parameters can be simultaneously demodulated by using the 2 × 2 matrix. Thirdly, an all-fiber sensor based on HCBF has been successfully created which displays excellent performance on human breath monitoring. The response time of the proposed sensor is around 0.15 s which enables the rapid and precise recording of breath signals. The applied distance between the fiber sensor and the human face is also investigated to reveal its influences on sensing results. Moreover, the HCBF sensor proves substantial insensitivity to temperature and curvature variation, which demonstrates its reliable sensing performance in different application environments. The all fiber-based light modulator and fiber sensors are investigated which will be beneficial to explore the novel applications of fibers with different configurations.
Rights: All rights reserved
Access: open access

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