Design and Investigation of Laser Sources and Sensing Schemes Using Gratings Filters

• Main Authors: Shien-Kuei Liaw, 廖顯奎
• Other Authors: Chow-Shing Shin
• Format: Others
• Language: en_US
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/20982092227001049758

博士 === 國立臺灣大學 === 機械工程學研究所 === 102 === This dissertation aims at the design and investigation of laser sources and various sensing schemes based on fiber Bragg grating (FBG) filters. Aside from the introduction in Chapter 1, Chapter 2 gives an overview of the mechanical properties of FBGs and optical amplifiers used in this dissertation. FBG family, their general principles, mechanical properties and some applications are introduced in particular. Several optical amplifiers based sensing light sources used in the subsequent chapters are also introduced. In Chapter 3, a wide-tuning range linear cavity tunable fiber laser is proposed by using a 3-point bending device to facilitate wavelength tuning mechanism for FBGs. Two parallel strain-tunable FBGs (TFBGs) are demonstrated in L band operation. A large tuning range of up to 21.5 nm with 0.1 nm precise resolution for each TFBG is obtained. The overlapping tuning range for two TFBGs is from 1565.5 to 1599 nm with only 2 dB power variation. Using a 10 M EDF and a 100 mW pumping laser diode, a stable lasing output power at 1582 nm is obtained, which has the threshold pump power and side mode suppression ratio (SMSR) of 10 mW and 50 dB, respectively. Temperature reliable test is also conducted. In Chapter 4, a good coherence light source for automatic optical inspection (AOI) and high-speed communication is designed. This light source is made of FBG and other components with the single-longitudinal-mode (SLM) feature. Temperature test of power stability is also performed. A 2*2 reconfigurable and multi-wavelength optical cross-connect for optical network using such coherence light source is presented. The abilities of FBG tuning and signals exchange are also demonstrated. In Chapter 5, a new type of FBG-based multi-wavelength fiber-lasers for long-distance parameters sensing is presented. The laser source is constructed using a fiber-pigtailed semiconductor as the gain medium. A 2x2 fiber loop mirror and FBGs are assembled to form a linear-cavity fiber laser. The laser output characteristics are studied, and the sensor performance under different sensing distances is evaluated. The experimental results show that this SOA-based laser sensor possesses a dynamic sensing distance up to 35 km at 350-mA injection current. Moreover, the strain detection ability is investigated and reliability test is carried out for this sensing light source. In Chapter 6, a FBG-based pendulum system for inclination sensing is investigated. The FBG acts as a sensing element to detect the element weight as well as the inclination angle in the vertical direction. To increase the sensing sensitivity, it is proposed to replace the conventional broadband light source with a fiber ring laser. The results show that the sensing power and peak-to-noise ratio are improved to 3.1 dBm and 65.3 dB, respectively. Meanwhile, the 3 dB bandwidth of light source is reduced to 0.06 nm. The resolution of inclination sensing could reach an accuracy value of 0.015 nm/degree. In Chapter 7, an embedded FBG-based sensing system to monitor the post-impact fatigue damage of composite materials is developed. The damage can be revealed by the broadening and splitting of FBG’s characteristic narrow peak in its reflected spectrum. The evolution of grating spectrum can therefore be used to monitor qualitatively the incurred damages of materials or structures. It is found that the FBG sensor can survive a low velocity impact as well as the subsequent fatigue loading. Finally, a summary of all research results of this dissertation is presented in Chapter 8. A few suggested future works including pressure sensing and accelerated aging test are offered as well.