內含光柵濾波元件之雷射光源及感測架構：設計與研製

Abstract

本論文的主旨為運用光纖光柵濾波器來研製雷射光源和檢測架構。 第二章我們對光纖光柵之種類、機械特性及其原理作介紹，以及舉例其應用。我們也對若干當作後續章節之感測光源之光放大器作簡介。 在第三章中提出一種寬波帶線型且波長可調之光纖雷射。利用3點彎曲元件來達成光柵波長可調功能，使用兩條光纖光柵來達成由1565.5 至1599 nm 之長波段操作。單一光纖光柵可調範圍達21.5 nm且解析度達0.1 nm。重疊波長可涵蓋 1565.5 至 1599 nm 且功率變動值小於2 dB。使用10 M 之摻鉺光纖和100 mW的泵激光源，我們得到位於1582 nm之穩定光輸出功率僅有10 mW功率閥值並有50 dB之邊模抑制比。在第四章中，我們運用光纖光柵組成之雷射光源配合若干光元件，來研製同調性佳之單縱模光纖雷射作為自動化光學檢測與高速光通訊之用。我們也提出光網路用之一雙向2x2可重構之多波長光交連器並利用本章同調性佳之光纖雷射，展示用光纖光柵波長可調與信號交換能力。 在第五章我們運用光纖光柵設計多波長光纖雷射提供長距離參數感測。利用半導體光放大器當作增益光源並以2×2光纖迴圈與光纖光柵完成該架構之腔體設計。本章研究雷射光源之輸出特性並比較不同傳感距離之量測性能。實驗結果發現此感測設計在350 mA的泵激光源注入電流可檢測距離達35公里，我們也針對此感測光源之應變檢測與可靠度作實驗評估。在第六章我們利用單擺與光纖光柵設計角度傾斜感測器。此例光纖光柵為傳感單元用於檢測傾斜角與物重。比較並使用環型光纖雷射來取代傳統寬帶光源，並驗證其可提高檢測的靈敏度。結果表明檢測功率可達3.1 dBm且峰值對訊雜比可提高至65.3 dB。同時光源 3 dB 頻寬可降為0.06 nm。基於上述優越性能，參數之精確判斷可大為提升，傾斜角分辨率可達0.015 nm/degree。 在第七章我們開發內嵌式光纖光柵感測器，來監控複合材料受衝擊後之疲勞破壞情況，藉由光纖光柵導致光頻譜變寬與分岐情形就可判讀複合材料品質上之變化。我們也發現光纖光柵可以承受低速衝擊以及後續疲勞負載。最後第八章為博士論文之結論與後續研究方向建議。

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.