High Efficiency Broadband Blue Laser Based on Quasi-Phase-Matched Periodically-Poled Lithium Tantalate

本篇論文主要由三大部分構成：準相位匹配與光參振盪器原理的介紹、光參-倍頻藍光雷射晶片之研製，以及光參-倍頻藍光雷射晶片之光學量測與特性分析。 理論部分，首先闡述非線性頻率轉換與準相位匹配理論，接著介紹光參振盪以及倍頻轉換理論。利用鉭酸鋰晶體在不同操作條件下配合理論去計算，滿足準相位匹配所需之週期大小。利用本實驗室發展的鎳金屬內擴散配合高壓電致極化反轉製程技術，應用於厚度0.75mm之共熔鉭酸鋰基片製作。實驗中設計光參-倍頻藍光雷射晶片，在倍頻部分做了三週期與五週期的設計，光參部份的週期為7.7576um，而倍頻部份的兩種設計分別為4.9514um、4.9865um、5.0218um，以及4.9514um、4.9689um、4.9865um、5.0041um、5.0281um，並成功研製出長13mm的高效率寬頻藍光雷射晶片。 光學量測部分，利用奈秒(~5ns)532nm綠光雷射做為泵浦源，設計一共振腔可共振930nm將所研製完成之雷射晶片置入，測量此光參振盪器之出光轉換效率。我們成功以350mW綠光泵浦搭配準相位匹配級聯狀光參-倍頻藍光雷射晶片，以及雷射共焦腔之設計，實現頻寬1.4nm，斜線效率21%之465nm的高效率寬頻藍光雷射，並得到54mW的藍光輸出，且藍光轉換效率達到15.4%。This thesis is composed of three parts：(1) the theory of quasi-phase- matching(QPM) and the QPM optical parametric oscillator(OPO), (2) the fabrication technique of one-dimensional periodically poled congruent grown lithium tantalite(LiTaO3) for cascade OPO-SHG 465nm blue laser chip, (3) the measurement and analysis of OPO-SHG blue light generators. First of all, I will introduce the mechanism of nonlinear frequency conversion and QPM theory, and its application to the optical parametric and second harmonic generation. By using Sellmeier equation, I design the QPM period of periodically poled LiTaO3 (PPLT) for the above application. By taking advantage of the nickel-diffusion assisted electric poling process, I fabricated cascaded OPO-SHG devices on 0.75mm-thick congruent LiTaO3 substrate. For cascaded OPO-SHG PPLT device, I design multi- SHG segment composed of 3 QPM periods with 4.9514 um, 4.9865 um, and 5.0218 um. Another SHG design is composed of 5 QPM periods with 4.9514 um, 4.9689 um, 4.9865 um, 5.0041 um and 5.0281 um. By this design, we achieve OPO-SHG blue laser with high slope efficiency and broad spectrum. Using a 532nm, bean of 5ns pulse width as the pump source, a 13mm long cascaded OPO-SHG chip in a concave laser cavity of 15mm length is shown to generate a 465nm high efficiency broadband blue laser. The spectrum is shown to have a 1.4 nm bandwidth and 21% slope efficiency. By this process, an average output power of 54mW blue light laser has been achieved under a 350mW input green pump, which corresponds to a conversion efficiency of 15.4%