利用液晶反射鏡之電控波長可調半導體雷射之進展

Abstract

本論文主要是對本實驗室新發展的將液晶反射鏡應用在波長可調半導體雷射系統作更進一步的研究與改進，並得到一些成果。 雷射系統採用一種摺疊望遠鏡式的光柵，外腔結構使用的元件包括一削角入射光柵、透鏡、與液晶反射鏡及雷射增益介質，並以電控的方法調制液晶反射鏡，使其在我們所要的空間位置回饋雷射光源，以達到系統單、雙波長乃至多波長的輸出。 液晶反射鏡採TN（twisted nematic）型的液晶盒結構，可以電控方式選取50個波長。元件響應時間為54.6ms，反射率為43﹪。 以一輸出面經過抗反射處理過的紅光半導體雷射（中心波長657nm）作為可調波長雷射系統的增益介質，如此作使我們更容易來調制單、雙波長，亦可得到三波長的輸出。調制波長範圍達10.4nm（I=1.54Ith）（液晶元件限制），旁模抑制比達25dB。 使用另一顆近紅外光半導體雷射（中心波長為832nm）作為增益介質，雷射輸出功率可達數十毫瓦，並可以單、雙、多波長輸出。單波長調制範圍達8.12nm（元件限制），旁模抑制比均有25dB以上。

In this thesis, we improved the tunable external-cavity semiconductor laser diode system which was developed by ourselves. The external cavity consists of a grazing-incidence grating, lens, liquid crystal spatial light reflector, and a semiconductor laser as the gain medium . The system can be operated in single、dual or multi-wavelength mode when we use the electronic-controlled liquid crystal spatial light reflector . The liquid crystal spatial light reflector we use is a TN cell. The laser system can output fifty wavelengths by controlled the liquid crystal spatial light reflector electronically. The response time of the cell is 54.6ms. The reflection ratio is 43﹪. When we used a anti-reflection coating red laser diode （center wavelength is 657nm）as the gain medium, the tuning range of the wavelength was 10.4 nm （limited by LC cell）（I=1.54Ith）. The side-mode-suppression-ratio（SMSR）of the laser was batter tnan 25 dB throughout this range. When we used a near infrared laser diode （center wavelength is 832nm）as the gain medium, the output power of the laser can achieve several tens of miniwatts. The tuning range of the wavelength is 8.12nm（limited by LC cell）. The SMSR of the laser was better than 25 dB throughout this range.