利用液晶空間光調制器之外腔式可調波長半導體雷射之研究

Abstract

本文首度報導一種新型的外腔式可調波長半導體雷射。 此雷射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、與液晶空間光調制器及雷射增益介質，並以電控的方法調制液晶空間光調制品，使其在我們所要的空間位置回饋雷射光源，以達到系統單或雙波長的輸出。 系統所使用的液晶空間光調制品為－TN (twisted nematic)型的液晶元件，我們以半導體製程的方法在 ITO (Indium Tin Oxide)玻璃上製作元件的電極圖形，再以Polyimide作旋轉九十度(twisted)配向，最後以真空法封入絲狀(nematic)液晶。 當我們以雷射投影筆用輸出功率1.5mW的雷射為增益元件，改變無件像素(pixel)時波長選取的範圍最大可到4nm，每個波長的旁模抑制比(SMSR)可達18dB以上。

The primiary focus of this thesis is we replace stripe mirror by liquid crystal spatial modulator in tunable external-cavity semiconductor laser diode systerm. The external cavity consists of a grazing-incidence grating, lens, liquid crystal spatial light reflector, and a semiconductor laser of laser pointer as the gain medium. The systerm can be operated in signle or dual-wavelength mode when we use the programmable liquid crystal spatial light reflector. The liquid crystal spatiial light reflector we use is a TN cell. We made ITO (Indium Tin Oxide) electrode pattern on glass by semiconductor process, polished twisted alignment layer, and bounded nematic liquid between two glasses. When we used the laser diode of 1.5mW as the gain medium, the tuning Mode-Suppression-Ratio(SMSR) of each wavelength is more than 18dB. The wavelength separation between the individual pixels are in good agreements with theoretical predictions.