1550 nm 可調波長半導體雷射之研究

Abstract

在本論文中，我們利用液晶像素反射鏡(LCPM)實現了電控可調單波長與多波長外腔半導體雷射在1550nm波段。在單波長的部分，若使用50個像素的液晶像素反射鏡，可調範圍為12.375 nm (1548.404 nm-1560.779 nm)，受限於液晶像素反射鏡上像素的數目，旁模抑制比均超過24.5 dB。在雙波長的部分，最小模間距為0.248 nm，最大模間距為12.329 nm，也是受限於液晶像素反射鏡上像素的數目。最大機械式可調範圍為49.2 nm。而且，我們的外腔半導體雷射也可同時產生三波長及四波長的輸出。 在1550 nm波段，我們在兩種可調外腔半導體雷射(Littman-type and NCTU/LEO-type)中，嵌入一個向列型液晶(E7)盒作為波長可調元件。整個波長可調完全是電子控制的。在 Littman-type 外腔半導體雷射中，同時改變向列型液晶元件的驅動電壓及半導體雷射的電流，我們可得到波長連續可調1.62 GHz(受限於半導體雷射電流所能改變的波長量)。在實驗室發展的外腔半導體雷射中，我們只要改變向列型液晶元件的驅動電壓，就可達到波長連續可調1.89 GHz (不需要同時改變半導體雷射的驅動電流)。而且當我們只改變液晶像素反射鏡的驅動電壓，也可得到波長連續可調1.13 GHz(不需要在腔內放向列型液晶元件和同時改變半導體雷射的電流)。

An electronically tunable single- and multiple- wavelength external-cavity diode laser (ECDL) at □=1550 nm is realized by using a liquid crystal pixel mirror (LCPM). We demonstrated single-wavelength tuning of a tunable ECDL (NCTU/LEO-type) from 1548.404 nm to 1560.779 nm and the side-mode-suppression-ratio (SMSR) is better than 24.5 dB throughout this range. The total tuning range was 12.375 nm which was limited by the number of pixels on the LCPM. Dual-wavelength mode spacing can be as small as 0.248 nm, while the farthest mode spacing is 12.329 nm was also limited by the number of pixels on the LCPM. The maximum tuning range (mechanical) was 49.2 nm (I = 1.54 Ith). Furthermore, it is possible to implement simultaneous oscillation of three or four wavelengths in our external-cavity diode laser system. Second, we demonstrated two tunable external-cavity diode lasers (Littman-type and NCTU/LEO-type) that incorporated an intracavity nematic liquid crystal (NLC ) cell as the wavelength-tuning device at 1550 nm. The approach is fully electronic ally control lable. In the Littman-type external-cavity diode laser, we varied the drive voltage of the NLC cell and laser diode injetion current simultaneously to demonstrate single-mode oscillation with mode-hop-free tuning over 1.62 GHz, which was limited by the laser wavelength tuned by changing the injection current. In our external-cavity diode laser (NCTU/LEO-type), we only varied the drive voltage of the NLC cell and demonstrated single-mode oscillation with mode-hop-free tuning over 1.89 GHz without modulation of the injection current. Furthermore, we only varied the drive voltage of the LCPM and demonstrated single-mode oscillation with mode-hop-free tuning over 1.13 GHz without incorporating an intracavity NLC cell in laser cavity and modulation of the injection current.