鎖模半導體雷射注入放大之研究

Abstract

我們利用MOPA (Master Oscillator Power Amplifier)架構，實現了一高平均功率、可多波長操作之電控波長可調皮秒級鎖模脈衝雷射系統。此雷射系統輸出之平均功率可達200mW，脈衝寬度為27ps，其旁模抑制比可達25dB （以三波長輸出時）。 主雷射（Master Laser）採外腔設計，外腔由削角入射光柵、透鏡及液晶像素反射鏡構成，具下列優點：（1）電控波長可調，（2）可多波長輸出，（３）可調制腔內色散以壓縮脈寬等。此主雷射系統的電控波長可調範圍在連續波及鎖模狀態操作下分別為6.16nm與5.94nm。在多波長操作情形下，若波長皆為相鄰而無間隔，可以有多至二十波長的輸出；若是波長間皆有間隔，不是相鄰，我們亦成功達成六波長的輸出，各波長的旁模抑制比最小為10dB，最大為26dB。當主雷射系統在鎖模狀態下，其輸出的脈衝寬度在壓縮之前為52.3ps，經過腔內色散延遲的最佳化後可壓縮至23.4ps，時間-頻寬乘積為0.614，約為轉換極限（0.44）的1.39倍，此時雷射輸出的平均功率為10mW。若將主雷射的光以平均功率0.85mW注入從雷射，經過放大後光平均功率可達200mW以上，即放大了23dB以上。此外，主雷射系統的電控波長可調特性與可多波長操作的特性仍然保有，並不會消失；脈衝寬度亦可以維持，不會變寬。

We have demonstrated a high-average-power, multi-wavelength, electronically wavelength tunable, mode-locked picosecond laser system by making use of MOPA (Master Oscillator Power Amplifier) configuration. The output average power is above 200mW, the pulse width is 27ps, and the SMSR (Side Mode Suppression Ratio) is 25dB (in 3-wavelength operation). The master laser takes advantage of an external cavity that is composed of a grazing-incident grating, a lens and a LCPM (Liquid Crystal Pixel Mirror). The advantages of the master laser are as follows: (1) electronically wavelength tunable, (2) multi-wavelength operation, (3) intra-cavity dispersion compensation. The tuning ranges of our master laser system in CW operation and mode-locking operation are 6.16nm and 5.94nm, respectively. Simultaneous generation of up to 20-wavelengths is demonstrated. The SMSR of the modes is from 10-26dB. After optimizing the intra-cavity dispersion, the mode-locked laser pulses reduced from 52.3ps to 23.4ps. The time-bandwidth product is 0.614 about 1.39 times transform limit (0.441). The output average power of the master laser is 10mW. By injecting 0.85mW(average power) of the master laser into the slave laser diode, the MOPA output is above 200mW, i.e. the gain is above 23dB. Besides, the characteristics of electronically wavelength tuning and multi-wavelength operation of master laser system are still preserved, and the pulse width is not significantly broadened.