在可控光回授下單石化二段式分布式回饋雷射之微波頻譜特性

Abstract

光學外差干涉是一種常見的利用光源產生射頻訊號方法，在我們的研究中，內含布拉格反射鏡之單石化二段式分布式回饋雷射可以藉由共振腔之間的相互作用來產生可調變的射頻訊號。由於光回饋效應會對雷射特性產生好的影響，尤其在雷射線寬的部分，所以我們提出了一套光回饋控制系統來研究在光回饋之下的射頻頻譜特性，結果顯示在施加最大的光回饋後，雷射線寬會降低至原本的一半寬度，而且在雷射兩面都加上光回饋時，我們可以測得最小的線寬。而且我們還研究雷射在不同光回饋強度之下的動態特性，為了分析多模訊號，我們建構了一個摺積頻譜來擬合自差法量測到的頻譜。此外，射頻訊號的線寬會隨著不同電流配置而改變，並在接近注入鎖定區域時顯現出較小的線寬。

Optical heterodyne is a common way to generate radio frequency (RF) signal by optical source. In our research, the monolithic two-section distributed feedback (DFB) laser with a distributed Bragg reflector (DBR) structure can generate a tunable RF signal by the interaction between each laser cavity. Due to the advantages of optical feedback effect on laser performance, especially the linewidth, we demonstrated a feedback controlling system to investigate the spectral characteristics of RF signal under different feedback level. Eventually, the linewidth reduced to almost half of intrinsic signal with the max controllable feedback intensity, and a narrow linewidth RF signal was detected when the both sections of our monolithic device were influenced by optical feedback. The dynamic behavior of RF signals under different feedback level was investigated. To analyze the multi-mode signal, we constructed a convolution spectrum which could be used to fit the lineshape measured by delayed self-homodyne technique. Besides, the linewidth of RF signal was changed by different current configuration and exhibited narrower near the injection locking region.