半導體雷射受回授光影響的不穩定性研究

Abstract

本論文以速率方程式為基礎,經由數值模擬與理論分析深入探討半導體雷 射受回授光的影響。降低線寬增強因子, 或是增加增益飽和因子、半導體 雷射空腔長度、 偏壓電流、 端面反射率將可減低延遲系統對回授量的敏 感度, 這些歸納結果可做為半導體雷射對回授光不敏感的一項指標。鬆弛 振盪頻率與外部空腔頻率的比值會決定出不同到混沌的路徑 ;當延遲比值 小於 0.8,亦就是在短距離的外部空腔長度時,是以週期加倍的路徑到混沌 狀態; 當延遲比值大於 0.9,也 就是在長距離的外部空腔長度時,是以近 似週期的路徑到混沌狀態;當延遲比值在 0.8與 0.9附近時,會出現次諧波 振盪的路徑。以本論文所觀察具有低阻尼因子之半導體雷射而言,第一個 振盪頻率起源於鬆弛振盪,第二個振盪頻率在長距離外部空腔下是起源於 外部空腔頻率,在短距離外部空腔下可能起源於系統的非線性耦合機制。 The intensity fluctuations and the routes to chaos in laser diodes with delayed optical feedback have been investigated. The minimum sensitivity to optical feedback is obtained by reducing the linewidth enhancement factor, and increasing the gain saturation factor, the diode cavity length, the bias current, and the reflectivity. The results may be considered also as guidelines for the design of laser diode without the susceptibility to optical feedback. As the feedback level is increased, the delayed system either undergoes the quasi- periodic route or the subharmonic-oscillation route or the period-doubling route to chaos, depending on the delay ratio. The period-doubling route dominates the transitions to chaos in the short external cavity for the delay ratio smaller than 0.8. The quasi-periodic scenario is mostly observed in the long external cavity for the delay ratio above 0.9. The subharmonic- oscillation route is favorable for the delay ratio around the region of 0.8 to 0.9.