以光激發法研究半導體量子結構之光學增益

Abstract

光學增益是決定半導體雷射特性的重要參數之一，量測上有許多方法可以採用，比如Hakki-Paoli 方法、Henry 方法、長度調變法(variable stripe length method VSL)，每個方法都有其優缺點，比如Hakki-Paoli 方法需要高解析度的頻譜分析儀、Henry 方法在光路的對準以及耦合上的困難。 長度調變法為本篇論文所討論的主軸，比較用電激發與光激發兩種方式達到長度調變法所量到的增益頻譜，以及使用半導體光大器架構來達到量測模態增益的目的，後者可以從低激發強度量到高激發強度，雖然作法上比較複雜，但是卻可以幫助彌補電激發光與光激發光的不足之處。 根據實驗結果，顯示長度調變法在低激發強度下，當材料仍處於吸收狀態時，無論是電激發或光激發，皆因為再吸收 (re-absorption)的效應而無法得到正確的增益頻譜。若使用半導體光放大器架構來量測單一波長的增益，則可以克服長度調變法在低激發強度下所遇到再吸收的問題。

Optical gain is one of the most important parameters which determine the properties of semiconductor lasers. There are several methods for optical gain measurement. Every method has its disadvantages such as high-resolution spectrometers required for Hakki-Paoli method, difficulties in optical alignment and coupling for Henry method. In this thesis, we focus firstly on the variable stripe length method, and compare the modal gain in optical pumping and current injection. Semiconductor optical amplifier(SOA) structures are used to measure the modal gain from low excitation to high excitation. Although the experimental setup is more complicated, it can be applied under some measurement conditions where the variable-stripe-length method using optical pumping or current injection will be inappropriate. Based on the results in our measurement and analysis, the variable-stripe-length method, either using electrical or optical pumping, can not be applied in absorption case under low excitation. If we use SOA structures to measure the gain at a certain wavelength, the difficulties encountered above can be overcome.