利用近場光學顯微術研究光子晶體雷射特性

Abstract

本論文主要是利用高空間解析度的近場光學顯微技術，藉由改變激發功率來研究光子晶體D0結構量子井雷射的特性。首先利用微光激螢光光譜探討光子晶體缺陷模態產生雷射時的光譜特性。激發功率增加使得缺陷模態強度增加、半高全寬變窄以及模態波長藍移。當共振腔產生雷射後，其強度呈現急遽增加、半高全寬窄於光譜解析、波長藍移漸緩。接著利用全譜線近場光學掃描實驗，探討光子晶體產生雷射過程中光強度、半高全寬以及波長在空間上的變化。光子晶體共振腔其光強度的空間分布主要受到共振腔場強分布以及雷射區域所影響。藉由觀察半高全寬改變的空間分布，則可以判斷雷射產生的區域。另外以低功率激發光子晶體時，缺陷中心的模態波長受到自由載子效應的影響而往短波長移動。當激發功率大於臨界功率後，自由載子電漿效應的影響逐漸成為次要改由局部加熱效應主導，此時缺陷中心的共振波長受到局部加熱而往長波長移動。

Scanning near-field optical microscopy (SNOM) with high resolution is used to study filed distribution and lasing characteristics of photonic crystal laser. By power-dependent micro-PL, we study the optical properties of lasing process in the cavity. Power-dependent micro-PL results show that PL intensity will be increased, FWHM narrowed and resonance wavelength blue shifted with slowing down gradually when the excitation power is increased. The variation of PL intensity, FWHM, and wavelength is observed during the lasing process by experiment of SNOM which can obtain the full spectra in space. The distribution of electric field and lasing region affect the PL intensity of spatial distribution in photonic crystal cavity. Observing spatial distribution of variation of FWHM can determine the area of lasing. Besides, photonic crystal is excited by the power which is below threshold, free carrier effect is dominant and shifts the resonance peak to shorter wavelength in the defective center. The influence of free carrier plasma effect becomes secondary gradually when excitation power is above threshold and then local heating effect becomes dominant influence. The resonance peak in defective center is local heated and it is shifted to longer wavelength.