波長可調及掃頻式半導體量子點光源

Abstract

光學斷層掃瞄系統近年來在生醫領域蓬勃發展，其系統所需之寬頻光源 若以半導體光源取代，將可改善系統複雜度、有效縮減體積並大幅降低售價， 且其發光波段恰與光通訊波段ㄧ致，也因此帶動光電領域之通訊光源研發； 其中最受注目的首推砷化鎵基板上以砷化銦量子點為增益介質的半導體光 源，此乃量子點本身的非均勻寬化效應為寬頻光源的最佳選擇。 NSC96 計劃中，我們以數位啁啾式堆疊量子點結構研製出增益頻寬超過 125nm 且具新奇發光特性之半導體量子點雷射。而NSC97 計畫中則以最佳化 量子點堆疊結構來研製具有實質寬頻的半導體寬頻光源。本年度目標將研製 可應用於光學斷層掃瞄系統之等效寬頻的掃頻式量子點光源。首先將以外腔 式架構實現波長可調量子點雷射，並量測此特殊堆疊量子點結構的波長可調 範圍；繼之，我們將繞射光柵架設在往復式快速掃瞄的裝置上，評估此外腔 式量子點雷射在最佳電流操作點下的波長掃描範圍及頻譜特性；最後將嘗試 研製量子點為主動區之多區段雷射共振腔結構，評估以光子晶體當作波長選 擇反射鏡並直接調變電流來實現波長可調及掃頻式光源的可行性，我們最終 希望將此元件交付生醫研發單位進行影像掃描的測試。

Optical coherence tomography (OCT) systems have attracted great attentions in bio-medical imaging in recent year. Light emitters for optical communication are therefore spotlighted because the optical communication wavelength band is coincident with the required emission wavelength band of the OCT. Of special interest is the long-wavelength semiconductor emitters based on gain medium of InAs quantum dots (QDs) grown on GaAs substrates. The inhomogeneous spectral broadening of self-assembled QDs is key to semiconductor broadband light sources. In NSC96, we have fabricated novel semiconductor lasers based on our digitally chirpy-stacked QD structure with gain bandwidth over 125 nm. While in NSC97, we will fabricate the semiconductor light emitters with broad emission spectrum based on the optimized QD structure. In this year of NSC98, we will develop wavelength tunable and swept QD light sources for Fourier Domain OCT. First, we will implement the tunable QD external cavity lasers with this specially designed QD structure and measure their wavelength tuning range. Then, swept QD external cavity lasers will be implemented by placement of diffraction grating on resonant scanner. The wavelength swept range and spectral characteristics will be evaluated under optimal operation current. Finally, we will carry out the feasibility study of tunable and swept light sources by multi-section QD lasers integrated with frequency-selective photonic crystal section and operated under direct current modulation. Our goal is to hand out the swept QD light sources to bio-medical research unit for OCT imaging test.