一維光子晶體之超低閾值液晶缺陷模雷射

Abstract

本篇論文提出一非對稱型一維光子晶體與液晶之複合結構，增強了光子能隙內之缺陷模共振強度。本研究藉由兩片基板之光子能隙重疊於能隙邊緣處，由能隙邊緣光遲滯所引起之高光子狀態密度，實現高強度的光波局域化，於非對稱型結構能隙內之缺陷模穿透率為對稱型結構的5–10倍。吾人將此非對稱型一維光子晶體結構摻入液晶與染料缺陷層，應用於光子晶體缺陷模雷射，並比較非對稱型與對稱型之缺陷模雷射特性。根據研究成果表示，非對稱型一維光子晶體之複合結構成功地降低激發缺陷模雷射之能量閾值達20倍之多，同時可藉由電壓控制液晶分子使缺陷模移動，進而調控雷射波長。因此，此非對稱型一維光子晶體結構除了可應用於大功率輸出之可調式光子晶體雷射外，還可應用於窄頻高對比之光濾波器；若改變一維光子晶體之單層膜光學厚度，使得光子能隙之中心反射波長於紅外線波段，則可應用於光通訊之可調式通道選擇器。

In this thesis, a structure enabling enhancement of the local intensity of defect modes in the photonic bandgap is demonstrated by using asymmetric one-dimensional (1-D) photonic crystal (PC) with a liquid-crystal (LC) defect layer. The asymmetric PC structure consists of two multilayer substrates with overlapped bandgaps in the band edges. Owing to the high photon density of states at the photonic band edge, the resulting defect modes exhibit strong resonance in the overlapped region, giving a transmittance of five to ten times higher than that of a symmetric counterpart. Further, a comparison of the characteristics of defect-mode lasing was made between the asymmetric and symmetric 1D PC structures consisting of a dye-doped LC defect layer. We found that the lasing threshold of the asymmetric 1D PC structure to be twenty times lower than that of the symmetric one. The lasing peak can also be controlled by the applied voltage. Therefore, this asymmetric structure holds promise for high-power tunable PC lasers and high-contrast narrow band-pass filter. Besides, the central reflection wavelength can be tuned to the near-infrared region by modulating the optical thickness of the single layer coating in the multilayer for potential applications in tunable optical communication devices.