Spatially Tunable Lasing Emission in Visible Region Based On Refilled Liquid Crystal Template Technique

Abstract

A spatially tunable photonic band-gap (PBG) and laser device whose tuning range can almost cover the entire visible region is successfully developed in this study through the cholesteric liquid crystal (CLC) polymer template refilling technique The device is fabricated in four stages namely the before-curing after-curing after-washing-out and after-refilling stages Experiment results show that the tunable spectral range for the PBG of the device covers nearly the entire visible region (409 nm to 775 nm) After refilling the template with a dye-doped nematic LC (DDNLC) which includes two types of dyes a broad fluorescence spectrum that almost covers the entire visible region is obtained via F?rster energy transfer effect resulting in a spatially tunable laser that can lase from the blue to the red regions (483 18 nm to 633 73 nm) In addition the spatially tunable laser mode between the single- and the multi-mode bandedge laser modes can be converted by varying the temperature The key to the laser-mode conversion is the birefringence of the refilled LC When the DDNLC that is refilled into the nanopores of the template is in the nematic phase the effective refractive indices of the LCs become slightly different across various nanopores of the template on the pumped region These cause multiple domains with slightly reduced PBG and band edge that in turn lead to multi-mode bandedge lasing emission After heating the refilled LCs to the isotropic phase the refractive indices in these nanopores at various positions of the template become identical resulting in the single-mode bandedge lasing emission In addition to the DDNLC-refilled single CLC template device the fabrication of a spatially tunable DDNLC-refilled merged cell which consists of two CLC templates with right and left handednesses is also achieved in this study This merged cell is hyper-reflective in the entire visible region and can provide an efficient resonance for either right- or left-circular fluorescence for lasing emission thus leading to a lower lasing threshold compared with that of the refilled single CLC template cell The refilled merged laser device possesses many advantages such as high stability lasing-mode convertibility wide tunabilities in both lasing wavelength and PBG and simultaneous right- and left-circularly polarized lasing output Thus the merged laser device has a high potential for applications in the fields of photonics optical communications and display

Date of Award	2015 Sept 7
Original language	English
Supervisor	Chia-Rong Lee (Supervisor)