Continuous tuning of lasing wavelength is achieved in cholesteric liquid crystal lasers by embedding a network of nanopores with an average size of 10 nm filled with liquid crystals inside a polymerized matrix with helical order. The device possesses both high transparency and a fast response time because the tuning is driven by local reorientation of the liquid crystal molecules in the nanopores.
[Show abstract][Hide abstract] ABSTRACT: During the past decade, photonic band edge lasers based on cholesteric
liquid crystals (CLCs) have attracted considerable interest as
self-assembled coherent, tunable lights sources. We report on recent
progress towards practical applications: (i) Electrical fine tuning of
laser emission by in-plane electric fields: the field-induced distortion
of the cholesteric helix allows for a controllable, continuous and
reversible shift of the band edge resonances. (ii) Improvement of lasing
performance by application of an electric field along the helical axis
of a system with negative dielectric anisotropy: the electric field
stabilizes the soft photonic structure against heating-induced
distortions. (iii) PDMSenclosed LC lasers for lab-on-a-chip
applications: We demonstrate the formation of a uniform planar
cholesteric texture between polydimethylsiloxane (PDMS) substrates and
narrow-band laser emission of a PDMS-enclosed LC laser. With PDMS being
the standard material for the fabrication of microfluidic devices, this
opens a simple and flexible route for the integration of coherent light
sources in lab-on-a-chip designs.
Proceedings of SPIE - The International Society for Optical Engineering 03/2013; 8642:09-. DOI:10.1117/12.2008373 · 0.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Fast (∼10 μs) and deformation-free electro-optic tuning of a liquid crystal is reported, achieved by macroscopic alignment and switching of nanosized, pseudo-nematic domains. The tuning mode can be achieved by photopolymerizing a mesogenic monomer–liquid crystal mixture in the liquid crystal phase, and forming nanosized pores in the polymer matrix. This concept is particularly effective in liquid crystals with spontaneous structure-forming capabilities: here this concept is applied to a cholesteric liquid crystal and demonstrate scatter-free tuning of the Bragg reflection band. It can also lead to new device applications such as thin-film optical amplitude modulators and linear polarization rotators.
[Show abstract][Hide abstract] ABSTRACT: The combination of photoluminescence (PL) and cholesteric liquid crystal (CLC) provides interesting complementary features for an optimized display application. Distortion of the Bragg lattice of CLCs decreases selective reflection but increases fluorescence intensity; recovery of a uniform lattice in turn results in increased reflection and decreased fluorescence. This complementary relationship between the fluorescence and the Bragg reflection gives rise to self-compensations for color shifts due to either dynamic slow response of CLC helix or mismatch of oblique incidence of light with respect to the helical axis. These color shifts have long been intrinsic unsolved limitations of conventional CLC devices. Thus, the complementary coupling between the fluorescence and the CLC Bragg reflections plays an important role in improving the color performance and the quality of moving images.
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