We report a room-temperature dual-frequency field assembly technique that is capable of fabricating large-areal size (~cm2 or larger), well-aligned cholesteric liquid crystals to thicknesses up to 2.2 mm, corresponding to period number N (thickness/index grating period) of nearly10,000 in the visible spectral regime. The method employs successive application of low- and high- frequency electric field on a thick cell of CLC starting mixture containing a nematic constituent of negative anisotropy. The low-frequency field creates conductive hydrodynamical instabilities that mash the mixture to a state with completely randomized orientation of the cholesteric helices; the next application of a high-frequency field at a field strength below the dielectric hydrodynamic instability reorient all the helices into uniform standing helices. Such extraordinarily thick chiral photonic crystals exhibit many never-before-realized chiral photonic properties such as giant rotation of optical polarization with high transmission (low scattering loss), polarization switching and ultrafast pulse modulation capabilities for visible to mid-infrared lasers, in addition to dynamic tunability by electrical, thermal, or optical means.
By virtue of their constituents’ soft matter attributes and easy susceptibilities to applied fields, liquid crystalline chiral photonic crystals exhibit highly tunable linear and nonlinear optical properties that allow applications throughout a very wide spectrum. In particular, nearly-mm thick 1-D chiral photonic crystals fabricated with cholesteric liquid crystal are shown to be capable of polarization rotation and switching of complex laser vector fields with response times that can be as fast as sub-picoseconds, and operating wavelength ranging from the visible to near- and mid-IR range. [Ref.: Nature Comm. 8, Article number: 727 (2017); PNAS 2021, 118 (16)].
An electrically tunable achromatic polarization rotator has been developed based on the hybrid splay-twist (HST) and hybrid-aligned super twist (HAST) liquid crystal. The continuous angular rotation, and achromatic operation across the entire visible spectrum. The tuning range of the polarization rotator is up to 90° or to 180° and the degree of linear polarization (DOLP) remains. Based on the HST-LC, the multi-functional smart glass is realized with light field, dimming and scattering control. This work provides possibilities in the design of optical systems and spatially polarization multiplexing elements. The designed smart glass provides novelties in smart (green) architecture.
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