Abstract
This study proposes a hybrid structure for a one-dimensional (1D) photonic crystal (PC) comprising a tristable cholesteric liquid crystal (CLC) as the defect layer. The CLC exhibits three optically stable states: the Grandjean planar (P), focal conic (FC), and uniform lying helix (ULH) configurations. Specifically, the reflection band of the CLC is set within the photonic bandgap (PBG) of the 1D PC. While the ULH and the FC states can be regarded as the light-on and light-off states for defect-mode peaks in the visible spectrum, respectively, switching the device from the ULH to the P state enables suppression of the transmission of partial defect modes within the PBG. This device possesses many alluring features, such as optical tristability at null applied voltage and transmission tunability of the defect modes, providing a new pathway for the design of multifunctional and energy-efficient optical switches, light shutters, multichannels, and wavelength selectors.
Highlights
Photonic crystals (PCs) have long been an intriguing research area in optics, since two pioneering works by Yablonovich [1] and John [2] were independently published in the late 1980’s
When a defect layer is inserted in a PC, defect-mode peaks in the spectrum, enabling the transmission of photons, will be generated within the photonic bandgap (PBG) as a result of breaking the structural periodicity
The tunability in defect-mode wavelength has been achieved in 1D PC hybrids, with a planar-aligned nematic and a twisted–nematic liquid crystal (LC) defect layer via the electrically/magnetically controlled birefringence and the adiabatic following effects, respectively [3,4,5]
Summary
Photonic crystals (PCs) have long been an intriguing research area in optics, since two pioneering works by Yablonovich [1] and John [2] were independently published in the late 1980’s. According to the orientation of molecular helical order direction (i.e., the helical axis), cholesteric textures—including the Grandjean planar (P), the focal conic (FC) and the fingerprint states—with distinct optical features have been well documented in the literature Both the P and FC textures are optically stable states in a planar-aligned CLC cell, and they are reversibly switchable by the electric field [17]. The ULH texture exhibits unidirectional helical axes aligned in parallel to the substrate plane, and behaves as a uniaxial optical plate cut along the optic axis, where the helical axis takes the role of the optic axis of the plate This texture does not scatter or reflect the incoming light, so its optical transparency is similar to that of the field-induced helix-free homeotropic (H) state of the cholesteric cell [18]. Potential applications of the proposed PBG structure are suggested, based on the electrical tunability and optical tristability of the spectral peaks of defect modes
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