In 1985 Fridriech and Wintgen proposed a mechanism for bound states in the continuum based on full destructive interference of two resonances which can be easily applied to the two- and three-dimensional wave systems. Here we explicitly show that this mechanism can be realized in one-dimensional quantum potential well, owing to destructive interference of electron paths with different spin in tilted magnetic field. Due to one-by-one correspondence between the spin of the electron and the polarization state of light, we have found numerous bound states in the continuum in the one-dimensional photonic system and experimentally confirmed them. The experimental set-up consists of the one-dimensional photonic crystal conjugated with a liquid-crystalline anisotropic defect layer and covered by metal film.

We consider a one-dimensional photonic crystal composed of alternating layers of isotropic and anisotropic dielectric materials. Such a system has different band structures for different polarizations of light. We demonstrate that if a defect layer is inserted into the structure, the crystal can support a polarized optical defect mode that is a bound state in the continuum (BIC). In the case of an anisotropic defect layer, by tilting the principle dielectric axes of the defect layer relative to those of the photonic crystal the BIC is transformed to a quasi-BIC. We derive an analytical expression for the decay rate of the resonance. An experimental setup with a liquid crystal defect layer is proposed to tune the $Q$ factor of the quasi-BIC through applying an external electric field. We speculate that the setup provides a simple and robust platform for observing optical bound states in the continuum in the form of resonances with tunable $Q$ factor.

Optical Tamm states localized at the edges of a photonic crystal bounded from one or both sides by a nanocomposite have been studied. The nanocomposite consists of metallic nanoinclusions, which have...

We propose to dynamically control the reflective color of a cholesteric liquid crystal (CLC) by electrically tuning the center wavelength (${\lambda }_{\text{c}}$) of the bandgap. The CLC, sandwiched in a planar-aligned cell with indium–tin-oxide electrodes, possesses negative dielectric anisotropy and thermo-responsive spectral properties. The helix in the Grandjean planar state, which is subject to vertically applied voltage, should be undisturbed in that the long molecular axis is initially perpendicular to the direction of the electric field. Surprisingly, when the frequency of the applied voltage is higher than a critical value, ${\lambda }_{\text{c}}$ of the CLC cell varies as a function of the voltage. The underlying mechanism is the voltage-induced temperature change through dielectric heating in the frequency regime of pseudo-dielectric relaxation, attributable to the significant equivalent resistance–capacitance circuit of the cell due to the use of electrode layers with finite conductance. The driving voltage enabling the tuning of ${\lambda }_{\text{c}}$ in the entire visible spectrum is as low as $12{\mathrm{V}}_{\mathrm{rms}}$ in a 5 μm thick cell at a frequency of 2 MHz. The proposed CLC cell, exhibiting a broad electrically tunable spectral range from the near-infrared to ultraviolet, holds great promise for developing tunable photonic devices such as multicolor reflectors, filters, and sensors.