Victor Ya. Zyryanov

Electro-optical device based on photonic structure with a dual-frequency cholesteric liquid crystal

An electrically tunable and polarizer-free photonic device is developed using a one-dimensional photonic crystal (PC) infiltrated with dual-frequency cholesteric liquid crystal (DFCLC) as a defect layer. The PC/DFCLC hybrid cell allows the employment of various frequency-modulated voltage pulses to regulate defect modes and switch between stable states. This device possesses many alluring features such as rapid bistable switching, intensity tunability, and wavelength tunability in the defect modes, and it requires no polarizers. It can be used as a filter, fast-speed shutter, or light-intensity modulator.

Multichannel photonic devices based on tristable polymer-stabilized cholesteric textures

We demonstrate in this paper an electrically tunable photonic device based on one-dimensional photonic crystal (PC) infiltrated with polymer-stabilized cholesteric texture (PSCT) as a central defect layer. With the hybrid PC/PSCT structure, not only is the wavelength of each defect mode switchable among three major stable states by various appropriate frequency-modulated voltage pulses, but also the intensity can be electrically tuned in multi-metastable states. As a result, an electrically controllable multichannel photonic device with several alluring features is proposed. It is wavelength-switchable, intensity-tunable, and polarizer-free and possesses optical tristability in the defect modes to reduce power consumption.

Tunable bi-functional photonic device based on one-dimensional photonic crystal infiltrated with a bistable liquid-crystal layer.

We investigated the optical properties of a one-dimensional photonic crystal infiltrated with a bistable chiral tilted homeotropic nematic liquid crystal as the central defect layer. By modulating the nematic director orientation with applied voltage, the electrical tunability of the defect modes was observed in the transmission spectrum. The composite not only is a general tunable device but also involves the green concept in that it can operate in two stable states at 0 V. Under the parallel-polarizer scheme, the spectral characteristics suggest a potential application for this device as an energy-efficient multichannel optical switch.

Spectral modulation of a bistable liquid-crystal photonic structure by the polarization effect

The light polarization has an effect on spectral properties of a multilayered photonic crystal infiltrated with a bistable chiral-tilted homeotropic nematic liquid crystal (LC) as a defect layer. By varying the direction of polarization of incident, linearly polarized light interacting with the birefringent LC, the tunability of defect modes in wavelength and amplitude and the broadening of the low-transmittance range can be realized in the transmission spectrum. The LC features two optically stable states and two voltage-sustained states. The bistability makes the device of low energy consumption. Such a hybrid can be used as not only a wavelength selector, optical shutter or multichannel switch but also a stopband-tunable device.

Optical properties of one-dimensional photonic crystal with a twisted-nematic defect layer

Spectral properties of an electrically tunable one-dimensional photonic crystal infiltrated with a twisted-nematic liquid crystal (PC/TN) are investigated. Two mesogenic materials with dissimilar optical anisotropies are examined for constituting the central defect layer. With the TN alignment of the defect layer embedded in the dielectric multilayers, the defect modes not only shift with the applied voltage but also switch between two major modes when the linear polarization angle of the incident light is altered. The superposition of the mixed-mode TN (MTN) and the photonic bandgap brings out a tremendous undulation in all range of the transmission spectrum. The defect modes falling at the centers of the MTN spectral humps are allowed to intensely transmit while the others are suppressed. As a result, we propose a monochromatic selector constructed by such a PC/MTN device with electrical tunability.

Bipolar Nematic Droplets with Rigidly Fixed Poles in the Electric Field

Abstract We have studied theoretically the reorientation process induced by the electric field inside a bipolar nematic droplet with rigidly fixed poles. Computer simulation has revealed the threshold director reorientation only in that part of a droplet, where the LC director is orthogonal to the applied field, and the nonthreshold reorientation in the rest of the droplet volume. A formula has been proposed to estimate the threshold field. The data obtained have allowed us to calculate a PDLC film transmittance in the framework of the anomalous diffraction approach and to interpret the oscillating behavior of the volt-contrast curve observed experimentally.

Electro-optical response of an ionic-surfactant-doped nematic cell with homeoplanar–twisted configuration transition [Invited]

This study is concerned with the optical response of an electro-optical material consisting of nematic liquid crystal as well as ionic surfactant as a dopant. The dopant is a key component to carry out the working of the resulting device through configuration switching. The operational principle is based on the surface anchoring transition induced by a steady electric field. The dynamic characteristics of the electro-optical cell can be considerably improved when the nematic layer is reoriented from the initially homeoplanar director configuration into the twisted state. Besides, a method to shorten the relaxation time is demonstrated by using a controlling pulse with a bipolar waveform.

Voltage-induced defect mode coupling in a one-dimensional photonic crystal with a twisted-nematic defect layer.

Defect modes are investigated in a band gap of an electrically tunable one-dimensional photonic crystal infiltrated with a twisted-nematic liquid crystal. Their frequency shift and interference under applied voltage are studied both experimentally and theoretically. We deal with the case where the defect layer thickness is much larger than the wavelength (i.e., the Mauguin condition). It is shown theoretically that the defect modes could have a complex structure with elliptic polarization. Two series of polarized modes are coupled with each other and exhibit an avoided crossing phenomenon in the case of opposite parity.

Switching of Defect Modes in a Photonic Structure with a Tristable Smectic-A Liquid Crystal

College of Photonics, National Chiao Tung University, Guiren District, Tainan, Taiwan 71150, R.O.C.Received May 31, 2012; accepted June 28, 2012; published online July 19, 2012A one-dimensional (1D) photonic crystal (PC) optical device based on smectic-A (SmA) liquid crystal (LC) as a defect layer is proposed. Thereversible tristability of the SmA LC is used to realize a low-energy-consumption device. With a voltage-induced scattering state, the PC–SmAhybrid cell can work as a polarizer-free optical switch. The variation of the effective refractive index of the LC substance enables the defect modesto appear at variable wavelengths, changing with the voltage-induced reorientation of the LC director. As a result, an electrically and thermallytunable multichannel optical device is achieved using this hybrid, optically tristable structure. # 2012 The Japan Society of Applied Physics

Chiral Optical Tamm States: Temporal Coupled-Mode Theory

The chiral optical Tamm state (COTS) is a special localized state at the interface of a handedness-preserving mirror and a structurally chiral medium such as a cholesteric liquid crystal or a chiral sculptured thin film. The spectral behavior of COTS, observed as reflection resonances, is described by the temporal coupled-mode theory. Mode coupling is different for two circular light polarizations because COTS has a helical structure replicating that of the cholesteric. The mode coupling for co-handed circularly polarized light exponentially attenuates with the cholesteric layer thickness since the COTS frequency falls into the stop band. Cross-handed circularly polarized light freely goes through the cholesteric layer and can excite COTS when reflected from the handedness-preserving mirror. The coupling in this case is proportional to anisotropy of the cholesteric and theoretically only anisotropy in magnetic permittivity can ultimately cancel this coupling. These two couplings being equal result in a polarization crossover (the Kopp–Genack effect) for which a linear polarization is optimal to excite COTS. The corresponding cholesteric thickness and scattering matrix for COTS are generally described by simple expressions.