Liquid Crystal Defect Layer Research Articles

Hybrid Tamm and quasi-BIC microcavity modes.

The microcavity in the form of a liquid crystal defect layer embedded in a one-dimensional photonic crystal is considered. The microcavity mode has a tunable radiation decay rate in the vicinity of a bound state in the continuum. It is demonstrated that coupling between the microcavity mode and a Tamm plasmon polariton results in hybrid Tamm-microcavity modes with a tunable Q factor. The measured spectral features of hybrid modes are explained in the framework of the temporal coupled mode theory.

Tunable optical filter based on one-dimensional periodic structure composed of SiO2 and anisotropic metamaterial (AMM) with a liquid crystal defect layer sandwiched by two SiO2

This paper reports the tunable transmission properties of asymmetric one-dimensional periodic structure (1DPS) composed of SiO2 and anisotropic metamaterial (AMM) layers with defect of liquid crystal (LC) sandwiched by two SiO2 layers, i.e., (SiO[Formula: see text]AMM)[Formula: see text]SiO[Formula: see text]LC[Formula: see text]SiO[Formula: see text](SiO[Formula: see text]AMM)3 using the transfer matrix method (TMM). We have studied the optical properties of the periodic structure (SiO[Formula: see text]AMM)3 [Formula: see text]SiO[Formula: see text]LC[Formula: see text]SiO[Formula: see text](SiO[Formula: see text]AMM)3 with a different incident angle of the electromagnetic wave for particular director angle of LC molecules. The tunability of the transmission property of the considered 1DPS shows that the transmittance depends upon the orientation of LC molecules. Such an asymmetric periodic structure (1DPS) composed of SiO2 and AMM with a defect of LC sandwiched by two SiO2 layers, (SiO2 [Formula: see text]AMM)[Formula: see text]SiO[Formula: see text]LC[Formula: see text]SiO[Formula: see text](SiO[Formula: see text]AMM)3, may be used as a tunable optical filter and bi-stable device.

Tunable transmission of a nematic liquid crystal as defect in a 1D periodic structure of dielectric materials by orientation and re-orientation of liquid crystal molecules.

In this paper, we investigate tunable transmission characteristics of a one-dimensional periodic structure (1DPS), designed with periodic dielectric materials containing a nematic liquid crystal (NLC) as a defect layer, on the basis of orientation and re-orientation of LC molecules. The nonlinear differential equation for the director of the liquid crystal under the light field is solved numerically. The relation between the liquid crystal director and the intensity of the electromagnetic wave (EMW) is derived. Transmittances of the liquid crystal defect layer in the 1DPS are calculated with the variation of the intensity of the incident wave and liquid crystal director tilt angles. By varying the director tilt angle of the liquid crystal molecules as well as the incident angle of the EMW, the shifting of the transmitted defect mode wavelengths is studied. Such study is helpful to understand how orientation and reorientation of the molecules affect the transmittance of the considered periodic structure when the EMW interacts with an embedded liquid crystal as a defect layer in the 1DPS of dielectric materials. Such photonic structure of dielectric materials with the liquid crystal layer as a defect layer can be used to fabricate bistable switches, optical filters, feedback lasers, etc.

Optical defect mode with tunableQfactor in a one-dimensional anisotropic photonic crystal

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 an anisotropic defect layer is inserted into the structure, the crystal can support an optical bound state in the continuum. By tilting the principle dielectric axes of the defect layer relative to those of the photonic crystal we observe a long-lived resonance in the transmission spectrum. We derive an analytical expression for the decay rate of the resonance that agrees well with the numerical data by the Berreman anisotropic transfer matrix approach. An experimental set-up with a liquid crystal defect layer is proposed to tune the Q-factor of the resonance through applying an external electric field. We speculate that the set-up provides a simple and robust platform for observing optical bound states in the continuum in the form of resonances with tunable Q-factor.

Temperature control of the ultra-short laser pulse compression in a one-dimensional photonic band gap structure with nematic liquid crystal as a defect layer

We investigate numerically the controllable chirped pulse compression in a one-dimensional photonic structure containing a nematic liquid crystal defect layer using the temperature dependent refractive index of the liquid crystal. We consider the structure under irradiation by near-infrared ultra-short laser pulses polarized parallel to the liquid crystal director at a normal angle of incidence. It is found that the dispersion behaviour and consequently the compression ability of the system can be changed in a controlled manner due to the variation in the defect temperature. When the temperature increased from 290 to 305 K, the transmitted pulse duration decreased from 75 to 42 fs in the middle of the structure, correspondingly. As a result, a novel low-loss tunable pulse compressor with a really compact size and high compression factor is achieved. The so-called transfer matrix method is utilized for numerical simulations of the band structure and reflection/transmission spectra of the structure under investigation.

Electrically Rotatable Polarizer Using One-Dimensional Photonic Crystal with a Nematic Liquid Crystal Defect Layer

Polarization characteristics of defect mode peaks in a one-dimensional (1D) photonic crystal (PC) with a nematic liquid crystal (NLC) defect layer have been investigated. Two different polarized defect modes are observed in a stop band. One group of defect modes is polarized along the long molecular axis of the NLC, whereas another group is polarized along its short axis. Polarizations of the defect modes can be tuned by field-induced in-plane reorientation of the NLC in the defect layer. The polarization properties of the 1D PC with the NLC defect layer is also investigated by the finite difference time domain (FDTD) simulation.

Spatial and electrical switching of defect modes in a photonic bandgap device with a polymer-dispersed liquid crystal defect layer.

This paper investigates the spectral properties of a one-dimensional photonic crystal (PC) containing an inhomogeneous polymer- dispersed liquid crystal (PDLC) as a defect layer. Experimental results indicate that the voltage-induced reorientation of LC molecules between the light-scattering and transparent states in the PDLC enables the electrical tuning of the transmittance of defect-mode peaks in the spectrum of the PC/PDLC cell. Specifically, owing to the unique configuration of the spatial distribution of LC droplet sizes in the defect layer, a concept concerning the spatial switching in the wavelength of defect modes is proposed. As a result, the PC/PDLC hybrid cell is suggested as a potential element for realizing an electrically tunable and spatially switchable photonic bandgap device, which is polarizer-free and requires no alignment layers in the fabrication process.

Temperature dependent transmission and optical bistability in a 1D photonic crystal with a liquid crystal defect layer

The transmission properties of a one-dimensional periodic structure with anisotropic defect layer is investigated using a transfer matrix method. A layer of homogeneously aligned nematic liquid crystal is taken as a defect. We show that the frequency and polarization of the defect mode is modified by changing the operating temperature and liquid crystal orientation. Also the temperature dependent nonlinear response of the defect structure is investigated. It is shown that the threshold intensity needed to achieve the bistability depends on the operating temperature. So, the structure can be used as a thermal switch at the frequency near the defect mode.

Tunable multifunctional magneto-optical devices based on magnetophotonic crystals comprising liquid crystal defect layers

In this paper, we are going to demonstrate how realization of tunable magnetophotonic crystals (MPCs) is possible through introduction and investigation of a couple of structures containing a single liquid crystal (LC) defect layer. Our starting point is the recently discussed issue according to which in such structures any alteration in optical characteristics of the LC component will cause changes to happen regarding the overall magneto-optical (MO) response of the LC-based MPC. It will be shown that our optimized MPC structures are not only powerful in most respects but also multifunctional. For instance, while a structure is capable of being operated as a sensing tool with regard to the very factor that tends to control its MO response, other modes of operation offer a function of a switchable optical filter and also a perfect MO isolator.

The Defect Modes Property Controlled by Temperature in One Dimensional Photonic Crystal with Liquid Crystal Defect Layer

The 5CB liquid crystal as defects will be introduced to one dimensional photonic crystal, taking advantage of temperature property of liquid crystal refractive index, the transmission spectrum of one dimensional liquid crystal defect photonic crystal defect modes was researched by the transfer matrix method(TMM). The numerical results indicated that when the temperature went up, one dimensional liquid crystal defect photonic crystal defect modes removed towards the long wavelength. When the temperature increased from 273k to 320k, the defect modes wavelength from 5121nm drifted to 5508nm, the wavelength shift was 387nm and the maximum of temperature sensitivity was 10.85nm/K, it was also observed that the temperature sensitivity decreased as the temperature increased.

Investigation of the tunable laser of one-dimensional photonic crystal with dye-doped nematic liquid crystal defect layer

We investigate the optical characteristics of the tunable laser of a one-dimensional photonic crystal (1D PC) containing Dye-doped nematic liquid crystal (NLC). The dielectric multilayer consisting of an alternating stack of SiO2 and TiO2 layers is used as the 1D PC whose defect layer is filled with the laser dye and NLC. The central wavelength of the stop band of the 1D PC is 650 nm. A second-harmonic light of a Q-switched Nd: YAG laser has a wavelength of 532 nm, and is used for excitation. With the temperature increasing from 25.5 ℃ to 48 ℃, the emission wavelength of the tunable laser is continuously shifted from 605.5 to 639.8 nm, the total wavelength shifts is 34.4 nm. With the external voltage increasing from 0 to 2.86 V, the emission wavelength of the tunable laser is shifted from 634.5 to 619.5 nm, the total wavelength shifts are 15 nm. The lasing threshold was about 12.3 J/pulse, and the linewidth of the emission peak was less than 1 nm.

Optomechanics of liquid crystals for dynamical optical response of photonic structures

We show that the mechanical effect of light on the orientational ordering of the crystallineaxis of a mesophase can be used to control the dynamics of the optical response of liquidcrystal infiltrated photonic structures. The demonstration is made using a one-dimensionalperiodic structure whose periodicity is broken by the presence of a nematic liquid crystaldefect layer. In this study we report on output light polarization and/or intensity dynamicsthat depend on the initial molecular ordering and incident light wavelength and intensity.

Reversible optical nonreciprocity in periodic structures with liquid crystals

We demonstrate how to achieve reversible nonreciprocal optical response in a periodic photonic structure with a pair of defects, one of them being a nonlinear liquid crystal defect layer. The twin defect structure is symmetric at low intensity and becomes asymmetric above an intensity threshold that corresponds to the optical reordering of the liquid crystal. We show that nonreciprocal effects can be reversed by changing the wavelength as a consequence of the wavelength dependent light localization at the defect mode inside the structure.

Optical Properties of a One-Dimensional Photonic Crystal Containing a Twisted Nematic Liquid Crystal Defect Layer

We analyze the optical properties of a one-dimensional photonic crystal containing a twisted nematic liquid crystal (NLC) defect layer. For randomly polarized light incidence, two photonic defect modes were found to appear in the photonic band gap of the one-dimensional photonic crystal, and were associated either with the molecular long axis experiencing the averaged extraordinary refractive index or the molecular short axis experiencing the averaged ordinary refractive index, of the defect NLC layer. Numerical analyses also revealed that the transmitted light at the defect mode is linearly-polarized light at an angle which is determined both from the twist angle of the twisted NLC and the resulting optical rotatory power. When the thickness of the defect layer is sufficiently thin, optical rotation can be ignored and the output polarization angle is at half the twist angle for the long axis mode and at 90 degrees to that for the short axis mode.

Analysis of defect mode switching response in one-dimensional photonic crystal with a nematic liquid crystal defect layer

We analyze the dynamic response and optical properties of a high-speed defect mode switching that is based on a tunable defect mode in a one-dimensional photonic crystal with a nematic liquid crystal defect layer. The electro-optic responses of the defect mode switching are calculated considering the director distributions in the defect layer, which are determined using continuum theory. The calculated defect mode switching exhibits a response on the order of microseconds in spite of the use of the reorientation of nematic liquid crystal molecules. From the calculation, it is found that the fast response is realized using a narrow peak shift and a fast part of the molecular reorientation. Furthermore, the dependences of the switching response are clarified on several physical parameters.

Low Driving Voltage Tunable Laser Based on One-dimensional Photonic Crystal Containing Liquid Crystal Defect Layer

ABSTRACT Electrical tuning of a wavelength of a defect mode lasing in a one-dimensional periodic structure has been demonstrated using a dye-doped nematic liquid crystal as a defect layer in the periodic structure. Lasing wavelength is widely tuned upon applying the electric field, which is due to the refractive index change in the defect layer caused by the field-induced realignment of the liquid crystal molecules.

Laser Action Based on Electrically Controllable Defect Mode in One-Dimensional Photonic Crystal Containing Conducting Polymer and Liquid Crystal Defect Layers

ABSTRACT Electrical tuning of the wavelength of a defect mode lasing in a one-dimensional photonic crystal has been demonstrated using a conducting polymer as an active emission layer and a nematic liquid crystal as an electrically tunable defect layer in the periodic structure. Lasing wavelength is widely tuned upon applying the electric field, which follows a defect mode shift due to the refractive index change in the nematic liquid crystal defect layer caused by field-induced realignment of the liquid crystal molecules.

Tunable Defect Mode in One-Dimensional Photonic Crystal with Liquid Crystal Defect Layer

ABSTRACT Electrical tuning of defect modes in a one-dimensional (1D) photonic crystal (PC) has been demonstrated using a ferroelectric liquid crystal (FLC) and a nematic liquid crystal (NLC) defect layers in the periodic structure. The transmission peak intensities for defect mode depends on the angle between LC molecular axis and polarization direction of the incident light. At defect mode wavelength, the 1D PC with LC defect layer transmits only the light with the polarization direction determined by the direction of extraordinary or ordinary optical axes in LC defect. Polarization direction of the light propargating through the 1D PC with in-plane NLC defect can be controlled based on field-induced in-plane realignment of NLC molecules.

Light propagation analysis and high‐speed electro‐optic switching in one‐dimensional photonic crystal with nematic liquid crystal defect layer

AbstractIt is possible by the application of voltage to control the local level in a one‐dimensional photonic crystal with a liquid crystal defect layer. In the present paper, a nematic liquid crystal is used and high‐speed switching is attempted on the basis of the shift of the localized state wavelength by the photonic bandgap and liquid crystal orientation control. First, by the finite‐difference time‐domain method, the optical propagation characteristics inside a one‐dimensional photonic crystal with a liquid crystal defect layer are analyzed. It is shown that optical switching by control of the localized state wavelength is possible. TiO2 and SiO2 are periodically laminated as a one‐dimensional photonic crystal. A nematic liquid crystal layer is introduced as a defect layer to disturb the periodicity, resulting in a one‐dimensional photonic crystal with a liquid crystal defect layer. By application of a voltage, the orientation of the liquid crystal defect layer is varied in an attempt to perform optical switching by electric field control of the localized state. High‐speed optical switching of microsecond order is successful with nematic liquid crystals. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 88(4): 46–53, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20087

Effect of Phase Retardation on Defect‐Mode Lasing in Polymeric Cholesteric Liquid Crystals

Lasing via a phase retardation defect modeis reported for the first time. The Figure shows the far‐field pattern of laser emission realized by inserting an anisotropic nematic liquid crystal (LC) defect layer between polymer cholesteric LC layers. The system mimics the cuticle ofPlusiotis resplendens, a beetle, using the birefringence of the anisotropic layer to achieve reflectance greater than the 50 % provided by simple cholesteric LC photonic bandgaps.