Browsing by Author "Timofeev, Ivan V."

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Chiral Optical Tamm States: Temporal Coupled-Mode Theory
(2017-04-01)
Timofeev, Ivan V.
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Pankin, Pavel S.
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Vetrov, Stepan Ya.
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Arkhipkin, Vasily G.
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Lee, Wei
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.
Dynamic Tuning and Memory Switching of Defect Modes in a Hybrid Photonic Structure
(2016-10-01)
Wang, Hsiao-Tsung
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Wu, Po-Chang
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Timofeev, Ivan V.
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Zyryanov, Victor Ya.
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Lee, Wei
We propose a memorable and electrically tunable photonic device by infiltrating a dual-mode chiral-doped dual-frequency liquid crystal (LC) as the central defect layer in a one-dimensional photonic crystal (PC). According to the transmission properties of this structure, the wavelength tunability of defect modes is obtained by manipulating the LC layer in the dynamic mode due to the electrically controlled birefringence effect. Moreover, the switching between two memorable states, the splay and pi-twist states, creates two distinct sets of defect modes at null voltage. The spectral characteristics of this device ensure its potential application as an energy-efficient multichannel wavelength filter.
Electro-optical and dielectric properties of polymer-stabilized blue phase liquid crystal impregnated with a fluorine-containing compound
(2018-10-01)
Wu, Po-Chang
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Chen, Hsin-Li
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Rudakova, Natalya V.
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Timofeev, Ivan V.
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Zyryanov, Victor Ya.
The effects of a fluorine-containing compound (4,4'-difluorobenzophenone; DF) on the electro-optical and dielectric properties of polymer-stabilized blue phase (PSBP) liquid crystals were investigated. When a PSBP cell was driven by an in-plane electric field, the addition of DF up to 2.7 wt% effectively reduced the operation voltage by-30%. Further inspection by dielectric spectroscopy indicated that the ionic concentration in PSBP decreased with increasing loading of OF. This finding can be ascribed to the complexation of impurity ions near the ketone group and carbon-fluorine bonds of the DF compound that restrained the ion transport after photopolymerization. As a result, the DF compound can be regarded as a superior ion-suppressor, enabling the reduction in the ionic effect and, in turn, the promotion of the electro-optical response of a PSBP. (C) 2017 The Authors. Published by Elsevier Inc.
Electro-thermally tunable reflective colors in a self-organized cholesteric helical superstructure
(2018-12-01)
Wu, Po-Chang
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Wu, Guan-Wei
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Timofeev, Ivan V.
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Zyryanov, Victor Ya.
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Lee, Wei
We propose to dynamically control the reflective color of a cholesteric liquid crystal (CLC) by electrically tuning the center wavelength (lambda(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 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 c in the entire visible spectrum is as low as 12 V-rms in a 5 pin 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. (C) 2018 Chinese Laser Press
Enhanced light absorption with a cholesteric liquid crystal layer
(2013-04-01)
Timofeev, Ivan V.
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Arkhipkin, Vasily G.
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Vetrov, Stepan Ya
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Zyryanov, Victor Ya
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Lee, Wei
We discuss the trapping features of cholesteric liquid crystal as a self-organized photonic crystal and suggest it for absorption improvement. The imperfection of the absorbing surface is manifested by the reflection originating from the indispensable impedance mismatch. The reflection can be suppressed by an additional surface coating to reflect the light back to the absorber once again. In the simple consideration this reflection loop is possible only twice. For a right-handed CLC coating, the boundary reflection switches the light polarization from left to right circular in the first loop and it switches in the second loop back to the left circular polarization before the emerging light finally escapes from the absorbing process. The enhancement of light absorption is possible in the frequency range as large as the photonic bang gap of the cholesteric layer, which can be adjusted as desired. (C) 2013 Optical Society of America
Geometric phase and o-mode blueshift in a chiral anisotropic medium inside a Fabry-Perot cavity
(2015-11-24)
Timofeev, Ivan V.
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Gunyakov, Vladimir A.
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Sutormin, Vitaly S.
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Myslivets, Sergey A.
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Arkhipkin, Vasily G.
Anomalous spectral shift of transmission peaks is observed in a Fabry-Perot cavity filled with a chiral anisotropic medium. The effective refractive index value resides out of the interval between the ordinary and the extraordinary refractive indices. The spectral shift is explained by contribution of a geometric phase. The problem is solved analytically using the approximate Jones matrix method, numerically using the accurate Berreman method, and geometrically using the generalized Mauguin-Poincare rolling cone method. The o-mode blueshift is measured for a 4-methoxybenzylidene-4'-n-butylaniline twisted-nematic layer inside the Fabry-Perot cavity. The twist is electrically induced due to the homeoplanar-twisted configuration transition in an ionic-surfactant-doped liquid crystal layer. Experimental evidence confirms the validity of the theoretical model.
Hybrid anchoring for a color-reflective dual-frequency cholesteric liquid crystal device switched by low voltages
(2015-11-01)
Hsiao, Yu-Cheng
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Timofeev, Ivan V.
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Zyryanov, Victor Ya
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Lee, Wei
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影像與生醫光電研究所
Cholesteric liquid crystal (CLC) materials used in electro-optical (EO) devices are characterized by high operating voltage and slow response speed, which hinders their further development in display applications. Dual-frequency CLCs (DFCLCs) can solve the problem of slow bistable transition, but the operating voltage is still high, especially in color-reflective DFCLC cells. Here we report a simple approach to lowering the switching voltage as well as to shortening the response time. This technique adopts hybrid surface treatment to modulate the structural arrangement of CLC molecules. Both planar-and vertical-alignment layers are employed and coated on one and the other substrates separately to improve the electro-optical properties of DFCLCs. We show that the threshold voltage for switching can be decreased to as low as 5 V and the shortest response time is measured to be 0.8 ms, which renders CLC EO devices including displays more practical for commercial purpose. (C) 2015 Optical Society of America
Narrowband Wavelength Selective Thermal Emitters by Confined Tamm Plasmon Polaritons
(2017-09-01)
Yang, Zih-Ying
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Ishii, Satoshi
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Yokoyama, Takahiro
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Thang Duy Dao
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Sun, Mao-Guo
This study experimentally demonstrates infrared wavelength selective thermal emission based on Tamm plasmon polaritons (TPPs). Unlike conventional TPP structures, which have a thin metal layer on a distributed Bragg reflector (DBR), the proposed structure has a thick metal under a DBR that is more robust for thermal radiation. The number of DBR pairs is a critical factor in maximizing the narrowband emission needed to satisfy the impedance matching condition, which varies with the choice of metal film. Optimum designs for four different metals, aluminum, gold, molybdenum, and tungsten, are presented. The temporal coupled-mode theory was introduced to explain the origin of the high Q-factor of the proposed structure, which can achieve a twice higher Q factor for the measured emissivity compared to typical plasmonic thermal emitters. The structure is one-dimensional, consisting of only multilayers and free from nanopatterning, offering a practical design in applications such as gas sensing, narrowband IR sources, and thermophotovoltaics.
Optical Tamm states at the interface between a photonic crystal and an epsilon-near-zero nanocomposite
(2017-08-01)
Vetrov, Stepan Ya
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Bikbaev, Rashid G.
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Rudakova, Natalya V.
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Chen, Kuo-Ping
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Timofeev, Ivan V.
The spectral properties of a one-dimensional photonic crystal bounded with a resonance-absorbing nanocomposite layer are investigated. The bulk concentrations of metal nanoparticles dispersed in a transparent nanocomposite matrix are determined at which the effective permittivity takes near-zero values. The transmission, reflection and absorption spectra of the investigated structures at the normal incidence of light are calculated. The demonstrated possibility of formation of the optical Tamm states at the interface between the photonic crystal and nanocomposite is ensured by the near-zero real and imaginary parts of the permittivity or only the imaginary part of the permittivity at the zero real part. The specific features of field localization at the optical Tamm state frequencies are examined.
Photo-manipulated photonic bandgap devices based on optically tristable chiral-tilted homeotropic nematic liquid crystal
(2016-10-31)
Huang, Kuan-Chung
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Hsiao, Yu-Cheng
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Timofeev, Ivan V.
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Zyryanov, Victor Ya.
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Lee, Wei
We report on the spectral properties of an optically switchable tristable chiral-tilted homeotropic nematic liquid crystal (LC) incorporated as a tunable defect layer in one-dimensional photonic crystal. By varying the polarization angle of the incident light and modulating the light intensity ratio between UV and green light, various transmission characteristics of the composite were obtained. The hybrid structure realizes photo-tunability in transmission of defect-mode peaks within the photonic bandgap in addition to optical switchability among three distinct sets of defect modes via photoinduced tristable state transitions. Because the fabrication process is easier and less critical in terms of cell parameters or sample preparation conditions and the LC layer itself possesses an extra stable state compared with the previously reported bistable counterpart operating on the basis of biased-voltage dual-frequency switching, it has much superior potential for photonic applications such as a low-power-consumption multichannel filter and an optically controllable intensity modulator. (C) 2016 Optical Society of America
Tunable narrow-bandpass filter based on an asymmetric photonic bandgap structure with a dual-mode liquid crystal
(2014-06-16)
Wang, Hsiao-Tsung
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Timofeev, Ivan V.
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Chang, Kai
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Zyryanov, Victor Ya.
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Lee, Wei
A one-dimensional asymmetric photonic crystal with dual-frequency liquid crystal as a central defect layer was demonstrated. Such asymmetric structure was characterized by the dramatic increase in intensity of the electric field of light localized at the overlapped photonic bandgap edges, thereby enhancing the observed transmittance of the spectral windows originating from the defect layer. The defect layer was made of a dual-mode liquid crystal that exhibited not only electrical tunability and switchability but also optical bistability. Consequently, tunable and bistable defect modes can be realized in the photonic structure. This asymmetric photonic crystal structure is promising and should be further explored for photonic device applications. (C) 2014 Optical Society of America