Spectral Peculiarities of Multilayer Cholesteric Wedge-Cell System with Dye-Doped Polymer Layer
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PTICAL MATERIALS
Spectral Peculiarities of Multilayer Cholesteric Wedge-Cell System with Dye-Doped Polymer Layer H. Gharagulyana, T. M. Sarukhanyana, A. V. Ninoyana, A. H. Gevorgyanb, *, and R. B. Alaverdyana a
b
Department of Physics, Yerevan State University, Yerevan, 0025 Armenia School of Natural Sciences, Far Eastern Federal University, Vladivostok, 690920 Russia *e-mail: [email protected] Received May 17, 2019; revised June 23, 2020; accepted July 3, 2020
Abstract—Spectral properties of the three-layered wedge-cell system of two identical cholesteric layers with an isotropic defect (dye-doped polymer layer) between them were investigated experimentally and theoretically. It was shown that multiple defect modes can be observed in this kind of system’s photonic band gap which widen the application range of system mentioned above such as low threshold lasing, multi-position trigger, multiwavelength filters, light shutters, etc. The supporting simulation was also provided showing an agreement between experimental results and theoretical calculations. The problem was solved by Ambartsumian’s layer addition modified method. Keywords: cholesteric liquid crystals, chirality, photonic bandgap, defect modes, tuning, laser dye, polymer layer DOI: 10.1134/S0030400X20100112
1. INTRODUCTION Nowadays one of the most recent trends in physics is the study of photonic crystals (PC) and various photonic structures based on them [1], namely, special attention has been paid to the study of optical properties of photonic structures based on liquid crystals (LC), including defects and inhomogeneities [2, 3]. Cholesteric liquid crystals (CLC) are the most wellknown representatives of 1D chiral PCs. Important peculiarities of these structures such as local positive optical anisotropy and helical distribution of the director field give the possibility to control them in a wide range of frequencies [4]. Like all PCs, CLCs also have a photonic band gap and its position and width depend on the pitch, as well as ordinary and extraordinary refractive indices of the cholesteric material [5]. For many innovative applications, this width needs to be widened. Generally, certain approaches are taken to increase the width of the photonic band gap (PBG) [6–9]. One of the approaches to widen the reflection band of the CLCs is the formation of a pitch gradient [10] and a better solution to this problem are so-called polymer-stabilized cholesteric liquid crystals (PSCLC) [11]. Because of the concentration gradient of the helix-winding chiral material the pitch varies continuously over the film thickness [12, 13]. PSCLCs have been studied as promising display materials and lasing medium [14]. An interesting method is offered by M. Duan et al. [15] aimed at forming a pitch gradient distribution or non-uniform distribution to
achieve broadband reflection in such structures. Another interesting consideration of such materials is proposed by another research group again aiming to extend the PBG [16]. For solving such kind of problems the second class
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