Optical Materials 98 (2019) 109419 Available online 30 September 2019 0925-3467/© 2019 Elsevier B.V. All rights reserved. Enhancement of thermal and electro-optical properties of photonic crystal fbers infltrated with a modifed 6CHBT nematic liquid crystal doped with gold nanoparticles Karolina Bednarska a, * , Paulina Oszwa a , Bartosz Bartosewicz b , Bartłomiej Jankiewicz b , Piotr Lesiak a , Sławomir Ertman a , Tomasz R. Woli � nski a a Faculty of Physics, Warsaw University of Technology, Koszykowa 75, Warszawa, Poland b Institute of Optoelectronics, Military University of Technology, Kaliskiego 2, Warszawa, Poland A R T I C L E INFO Keywords: Liquid crystals Nanoparticles Photonic crystal fbers ABSTRACT In this paper we present the obtained experimental results for enhancing the parameters of photonic crystal fbers infltrated with a modifed 6CHBT doped with gold nanoparticles. By admixing a special liquid crystalline ma- terial we were able to widen the working temperature range of our samples. Doping our liquid crystal mixture with nanoparticles visibly enhances the thermal and electro-optical properties of the infltrated photonic crystal fbers. Additionally, the use of a specially designed four microelectrode system allowed to decrease voltage. Thanks to the introduced modifcations we noticed a signifcant reduction of threshold voltages (up to 44%), rise times (up to 30%) and fall times (up to 50%). 1. Introduction In the past few decades, nanoparticles (NPs)-doped liquid crystals (LCs) have gained a growing interest due to the ability to easily tune the properties of such composite materials. Depending on the type of NPs (metallic, ferroelectric, dielectric, etc.), their size, shape, concentration or surface coating, NP-doped LCs can exhibit different characteristics [1–4]. Metallic NPs seem very promising for applications in devices, due to their ability to improve the LC parameters. Gold (Au), silver (Ag) and titanium (Ti) NPs are known to visibly decrease the threshold voltage and response times of the NP-doped LC composites [5–10]. These effects are attributed to local changes in the orientational order of the LCs. In most reported cases the presence of metallic NPs tended to decrease the nematic to isotropic (N–I) phase transition temperature. The exceptions in this effect (i.e. increase of the N–I transition temperature) are known and suggest that surface coating composition may alter this parameter [6,11]. Pandey et al. [6] explain that the inclusion of spherical NPs in- creases the stability of the nematic phase and consequently – increases the N–I transition temperature. Infltrating different structures with NP-LC composites yielded many interesting effects, of which the most promising for use in devices appear in combination with photonic crystals [12]. Infltrating photonic crystal fbers (PCFs) with LCs provides an easy way to tune their properties. This type of fbers, called photonic liquid crystal fbers (PLCFs), has been studied for over a decade now [13–16]. Thanks to the use of LCs, the optical properties of PLCFs can be tuned thermally or by using elec- tric/magnetic felds [13–18]. Both of these factors can be used to in- fuence the spectral properties of PLCFs – the tuning changes the positions of photonic bandgaps. Electric felds have been also shown to tune the polarization properties of PLCFs [19]. Additionally, switching between two propagation mechanisms in PLCFs can be realized through temperature tuning [20]. All-optical tuning of PLCFs was frst realized by Alkeskjold et al. [21] through a local modifcation of optical prop- erties of dye-doped LC. One of the frst attempts to use NP-doped LCs in PLCFs was carried out by Scolari et al. [22]. The authors showed that infltrating PLCF with barium titanite (BaTiO 3 ) NP-doped LC can result in interesting features, namely frequency modulation response and tunable attenuation of transmission spectrum. In [23] Siarkowska et al. presented the tuning of propagation spectra in pure TiNP-doped PLCF with temperature. In previous works [24,25] it has been shown that infltrating PCFs with AuNP-doped LCs modifes their electro-optic and thermal properties. In particular, the results indicated a decrease in threshold voltages, reduction in rise times and lowering of the N–I phase transition temperatures with an increasing concentration of NPs. * Corresponding author. E-mail address: karolina.bednarska.dokt@pw.edu.pl (K. Bednarska). Contents lists available at ScienceDirect Optical Materials journal homepage: http://www.elsevier.com/locate/optmat https://doi.org/10.1016/j.optmat.2019.109419 Received 16 July 2019; Received in revised form 8 August 2019; Accepted 23 September 2019