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Dielectric singularities (DSs) constitute one of the most exotic features occurring in the effective permittivity of artificial multilayers called hyperbolic metamaterials (HMMs). Associated to DSs, a rich phenomenology arises that justifies the ever-increasing interest profuse by the photonic community in achieving an active control of their properties. As an example, the possibility to “canalize” light down to the nanoscale as well as the capability of HMMs to interact with quantum emitters, placed in their proximity, enhancing their emission rate (Purcell effect), are worth mentioning. HMMs, however, suffer of an intrinsic lack of tunability of its DSs. Several architectures have been proposed to overcome this limit and, among them, the use of graphene outstands. Graphene-based HMMs recently shown outstanding canalization capabilities achieving λ/1660 light collimation. Despite the exceptional performances promised by these structures, stacking graphene/oxide multilayers is still an experimental challenge, especially envisioning electrical gating of all the graphene layers. In this paper, we propose a valid alternative in which indium-tin-oxide (ITO) is used as an electrically tunable metal. Here we have numerically designed and analyzed an ITO/SiO2based HMM with a tunable canalization wavelength within the range between 1.57 and 2.74 μm. The structure feature light confinement of λ/8.8 (resolution of about 178 nm), self-focusing of the light down to 0.26 μm and Purcell factor of approximately 700. The proposed HMM nanoarchitecture could be potentially used in many applications, such as ultra-fast signal processing, high harmonic generation, lab-on-a-chip nanodevices, bulk plasmonic waveguides in integrated photonic circuits and laser diode collimators.

Dielectric Singularities (DSs) constitute one of the most exotic features occurring in the effective permittivity of artificial multilayers called Hyperbolic Metamaterials (HMMs). Associated to DSs, a rich phenomenology arises that justifies the ever-increasing interest profuse by the photonic community in achieving an active control of their properties. As an example, the possibility to “canalize” light down to the nanoscale as well as the capability of HMMs to interact with quantum emitters, placed in their proximity, enhancing their emission rate (Purcell effect), are worth mentioning. HMMs, however, suffer of an intrinsic lack of tunability. Several architectures have been proposed to overcome this limit and, among them, the use of graphene outstands. Graphene-based HMMs recently shown outstanding canalization capabilities achieving λ/1660 light collimation. Despite the exceptional performances promised by these structures, stacking graphene/oxide multilayers is still an experimental challenge, especially envisioning electrical gating of all the graphene layers. In this paper, we propose a valid alternative in which indium-tin-oxide (ITO) is used as an electrically tunable metal. Here we describe an ITO/SiO2 based HMM with electrically tunable canalization wavelength within the range between 1.57 μm and 2.74 μm. The structure we propose feature light confinement of λ/8.8 (resolution of about 178 nm), self-focusing of the light down to 0.26 mm and Purcell factor of approximately 700. The proposed HMM nanoarchitecture could be potentially used in applications like ultra-fast signal processing, high harmonic generation, lab-on-a-chip nanodevices, bulk plasmonic waveguides in integrated photonic circuits and laser diode collimators.

In this work, switchable liquid crystal infrared filter is presented. The tailored superfluorinated liquid crystal material exhibiting low parasitic absorption at the operating range has be...

In this work we present phase shifters with cholesteric liquid crystal (ChLC) for the terahertz (THz) range with fast modulation. The phase shift of presented phase shifters is equal ∼π at 2.5 THz. The characterization of the phase shifters was done by using terahertz time-domain spectroscopy from 0.3 THz up to 3 THz. Also electro-optical measurements were made to obtain response times of ChLC.

In this paper, we present the results of the terahertz measurements of liquid crystal (LC) ferroelectric BaTiO3 nanoparticles (nps) suspensions in the range of frequency from 0.3 up to 3.0 THz. Two different sol-gel methods and the harvesting technique were used to fabricate the nanoparticles. Five LC materials served as hosts for the suspensions: two single compounds: 6CHBT and 2,3′,5′-trifluoro-4-(4-pentylcyclohexyl)-4′-(trifluoromethoxy)-1,1′-biphenyl, and three mixtures: 1867, 2037 and 2020. We characterise, for the first time, the refractive indices and absorption parameters of suspensions with harvested nps in the terahertz range and show how the process of the nps’ preparation affects their response. We observed the increase of birefringence for few LC suspensions in comparison with the pure LCs. The highest increase of birefringence was for 2020 suspension with one kind of ferroelectric nps. On the other hand in most cases the addition of ferroelectric nps to LC causes the increase of its ...

The structural and optical evolution of the ZnS thin films prepared by atomic layer deposition (ALD) from the diethylzinc (DEZ) and 1,5-pentanedithiol (PDT) as zinc and sulfur precursors was studied. A deposited ZnS layer (of about 60 nm) is amorphous, with a significant S excess. After annealing, the stoichiometry improved for annealing temperatures &ge, 400 &deg, C and annealing time &ge, 2 h, and 1:1 stoichiometry was obtained when annealed at 500 &deg, C for 4 h. ZnS crystallized into small crystallites (1&ndash, 7 nm) with cubic sphalerite structure, which remained stable under the applied annealing conditions. The size of the crystallites (D) tended to decrease with annealing temperature, in agreement with the EDS data (decreased content of both S and Zn with annealing temperature), the D for samples annealed at 600 &deg, C (for the time &le, 2 h) was always the smallest. Both reflectivity and ellipsometric spectra showed characteristics typical for quantum confinement (distinct dips/peaks in UV spectral region). It can thus be concluded that the amorphous ZnS layer obtained at a relatively low temperature (150 &deg, C) from organic S precursor transformed into the layers built of small ZnS nanocrystals of cubic structure after annealing at a temperature range of 300&ndash, 600 &deg, C under Ar atmosphere.

In this work liquid crystal (LC) modulators are considered. First one is based on electrically controlled birefringence (ECB) effect. A transducer with the thickness of 59 μm was prepared and liquid crystal material designed for infrared applications was used. The LC material shows mesomorphic phase in the room temperature and it has decreased absorption bands in the mid-infrared range (3 – 5 μm). The other considered modulator is a Fabry-Perot interferometer which can be used as a narrow band filter.

In this work, we present the results of terahertz measurements of five nematic liquid crystal materials. Optical properties like refractive indices, birefringence and absorption coefficients of liquid crystals (LCs) for ordinary and extraordinary polarisation were compared. The aim of this study was to check the impact of the structure of LC molecules on above properties. The compounds with different core structure and various number of laterally substituted fluorine atoms were chosen. A standard terahertz Time-Domain Spectrometer to measurements from 0.3 THz to 3 THz was used.

In this paper a two liquid crystal (LC) modulators for mid-wave infrared radiation (MWIR) are presented. A two electrooptical effects (EOE) in liquid crystalline structures have been utilized for MWIR modulation: electric field induced cholesteric - nematic (Ch-N*) phase transition (ChN mode) and switching of the twisted-nematic (TN) structure (TN mode). At the Ch-N* mode an intensity modulation depth was of order of 15% but there wasn’t a dark state. In case of the modulation induced at TN mode was near full. These modulators are quite slow, switching times are order of a few hundreds of milliseconds for Ch-N* mode electrooptical effect and dozens of minutes in case of TN mode.

In this article, optical properties of four fluoro-substituted 4-propyl-4′-[(4-ethylphenyl)ethynyl] biphenyls and liquid crystal mixture A are presented in the terahertz (THz) range. Birefringence, refractive indices and absorption coefficients for ordinary and extraordinary ray of liquid crystals are described in the range of 0.3 to 3.0 THz. It shows that the measured parameters are dependent on the number and placement of fluorine atoms in the molecules. Measurements have been performed using time-pulsed spectroscopy.

In this paper, the measurement results of 10 nematic liquid crystals from the homologous series of 4-(trans-4′-n-alkylcyclohexyl) isothiocyanatobenzenes (CHBT) in the range of 0.3–3 THz are presented. Birefringence, refractive indices and absorption coefficients for ordinary and extraordinary rays versus frequency are described. In addition, temperature dependence of these parameters is shown. The purpose of this study was to investigate the effect of alkyl chain length on the properties of liquid crystals in the THz range.

W1832A, a dual-frequency, multi-component nematic mixture prepared at the Military University of Technology, was investigated by means of dielectric spectroscopy over a wide frequency range (100 Hz–10 MHz) and over a wide temperature range (−60°C–100°C). At the temperature of −60°C it is still a nematic. The investigated mixture changes the sign of dielectric anisotropy at temperature and frequency domains. High-precision dielectric spectroscopy studies of molecular motions (around short (S) and long (L) molecular axes) were performed using cells of 5 μm thickness. Gold electrodes in measuring cells were spin-coated with agents for homogenous and homeotropic alignments. In the low-temperature region these motions are hindered enough to observe intra-molecular motions, which typically (at room temperature) are observed in THz frequency range of the measuring field. S molecular motion is eliminated from the measurement range at temperatures below −15°C, while L mode is still observed at −60°C. Dielectric sp...

Properties of liquid crystal materials in THz frequency range can be interesting from application point of view. In this paper the influence of short and long molecules added to liquid crystal 6CHBT were investigated. Change of refractive indices and absorption coefficients for 6CHBT mixtures were compared in the 0.3 - 3 THz frequency range. Influence of temperature on the mentioned parameters of liquid crystal were investigated. Our study show that even a slight change in shape and the composition of the molecules dopants affects the macroscopic properties of liquid crystal. These properties depend on the length of chains, the number of benzene or cyclohexane rings or the spatial distribution of molecules and the interactions between them in the liquid crystal mixture. Spectra measurements on the terahertz time-domain spectrometer were performed.

Liquid crystals (LCs) with high optical anisotropy are very desirable for different applications in devices, such as filters, phase shifters, or phase gratings [T. Gobel, P. Meissner, A. Gaebler, M. Koeberle, S. Mueller, and R. Jakoby, Dual-Frequency Switching Liquid Crystal Based Tunable THz Filter, CLEO, Baltimore, MD, 2009; C.-Y. Chen, T.-R. Tsai, C.-L. Pan, and R.-P. Pan, Room temperature terahertz phase shifter based on magnetically controlled birefringence in liquid crystals, Appl. Phys. Lett. 83 (2003), pp. 4497–4499; and C.-J. Lin, C.-H. Lin, Y.-T. Li, R.-P. Pan, and C.-L. Pan, Electrically controlled liquid crystal phase grating for terahertz waves, IEEE Photon. Technol. Lett. 21 (2009), pp. 730–732]. We present spectral studies of LCs with large optical anisotropy in the range from 0.3 to 3 THz. Nematic LC mixtures which have Δn > 0.30 for visible frequency range, i.e., 1825 (Δn = 0.42 at 633 nm) were measured. Properties of LC materials like birefringence, absorption coefficients, and refractiv...

We show that a hybrid LC-ferroelectric nanoparticle suspension of liquid crystal E7 doped with BaTiO3 nanoparticles leads to 10% increase in birefringence in the THz region of spectrum as compared to pure E7. Doped liquid crystals can be used to increase performance of THz modulators and waveplates. BaTiO3 nanoparticles used in the mixture were synthesised with the sol gel technique, and their refractive index has been measured in THz in powder form and in solution.