Refractive index of nematic liquid crystals in the submillimeter wave region

Abstract

Large electro-optic effects of liquid-crystal materials are attractive in applications to various optical devices in a wider wavelength region. Fundamental optical properties in the submillimeter wave region, such as refractive indices and transmission losses for some cyanobiphenyl nematic liquid crystals, have been investigated for the first time, to our knowledge, with a submillimeter laser. Refractive indices of the liquid crystal materials for ordinary and extraordinary rays are a little larger than those in the visible region, and a larger birefringence comparable with the visible region can also be obtained. Although the loss level is larger by ~2 orders of magnitude than that of quartz plate, which is an excellent window in the submillimeter wave region, the transmission of the liquid crystal cell is high enough.

Broad spectrum measurement of the birefringence of an isothiocyanate based liquid crystal

“…1 and 2. The values of the refractive index in the terahertz region and at 30 GHz both perpendicular and parallel to the alignment direction were lower compared to the values in the optical range (Table 1), which is expected and is in agreement with previous research on other nematic LCs in the terahertz [1,13,24] and gigahertz [3,25] regions. Importantly, in both GHz and THz regions of the spectrum the birefringence in LCMS is much higher than of the LCs based on cyanobiphenyls.…”

“…Their anisotropy and sensitivity to external fields have led to numerous display and nondisplay applications. Moreover, LCs are very promising materials at microwave [1][2][3][4][5][6][7][8] and terahertz (THz) frequencies [9][10][11][12][13] due to low losses and comparatively high anisotropy. LCs are particularly suitable for operation at frequencies beyond 10 GHz as the dielectric loss decreases with increasing frequency [14], making them attractive for phase modulating devices.…”

Measurement of Dielectric Anisotropy of Some Liquid Crystals for Microwave Applications

“…The dielectric tunability, defined as below, was calculated from measured data. Pentyl cyano-biphenyl (K15) is a well known nematic LC, which has been measured in the RF frequency range by various methods [1,3,14]. For comparison purposes, we intended to choose data measured similarly to our method (reflective coaxial method).…”

“…In comparison to the existing candidates such as ferroelectric ceramic materials, liquid crystals (LCs) have drawn attention in recent years mainly because of low losses in microwave frequencies and comparatively high anisotropy [1][2][3][4][5]. For this reason, intensive research has focused on applications of LC in GHz.…”

High-frequency dielectric relaxation of liquid crystals: THz time-domain spectroscopy of liquid crystal colloids

“…On the other hand, there has been technological interest in the application of LCs as a phase shifter in the THz frequency range [10]. The ordinary and extraordinary dielectric functions of LCs such as 4−(trans−4'−pentylcyclohexyl)−benxonitrile and 4'−n−pentyl−4−cyanobiphenyl at THz frequencies were previously determined using an LC confined cell [11,12,13,14].…”