The Characterization and Application of Two Liquid Crystal Mixtures in the Low THz Region

Abstract

In the previous work, two new nematic liquid crystal (NLC) mixtures, E7-2 and S200-2, were produced by adding eight LC monomers to two commercial LCs S200 and E7, respectively. At λ = 589 nm, the birefringence (∆n) characteristics of the two LC nematic mixtures E7-2 (∆n = 0.260) and S200-2 (∆n = 0.298) are greater than those of the commercial LC E7 (∆n = 0.224) and S200 (∆n = 0.266). The properties (T N-I , ε // , ∆ , K 11 , and K 33 ) of these four NLCs were measured. A double-layer metal loop arrays modulation structure based on metamaterial (MM) metal-dielectric-metal (MDM) was designed and fabricated for use in the THz frequency range. The results show that the LC mixtures E7-2 and S200-2 have greater modulation depth (MD) and less modulation insertion loss (IL) than E7 and S200 at THz frequencies. The results show that LC mixtures have significant potential for designing active tunable LC-based devices in the THz and visible light range.there has been increasing interest in characterizing LC materials as a tunable materials unit for THz applications, such as modulators [15], filters [16], phase shifters [17,18], switches [19], and absorbers [20]. High birefringence nematic liquid crystals have been broadly researched to satisfy the needs of the extensive variety of optical infrared range photonics devices [21]. Compared to NLCs for use in the visible region, these NLCs show weak birefringence in THz regions. Some papers demonstrated that the birefringence exhibited by LCs is relatively low in the THz band [22,23]. The relatively low birefringence can lead to performance limitations for THz electronically tunable devices. An effective way to solve these problems is to synthesize high birefringence LC compound materials. Recently, Vieweg et al. reported the birefringence of the LC mixture BL037, from ∆n = 0.16 at 0.5 THz to ∆n = 0.2 at 2.5 THz [24]. Wang et al. proposed a new LC mixture, called NJU-LDn-4, with a large birefringence of 0.306 from 0.4 to 1.6 THz [25]. Reuter et al. proposed the high birefringence LC mixtures 1852 (∆n = 0.33 at 0.5 THz) and 1825 (∆n = 0.38 at 0.5 THz) [26].In the previous work, two new NLCs mixtures (E7-2 and S200-2) were proposed [27], which can be used to construct tunable THz devices due to tunable dielectric properties. In this paper, the more physical properties of these mixture LCs were measured and analyzed. Currently, to develop effective terahertz modulators and switches, electromagnetic metamaterials, an artificial composite material, are essential components. They consist of two-or three-dimensional arrays of tailored metallic unit cells [28]. In order to directly manipulate THz waves, we demonstrated THz LC modulators based on electromagnetic metamaterials and E7-2, S200-2 LC mixtures. The experimental results show that the metrics ∆T, MD, and IL of these mixture-based LCs can be significantly higher than those of commercial LCs in their working frequency band. This suggests that two high birefringence NLCs can also be used to fabricate highly efficient and functional...

Microwave Liquid Crystal Technology

“…Beside the advancement of microwave components and systems, the development of novel and improved LC mixtures is key component for the success of the whole Microwave Liquid Crystal Technology. In [6] two new nematic liquid crystal mixtures are proposed by adding LC monomers to commercial LC. This and also the addition of nanofibers as in [4] are two examples for recent material development.…”