Distinct optical properties of hydrogen-bonded liquid crystal materials in millimeter-wave region

Abstract

General liquid crystal (LC) materials have considerably large birefringence in wide frequency regions in the electromagnetic wave spectra, extending to the THz, millimeter wave (MMW), and microwave. LC materials can potentially be applied to some excellent control devices in novel frequency regions as display devices in optics regions. However, the birefringence of LC materials synthesized for display applications generally decreases by approximately half in the MMW region. Furthermore, the small remaining absorption loss in the MMW region must lead to a fatal device loss, as the LC layer becomes extremely large in the application field. New LC materials beyond the display application have been desired in novel LC application fields. In this work, a new class of LC materials consisting of hydrogen bonding is evaluated in the MMW region for the first time. Some optical properties different from those of conventional LC materials are discovered. The most distinct property is that the birefringence of the hydrogen-bonded LC materials in the MMW region becomes considerably larger than that in visible rays, which is totally inversion in relation with conventional LC materials. The absorption coefficients are as small as those of the best LC materials developed for microwave applications. Although some disadvantages are associated with the application of actual devices in this stage, the distinct dispersion properties make a breakthrough imminent in this application fields.