We review our theoretical and experimental studies on a class of liquid crystal (LC) photonic devices, i.e., terahertz (THz) phase gratings and beam steerers by using LCs. Such gratings can function as a THz polarizer and tunable THz beam splitters. The beam splitting ratio of the zeroth-order diffraction to the first-order diffraction by the grating can be tuned from 10:1 to 3:5. Gratings with two different base dimensions were prepared. The insertion loss is lower by approximately 2.5 dB for the one with the smaller base. The response times of the gratings were also studied and were long (tens of seconds) as expected because of the thick LC layer used. Accordingly, the devices are not suitable for applications that require fast modulation. However, they are suitable for instrumentation or apparatuses that require precise control, e.g., an apparatus requiring a fixed beam splitting ratio with occasional fine tuning. Schemes for speeding up the device responses were proposed. Based on the grating structure, we also achieved an electrically tunable THz beam steerer. Broadband THz radiation can be steered by 8.5° with respect to the incident beam by varying the driving voltages to yield the designed phase gradient.
Part of the book: Liquid Crystals
High-dielectric constant glasses are prerequisite for developing terahertz (THz) components and systems. Oxyfluorosilicate (OFS) glasses have been developed and their THz properties have been characterized by using THz-time domain spectroscopy (THz-TDS) measurements. High-dielectric constant (8–13) and low loss (6–9/cm) properties in the THz region have been demonstrated and their dielectric properties have been studied using the single oscillator-based model through a comparison with other multi-component silicate oxide glasses. Unified single oscillator model, which can distinguish the electronic and ionic contributions to the dielectric property, has been applied in this analysis. The physical origin of the dielectric constant enhancement and the importance of interplay between the electronic polarizability and ionicity in high-dielectric constant glasses have been revealed. This study has demonstrated the usefulness of THz-TDS technique for characterizing dielectric properties of multi-component glasses in detail.
Part of the book: Trends in Terahertz Technology