Control of enhanced THz transmission through metallic hole arrays using nematic liquid crystal

Abstract

We demonstrate frequency tuning of enhanced THz radiation transmitted through a two-dimensional metallic hole array (2D-MHA) by controlling the index of refraction of the medium filling the holes and adjacent to the 2D-MHA on one side. The medium is a nematic liquid crystal (NLC) and its index of refraction is varied using magnetically controlled birefringence of the NLC. With the NLC, the peak transmission frequency of the 2D-MHA shift to the red by 0.112 THz and can be tuned from 0.193 to 0.188 THz. The peak transmittance is as high as 70% or an enhancement of 2.42 times, considering the porosity of the 2D-MHA. As a tunable THz filter, this device exhibits a continuous tuning range of 4.7 GHz , a low insertion loss of 2.35 to 1.55 dB and a quality factor of ~ 4-5.

Ultrafast optical switching of the THz transmission through metallic subwavelength hole arrays

“…Shorter recovery times at room temperature may be achieved by using a direct band-gap semiconductor. It should be noted that the switching times reported here are orders of magnitude faster than the ͑greater than milliseconds͒ switching times attainable for the thermal switching of semiconductor carrier densities 20 and alignment of liquid crystals 21 previously demonstrated for arrays.…”

“…One of the main advantages that optical switching of transmission offers over thermal 20 and magnetic 21 switchings is fast switching times. In Fig.…”

“…Enhanced transmission through semiconductor [17][18][19] hole arrays has recently been reported in the THz frequency regime. Rivas et al 20 have recently demonstrated thermal switching of THz transmission by modifying with temperature the density of free carriers in a silicon array, while Pan et al 21 demonstrated magnetic switching by using a nematic liquid crystal in a metal array. Switching has also been demonstrated by utilizing the metal-insulator transition in vanadium oxide hole arrays.…”

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].…”

Liquid Crystal Colloids Studied by THz Time-Domain Spectroscopy

“…This allows us to interpret intermolecular interaction, and hence allowing the study of molecular assembly= packing and motion in LC phases. The published work on refractive indices of LCs in the range of THz frequency is, however, limited [15][16][17][18][19].…”