Hyperbolic Bismuth–Dielectric Structure for Terahertz Photonics

Abstract

Hyperbolic medium is a special class of strongly anisotropic materials described by diagonal permittivity tensor with the principal components being of the opposite signs, which results in a hyperbolic shape of isofrequency contours. These media support propagating electromagnetic waves with extremely large wave vectors exhibiting unique optical properties and applications such as negative refraction, subwavelength imaging, radiative heat transfer manipulation, enhancing spontaneous emission rate (Purcell factor), biosensing, and nanoscale light confinement. Hyperbolic metamaterials have been experimentally realized for optical, infrared, and microwave frequency ranges. For the terahertz (THz) frequency range, graphene‐based and bismuth‐based media are only theoretically predicted to have a hyperbolic dispersion relation. Herein, the experimental evidence of such dispersion in bismuth–dielectric materials at THz frequencies is shown. THz waveforms transmitted through ultrathin bismuth film/dielectric substrate structures are measured and the negative time delay caused by transition between the elliptic and hyperbolic dispersion at bismuth thickness increase is revealed. In the hyperbolic regime, the switching between effective near‐zero and negative refractive index regime is demonstrated, which depends on the bismuth film thickness and dielectric substrate optical properties. The outcomes demonstrate the possibility for realizing easy planar hyperbolic media for THz photonics, sensing, imaging, and communication systems.

Terahertz radiation detector based on thermoelectric material Bi-=SUB=-88-=/SUB=-Sb-=SUB=-12-=/SUB=--=SUP=-*-=/SUP=-

“…The study [14] showed, that the charge carrier plasma frequency, which determines the upper frequency limit of the possibility of detecting radiation, in bulk bismuth lies within the range from 93 to 99 THz (depending on the radiation polarization) at the temperature of 300 K. In case of cooling to the temperature of 80 K the plasma frequency decreases to the values of 59−62 THz, that is in good agreement with the results of the study [15], in which the features of the reflection spectra of doped bismuth−antimony crystals were studied in the long-wave infrared spectrum. However, as shown in the study [16], with a decrease in the bismuth film thickness up to the values of 40 to 150 nm at a temperature of 300 K a decrease in the plasma frequency (compared to bulk samples) up to 55 THz at a thickness of 40 nm and up to 67 THz at a thickness of 150 nm is also observed. Consequently, under the effect of monochromatic radiation of 0.14 THz in Bi 88 Sb 12 at 300 K the radiation absorption will be observed, and to describe the processes the theory of internal photoeffect for semiconductors may be used.…”

Frequency-Selective Surface Based on Negative-Group-Delay Bismuth–Mica Medium

“…The thickness of the bismuth film was chosen toachieve high conductivity and to provide transmission at the same time [37,38]. A thin, almost transparent mica substrate was chosen for THz waves due to its stable geometry and its ability to grow a high-quality bismuth film with a large average crystallit size.…”

On-Chip Integration of a Plasmonic FET Source and a Nano-Patch Antenna for Efficient Terahertz Wave Radiation

“…The dispersion of the HMM conforms to a hyperboloid shape [63], with one directional component of permittivity (ε) extending infinitely in the direction where ε is negative. Effective metamaterials with hyperbolic dispersion have been experimentally realized using layered metal-dielectric structures in a repeated stack, or via nanowire arrays, in the terahertz regime [64], generally achieved using a semiconductor such as graphene as opposed to a metal in the layered structure [65], and also in the optical range [66], for sub-wavelength imaging [67,68], focusing [69], and other applications [70][71][72]. A common approach is to use highly conductive metals, such as gold or silver, for the metallic component, and dielectrics such as SiO 2 for the dielectric component.…”