Terahertz frequency bandpass filters

Abstract

The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. The design, measurement, and analysis of a range of artificial materials for use at terahertz frequencies are described. The chosen structures consist of arrays of cylindrical gold-plated pillars with period comparable to the wavelength of incident radiation. An ultraviolet ͑UV͒ micromachining approach to the fabrication of these high aspect-ratio pillars is described using the negative epoxy-based resin SU8. Lattice fence structures are also realized using the same method. Terahertz ͑THz͒ frequency time domain spectroscopy is performed on these structures in the range 200 GHz to 3.0 THz and the relative transmission of the structures is determined. The pass and stop bands are observed with peak transmission of up to 97%. Finite difference time domain simulations and complex photonic band structure calculations are shown to provide good descriptions of the electromagnetic properties of the structures and are used to interpret the observed transmission spectra.

Negative refraction and the spectral filtering of terahertz radiation by a photonic crystal prism

“…The technique is thus ideal for producing photonic devices that operate in the THz region of the electromagnetic spectrum. In recent work, we have shown how such devices can be used to filter THz radiation at normal incidence [16], and further theoretical developments of these ideas have considered waves that are obliquely incident on a prism structure of metallic pillars arranged on a hexagonal lattice [15]. The first two photonic bands of the basic hexagonal lattice system, with the electric field polarized parallel to the pillars' axis, are shown in Fig.…”

“…The inclusion of a loss term has the additional effect of reducing the value of f J by a few percent. Details of the basic fabrication methods employed have been published elsewhere [16], but in brief, high-aspect-ratio polymer pillars are formed by backside UV exposure of SU-8 50 on a glass substrate, before being sputtered with gold. Because the gold thickness is greater than the electromagnetic radiation skin depth, the pillars behave in effect like solid metallic rods.…”

Micromachined Devices for Use in Terahertz Applications

“…They showed that the effective plasma frequency is a function of the array geometry and is independent of the bulk plasma frequency of the metal. However, to produce an effective plasma frequency in the THz regime, the rods need to be of the order of tens of microns diameter and of sufficient length to fully confine the incident beam [10]. This 'microbrush' type of structure is difficult and expensive to fabricate using manual assembly type techniques.…”

“…2 shows an overview of the process flow used to fabricate arrays of microrods. The details of the fabrication process can be found in [10]. The key novelty is the use of backside UV exposure of SU8-50 which can produce structures with diameters as small as 30 µm and heights in excess of 1.5 mm.…”

“…Fig. 3 also includes the passbands predicted by both complex band theory calculations [10] and Finite Difference Time Domain (FDTD) simulations. Both can be seen to provide an excellent match to the experimental data.…”