The evaluation of electromagnetic material parameters from metamaterial structures has received much attention in the literature. Among others, one method is to retrieve the material parameters from the reflection and transmission measurements of the sample material. It has been found that the electromagnetic material parameters depend on the angle of incidence. Although based on the Nicholson-Ross-Weir technique, the proposed extraction technique has no limitations on the angle of incidence. The proposed extension of the NRW extraction technique is used to study a fishnet structure fabricated by nanoimprint lithography. Silver (Ag)- Magnesium Fluoride (MgF2) - silver (Ag) was deposited on the thick PMMA layer before directly imprinted by a stamp. The effective material parameters have been found to characterise the imprinted fishnet structure.
Optical metamaterials are able to achieve optical properties that do not exist in nature. Approaches to the homogenization of optical metamaterials are becoming more and more complex in the desire to achieve accurate representation. Here we propose to modify an existing retrieval approach for metamaterials to characterize their properties. To extract the effective refractive index and material parameters from reflection and transmission coefficients for double negative metamaterial in the optical regime, the modified Nicholson-Ross-Weir (NRW) method is used. In order to obtain a true picture of these metamaterials, as a function of angle of incidence of the illumination, it is important to present not only the effective parameters of permittivity and permeability but also some other important parameters such as coupling coefficients, that represent the inherent anisotropy.
Beam-steering techniques are required to fully exploit terahertz imaging systems. We propose and model a device employing artificial dielectric techniques to provide a variable phase-control medium. The device consists of two interlocking artificial dielectric surfaces that are initially aligned parallel to each other. By mechanically introducing a relative tilt between the plates, a transmitted wave is subjected to a graded phase delay and thus the beam is steered away from the normal. Continuous and large steering angles are possible. We predict a practical device constructed from a silicon substrate could steer TE beams by up to 4.6 degrees.
In this Paper we investigate a tunable metallic photonic crystal filter with a novel mechanical tuning method, suitable for use in terahertz frequency applications. Tuning has been demonstrated in a micrometer-driven prototype at 70 - 110 GHz in accordance with rigorous full-vector electromagnetic simulations (finite-difference time-domain). The measured pass band has a Q of 11 and can be tuned over a 3.5 GHz range. The insertion loss is only 1.1 to 1.7 dB, while the stop band attenuation is >10 dB. The filter has the advantages of inexpensive, robust and compact construction and tunable operation that readily scales to any desired terahertz frequency.
Micromachining of ultra-high frequency waveguide structures requires etching with vertical sidewalls and flat bottoms simultaneously. The required geometries can be difficult to achieve using a single-step orientation dependent etching (ODE) process without incurring a severe mask-undercutting penalty. This may inhibit the production of isolated convex structures, such as the central pillars that are required to couple radiation into the waveguide. In this paper we will described a new technique for ODE of deep, vertical sidewall structures in (100) Si with reduced undercut etching. The process uses a two stage KOH/IPA etch with a mask pattern that is designed to compensate for the differing etch rates on the Si planes. To date we have achieved overall etch depths of 350 microns, with a lateral undercut of as little as 275 microns, compared with a 350 micron undercut for a single-stage etch. The sidewalls are at exactly 90 degrees to the surface of the (100) Si, and the bottoms of the trenches are smooth and flat. Using the process we have also been able to routinely fabricate isolated, square pillars as small as 50 X 50 square microns, and over 300 microns high. The process enables structures to be made that might previously only have been possible with high-density-plasma dry etch techniques. The new technique has clear advantages of low cost and high throughput.