Flat, Lightweight optics have the potential to significantly reduce the cost of space-based observing by allowing for reduced vehicle sizes and launch costs. We have designed, manufactured, and tested a metamaterial flat lens which operates at 480GHz. 480GHz was chosen as an intermediate step to designing a 557GHz lens, which is a frequency that has scientific importance as it is a ground-state water transition line, but nearly impossible to observe from the ground or from a balloon due to water in the atmosphere. The lens is constructed from polyimide (generic Kapton) and aluminum. The metamaterial design consists of ten layers of sub-wavelengthsized aluminum squares, sized via optimization to achieve the ideal phase transformation to create a 150mm focal distance at 480GHz. This optimization process also creates an effective anti-reflection quality. The lens has an aperture size of 124mm and an f-number of f/1.2. It weighs approximately three grams and is 110 microns thick. We have demonstrated the lens has near diffraction-limited beam performance with roughly 2.5dB of loss. The loss was measured using a radiometric y-factor method, using a room-temperature absorber as the hot load and an absorber submersed in liquid nitrogen as the cold load. The beam performance was measured using a near-field scan of the lens with a waveguide probe at the focus to illuminate the lens and a second probe to measure the phase and magnitude of the near-field collimated output. The loss was roughly 1.5 dB higher than expected in our design simulations.
In this manuscript, a rapid design process flow for multi-layered Terahertz (THz) optical components for Cosmic Microwave Background (CMB) telescopes using artificial dielectric metamaterials made up of periodic 2D grid of metal squares embedded in a dielectric material with a fixed interlayer spacing, termed ”capacitive grids”, is discussed. The modeling of such metamaterials using ideal RF transmission line sections to achieve an arbitrary value of refractive index and their fabrication using aluminum embedded in a polyimide dielectric is presented. Finally, the design and HFSS simulations results of a stepped-impedance low-pass quasi-optic metamaterial filter is discussed as an application of such a rapid design methodology in designing complex quasi-optical components with variable refractive indices in the millimeter wave and THz astronomy applications.
We have developed a cost-effective, quad-frequency band THz imager for real-time THz imaging applications operating
at 220GHz, 320GHz, 420GHz, and 520GHz frequency bands. The new sensor is based on antimonide-based
heterostructure backward diodes impedance matched and monolithically integrated with high-gain, narrowband planar
antennas. The antennas are dual-linearly polarized to allow direct measurement of beam polarization. This paper details
the fabricated THz detector array and the high-speed, low-noise readout electronic chain. Experimental results on the
performance of the readout chain and simulations of the expected THz detector performance are presented.
The widespread adoption of THz based applications has been hindered by the lack of a real-time, broad-band, cost-effective
THz camera with sufficient sensitivity to enable applications in markets as diverse as security, non-destructive
evaluation, and biomedical imaging. This technological gap can be filled through the development of an 80 x 64 pixel
array of Sb-heterostructure backward diodes (Sb-HBDs) monolithically integrated to broadband (600 GHz - 1200 GHz)
antennas that can be directly flip-chipped to a CMOS voltage-mode readout integrated circuit (ROIC). This paper
outlines the current progress of the project.
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