Silicon Lens Optimization to Create Diffuse, Uniform Illumination from Incoherent THz Source Arrays

Arrays of terahertz (THz) sources provide a pathway to overcoming the radiation power limitations of single sources. Several independent sources of THz radiation may be implemented in a single integrated circuit, thereby realizing a monolithic THz source array of high output power. Integrated THz sources must generally be backside-coupled to extended hemispherical dielectric lenses in order to suppress substrate modes and extract THz power. However, this lens also increases antenna gain and thereby produces several non-overlapping beams. This is because individual source pixels are relatively large. Hence, their spatial separation on-chip translates to angular separation in the far-field. In other words, there are gaps in their field of view into which very little THz power is projected. Therefore, they cannot homogeneously illuminate an imaging target. This article presents a simple, practical, and scalable method to convert arrays of incoherent THz sources into a diffuse, uniform illumination source without the need for reducing pixel size. Briefly, individual beam divergence is optimized by tailoring the dimensions of the extended hemispherical dielectric lens such that the far-field beams of adjacent source pixels overlap and combine to form a uniform far-field beam. We applied this method to an incoherent 8 × 8-pixel THz source array radiating 10.3 dBm at 0.42 THz as a proof of concept and thereby realized a 10.3-dBm 0.42-THz diffuse, uniform illumination source that was then deployed in a demonstration of THz active imaging.

A Distributed Terahertz Metasurface with Cold-Electron Bolometers for Cosmology Missions

We developed and tested a 2D periodic array of cold-electron bolometers arranged into a wideband frequency selective metasurface that absorbs more than 70% of the incident power in the frequency range 100–800 GHz. The array had 10 × 10 unit cells, each containing four bolometers incorporated into a ring. The chip with bolometers was mounted on the back side of the silicon lens without a back-reflector. Preliminary experiments demonstrated voltage responsivity as high as 109 V/W for the current-biased series array. Simulation of the noise performance shows realization of background noise-limited performance with NEPtot < NEPphot for the optical power load P0 > 15 pW. Results of numerical simulation made for the unit cell of the array are presented together with the equivalent diagram based on lumped network elements. The unit cell also was developed numerically to operate in two radiation modes.

Design and Comparative Analysis of Ultra-wideband and High Directive Antennas for THz Applications

This work presents a comprehensive detailed comparative study of the three ultra-wideband and high directive antennas for the THz imaging, spectroscopy, and communication applications. Three different types of photoconductive antennas (log-spiral, Vivaldi, and bowtie antennas) are designed and simulated in the frequency range of 1 to 6 THz in the CST microwave studio (MWS). The enhanced directivity of the designed PCAs is achieved with the integration of the hemispherical silicon-based lens with the PCA gold electrode and quartz substrate of the proposed antennas. The performance of the designed PCAs is compared in terms of impedance and axial ratio bandwidths, directivity, and radiation efficiency of the proposed antennas. The reported log spiral, Vivaldi PCAs with added silicon lens exhibit the -10 dB impedance bandwidth of 6 THz, 3dB AR bandwidth of 5 THz, 6 THz, and 6 THz and peak total radiation efficiencies of 45%, 65%, and 95% respectively.

Beam Profile Characterisation of an Optoelectronic Silicon Lens-Integrated PIN-PD Emitter between 100 GHz and 1 THz

Knowledge of the beam profiles of terahertz emitters is required for the design of terahertz instruments and applications, and in particular for designing terahertz communications links. We report measurements of beam profiles of an optoelectronic silicon lens-integrated PIN-PD emitter at frequencies between 100 GHz and 1 THz and observe significant deviations from a Gaussian beam profile. The beam profiles were found to differ between the H-plane and the E-plane, and to vary strongly with the emitted frequency. Skewed profiles and irregular side-lobes were observed. Metrological aspects of beam profile measurements are discussed and addressed.