arXiv subjects

Matthew A. Koc

Publications and source records attributed to Matthew A. Koc.

5 recordsLinked to original sources

arXiv2026

Laser-micromachined silicon-platelet feedhorns for large-scale submillimeter and millimeter-wave focal planes

We present the fabrication and characterization of the first silicon-platelet feedhorn arrays produced using laser micromachining. First, we present a demonstration of the technology for the millimeter-wave band of 80~GHz to 170~GHz, i.e. covering the 90/150~GHz bands typical of CMB experiments. Next, we expand the technology to large-scale production on 150~mm wafers and demonstrate operation at submillimeter wavelengths. This feedhorn array is optimized for operation in a band centered at 350~GHz (330~GHz to 370~GHz) and is being deployed as one of the focal plane elements of the CCAT 350~GHz module of Prime-Cam. We present the design and fabrication processes for these feedhorn arrays and compare the optical performance directly to simulation and to feedhorns of identical design but produced using traditional deep reactive-ion etching (DRIE). We conclude with a discussion of future expansions of this technology, including the potential of sidewall control and using thicker (and thus fewer) wafers, which could significantly reduce production costs and labor.

astro-ph.IM↗

arXiv2026

CCAT: Silicon-Platelet Feedhorns for Submillimeter Wavelengths

Silicon-platelet feedhorn arrays are an established technology at millimeter wavelengths that, for some applications, can provide significant advantages over traditional direct-machined metal feedhorns. The Prime-Cam focal planes operating in the 350 GHz ($\sim$860 $\mathrmμ$m) and 850 GHz ($\sim$350 $\mathrmμ$m) bands are anticipated to carry the first silicon-platelet feedhorn arrays to operate fully at submillimeter wavelengths, representing a significant step forward in the application of this technology. In particular, the feedhorns designed for operation in the 850 GHz band represent a 3x increase in frequency compared to previously demonstrated and deployed devices of this type. Here we present a demonstration of silicon-platelet feedhorns at these submillimeter wavelengths, including in-lab performance characterization. We present fabrication metrology, room-temperature beammaps, and cryogenic optical efficiency measurements where the feedhorns are coupled to prototype CCAT Prime-Cam detectors. We show that feedhorn performance measurements are well matched to simulation and compare that performance directly to traditional, direct-machined metal feedhorns.

astro-ph.IM↗

arXiv2025

Spectral Characterization of a 90 GHz CLASS Pixel

The Cosmology Large Angular Scale Surveyor (CLASS) is an experiment designed to measure the polarization of the cosmic microwave background on large angular scales to probe cosmic reionization and search for the inflationary $B$-mode signal. CLASS is a multi-frequency ensemble of telescopes with bands centered at 40, 90, 150, and 220 GHz. Each telescope has arrays of feedhorn-coupled transition edge sensor bolometers at the focal plane. The frequency response is primarily defined by the on-chip bandpass filter with additional contributions coming from the feedhorn, orthomode transducer, and 180-degree hybrid. In this study, we compare simulations and measurements of the frequency response of single pixel witness devices in the 90 GHz band with and without the bandpass filter. For the first time, we can separate the effects of the bandpass filter from the other microwave components using Fourier transform spectroscopy and design splits of the pixel. The results show that the -3 dB band edges are at 80 GHz and 108 GHz. The measurements demonstrate a robust method for characterizing the spectral response of individual components, which is crucial for optimizing the performance of future detector arrays.

astro-ph.IM↗

arXiv2025

Development of Silicon Micromachined Waveguide Filter-Banks for On-Chip Spectrometers

Development of high-speed, spatial-mapping spectrometers in the millimeter and far-infrared frequencies would enable entirely new research avenues in astronomy and cosmology. An "on-chip" spectrometer is one such technology that could enable Line Intensity Mapping. Recent work has shown the promise of high-speed imaging; however, a limiting factor is that many of these devices suffer from low optical efficiency. Here we present the fabrication of a metalized, Si waveguide filter-bank fabricated using deep reactive ion etching for use in millimeter spectroscopy. Our design simultaneously provides high-density pixel packing, high optical efficiency, high spectral resolution, and is readily compatible with simple and multiplexable MKID arrays. Gold plated test waveguide and filter show excellent match to simulations with a measured resolving power of 263 and a loss quality factor of 1116 at room temperature. The results show promise for extending the measurements to larger, multi-wavelength designs.

astro-ph.IM↗

arXiv2025

Simons Observatory: Characterization of the Large Aperture Telescope Receiver

The Simons Observatory (SO) is a ground-based cosmic microwave background (CMB) survey experiment that currently consists of three 0.42m small-aperture telescopes (SATs) and one 6m large-aperture telescope (LAT), located at an elevation of 5200m in the Atacama Desert in Chile. At the LAT's focal plane, SO will install >62,000 transition-edge sensor detectors across 13 optics tubes (OTs) within the Large Aperture Telescope Receiver (LATR), the largest cryogenic camera ever built to observe the CMB. Here we report on the validation of the LATR in the laboratory and the subsequent dark testing and validation within the LAT. We show that the LATR meets cryogenic, optical, and detector specifications required for high-sensitivity measurements of the CMB. At the time of writing, the LATR is installed in the LAT with six OTs (corresponding to >31,000 detectors), and the LAT mirrors and remaining seven OTs are undergoing development.

astro-ph.IM↗