A High Efficiency Superconducting On-chip Filterbank with Directional Filters for Integral Field Units in the Sub-millimeter Regime

TL;DR

This paper presents a superconducting on-chip filterbank with directional filters achieving 75% efficiency, enabling large-area spectral mapping in astronomy's sub-millimeter regime.

Contribution

It introduces a high-efficiency filterbank design using directional filters, significantly improving on previous low-efficiency on-chip filterbanks.

Findings

Achieved an average peak coupling efficiency of 75%.

Operates effectively between 125 GHz and 220 GHz.

Uses directional filters to enhance efficiency.

Abstract

Integrated superconducting spectrometers are developing to the point that they are enabling integral field units, providing large area spectral mapping capabilities for astronomy in the sub-millimeter band. However, these integral field units are only worthwhile if they have a high efficiency, but to date the efficiency of on-chip filterbanks has been quite poor. Here we demonstrate a filterbank with high efficiency by using directional filters. Using a cryogenic thermal load and a noise measurement in combination with a continuous-wave terahertz source to obtain the spectral response of the filters, we are able to accurately measure the filterbank efficiency, accounting for all quasi-optical elements within our setup. We experimentally obtain an average peak coupling efficiency to the detectors of 75% in a filterbank that sparsely samples between 125 GHz to 220 GHz using filters with a mean loaded quality factor of 19.6. Our results demonstrate that a filterbank with a high efficiency is achievable using directional filters, giving a clear route towards efficient integral field units.