On the Design of Wideband Sub-mm Wave Superconducting Integrated Filter-bank Spectrometers

25 Jul 2019, 17:45
1h 15m
Piazza Città di Lombardia (Milano)

Piazza Città di Lombardia

Milano

Piazza Città di Lombardia, 1, 20124 Milano MI
Poster Low Temperature Detector Applications Poster session

Speaker

Alejandro Pascual Laguna (SRON)

Description

Sub-mm wave on-chip filter-bank spectrometers disperse THz radiation by means of shunted band-pass filters whose ideal frequency response is a matched-filter to the Lorentzian-shaped spectrum of broadened extra-galactic emission lines, resulting in a resolution requirement of $R=f/\delta{f}\sim{}500$. Furthermore, the instantaneous bandwidth of operation should be as wide as possible to allow for blind spectroscopic scans. For the implementation of these filter-banks we studied in detail co-planar filters, consisting of a single patterned superconducting film, and microstrip filters. A filter with $R=500$ needs to have a low enough loss ($1/\tan\delta = Q_i>5000$) to limit unwanted signal attenuation. We found that co-planar filters are strongly limited by radiation losses, especially for sub-mm waves. Hence, we designed in Sonnet a filter based on a microstrip half-wave resonator, free from spurious resonances within an octave band. For the dielectric we use PECVD a-Si, with a measured $Q_i∼10^4$. The high stress of a-Si sets however a maximum thickness of ~300 nm, which imposes sub-micron featured filters. With the aid of a circuit model developed in-house we predict the interaction between filters when arrayed in a filter-bank configuration. This code made obvious three extra requirements for large filter-banks: (1) a low reflection off-resonance per filter is needed (reflection <-20 dB), (2) the high frequency filters must lead in the filter-bank to limit their losses, and (3) the inter-filter spacing in the thru-line must be $\lambda/4$, and cannot be a higher odd multiple, in order to avoid the coherent addition of reflections from the filters to fall within an octave band. Based on these constraints we designed a filter-bank with 347 efficient channels sampling an octave bandwidth (220-440 GHz) with a resolution of $R=400$. A set of demonstrators with narrower bandwidth are being fabricated and their measurements will follow.

Less than 5 years of experience since completion of Ph.D Y
Student (Ph.D., M.Sc. or B.Sc.) Y

Primary authors

Alejandro Pascual Laguna (SRON) Kenichi Karatsu (TU Delft) Prof. Andrea Neto (Delft University of Technology) Akira Endo (Delft University of Technology) Prof. Jochem Baselmans (SRON)

Presentation Materials