An Enhanced Intersecting-Lines Method for Optical Loss Characterization in SIS Heterodyne Receivers
Abstract
Accurate knowledge of radio-frequency (RF) losses in front of superconductor--insulator--superconductor (SIS) mixers is essential for optimizing millimeter- and terahertz heterodyne receivers. However, such losses are difficult to extract from conventional hot/cold-load measurements because the measured receiver noise combines contributions from the input optics, the mixer, and the intermediate-frequency chain. In this work, we present a numerical implementation of the straight-line, or intersecting-lines, method for estimating input-referred RF noise and optical loss from standard Y-factor measurements. Hot/cold IF spectra are acquired while sweeping the local oscillator (LO) pumping level from under-pumped to over-pumped operation, so that each IF frequency bin gives a family of linear relations between receiver output power and input load temperature. We evaluate all pairwise intersections between these lines and analyze the crossing cloud to obtain the effective RF input noise. We repeat the analysis across the IF band and multiple LO tunings which provides a frequency-resolved characterisation of the input losses over the full band. Our implementation turns the straight-line technique into a reproducible framework for receiver characterisation and relative optical-loss comparison in low-loss front-end configurations.
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BibTeX
@misc{joint2026enhanced,
title = {{An Enhanced Intersecting-Lines Method for Optical Loss Characterization in SIS Heterodyne Receivers}},
author = {François Joint and Magnus Strandberg and Denis Meledin and Igor Lapkin and Sven-Erik Ferm and Mathias Fredrixon and Leif Helldner and Alexei Pavolotsky and Erik Sundin and Victor Belitsky and Vincent Desmaris},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.24838},
eprint = {2610.24838},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.24838},
}
RIS
TY - UNPB
TI - An Enhanced Intersecting-Lines Method for Optical Loss Characterization in SIS Heterodyne Receivers
AU - François Joint
AU - Magnus Strandberg
AU - Denis Meledin
AU - Igor Lapkin
AU - Sven-Erik Ferm
AU - Mathias Fredrixon
AU - Leif Helldner
AU - Alexei Pavolotsky
AU - Erik Sundin
AU - Victor Belitsky
AU - Vincent Desmaris
PY - 2026
DA - 2026/10/17
PB - arXiv
DO - 10.48550/arxiv.2610.24838
UR - https://arxiv.org/abs/2610.24838
AB - Accurate knowledge of radio-frequency (RF) losses in front of superconductor--insulator--superconductor (SIS) mixers is essential for optimizing millimeter- and terahertz heterodyne receivers. However, such losses are difficult to extract from conventional hot/cold-load measurements because the measured receiver noise combines contributions from the input optics, the mixer, and the intermediate-frequency chain. In this work, we present a numerical implementation of the straight-line, or intersecting-lines, method for estimating input-referred RF noise and optical loss from standard Y-factor measurements. Hot/cold IF spectra are acquired while sweeping the local oscillator (LO) pumping level from under-pumped to over-pumped operation, so that each IF frequency bin gives a family of linear relations between receiver output power and input load temperature. We evaluate all pairwise intersections between these lines and analyze the crossing cloud to obtain the effective RF input noise. We repeat the analysis across the IF band and multiple LO tunings which provides a frequency-resolved characterisation of the input losses over the full band. Our implementation turns the straight-line technique into a reproducible framework for receiver characterisation and relative optical-loss comparison in low-loss front-end configurations.
ER -