Quantum & Optical Space Links | Dr. Jorge Querol

Performance analysis of the Cassegrain telescope on the QKD with Mathieu-Gauss Beams

Mon, 11 May 2026 00:00:00 +0000

Abstract & Overview

Mathieu-Gauss beams (MGBs), a distinctive class of structured light generated by modulating the angular and radial components of Gaussian beams with Mathieu functions, exhibit propagation characteristics that make them promising candidates for free-space optical (FSO) and quantum communication links. In this study, the scintillation behaviour of MGBs under weak atmospheric turbulence is analysed to derive the effective visibility and to quantify its impact on the quantum bit error rate (QBER) and secret key rate (SKR) in quantum key distribution (QKD) systems employing Cassegrain-type transmitters. Numerical simulations are performed using a random phase screen method based on the modified von Kármán spectrum for even and odd MGB modes under various telescope configurations. QBER is modelled as a function of effective visibility derived from the scintillation index. The results demonstrate that the use of a Cassegrain telescope significantly suppresses scintillation-induced degradation, reduces QBER, and enhances SKR, with improvements of up to 80% compared to free-space propagation without telescopic correction. However, the performance enhancement is strongly mode-dependent, with certain MGB orders exhibiting greater turbulence resilience. These findings highlight the importance of transmitter geometry and beam-structure optimisation in improving the robustness and efficiency of structured-light-based FSO-QKD systems.

Publication Metadata

Authors: S. Oktay, Mert Bayraktar, Francesco Vista, Jorge Querol, Yves Schmit, S. Chatzinotas
Venue: Scientific Reports (2026)
Research Areas: AI & Neuromorphic SatCom, Beamforming & MIMO, Quantum & Optical Space Links
DOI: 10.1038/s41598-026-51915-y
Open Access Repository: ORBiLu – University of Luxembourg

Effect of the Cassegrain Telescope on the scintillation of Mathieu-Gauss beams

Thu, 18 Sep 2025 00:00:00 +0000

Abstract & Overview

The scintillation index plays a crucial role in the performance of free space optics (FSO) and quantum key distribution (QKD) systems. Enhancement in the scintillation index causes an increase in the bit error rate and a decrease in the key rate. In this paper, we studied the effect of the Cassegrain telescope on the scintillation of Mathieu-Gauss beams (MGB) in a weak turbulent atmosphere. We model the atmosphere by using the random phase screen numerical approach. We benefit from the hard aperture function when modeling the telescope. We compare the point-like scintillation values with and without the Cassegrain telescope. We research even and odd modes of the MGB. We observe that the scintillation index decreases drastically when using the Cassegrain telescope. In addition, we investigate that the scintillation index decreases when the expansion order rises. Similarly, we see that there is an inverse relation between the first complex expansion coefficient at a short distance. An increase in the second complex expansion coefficient shows its advantage at longer distances by mitigating scintillation. We anticipate that our results will be useful for the optical engineers to design FSO and QKD systems.

Publication Metadata

Authors: Mert Bayraktar, Francesco Vista, Jorge Querol, Yves Schmit, Symeon Chatzinotas
Venue: IEEE International Conference on Space Optical Systems and Applications (ICSOS) (2025)
Research Areas: AI & Neuromorphic SatCom, Beamforming & MIMO, Quantum & Optical Space Links
DOI: 10.1117/12.3063944
Open Access Repository: ORBiLu – University of Luxembourg

L-band vegetation optical depth estimation using transmitted GNSS signals: Application to GNSS-reflectometry and positioning

Wed, 01 Jan 2020 00:00:00 +0000

Abstract & Overview

At L-band (1–2 GHz), and particularly in microwave radiometry (1.413 GHz), vegetation has been traditionally modeled with the τ-ω model. This model has also been used to compensate for vegetation effects in Global Navigation Satellite Systems-Reflectometry (GNSS-R) with modest success. This manuscript presents an analysis of the vegetation impact on GPS L1 C/A (coarse acquisition code) signals in terms of attenuation and depolarization. A dual polarized instrument with commercial off-the-shelf (COTS) GPS receivers as back-ends was installed for more than a year under a beech forest collecting carrier-to-noise (C/N0) data. These data were compared to different ground-truth datasets (greenness, blueness, and redness indices, sky cover index, rain data, leaf area index or LAI, and normalized difference vegetation index (NDVI)). The highest correlation observed is between C/N0 and NDVI data, obtaining R2 coefficients larger than 0.85 independently from the elevation angle, suggesting that for beech forest, NDVI is a good descriptor of signal attenuation at L-band, which is known to be related to the vegetation optical depth (VOD). Depolarization effects were also studied, and were found to be significant at elevation angles as large as ~50°. Data were also fit to a simple τ-ω model to estimate a single scattering albedo parameter (ω) to try to compensate for vegetation scattering effects in soil moisture retrieval algorithms using GNSS-R. It is found that, even including dependence on the elevation angle (ω(θe)), at elevation angles smaller than ~67°, the ω(θe) model is not related to the NDVI. This limits the range of elevation angles that can be used for soil moisture retrievals using GNSS-R. Finally, errors of the GPS-derived position were computed over time to assess vegetation impact on the accuracy of the positioning.

Publication Metadata

Authors: Adriano Camps, Alberto Alonso-Arroyo, Hyuk Park, Raul Onrubia, Daniel Pascual, Jorge Querol
Venue: Remote sensing (2020)
Research Areas: JCAS & Earth Observation, GNSS & Positioning, Quantum & Optical Space Links
DOI: 10.3390/rs12152352

‘Ionospheric scintillation impact on GNSS-R altimetry

Mon, 01 Jan 2018 00:00:00 +0000

Abstract & Overview

This research contribution by A Camps, H Park, E Lancheros, R Onrubia et al. (2018), published in GNSS+ R, Ann Arbor, MI, USA, Tech. Rep, investigates “‘Ionospheric scintillation impact on GNSS-R altimetry” within the domains of JCAS & Earth Observation, GNSS & Positioning, Quantum & Optical Space Links. The work is part of Dr. Jorge Querol’s research portfolio in advanced satellite communications, non-terrestrial networks (NTN), and radio-frequency signal processing at SnT (University of Luxembourg) and UPC-BarcelonaTech.

Publication Metadata

Authors: A Camps, H Park, E Lancheros, R Onrubia, D Pascual, Jorge Querol
Venue: GNSS+ R, Ann Arbor, MI, USA, Tech. Rep (2018)
Research Areas: JCAS & Earth Observation, GNSS & Positioning, Quantum & Optical Space Links