Hierarchical fringe tracking

Romain G. Petrov; Fatmé Allouche; Massinissa Hadjara; Abdelkarim Boskri; James Leftley; Amokrane Berdja; Stéphane Lagarde

doi:10.1117/12.3018417

28 August 2024 Hierarchical fringe tracking

Romain G. Petrov, Fatmé Allouche, Massinissa Hadjara, Abdelkarim Boskri, James Leftley, Amokrane Berdja, Stéphane Lagarde

Author Affiliations +

Proceedings Volume 13095, Optical and Infrared Interferometry and Imaging IX; 130952H (2024) https://doi.org/10.1117/12.3018417
Event: SPIE Astronomical Telescopes + Instrumentation, 2024, Yokohama, Japan

Conference Poster

Abstract

Hierarchical Fringe Trackers (HFT) maximize the sensitivity and accuracy of fringe tracking. Their performances are independent from the number of apertures. They cophase pairs of telescopes, then pairs of pairs and so on. We report the key results of mathematical analysis, design, manufacturing, optical tests and simulated performances of 4 telescopes HFT chips for the VLTI and 6 to 8 telescopes HFT chips for CHARA or a VLTI extension. An end-to-end simulation with realistic input piston and flux, based on the experimental characterization of the signals on the test bench, validates the servo loop and state machine architectures and supports the performance analysis, confirming the expected performance gain of about 3 magnitudes (with a limiting magnitude K>16 on the VLTI with UTs) and the fact that the performances do not decrease with the number of apertures. The performance gain is based on the combination of the HFT architecture with a very broad band HFT covering the 1.1 to 2.2μm domain with 3 to 5 HFT chips working in broad sub bands in J, H and K. Analysis of fringe jumps and losses at the sensitivity limit show that an HFT manages then more efficiently than the standard pairwise architecture. The impact of HFT characteristics on AGN science programs for optical interferometers is illustrated, showing that this architecture is the key for fascinating applications including direct distance measurements of AGNs accurate enough to contribute to the Hubble tension problem.

Citation Download Citation

Romain G. Petrov, Fatmé Allouche, Massinissa Hadjara, Abdelkarim Boskri, James Leftley, Amokrane Berdja, and Stéphane Lagarde "Hierarchical fringe tracking", Proc. SPIE 13095, Optical and Infrared Interferometry and Imaging IX, 130952H (28 August 2024); https://doi.org/10.1117/12.3018417

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