Share Email Print
cover

Proceedings Paper

Hierarchical fringe tracking
Author(s): Romain G. Petrov; Thami Elhalkouj; Abdelkarim Boskri; Jean-Pierre Folcher; Stéphane Lagarde; Yves Bresson; Zouhair Benkhaldoun; Mohamed Lazrek; Suvendu Rakshit
Format Member Price Non-Member Price
PDF $14.40 $18.00
cover GOOD NEWS! Your organization subscribes to the SPIE Digital Library. You may be able to download this paper for free. Check Access

Paper Abstract

The limiting magnitude is a key issue for optical interferometry. Pairwise fringe trackers based on the integrated optics concepts used for example in GRAVITY seem limited to about K=10.5 with the 8m Unit Telescopes of the VLTI, and there is a general “common sense” statement that the efficiency of fringe tracking, and hence the sensitivity of optical interferometry, must decrease as the number of apertures increases, at least in the near infrared where we are still limited by detector readout noise. Here we present a Hierarchical Fringe Tracking (HFT) concept with sensitivity at least equal to this of a two apertures fringe trackers. HFT is based of the combination of the apertures in pairs, then in pairs of pairs then in pairs of groups… The key HFT module is a device that behaves like a spatial filter for two telescopes (2TSF) and transmits all or most of the flux of a cophased pair in a single mode beam. We give an example of such an achromatic 2TSF, based on very broadband dispersed fringes analyzed by grids, and show that it allows piston measures from very broadband fringes with only 3 to 5 pixels per fringe tracker. We show the results of numerical simulation indicating that our device is a good achromatic spatial filter and allowing a first evaluation of its coupling efficiency, which is similar to this of a single mode fiber on a single aperture. Our very preliminary results indicate that HFT has a good chance to be a serious candidate for the most sensitive fringe tracking with the VLTI and also interferometers with much larger number of apertures. On the VLTI the first rough estimate of the magnitude gain with regard to the GRAVITY internal FT is between 2.5 and 3.5 magnitudes in K, with a decisive impact on the VLTI science program for AGNs, Young stars and planet forming disks.

Paper Details

Date Published: 24 July 2014
PDF: 9 pages
Proc. SPIE 9146, Optical and Infrared Interferometry IV, 91462P (24 July 2014); doi: 10.1117/12.2056677
Show Author Affiliations
Romain G. Petrov, Lab. Joseph-Louis Lagrange, CNRS, Observatoire de la Côte d'Azur (France)
Univ. de Nice Sophia-Antipolis (France)
Thami Elhalkouj, Univ. Cadi Ayyad (Morocco)
Abdelkarim Boskri, Univ. Cadi Ayyad (Morocco)
Jean-Pierre Folcher, Lab. Joseph-Louis Lagrange, CNRS, Observatoire de la Côte d'Azur (France)
Univ. de Nice Sophia-Antipolis (France)
Stéphane Lagarde, Lab. Joseph-Louis Lagrange, CNRS, Observatoire de la Côte d'Azur (France)
Univ. de Nice Sophia-Antipolis (France)
Yves Bresson, Lab. Joseph-Louis Lagrange, CNRS, Observatoire de la Côte d'Azur (France)
Univ. de Nice Sophia-Antipolis (France)
Zouhair Benkhaldoun, Univ. Cadi Ayyad (Morocco)
Mohamed Lazrek, Univ. Cadi Ayyad (Morocco)
Suvendu Rakshit, Lab. Joseph-Louis Lagrange, CNRS, Observatoire de la Côte d'Azur (France)
Univ. de Nice Sophia-Antipolis (France)


Published in SPIE Proceedings Vol. 9146:
Optical and Infrared Interferometry IV
Jayadev K. Rajagopal; Michelle J. Creech-Eakman; Fabien Malbet, Editor(s)

© SPIE. Terms of Use
Back to Top