The Planar Optics Phase Sensor: a study for the VLTI 2nd Generation Fringe Tracker

TL;DR

This paper introduces the Planar Optics Phase Sensor, a compact integrated optics-based fringe tracker designed for the VLTI's second-generation instruments, capable of real-time optical path difference measurement for 4 to 6 telescopes.

Contribution

It proposes a novel integrated optics fringe sensor concept for VLTI, enabling multi-telescope operations with real-time fringe measurement using spectral dispersion.

Findings

Conceptual analysis supporting the design

Expected on-sky performance estimates

Proposed design for implementation

Abstract

In a few years, the second generation instruments of the Very Large Telescope Interferometer (VLTI) will routinely provide observations with 4 to 6 telescopes simultaneously. To reach their ultimate performance, they will need a fringe sensor capable to measure in real time the randomly varying optical paths differences. A collaboration between LAOG (PI institute), IAGL, OCA and GIPSA-Lab has proposed the Planar Optics Phase Sensor concept to ESO for the 2nd Generation Fringe Tracker. This concept is based on the integrated optics technologies, enabling the conception of extremely compact interferometric instruments naturally providing single-mode spatial filtering. It allows operations with 4 and 6 telescopes by measuring the fringes position thanks to a spectrally dispersed ABCD method. We present here the main analysis which led to the current concept as well as the expected on-sky performance and the proposed design.