A correlation-locking adaptive filtering technique for minimum variance integral control in adaptive optics

TL;DR

This paper introduces CLOSE, a real-time adaptive filtering technique for AO systems that automatically optimizes modal gains to achieve minimum variance control, improving performance under various noise and seeing conditions.

Contribution

The paper presents CLOSE, a novel, scalar-parameter-based adaptive filtering method that automatically tunes modal gains in AO systems, addressing optical gain issues in high-order systems for extremely large telescopes.

Findings

CLOSE effectively optimizes modal gains in simulations of AO systems.

The technique demonstrates robustness to transient effects and noise variations.

CLOSE improves AO correction by compensating for optical gain phenomena.

Abstract

We propose the Correlation-Locking Optimization SchEme (CLOSE), a real-time adaptive filtering technique for adaptive optics (AO) systems controlled with integrators. CLOSE leverages the temporal autocorrelation of modal signals in the controller telemetry and drives the gains of the integral command law in a closed servo-loop. This supervisory loop is configured using only a few scalar parameters, and automatically controls the modal gains to closely match transfer functions achieving minimum variance control. This optimization is proven to work throughout the range of noise and seeing conditions relevant to the AO system. This technique has been designed while preparing the high-order AO systems for extremely large telescopes, in particular for tackling the optical gain (OG) phenomenon -- a sensitivity reduction induced by on-sky residuals -- which is a prominent issue with pyramid wavefront sensors (PWFS). CLOSE follows upon the linear modal compensation approach to OG, previously demonstrated to substantially improve AO correction with high order PWFS systems. Operating on modal gains through multiplicative increments, CLOSE naturally compensates for the recurring issue of unaccounted sensitivity factors throughout the AO loop. We present end-to-end simulations of the MICADO instrument single-conjugate AO to demonstrate the performances and capabilities of CLOSE. We demonstrate that a single configuration shall provide an efficient and versatile optimization of the modal integrator while accounting for OG compensation, and while providing significant robustness to transient effects impacting the PWFS sensitivity.