Status of an extreme adaptive optics testbench using a self-referenced Mach-Zehnder wavefront sensor

Extreme adaptive optics (XAO) systems have severe difficulties to meet the following high contrast requirements: high speed (>1kHz) and high accuracy (∼10 nm) at 5-10 cm spatial scale. An innovative high order adaptive optics system using a self-referenced Mach-Zehnder wavefront sensor has been proposed to counteract these limitations. This wavefront sensor estimates the phase by measuring directly intensity differences between two outputs, but has a limited dynamical range. In this paper, we report on our latest results with the XAO testbed in operation in our lab, and dedicated to high contrast imaging with 30m-class telescopes. A woofer-tweeter architecture is used in order to deliver the required high Strehl ratio (>95%). We present our latest laboratory results, including fine calibration and closed loop performance. This work is carried out in synergy with the validation of fast iterative wavefront reconstruction algorithms, and the optimal treatment of phase ambiguities in order to mitigate the dynamical range limitation of such a wavefront sensor.