Upgrading SPHERE with the second stage AO system SAXO+: Hardware interface integration

SAXO+, the upgrade of the SPHERE adaptive optics (AO) system, is about to enter its Assembly, Integration, and Testing (AIT) phase following the Final Design Review (FDR) at ESO in May 2025, with first light scheduled for 2028 on the VLT. The SAXO+ project aims to enhance the performance of SPHERE, particularly in terms of contrast, by implementing a second-stage adaptive optics system that will operate in conjunction with the existing first-stage system (SAXO). The Real-Time Controller (RTC) is a key component of the SAXO+ system. It is based on the COSMIC platform for the hard real-time layer and on the ESO RTC Toolkit for the soft real-time layer. The SAXO+ RTC has been designed to be flexible and modular, supporting the implementation of various control strategies, including techniques based on artificial intelligence (AI). This second stage will feature a pyramid wavefront sensor (PWFS) operating at high frame rates—up to 3 kHz—, a new deformable mirror (DM) with 952 actuators and a sFPDP link to ensure coordination with the first stage. The integration of these interfaces remains a significant challenge, requiring careful coordination between hardware timing, data formats and real-time processing constraints to guarantee overall system stability and performance. In this paper, we present the SAXO+ RTC software development current status and the hardware interface integration. We also present preliminary performance results of the RTC, including latency and jitter measurements for sFPDP and camera acquisition. Finally, we discuss the next steps in the development of the SAXO+ RTC, focusing on system integration and testing during the project’s AIT phase.