Multi-wavelength and field diversity phase retrieval for large-scale on-line wavefront sensing for segmented space...

Space-based segmented telescopes require accurate sensing of segment-level co-phasing errors and field-dependent continuous aberrations under thermal and mechanical disturbances. Conventional single-wavelength phase retrieval is constrained by the 2π phase-wrapping ambiguity and often relies on mechanically generated phase diversity, limiting its sensing range and long-term reliability. This paper proposes a fixed-channel multi-wavelength and field diversity phase-retrieval framework. Dedicated wavefront sensing detectors are positioned at different field locations and fixed axial offsets relative to the nominal focal plane, while narrowband filters assign distinct wavelengths to the individual sensing channels. Field, defocus, and wavelength diversity can therefore be acquired simultaneously without moving components. The collected point spread functions (PSFs) are jointly used to reconstruct segment-level co-phasing errors and field-dependent continuous aberrations. Wavelength diversity extends the unambiguous piston range, whereas additional wavelength-field channels provide complementary constraints for robust reconstruction. Numerical simulations show that inter-segment piston errors over a range of 0-2 µm can be reliably reconstructed using four wavelength-field sensing channels, exceeding the unambiguous range of conventional single-wavelength sensing. Monte Carlo results show that the mean root-mean-square wavefront error (RMS WFE) at all four sensing fields remains below λ/40 over peak signal-to-noise ratio (PSNR) levels of 20-50 dB, where λ=633nm. With additional wavelength-field sensing channels, the investigated piston range is extended to 0-4 µm, accompanied by improved convergence robustness and reconstruction consistency. These results demonstrate the potential of the proposed fixed-channel framework for large-range on-line wavefront sensing in future segmented space telescopes.