Using multi-wavelength phase diversity to improve the detection range of piston in multi-aperture

Multi-aperture optical systems provide a solution that can enhance resolution without the requirement for a large-diameter single-aperture system. However, one of the challenges of multi-aperture optical systems is the detection of the piston. The phase diversity (PD) technique can detect non-continuous co-phase errors and is often used for the detection of multi-aperture piston. The PD technique estimates the wavefront aberration of the optical imaging system and the target image by acquiring an image of the focal plane of an unknown target passing through the optical system and one or more images of known aberration (often chosen to be defocused). The PD technique is usually converted to a nonlinear optimization problem, but the optimization process may fall into local minima due to 2π piston ambiguity. Such a 2π piston ambiguity problem can be solved by using broadband light with multiple wavelengths. In this paper, a multi-wavelength phase diversity technique based on optimized grid search is used, which improves the detection range so that the piston and the final evaluation function values will be more likely to be within the correct range, and improves the solution success rate compared to the unoptimized grid search method.