Method of optimizing deterministic small free-form surfaces for off-axis optical systems with extremely low aberration

Abstract

A mapping model of arbitrarily shaped surfaces and the system image quality is constructed to examine the optimization of the residual aberration of an off-axis optical system to construct an off-axis optical system with very small aberrations. First, orthogonal surfaces are chosen within the arbitrary aperture. The mapping relationship between the orthogonal surfaces and system wavefront aberration is then established. Finally, the surfaces required for optimization are acquired by solving the mapping relationship through singular value decomposition and the Gauss–Newton algorithm. The residual aberration of the system is optimized using free-form surfaces with small deviations. In this paper, the residual aberration of an off-axis optical system with a non-circular aperture is optimized by adopting the above method, with the residual aberration of the system reducing from 0.549 nm (root-mean-square, RMS) to 0.443 nm (RMS) after adding a small free-form surface to a single lens, and to 0.393 nm (RMS) after adding small free-form surfaces to two lenses. The optical system with a circular aperture is optimized and the residual aberration of the system is reduced from 2 nm (RMS) to 0.47 nm (RMS).