Zernike monomials in wide field of view optical designs.

Abstract

Zernike polynomials are universal in optical modeling and testing of wavefronts; however, their polynomial behavior can cause a misinterpretation of individual aberrations. Wavefront profiles described by Zernike polynomials contain multiple terms with different orders of pupil radius (ρ). Zernike polynomials are a sum of high and low orders of ρ to minimize the RMS wavefront error and to preserve orthogonality. Since the low-order polynomials are still contained in the net Zernike sum, there is redundancy in individual monomials. Monomial aberrations, also known as Seidel or primary aberrations, are useful in studying an optical design's complexity, alignment, and field behavior. Zernike polynomial aberrations reported by optical design software are not indicative of individual (monomial) aberrations in wide field of view designs since the low-order polynomials are contaminated by higher order terms. An aberration node is the field location where an individual (monomial) aberration is zero. In this paper, a matrix method is shown to calculate the individual monomial aberrations given the set of Zernike polynomials. Monomial aberrations plotted as a function of field angle (H) indicate the field order (Hn) and the location of true aberration nodes. Contrarily, Zernike polynomial versus field (ZvF) plots can indicate false aberration nodes, due to the polynomial mixing of high- and low-order terms. Accurate knowledge of the monomial aberration nodes, converted from Zernike polynomials, provides the link between a ray-trace model or lab wavefront measurement and nodal aberration theory (NAT). This method is applied to two different optical designs: (1) 120° circular FOV fish-eye lens and (2) 120∘×4∘ rectangular FOV, off-axis, freeform four-mirror design.