Spherical lens aberration minimization method for short-range free-space light transmission

Abstract

Spherical aberrations of lenses lead to increased spot radii on the focal plane. Several methods, such as optimizing thickness and radii or building lens groups, are known to minimize these spherical aberrations. Here, an innovative method for spherical aberration minimization is introduced; it can be used for short-range free-space optical communication systems, such as unit power afocal relay trains, lens waveguides, and periodic lens systems. This spherical aberration compensation principle is based on the combination of two identical spherical convex lenses at an optimal distance. Due to the higher refractive power for rays with an larger axis distance, rays from the outer area of the first lens intersect the inner area of the second lens, and vice versa. With this setup, the radial refractive power deviation of the two lenses compensate each other. Analytic calculations and numerical simulations are done to confirm this behavior, and measurements using two symmetric spherical lenses with polymer optical fibers as light feed confirm the calculations. Simulations and measurements show a very good matching behavior except for an unknown systematic error. At a lens distance of 300 mm, the optical attenuation decreased by ∼2 dB compared with a very small lens distance. This leads to the conclusion that this proposed spherical aberration minimization method works as theoretically predicted.