Wavefront sensing techniques are mainly needed in an adaptive optics system for high resolution imaging. One of them is a Shack-Hartmann method which is composed of very simple structure. Although the method is widely utilized, it also has the limitation for the measurable magnitude of wavefront aberrations. To overcome the problem, the improved Shack-Hartmann method for larger aberrated wavefronts has been proposed. In this paper, the principle of the proposed method and the numerical evaluation of the performance of the proposed method are presented.
A Shack-Hartmann wavefront sensor (SHWFS) which consists of a microlens array and an image sensor has been
used to measure the wavefront aberrations in various fields owing to its advantages such as simple configuration.
However, a conventional SHWFS has the finite dynamic range. The dynamic range cannot be expanded without
sacrificing the spatial resolution and the sensitivity in a conventional SHWFS. In this study, the SHWFS using
a dual microlens array to solve the problem is proposed. In the proposed method, an astigmatic microlens is
arranged at the center of a group of 2 x 2 spherical microlenses. A pattern image including spots and linear
patterns is obtained at the focal plane by the dual microlens array. The pattern image can be separated into two
images as if two microlens array with different diameter were used by discriminating spots from linear patterns
with the pattern matching technique. The proposed method enables to expand the dynamic range of an SHWFS
by using the separated two images. The performance of the proposed method is confirmed by the numerical
simulation for measuring a spherical wave.