Simulation of wavefront shaping through scattering media

Abstract

Wavefront shaping technique makes it possible to overcome limitations for optical imaging in strongly scattering media. Various wavefront shaping algorithms are used in order to find an optimal incident optical field. However, in many cases such experiments appear to be very time consuming and suffer from instability of the scattering media. So, it seems reasonable to use computer simulation in this field. In this paper we use two different approaches to simulate the light focusing through scattering media. The first approach consists in numerical solution of Maxwell equations for the set of spherical particles in random positions, which represent the scattering media. The result of the solution represents the scattering matrix of the media. This matrix is used to simulate propagation of spatially modulated light in the “frozen” stochastic media. As entries of the scattering matrix appear to be random variables with Gaussian distribution, they could be set heuristically for modeling purposes. This makes possible modeling of the wavefront shaping with large number of orthogonal modes of incident light. We considered four focusing techniques: continuous sequential algorithm and focusing using useful properties of Hadamard matrix with a phase-only and binary amplitude modulation (BAM). We represent results on convergence of the algorithms and focal intensity enhancement. We examined spatial variations of intensity enhancement, while scanning the focal point in observation plane. We found, that the intensity enhancement strongly correlates with the speckle from unmodulated illumination, when the BAM is used for wavefront shaping. In the case of phase-only modulation, only weak correlations were observed.