Optical phased arrays for wavefront shaping in forward scattering media

Abstract

High-resolution optical imaging in thick tissue samples remains elusive, mainly because of the scattering exhibited by the tissue. With increasing depth, the number of nonscattered photons exponentially decreases – limiting the use of conventional imaging techniques at depth. Wavefront shaping is a novel technique that aims to enable imaging at depth by refocusing the scattered light. However, significant wavefront-control hardware improvements are necessary to unlock the applications in in vivo microscopy. Optical phased arrays (OPAs), realized in integrated photonics, can provide improvements in the pixel pitch, operation speed, and system compactness compared to conventionally employed spatial light modulators. We compare different OPA designs for focusing in tissue-like forward-scattering samples. OPA design trade-offs, such as the array pitch, number of antennas, and antenna emission profile, are experimentally studied, and their influence on the device performance is highlighted. We do this for increasing thickness of the forward-scattering sample and observe two distinct regimes. The devices, operating at the wavelength of λ = 852 nm, were fabricated on a SiN photonics platform suitable for both near-infrared (NIR) and visible (VIS) light.