Refractive index tomography of direct fs-laser written waveguides

Abstract

We present a tomographic reconstruction algorithm that is able to reconstruct waveguide profiles from a set of intensity images taken at different illumination angles. Very recently, such algorithms have become the state of the art in the community of bio imaging, but have never been applied to direct laser written structures such as waveguides. We adapt the algorithm to our application of characterizing translation-invariant structures and extend it to jointly estimate optical aberrations introduced by the imaging system. We show that a correct estimation of these aberrations is necessary for making effective use of high-angle tomographic data. Furthermore, we present a novel method for cross-validating our RI reconstructions by comparing en-face widefield images of thin waveguide sections with matching simulations based on the retrieved RI profile.