Quantitative phase imaging of fiber Bragg gratings in multicore fibers.

Fiber Bragg gratings (FBGs) and multi-core fibers (MCFs) have independently demonstrated high levels of performance in numerous diverse applications. When integrated together, the devices can offer enhanced performance as well as open more applications. In all of these cases, the refractive index (RI) characterization of the FBGs is crucial in monitoring and validating the fabricated devices. To accomplish this, quantitative phase imaging (QPI) is a promising RI characterization candidate satisfying all of the requirements: noninvasive measurement, quantitative characterization, sub-micrometer resolution, no a priori knowledge, and 3D reconstruction. In this paper, we propose a new QPI method for characterization of the RI distribution of multiple FBGs in a single MCF. We have identified the key challenges associated with this approach: the pixel integration effect, aliasing effect, numerical aperture requirement, and characteristic functions recovery. We have further identified approaches for overcoming each of these challenges that have previously impeded this direction of research. The proposed method is supported by simulations of 2D and 3D gratings.