The transport-of-intensity equation (TIE) describes a deterministic relation between the intensity distribution
in different focal planes and the corresponding phase distribution. A Green's function solution of the TIE is
used to retrieve the phase distribution of an object considering specific boundary conditions. This leads to an
accurate reconstruction of the properties of phase objects, e.g. the refractive indices and thus the numerical
aperture (NA) of optical fibers. The required intensity distributions are captured simultaneously by the use of
a multi-camera microscope. The TIE is solved using a computer algorithm, which can be massively parallelized.
This offers the application of general purpose computation on graphics processing units (GPGPU). Therefore
real-time reconstruction of the phase distribution is possible.