High-resolution tomographic interferometry of optical phase elements

Decades ago tomographic interferometry was successfully applied to the measurement of phase objects in a large scale. Recently the application field was extended to nearly micro scale, for example optical fibers. Nevertheless, the geometry of tested objects was usually relatively simple and the spatial resolution at the level of several microns was always a barrier. In this paper we investigate the possibility of tomographic reconstruction of complex phase objects by means of tomographic interferometry. The analyses have been performed on the photonic crystal fiber, which is not only a high-resolution object, but additionally contains periodic structures. The influences of the following factors are investigated: proper matching of the immersion liquid, mechanical imperfections of the rotation, geometry of the fiber, polarization of the illumination beam and type of reconstruction algorithm. In addition to experimental results, the numerical simulation of wavefront propagation through the fiber is performed. According to the results, the high - resolution reconstruction of the three-dimensional refractive index distribution in the object containing a periodic structure is possible, however limited by several conditions, as described in the paper.