Relation between substructure position of phase objects in optical axial direction and phase information in quantitative phase imaging

Substructure position of biological cells and tissues owns much more information about the state and evolution of these cells and tissues. Comparing with the substructure position of these biological objects at the plane perpendicular to the optical axial, the substructure position of these objects in optical axial direction is hard to be measured by the general quantitative phase imaging (QPI). Here, based on the split-step beam propagation theory, we numerically investigate the relation between substructure position of phase objects in optical axial direction and phase information in QPI. Five groups of two-sphere model with the internal sphere at different positions in optical axial direction are studied. The results show that the position of the internal sphere in optical axial direction does not change the general morphology of the phase map, but it leads to some differences near the boundary of the internal sphere. Further, we get the relation between the maximum positive phase deviation and the position of the internal sphere in optical axial direction. Such a relation will provide the theoretical basis for the analysis of experimental results in phase imaging.