Identification of 3D Objects using Correlation of Holograms

A hologram is the 2D recording of the amplitude and phase of an object. Often the phase contains the information of the depth of a 3D object. In our previous work, the 3D mapping of different surfaces have been performed using digital holographic topography. For instance, multi-wavelength digital holography has been used to resolve deformations/depths which are in the order of several microns to centimeters. Now, 2D correlation has been extensively used as a pattern recognition tool to distinguish between different 2D objects. For 3D object correlation, a novel technique involving 2D correlation of holograms is proposed, enabling identification of the 3D object. As a proof-of-principle, in this work holograms of objects which have identical intensity features and different depth profiles are computer generated as well as optically recorded. Then 2D correlation is applied to distinguish the objects. An additional advantage of this method is that one can compare phase/depth information without performing additional numerical steps such as phase unwrapping.