Optical identification system of three-dimensional random phase object by use of speckle patterns in propagation distances

An optical identification system of a three-dimensional (3D) random phase object by use of speckle patterns in different propagation distances is proposed and evaluated experimentally. The 3D random phase object is used as a 3D key. It can be secure when the scattering is strong enough because the interferometric measurement is not applied. The identification is implemented by evaluating crosscorrelation value between the measured and stored speckle patterns. To achieve a higher level of identification, two speckle patterns obtained at different propagation distances are used. The tolerance of 3D position of 3D random phase object are evaluated. We also investigate the influence of occlusion and binarization of speckle patterns on identification capability.