Optical authentication method using a three-dimensional phase object with various wavelength readouts.

An optical system for authentication using a 3D (3D) random phase object with various wavelength readouts is proposed. The 3D phase object without surface modulation is secure when the scattering is strong enough because it prevents from the interferometric measurement. The identification is implemented by the correlation between a measured speckle pattern of the 3D phase object and stored speckle patterns. For accurate identification, two speckle patterns of the 3D object obtained by illuminating two wavelengths are used. Experimental demonstrations and numerical evaluations of wavelength selectivity are presented.