A technique of computational image encryption and optical decryption based on computer generated holography and time-averaged moir´e is investigated in this paper. Dynamic visual cryptography (a visual cryptography scheme based on time-averaging geometric moir´e), Gerchberg–Saxton algorithm and 3D microstructure manufacturing techniques are used to construct the optical scheme. The secret is embedded into a cover image by using a stochastic moir´e grating and can be visually decoded by a naked eye. The secret is revealed if the amplitude of harmonic oscillations in the Fourier plane corresponds to an accurately preselected value. The process of the production of 3D microstructure is described in details. Computer generated holography is used in the design step and electron beam lithography is exploited for physical 3D patterning. The phase data of a complex 3D microstructure is obtained by Gerchberg-Saxton algorithm and is used to produce a computer generated hologram. Physical implementation of microstructure is performed by using a single layer polymethyl methacrylate as a basis for 3D microstructure. Numerical simulations demonstrate efficient applicability of this technique.
The main focus of the paper is the development of technological route of the production of complex 3D microstructure,
from designing it by the method of computer generated holography till its physical 3D patterning by exploiting the
process of electron beam lithography and thermal replication which is used for biomedical application. A phase data of a
complex 3D microstructure was generated by using Gerchberg-Saxton algorithm which later was used to produce a
computer generated hologram. Physical implementation of microstructure was done using a single layer polymethyl
methacrylate (PMMA) as a basis for 3D microstructure, which was exposed using e-beam lithography system e-Line and
replicated, using high frequency vibration. Manufactured 3D microstructure is used for designing micro sensor for
The well-known phase-shifting approach for three-dimensional surface measurement uses multiple fringe patterns along with the phase-shifting algorithm to obtain 3-D profiles with high accuracy though this approach is not applicable for dynamic object measurement techniques such as time-averaged holography and in cases when only a single interference fringe pattern is available. In this case the fringe tracing method can be used that is based on localization of centers of interference fringes. We propose a technique for the reconstruction of the contour map from fringe patterns which comprises standard image processing techniques and a scheme for reconstruction of the map of continuous curves from the binary matrix of pixels representing fringe centers. The approach of image division into grid cells is taken and such problems as derivation of approximate line equations in each cell using Hough transformation, grouping contacting cells into curves and interpolation between curves with fractures are solved. The functionality of this approach is demonstrated for a demanding optical image containing fractures and noise.
Low-cost effective characterization methodology was developed that allows indirect evaluation of mechanical,
geometrical and optical parameters of periodical microstructures in the cases when traditional measurement techniques
are not suitable. Proposed methods are applicable for optimization and control of technological processes.
Laser diffractometer is used in the experimental works for measurement of optical parameters of periodical
microstructure and estimation of geometrical parameters with an error of less than 5% by comparing theoretical and
experimental values of diffraction efficiencies of periodical microstructures. This method is suitable for geometry control
of periodical microstructures during all technological process.
Also an efficient method was developed that is capable to estimate with an error of 5% the depth of periodical microstructures, which have characteristic depths that are larger than the wavelength of coherent light used in the experiment.
Quality of periodical microstructures is sensitive to thermal conditions during replication process. Therefore an experimental setup based on Michelson interferometer was developed for the investigation of induced thermal deformation. The radius and stress kinetics could be analyzed for different thickness of coated polymer.
These are the problems that are considered in this paper.