Method of Asymmetric Optical Encryption of Images Using Spatially Incoherent Illumination

The method of asymmetric encryption of images based on the double optical encryption with spatially incoherent illumination is presented. Numerical simulations of the presented method in various modifications are carried out and their efficiency is estimated. The modification providing the best balance between maintaining the advantages peculiar to the optical encryption and quality of the decoded images is chosen. In this case the value of the normalized standard deviation (NSTD) of the decoded image from original one for asymmetric encryption differs no more than by 8% from NSTD of standard optical encryption with spatially incoherent illumination

Coefficients Quantization at Off-axis Digital Hologram Wavelet Compression

Digital holographic information is compressed for storage of 2D- or 3D-objects amplitude and phase distributions, fast transmission, analyzing and displaying of these data. In this paper features of application of wavelet transforms for off-axis digital holograms compression are considered. The combined technique based on zero and twin orders elimination, wavelet compression of the amplitude and phase components of obtained Fourier spectrum and further additional compression of wavelet coefficients by thresholding and quantization is analyzed. Numerical experiments on reconstruction of images from the compressed holograms are performed. The comparative analysis of applicability of various wavelets and additional quantization of coefficients is performed. Obtained results demonstrate possibility of 180 and more times compression using iterative and noniterative methods of coefficients quantization and threshold zeroing less 80% of wavelet coefficients. Keywords: digital holography, hologram compression, wavelets, quantization, thresholding, digital image processing

Observation of Spin Relaxation Anisotropy in Semiconductor Quantum Wells

Spin relaxation of two-dimensional electrons in asymmetrical (001) AlGaAs quantum wells are measured by means of Hanle effect. Three different spin relaxation times for spins oriented along [110], [1-10] and [001] crystallographic directions are extracted demonstrating anisotropy of D'yakonov-Perel' spin relaxation mechanism. The relative strengths of Rashba and Dresselhaus terms describing the spin-orbit coupling in semiconductor quantum well structures. It is shown that the Rashba spin-orbit splitting is about four times stronger than the Dresselhaus splitting in the studied structure.Comment: 4 pages, 3 figure

Computer-Generated Holography Methods for Data Page Reconstruction Using Phase-Only Medium

Achievements in the field of high-speed spatial modulation electrooptic components provide the possibility to create perspective optical-digital diffractive systems for information storage and processing that outperform modern electronic counterparts by utilizing throughput, energy efficiency, and reliability. This work presents a study of computer-generated holography methods that allow the formation of spatially-modulated information signals (data pages) with high accuracy using phase-only spatial light modulators. Computer-generated Fourier hologram fringe patterns were formed using bipolar intensity and double-phase coding. Numerical and experimental results of both methods’ implementation are compared. It was determined that bipolar intensity holograms provide higher data density on the data page if complex digital modulation methods such as multilevel amplitude and phase or quadrature modulation are used to represent data points. Double-phase coding can offer perspective for multilevel amplitude or multilevel intensity modulated data page reconstruction; however, exact control of phase modulation characteristics is required to obtain high reconstruction quality