Optical Memory and Neural Networks最新文献

Multiplexing a signal using the largest number of freedom degrees is an important task in the field of optical information transmission. Variations in the beams amplitude-phase structure can provide a wide range of possibilities for encoding and multiplexing optical signals and do not require complex optical systems or expensive devices. The paper analyzes the results of focusing laser radiation using phase vortex shifted lens quantized at a given level. It is shown that a shifted quantized lens makes it possible to obtain a variable number of local intensity maxima out of the optical axis. The use of a shifted quantized vortex lens made it possible to register a useful signal and detect both individual vortex beams and their superpositions out of the optical axis. We can also note that studies of the quantization parameter influence on the propagation of beam intensity have shown the possibility of eliminating fixed diffraction orders. Individual quantization levels produce diffraction orders that account for equal shares of energy (weights), and are thus candidates for more complex detection tasks that also include weight recognition.

The present paper is concerned with the analytical and numerical investigation of the dynamics of a broad-area vertical-cavity surface-emitting laser (VCSEL). It is shown that the adiabatic polarization elimination does not affect the modulation instability developing in the system. The efficiency of the method of external injection at different shapes of the pump current profile is verified. It is shown that for effective stabilization by optical injection beam with minimum amplitude it is necessary to use pump current profiles with smoother edges.

The description of the role of absorption in interference resonators is important for characterization of metal-insulator-metal structures. To study the resonance characteristics of the interference structures the conditions of excitation of their eigenmodes were analyzed. The mode excitation conditions determined by the dispersion relations were obtained for the waveguide, Fabry-Pérot, symmetric and antisymmetric plasmonic normal modes. The approximations of the dispersion relations in the form of analytical functions were implemented to describe the behavior of the resonance positions in far-field spectra depending on the parameters of the layers.

We investigate the spin angular momentum of a superposition of two vector light beams with rotational symmetry. One beam is cylindrically polarized and another is linearly polarized. Radial form of these beams can be arbitrary (Laguerre-Gaussian, Bessel-Gaussian, or some other). For such a superposition, an analytical expression is derived for the spin angular momentum and two its properties are obtained. At first, we found that altering the coefficients does not affect the form of the spin angular momentum distribution, while the intensity distribution is changed. At second, we found that maximal spin angular momentum is generated if both beams are of equal power.

Various types of diffraction and plasmonic elements are discussed that provide modern development of sensors in different applications such as analysis of the mode composition of radiation and wavefront aberrations based on multichannel filters, detection of the polarization state using diffraction microstructures, as well as biochemical analysis using metal-insulator-metal waveguides. The considered types of sensors are promising in the field of optical communications, quantum information, materials testing, environmental monitoring.

Topological charge is an important characteristic of a laser beam and is closely related to orbital angular momentum. Although in most cases the charge is conserved when a beam propagates in space, the opposite examples are known. We formulate and prove a general theorem for conservation of topological charge, which involves not only charges in the plane perpendicular to the propagation axis, but also in planes parallel to the propagation axis. Charges of the second type can be identified to some approximation with spatiotemporal charge, which have been widely studied in recent years.

The study presented in this paper is devoted to the development of technology for detecting osteoporotic changes in vertebral bodies according to computed tomography data based on the analysis of groups of textural features. This technology will be of interest to radiologists when assessing the structure of vertebral bodies in patients with osteoporosis, and especially in patients with malignant neoplasms, in which the disease proceeds with a decrease in bone mineral density. Automation of the analysis process will significantly reduce the time spent by a radiologist on the evaluation of vertebral bodies, including when evaluating the effectiveness of osteoporosis treatment. During the development process, the most informative group of signs was identified, which allows achieving high accuracy in detecting signs of osteoporotic changes in the vertebral bodies in 94.5%.

A metrological device—Hartmannometer—based on a Shack-Hartmann wavefront sensor for measuring the flatness of optical surfaces was developed and researched, and the results were compared with the results obtained from measurements using a Fizeau interferometer. The paper presents a method for calibrating a Hartmannometer, and also compares the results of measuring a test optical surface using the developed device and a classical Fizeau interferometer. The total amplitude of wavefront distortions measured using a Fizeau interferometer was 0.127 μm (standard deviation 0.022 μm). The Hartmannometer showed distortions amplitude of 0.131 µm (standard deviation 0.024 µm).

In this work, we studied the photoinduced polarimetric and optical properties of the photosensitive carbazole-based azopolymer prepared in the form of thin films. Poly-N-(2,3-epoxypropyl)carbazole was used as a polymer matrix, which was copolymerized with the commercially available azo dye Solvent Yellow 3. Thin films of µm thicknesses were obtained by home-made rod-coating techniques. Polarization holographic recording was applied for direct diffraction gratings patterning. The polarization states of the recording beams were P–P, S–S, ±45° and left-right circular. The optical path of the probe beam passing through investigating media is defined by the summary changes in surface topography and volume anisotropy. The periodically modulated polarization/amplitude interference patterns produced by the gratings were investigated by in situ measurements of the diffraction efficiency (DE) kinetics in the first diffraction order at the DE saturation value. The surface relief was measured by AFM. A comparison of the behavior of azopolymer films during the recording of diffraction gratings with different polarization configurations of recording beams was carried out. The presented results confirm the possibility of recording not only the amplitude and phase of light, as in scalar holography, but also the polarization states of interfering beams. The angular dependences of the probe beam azimuth and ellipticity were analyzed, and some peculiarities of azopolymer photoinduced changes are discussed.

Determining the order of a vortex beam is an important problem in optics. One way is to insert an astigmatic distortion. However, other types of aberrations, such as coma, can also be useful in determining the topological charge of a vortex beam. The influence of the type and magnitude of aberrations on the distortion of the intensity pattern of vortex beams is investigated using Gauss-Laguerre modes of different orders.