卷 63, 编号 10 (2018)

Advanced techniques for optical manipulation of nanoscale objects are presented. Possible mechanisms of enhancement of the effect of light on nanoobjects are listed. Enhancements by plasmon effects, field amplification in high-Q resonators, and collective effects are characterized. These methods are suitable for manipulation of various nanoobjects: quantum dots, nanowires, nanotubes, and cell organelles. Techniques for the measurement of forces at nanometer scales with atomic force microscopes are discussed.

The paper presents the results of studies of a fiber-optic structure whose principle of operation is based on the transformation of the core and cladding modes in a segment of SM630 fiber with a small core and a depressed inner cladding. The mode structure of a double-clad fiber is analyzed, and the causes of the dips in the transmission spectrum are explained. The transmission spectra of the proposed structure with a bent segment of SM630 fiber are measured. A shift of the resonances to the long-wave region with increasing curvature of the fiber is observed. A bending sensor based on this effect is developed. The dependence of the shift of the resonance wavelengths on the temperature and strain of the fiber and the refractive index of the ambient medium is measured. It is shown that, upon etching of the fiber and the reduction in the diameter of the outer cladding, the resonances shift toward shorter wavelengths. Chitosan coating sensitive to the chemical composition of the ambient medium is deposited on the fiber by layer-by-layer assembly; such coating can be used to develop an acidity sensor.

Three-dimensional problems of synthesis and analysis of polyfocal constrained lenses are considered. It is shown that such lenses can have up to five focal points on each side. The problem of synthesis of a pentafocal lens in the general case is reduced to three transcendental equations and, of a quadrifocal lens, to two transcendental equations. In the case of a pentafocal lens with three focuses in the symmetry plane of the lens, forming plane wave fronts at the output, the synthesis problem is reduced to one transcendental equation; in all other cases of plane front formation, an analytical solution of the problem is obtained. An analytical solution is also obtained for the problem of synthesis of a quadrifocal lens with three symmetry planes. An analytical solution is also found for the problem of synthesis of a quadrifocal lens with two symmetry planes forming in the plane of symmetry four plane fronts with simultaneous fulfillment of the aplanatic conditions (Abbe sines) in the orthogonal plane. Examples of solving the synthesis problems with the optimization of parameters in order to minimize the mean square aberration of the eikonal are given. In the two-dimensional case, the dependence of the mean square aberration of the eikonal on focal distances is studied and it is shown that there is an optimal ratio of focal distances providing its minimum.

A new approach to processing and analysis of noisy data inherent to the optical systems of Earth remote sensing systems is proposed and investigated. This approach involves the system integration of several conceptual ideas based on the multiscale representation of fractal sets, recursive scans, and wavelet transforms, making it possible to improve the signal detection efficiency under complex background‒target conditions.

A new approach to solution of the problem of remote determination of spectrally complex optical signals and identification on this base of two objects out of a set of possible spatially inseparable objects located in one small ground pixel is considered. Computer simulation is performed; it is shown that the results of measurements of the mean powers of filtered signals at the outputs of two (or more) selected reference multiband acoustooptical filters (MAOFs) can ensure subsequent programmed (digital) separation of spectrally complex optical signals and identification of the objects corresponding to these signals. By the example of an arbitrarily chosen group of ten types of objects and three types of the background, computer verification of the new method is carried out with the use of realizable parameters of modern MAOFs. It has been found that, in conditions of the actual accuracy of setting and/or measuring of the energy of the main components of the problem (~1%), this method can provide unambiguous correct decision about the type of the object located on part of a pixel with a probability of ~99.9%.

A novel differentially coherent communication scheme based on the use of chaotic radio pulses as information carriers is proposed. The scheme uses only delay components with a short duration. Hence, as compared to known analogs, its practical implementation is simplified in the microwave frequency range. Computer simulation of data-transfer process is performed, and noise immunity in channels with white noise is estimated.

The dispersion and isofrequency characteristics of surface spin waves in a tangentially magnetized metal–dielectric–ferrite–dielectric–metal structure are studied. It is found that the dispersion surface of spin waves in this structure goes from the frequency axis in a wide frequency interval, in a part of which the isofrequency dependences of the waves have the form of a closed loop starting at k → 0. It is found that the dispersion surface can simultaneously have bell-shaped regions, in which the isofrequency dependences near the vertex are similar to ovals, and saddle-like regions, in which the isofrequency dependences near the saddle point are similar to hyperbolas. It is established that the range of possible orientations of the wave vector at a given frequency can be wider than the interval limited by the cutoff angles. It was found that the cross section of the dispersion surface by an angle exceeding the maximum cutoff angle is a dispersion relation with a limited interval of wavenumbers.

Propagation of spin waves in a structure based on orthogonal waveguides of different widths (magnetic crosses) has been numerically investigated. For the case of an in-plane magnetized thin-film ferrite structure in the form of a dual cross formed by three straight microwaveguides, the effect of the order of placement of waveguides of different width in the path of the spin wave on the amplitude of output signals recorded at different ends of the structure has been analyzed. It has been shown that the ratio of the amplitudes of the output signals arriving from different arms of the “cross” can be changed by changing the order of succession of narrow and wide waveguides with respect to the input transducer.

A brief survey of the studies devoted to relation between currents measured in the external circuit and parameters of a heterogeneous specimen, including the case of an anisotropic permittivity and capacitance effects is presented.

Controlled deposition of DNA on graphene films obtained with the aid of mechanical splitting of graphite on a substrate with an epoxy sublayer is demonstrated. The DNA molecules are visualized using AFM.

Excess carrier capture into quantum wells (QWs) of undoped AlGaAs/GaAs and modulation-doped n-AlGaAs/GaAs heterostructures has been investigated by means of photoluminescence spectroscopy. The oscillatory dependence of the photoluminescence (PL) intensity on the quantum well width caused by the resonant capture of carriers into the well has been confirmed for structures of both types. Dependences of the integral PL intensity on temperature and optical excitation density in structures with different (resonant and oscillation minimum) capture conditions have been examined. It is demonstrated that, in undoped structures, these dependences are identical at the resonant and weak capture, whereas, in doped structures, the capture efficiency strongly affects their behavior. In doped structures with weak capture, the dependence of the PL intensity on the excitation density is linear, while, in resonant structures, it is superlinear due to the growth of the hole capture rate with increasing excitation. The shift of the transition energy observed in resonant doped structures with increasing excitation is explained by accumulation of the positive charge resulting from the difference between the electron and hole capture rates. The hole capture times at the oscillation maximum and oscillation minimum have been found to be ~15 and 800 ps, respectively.

It was found that self-modulation of the spectrum of high-intensity stimulated radiation of a thin (about 1 μm) GaAs layer can be represented as switching of spectral modes of radiation caused by stimulated Raman scattering (SRS). It is shown that the SRS results from modulation of population of energy levels upon interband oscillations of electrons in the presence of the radiation field. It is shown that such oscillations become possible owing to the slowing down of elimination of deviations from the Fermi distribution due to energy transport of carriers. It is clarified that the oscillations are synchronized owing to the SRS.

Power allocation plays a significant role in performance enhancement of cognitive radio (CR) system as it needs to not only limit the interference to primary users (PUs) but also maintains a minimum quality-of-service (QoS) requirements of secondary users (SUs) with a limited available resource. In many cases, traditional analytical optimization methods require a specific structure of objective function and constraints, hence, may not be applied directly to power allocation and also demand high computational complexity. This paper investigates the effectiveness of classical genetic algorithm (GA) in power distribution of sensing-free, location-aware underlay spectrum sharing based CR system models. GA has been implemented to optimize the various performance parameters of the system models. The performance of GA has been validated and compared with that of interior point method (IPM) and successive approximation solved by CVX toolbox. Simulation results depict that GA reaches closer to optimal value with a reduced computational time.