Optoelectronics, Instrumentation and Data Processing (v.54, #6)

Multichannel Confocal Microscope Based on a Diffraction Focusing Multiplier with Automatic Synchronization of Scanning by V. P. Bessmeltsev; M. V. Maksimov; V. V. Vileiko; N. V. Goloshevskii; V. S. Terent’ev (531-537).
Implementation of a laser scanning confocal microscope is described, where the specimen is scanned by an array of illuminating beams, which significantly increases the velocity of object image construction. The array formation is provided by using a diffractive optical element. Scanning by the array of laser beams over the specimen is performed by galvanometric scanners with moving refractive plane-parallel plates. Owing to application of such a scanning device, the beams in the illuminating channel and the signal beams in the receiving channel pass through one motionless array of confocal diaphragms; as a result, the scanning beams in the specimen plane and the signal beams in the plane of the photodetector matrix can be used without an additional synchronized pair of scanners. The proposed confocal microscope can be applied in problems that require a fast response.
Keywords: multichannel confocal microscope; diffractive optical element; shifted plane-parallel plates

Stretch Vibrations of CH2 as a Measure of Conformational and Lateral Orders in Fatty Acid and Phospholipid Layers by S. V. Adishchev; T. A. Duda; Yu. V. Zaitseva; V. A. Zykova; A. G. Milekhin; K. A. Okotrub; N. V. Surovtsev (538-545).
The intensity of the line of antisymmetric vibrations of CH2 in the Raman spectrum of molecular layers of fatty acids and phospholipids is sensitive both to the molecular order in the layer (lateral order) and to the conformational order of the hydrocarbon chain of the molecule. Though the intensity of this line is widely used as an indicator of order in molecular layers containing hydrocarbon tails, the nature of sensitivity of the line of antisymmetric vibrations to the order is still disputable. This issue has been experimentally studied, and it has been demonstrated that disordering leads to redistribution of vibrational modes and to changes in polarizability of antisymmetric vibrations. A hypothesis is proposed that the intensity of the line of the Raman scattering of antisymmetric vibrations of CH2 is determined to a large extent by their interaction with electron excitation of the hydrocarbon chain.
Keywords: Raman scattering; order indicator; hydrocarbon chain

A method for studying internal phase inhomogeneities in transparent optical materials by point-to-point three-dimensional laser heterodyne microprobing is proposed. The light microprobe in this case is a traveling micrograting formed in the zone of overlapping of two focused coherent light beams: reference and signal. The size of the microprobe in the x, y, z directions and the degree of influence of spherical aberration with a change in the microprobing depth are estimated. The capabilities of the method are illustrated by examples of detection and subsequent imaging of phase inhomogeneities in the volume of laser ceramics and its random layers.
Keywords: laser heterodyne microprobing; optical materials; phase microinhomogeneity

Characteristics of spatially non-invariant telecentric projection systems, which are widely used in practice, are considered within the framework of wave optics. In the class of the Fresnel functions, the pulse response of the system is precisely calculated for various values of the projection objective and filter apertures. It is found that the response consists of two components, which determine the invariant and non-invariant properties of the system, respectively. Based on the approximation of the Fresnel function by elementary functions proposed previously by the author, an analytical expression for the pulse response is derived for the first time, and the response behavior is studied for various relationships of the objective and filter apertures. The correctness of choosing the parameters of the known quasi-invariant optical systems is analyzed. Recommendations on choosing the filter aperture are given to improve their spatially invariant characteristics. In contrast to available optical and geometrical methods, the proposed approach allows one to obtain reliable information about the character of wave field transformations in the considered systems.
Keywords: light diffraction; telecentric projection systems; Fourier optics; dimensional inspection

Advanced Design of Scanning Infrared Focal Plane Arrays by S. A. Dvoretskii; A. P. Kovchavtsev; I. I. Lee; V. G. Polovinkin; G. Yu. Sidorov; M. V. Yakushev (569-575).
Modern designs of time delay and integration (TDI) IR linear scanning focal plane arrays (IR FPAs) are analyzed. Advanced designs of linear IR FPAs with increased sensitivity and spatial resolution are proposed. The analysis is based on Monte-Carlo simulation of the diffusion of photogenerated charge carriers in photodiode arrays based on mercury–cadmium–telluride epitaxial layers taking into account the main photoelectric and design parameters of the detectors and optical system.
Keywords: scanning IR FPA; photodiode; local quantum efficiency; point source; threshold sensitivity; spatial resolution

Nano-photonics is an emerging area of optical materials, which would take the optointegrated circuits towards progress. Photonic crystal (PC) based power splitters are useful constituents for the design of photonic integrated circuits (PICs). They are very important devices for connecting different building blocks on an integrated optical chip. In this paper, a two-dimensional PC Y-junction power splitter (21×15 μm) based on the resonance effect with circular air holes etched on a hexagonal lattice with a period a is proposed. The plane wave expansion (PWE) and finite difference time domain (FDTD) techniques are used for analyzing the structure. The simulation results show that the optimum resonance occurs when the radius of the defect hole is 0.3a, leading to the maximum and equal power distribution.
Keywords: photonic crystal; photonic bandgap; power splitter; defect hole; PWE

Various methods of spectral-spatial classification of hyperspectral data are reviewed. Papers devoted to the most popular ways of using spatial information for increasing the accuracy of classification maps are considered. It is shown that the best results are obtained by using preprocessing of “raw” data before the procedures of pixel-wise spectral classification. Disadvantages, limits, and possible directions for developing existing methods are investigated and analyzed.
Keywords: remote sensing; hyperspectral images; surface type classification; spectral and spatial features

Measuring the Quantitative Characteristics of Local Vortices on a Plane of a Deformed Material by V. V. Kibitkin; A. I. Solodushkin; V. S. Pleshanov (600-607).
A problem for determining the center, size, and spatial distribution of displacements of a vortex on the basis of a plane vector field is under consideration. A seed algorithm is proposed instead of typical contour scanning, and specific circulation is used as a criterion for determining the center of a vortex flow. In order to increase the stability of this algorithm, a parameter playing the role of a threshold is introduced. A Monte-Carlo method is used to study the influence of measurement errors on the accuracy in determining the coordinates of a hard rotation center, and the relationship between the false alarm probability and the threshold level is established. The use of the least squares method for calculating the spatial distribution of displacements is shown. This approach is demonstrated on the example of a real vector field measured in the vicinity of a main crack tip.
Keywords: digital image correlation method; vector field; vortex; error; Monte-Carlo method; deformation; pseudoimage

Quantization Noise of Multilevel Discrete Wavelet Transform Filters in Image Processing by N. I. Chervyakov; P. A. Lyakhov; N. N. Nagornov (608-616).
The effect of the quantization noise of the coefficients of discrete wavelet transform (DWT) filters on the image processing result is analyzed. A multilevel DWT method is proposed for determining the effective bit-width of DWT filter coefficients at which quantization noise has little effect on the image processing result. The dependence of the peak signal-to-noise ratio (PSNR) in DWT of images on the wavelet used, the effective bit-width of the coefficients, and the number of processing levels is revealed. Formulas are derived for determining the minimum bit-width of the coefficients that provide high quality of the processed image (PSNR ≥ 40 dB) depending on the wavelet used and the number of processing levels. Experimental modeling of a multilevel DWT image confirmed the results obtained. In the proposed method, all data are represented in fixed-point format, making possible its hardwareefficient implementation on modern devices (FPGA, ASIC, etc.).
Keywords: discrete wavelet transform; digital image processing; quantization noise; bit-width; fixedpoint format

Identification of the Dynamics of a Moving Object with the Use of Neural Networks by Yu. N. Zolotukhin; K. Yu. Kotov; A. M. Svitova; E. D. Semenyuk; M. A. Sobolev (617-622).
A method for identification of the dynamics of a quadrotor-type vehicle is proposed. The method is based on the Elman recurrent neural network, which corresponds to the canonical form of a dynamic system in the space of states and does not require structural correction. The results of a numerical experiment reveal the convergence of the network learning algorithm with the use of an extended Kalman filter.
Keywords: identification of the dynamics; quadrotor; extended Kalman filter; Elman recurrent neural network

The results of calculation of the spatial distribution of the local quantum efficiency over the area of photodiode-based IR focal plane arrays (IR FPA) are presented. The diffusion of photogenerated charge carriers in the absorber layer of the array was calculated by Monte-Carlo simulation. Methods of reducing the amount of necessary calculations based on using the symmetry properties of the array are discussed. Requirements for the photoelectric and design parameters (absorber-layer thickness, chargecarrier diffusion length and optical absorption length in this layer, the ratio of the size of n–p junctions to the geometrical dimensions of the detector pixels) are formulated that ensure the threshold sensitivity and spatial resolution of IR FPAs.
Keywords: infrared focal plane array (IR FPA); photodiode; detector; local quantum efficiency; spatial resolution