Search

This paper examines the feasibility of producing multiplexed Bragg gratings for use as diffractive optical elements (DOEs) by coherent optical replication of a surface-relief phase grating into thick-film photosensitive materials. The use of such DOEs in light guide plates (LGPs) for optical imaging systems ensures energy-efficient light input into and output from LGPs and allows one to minimise their weight and size. We present simulation results for the interference structure fabrication process and recording of a series of multiplexed diffraction gratings in photosensitive materials.

Optical sensors of linear displacements with diffraction gratings serving as the measurement scales are investigated. A method of stabilization of the phase difference of quadrature measurement signals, consisting in the use of an analyzing scale with a special structure, is proposed. A design of an optical encoder based on the method is proposed. Mathematical simulation of the phase shift of the measurement signals as a function of the parameters of the diffraction grating is performed, and the results of the simulation are presented. The RCWA method is used to simulate the passage of radiation through the optical system. The optimal parameters of the structure of the analyzing scale are calculated. Experimental investigations of a mock-up of the encoder are performed and results of measurements of the phase difference of the measurement signals are presented.

This paper describes the experiment on multiplexing recording using a phase mask to create augmented reality waveguides. The study is distinguished by the application of photo-thermo-refractive glass as both holographic and substrate materials. The presented approach allows us to obtain the diffraction efficiency above 15% in each of the multiplexed gratings for sevenfold recording. The images output with the manufactured planar waveguide prototype are presented.

An augmented reality display based on a planar waveguide made in photo-thermo-refractive glass had been demonstrated. The monolithic integration of multiplexed volume Bragg gratings with the waveguide platform provided in/out-coupling and image transmission from a portable projector. Design and calculation of the grating configuration was performed. The optical replication method was simulated and implemented for manufacturing the multiplexed coupling elements. Resulted field of view was limited by the projection system of the prototype, however can be expanded beyond 50o.

Linear displacement encoders are necessary in field of machine tools, metrology and electronic industry. Those devices provide nanometric resolution when constructed according to the interferometric scheme. Mathematical modeling of signal transfer process into its optical system to analyze an interference field is described. Signal intensity depending on a small displacement of moving grating phase shift correlations is considered. A sample model of the linear optical encoder is developed based on the optical scheme under research.

Optical position encoders working according to the interference method consists of a measurement scale and a measuring head moving along each other. The scale has a reflection diffraction grating on its surface and the measuring head has a transmission diffraction grating with same period inside. Laser light passing and diffracting through these two gratings creates an interference signal on an optical detector. Decoding of the interference signal phase allows to determinate current position. Known optical position encoders use complex optical schemes and some phase optical elements to form several quadrature signals with different phase for higher encoder accuracy. Previously we researched such kind of schemes [1, 2]. In this paper we propose to use a common optical scheme without phase elements but with a complex structured measuring head grating for this purpose to simplify an optical scheme and alignment requirements. The optical scheme of position encoder based on measuring head grating with specific structure is research and described in this paper.

A holographic wavefront sensor scheme using a phase-only spatial light modulator (SLM) with reduced cross-talk noise influence is proposed. A novel method for plane wave aberration measuring using a phase-only computer-generated hologram is devised. The proposed scheme and algorithm are validated with numerical simulations and experiments.

The article presents a two-stage scheme for obtaining volume color security holographic stereograms. These holograms are digital holograms. The H1 - hologram is recorded at the first stage. The final holographic stereogram is recorded at the second stage. The image of the H1-hologram is reconstructed in the plane of pupils of the observer's eyes, when 3-D images are reconstructed from holographic stereograms. The quality of the 3-D images reconstructed from hologram stereograms directly depends on the degree of blurring of the H1 image - the hologram. The article shows mathematical calculations describing the effects of the spectral and angular selectivities of a three-dimensional color security holographic stereogram on the process of reconstructing 3-D images (the degree of blurring of the H1 image-hologram). It is shown, that the quality of security elements, such as the "flip-flop effect", for this type of hologram, has a more pronounced effect in the vertical plane than in the horizontal plane. This is due to the large influence of the spectral and angular selectivities in the vertical plane, than in the horizontal one when reconstructing the images. Photos of images, reconstructed from a three-dimensional color security holographic stereogram, are also presented in the article. These photos confirm the correctness of the presented calculations.

That paper focuses on diffraction gratings consisting some period failures provided by the errors of the electronbeam lithography method. Samples of lithographic phase gratings were tentatively analyzed to describe that technological errors. A small linear modulation of the period or a joint of a frame edges can cause not only diffraction efficiency losses but also functional breakdown. A simulation of the diffraction of a monochromatic wave at the described diffraction phase structures is carried out. Described diffraction gratings have interest in field of linear displacement encoders.

Optical position encoders working according to the interference method consists of a measurement scale and a measuring head moving along each other. The scale has a reflection diffraction grating on its surface and the measuring head has a transmission diffraction grating with same period inside. Laser light passing and diffracting through these two gratings creates an interference signal on an optical detector. Decoding of the interference signal phase allows to determinate current position. Known optical position encoders use complex optical schemes and some phase optical elements to form several quadrature signals with different phase for higher encoder accuracy. Previously we researched such kind of schemes [1, 2]. In this paper we propose to use a common optical scheme without phase elements but with a complex structured measuring head grating for this purpose to simplify an optical scheme and alignment requirements. The optical scheme of position encoder based on measuring head grating with specific structure is research and described in this paper.

In this paper, dependencies of the angular and spectral selectivity on the incidence angle of the reference beam in a scheme for obtaining reflection and transmission holograms are obtained and analyzed. It is shown that for obtaining color holographic stereograms a scheme for obtaining transmission holograms is more suitable. While the angular selectivity of reflection and transmission color holograms is the same, the spectral selectivity of the reflection hologram is much higher at all wavelengths of recording. A method and equipment for one-step digital recording of color full-parallax holographic stereograms with rasterless image are developed. Samples of color full-parallax security holographic stereograms with a “flip-flop” effect in the image were obtained. The quality of the reconstructed image verifies high spectral selectivity for this type of holograms.

The article describes a new optical scheme of noncontact sensor for measuring linear displacement - linear encoder. This sensor is an optical device in which the measurement of displacement is performed by analyzing the optical signal, which pass through two diffraction gratings, one of which is moved relative to the other. The optical signal is obtained by the diffraction of light in these diffraction gratings and subsequent interference of diffracted beams. Often this type of sensors are multi-channel devices with symmetrically positioned of detectors. This scheme is proposed to use a multisection phase mask that allows to make a small-sized sensor. Sections of this multi-section phase mask are the optical windows and they made the final interference signals to be shifted relative to each other in phase. The number of sections in the multi-section phase mask can be varied. Estimated sufficient number of sections is four or more.

Visual security elements used in color holographic stereograms - three-dimensional colored security holograms - and methods their production is describes in this article. These visual security elements include color micro text, color-hidden image, the horizontal and vertical flip - flop effects by change color and image. The article also presents variants of optical systems that allow record the visual security elements as part of the holographic stereograms. The methods for solving of the optical problems arising in the recording visual security elements are presented. Also noted perception features of visual security elements for verification of security holograms by using these elements. The work was partially funded under the Agreement with the RF Ministry of Education and Science № 14.577.21.0197, grant RFMEFI57715X0197.

Optical position encoder consists of movable coding grating and fixed analyzing grating. Light passing and diffracting through these two gratings creates interference signal on optical detector. Decoding of interference signal phase allows to determinate current position. Known optical position encoders use several accurate adjusted optical channels and detectors to gather several signals with different phase for higher encoder accuracy. We propose to use one optical channel with several-section analyzing diffraction grating for this purpose to simplify optical scheme and adjusting requirements. Optical scheme of position encoder based on four-section analyzing diffraction grating is developed and described in this paper.

The paper presents the practical results of recording holographic stereograms. Advantages and disadvantages of methods for producing holographic stereograms using diffusers with different indicatrices scattering of the radiation in the object branch and without the use of a diffuser are presented. A new security element - multi-color microtext, is presented. Shows how to use multi-color microtext as a hidden security element. The method of multi-color microtext visualization is shown. The work was partially funded under the Agreement with the RF Ministry of Education and Science no. 14.577.21.0197, grant RFMEFI57715X0197.

The optical scheme of holographic printer for obtaining of holographic stereograms with an increasing field of view is proposed. Conventional holographic printers allow obtaining holographic stereograms with the field of view up to 90°. Proposed scheme allows increasing field of view up to 120°. The optical scheme is based on a diffuser and a diffraction optical element, the high-aperture diffractive lens. The experience of using the composite holographic lens and the amplitude diffractive lens based on a binary Fresnel zone plate as a high-aperture diffractive lens is described. Samples of high-aperture diffractive lens with f-number f/0.3 are obtained and investigated. Samples of holographic stereograms are obtained using samples of high-aperture diffractive lens.

The fundamental methods for analyzing the parameters of diffraction gratings (DGs) are presented. The features of the application of DGs as measurement scales in a linear-displacement sensor system are analyzed. A method and quality criteria for monitoring the parameters of real samples of measurement scales are proposed. These criteria generalize all diffraction efficiencies that affect the formation of quadrature signals in the system of an interferometric linear-displacement sensor.

Method for the analysis of plasmonic gratings is developed. The mathematical research of the spectral-angular characteristics of plasmonic gratings is realized. The dependency of spectral-angular characteristics on geometric parameters of the plasmonic grating are disclosed. Samples of plasmonic gratings are obtained. The results of mathematical modeling and theoretical studies are confirmed by the experimental samples. Spectral-angular characteristics of the plasmonic gratings samples qualitatively repeat theoretically modeled characteristics.

A method of computer generation and projection recording of microholograms for holographic memory systems is presented; the results of mathematical modelling and experimental implementation of the method are demonstrated.

Security holograms (SH) are widely used for authenticity protection of document and product due to difficulties of such a protection mark falsification. Mass production of SH uses widespread technology of hot foil or lavsan paper stamping. The quality of holograms significantly depends on perfection of nickel master-matrix that is used in stamping equipment. We represent the method for automated quality inspection of nickel mastermatrix based on digital processing of its surface relief images. Proposed processing algorithm is based on combination of image spatial frequency analysis and image matching using distortion invariant correlation filters. The results of our method application for real master-matrix inspection are shown in this paper.

The mathematical model of signal conversion carried out by holographic optical element (HOE) in holographic stereogram (HS) is presented. Expression for the point spread function (PSF) of HOE in the plane of an observer is obtain as well as the expression for the optimal number of perspectives and plans of HS. Relationship between the observation distance, the size and number of perspectives in HS HOE are considerate. Constraints and future prospects of art and security holography development are disclose. The approach how to optimize HS parameters (such as holopixel size and perspectives number) for current 3D image and HS application is proposed.

Necessity of devices and systems for identity verification and individualization of security holograms (SH) is growing together with the growth of SH production. The hidden coded micro image as a set of points (bits) was chosen as a new security element. This image is separately added into hologram by laser perforation on the final stage of SH production after replication. Such element is different for different SH, that allows not only controlling identity of SH, but also distinguishing one hologram from another. Designed optoelectronic system HOLOINID consists of two blocks: laser microperforator for SH individualization and optoelectronic device for micro-images readout and SH identification. Specialized software allow control the laser microperforator, process micro-images received by reading optoelectronic device using certain algorithm, and make a decision about SH identity. The block of laser microperforator for SH individualization works due to the high power density of the laser radiation in a focused spot forming at the SH metalized thermolacquered layer. Hidden coded image represents a set of optical bits (which form information field) and check objects for image capturing and processing. Optical point (bit) size is usually 30..50 μm while period between points is 70 μm. Advantage of laser miroperforator for SH individualization is ability to get hidden coded images in holograms without SH surface layer damage. It is possible to get by using high-aperture short-focus optical system. Know-how of the technology is an ability to use laser microperforation as in thermolacquered layer (which is lied between lavsan layers and metalized layer) and in metalized layer (for SH on hot stamping foil).

Holographic screen (HS) is designed for using in 3D displays. HS is produced as a hologram of converging light wave and it presents an interference pattern of the reference and the object beams as a diffraction grating with variable pitch registered in the recording medium. While a color image is projected on such screen the problem of perception of the undistorted color image by the observer is appeared (due to the inherent angular dispersion of a grating with different values for different wavelengths) because the observation zones are displaced in space for each spectrum section. The problem is solved due to recording the HS by the object beam from the set of point sources, i.e. recording lengthy in the appropriate direction diffuser. With this type of HS, the observation zones, providing an undistorted perception of full-color images, are located in the imposition of lengthy images of projectors' pupils corresponding to different spectral components of projectors' radiation beams. To form an image, different projectors can be used in the display: slide projectors, video projectors based on LCD- or DMD-panels, etc. Three-dimensional images of both static and dynamic scenes can be viewed as video films at the appropriate information flows synchronization which are received by the projector from external sources.

The urgency of application of the optoelectronic analyzer for security holograms identification in real time for paper documents and plastic cards is obvious. The spatial-frequency spectrum analyzing method for security hologram is offered. The essence of the method consists in reception of the security holograms (SH) microstructure spatialfrequency spectrum (SFS), description SH SFS by means of integral, peak and combined parameters, and identification analyzed SH by the correlation recognition method by comparison of analyzed SH SFS parameters with reference SH SFS parameters. For this purpose it is enough to illuminate SH by laser or light-emitting diode (LED) radiation to construct by Fourier lens SH SFS, to register it with matrix receiver of radiation, and to process a signal in the electronic block. The mathematical model of a spatial-frequency spectrum of the SH is constructed and investigated. We will consider SH SFS in the limited sector of spatial frequencies. It is possible to describe SH SFS in terms of integral parameters, peak parameters, and their combinations. A series of such parameters is offered. Several SH identification algorithms is offered. The optical scheme of optoelectronic spectrum analyzer for identification SH is offered and experimentally investigated.

Fundamental principals of the utilization of computers in the design of heterocyclic structures and reactions are examined and systematized in this review. The authors' original GREN program, which lists the recyclizations of heterocycles, and Heterocycland program, which is based on the previously proposed [2] “structure-synthesis” concept and is used for the retrosynthesis of six-membered heterocycles, are examined concisely.

The new modified holograms multiplexing method using normal to holographic recording media reference beam incidence and off-normal signal beams incidence is offered for application in holographic memory system having high information capacity and high data rate. Signal beams are located around reference beam concentrically. In this case quantity of multiplex holograms in the same area of recording media is equal to quantity of signal beams. Experimental holographic memory system model applying offered method is tested. Possibility of multichannel optical head application for data recording and retrieving is shown. Offered multiplexing method advantages consist in following: obviating of the necessity of recording media rotation; crosstalk noise free restored data page images; possibility of thin holographic recording media application.

A holographic sight permits fast choice of the aiming sign in a variety of environmental conditions. The aiming sign, the target and the place are observed simultaneously. The aiming mark doesn't require accommodation of the eyes. Position of the aiming mark in the target plane provides the shooting at the stacking of the aiming mark to the target independently on observing angle and position of the shooting. Second advantage of holographic sight is hiding of the shooter. In this paper, a design of the optical scheme for parallax control of the holographic optical element (HOE) and the holographic sight with HOE is discussed. A solution for the removal of the aiming sign parallax has been proposed. The parallax is defined as non-coincidence of the target plane and plane of the aiming sign and depends on the aberrations of the holographic optical element.

Methods for recording of holograms with an encoded hidden image (security holograms) and a reading-decoding optoelectronic system are presented in this paper. Security holograms are used as means for control of authenticity of the protected objects. Some modifications of the recording schemes with the code mask in the object beam are proposed. The main problem to be solved is connected with the required precision of the hologram positioning in the readout device. The algorithm of reconstruction of the decoded image is proposed in this paper. The main feature of this algorithm is the presence of the optical and electronic decoding. It allows producing of better than previously protected holograms. As an additional measure of protection of the hologram it is proposed to use the predetermined elements of the hidden image for checking of the hologram authenticity.

The method and the optical system for making rainbow multiplex holograms are described. The making of rainbow multiplex holograms is a very difficult task, because the optical component requirements are very high. The optical system for the recording rainbow multiplex holograms is a modified optical system for two-step technology. Using computer graphics, we can create an object that the 3D information. This computer-generated graphic object is divided into several view aspects, which are used to synthesize the composite hologram of Leith. The composite hologram consists of several slits, each of them is a number of a simple holograms. The image, reconstructed from the composite hologram of Leith, is projected to the plane of the rainbow multiplex hologram. The proposed technique gives a high quality reconstructed image.

The method of measuring modulated transfer function of rainbow holographic image is described. The 12 rainbow holograms of special object by using one-step technique was recorded. The rainbow holographic image was obtained from a white-light source. The comparison of obtained results with viewer sensory characteristics is presented.

This paper discusses questions associated with the fabrication of flat and spherical holographic mirrors intended to operate as part of the eyepiece system of night-vision glasses on a layer of dichromated gelatin. A method is proposed for recording holographic mirrors, and principles are proposed for calculating the parameters of the optical system of the apparatus for recording them. A process is presented, along with the results of work on the fabrication of holographic mirrors.

A microhologram-multiplexing method that makes it possible to increase the rate at which information is recorded and read out is proposed and investigated. An optical system for implementing the given method has been developed and experimentally tested. It is shown that holograms can be multiplexed by using a multichannel recording head, and that they can be read out simultaneously by using a multichannel readout head. The proposed multiplexing method and the optical system developed for creating archival optoholographic memory systems have the advantages that there is no need to mechanically displace the elements of the system during multiplexing at the recording stage nor during reconstruction of the multiplexed holograms, that there is no crosstalk in the beams reconstructed from the multiplexed holograms, and that relatively thin recording media can be used for recording.

The acylation and carbomethoxylation of 2-methylindolizine were studied. In most cases minor amounts of the 1-substituted isomers were isolated in addition to the “usual” products of substitution in the 3 position. The data from the PMR and mass spectra of the 2-methyl-3- and 1-acylindolizines obtained are discussed.

An approach to the construction of models for thermal decomposition of organic compounds based onrecombination reaction networks was developed. Each species (molecule, ion, or radical) is considered as a potential reagent. It was suggested that the newly formed species can react with all other species which are already present in the reaction mixture. The results of reactions are represented as a bipartite graph whose vertices are formed either by species generated or by the descriptions of interactions, while the oriented edges determine the relations between the reagents and the reaction products. Based on analysis of the experimental data on the mechanisms of thermal decomposition, empirical rules were developed for simulating possible thermal decomposition reactions of the major classes of energetic compounds. The proposed approach allows one to describe the complete spectrum of reactions occurring in the course of thermal decomposition. The approach was realized in the CASB computer program and was exemplified by simulation of thermal decomposition of methyl, ethyl, and isopropyl nitrates. All stages of the mechanisms (some of which have been reported in the literature) were reproduced. A number of new decomposition reactions, which have not been studied experimentally, are suggested.

An optical position encoder uses two difraction gratings in a measurement scale and measuring head for generating cosine measurment signals. This report is about special subperiod structuring of thees gratings for generating of two signals with quadrature phase shift for better the resolution of an optical position encoder.