Acousto-optic Processor Research Articles

Application of bioradiophotonics methods for the processing of bioelectric signals

The application of modern and perspective bioradiophotonics methods on the basis of optical and acousto-optic devices for the processing of bioelectric signals (BES) have been considered. The basic application difficulties of these methods are connected with the fact that the studied signals are of low frequencies, and development of special actions are required for the processing devices adapting. It has been proposed to introduce into acousto-optic processing system with time integration the bioelectric signals using method of high frequency carrier with linear frequency modulation which is modulated by low frequency signal. The system configuration has to provide the realization of convolution procedure; hence, the used Bragg cells must be oriented oppositely to each other. The performed analysis has shown that it is possible to realize both signal power spectrum calculation and its wavelet transform; the presence of carrier is obligatory for both kinds of processing. Also, the method of the preliminary BES compression has been proposed for its transmission into the high frequency area. In this case, the possibility occurs to introduce the signal into the acousto-optic processing system with spatial integration. In the simple acousto-optic correlator with the reference transparency the envelope of the correlation function is formed depending on time. Using the set of the reference transparencies in the multichannel correlator, it is possible to realize the prolonged BES wavelet analysis using the mother wavelet. The optical preliminary BES processing can be also performed using liquid crystal arrays. The analysis of the processing of electrocardiac signals obtained from the experimental animals (rats) has been listed using the liquid crystal array for the signal introduction into optical processing system. It has been shown that both spectral and wavelet processing can be realized in this case without using of the high frequency carrier by the low frequency signal. The use of the obtained results will make it possible to create a new family of devices for wavelet processing of bioelectrical signals implemented in real time which will make an important contribution to improving the diagnosis of diseases of the cardiovascular system, the cortex, and the central nervous system.

Acousto-optic wavelet processing of bioelectric signals

Wavelet analysis is one of the most efficient methods of the informative signals characteristics investigation. First shown the possibility of informative signals wavelet processing by means of the acousto-optic processor with time integration. The possibility of the realization of both power spectrum calculation and performance of wavelet transform of bioelectric signals in the real time mode has been proved. The analysis is listed which describes its operation in different modes. Keywords: wavelet analysis, bioelectric signals, acousto-optic processors, time integration

Акустооптическая вейвлет-обработка биоэлектрических сигналов

Wavelet analysis is one of the most efficient methods of the informative signals characteristics investigation. First shown the possibility of informative signals wavelet processing by means of the acousto-optic processor with time integration. The possibility of the realization of both power spectrum calculation and wavelet transform performance of bioelectric signals in the real time mode has been proved. The analysis is listed which describes its operation in different modes

Using the features of the photoelastic effect to measure the parameters of optoelectronic devices

The features of the photoelastic effect are discussed and it is shown that they can be used to measure the parameters of a laser and a photodetector, which are the main units of any optoelectronic product. A brief review of the known methods for measuring the parameters of a laser and a photodetector is carried out, and some limitations in their application are noted. The possibility of using the features of the photoelastic effect for
 measuring the parameters of the inertia of the photodetector is theoretically substantiated. A formula for calculating the response at the output of an acousto-optic processor to a rectangular input action is derived and used to separately estimate the time of crossing the optical beam by an elastic wave packet and the inertia of the photodetector. It has also been proven that by choosing a short input action, the features of the photoelastic effect can be used to determine the configuration of the cross section of the laser beam and the law of the distribution of the power flux density in it. The results of theoretical studies have been tested by numerical calculations and confirmed by experimental measurements.

Acousto-optic Light Pulse Shaper for Measuring the Parameters of Photo-detectors

The paper emphasizes that intensive utilization of the optical range increases the need for the development of new optoelectronic devices. Accordingly, there is a growth in the need for effective methods and tools to study photoelectric properties of semiconductor materials, including photo-detectors.In the paper we have analyzed the well-known methods and tools for measuring the photo-detector parameters, defined the restrictions in their applications, and proved that it is relevant to create a measuring system, the parameters of which are easily adapted to the study of photoelectric characteristics of a wide range of semiconductor materials, including photo-detectors.The scheme and principle of operation of the acousto-optic processor and the features of the photo-elastic effect are discussed, and it is proved that they can be used to form a light pulse of required duration and power. The expressions obtained for calculating the response at the acousto-optic processor output enable us to estimate separately the effects of time of crossing the optical beam by the elastic wave packet and the photo-detector inertia.The capability to determine the time of crossing the optical beam by the elastic wave packet and taking it into account as a device error has been substantiated. The proposed formulas have been tested and by numerical analysis based on the datasheet specifications of the FD-24K photodiode, the effectiveness of the obtained expressions has been convincingly proven.The inertia parameters of a particular sample of the FD-24K photodiode are experimentally studied. The emphasis is upon measuring the rise time of the transient response of the object under study. The exact rise time value of the transient response of the experimental FD-24K sample was approximately 7 μs, which is less than that indicated (≤10 μs) in the product certificate. In real life, such a measurement is necessary when selecting the photodiode pairs with identical parameters.By comparing the results of numerical analysis and experimental studies, it has been convincingly proven that the features of the photo-elastic effect can be used to construct a light pulse shaper with the required parameters.

Photo-elastic Effect Features Used for Measuring Laser Radiation Parameters

The article discusses the photo-elastic effect features in acousto-optic processors for processing pulse signals on the time axis. The photo-elastic interaction in these devices is divided into two areas. In the first area, the input pulse duration is longer than the time of intersecting the optical beam by the elastic wave packet. This particular area is widely used in the practical applications of these processors, where it is a priori assumed that the input pulse duration is longer than the time for the elastic wave packet to intersect the optical beam.In the second area, the input pulse duration is less than the time for the optical beam to be intersected by the elastic wave packet. The objective of this work is to study the photo-elastic effect features in this area. It was established that in this area the pulse duration at the processor output is equal to the time for the optical beam to be intersected by the elastic wave packet and does not depend on the input pulse duration, which is permissible in some cases (for example, in radar pulse existence rather than its duration is recorded). It is shown that in the second area, the output pulse is formed as the sum of three terms. The first term corresponds to the elastic wave packet entering the optical beam. The second term corresponds to the elastic wave packet advancement in the optical beam aperture, and the third one keeps with the elastic wave packet leaving the aperture of the optical beam. The corresponding equations for calculating the pulse at the device output are obtained. The numerical calculations have proved the provisions and patterns established. The numerical modeling results were tested experimentally using a prototype of an acousto-optic processor with direct detection. The analysed results of theoretical and experimental studies unequivocally confirmed that the obtained formulas, formulated statements, and established provisions can be used to expand the functionality of acousto-optic processors, both with direct detection and of heterodyne type. It is shown that with a significant decrease in the input pulse duration relative to the time during which the optical beam is intersected by the elastic wave packet, the latter is converted into a scanning line and can be used to measure the geometric and energy characteristics of the quasi-coherent light.

An Acousto-Optic Method for Measuring the Energy-Geometric Parameters of Laser Radiation

Abstract—The features of acousto-optic interaction are considered for the case where the duration of an acoustic pulse is much shorter than the time of crossing an optical beam by an elastic wave packet. It is shown that under these conditions the acoustic wave packet turns into a scanning element, which extracts information about the energy-geometric parameters of the cross section of the laser beam. The sequence of extracting information about the configuration of the laser beam cross section and the law of distribution of the power flux density in it is described. The established provisions and patterns are confirmed by numerical calculations. The results of numerical analysis were tested experimentally on a prototype of an acousto-optic processor with direct detection. A comparative analysis of the results of theoretical and experimental studies in the context of the effectiveness of the proposed method for measuring the energy-geometric parameters of laser radiation has been carried out.

Advanced rutile-made acousto-optical cell designed for precise parallel optical spectrum analysis in ultrahigh-frequency regime of the noncollinear two-phonon light scattering

We present an original approach to precise optical spectrum analysis based on combining the nonlinear acousto-optical processing with the cross-disperser technique. This novelty gives us a possibility to overlap all the visible range by the parallel analysis with a gained spectral resolution. For this goal, an advanced rutile-made acousto-optical cell has been designed and tested as dynamic acoustic grating at ultrahigh-frequency to provide the needed slit density to increase the resolving power and the nonlinear apodization to improve the profile of a resolvable spot. Theoretical estimations were developed for low-loss 6-cm rutile-crystal at λ=440 nm, and they show that one can expect the spectral resolution 0.0609 Å, resolving power 72,250, and the number of resolvable spots ∼39,200. The illustrative proof-of-principle experiments with that rutile-crystal-made acousto-optical cell have been carried out. Experimentally we have obtained the spectral resolution ∼0.0815 Å and resolving power ∼54,000.

Precise parallel optical spectrum analysis using the advanced two-phonon light scattering combined with the cross-disperser technique.

We develop an advanced approach to the optical spectrometer with acousto-optical dynamic grating for the Guillermo Haro astrophysical observatory (Mexico). The progress consists of two principle novelties. First is the use of the acousto-optical nonlinearity of two-phonon light scattering in crystals with linear acoustic losses. This advanced regime of light scattering exhibits a recently revealed additional degree of freedom, which allows tuning of the frequency of elastic waves and admits the nonlinear apodization improving the dynamic range. The second novelty is the combination of the cross-disperser with acousto-optical processing. A similar pioneering step provides an opportunity to operate over all the visible range in a parallel regime with maximal achievable resolution. The observation window of the optical spectrometer in that observatory is ∼9 cm, so that the theoretical estimations of maximal performances for a low-loss LiNbO3 crystal for this optical aperture at λ=405 nm give spectral resolution of 0.0523 Å, resolving power of 77,400, and 57,500 spots. The illustrative proof-of-principle experiments with a 6 cm LiNbO3 crystal have been performed.

Implementation of information security and confidentiality at a physical level of grid wireless interface

A new method for information protection using acousto-optic processing of broadband signals in the spectral domain is proposed to provide wireless access to spatially distributed information and computational resources of a grid network. The method allows network capacity of up to 11.5 Gbit/s, which is impossible for wireless access based on conventional digital electronics.

An Advanced Multi-Band Acousto-Optical Radio-Wave Spectrometer with Multi-Channel Frequency Processing for Astrophysical Studies

We present an advanced schematic arrangement of the radio-wave spectrometer with a few parallel optical arms for processing the data flow. This arrangement includes two principal novelties. First of them consists in the proposed design, where each individual optical arm exhibits its original performances providing parallel multi-band observations within a few different scales simultaneously. These optical arms have the beam shapers providing both the needed incident light polarization and apodization to increase the dynamic range. After parallel acousto-optical processing, data flows of all the optical arms are united by the joint CCD matrix on the stage of the combined electronic data processing. The second novelty is in usage of unique wide-aperture bastron-based acousto-optical cell providing one of the best performances at the middle-frequencies (about 500 MHz) in comparison with the other available crystalline materials in this range. Such multi-band capabilities have a number of applications in astrophysical scenarios at different scales: from objects in the distant universe to planetary atmospheres in the Solar system. Thus one yields the united versatile instrument, which provides comprehensive studies of astrophysical objects simultaneously with precise synchronization in various frequency ranges.

An increase in the resolution of acousto-optic processors

An increase in the resolution of the acousto-optic devices for data processing is discussed in the framework of the general problem that involves the improvement of parameters of such devices. A method for an increase in the resolution of the acousto-optic processor that employs the Doppler shift of the frequency of the diffracted beam is proposed.

Experimental investigation of the optical Wigner processor

An acoustooptic Wigner processor was constructed and investigated. The processor operating at the frequency about 130 MHz permits to get the time-frequency distribution of radiosignals. The experiment carried out for linear frequency modulated signals showed that this device has an advanced resolution and frequency determination precision in comparison with the acoustooptic current spectrum analyzer.

High-Resolution Broadband Millimeter-Wave Astrophysical Spectrometer with Triple Product Acousto-Optical Processor

An advanced conceptual design of a high-bit-rate triple product acousto-optical processor is presented that can be applied in a number of astrophysical problems. We briefly describe the Large Millimeter Telescope as one of the potential observational infrastructures where the acousto-optical spectrometer can be successfully used. A summary on the study of molecular gas in relatively old (age > 10 Myr) disks around main sequence stars is provided. We have identified this as one of the science cases in which the proposed processor can have a big impact. Then we put forward triple product acousto-optical processor is able to realize algorithm of the space-and-time integrating, which is desirable for a wideband spectrum analysis of radio-wave signals with an improved resolution providing the resolution power of about 105 - 106. It includes 1D-acousto-optic cells as the input devices for a 2D-optical data processing. The importance of this algorithm is based on exploiting the chirp Z-transform technique providing a 2D-Fourier transform of the input signals. The system produces the folded spectrum, accumulating advantages of both space and time integrating. Its frequency bandwidth is practically equal to the bandwidth of transducers inherent in acousto-optical cells. Then, similar processor is able to provide really high frequency resolution, which is practically equal to the reciprocal of the CCD-matrix photo-detector integration time. Here, the current state of developing the triple product acousto-optical processor in frames of the astrophysical instrumentation is shortly discussed.

Hybrid acousto-optic Fourier processor for imaging spatially inhomogeneous acoustic fields

A new method is proposed for imaging spatially inhomogeneous acoustic fields. The approach is based on the Fourier transform of a coherent light field formed as a result of the Bragg diffraction of a probing laser beam on an ensemble of quasi-plane acoustic waves in a lithium niobate crystal. These waves appear as a result of the transformation of an imaged acoustic field by a spherical acoustic lens. The proposed method has been experimentally verified using model multielement acoustic sources.

Recognition of Optical Layered Binary Phase Shift Keying Labels Using Coherent Acoustooptic Processor for Hierarchical Photonic Routing

Wavelength-selective optical processing using collinear acoustooptic (AO) switches will be useful in photonic routing systems. We have studied the applications of this processing to optical label recognition in label routers. We propose the recognition of hierarchical routing labels encoded in the binary-phase-shift-keying (BPSK) format using an AO processor consisting of optical delay waveguides and parallel double-stage AO switches. Using wavelength-multiplexed hierarchical labels, simple processing using the AO processor can be realized. The recognition characteristics are analyzed and numerically confirmed by computer simulation.

Acousto-optic image processing

Acousto-optic processing of images is based on the angular selectivity of acousto-optic interaction resulting in spatial filtration of the image spectrum. We present recent theoretical and experimental investigations carried out in this field. Much attention is given to the analysis of the acousto-optic cell transfer function form depending on the crystal cut, the geometry of acousto-optic interaction, and the ultrasound frequency. Computer simulation results of the two-dimensional acousto-optic spatial filtration of some elementary images are presented. A new method of phase object visualization is suggested and examined that makes it possible to separate amplitude and phase information contained in an optical image. The potentialities of the acousto-optic image processing are experimentally demonstrated by examples of edge enhancement and optical wavefront visualization effects.

Acousto-optic processing of images in visible and ultraviolet light

The paper concerns processing of optical images by means of tunable acousto-optic filters. Experimental and theoretical research showed that longitudinal chromatic aberrations cause a suffcient decay of the spatial resolution in the devices. It is shown that a proper choice of an optical cheme of an imager reduces the longitudinal aberrations all over the tuning range of the filters.

Wavelength-Division-Multiplex Photonic Routers with Collinear Acoustooptic Processing for Optical Label Matching in Spectral and Time Domains

A collinear acoustooptic (AO) switch has a feature of wavelength-selective switching for wavelength-division-multiplexed (WDM) signals. This feature can be used for photonic packet routing in WDM photonic networks. In this study, the application of collinear AO switches to a label recognition processor in a photonic routing system is investigated. An optical label is assumed to be encoded in spectral and time domains. Collinear AO switches are considered for use in label recognition by using multiple wavelength switching with rf control signals at multiple frequencies. By employing a combination of encoding in spectral and time domains, flexibility in routing control, and the number of represented labels can be increased. Numerical examples of label recognition are also presented.

Optical image processing by means of acousto-optic spatial filtration

Results are presented of a theoretical and experimental study of a new method of optical image processing based on two-dimensional acousto-optic filtration of the spatial spectrum of images. Most attention is concentrated on the analysis of the acousto-optic cell transfer function form and its dependence on crystal cut, geometry of acousto-optic interaction and ultrasound frequency. Results of computer simulation of acousto-optic spatial filtering are illustrated by the example of an object in the form of an amplitude grating. Experiments investigating the transfer functions of acousto-optic cells with collinear and tangential geometry of acousto-optic interaction are described. Acousto-optic image processing is demonstrated experimentally using the example of the edge enhancement effect for some elementary images.