Acousto-optic Spectrum Analyzer Research Articles

Application of the flicker noise filtering algorithm by changing the modulation frequency in an acousto-optic spectrum analyzer

The article discusses the noise characteristics of the system for collecting data and processing spectral signals in an ozonometer. Low-frequency flicker noise introduces significant distortions into the useful signal path. In order to reduce low-frequency flicker noise, a method was developed based on the use of modulation of the useful signal at the output of the acousto-optic spectrum analyzer with a certain frequency. This method creates an artificial filter. The choice of the modulation frequency determines the frequency response of this filter. It is necessary to choose it such that the maximum signal attenuation is in the low frequency region, where the influence of flicker noise is strong. In this work, a noise signal was simulated using the Matlab environment and its filtering by changing the modulation frequency of the synthesized signal.

A METHOD FOR IMPROVING THE QUALITY INDICATORS OF A DISTRIBUTED FORENSIC INFORMATION SYSTEM

Subject of research: the process of monitoring the quality indicators of a computer network of a forensic information system using methods for increasing the frequency resolution of acousto-optic spectrum analyzers. The aim of this work is the possibility of increasing the QoS indicators of a computer network by achieving the potential accuracy of estimating the frequencies of two simultaneously arriving radio pulses using the super-Rayleigh resolution method in acousto-optic spectrum analyzers (AOSA). The following tasks are solved in the article: analysis of various information systems of forensic examination and the tasks that they solve; analysis of the use of acousto-optic spectrum analyzers to determine the parameters of the transmitted signal in a distributed forensic system; derivation of an analytical expression for evaluating the potential accuracy of the frequency detuning value of two pulses. The following methods and models are used: models and methods of systems theory (based on the information approach), models and methods for constructing distributed systems and their components in accordance with various hierarchical levels of their organization and operating conditions; models and methods of theories of propagation and interaction of electromagnetic waves with wave structures of various physical nature. The following results were obtained: The analysis has established that forensic information systems are distributed in nature and impose high requirements on the quality of the functioning of telecommunications equipment of the corresponding computer networks (CN). To meet these requirements, it is necessary to improve the systems for monitoring, protecting and transmitting information in the corresponding CN, which is impossible without solving the problem of monitoring signal parameters. Research has been carried out on the use of AOSA to ensure control over communication channels of computer networks. It was found that most of the AOSA frequency resolution methods have limitations associated with the Rayleigh criterion, which significantly limits the potential for frequency separation of pulses. The use of the method of super-Rayleigh resolution of narrow-band pulses in terms of their arrival time is proposed. An analytical expression is obtained to estimate the potential accuracy of determining the value of the detuning in the frequency of two pulses. Conclusions. The forensic information system is a complex heterogeneous distributed system. To improve the efficiency of its functioning, it is necessary to control the parameters of the signal propagating in the network. The use of the super-Rayleigh resolution method in AOSA will increase the resolution of AOSA by increasing the frequency resolution of two non-simultaneous radio pulses of long duration.

MEANS OF IMPROVING THE QUALITY OF SERVICE OF THE COMPUTER NETWORK OF THE FORENSIC INFORMATION SYSTEM

The relevance of research. In modern forensic practice, computer networks (CN) are an integral part of computer-technical examination, therefore, ensuring their normal functioning becomes a vitally important task. In this regard, the theory of the construction, modification and operation of digital telecommunication systems raises a fairly general problem of digital signal processing, network synchronization and its stability. A solution to this problem was devoted to research, which analyzed the characteristics of the stability of the network and proposed methods for measuring the physical parameters that determine it. Many of the studies conducted were based on the use of frequency measurements in communication channels of computer networks for transmitting information. Acousto-optic spectrum analyzers (AOSAs) are widely used in forensic information system networks improving the QoS of forensic computer networks. The subject of the research: resolution of acousto-optical spectrum analyzers. The purpose of the research to improve the quality of diagnostics of parameters of computer information transmission networks based on the use of the developed signal processing technique in acousto-optic spectrum analyzers, which allows increasing the resolution of AOSA by increasing the frequency resolution of two non-simultaneous long-duration radio pulses. The results of the research. The research presents analysis of the influence of the frequency parameters of the computer network on the implementation of the relevant requirements for quality of service. Studies have been carried out on possible ways to increase the resolution of AOAC in frequency. The nonlinear characteristics of AOSA were studied, which made it possible to modernize methods for increasing the frequency resolution. The classical method of processing radar signals is used, which allows determining the delay time of arrival of a sufficiently long pulse with an accuracy significantly exceeding the pulse size. When analyzing the operation of AOSA, it is taken into account that the signal photoelectron flux in the acousto-optical spectrum analyzer is known to be described by the Poisson distribution. But one of the main properties of random variables distributed according to Poisson's law is the lack of cross-correlation of the components of the Poisson stream. This assumption can significantly increase the frequency resolution of AOSA. Conclusions. The research ascertains analytical relationship for the dispersion of the signal frequency measurement. The research proposes a technique for processing signals in AOSA, allowing to increase the resolution of AOSA by increasing the frequency resolution of two non-simultaneous radio pulses of long duration.

METHOD FOR THE DIAGNOSTICS OF SYNCHRONIZATION DISTURBANCES IN THE TELECOMMUNICATIONS NETWORK OF A CRITICAL USED COMPUTER SYSTEM

Relevance of the study. To improve the quality of service (QoS), the work of all network technologies, protocols, and individual traffic management mechanisms is constantly optimized. It is known that the quality of information transmission in modern telecommunication equipment is affected by the quality of synchronization devices. Synchronization is a means of maintaining the operation of all digital equipment in a data transmission network at one average speed, which must exist at three levels: bit synchronization, synchronization at the level of channel intervals (time slot) and frame synchronization. Therefore, the lack of synchronization of the computer system at the required level can lead to a significant decrease in QoS. At the same time, the requirements for ensuring these indicators are significantly tightened in the face of an increase in the load of network resources. Subject of study: computer system synchronization. The aim of the article is to develop a method for diagnosing synchronization disturbances in the telecommunications network of a computer system of critical application by increasing the resolution of an acousto-optical spectrum analyzer. Research results. The influence of non-stationary data transmission in the telecommunications subsystem of the computer system under study is analyzed. The analysis and classification of the causes of computer network synchronization failure of a critical application computer system is carried out. The article describes the consequences of a violation of computer network stabilization for ensuring the quality of service provided by various frequently used services. Proposed the use of acousto-optic spectrum analyzer with spatial integration for diagnostics of violations of the synchronization network. In work the analysis of the use of acousto-optic spectrum analyzers. The conducted research allowed us to obtain an analytical expression for the output signal of the spectroanalyzer when two rectangular pulses with different carrier frequencies, durations and delay times are received at its input. This result, as well as the numerical calculations provided, allowed us to develop General recommendations for increasing the resolution of the acousto-optical spectrum analyzer, and thus create theoretical prerequisites for improving the synchronization of the computer system. The given analytical relations and numerical estimates were experimentally verified by means of system simulation. Conclusions. As a result of the research, a method of diagnostics of synchronization violations in the telecommunications network of a computer system of critical application was proposed. The method is based on increasing the resolution of the measuring system based on an acoustooptic spectrum analyzer.

Statistic Model of Homodyne Acousto-Optic Spectrum Analyzer

Introduction. Acousto-optic spectrum analyzers interferometric schemes have been developed to increase dynamic range. It was assumed that dynamic range, expressed in dB, would double. An expected increase was not achieved yet.Aim. To analyze the homodyne acousto-optic spectrum analyzer noise characteristics, to estimate the signal-tonoise ratio and the dynamic range.Materials and methods.A mathematical model was compiled which took into account the need to form quadrature components to obtain an amplitude spectrum of an input signal, shot noise and readout noise.Results. An interferometric scheme did not allow to achieve dynamic range doubling compared to an acoustooptical power spectrum analyzer. The dynamic range increase was less than 1.35 dB. Constant illumination led to a significant increase of the spectrum analyzer self-noise due to shot noise, compared to which thermal noise and readout noise became insignificant. The spurious-free dynamic range estimation expression was obtained. It was prior determined by acousto-optic interaction nonlinearity. With typical analyzer blocks parameters the spurious-free dynamic range covered a single-signal dynamic range. Signal-to-noise ratio estimation expression was presented.Conclusion. The homodyne acousto-optic spectrum analyzer single-signal dynamic range is determined primarily by the photosensor saturation charge. One needs to optimize their relation by taking into account light source power, acousto-optical modulator diffraction efficiency and photosensor saturation charge. Presented noise model gives more accurate estimation of the dynamic range with an error of 1 dB.

ON USING PERIODIC REFERENCE SIGNAL IN HOMODYNE ACOUSTO-OPTIC SPECTRUM ANALYZER

Introduction. For a homodyne acousto-optic spectrum analyzer functioning a reference optical channel must be organized. The signal in this channel should provide uniform reference illumination throughout the spatial frequency range. In the general case, the spectrum analyzer functioning can be considered with a continuous photosensor and photosensor with charge accumulation. With the last one, the signal in the reference channel is proposed to be a wideband pulses periodic sequence. Objective. Analyze the spectrum analyzer functioning with a periodic reference signal. Materials and methods. We derive the mathematical expression to describe the influence of the reference signal structure on the analyzer’s output signal for the cases of continuous photosensor and photosensor with charge accumulation. Results. It is shown that in the case of continuous photosensor, the reference signal periodicity does not lead to characteristics degradation. However, in the case of many frequency resolution points it is impractical, since each photodetector signal is parallel, processing is required: filtering, amplification and digitization. In the case of using of the charge accumulation sensor, the discrete frequency grid appears, which means signals omissions in frequency. This can be avoided by choosing the accumulation time equal to the minimum among the values of the acousto-optic modulator time aperture and the reference signal period, which is hard to implement, or still leads to the signal omissions in frequency or time. Conclusion. To perform a real-time mode in the homodyne acousto-optic spectrum analyzer, the reference signal must be either non-periodic, which raises the question of its synthesis, or a continuous photodiode array should be used.

QUADRATURE COMPONENTS FORMING METHOD FOR HOMODYNE ACOUSTO-OPTIC SPECTRUM ANALYZER

Introduction. Among acousto-optic spectrum analyzers with spatial integration, schemes based on optical interferometers provide the largest dynamic range. Nevertheless, they form the signal amplitude spectrum on a certain spatial carrier. Formation of quadrature components can eliminate this spatial carrier. The two-dimensionality of the transformations performed in optical processors provides this elimination by reading of the additional charge of matrix photosensor lines. A renowned method implements this approach using four lines, which in turn determines the estimation time of the signal spectrum.Objective. The objective of the work is to study the possibility of time reduction of the spectrum estimation.Materials and methods. The paper presents the description of two methods of forming the necessary components.The first method uses three photosensor lines, the charge distribution in which has the spatial carrier phaseshifted by 90 ° from line to line. The second method forms the necessary distributions sequentially in three accumulation cycles by means of variation of the initial phase of the reference signal. By the mathematical proof, three distributions with a 90 ° relative phase shift are sufficient to eliminate the spatial carrier.Results. In the first method, reduction of the spectrum estimation time is insignificant, but the parallel distributions formation affords not to impose additional requirements on the signal spectrum. The second method, due to the possibility of using any three sequentially formed distributions for estimation, is potentially three times faster than the first method, but requires the stationary signal spectrum within three accumulation cycles. Researchers can implement this meth-od using a linear photosensor or TDI photosenor. In addition, the method is less demanding to optical scheme parameters.Conclusion. The proposed quadrature components formation methods provide time reduction of the spectrum estimation in interference acousto-optic spectrum analyzers and simplify their design.

Comparison of the operation of an acousto-optic spectrum analyzer and an acousto-optic pseudo-Wigner processor by analyzing the time–frequency distributions of frequency-modulated signals

This paper compares the accuracy of the time–frequency distributions and their resolving power in the frequency–time plane of frequency-modulated radio signals when they are obtained by means of an acousto-optic spectrum analyzer and a pseudo-Wigner processor. Signals with linear frequency modulation and signals in which the frequency depends on time to a power greater than the first are considered. The results of numerical modeling are presented.

An optoelectronic processor for registration of radiation of pulsars

An optoelectronic processor (OEP) intended for recording radiation of pulsars with compensation of their dispersion distortions in real time in a wide frequency band and summation of output signals, synchronous with the pulse repetition period, is developed. The OEP includes an acousto-optic spectrum analyzer and a digital signal processor. The structure, principle of operation, and hardware implementation of the pulsar OEP are considered. The results of the experimental study and application of the OEP for observing pulsars on a radio telescope are given. The reception band of the pulsar OEP is 80 MHz.

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.

Potentials of acousto-optical spectrum analysis on a basis of a novel algorithm of the collinear wave heterodyning in a large-aperture KRS–5 crystalline cell

The technique under proposal for a precise spectrum analysis within an algorithm of the collinear wave heterodyning implies a two-stage integrated processing, namely, the wave heterodyning of a signal in a square-law nonlinear medium and then the optical processing in the same solid state cell. The technical advantage of this approach lies in providing a direct multichannel parallel processing of ultra-high-frequency radio-wave signals with essentially improved frequency resolution. This technique imposes specific requirements on the cell's material. We focus our attention on the solid solutions of thallium chalcogenides and take the TlBr-TlI (thallium bromine-thallium iodine) solution, which forms KRS-5 cubic-symmetry crystals with the mass-ratio 58% of TlBr to 42% of TlI. Analysis shows that the acousto-optical cell made of a KRS-5 crystal oriented along the [111]-axis and the corresponding longitudinal elastic mode for producing the dynamic diffractive grating can be exploited. With the acoustic velocity of about 1.92 × 105 cm/s and attenuation of ∼10 dB/(cm GHz2), a similar cell is capable of providing an optical aperture of ∼5.0 cm and one of the highest figures of acousto-optical merit in solid states in the visible range. Such a cell is rather desirable for the application to direct 5000-channel parallel spectrum analysis with an improved up to 10−5 relative frequency resolution.

Acousto-optical spectrum analysis of ultra-high-frequency radio-wave analogue signals with an improved resolution exploiting the collinear acoustic wave heterodyning

This article is devoted to the problem of improving the frequency resolution inherent in a parallel acousto-optical spectrum analysis via involving an additional nonlinear phenomenon into the data processing. In so doing, we examine possible application of the wave heterodyning to the real-time scale acousto-optical analysis of the frequency spectrum belonging to ultra-high-frequency radio-wave signals peculiar, for example, for radio-astronomy. The nonlinear process of wave heterodyning is realized through providing a co-directional collinear interaction of the longitudinal acoustic waves of finite amplitudes. This process, which is beforehand studied theoretically and investigated experimentally via the acousto-optical technique as well, allows us either to improve the frequency resolution of spectrum analysis at a given frequency range or to increase by a few times the current frequencies of radio-wave signals under processing. The first step along this way is connected with the experimental modeling of the acoustic wave heterodyning in solids via exploitation of the specific acousto-optical cell based on a liquid, which allows the simplest realization of a cell with the needed properties. Then, these theoretical and practical findings are used in our experimental studies aimed at creating a new type of acousto-optical cells, which are able to improve the resolution inherent in acousto-optical spectrum analyzer operating over ultra-high-frequency radio-wave signals. In particular, the possibility of upgrading the frequency resolution through the acoustic wave heterodyning is experimentally demonstrated using the cell made of lead molybdate crystal. The obtained results demonstrate practical efficiency of the novel approach presented.

Efficiency of acoustooptic spectrum analyzers in measurements and suppression of narrowband interferences during adaptive quasi-optimal detection of wideband signals

Two scenarios related to the overlay problem (of combining no less than two radio communications systems operating simultaneously in the same area in the same frequency range) are considered. The accuracy characteristics and design features of acoustooptic spectrum analyzers used to solve this problem are estimated.

Acoustooptical processor used for pulsar radio emission observations

A new type of acoustooptical processor (AOP) for the investigation of pulsar radio emission is proposed that provides for the compensation of signal dispersion in a broad frequency range. The AOP is based on an acoustooptical spectrum analyzer with a CCD photodetector operating in a special shift-and-add mode, which allows spectral components of the input signal to be added with a controlled time delay immediately in the CCD photodetector. The proposed AOP was successfully used on an RT-64 radio telescope (Kalyazin Radio Astronomy Observatory) for the observation of pulsars at 1.4 GHz in a bandwidth of 45 MHz.

AO-spectrum analyzer implementation into CDMA-telecommunications with enhanced SIR-factors.

The devices for real-time narrowband interference measurements within the code division multiple access (CDMA) cellular communication system on the base of the acousto-optic spectrum analyzer (AOSA) with satisfactory performances can be designed. The overlay model giving significant advantages in the interference immunity for simultaneous operation of the wideband (CDMA) and the narrowband time division multiple access (TDMA) cellular systems is proposed.

Spectroscopic Observations in the 3-mm Wavelength Range at CrAO RT-22 Radiotelescope Using an Acousto-Optical Spectrum Analyzer

Within the framework of a multi-year program of dense interstellar gas studies, we performed a new series of observations at the CrAO RT-22 radiotelescope in July 1998 using an improved 3-mm wavelength receiving facility. An acousto-optical spectrum analyzer (AOS) was used for the first time for the spectral analysis of incoming radiation. The AOS has larger bandwidth compared to the filter spectrum analyzer used previously and simplifies tuning SIS-mixer circuits and frequency converters. Using this facility, we observed a number of star-forming regions including clouds associated with bright IR sources and ultracompact HII regions as well as clouds with high-velocity outflows in the HCO+, 13CO, HCN, and CS molecule lines.

Temporal resolution in information processing in an acousto-optic spectrum analyzer with sequential readout of the information

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text S. B. Gurevich, B. S. Gurevich, A. M. Petskus, I. A. Akkoziev, and S. A. Alymkulov, "Temporal resolution in information processing in an acousto-optic spectrum analyzer with sequential readout of the information," J. Opt. Technol. 67, 123- (2000) Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

An interferometric spectrum analyzer with high dynamic range

The dynamic range improvement and realization of the acousto-optic spectrum analyzer are reported. When two RF signals of equal strengths and frequencies f 1 and f 2 are applied simultaneously to the signal Bragg cell, the analyzer demonstrates a dynamic range of 50 dB and frequency resolution 10 kHz.

Radiometers, autocorrelators, and matched-filter receivers by means of acousto-optic spectrum analysis

Acousto-optic spectrum analyzers provide a convenient means of separating wide-bandwidth signals into their frequency components. By a change in the rf input signal into the spectrum analyzer and by the provision of additional digital postprocessing, it is possible to perform radiometry, signal autocorrelation, and matched-filter reception. Although the acousto-optic device has a space-integrating architecture, the matched-filter receiver can be implemented for signals having time durations much longer than the acousto-optic cell. The resulting signal-to-noise ratio improvements from the receiver are consistent with the time-bandwidth product of the waveform, rather than the time-bandwidth product of the acousto-optic device. A mathematical foundation of the processor is presented along with specific receiver implementations. Computer-simulation and experimental results demonstrate key findings. In one experimental example, a linear-frequency-modulated waveform is matched-filter processed to recover a signal that is -24 dB with respect to the input noise floor.

Effect of partial spatial coherence of injection-laser radiation on the resolution of an acousto-optical spectrum analyzer

Effect of partial spatial coherence of injection-laser radiation on the resolution of an acousto-optical spectrum analyzer