Bragg Cell Research Articles

Analysis of the Functional Capabilities of Technical tools for Measuring Aircraft Mechanical Parameters

The purpose of research is to analyze the functionality of classical and advanced sensors for controlling the mechanical parameters of aircraft using the example of strain and vibration sensors to identify their current areas of development.Methods. Research methods are based on the concepts of the theory of sensory systems, the theory of diagnostics and forecasting of the technical condition of aircraft. Methods of multi-criteria analysis, parametric and structural synthesis are used. The principles of operation, as well as the functionality of the main classical sensors used in aircraft to control the parameters of deformation and vibration, are analyzed. A critical assessment of the possibilities of using the analyzed sensors for implementation in various tasks of aviation diagnostics of mechanical parameters has been made.Results. It has been established that the impact of flight loads on the airframe and critical components of aircraft is accompanied by the appearance of hidden deformations in the form of mechanical stresses, which are divided into two components: normal and tangential. Analytical dependencies are obtained for calculating the above quantities using fiber-optic sensors with distributed Bragg cells that convert the change in their own linear dimensions into a change in the reflected wavelength. A necessary condition for obtaining correct measurement results is the temperature compensation of the cells, which makes it possible to localize the places of deformations with an accuracy up to the location of a particular cell. The practical results of using alternative sensors for detecting hidden deformations (cracks) based on radio frequency identification methods in various frequency ranges are presented.Conclusion. The development of the method for diagnosing stress-strain states of aircraft complex units is the use of frequency-Doppler fiber-optic sensors with a high signal-to-noise ratio and a spherical radiation pattern, which will allow developing technical means for monitoring the dynamics of internal deformations of controlled units in real time. As promising areas of research in the field of creating new sensors with new physical properties, fiber-optic Bragg sensors with an inclined grating should be considered.

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.

Terahertz imaging using optically controlled Fourier-basis structured illumination.

We demonstrate that a new type of structured-illumination imaging may be migrated from the optical to the terahertz domain. This Fourier-basis technique involves illuminating a target with rapidly moving sinusoidal fringes of controllable spatial frequency and orientation, while measuring the scattered radiation on a single fast detector. This initial proof-of-concept demonstration is purely one-dimensional since the fringe orientation is fixed, but the technique is readily extensible to two dimensions. The fringes are first generated in the near-infrared (808 nm) by passing a high-power laser beam through an acousto-optic Bragg cell driven by a superposition of two RF signals slightly offset in frequency, blocking the undeflected beam, and refocusing the two diffracted beams onto a metal-backed semiconductor wafer. The laser can be amplitude modulated to slow down the moving fringes to accommodate the semiconductor's temporal response. The semiconductor acts as an optically addressed spatiotemporal modulator for a THz beam illuminating the same area. The periodic optical fringes effectively transform the semiconductor into a reflective THz diffraction grating with a programmable period. The diffracted THz radiation is then imaged onto the remote target plane, where the diffraction orders interfere pairwise to create traveling THz fringes. Scattered radiation from the target is collected by a simple receiver operating in "light bucket" mode, which produces an output signal consisting of a superposition of sinusoidal tones, one for each spatial Fourier component of the target. We present measurements of the THz fringe projector's performance and compare with a model of the semiconductor modulator's operation. Finally, we present Fourier-reconstructed images of pairs of point targets as an initial demonstration of THz Fourier-basis agile structured illumination sensing imaging.

Production of dichromatic light with a rotating polarization vector using a single Bragg cell

We propose an approach for producing a rotating polarization vector of dichromatic light controlled by the acoustic frequency. This approach is based on diffraction of one of the eigenmodes for each monochromatic component during two passes of dichromatic light through a gyrotropic acousto-optical cell and is demonstrated using rotation in the polarization of dichromatic light generated by an Ar laser at wavelengths of 0.488 µm and 0.514 µm using a paratellurite acousto-optical cell operating at 108 MHz.

Practical results and prospects of using fiber optical sensors of acoustic emission for diagnosting the technical condition of aircraft units

Peripheral sensors for measuring aircraft parameters are an integral part of any system for diagnostics and forecasting of technical condition. Their principle of operation in relation to operation at aviation complexes is to convert mechanical, electromagnetic or light quantities into electrical ones for their subsequent processing. The process of radiation of disturbances propagating in the material caused by the dynamic local rearrangement of the structure of materials under the action of internal stresses leading to a change in the crystal lattice or the movement of micro- and / or macrodefects is called acoustic emission. So, the analysis of differences in the form of acoustic waves allows the classification of the type of deformation: crack or plastic deformation, which allows you to more accurately determine the current state of the airframe or diagnosed nodes. The principle of operation of such sensors is based on the effect of converting the linear dimensions of a Bragg cell, made on an optical fiber, into a change in the reflected wavelength. A necessary condition for obtaining correct results of measurements of stress states is the need for temperature compensation of the Bragg cells, which is achieved by introducing additional cells that are mechanically decoupled from the material being diagnosed and react only to the temperature component. The advantage of this method is the absence of the need for additional adjustment of the cells and their alignment, as well as the independence of measurements from the effects of electromagnetic radiation; the sensors are lightweight, vibration-resistant, and insensitive to electromagnetic fields. The article presents the practical results of using fiber-optic acoustic emission sensors for diagnosing the technical condition of critical components and assemblies of aircraft, as well as outlines the prospects for their deepest integration into a unified information and analytical system for diagnosing and predicting the technical state of aviation complexes. The developed technical solutions aimed at simplifying the methods of processing broadband acoustic emission signals, which make it possible to design acoustic emission sensors based on optical fiber, are structurally simpler and cheaper, with an increased signal-to-noise ratio, due to one conversion of an acoustic-optical signal into an electrical one.

The Elastic Wave Propagation in Rectangular Waveguide Structure: Determination of Dispersion Curves and Their Application in Nondestructive Techniques

The use of mechanic waves for assessing structural integrity is a well-known non-destructive technique (NDT). The ultrasound applied in the guided wave in particular requires significant effort in order to understand the complexities of the propagation so as to develop new methods in damage detection, in this case, knowing the interaction between the wave propagation and the geometry of the waveguides is mandatory. In the present work, the wave propagation in rectangular steel rod is presented. In this study, the section dimensions were fixed as 5 × 15 [mm], a typical element of the flexible riser structural amour commonly used in the offshore oil industry. The studies here presented were restricted to [0, 100 KHz] frequencies. This frequency interval is in the range of commercial waveguide equipment commonly applied in ducts in NDT applications. The computation of the dispersion curves is performed by using three different methodologies: (i) analytical solutions, (ii) a method that combines analytical approaches with finite element methods (SAFE), and (iii) experimental method that extracted information from the rod using laser vibrometers and piezoelectric actuators. Finally, two applications based on the dispersion curves determined in the rectangular waveguide are presented to illustrate the possibilities of the curve dispersion knowledge related to the specific geometry in the development and application linked to NDT. The first application consists on showing the possibilities of the techniques that use a fiber grating Bragg cell (FGB) to measure the wave displacement and the second application involves the simulation of pre-fissured prismatic waveguide aimed at searching to induce three characteristic acoustic events. The model was built combining the finite element method and a version of the discrete element method.

Broadband Acousto-Optic Modulation of Optical Radiation

Abstract—For broadband modulation of the intensity of optical radiation, the tandem arrangement two acousto-optic (AO) Bragg cells are proposed in which acoustic waves propagate in opposite directions. The device allows modulation of optical radiation in the acoustic frequency band of ~6 MHz at four times the frequency of the sound. The possibility of switching the modulation frequency from 2f to 4f, where f is the frequency of sound, by simply turning the output polarizer is demonstrated. The method is experimentally tested for modulating radiation with a wavelength of 0.63 × 10–4 cm using two AO cells made of paratellurite operating at a center frequency of 22 MHz.

Image intensity recovery with mitigation in the presence of gamma–gamma atmospheric turbulence using encrypted chaos

Mitigation of image distortion under modified von Karman-type phase turbulence has been examined by using acousto-optic (A-O) chaos waves generated via feedback in a Bragg cell. The chaos wave transferred to the optical carrier either over an image-bearing transparency (with the image reconstructed with appropriate lensing), or alternatively the two-dimensional image (both static as well as dynamic) is embedded in the chaos wave and propagated over the turbulent layer. These investigations demonstrate that the properties of chaos waves including relative immunity from variations in the propagation path enable reduction or mitigation of the image distortion under turbulent conditions. Mitigation of image distortion is explored using propagation through a turbulent atmospheric layer characterized by gamma–gamma type intensity fluctuations. Standard weak, moderate, and strong turbulence conditions are applied for the numerical analysis based on the corresponding structure parameters. Following standard approach, the relevant probability density functions are generated using small- and large-scale eddies (α and β numbers) incorporated into the turbulence model. In addition, mitigation of image distortion due to gamma–gamma turbulence is examined for propagation along a low-altitude slanted path with a fixed slope and different elevation angles using A-O chaos along with the Huffnagel–Valley model. Stationary images are transmitted under nonchaotic and chaotic conditions, and the corresponding distortions in the received images are measured using the conventional metric of bit error rates. The system performances under nonchaotic and chaotic transmissions are compared with the intent to establish that packaging a signal within a chaos wave offers a degree of distortion mitigation.

Refractive Index Measurement of Lithium Ion Battery Electrolyte with Etched Surface Cladding Waveguide Bragg Gratings and Cell Electrode State Monitoring by Optical Strain Sensors

In this scientific publication, a new sensor approach for status monitoring, such as state of charge and state of health, of lithium ion batteries by using special Bragg gratings inscribed into standard optical glass fibers is presented. In addition to well-known core gratings, embedded into the anode of 5 Ah lithium ion pouch cells as a strain monitoring unit, the manufacturing of a surface cladding waveguide Bragg grating sensor incorporated into the cell’s separator, that is sensitive to changes of the refractive index of the surrounding medium, is demonstrated. On the basis of the experiments carried out, characteristics of the cell behavior during standard cyclization and recognizable marks in subsequent post-mortem analyses of the cell components are shown. No negative influence on the cell performance due to the integrated sensors have been observed; however, the results show a clear correlation between fading cell capacity and changes of the interior optical signals. Additionally, with the novel photonic sensor, variations in the electrolyte characteristics are determinable as the refractive index of the solution changes at different molar compositions. Furthermore, with the manufactured battery cells, abuse tests by overcharging were conducted, and it was thereby demonstrated how internal battery sensors can derive additional information beyond conventional battery management systems to feasibly prevent catastrophic cell failures. The result of the research work is an early stage photonic sensor that combines chemical, mechanical and thermal information from inside the cell for an enhanced battery status analysis.

High-frequency acousto-optic light modulation by double propagation of the beam through two Bragg cells

A method of light modulation in a wide acoustic frequency band by means of light transmission through two identical acousto-optic (AO) Bragg cells, in which acoustic waves propagate in opposite directions, is proposed and investigated. The peculiarities of the method make it possible to compensate the shift between the interfering beams caused by beam deviation during the AO diffraction process. The method is implemented experimentally with two AO cells fabricated from paratellurite for high-frequency light modulation for a wavelength of 0.63 μm.

High-frequency acousto-optic modulation of light when radiation passes twice through two Bragg cells

High-frequency acousto-optic modulation of light when radiation passes twice through two Bragg cells

Laser-Doppler vibrometer microscope with variable heterodyne carrier

The generation of a heterodyne carrier frequency for coherent detection via offset-locking in an optical phase-locked loop was demonstrated in communication, spectroscopy and other fields. In state-of-the-art laser-Doppler vibrometers (LDV), common acoustooptic devices (Bragg cells) allow efficient heterodyning with a static frequency. Moving mechanical parts vibrate in many technical applications, e.g. moving cars, trains, robots, ect.. In such applications, a large laser-Doppler-shift generated by the movement impairs the measurement of the relevant vibrations. A variation of the frequency offset of the interfering laser beams can suppress the Doppler effect of high-speed movements with slow speed variations and adjusts the signal spectrum to the optimal value. Thus, the electronic bandwidth can be set to an optimal value within the modulation bandwidth of the relevant vibrations. However, Bragg cells are not well applicable to shift laser frequencies without affecting the interferometer adjustment. In this paper, we propose offset locking of two independent lasers with an optical phase-locked loop to exploit the possibility of flexible heterodyne-carrier generation for laser-Doppler vibrometry. We demonstrate a LDV setup with offset locked visible DBR semiconductor lasers for a flexible heterodyning up to 200MHz and present first measurements.

Performance Analysis of U-FBG Fiber System using different Sizes of Bragg Cell

Performance Analysis of U-FBG Fiber System using different Sizes of Bragg Cell

Acousto-Optical Modulators for Free Space Optical Wireless Communication Systems

A free space optical (FSO) wireless communication system is proposed and analyzed in this paper. An incident laser beam is aligned to hit a Bragg cell at the Bragg angle. At the same time, input data bits to be transmitted control the frequency of the RF signal, which in turn controls the acoustic wave propagating in the Bragg cell. As such, different diffracted beams will be obtained based on the frequency of the generated acoustic wave signal in the Bragg cell. The different beams represent variant signals in a constellation diagram and will be used to convey information from the source to the destination. A receiver with multiple photodetectors aligned to the variant diffracted beams is considered. An optimum receiver should consider the different angles and intensities of the transmitted beams to retrieve information bits. The average bit error probability of the wireless communication system is obtained through Monte Carlo simulations and validated analytically. Besides, the impact of different system and channel parameters is investigated. Reported results reveal significant enhancements of the proposed algorithm as compared with conventional state-of-the-art FSO systems.

Secure free-space communication, turbulence mitigation, and other applications using acousto-optic chaos.

Use of acousto-optic (A-O) chaos via the feedback loop in a Bragg cell for signal encryption began as a conceptual demonstration around 2008. Radio frequency (RF) chaos from a hybrid A-O feedback device may be used for secure communications of analog and digital signals. In this paper, modulation of RF chaos via first-order feedback is discussed with results corroborated by nonlinear dynamics, bifurcation maps, and Lyapunov analyses. Applications based on encryption with profiled optical beams, and extended to medical and embedded steganographic data, and video signals are discussed. It is shown that the resulting encryption is significantly robust with key tolerances potentially less than 0.1%. Results are also presented for the use of chaotic encryption for image restoration during propagation through atmospheric turbulence.

Comprehensive time average digital holographic vibrometry

This paper presents a method that simultaneously deals with drawbacks of time-average digital holography: limited measurement range, limited spatial resolution, and quantitative analysis of the measured Bessel fringe patterns. When the frequency of the reference wave is shifted by an integer multiple of frequency at which the object oscillates, the measurement range of the method can be shifted either to smaller or to larger vibration amplitudes. In addition, phase modulation of the reference wave is used to obtain a sequence of phase-modulated fringe patterns. Such fringe patterns can be combined by means of phase-shifting algorithms, and amplitudes of vibrations can be straightforwardly computed. This approach independently calculates the amplitude values in every single pixel. The frequency shift and phase modulation are realized by proper control of Bragg cells and therefore no additional hardware is required.

SU‐C‐204‐04: Irradiation of Human Cell Lines Using Various Ions

Purpose:The purpose of this study is to investigate and quantify the biological effects of ion radiation using several human cell lines. We aim to answer the question of whether carbon ion the most ideal ion species for heavy ion radiotherapy.Methods:The cells were irradiated at different positions along the pristine Bragg peak of several ions with different atomic number. The biological effectiveness was evaluated using the clonogenic cell survival assay. Irradiation of three human lung cancer cell lines and a fibroblast cell line were undertaken using the charged particle beam at the NASA Space Radiation Laboratory at Brookhaven National Lab. Four mono‐energetic ion beams (carbon, oxygen, helium and lithium) were used to irradiate the cells. Water or media‐filled T25 flasks were lined up along the beam line so that the cell‐containing surfaces of the flasks were placed at a specific depth along the pristine Bragg curve. Four depths along the curve, representing entrance point, rising peak, peak and distal fall off, were selected to determine biological effectiveness. Gaf‐chromic films were placed between the flasks to monitor the irradiation as soon as it was finished.Results:For all ion radiations, the maximum cell killing effect occurs at either peak or distal fall off, depending on the cell lines. For instance, for the fibroblast cell line AGO1522, RBEs of 1.4, 1.2, 1.4 and 1.9 were observed at the Bragg peak for Helium, Lithium, Carbon and Oxygen ions. Comparing positions, RBEs of 0.9, 1.2, 1.4 and 1.8 were observed for carbon irradiation of AGO‐1522 cells positions corresponding to entrance, rising peak, peak and distal fall off.Conclusion:RBE values differ with position in the Bragg peak, ion species and cell line. Ions other than carbon may prove more effective in certain irradiation conditions and may contribute to optimized heavy ion therapy.

Features of the dependence of the diffraction efficiency of an acousto-optic Bragg cell with multielement traveling wave transformer on its geometric parameters

An equation for calculation of the diffraction efficiency of an acousto-optic Bragg cell with multielement traveling wave transformer taking into account the exponential distribution of the acoustic field along of the transformer is obtained. The results of theoretical and experimental studies of the dependence of the diffraction efficiency of the Bragg cell on the number of radiating elements in the piezoelectric traveling wave transformer are given. Nonlinear behavior of the dependence of the diffraction efficiency on the number of radiators in the considered transformer is analyzed.

Acousto-optics bandwidth broadening in a Bragg cell based on arbitrary synthesized signal methods.

In this work, we present the advantages of driving a multichannel acousto-optical deflector (AOD) with a digitally synthesized multifrequency RF signal. We demonstrate a significant bandwidth broadening of ∼40% by providing well-tuned phase control of the array transducers. Moreover, using a multifrequency, complex signal, we manage to suppress the harmonic deflections and return most of the spurious energy to the main beam. This method allows us to operate the AOD with more than an octave of bandwidth with negligible spurious energy going to the harmonic beams and a total bandwidth broadening of over 70%.

Исследование объемных акустических волн СВЧ-диапазона, возбужденных встречо-штыревым преобразователем

Excitation of bulk and surface acoustic waves with the interdigital transducer (IDT), which is deposited on the surface of piezoelectric crystal, is widely used in the development of devices in acoustoelectronics and in the design of the microwave acousto-optic deflectors. Excitation of bulk acoustic waves by IDT in the devices on surface acoustic waves leads to the appearance of spurious signals. At the same time excitation of bulk acoustic waves with IDT from the surface of lithium niobate crystals allows creating high frequency acousto-optic deflectors, which makes possible to significantly simplify the technology of their production. Therefore, significant attention is paid to the task of excitation and distribution of bulk acoustic waves with IDT including recent times by the method of simulation of their excitation and distribution. The obtained theoretical results require experimental verification. This paper documents the visualization of acoustic beams excited with IDT from the XY-surface of lithium niobate crystals. The Bragg cells with LiNbO3 crystals coated with IDT with a different period of electrodes were manufactured for the experimental research of excitation and distribution of bulk acoustic waves. Visualization results have shown that the acoustic waves excited with IDT distribute in both the Fresnel zone and the Fraunhofer zone. The length of these zones is caused by individual elementary emitters of which consists the IDT (by their size). At the same time the far zone for IDT is located at distances much greater than the actual size of the LiNbO3 crystals. This peculiarity is not always taken into account when calculating diffraction. The achieved results can be used to design high-frequency acousto-optic devices, as well as in the development of devices based on surface acoustic waves.