Acousto-optic System Research Articles

Acousto-Optic Deflector-Principles, Working and Applications

Acoustic optic deflectors (AOD) have gained a lot of popularity as a fast way to scan the laser beam in optical coherence systems. It produces an acoustic wave that deflects the laser beam in a single direction. There are many factors to consider when choosing different solutions for acousto-optic spectral systems, but no comprehensive analysis or summary of these factors exists. In addition to summarizing the most popular optical schemes for acousto-optic spectral systems, this paper explains the basic principles of acousto-optic devices. A simulation study has also been performed to represent the characteristics of AOD in a practical environment. Additionally, applications of acousto-optic spectral systems in a few common fields are presented.

The Calibration Methods of Geometric Parameters of Crystal for Mid-Infrared Acousto-Optic Tunable Filter-Based Imaging Systems Design.

AOTF calibration is a complex topic that has various aspects. As far as geometric calibration is concerned, it includes not only processing errors and fixing errors in the optical system, but also the error of geometric parameters of crystal (GPC). GPC is the preset input in the optical design and optimization of Zemax, which determines the key parameters, including the spatial resolution, the field of view, and aberration. In particular, the compensation of aberration during the optical design requires accurate values of GPC. However, it is currently considered ideal. Therefore, two calibration methods based on the principle of parallel tangent are proposed: (1) the minimum-central wavelength method; (2) the minimum-frequency method. The deviation of the parallel tangent incident angle calibrated by the two methods is 0.03°. As a result, the tuning curve calculated in theory with the calibrated geometric parameters of AOTF is consistent with the tuning curve measured in practice.

Acousto-optical camera for super-resolution imaging

I will present a hybrid acousto-optical imaging system that probes the environment with acoustic waves, converts the back-scattered sound into a coherent optical field on an aperture using an acousto-optical metasurface, and focuses the latter into an image with existing optical lenses. Preliminary theoretical analysis and experiments show that this approach can produce images of significantly higher resolution than possible with conventional methods, thus enabling high quality images produced with low frequency probing sound. Our imaging approach takes advantage of the best properties of optic and acoustic waves, namely, (1) the high image quality produced by existing optical systems and (2) the ability of low frequency acoustic waves to penetrate most materials. An additional advantage of our method is that it puts essentially no constraints on the sound source. For example, the source could have low directivity and may consist of a single transducer or it could even miss when imaging noisy environments. In the latter scenarios, our imaging method becomes purely passive.

Repetition rate tunable single-longitudinal-mode acoustic-optical Q-switched nanosecond laser

Repetition rate-tunable single-longitudinal-mode (SLM) lasers are in wide demand for light detection and ranging. This study proposes an SLM acoustic-optical Q-switched Nd:YVO4 laser based on a short-cavity scheme. The laser system consists of a laser diode (LD) pump source, coupling optics, input mirror coupler (IC), Nd:YVO4 crystal, acousto-optic Q-switching system (AOQS), and output mirror coupler (OC). The mode selection is theoretically analyzed and confirmed from the experimental setup. The laser output obtains a 10 ns pulse duration, SLM with a linewidth of 279.43 MHz, and good stability that is maintained in the range of 1 to 4 kHz. The results demonstrate that the proposed method is a simple and robust source-laser scheme for high-power systems.

Review of acousto-optic spectral systems and applications

Acousto-optic devices represented by acousto-optic tunable filters (AOTFs), have the advantages of wide wavelength range from the ultraviolet to the long-wave infrared and fast wavelength switching speed. Nowadays, acousto-optic spectral systems have become very important scientific instruments in laboratory. There are many factors to be considered when we choose different solutions for acousto-optic spectral systems, but there is no comprehensive analysis and summary of them. This paper explains the working principle of the acousto-optic devices and summarizes the most common optical schemes for acousto-optic spectral systems. We also analyzed their characteristics of application conditions. In addition, specific applications of acousto-optic spectral systems in some common fields are presented.

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.

Experimental Analysis of Tunable Optical Spectral Imaging System Using a Grating in the Pupil Function

Hyperspectral imaging (HSI) systems have been demonstrated as a powerful imaging technique due to their high spectral resolution. HSI can obtain the spectrum for each pixel in the image of a scene, a feature that can be exploited to design optical systems with the purpose of analyzing and characterizing objects and identifying processes within the visible electromagnetic spectrum (bandwidth). In this paper, we present an HSI system comprising a diffraction grating placed in the exit pupil of our optical configuration. The spectrum for each pixel associated with the object appears in the first order of diffraction. We used this system to characterize and tune the required spectral band of the image of the captured object obtaining more information than with an optical imaging system. Accordingly, the proposed optical system is suitable to obtain spectral and hyperspectral imaging at low cost compared to an acousto-optic system or other HSI. The scanning system captures hundreds of spectral images associated with the object, obtaining a maximum spectral resolution of 0.26nm or 260 pm for one of our configurations.

Self-synchronized reflection-mode acousto-optic imaging system utilizing nanosecond laser pulses.

We present an acousto-optic imaging system operating in reflection-mode and utilizing a pair of compact, triggerable lasers with 532 and 1064 nm wavelength and nanosecond pulse duration. The system maps the fluence rate distribution of light transmitted through optically scattering samples. The imaging is performed using an acousto-optic probe comprising an ultrasound linear array with attached optical fiber on one side and a camera on the other. The described hardware configuration images samples with access restricted to one side only and ensures mobility of the entire setup. The major challenge of the introduced approach is mitigating the effects of laser parameter instabilities and precise synchronization of ultrasound and laser pulses. We solved this issue by developing an electronic feedback circuit and a microcontroller-based synchronization and control system triggering the ultrasound scanner. Schematics and details regarding control algorithms are introduced. The imaging performance of the system is demonstrated on examples of results obtained for solid, acoustically-homogeneous and optically scattering phantoms with and without light absorbing inclusions present. Adjusting the size and location of the region of interest within the camera sensor matrix and the number of laser pulses illuminating every frame allows for significant improvements in terms of the achievable peak signal to noise ratio. We demonstrate that the developed synchronization algorithm and system play a crucial role in ensuring imaging quality and accuracy.

Reflection-mode acousto-optic imaging using plane wave ultrasound pulses.

.Significance: Performance of an acousto-optic imaging system is limited by light fluence rate and acoustic pressure field distributions characteristics. In optically scattering media, the former determines the achievable contrast, whereas the latter the imaging resolution. The system parameters can be shaped by changing relative positions of ultrasound (US) transducer array and optodes. However, in the case of many potential clinical applications, optimization possibilities in this regard are limited, as a sample is accessible from one side only and using a water tank for coupling is not feasible.Aim: We investigate the possibilities of improving performance of an acousto-optic imaging system operating in reflection mode geometry with linear US array in direct contact with a sample using plane wave instead of focused US pulses.Approach: Differences in acoustic pressure field distributions for various transducer excitation patterns were determined numerically and experimentally. Acousto-optic images of phantoms with and without optically absorbing inclusions were acquired by measuring laser speckle contrast decrease due to the light modulation by plane wave and focused US pulses with different apodization patterns.Results: The residual acoustic pressure field components occupy relatively large volume and contribute to light modulation. Using nonsteered plane wave US pulses instead of focused ones allows one to mitigate their influence. It also allows one to obtain clear two-dimensional reconstructions of light fluence rate maps by shifting transducer apodization along the lateral direction.Conclusions: Using nonsteered plane wave US pulses allows one to achieve better imaging performance than with focused pulses in the assumed system geometry.

Acousto-Optic Comb Interrogation System for Random Fiber Grating Sensors with Sub-nm Resolution.

The broad-frequency response and nanometer-range displacements of ultrasound detection are essential for the characterization of small cracks, structural health monitoring and non-destructive evaluation. Those perturbations are generated at sub-nano-strain to nano-strain levels. This corresponds to the sub-nm level and, therefore, to about 0.1% of wavelength change at 1550 nm, making it difficult to detect them by conventional interferometric techniques. In this paper, we propose a demodulation system to read the random fiber grating spectrum using a self-heterodyne acousto-optic frequency comb. The system uses a self-heterodyne approach to extract phase and amplitude modulated signals to detect surface acoustic waves with sub-nanometer amplitudes in the frequency domain. The method can detect acoustic frequencies of 1 MHz and the associated displacement. The system is calibrated via phase detection with a heterodyne interferometer, which has a limited frequency response of up to 200 kHz. The goal is to achieve sub-nanometer strain detection at MHz frequency with random fiber gratings.

Effect of Square Shaped Acousto–Optic Modulators on the Bragg Diffraction

The COMOSOL multiphysicsis used to design various optical systems, including the design of the acousto-optic modulator system. Its work depends on the special inputs of the program, such as the characteristics of the laser used and the frequencies of the sound waves. A square modulator was designed with dimensions 3x3 mm, and a quartz crystal was used, in which the interaction of light and sound occurs. Different number of orders diffraction are generated called the Bragg angle, and their number varies with different inputs. The modulator is created by entering the value of the radio frequency up to 100 volts. Through our results, the efficiency increases at the frequency of 400 kHz after changing the frequencies of 200, 300 and 400 kHz. The values of the stress are: 1.24 × 106 P a, 1× 106 P a, 3.8× 106 P a, and the estimated shift is about 0.7, 0.4 and 0.9 mm, there were three frequency values considered: 200, 300, and 400 kHz. respectively. The far field shape show two orders are appeared at 200 kHz and 300 kHz frequencies they are: zero order and first order but they are different in the value of Bragg angles but in 400 kHz shown approximate three orders, they are: zero, first, and new generation of second order with the different in the value of Bragg angles.

Diffraction efficiency of a double-pass acousto-optic modulation system

espanolSe describe la caracterizacion de un sistema de modulacion acusto-optico y la optimizacion del set up para mejorar la eficiencia de la difraccion en configuraciones de paso simple y doble. En la configuracion de paso simple, el sistema consta de un modulador acusto-optico, un oscilador controlado por voltaje (V.C.O) y un amplificador de radiofrecuencia, en la cual, se caracterizo la eficiencia de la difraccion y la potencia optica del haz difractado en funcion de la radiofrecuencia aplicada. Adicionalmente, tomando como referencia la necesidad de corregir la variacion del angulo de difraccion que se puede tener cuando se modula en frecuencia el sistema en paso simple, se presenta su correccion por medio de la implementacion de la configuracion en paso doble. La configuracion de paso doble, consta de un VCO que controla la senal acustica entrante al modulador, un modulador el cual difracta la luz incidente y esta pasa por una lamina retardadora para evitar la retro reflexion del haz; despues usando un iris se deja pasar solo el orden 1 de difraccion luego se usa un espejo plano el cual direcciona el laser en la segunda pasada de este en el modulador. Una vez optimizado el sistema en paso doble se procedio a obtener la curva de eficiencia de difraccion y potencia en funcion de la frecuencia. Este trabajo se presenta como una herramienta actualizada para la caracterizacion e implementacion de un sistema de modulacion acusto-optico en configuracion de doble paso. EnglishWe described the characterization of an acousto-optic modulation system and the optimization of the set up to improve the efficiency of diffraction in single and double-pass configurations. In the singlepass configuration, the system consists of an acousto-optic modulator, a voltage-controlled oscillator (VCO) and a radio frequency amplifier, in which the diffraction efficiency and the optical power of the diffracted beam were characterized in the function of the applied radiofrequency. Additionally, taking as a reference the need to correct the variation of the diffraction angle that may occur when the system is modulated in frequency in a simple step, its correction is presented by means of the implementation of the configuration in double step. The double-pass configuration consists of a VCO that controls the incoming acoustic signal to the modulator, a modulator which diffracts the incident light and this passes through a retarder sheet to avoid the retroreflection of the beam; Then, using an iris, only order 1 of diffraction of the beam was allowed to pass and a plane mirror was used for working in the infrared which directs the laser in the second pass of it in the modulator. Once the double-pass system had been optimized, the diffraction efficiency curve was obtained. This work is presented as an updated guide for the implementation of an acousto-optic modulation system in a double-pass configuration.

Acousto-optic Design to Measure Glucose Level for Diabetic Patients Non-invasively

Due to increasing numbers of diabetic patient and the dangerous of life threatening some cases that need a continuous monitoring of the glucose level. Recently the demand for a non-invasive system is raised. This study aims to design an optimized noninvasively acousto-optic monitoring glucose system device to limit the possibility of secondary risk that raised from infection of invasive blood sample or from glucose fluctuation due to fewer number of glucose checking. There is a great demand for painless, glucose sensitive and commercial equipment. The current design methodology depends on the liaison between the penetrated electromagnetic wave through tissue and glucose level based on acousto-optic interaction technique. We can exceed the complication of acousto-optic design for biological tissue testing practically, the complication are with light and sound penetration, heat generation, and others. This work study both of Raman-Nath and Bragg interaction methods of acousto-optic technique with their advantages and disadvantages, with the possibility to reach the optimization in sensing blood glucose.

任意偏振光保偏的声光衍射效率增强系统的研究

任意偏振光保偏的声光衍射效率增强系统的研究

Calculation Model of Projectile Explosion Position by Using Acousto-Optic Combination Mechanism

In order to accurately calculate the projectile explosion position, this paper takes the five acoustic sensors as a basic array, and proposes a test method for the projectile explosion position based on acousto-optic combination detection of triangular basic array and form acousto-optic combination test system. Combining with the spatial layout of triangular basic array, we derive the calculation model of projectile explosion position parameters of each basic array; use the wavelet transform analysis method to filter the acoustic sensor signal, and utilize the cross-correlation function to establish the time delay estimation processing model of the projectile explosion acoustic signal in the same basic array and obtain the time difference of each sensor in the basic array. According to the basic array acoustic sensor collected signal in experiments, we analyze the distribution characteristics of acoustic signal strength generated by different projectile explosion, and calculate the projectile explosion position. By comparing with the height parameter data collected and processed by high-speed camera, the results show that the measurement accuracy of the proposed method is better than 0.6m in the range of 150m $\times150\text{m}$ , which verify the efficiency of the measurement method of projectile explosion position by using acousto-optic combination test mechanism.

Acousto-optic imaging using focused and plane wave ultrasound pulses

Acousto-optic imaging exploits the effects of modulation of light by acoustic waves propagating in an optically scattering medium to determine its optical properties. The imaging resolution is determined by the acoustic pressure field distribution inside the sample. In the ideal case, this distribution should be limited to a relatively small, strictly defined volume within which the light modulation occurs. Practical applications of this technique impose specific requirements on transducers configuration which constitute additional limitations on shaping the acoustic pressure field characteristics. We investigate the possibilities of improving performance of an acousto-optic imaging system utilizing a linear ultrasound array by comparing results obtained using plane wave and focused pulses and different apodization patterns. Acoustic pressure field distributions were determined numerically and with hydrophone measurements. We introduce an ultrasound focus quality coefficient in order to describe and compare the confinement of the expected light modulation volume. Acousto-optic images were obtained experimentally by measuring contrast decrease of the interference patterns of a laser light transmitted through samples and recorded by a camera. The results show that for focused pulses the off-focal pressure field components have significant influence on the determined values, and that this issue can be mitigated by using plane wave imaging.

Acousto-optic modulation in lithium niobate on sapphire

We demonstrate the first acousto-optic modulators in lithium niobate films on sapphire, detailing the dependence of the piezoelectric and optomechanical coupling coefficients on the crystal orientation. This platform supports highly confined, strongly piezoelectric mechanical waves without suspensions, making it a promising candidate for broadband and efficient integrated acousto-optic devices, circuits, and systems.

Issues of constructing scanning hybrid 3D measuring heads for high-precision contact and non-contact coordinate measurements of product dimension

The article presents a model of mechanical contact of a spherical tip and a product with small forces according to elastic deformations (further – deformations) taking into account the appearance of material deformations in the gap between them along the perimeter of the contact zone in the form of so-called piles-up. Dependences are obtained that link the gap with the deformation and the piles-up size. A graph is constructed for these parameters, the general form of which is close to the function of a single jump ∼1(l-Rpile), where Rpile is the radius of the pile-up.The developed design and operating principle of the scanning hybrid fiber-optical measuring head (FOMH) based on the use of a small-sized spatial light modulator in the form of a fiber-optic piezoscanner with the formation of scanning movements of the laser beam and the measurement of gaps between the tip and the product are described. The possibilities of providing high-precision measurements of laser beam deflection angles during scanning movements by using acousto-optic heterodyne interference measurement systems are considered.

Multiple-band frequency locking in an acousto-optic system with optoelectronic feedback

In this paper, we introduce and analyze both experimentally and theoretically multiple-band frequency locking, which becomes possible in an acousto-optic (AO) system with optoelectronic feedback. This effect is observed in a system combining a collinear AO cell and positive electronic feedback. The feedback signal is formed with the optical heterodyning effect, which occurs at the AO cell output and takes place in the special regime of collinear AO diffraction. It is shown for the first time, to the best of our knowledge, that frequency locking is possible in this system when connecting an external RF generator not only in one band near the self-oscillation frequency, but in several bands. The existence of as many as nine frequency-locking bands is predicted. The number of frequency-locking bands and their widths depend on the feedback gain and RF generator signal magnitude.

Development of an acousto-optic system for hyperspectral image segmentation

Development of an acousto-optic system for hyperspectral image segmentation