Acousto-optic Effect Research Articles

Frequency tuning of a squeezed vacuum state using interferometric enhanced acousto-optic effect

Quantum frequency conversion is one of the important tools for quantum information processing. So far, the frequency conversion of continuous variable quantum state in radio frequency range has not been demonstrated yet. Here, we experimentally demonstrate the optical frequency fine tuning of a squeezed vacuum state by using an acousto-optic modulator based bi-frequency interferometer. The systematic efficiency of the frequency tuning device is 91%, which is only confined by the optical transmission efficiency of the acousto-optic modulators. The amount of frequency tuning is 80 MHz, which is orders of magnitude larger than the line-width of the laser used to generate the squeezed state and can, in principle, be further extended. A squeezed vacuum state with −3.47 ± 0.02 dB squeezing level is sent to the frequency tuning device, and a squeezing level of −1.98 ± 0.02 dB is directly measured by a fiber coupled homodyne detector after the frequency tuning. Our scheme can also be applied to a variety of other quantum optical states as well and will serve as a handy tool for quantum networks.

Optical interferometry based acoustic field characterization using physics informed neural networks

The acousto-optic effect offers a non-contact way of measuring and visualizing acoustic fields in transparent fluids. Acoustic density fluctuations induce changes in the media's refractive index that can be measured using interferometry. While sensing methods based on acousto-optics have gathered increasing attention, many of such methods are only sensitive to projections of the acoustic field along the optical path, limiting the fields that can be characterized to one or two dimensions, or requiring complex experimental setups. Recently, reconstruction methods that abide by the physics of acoustic wave propagation showed unparalleled performance compared with classical reconstruction methods, reducing the sampling requirements and enabling to characterize three-dimensional acoustic fields. Nonetheless, such reconstruction methods rely on discrete approximations which might be poor at describing spatially complex fields. In this work we use physics-informed neural networks (PINNs) to estimate the acoustic pressure over space from interferometer measurements. The network is flexible enough to represent complex acoustic fields, while its output is constrained to fulfill the wave equation. Once trained on the data available for a given experiment, the PINN can estimate the acoustic pressure at arbitrary positions. The approach is tested in an experimental study, showing an improved performance compared with state-of-the-art reconstruction methods.

Simultaneous underwater beam steering and PAM4 transmission enabled by the acousto-optic effect

Simultaneous underwater beam steering and PAM4 transmission enabled by the acousto-optic effect

STAR-FDTD: space-time modulated acousto-optic guidestar in disordered media

Abstract We developed a 2D Finite-difference time-domain (FDTD) method for modeling a space-time modulated guidestar targeting wavefront shaping applications in disordered media. Space-time modulation in general (a particular example being the acousto-optic effect) is used here as a guidestar for the transverse confinement of light around the tagged region surrounded by disorder. Together with the guidestar, the iterative optical phase conjugation (IOPC) method is used to overcome the diffusion of light due to multiple scattering. A phase sensitive lock-in detection technique is utilized to estimate the steady-state amplitude and phase of the modulated wavefronts emerging from the guidestar region continuously operating in the Raman-Nath regime. As the IOPC scheme naturally converges to the maximally transmitting eigenchannel profile, one could use the position of the guidestar within the disorder to channelize the maximal transmission through the tagged region. The associated code developed in MATLAB® is provided as an open source (The MIT License) package. The code package is referred by the acronym STAR-FDTD where STAR stands for Space-Time modulated Acousto-optic guidestaR.

Evaluation of the Acousto-Optic Figure of Merit and the Maximum Value of the Elasto-Optic Constant of Liquids.

The elasto-optic properties of liquids on the basis of the first principles of acousto-optics were theoretically investigated. A relationship for calculating the elasto-optic constant of liquids using only the refractive index was obtained. The refractive index values corresponding to the maximum elasto-optic constant for polar and nonpolar liquids were determined. Calculations for about 100 liquids were performed and compared with known experimental data. This study significantly extends our understanding of the acousto-optic effect and has practical applications for predicting the elasto-optic constant of a liquid and estimating its wavelength dispersion.

Polymer-dispersed liquid-crystal coatings for ultrasound visualization: Experiment and theory.

Polymer dispersed liquid crystal (PDLC) films are formed of droplets of liquid crystal (LC) held in a polymer matrix. Similar to aligned LC films, PDLCs exhibit the acousto-optic (AO) effect when excited by acoustic waves of sufficient amplitude, whereby the PDLC film becomes transparent in the excited regions (acoustic clearing). Despite decades of research there is still debate over the mechanisms of the AO effect for the case of LC films, with several competing theories, and AO effects in PDLC have not been studied theoretically. This paper explores the AO effect in PDLC both experimentally and theoretically, and attempts a theoretical description of the observed phenomena based on the theoretical approach by Selinger etal. for aligned LC films. The acousto-optic effect in PDLC is shown to be due to direct interaction of acoustic waves with LC droplets, rather than due to compression of the droplet itself. Polarizing microscopy revealed changes in droplet shape at excited points. This is consistent with reorientation as a contributing factor, possibly coexisting with flows at higher excitation powers. In previous experimental studies PDLC films were prepared with cover slides, in the same way as LC AO cells, significantly limiting applications by adding complexity to the design. Also, to exhibit AO clearing it was considered that the PDLC needed to be prepared with high LC concentrations (over 75% by weight). We demonstrate that no cover slide is necessary, and that PDLC coatings without a cover have improved sensitivity to acoustic waves. We demonstrate the AO effect for LC concentrations as low as 40% by weight. The ability to use standard composition PDLC, with no top cover, is paving the way to paint-on visual ultrasound sensors.

Lithium niobate on insulator – fundamental opto-electronic properties and photonic device prospects

Abstract Lithium niobate on insulator (LNOI) combines a variety of optoelectronic properties and can meet practical performance requirements that are uncommon in optoelectronic materials. This review introduces the fundamentals and the photonic device concepts that arise from the LNOI materials platform. Firstly, the nonlinear optical response of LNOI is presented, including birefringent phase matching (BPM), modal phase matching (MPM), and quasi-phase matching (QPM). The tunable properties are also introduced, including electro-optical (EO), thermo-optical (TO), and acousto-optical (AO) effects. The structures of nonlinear optical devices, such as ridge waveguides (including periodically polarized inversion waveguides), Mach–Zehnder interferometer (MZI) modulators and micro-resonators (such as disks and rings) are demonstrated. Finally, the future of LNOI devices is discussed. In the already mature and developed optoelectronic material systems, it is rare to find one particular material system supporting so many basic optical components, photonic devices and optoelectronic devices as LNOI does in the field of integrated photonic chips.

Laser Doppler Vibrometer measurements of the 3D pressure field for the estimation of the radiation force produced by an acoustic standing-wave levitator

Acoustic levitation devices use powerful ultrasonic standing waves to levitate objects in mid-air. We have created a system and method to measure the full harmonic content of the acoustic field accurately. Our study revealed that levitated particles alter the pressure field in a way that is not immediately apparent from the first harmonic alone, highlighting the importance of precise and non-invasive measurement techniques. Our method uses computational tomography and optical sensing with the acousto-optic effect and a 3 DOF mechanical scanner. Our experiment results in a detailed 3D pressure distribution map for each harmonic of the ultrasonic acoustic field that generates the levitation forces.

Correlations between the optical phase modulation and the optical frequency and phase shifts in ultrasound-modulated optical tomography

In ultrasound-modulated optical tomography, ultrasound causes the phase of incident light to vary periodically with ultrasound. The periodic variation in phase is known as phase modulation. The phase modulation causes the modulated light intensity to vary periodically with the ultrasound, which is called ultrasonic modulation of light. As is well known, incident light is shifted in frequency and phase by ultrasound in acousto-optic effect, and the tomography is based on the effect. However, the correlations between the phase modulation and the frequency and phase shifts in the ultrasonic modulation of light have been ignored. In this paper, the correlations are investigated theoretically and experimentally in detail. Studies reveal that the modulated light is phase-modulated by the frequency and phase shifts, and the frequency shift is the fundamental cause for the ultrasonic modulation of light. Studies show that the frequency shift, rather than the phase shift, causes the modulated light intensity to vary periodically with the ultrasound. Additionally, the modulated light intensity signal is composed of cosine signals with frequencies Ω, 2Ω, 3Ω, etc, and the amplitude of the cosine signals depends on the amplitude of the phase modulation. Then, the modulated light intensity signal contains relatively more cosine signals with high frequency as the amplitude of the phase modulation increases. At last, for the ultrasound with lower power, the amplitude ratio of cosine signals with frequencies of 2Ω and Ω increases as the scattering coefficient of turbid media increases. Studies find that both the frequency-shifted light and the amplitude ratio can be used to image turbid media.

Self-Mixing Interferometer for Acoustic Measurements through Vibrometric Calibration.

The Self-Mixing Interformeter (SMI) is a self-aligned optical interferometer which has been used for acoustic wave sensing in air through the acousto-optic effect. This paper presents how to use a SMI for the measurement of Sound Pressure Level (SPL) in acoustic waveguides. To achieve this, the SMI is first calibrated in situ as a vibrometer. The optical feedback parameters C and α in the strong feedback regime (C≥4.6) are estimated from the SMI vibrometric signals and by the solving of non-linear equations governing the SMI behaviour. The calibration method is validated on synthetic SMI signals simulated from SMI governing equations for C ranging from 5 to 20 and α ranging from 4 to 10. Knowing C and α, the SMI is then used as an acoustic pressure sensor. The SPLs obtained using the SMI are compared with a reference microphone, and a maximal deviation of 2.2 dB is obtained for plane waves of amplitudes ranging from 20 to 860 Pa and frequencies from 614 to 17,900 Hz. The SPL measurements are carried out for C values ranging from 7.1 to 21.5.

Acousto-optic sensing: A scattering interpretation

Acousto-optic sensing consists in using (laser) light as the sensing element in order to measure, visualise and study acoustic phenomena in a remote, non-invasive manner. One of the most common sensing techniques involves measuring acoustically-induced phase shifts of an optical probing beam by means of interferometry. Arguably, the main fundamental limitation of such sensing technique is that it provides projections of the acoustic field, instead of acoustic quantities at specific locations. In this study we examine the theory of spontaneous light scattering in transparent media, and use this framework to formulate a general acousto-optic sensing problem. Preliminary results based on numerical simulations indicate that light scattering could be applied to the measurement of acoustic pressure fluctuations. Some of the main challenges associated with the principle—mainly related to the weaknesses of the acousto-optic effect in air and relatively low signal-to-noise ratio—as well as the main fundamental differences from conventional interferometry techniques are discussed in this study.

Characterization of flexural acoustic waves in optical fibers using a fiber-tip interferometer

An experimental study using a fiber-tip interferometer (FTI) to characterize traveling flexural acoustic waves (TFAWs) along an optical fiber is reported. The measurements carried out with the FTI are performed following two different procedures: one of them relies on adjusting the interferometer at the quadrature condition and the other extracts the information from the amplitudes of the fundamental and second harmonic of the interference signal. From our measurements, the detection limit of the FTI is 0.5 nm and the upper limit of the linear regime is 30 nm. These results validate the use of the FTI to detect nanometric displacements associated to the amplitude of acoustic waves along an optical fiber. Parameters such as the acoustic wavelength, attenuation coefficient, and phase velocity are measured for a range of acoustic frequencies around the 2 MHz region. Furthermore, and supported by the in-fiber acousto-optic (AO) effect produced by TFAWs, parameters associated to an acoustic wave packet such as the group velocity and the group attenuation coefficient are also determined. This set of experimental results provide useful information of the mechanisms underlying the propagation of TFAWs along an optical fiber and its corresponding AO effect.

Acousto- and acousto-optic effects in liquid crystals: An overview

An overview of the following three aspects of the acoustical and related optical behavior of liquid crystals, namely i) ultrasonic studies, ii) acousto-optical effects, and iii) surface wave induced optical effects have been discussed. The temperature dependent ultrasound velocity has been used for the evaluation of the adiabatic compressibility (kS) and the acoustic impedance (Z). A correlation between thermodynamic functions and thermo-elastic properties facilitated the evaluation of the specific heat at constant volume (CV), the ratio of specific heats (g) and the isothermal compressibility (kT) across liquid crystal-isotropic phase transition. Acousto-optical effect in liquid crystals has been described in terms of molecular reorientation related to flows and turbulences due to acoustic vibration and radiation pressure in the medium. One important aspect of the acousto-optical effects is the surface wave induced optical effects. The change in transparency of a normal layer of liquid crystal under crossed polarizers are discussed which is interpreted as a consequence of the rotation of the optic axis. In addition, the acoustic emission occurring from homeotropically-aligned liquid crystals irradiated by surface acoustic waves are also discussed.

ACOUSTO-OPTICAL RECEIVER OF AN OBSTRUCTION PASSIVE RADAR SYSTEM

The subject of research in the article is the passive radar system of a warship. The purpose of the work was to review the characteristics use of the acousto-optical receiver in the new passive radar system of the warship, to investigate the peculiarities of acoustooptic effect and the relevant synthesis of methods and tools for measuring the photodetector photoelectric characteristics and, in addition, to investigate the energy-and-geometric parameters of laser radiation Justification. It is shown that the transition, impulse and frequency characteristics are taken as the main means to determine the operating and technical parameters of the acousto-optical delay line. It is not possible to unambiguously extrapolate these characteristics to the known models of the characteristics of the acousto-optic radar receiver created on AODL. Research results. In the context of this postulate, mathematical models of the main characteristics of AODL were developed. On the basis of the synchronous compensation pulse obstacles applied to the passive radar acousto-optic receiver on military ships, the full compensation of the obstacles is determined for the effective reception of signals from the acousto-optic receiver. In radar stations (radar), the main attention is focused on the statistical properties of the useful signal and passive obstacles, the speed (frequency) of the signal passing through the passive obstacle and the space-time differences. The recommendations. These features are recommended to be used only in special cases where the target is outside the reflectors for informational duration, amplitude and differences between passive obstacles, obstacle silencing and signal separation. Conclusion. Applying the full attenuation of the band filter and synphase barrier organizers, whose frequency characteristics do not depend on the tuning frequency, it is possible to provide full compensation of obstacles during the effective reception of signals by the acousto-optic receiver in the passive radar system of warships based on the proposed method for high resistance to obstacles, pulse obstacle compensation.

Laser beam array spot steering customized trajectories using the acousto-optic effect.

We demonstrate a proof of principle of a technique for array laser beam steering according to a generalized elliptical path, using the acousto-optic effect. We explore the dynamic trajectories of the diffraction orders of a Gaussian beam, diffracted by a dynamic 2D sinusoidal phase grating. The latter is generated by two crossed acoustic waves propagating in a transparent medium, giving rise to 2D dynamic sinusoidal refractive index variation. We particularly emphasize the case where the two crossed acoustic waves are modulated in frequency and have a phase difference. In such case, the resulting diffraction orders are dynamic and follow some particular trajectory's shapes, from linear and circular to generalized elliptical shapes. Inspired by Poincaré and Bloch spheres used to represent polarization and quantum states, we suggest the sphere volume trajectory shape to represent all trajectories' shapes of all diffraction orders.

Microfiber evanescent-field photothermal gas detection using acoustic-induced mode-dependent frequency shift

Abstract In this study, we experimentally showcase the microfiber evanescent-field photothermal gas detection by exploiting all-fiber MHz-level frequency shift scheme. Based on the acousto-optic interaction effect, the low-frequency shifts of 0.9 MHz and 1.83 MHz can be obtained through the cyclic conversion between the transverse core modes LP01 and LP11 in the few-mode fiber. Our proposed all-fiber frequency shifters show flexible MHz-level up(down) frequency shifts with superior sideband rejection ratio (over 40 dB) and low insertion loss (less than 1 dB). Furthermore, an all-fiber heterodyne interferometric detection system is implemented by leveraging the above low-frequency shifters, in which around 1-μm-diameter microfiber is investigated for photothermal gas detection. A pump-probe configuration is employed to obtain the photothermal effect induced by the gas absorption of the modulated evanescent field. By demodulating the phase of the beat signal output by the interferometer, an equivalent detection limit (1σ) of 32 ppm and a response time of 22 s are achieved for ammonia, as well as 0.24 % instability within 48 pump cycles. Given its compact all-fiber configuration and high sensitivity with fast response, the experimental results can pave the way for widespread applications like heterodyne detection, fiber optical sensors, and interplanetary coherent communications.

POSSIBILITIES OF USING OPTICAL RADIATION DIFFRACTION MANAGEMENT METHODS ON REFLECTIVE COATINGS OF ARMAMENT AND MILITARY EQUIPMENT FOR ITS PROTECTION AGAINST AMMUNITION WITH SEMI-ACTIVE LASER GUIDANCE SYSTEMS

The article substantiates the need to improve the existent methods of combat defense and combat equipment (DAM) against bombs (guided combat munitions from UAVs, stray combat munitions, etc.)with semi-active laser targeting systems (LSA) on the basis of controlled reflective coatings. Methods of management the diffraction of optical radiation on reflecting coatings are based on applications in coating materials. At the same time, the reflecting properties can be purposefully changed by applying acousto-optical, electro-optical and thermos-optical effects. The acousto-optic method of diffraction control involves the spatial modulation of the beating coefficient in the medium, which is carried out by ultrasonic (acoustic) waves. During the distribution of ultrasound in the reflective coverage (areas of compression and discharge of the material of the waves distribution) appears in the reflective coverage. A purposeful change of descriptions of the acoustic wave leads to the possibility of forming the reflecting phase grating with a given parameter on which it will diffract a radiation. The electro-optical method of management the diffraction of laser radiation is based on the phenomenon of induced anisotropy of media under the influence of a field (electro-optical effect). However, the creation of reflective diffractive elements (coatings)using the electro-optical effect is limited by a number of disadvantages of this method. The thermo-optical method of management light diffraction consists in changing the optical constants of reflective coatings under the influence of temperature. On the basis of the multilayer interference systems (MLIS) with tapes, peak and phase diffraction gratings can be implemented. The use of MLIS coatings with ribbons in the display allows you to implement the functions of selecting and unlocking coatings in the infrared range. The last two methods are of the greatest practical interest since, unlike, the electron-beam method they allow heating a fairly large surface area of the coating. The implementation of diffraction control of optical radiation on the reflective coatings of DAM samples will allow to remove the ammunition control system with semi-active LSA from the working state as a result of the aiming point fluctuation.

Thin-film lithium niobate photonic integrated devices: Advances and oppotunities

<sec>Lithium niobate, known as one of the most widely used nonlinear optical crystals, has recently received significant attention from both academia and industrial circles. The surge in interest can be attributed to the commercial availability of thin-film lithium niobate (TFLN) wafers and the rapid advancements in nanofabrication techniques. A milestone was achieved in 2020 with the successful fabrication of wafer-scale TFLN photonic integrated circuits, which paved the way for mass-producible and cost-effective manufacturing of TFLN-based products.</sec><sec>At present, the majority of research on TFLN photonic integrated devices focuses on light manipulation, i.e. field modulation and frequency conversion. The electro-optic, acousto-optic, photo-elastic and piezo-electric effects of lithium niobate are harnessed to modulate the amplitude, phase and frequency of light. The second-order and third-order nonlinearities of lithium niobate enable frequency conversion processes, which leads to the development of frequency converters, optical frequency combs, and supercontinuum generation devices. These exceptional optical properties of lithium niobate enable the electromagnetic wave to manipulate covering from radio-frequency to terahertz, infrared, and visible bands. Using the outstanding performance of TFLN photonic integrated devices, including remarkable modulation rate, wide operation bandwidth, efficient nonlinear frequency conversion, and low power consumption, diverse applications, such as spanning optical information processing, laser ranging, optical frequency combs, microwave optics, precision measurement, quantum optics, and quantum computing, are demonstrated.</sec><sec>Additionally, it is reported that TFLN-based lasers and amplifiers have made remarkable progress, and both optical and electrical pumps are available. These achievements include combining gain materials, such as rare-earth ions or heterostructures, with III-V semiconductors. The integration of low-dimensional materials or absorptive metals with TFLN can also realize TFLN-based detectors. These significant developments expand the potential applications of TFLN photonic integrated devices, thus paving the way for monolithic TFLN chips.</sec><sec>The versatility and high performances of TFLN photonic integrated devices have made revolutionary progress in these fields, opening up new possibilities for cutting-edge technologies and their practical implementations. In this point of view, we briefly introduce the development of TFLN nanofabricationn technology. Subsequently, we review the latest progress of TFLN photonic integrated devices, including lasers, functional nonlinear optical devices, and detectors. Finally, we discuss the future development directions and potential ways of TFLN photonics.</sec>

Direct Underwater Sound Velocity Measurement Based on the Acousto-Optic Self-Interference Effect between the Chirp Signal and the Optical Frequency Comb

Underwater sound speed plays a vital role in maritime safety. Based on the acousto-optic self-interference effect, we proposed a new method to measure underwater sound speed utilizing Raman–Nath diffraction, generated by the acousto-optic effect between an optical frequency comb and pulsed chirp signal. When the pulsed chirp travels between the measurement and reference arm in the experimental setup that we constructed, the same signal resulting from acousto-optic self-interference is produced. The time gap between the two identical signals represents the time interval. Thus, we can determine the time-of-flight using cross-correlation. The optical path difference between the two arms is double the flight distance of ultrasonic waves and can easily be obtained using femtosecond laser interferometry. The time gap and the distance can be used to measure sound speed. The experimental results show that the chirp signal improves the signal-to-noise ratio and expands the applicable time-of-flight algorithm. The waveform pulse width after cross-correlation is 1.5 μs, compared with 40 μs before. The time-of-flight uncertainty can achieve 1.03 ns compared to 8.6 ns before. Uncertainty of sound velocity can achieve 0.026 m/s.

Analysis of Acousto-Optic Figure of Merit in KGW and KYW Crystals.

Monoclinic potassium rare-earth crystals are known as efficient materials for solid-state lasers and acousto-optic modulators. A number of specific configurations for acousto-optic devices based on those crystals have recently been proposed, but the acousto-optic effect of those crystals has only been analyzed fragmentarily for some interaction directions. In this work, we numerically searched for the global maxima of an acousto-optic figure of merit for isotropic diffraction in KGd(WO4)2 and KY(WO4)2 crystals. It was demonstrated that the global maxima of the acousto-optic figure of merit in those crystals occur in the slow optical mode propagating along the crystal's twofold symmetry axis and in the acoustic wave propagating orthogonally, both for quasi-longitudinal and quasi-shear acoustic modes. The proposed calculation method can be readily used for the optimization of the acousto-optic interaction geometry in crystals with arbitrary symmetry.