Acousto-optic Interaction Research Articles

Acousto-optic spatial frequency filter operating in the intermediate region of acousto-optic interaction

The characteristics of an acousto-optic spatial frequency filter designed for processing of two-dimensional images and operation in the intermediate region of acousto-optic diffraction are investigated. The advantage of such filters over filters operating in a Bragg regime is the possibility of operation at significantly lower acoustic frequencies, which allows the passband of spatial frequencies to be increased and the limiting resolution to be decreased. Transfer functions of diffraction orders are obtained. The use of the first diffraction order is demonstrated to allow selection of the two-dimensional image contour. The two-dimensional image edge enhancement of the image transmitted by optical emission at a wavelength of 0.63×10−4cm is experimentally demonstrated using a TeO2 spatial filter operating at a frequency of 15 MHz.

ОПТОЭЛЕКТРОННЫЕ ПРИБОРЫ НА ОСНОВЕ ДИФРАКЦИОННЫХ РЕШЕТОК ОТ СТОЯЧИХ УПРУГИХ ВОЛН

Relevance Currently, optoelectronic devices based on diffraction gratings from standing elastic waves are widely used. This is due to the fact that such devices are small in size, allow realtime measurements and have high accuracy, speed and reliability. A review of foreign patents and scientific and technical literature shows that in Japan, the USA, Germany and other countries, intensive work has been carried out in recent years to create optoelectronic devices as part of information-measuring systems based on the use of diffraction gratings from standing elastic waves. Such work is also carried out in Russia. Today, optoelectronic devices are widely used in various fields of industry, medicine, ecology, etc. Aim of research It is necessary to investigate the prospects of research on the development of optoelectronic devices based on diffraction gratings from standing elastic waves. It is necessary to consider the physics of processes in the field of acousto-optic interactions. It is important to give the main characteristics and possible applications of optoelectronic devices based on diffraction gratings from standing elastic waves. Research objects Light and sound waves interacting with each other when they pass through the same medium, diffraction grating, optoelectronic device. Research methods Mathematical methods of calculation and analysis. Results The need for research in the field of optoelectronic devices based on diffraction gratings from standing elastic waves is formulated. It is shown that when passing through the same medium, light and sound waves interact with each other. Light is scattered on a sound wave, as on a diffraction grating. Recommendations for the design of optoelectronic devices based on diffraction gratings from standing elastic waves are proposed. Possible areas of application of optoelectronic devices based on diffraction gratings from standing elastic waves are considered. Keywords: acousto-optics, waves, modulator, diffraction grating, optoelectronic device

Thin-Film Lithium Niobate Based Acousto-Optic Modulation Working at Higher-Order TE1 Mode

Acousto-optic modulation (AOM) is regarded as an effective way to link multi-physical fields on-chip. We propose an on-chip AOM scheme based on the thin-film lithium niobate (TFLN) platform working at the higher-order TE1 mode, rather than the commonly used fundamental TE0 mode. Multi-physical field coupling analyses were carried out to obtain the refractive index change of the optical waveguide (>6.5×10−10 for a single phonon) induced by the enhanced acousto-optic interaction between the acoustic resonator mode and the multimode optical waveguide. By using a Mach-Zehnder interferometer (MZI) structure, the refractive index change is utilized to modulate the output spectrum of the MZI, thus achieving the AOM function. In the proposed AOM scheme, efficient mode conversion between the TE0 and TE1 mode is required in order to ensure that the AOM works at the higher-order TE1 mode in the MZI structure. Our results show that the half-wave-voltage-length product (VπL) is <0.01 V·cm, which is lower than that in some previous reports on AOM and electro-optic modulation (EOM) working at the fundamental TE0 mode (e.g., VπL > 0.04 V·cm for AOM, VπL > 1 V·cm for EOM). Finally, the proposed AOM has lower loss when compared with EOM because the electrode of the AOM can be placed far from the optical waveguide.

Modes of wide-aperture acousto-optic diffraction in a uniaxial birefringent crystal

Acousto-optic (AO) anisotropic interaction in uniaxial birefringent crystals is a widespread and versatile approach to tunable spectral filtration of light. Its principal constraints are limited values of spectral and angular bandwidth restricting the light transmission and imaging performance of AO filters. A way to overcome these drawbacks is simultaneous Bragg diffraction of two or more light beams. In this paper, we discuss and compare the main features of four available modes of anisotropic wide-aperture AO interactions in uniaxial birefringent crystals. We calculate the angular aperture, spectral resolution and other parameters and estimate the spectral image quality features related to each one. Theoretical consideration and computational modeling are carried out for tellurium dioxide (TeO2)—the main AO crystal. Derived results are important for the development of AO imaging devices, particularly multi-channel AO tunable filters.

Collinear acousto-optical filtration of polychromatic Bessel light beams in lithium niobate crystals

The features of collinear acousto - optical filtration of quasi - diffractive Bessel light beams of o- and e-type in uniaxial crystals are investigated. Using the method of overlap integrals, an expression is found for the diffraction efficiency depending on the parameters of the acousto-optical interaction, as well as on the values of the overlap integrals. It is shown that for the zero-order mode of a Bessel light beam for a lithium niobate crystal under conditions of transverse phase synchronism and in the optical spectrum range of 0.4-0.7 μm, the filter bandwidth of ∼0.2 nm is achievable; with an increase in the order of the mode m≥1, the increase in the bandwidth is insignificant and is ∼0.23 -0.24 nm.

Wide-angle acousto-optic devices based on isotropic light scattering in biaxial crystals

Using the example of a rhombic crystal of alpha-iodic acid, a detailed study of new variants of acousto-optic isotropic light scattering in oblique sections of biaxial crystals, whose refractive surface contains a concave portion, is carried out. For these cases, the frequency dependences of the Bragg angles and the ranges of acousto-optic interaction are calculated. The possibility of implementing a unique, simultaneously broadband and wide-angle variant of light scattering is established. It is shown that the two-dimensional transfer function of such acousto-optic geometry has a complex X-shaped structure that has no analogues among uniaxial crystals. The possibility of applying this diffraction regime in light beam spatial filtering devices is studied.

Dependence of the energy efficiency of the acousto-optic modulator of terahertz radiation on the dimensions of the ultrasound transducer

The paper presents results of experimental investigation of an acousto-optic modulator of terahertz radiation based on liquefied sulfur hexafluoride. It was found that the intensity of diffracted radiation at a fixed ultrasound power depends on the dimensions of the ultrasound transducer. The optimal size of the ultrasound transducer in the direction orthogonal to the plane of the acousto-optic interaction was determined, at which the maximum energy efficiency of the acousto-optic modulator was achieved.

Acousto-Optical Volumetric Sensing of Acoustic Fields

The characterization of sound fields over space is fundamental in acoustics. Yet, the volumetric acquisition of sound fields using conventional electromechanical transducers is challenging due to the high sampling requirements needed in a three-dimensional domain. In this study, we introduce an acousto-optic sensing method to remotely sample acoustic fields in a volume using a sparse set of noninvasive optical measurements. Optical methods that use light as a sensing element have drawn significant attention recently, since they allow for remote, noninvasive sampling of acoustic fields with fine spatial resolution. The practical deployment of optical sensing in acoustics, however, has been hindered by the limited acquisition of data available, and the unsuitability of existing methods to reconstruct sound fields in scarce-data regimes. The proposed methodology relies on projecting the measured data on a basis that satisfies the wave equation, thus alleviating the measurement requirements associated with traditional reconstruction methods. The proposed approach leads to accuracy improvements of 20 dB relative to current methods, and a 90% reduction of measured data. We demonstrate the approach experimentally by reconstructing in situ the three-dimensional sound field inside a room from remote measurements of the acousto-optic interaction. These results are key to advancing the use of acousto-optical sensing methods, which are currently limited to simplified domains. The work presented in this paper brings about the possibility to solve so far intractable problems, such as the volumetric and remote acquisition of complex three-dimensional acoustic fields.

Temperature Effects in an Acousto-Optic Modulator of Terahertz Radiation Based on Liquefied SF6 Gas.

The acousto-optic (AO) diffraction of terahertz (THz) radiation in liquefied sulfur hexafluoride (SF) was investigated in various temperature regimes. It was found that with the increase in the temperature from +10 to +23 C, the efficiency of the AO diffraction became one order higher at the same amplitude of the driving electrical signal. At the same time, the efficiency of the AO diffraction per 1 W of the sound power as well as the angular bandwidth of the efficient AO interaction were temperature independent within the measurement error. Increase of the resonant sound frequency with decreasing temperature and strong narrowing of the sound frequency bandwidth of the efficient AO interaction were detected.

Topological insulator in two synthetic dimensions based on an optomechanical resonator

Topological insulators (TIs) implemented in synthetic dimensions have recently emerged as an attractive platform to explore higher-dimensional topological phases in compact systems. Here, we present a two-dimensional TI within a single-ring resonator enabled by acousto-optic interactions and electro-optic modulation. In our system, the synthetic dimensions are represented by the range of discrete optical modes supported by the ring resonator and their azimuthal angular order. Gauge fields responsible for the topological order in the synthetic lattice are realized by an array of racetrack couplers coupled to the resonator. We reveal topological bulk and chiral edge bands in time-resolved absorption/transmission spectra, and we show that the proposed system can support reconfigurable and nonreciprocal frequency conversion controlled by the probe frequency detuning. Interestingly, we also show that realistic phase mismatch and disorder in acousto-optic scattering can enable an amorphous TI phase in synthetic space, demonstrating robust nonreciprocal frequency conversion in this regime.

Collinear acousto-optic interaction of optical and acoustic vector beams. Summation of the polarization orders of topological defects

We analyze backward collinear acousto-optic (AO) interactions of optical and acoustic vector beams in the centrosymmetric crystals with cubic symmetry. It is shown that the above interactions lead to appearance of diffracted elliptical vector optical beam, which can be transformed into cylindrical vector beam under certain conditions. A summing rule for the polarization orders of interacting beams is formulated. A number of important particular conclusions can be drawn from this general rule: (i) when the interacting optical and acoustic beams have the same modules but the opposite signs of polarization orders, the AO interaction of these beams gives rise to annihilation of topological defect in the diffracted beam, (ii) when, contrary to the incident optical beam, the acoustic beam represents a vector beam, the topological defect of polarization state is transferred from the acoustic beam to the diffracted optical beam in the course of AO diffraction, and (iii) when the incident optical beam is a circularly polarized defect-free beam and the acoustic beam contains a topological defect of polarization state, this defect is transformed into a topological defect of phase of the diffracted optical beam, creating an optical vortex in the course of AO diffraction.

Integrated acousto-optic interaction at ultrahigh frequencies

With the development of nanoscale transducers, surface acoustic wave (SAW) with frequencies above 10 GHz can now be excited on the optical waveguides. However, the fundamental mode is very difficult to be excited for SAW at ultrahigh frequencies. Moreover, as the wavelength of SAW is reduced to below the optical wavelength, the acoustic field across the optical waveguide can no longer be approximated as uniform but is spatially periodic. Here, we develop a discussion about integrated acousto-optic (AO) interaction at ultrahigh frequencies. The electromechanical coupling coefficients of different modes are evaluated for SAW at ultrahigh frequencies. The acousto-optic overlap is analyzed to evaluate integrated AO interaction for each given acoustic wavelength and optical waveguide size. An analytic model is presented for integrated AO interaction at ultrahigh frequencies. The research shows that it would be a trade-off for the design of an integrated AO device with ultrahigh frequencies.

Photon–phonon spin–orbit interaction in optical fibers

Spin–orbit interaction (SOI) is a striking physical phenomenon in which spin and orbital features of a particle or a wave field affect each other. Recently, there has been significant interest in the SOI of light as it accompanies a number of fundamental light–matter interaction processes, enabling intriguing applications. We demonstrate the spin-orbit coupling between photons and phonons, in contrast to recently reported studies dealing with a “single-field” SOI. We show that the spin angular momentum of phonons can be transformed into the orbital angular momentum of photons, and vice versa, during the fiber acousto-optic interaction. This results in the acoustic-spin-dependent, dynamically tunable generation of topologically charged optical vortex beams directly from a Gauss-like mode. This type of optical mode conversion can be useful in such vortex-based photonics applications as micromechanics, classical and quantum information technologies, and simulation of quantum computing. This particular example of a “two-field SOI” shows that the concept of spin-orbit coupling can be generalized to describe the interaction between elementary excitations of different physical nature. Our findings indicate that SOI-assisted effects might be found in physical systems with photon–phonon, magnon–phonon, electron–phonon, and other interactions, enabling tailored topologically charged multiparticle states in photonics, spintronics, plasmonics, etc.

Analysis of giant forward Brillouin gain enhancement in double-disk microcavities by tailoring optical forces

Stimulated Brillouin scattering in whispering gallery resonators has numerous potential applications. However, previously reported approaches are difficult to integrate and the Brillouin gain coefficient is small. We propose here a new approach to achieve giant forward stimulated Brillouin scattering (FSBS) and lasing on chip with double-disk microcavities made of silica glass. By considering the thickness of air gap to tailor optical forces especially radiation pressure in these double-disk microcavities, giant Brillouin gain enhancement can be realized in the intermode FSBS. The numerical simulation results indicate that for double-disk microcavity within the radius range of 50 μm, stimulated Brillouin scattering gain is ten times larger than that of single-disk microcavity up to 74.3 m−1W−1 with Rayleigh acoustic mode and 102 to 103 times larger up to 6361.19 m−1W−1 with symmetric Lamb acoustic mode. Correspondingly, the on-chip pump power threshold of Brillouin lasing can be reduced to 55 μW with the slope efficiency of 8.0%. Our proposed double-disk microcavities offer an effective and simple method to implement Brillouin lasing and can find versatile applications of acousto-optic interaction on all-integrated CMOS compatible chip.

Observation of Acoustic Charge Transport in GaN-Based Quantum Well Structures Under Surface Acoustic Wave Excitations.

Though the acoustoelectric and acoustooptic interactions have been widely studied on III-V semiconductors, most studies were conducted at low temperature to avoid the influence of lattice scattering. Here, we demonstrate larger-than-1-GHz optical oscillation and acoustic charge transport at room temperature from a nitride-based LED (light-emitting diode) by acoustic wave excitation. The optical oscillation is generated by the harmonics of acoustic waves, while the acoustic transport of carriers was observed from the LED light output at different acoustic excitation frequencies. Furthermore, with the change of bias voltage, the frequency response of light output varies correspondingly due to the thermal disturbance that affects the lattice vibration and acoustic wave propagation. The results also suggest that we are able to achieve a tunable optical resonant frequency by varying bias voltages without changing the LED structure.

Spatiospectral transformation of noncollimated light beams diffracted by ultrasound in birefringent crystals

Spatiospectral structure of wave phase matching in birefringent crystals has a strong dependence on the geometry of the acousto-optic interaction and incident light spectrum. This dependence defines details of light beam profile transformation. It is especially important for imaging applications related to a large angular aperture and a wide spectral bandwidth of the incident light. In this paper, we demonstrate accurate three-dimensional plotting of a light transmission pattern without small birefringence approximation. The rather complicated shape of the phase-matching locus in the spatiospectral domain inevitably leads to residual spatially nonuniform chromatic aberrations in the spectral image. Theoretical consideration and computational modeling are confirmed by the experiments on Bragg diffraction in paratellurite crystal. The results are especially important for the development of acousto-optical imaging devices and laser beam shaping technologies.

High-performance phoxonic cavity designs for enhanced acousto-optical interaction.

Effective confinement of light and sound is achieved through a one-dimensional phoxonic crystal (PxC) cavity. In particular, co-localization of gigahertz phonons and infrared photons in a cavity created by introducing a defect inside a multilayer PxC has been performed. The incident elastic waves can control the refractive index variation of the dual phononic-photonic cavity layer. We also studied the acousto-optic (AO) effect in four AO materials, each located in the cavity layer between two identical Bragg mirrors. The cavities are designed to have high-quality factors for both photon and phonon resonances, which are proportional to their lifetime and allow for a much stronger photon-phonon interaction. The AO effect causes a shift in the optical mode of the photonic band gap. The values of the refractive index of the AO cavities layer are estimated as a function of time based on the elastic strain perturbation using the relevant photo-elastic relations. The phoxonic band gaps and transmission spectra for both unperturbed and elastically perturbed PxC structures are derived depending on the transfer matrix method. In our results, the selected AO cavity of PbMoO4 provided the strongest AO coupling, in which the maximum wavelength shift of the resonant photonic modes reached 113.3 nm. In addition, 11.9 nm is the maximum displacement amplitude of the confinement elastic wave of the same nanocavity. The TeO2 cavity provided the highest Q values for both photonic and phononic modes of 7093 and 175, respectively. We think this research could open the way to study the properties of linear elastic materials to design extremely miniaturized AO devices.

Acousto-optic modulation of light polarisation in monoclinic crystals

A configuration of a laser polarisation modulator based on isotropic acousto-optic interaction is proposed. Polarisation control is performed by a 2D acousto-optic cell based on one monoclinic single crystal. A possibility of implementing this modulator on the basis of a KY(WO4)2 crystal is demonstrated.

Types of acousto-optic interactions between acoustic and circularly polarized optical waves:case of Pb5Ge3O11 crystals.

In the present work, we analyze acousto-optic (AO) interactions between acoustic waves (AW) and circularly polarized optical eigenwaves in gyrotropic crystals. We find that the AO diffraction of circularly polarized eigenwaves can be divided into six different interaction types. Contrary to the AO interactions analyzed earlier for the case of linearly polarized optical eigenwaves, we distinguish three isotropic interaction types and three anisotropic ones. Moreover, unlike the isotropic AO interactions of linearly polarized eigenwaves of no-no and ne-ne interaction types, the effective elasto-optic coefficient (EEC) in the case of interactions between circularly polarized eigenwaves does not depend on the sign of an incident circular optical wave. The anisotropy of the EEC and AO figure of merit is analyzed for a particular case of lead germanate crystals, Pb5Ge3O11. We demonstrate that the maximal AO figures of merit are achieved for type I isotropic diffraction at the quasi-longitudinal AW. Our calculations are confirmed by the experimental data obtained for the EEC using the Dixon-Cohen method. The experiment is concerned with the AO interactions of circular eigenwaves in Pb5Ge3O11.

Vertical Engineering for Large Brillouin Gain in Unreleased Silicon-Based Waveguides

Strong acousto-optic interaction in silicon-based waveguides generally requires releasing of the silicon core to avoid mechanical leakage into the underlying silica substrate. This complicates fabrication, limits thermalization, reduces the mechanical robustness and hinders large area optomechanical devices on a single chip. Here, we overcome this limitation by employing vertical photonic-phononic engineering. Specifically, the insertion of a thick silicon nitride layer between the silicon guiding core and the silica substrate contributes to reduce GHz-frequencies phonon leakage enabling large values of the Brillouin gain in an unreleased platform. We get values of the Brillouin gain around 300 (Wm)$^{-1}$ for different configurations, which could be further increased by operation at cryogenic temperatures. These values should enable to observe Brillouin-related phenomena in cm-scale waveguides or in more compact ring resonators. This finding could pave the way towards large-area unreleased cavity and waveguide optomechanics on silicon chips.