Collinear Acousto-optic Interaction Research Articles

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.

Optimum Length of Collinear Acousto-Optic Interaction in an Absorbing Medium

The regimes of forward and backward collinear acousto-optic diffraction are studied. The optimum length of acousto-optic interaction when the maximum intensity of diffracted radiation is achieved is calculated. The dependences of the optimum length and the maximum intensity of diffracted radiation on the attenuation of sound and absorption of light in an absorbing medium are obtained.

Backward Collinear Acousto-Optic Interaction in KRS-5 Crystal and Its Nonreciprocal Effect

Backward collinear acousto-optic interaction (i.e., the Bragg reflection of an electromagnetic wave from an ultrasound wave in KRS-5 crystal) is considered. The main parameters of interaction are shown to depend on the wavelength of electromagnetic radiation. Particular attention is given to acoustic-optic nonreciprocal effects. The optimum spectral ranges for the application of backward collinear interaction are determined.

Investigation of acoustic beam reflection influence on the collinear acousto-optic interaction characteristics

Significant part of acousto-optic devices apply the acoustic beam reflection to arouse the desired type of acoustic mode propagating along the required direction in crystal. The influence of acoustic beam reflection process on the ultrasound field structure in the acousto-optic cell and the collinear acousto-optic diffraction characteristics is examined in this paper. The investigation is carried on the example of the collinear acousto-optic filter fabricated on the base of calcium molybdate crystal. It is shown that the reflection process changes the acoustic field structure and affects the acousto-optic filter transmission function shape and diffraction efficiency.

Effect of feedback loop on the resolution of acousto-optic spectrometer

An acousto-optic spectrometer based on a collinear acousto-optic cell with feedback loop has been theoretically and experimentally investigated. It is shown that the introduction of optoelectronic feedback affects to a great extent the characteristics of collinear acousto-optic interaction and makes it possible to increase significantly the accuracy of determining the wavelength of incident optical signal.

Backward Collinear Acousto-optic Interaction in Germanium Crystal in Terahertz Spectral Range

The purpose of this research was to find a way and to observe the so-called “backward” collinear acousto-optic (AO) interaction in case of bulk optic and acoustic waves. We found that single crystal germanium is so far one of the best materials to observe the backward interaction in the terahertz (THz) range. This type of diffraction takes place when wave vectors of electromagnetic and acoustic waves are collinear while the diffracted and incident electromagnetic waves propagate in opposite directions. A theoretical analysis of the bulk AO interaction is presented. The model takes into account attenuation of acoustic and electromagnetic waves in the medium. Results of our calculations were used to develop a prototype of a tunable collinear AO filter based on germanium.

Transmission function of collinear acousto-optical interaction occurred by acoustic waves of finite amplitude

New physical aspects of collinear acousto-optical interaction, occurred by acoustic waves of finite amplitude, are revealed and analyzed in crystalline materials exhibiting moderate linear acoustic losses. The analysis is performed in the regime of continuous traveling waves allowing a specific mechanism of the acousto-optic nonlinearity. Our consideration has shown that such nonlinearity together with linear acoustic losses is able to affect the transmission function inherent in collinear interaction. In particular, the mere presence of linear acoustic losses by themselves leads to broadening the width of the transmission function beginning already from very low levels of the applied acoustic power. Moreover, the transmission function exhibits a marked and quasi-periodical dependence on the applied acoustic power density, and that periodicity is governed by the linear acoustic losses. As a result, the transmission function can be significantly narrowed near isolated points at the cost of decreasing the interaction efficiency. These novelties related to collinear acousto-optical interaction accompanied by moderate linear acoustic losses have been studied and confirmed experimentally with an advanced acousto-optical cell based on calcium molybdate (CaMoO4) single crystal and controlled by acoustic waves of finite amplitude.

The nonreciprocal effect under low- and high-frequency collinear acousto-optic interactions

The nonreciprocal effect under collinear acousto-optic interaction in the low- and high-frequency regimes is studied theoretically. The magnitudes of nonreciprocity determined from the ultrasonic frequency and from the wavelength of light are shown to be quantitatively identical. An expression that governs the magnitude of the nonreciprocity and that is valid for both low- and high-frequency regimes of the collinear acousto-optic interaction is obtained. The shape and width of the frequency characteristic of the collinear acousto-optic interaction calculated in the low diffraction efficiency approximation are shown to be the same in the low- and high-frequency regimes. The dependence of the frequency bandwidth of the collinear acousto-optic interaction on the ultrasonic-wave attenuation and diffraction efficiency is obtained. The magnitude of the nonreciprocal effect in some of the crystals used in acousto-optics is estimated numerically. The nonreciprocity of the collinear interaction is shown to be substantially stronger in the high-frequency regime relative to the low-frequency regime. Sapphire is proved to be an optimal material for experimental realization of the nonreciprocal effect in the high-frequency regime.

Polarization effects at collinear acousto-optic interaction

Collinear acousto-optic diffraction of an arbitrarily polarized optical radiation is studied theoretically and experimentally. It is shown that in the general case the diffracted light spectrum at the acousto-optic cell output consists of four components with different frequencies and polarizations. Beatings of these components lead to intensity modulation of the light passed through an output analyzer. Dependences of output intensity components on ultrasound frequency and acoustic power are examined for different orientations of the polarizer and the analyzer. Experimental investigations are carried out with a collinear acousto-optic cell fabricated with calcium molybdate single crystal.

Conditions for observation of the nonreciprocal effect in a collinear acoustooptic filter at various wavelenghts of light radiation

The features of the nonreciprocal effect observed during collinear acoustooptic interaction in a lithium niobate crystal are investigated theoretically and experimentally. It is shown that one of the main reasons that restrict the possibility of observation of the nonreciprocal effect in the crystal is damping of an acoustic wave. It is proved that, when an acoustooptic cell is illuminated with monochromatic light, the ultrasound damping increases the frequency band of the collinear acoustooptic interaction, a circumstance that affects the possibility of observation of the nonreciprocal effect in an acoustooptic experiment. The conclusion that the creation of acoustooptic filters having a high spectral resolution and operating at acoustic microwaves necessitates taking into account the nonreciprocal effect is drawn.

Collinear acousto-optic interaction in a single tellurium crystal

The problem of designing acousto-optic imaging filters based on tellurium crystal is discussed. The measurement and calculation results of acousto-optic properties of tellurium are presented. The collinear acousto-optic interaction in tellurium crystal is experimentally implemented for the first time at the light wavelength of 10.6 μm.

Collinear diffraction of divergent optical beams in acousto-optic crystals

Peculiarities of collinear acousto-optic interaction of a strongly divergent optical beam are examined theoretically by examples of two crystals widely used in acousto-optics: calcium molybdate (CaMoO(4)) and paratellurite (TeO(2)). These materials demonstrate essentially different diffraction characteristics because of peculiar features of optical and acousto-optic anisotropy in these crystals. The dependence of the integral diffraction efficiency and the transmission band of collinear acousto-optic filters on the optical beam divergence and acoustic power is studied. It is shown that with increasing light divergence these characteristics of the filter are worsened according to the same law, and the product of the relative bandwidth and the diffraction efficiency remains constant and independent of the optical wavelength and the acousto-optic interaction length.

Harmonic modulation of light by means of collinear acousto-optic interaction

The collinear anisotropic interaction of light with a standing acoustic wave generated in a lithium niobate crystal is discussed. Diffraction may be applied for harmonic modulation of laser light. The analysis of the light modulation is based on the concept of vector diagrams. A set of differential equations is derived to describe up to five interacting optic waves in the material. It is shown that solution of the equations by the method of successive approximations yields amplitudes of electric fields corresponding to diffracted and transmitted optical beams at the output of the crystal. Dependences of the amplitudes of the interacting waves on the acoustic frequency and length of the acousto-optic interaction are also discussed.

Nonreciprocity of acousto-optic interaction in collinear tunable acousto-optic filters

The investigation of a nonreciprocal effect for the example of collinear acousto-optic interaction is presented. It is shown that this effect influences the parameters of diffraction and the operation of modern acousto-optic devices, particularly acousto-optic tunable filters (AOTFs), at the frequencies of ultrasound of about 1 GHz and higher. The analytical expressions are obtained, and the calculations of the nonreciprocal effect for different acousto-optic materials are carried out. The effect is registered experimentally at the optic wavelengths of 633 and 532 with the help of a collinear AOTF on the base of a lithium niobate crystal.

Influence of nonreciprocal effect on the operation of a collinear acousto-optic filter

The nonreciprocal effect is studied theoretically and experimentally by the example of collinear acousto-optic interaction in a birefringent crystal. It is shown that this effect at ultrasonic frequencies ∼1 GHz and above considerably influences the parameters of modern acousto-optic devices, in particular, tunable acousto-optic filters. The nonreciprocal effect is estimated for different acousto-optic materials.

Efficiency of collinear acoustooptic interaction in an anisotropic medium

Collinear acoustooptic interaction in crystals with different values of birefringence is theoretically studied. The crystal medium is considered as a system of thin layers where the orientation of optical indicatrix varies from layer to layer due to the presence of an ultrasonic wave. For collinear diffraction in LiNbO3, α-SiO2, Te, CaMoO4, and Tl3AsSe3 crystals, expressions for the transmitted and diffracted intensities are obtained by means of acoustooptic methods and a new method based on the Jones calculus.

Design of tapered SAW waveguide for wavelength‐selective optical switches using weighted acoustooptic interaction

AbstractOptical wavelength‐selectivity in optical switches using waveguide‐type collinear acoustooptic interaction is studied from the viewpoint of sidelobe suppression. It is found that the sidelobe level can be reduced from −9.3 dB to −20 dB by weighting the coupling coefficient over the interaction region. A method to realize the sidelobe suppression by means of modifying the surface acoustic wave (SAW) waveguide is proposed and theoretically analyzed to design the SAW waveguide. A sidelobe suppression at −20 dB is realized with a SAW waveguide of a dense‐flint glass strip whose width and thickness are varied accordingly in the ranges of 700 to 26 µm, and 0.4 to 1.0 µm, respectively, on a Y‐X LiNbO3 substrate. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 154(1): 36–46, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20251

Scattering light by short acoustic pulses in a crystalline collinear cell and coherent processing of ultra-high frequency radio-wave electronic pulses

We present the study of collinear light scattering by relatively short acoustic pulses in birefringent crystals providing that both the acoustic attenuation and spreading the acoustic beam are allowed for. The exact and closed analytical model for the phenomenon described is developed. The peculiarities of collinear acousto-optical interaction in the cells made of lithium niobate single crystal are considered for the traveling-wave regime. The feasibility of applying such an effect to perform a coherent optical processing of ultra-high frequency (UHF) radio-wave electronic pulses is analyzed and the corresponding opto-electronic algorithm is elaborated. The results of preliminary experiments, exhibiting an opportunity for the data processing in anti-radar system, are presented.

Collinear Diffraction of a Divergent Light Beam by Ultrasound in a Paratellurite Crystal

The collinear acousto-optical interaction of a divergent light beam with ultrasound along the approximate [110] direction in a TeO2 paratellurite crystal is investigated theoretically and experimentally. The collinear diffraction is studied at an ultrasonic frequency f ≈ 149 MHz under exposure of the crystal to an uncollimated laser light beam at a wavelength λ = 633 nm and at an angle of divergence as large as 4°. It is shown that the collinear diffraction along the direction forbidden for acousto-optical interactions of plane waves occurs only under conditions where the light beam is uncollimated and the diffraction efficiency increases with an increase in the divergence of the light beam. It is proved that the attenuation of an acoustic wave brings about a decrease in the diffraction efficiency and an increase in the transmission bandwidth of the device used. A model of the collinear acousto-optical filter based on a paratellurite crystal with an interaction length l = 2.7 cm is analyzed. The collinear acousto-optical filter is characterized by a high resolving power (∼3000), a high diffraction efficiency (I1/I0 ≈ 0.8), and a large angular aperture (Δϕ ≈ 4°). This makes collinear diffraction promising for use in acousto-optical filters based on paratellurite crystals.

FDTD analysis of wavelength‐selective optical switch using collinear acoustooptic interaction for WDM routing

AbstractA waveguide‐type collinear acoustooptic device can work as a wavelength‐selective switch for wavelength division multiplexed (WDM) light. Therefore, its applications to WDM routing switching are expected. In this paper, in order to evaluate the wavelength‐selective switching characteristics of the device consisting of a directional coupled waveguide and a Y‐branch, simulation is carried out by the FDTD method. The results of the simulation are compared with those of the coupled mode theory, and agreement between them is confirmed. A method of propagating an optical pulse is studied in the segment‐divided region in order to analyze the acoustooptical coupling characteristics in a long scale interaction region. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 87(6): 18–27, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20064