1 September 1991 Development of wideband 16-channel acousto-optical modulators on the LiNbO3 and TeO2 crystals
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The modern tendenci es i n the techni ques of acoustoopti c ( AO) data proceasing stinulate the technology development of the rnultichannel AO devices eleroental base, in the first turn nultichannel Bragg modulators' ' Z The demands made to them in the composition of the high-production signal and algebraic processors can be deVided into two groups. The demands of the large working band and the modulators high diffraction efficienty can be attributed to the first one. The realization of high indices on these parameters is based in the main on the technique achievements of the one channel AO modulators , progress i n worki ng out of whi ch i s defi ned by the successes in synthesizing of the new high effective AO materials, or achivernents in looking for the high effective cut-offs of the known crystals. The given criterion can be indicated by the value of AO quality coefficient M of the material for isotropic or anisotropic wide-band diffraction. Such important parameters as the admissible level of the interchannel coupling, the identity degree of the amplitude and phase-frequency channel characteri sti cs , quantity and densi ty of channel arrangement on the crystal can be attributed to the second group. The complex of these requl rements causes the more hard cri ten a i n selecting the material of the modulator sound wire and the AOl geometry, adding them by the physical parameters, playing the secondary role for one-channel modulators. To those in particular there have been attn buted the coeffi ci ents of the quadrati c acousti c ani sotropy showing the relative increasing or decreasing of the beam ( energetic) sound di vergence on compari son wi th the di ffracti on one. The value of these coefficients can greatly influence on the density of channel arangeroent in some cases. For example in widely used in acoustooptic mnodulators on TeO for slow shi fted waves near di recti on (11 0) the acoustic beam divergence forces in 50 times on comparison with the diffraction one. This circumstance limits essentially the use of the gi yen cut-off s TeO for building of the multichannel AO processor. In the given work we examine the main physical and technological aspects in the domain of development of wide-band multichannel microwave AO modulators of two different types: 1 - modulators on the crys— tal LiNJ on the base anisotropic AO interaction in YZ plane and the excitation of the acoustic waves on the crystal surface by the slotted transducer; 2 - isotropic modulators on the crystal TeO i-cut-ting with piezotransducer on the crystal LiNbO plates. The technology of the modulators with the surface excitation of the acoustic waves is more simple than the technology of the modulators with the plate or film transducer, but demands optimization of the interaction geometry with the joint calculation acoustooptical and piezoelectrical properties. the base of expression taking into account optical , acoustic and piezoelectrical anizotropy of the crystals by the numerical methods there have been analyzed the angular dependences of the AO quality coefficient M for isotropic and anisotropic geometries AO interaction in the crystal LiNW . There have been determined that the absolute maximum of the value M is achieved for the wide-band anisotropic light diffraction on the slow shifted waves of the IZ crystal plane. In the maximum M region the slow shifted waves possess the cross piezoactivity, moreover the coefficient of the electromechanical coupling L. for the given type of piezoactivity also reaches the absolute maxinum, that gives the possibility sufficiently effectively excite these waves on the crystal plane and develop simple from the technological point of view one channel and multi channel anisotropic microwave AO modulators. The analysis of the acoustooptical and acoustic anisotropy of the crystal TeO allows us to suppose that the most acceptable geometry of the AC interaction for building rnultichannel Bragg modulators correspond to the isotropic light diffraction on the longitudinal waves i n the di recti on ( 001 ) . This geometry is characteri zed by the peak anisotropy M relatively the acoustic wave deviation from the direction (001) in the sector 100 and by the small values of the quadratic acoustic anisotropy coefficients W.
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Lev Bokov, Anatoly Ja. Demidov, Anatoly S. Zadorin, Igor Kushnarev, Leonid J. Serebrennicov, Sergey N. Sharangovich, "Development of wideband 16-channel acousto-optical modulators on the LiNbO3 and TeO2 crystals", Proc. SPIE 1505, Optics for Computers: Architectures and Technologies, (1 September 1991); doi: 10.1117/12.47023; https://doi.org/10.1117/12.47023

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