Three-channel Fourier processing of optical images using a single acousto-optic filter

Котов В.М., Аверин С.В., Зенкина А.А., Белоусова А.С. Трёхканальная фурье-обработка оптических изображений с использованием одного акустооптического фильтра // Оптический журнал. 2023. Т. 90. № 12. С. 73–84. http://doi.org/10.17586/1023-5086-2023-90-12-73-84

Kotov V.M., Averin S.V., Zenkina A.A., Belousova A.S. Three-channel fourier processing of optical images using a single acousto-optic filter [In Russian] // Opticheskii Zhurnal. 2023. V. 90. № 12. P. 73–84. http://doi.org/10.17586/1023-5086-2023-90-12-73-84

Subject of study. Investigation of the possibility of two-dimensional Fourier processing of images in three channels using one spatial frequency filter. Aim of study. Development of a three-channel spatial frequency filter based on an acousto-optic cell made of paratellurite (TeO₂) as the most promising and widely used material at the moment. Method. The method is based on the use of the slices of a paratellurite crystal, which provide a regime of highly efficient acousto-optic diffraction in two symmetric Bragg orders. Calculations show that the most efficient diffraction in two symmetric orders in paratellurite occurs when optical radiation propagates near the optical [001] axis of the crystal, while the acoustic wave propagates along the [110] direction. In this case, the diffraction should be accompanied by the change in the polarizations of the diffracted beams relative to the polarization of the incident radiation, which occurs only if the acoustic wave is transverse with a shift direction along  [1`10]. When using acousto-optic diffraction in two symmetric Bragg orders, the plus first, zero, and minus first orders serve as output channels. Transfer functions of diffraction orders are obtained and analyzed. A feature of the formation of transfer functions using one acousto-optic cell is revealed, which consists in the fact that each element of the transfer function is separated from the corresponding element of the "neighboring" transfer function strictly by an angle equal to the double Bragg angle K/k, where K and k are the values of the sound and light wave vectors. This leads to the need of search for suitable sections simultaneously in all distributions of transfer functions related by the condition of fulfillment of strong Bragg synchronism. Main results. Fourier processing of an image in three channels using the single acousto-optic spatial frequency filter has been demonstrated for the first time. The operation of differentiation over two channels and integration over the third channel of  two-dimensional image carried by radiation at a light wavelength of 0.63 µm has been experimentally obtained. The paratellurite acousto-optic cell operating at a sound frequency of 43.5 MHz in the acousto-optic diffraction mode in two symmetric Bragg orders was used as the spatial frequency filter. Practical significance. With an increase in the number of channels, it becomes possible to solve a wider range of tasks, for example, in the process of processing, focus on some areas of the image using one channel, on others — using others, “smooth out” the roughness of the image, etc.

the work was supported by the Russian Science Foundation (Project № 22-21-00059).