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

Le résumé fourni par la source

Subject of study. This study investigated the possibility of the two-dimensional Fourier processing of images in three channels using a spatial frequency filter. Aim of study. This study aimed to develop a three-channel spatial frequency filter based on an acousto-optic cell made of paratellurite (TeO2), which is the most promising and widely used material currently. 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, whereas 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 [11¯0]. When using acousto-optic diffraction in two symmetric Bragg orders, the plus first, zeroth, and minus first orders serve as output channels. The transfer functions of the diffraction orders are obtained and analyzed. A feature of the formation of the transfer functions using an acousto-optic cell is revealed: 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, respectively. This leads to the need to search for suitable sections simultaneously in all the distributions of the transfer functions related by the condition of fulfillment of strong Bragg synchronism. Main results. The Fourier processing of an image in three channels using the single acousto-optic spatial frequency filter has been demonstrated for the first time to our knowledge. The operation of differentiation over two channels and integration over the third channel of a 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 increasing number of channels, it becomes possible to solve a wider range of tasks, such as focusing on some areas of the image using one channel and “smoothing out” the roughness of the image.

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