B.S. Gurevich

One of the most important problems of the radio electronics is the problem of the wideband RF signals processing and transmission. The high analysis velocity is often required, and the parallel mode of the signal processing has to be performed in order to provide this. The natural solution of the problem of the processing velocity increasing is application of optical information processing methods, and preferably - acousto-optic methods. The common requirement of the processed RF signal high frequency bandwidth means the need of distinguishing the maximum amount of resolvable positions of the diffracted light beam in the acousto-optic unit, which is often called as an acousto-optic device (AOD) resolving power. Along with that the problem of the criterion according to which two adjacent spots are considered to be resolved, seems to be very important. The most common criterion is Raleigh criterion which occurred historically from the need to distinguish stars in astronomic observations; it was proposed by Lord Raleigh in correspondence with E.Abbe-s investigations in the end of 19th century. This criterion proceeds from diffraction theory, and it is rather conditional. Moreover, the basic intention of the radio electronic complexes as well as of the AODs involved in them, is to transmit the maximum amount of information with minimum losses. In this sense the Raleigh criterion looks not optimal because it does not take into consideration the quantitative description of the amount of information processed and transmitted by the device. Hence, it is useful to define the AOD resolving power according to another criterion which would consider the amount of information processed by the system. In order to realize this, it is necessary that the new criterion would involve both the number of the transmitted gray scale levels in each resolved position of light beam at AOD output and the level of noise which accompanies the signal. In this case the unilateral correspondence will be established between the resolving power defined according to the information criterion and amount of information which could be transferred by the device. The theoretical and experimental investigations which have been performed in this work, allowed to avoid the diffraction approach to the resolving power which was the basis of Raleigh criterion, and to establish a new criterion which can be formulated as following: Two positions of diffracted light beam are considered to be resolved if the given beforehand amount of gray scale levels can be distinguished in each position independently, with the probability not less than that given beforehand. The experiments which have been carried out with the AODs involves into the systems of wideband RF signals processing, showed the usefulness of application of the elaborated criterion, on the basis of which the AOD metrology can be developed. The basic difficulty in the proposed criterion application is more psychological than technical because it is often difficult to force the customer to appoint the admissible probability of non-distinguishing of the information unit.