The thesis is devoted to the decision of a scientific problem of increase of efficiency of coherent optical spectrum analyzers which are a part of optical systems of information processing, by coordination of parameters of their components. The increase in efficiency is achieved through the use in coherent optical spectrum analyzers of the input transparency in the form of a space-time discrete light modulator and a matrix detector. The harmonization of the parameters of the modulator, Fourier lens and matrix detector allowed to improve the technical characteristics of coherent optical spectrum analyzers. The criterion of efficiency is the proposed parameters (technical characteristics) of coherent optical spectrum analyzers: operating range of spatial frequencies; spatial bandwidth product; spatial spectral resolution.
The dissertation, based on the Fresnel scalar theory of diffraction, analyzes the propagation of coherent light through a generalized optical system of a coherent optical spectrum analyzer, which consists of a laser, an input transparent, a Fourier lens and a matrix detector. Researches of the methodological error of measuring the spatial frequency of the signal spectrum using a coherent spectrum analyzer have shown that the known formulas used to determine the spatial frequency are valid only for the paraxial region. A new method for calculating the relative error was developed, the application of which on the example of a given spectrum analyzer showed that the Fresnel approximation within the diffraction angle from 0 ° to 10 ° provides a relative error of less than 1.5%.
It is substantiated that the use in digital coherent optical spectrum analyzers of matrix devices of input and output of optical signals allows to investigate and process two - dimensional optical signals which change in space and time. However, this requires the conversion of the input and output signal into a discrete digital form, which distorts the spatial spectrum of the signal at the output of digital coherent optical spectrum analyzers. To research such distortions, a physico-mathematical model of digital coherent optical spectrum analyzers was developed and models of their individual components were proposed. The choice of the main characteristics of coherent spectrum analyzers is substantiated and methods of calculation of these characteristics are developed.
Methods for calculating the characteristics of coherent optical spectrum analyzers, when an opaque screen with a rectangular hole is chosen as the input test object, are considered. The research of the characteristics of coherent optical spectrum analyzers showed that the operating range of spatial frequencies is limited by the parameters of the optical system of coherent optical spectrum analyzers. On the basis of the developed physical and mathematical model of digital coherent optical spectrum analyzers the peculiarities of using matrix light modulators are substantiated, namely:
1. The distribution of the field amplitude in the plane of spectral analysis of coherent optical spectrum analyzers is the result of the sum of diffraction maximum that depend on the spatial spectrum of the image, which is distorted by the pulse response of the spectrum analyzer. The position of the maximum is determined by the period of the matrix structure of the spatial modulator of light, their width - the size of the modulator.
2. Minimal distortions in the measurement of the spectrum of the image will be in the case when in the formation of the distribution of the field amplitude in the plane of analysis involves only maximum of zero order.
To confirm the results of theoretical researches of coherent optical spectrum analyzers, a laboratory stand of optical spectrum analyzer was developed and created, which allowed to conduct the researches: measured the distribution of light intensity in the diffraction pattern formed by the test object; determining the correspondence of the position of diffraction maximum in the plane of spectral analysis to their spatial frequency; measuring the spectrum of test objects obtained using two lasers with different wavelengths; measurement of generalized characteristics of coherent optical spectrum analyzers. The experimentally obtained diffraction patterns from test objects in the form of a slit, a round diaphragm, a diffraction grating, the intensity of which was confirmed by the results of theoretical modeling. The spatial spectrum of a transparent two-dimensional structure are obtained, the research of which allows to determine the average sizes and variance of the dimensions of tissue cells. This method can be widely used in the textile industry. The research results obtained in the dissertation were used at SDPSE Arsenal, which is confirmed by the act of implementation.
