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The characterization of analog optical links was examined, and it is shown that the study, accounting, and reduction of nonlinearities introduced by the elements of an optical link into the output signal during photodetection are of particular practical interest. Methods for the analysis of nonlinear distortions of analog optical paths with external modulation are presented, and it is proposed to use high-resolution optical spectrum analyzers for their characterization. The analysis methods use the results of measurements of the optical spectrum, which directly characterize the optical signal of the link without taking into account the effect of nonlinearities introduced during photodetection. An analytical model of the process of modulation of monochromatic light radiation by a two-tone radio frequency signal using an electro-optical Mach–Zehnder modulator is presented. The mutual interaction between the nonlinear spectral components of the optical modulated signal and the radio frequency signal at the photodetector output was examined. The optical and radio frequency spectra of AOL signals were experimentally studied on a specially assembled measurement stand. The results of experiments on measuring the spurious free dynamic range (SFDR) of analog optical paths using high-resolution radio frequency and optical spectrum analyzers are presented. Possible reasons for the degradation of the SFDR during photodetection are discussed. Using an analytical model of the nonlinearities of the Mach–Zehnder modulator, the contribution of the nonlinearity of photodetection to the distortions of the output signal of the optical link was experimentally estimated, and the differences in the power of cross-modulation products for high frequency photodiodes of two types were demonstrated. [ABSTRACT FROM AUTHOR]

The present state of the metrological facilities for measuring the total harmonic distortion factor, based on digital methods of measuring and synthesizing signals, is considered. The principal metrological characteristics of the SK6-20 calibrator-meter, the SK6-122 generator-calibrator and the SK6-20A metercalibrator are presented. [ABSTRACT FROM AUTHOR]

A method of estimating nonlinear distortions, which differs from the well-known ones in that it enables one to determine the nonlinear distortions of random signals, which carry useful information, is described. A new criterion is proposed for estimating these distortions, the basis of which is a calculation of the mean value of the relative change in the gain of the circuit which introduces the distortions. A block diagram of the measuring circuit is presented. [ABSTRACT FROM AUTHOR]