Evaluation of the influence of small deviations of the control signals of the Mach-Zehnder modulator on the optical and radio frequency spectra of the modulated signal

This article addresses a pressing issue in microwave photonics: the development and measurement of the characteristics of ultra-high-frequency optical modulation systems based on Mach-Zehnder modulators. Using ultrahigh-resolution optical spectrometers to measure the spectral composition of a modulator during operation allows us to identify features that cannot be measured after photodetection. Three types of control signal deviations are investigated: operating point setting accuracy, attenuation inequality in the modulator arms, and inequality in the absolute values of signal voltages on different arms of the modulator. The presented spectral compositions of the optical and radio-frequency spectra, obtained through numerical simulation and experiments on modulating radiation with a sinusoidal signal in different operating modes of a standard Mach-Zehnder modulator, allow us to evaluate the infl uence of these effects. It is shown that for deviations less than 1 %, the greatest contribution to spectral distortion is due to the accuracy of the operating point setting. Experimental evaluation methods are proposed for measuring deviation. The obtained results and conclusions provide new opportunities for assessing the manufacturing quality of standard modulators, as well as the accuracy of operating point control systems.