Bragg Wavelength Temperature Shift and the Measurement Error of the Microwave Signals Instantaneous Frequency

The main sources of measurement errors in the microwave signals instantaneous frequency measuring systems (IFM-systems) with frequency-amplitude conversion based on the fiber Bragg gratings (FBG) include temperature shifts of the center wavelength of the optical carrier source, the operating point of the amplitude Mach-Zehnder modulator (MMZ), the Bragg wavelength of the FBG, and the difference in the characteristics of the optoelectronic conversion of two photodetectors for constructing the amplitude comparison function (ACF). The first three are in the nature of temperature fluctuations, the latter can be minimized when calibrating the device or eliminated by using switching solutions using a single photodetector. In this work, the existing solutions for stabilizing the temperature of the FBG are investigated, their efficiency is estimated, and the influence of the spectral shape of the gratings on the metrological characteristics of the beat-based IFM-systems is studied. The possibility of reducing the measurement error of the instantaneous frequency to several or tens of kilohertz when using a triangular and Gaussian FBG is shown.