CD Monitoring Based On Bragg Notch Filter Reflection Spectrum Analysis

New approaches are presented to the process of measuring the chromatic dispersion of a high-speed communication channel based on the classical method for determining the ratio of the radio frequency signal power. The power ratio is recorded at the output of two identical photodetectors, one of which is equipped with a Bragg notch filter at the carrier frequency. New approaches are based on preliminary amplitude modulation of an optical carrier with a a radio clock signal frequency with the formation of an additional amplitude-unbalanced probe radiation to determine the shift between the central wavelengths of the communication channel and the Bragg notch filter, and also the use of methods to increase the signal-to-noise ratio of the measurements. For each position of the filter, an analysis of the parameters of the low-frequency signals at the output of the photodetector is made and the amplitude of the oscillations at DC, single and double probing frequencies are determined. As a result, a single-valued relationship was found between the resulting amplitudes at the output of the photodetector and the position of the central wavelength of the Bragg notch filter. Elimination of the influence of the spectral shift makes it possible to obtain a gain of up to 3 dB for the accuracy of measurements. The registration of information at the probing frequency or doubled probing frequency allows obtaining a gain in the signal-to-noise ratio of measurements up to 10–13 dB and performing chromatic dispersion measurements at a signal-to-noise ratio at a clock frequency of 3–5 dB. The penalty for using additional probing frequencies is up to 1 dB.