Simplified probability-maintained noise power ratio method for nonlinear distortion measurement in fiber-optic communications

With the advent of higher baud rates and modulation orders in optical fiber communication systems, device nonlinearities have emerged as a critical limiting factor. In this Letter, we propose a simplified probability-maintained (PM) notch signal generation technique, along with its associated post-processing method, to enable accurate nonlinearity measurement. The feasibility of the proposed method is verified through comprehensive simulations and experimental comparisons with the existing methods. This method offers the advantages of low-complexity probing signal generation and can be readily implemented using a real-time spectrum analyzer (RTSA). It experimentally achieves an estimation error within 0.5 dB when the noise power ratio (NPR) is around -20 dB, thereby facilitating precise nonlinearity characterization at frequencies of interest.