Nonlinearity-tolerant OSNR estimation method based on correlation function and statistical moments

We propose a fiber nonlinearity-tolerant optical signal-to-noise ratio (OSNR) estimation method for high speed long haul coherent optical fiber transmission system. The correlation function of the amplitude noise and a calibration factor ξ are utilized to correct nonlinearity-induced distortions for the first time when the statistical moments-based method (SMB method) is applied. ξ depends on not only transmission distances but also launch powers. Besides, we put forward a fitting formula for optimal ξ and OSNR estimation results still keep valid regardless of transmission distances and launch powers. Compared with current existing OSNR estimation methods, the proposed method functions well in highly nonlinear systems and is demonstrated to be feasible and more accurate. OSNR estimation errors are below 0.94 dB after calibration over a wide OSNR range from 10 dB to 28 dB in a 112-Gb/s polarization-multiplexed quadrature phase shift keying (PM-QPSK) system when the launch power is up to 8 dBm and the transmission distance is as long as 2000 km.