Window-split structured frequency domain Kalman equalization scheme for large PMD and ultra-fast RSOP in an optical coherent PDM-QPSK system

Abstract

A window-split frequency domain Kalman scheme is proposed in this paper for the equalization of large polarization mode dispersion (PMD) and ultra-fast rotation of state-of-polarization (RSOP) which is an extreme environment due to the Kerr effect and the Faraday effect under the lightning strike near the fiber cables. In order to carry out the proposed Kalman scheme, we give a simplified and equivalent fiber channel model as a replacement for the general model of the polarization effect of the co-existence of PMD and RSOP. With this fiber channel model, we can conduct compensation for PMD in the frequency domain and tracking RSOP in time domain. A half analytical and half empirical theory for the initialization of the process and measurement noise covariance is also presented in theory and verified by the numerical simulation. The performance of the proposed Kalman scheme is checked in the 28Gbaud PDM-QPSK coherent system built on both simulation and experiment platforms. The simulation and experiment results confirm that compared with the generally used constant modulus algorithm (CMA), the proposed scheme provides excellent performance and stability to cope with large range DGD from 20ps to 200ps and RSOP from 200krad/s to 2Mrad/s, with less computational complexity.

Time Domain Equalization and Digital Back-Propagation Method-Based Receiver for Fiber Optic Communication Systems

“…DSP techniques are a powerful tool to compensate optical fiber transmission impairments in single carrier systems as shown by many researchers to achieve high capacity and error-free transmission. In [18], a frequency domain equalizer has been suggested for FOCS to minimize PMD losses. Some researchers [19] have shown an analysis of coupling behaviors for two linear polarized modes using DSP up to 10 km transmission range.…”

“…where ε out and ε in present output and input power values of optical fiber and l is the fiber length. Similarly, OFCD effect is mentioned in Equations (18) and (19) given as…”

Polarization de-multiplexing using a modified Kalman filter in CO-OFDM transmissions

“…Polarization-division multiplexing (PDM) is a straightforward way to use the two orthogonal polarizations of a lightwave to double the spectrum efficiency of coherent optical (CO) systems [1] . Thanks to digital signal processing (DSP), polarization de-multiplexing and channel equalization can be implemented in the digital domain at the receiver.…”

“…Moreover, since Kalman filtering is system-dependent, the initialization of the process and measurement noise covariance Q and R is challenging, which needs much more time to adjust for convergence and affects the performance of Kalman filtering significantly. In general, it is difficult to have a common method to decide the optimum values of Q and R in different systems; then, it is desirable to increase the tolerance for process and measurement noise covariance of Kalman filtering [1] .…”

“…There are various impairments in the optical transmission systems, such as chromatic dispersion (CD), FO, and PN [1] . Instead of the CMA algorithm or other adaptive filter algorithms, which calculate the tap coefficients of a digital finite impulse response filter, the Kalman filters can use a mathematical model with the transmission impairments to mitigate their effects [15] .…”