1. Introduction
With the dramatic development of cloud computing, online HD video, high speed wireless access and other technology, the demand for network bandwidth increased exponentially year by year. 100Gbit/s polarization division multiplexing quadrature phase-shift keying (PDM-QPSK) single carrier system with coherent detection and digital signal processing (DSP) has been commercially deployed. 400Gbit/s and even 1Tbit/s system are expected soon [1]. [1]. With the increase of symbol rate, polarization effects play a more and more important role. On the one hand, by utilizing PDM, the rate of transmission will be doubled. On the other hand, polarization effects lead to the degradation of system performance. Polarization effects in fiber-optic communication systems are usually related to fiber birefringence. Fiber birefringence changes randomly over time, reflecting the environmental conditions like the air temperature. That random behavior affects two distinct things: the first is the rotation of states of polarization (RSOP), the second is the polarization mode dispersion (PMD). States of polarization (SOP) of optical signals change randomly during transmission, due to the time-varying birefringence distributed along the fiber, whose time variation can be as fast as several hundred /symbol of the Stokes vector on the Poincare sphere [2]. PDM system is more sensitive to SOP. Hence, a joint scheme with high-speed tracing of RSOP and PMD is significant for optical communication system.