Low overhead phase-encoded pilot assisted ultra-fast RSOP tracking algorithm

We propose a low overhead duty cycle ultra-high-speed rotation of the state of polarization (RSOP) tracking algorithm based on phase-encoded pilot. Under extreme environmental conditions such as lightning strikes, rotational crosstalk of more than several Mrad/s can be induced in the two orthogonal polarization states of the polarization-multiplexed signals in the optical fiber, and the large polarization crosstalk impairments can lead to signal decoding failures at the receiving end. Existing rotation of the state of polarization tracking algorithms need to insert pilot sequences with large overhead, and after reducing the overhead share of the pilot frequency they face equilibrium failure under high speed RSOP. To address the limitations, we design a pilot sequence with a low overhead duty cycle and with chirp phase coding and modulus constancy properties. By inserting a well-designed phase-encoded pilot sequence, it can not only be used for time-synchronization but also assist the adaptive MIMO equalization module for polarization rotation recovery by taking advantage of the chirp phase encoding and modulus-constant property. For a single-frame transmission data block with a length of 71,680 symbols, the number of inserted pilot sequences is 1,152, of which the first 128 symbols are used to compute the mutual correlation for time-frequency synchronization by sliding the data block at the receiver side, and the last 1,024 symbols are used to assist the adaptive equalization module to do the equalization coefficient convergence calculation, resulting in a pilot overhead as low as 1.61%. The CMA module in the adaptive equalization module is used for pre-equalization, and the RDE module performs real-time equalization coefficient updating to track the ultra-high-speed RSOP with the assistance of the pilot sequence. In the coherent fiber optic communication system with 64 GBaud DP-16QAM modulated transmission in a laboratory environment, a polarization scrambler is used to simulate a polarization rotation of 10 Mrad/s, and the BER at the receiving end is as low as 1.9e-3 after 25km and 50km segmented single-mode fiber transmission.