Adaptive compensation of multiple distortions with only pilot tones for flexible coherent transmission systems

• CD, XPM, LPN and LFO can be adaptively compensated with only pilot tones (PTs).
• This method can reduce the system complexity and spectrum efficiency cost.
• XPM compensation performance can be improved by using the double sideband PTs.

In this paper an adaptive multiple distortions compensation method based on amplitude modulated pilot tones (AM-PTs) is proposed for flexible single carrier optical coherent transmission systems. At the transmitter a pair of AM-PTs are generated from the optical carrier and inserted at the double sidebands of the optical signal. At the receiver the field of the AM-PT is recovered with the main signal and fully utilized for the estimation of both linear and ultra-fast nonlinear distortions including chromatic dispersion (CD), laser phase noise (LPN), local oscillator frequency offset (LFO) and cross phase modulation (XPM), thus avoiding the spectral efficiency and complexity cost due to the insertion of different pilots for the estimation of different distortions. The four distortions can be estimate from a simple analytical procedure or directly from the AM-PT fields. Thus the distortion estimation and XPM compensation process can be greatly simplified compared to the non-pilot-aided compensation algorithms. Furthermore the distortion estimation accuracy is not compromised and in inhomogeneous networks the XPM estimation accuracy is even better compared to the previous pilot-aided methods. Numerical simulations are then used to demonstrate the effectiveness and efficiency of this method.