Analysis of RF-Pilot-Based Phase Noise Compensation for Coherent Optical OFDM Systems

In coherent optical long-haul transmission systems, orthogonal frequency-division multiplexing represents a promising modulation format. However, due to long symbol length, laser phase noise can be a major impairment. In this manuscript, the RF-pilot-based phase noise compensation scheme is analyzed and compared to conventional common-phase error compensation. It has been shown that the RF-pilot-based phase noise compensation scheme allows for a considerable increase in tolerable laser linewidth as compared to conventional common-phase error compensation at the cost of an increase in system complexity. For a 112-Gb/s transmission scheme, the tolerable linewidth is increased by a factor of ten as compared to common-phase error compensation.

I. Introduction

Orthogonal frequency-division multiplexing (OFDM) is a promising modulation scheme for next-generation optical long-haul transmission systems. These systems need to transmit 112-Gb/s Ethernet traffic within a 50-GHz wavelength grid over distances of up to 2000 km. In recent years, a variety of coherent optical transmission schemes combined with digital signal processing (DSP) have been proposed and demonstrated, that provide a large tolerance towards impairments like chromatic dispersion (CD), polarization-mode dispersion, and cascaded filtering [1]–[3]. It is known that in coherent optical transmission systems, laser phase noise represents a major performance impairment that must be compensated for [4], [5]. In particular, because of its long symbol size, OFDM requires an effective compensation mechanism.