Phase Noise Influence in Long-range Coherent Optical OFDM Systems with Delay Detection, IFFT Multiplexing and FFT Demodulation

TL;DR

This paper analyzes the impact of dispersion-induced phase noise on long-range coherent optical OFDM systems, providing an analytical BER model and comparing system performance over varying distances.

Contribution

It introduces an explicit analytical model for phase noise effects, including EEPN, in CO-OFDM systems with IFFT/FFT processing, and compares their performance to single-channel QPSK systems.

Findings

Phase noise variance increases with transmission distance.

CO-OFDM systems have shorter maximum transmission distances than single-channel QPSK for the same capacity.

Analytic BER expressions are derived considering phase noise and EEPN effects.

Abstract

We present a study of the influence of dispersion induced phase noise for CO-OFDM systems using FFT multiplexing/IFFT demultiplexing techniques (software based). The software based system provides a method for a rigorous evaluation of the phase noise variance caused by Common Phase Error (CPE) and Inter-Carrier Interference (ICI) including - for the first time to our knowledge - in explicit form the effect of equalization enhanced phase noise (EEPN). This, in turns, leads to an analytic BER specification. Numerical results focus on a CO-OFDM system with 10-25 GS/s QPSK channel modulation. A worst case constellation configuration is identified for the phase noise influence and the resulting BER is compared to the BER of a conventional single channel QPSK system with the same capacity as the CO-OFDM implementation. Results are evaluated as a function of transmission distance. For both types of systems, the phase noise variance increases significantly with increasing transmission distance. For a total capacity of 400 (1000) Gbit/s, the transmission distance to have the BER < 10^-2 for the worst case CO-OFDM design is less than 800 and 460 km, respectively, whereas for a single channel QPSK system it is less than 1400 and 560 km.