Polarization Multiplexed Optical OFDM System With a Beat Interference Cancellation Receiver

Jianxin Ma,Zhiqi Hu

doi:10.1109/jphot.2020.3036030

Abstract

A novel beat interference cancellation receiver (BICR) is proposed to cancel the signal-signal beat interference (SSBI) for polarization division multiplexed (PDM) optical orthogonal frequency division multiplexing (OOFDM) system, where two single sideband (SSB) OOFDM signals are polarization multiplexed along with their offset optical carriers (OCs) located at opposite sides. At receiver, the PDM SSB-OOFDM signal is equally power split into four beams with one or two OCs filtered out, and then fed into two balanced photodiode pairs for recovering the RF-OFDM signals with SSBI cancellation. The PDM SSB-OOFDM system is insensitive to fiber polarization mode dispersion since the proposed BICR is implemented without polarization-sensitive devices. Moreover, the spectral efficiency is greatly improved because of PDM and the small guard band since the SSBIs are eliminated. The proposed BICR scheme is validated with a simulation link of 112 Gbps 16-QAM PDM SSB-OOFDM signals. After 120km SSMF transmission, the EVM keeps below forward error correction limit of 16.3%.

Highlights

With the advent of 5G and big data, more and more terminal devices are connected to the network, which leads to exploding increase of the transmission capacity requirements
In 2019, we have proposed a misaligned optical carrier (MOC) polarization division multiplexed (PDM) single sideband (SSB)-orthogonal frequency division multiplexing (OOFDM) system based on a single beat interference cancellation receiver (BICR) to avoid the polarization mode dispersion (PMD) [28], but the spectrum efficiency (SE) is low since the misaligned optical carriers (OCs) at the same sideband leave a blank spectrum gap
To generate the Orthogonal frequency division multiplexing (OFDM) signal for the X-polarization, a pseudo random bit sequence (PRBS) with the length of 65535 and bit rate of 56 Gbps is mapped into 16384 16-QAM symbols; the 16-QAM symbols are serial-toparallelly converted to facilitate 128-subcarrier modulation by inverse fast Fourier transform (IFFT) and form 128 OFDM symbols; a cyclic prefix consisting of 32 sample points is added for each OFDM symbol to resist the inter-symbol interference; at last, the analog baseband OFDM signal is obtained after parallel-to-serial conversion and digital-to-analog conversion

Summary

Introduction

With the advent of 5G and big data, more and more terminal devices are connected to the network, which leads to exploding increase of the transmission capacity requirements. Compared with intensity modulation direct detection system with double sideband (DSB) optical spectrum, the single sideband (SSB) OOFDM system can avoid the power fading and bit walk effects caused by the CD, but, in the photocurrent, the signal-signal beat interference (SSBI) may overlap with the RF-OFDM signal in frequency domain, which degrades the link performance and limits the SE [12], [13]. After suppressing one or two OCs properly by optical bandpass filters (OBPFs), the four optical signals are photodetected by two pairs of the balanced photodetector (BPD) pairs with the undesired SSBIs cancellation This proposed PMD SSB-OOFDM system can eliminate SSBI to reduce the GB, and resist the PMD without MIMO technology and polarization stabilizer. The simulation results show that the EVMs maintain below the forward error correction (FEC) limit of 16.3% after 120 km standard single-mode fiber (SSMF) transmission

Principle of the MOC PDM-SSB-OOFDM Link

Simulation Setup and Results

Conclusion