Journal
JOURNAL OF LIGHTWAVE TECHNOLOGY
Volume 39, Issue 9, Pages 2714-2724Publisher
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
DOI: 10.1109/JLT.2021.3057680
Keywords
Optical transmitters; Laser noise; Phase noise; Chromatic dispersion; Estimation; Optical noise; Nonlinear optics; Carrier phase estimation; chromatic dispersion; coherent optical transmission systems; laser phase noise
Funding
- FEDER, through the CENTRO 2020 Programme [ORCIP CENTRO01-0145-FEDER-022141]
- FCT/MCTES through Project FreeComm-B5G [UIDB/EEA/50008/2020]
- la Caixa Foundation [100010434]
- [LCF/BQ/PR20/11770015]
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This article introduces the multi-subcarrier modulation as a notable feature in the latest generation of high-speed coherent optical transceivers, and proposes a novel pilot-based joint-subcarrier CPE method based on a dual-reference subcarrier approach. Numerical results demonstrate that the proposed method enables near-optimum performance at symbol-rates per subcarrier as low as 1 Gbaud over ultra-long-haul distances.
Multi-subcarrier (MSC) modulation is recently standing out as a notable new feature in the latest generations of high-speed coherent optical transceivers, providing distinctive advantages over legacy single-carrier systems. However, the transition from single-carrier to MSC modulation still requires significant optimization of digital signal processing subsystems, in order to maximize the inherent potential of subcarrier multiplexing. In this article, the penalty associated with the usage of carrier phase estimation (CPE) methods inherited from single-carrier systems is quantitatively studied and the need for enhanced MSC-tailored solutions is evidenced. A novel pilot-based joint-subcarrier CPE method based on a dual-reference subcarrier (DRS) approach is described and numerically assessed. The proposed DRS-CPE exploits the frequency-dependent walk-off effect imposed by chromatic dispersion (CD) to enable the separation of phase noise processes incurred by the transmitter and local oscillator lasers, thereby allowing to effectively apply joint-subcarrier CPE independently of the symbol-rate per subcarrier. Our numerical results demonstrate that the proposed DRS-CPE enables to operate with near-optimum performance at symbol-rates per subcarrier as low as 1 Gbaud over ultra-long-haul distances.
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