Nonlinear mitigation on subcarrier-multiplexed PM-16QAM optical systems.

Area of Science:

• Optical communication systems
• Digital signal processing
• Nonlinear optics

Background:

• Multi-subcarrier (MSC) transmission with polarization-multiplexed 16-ary quadrature amplitude modulation (PM-16QAM) is crucial for high-capacity optical networks.
• Nonlinear effects, such as self-channel interference (SCI) and nonlinear phase noise (NLPN), degrade transmission performance and limit reach.
• Effective nonlinear mitigation strategies are essential for enhancing the capacity and reach of these systems.

Purpose of the Study:

• To comprehensively evaluate the benefits of nonlinear mitigation strategies for MSC-PM-16QAM transmission systems.
• To quantify the reach gains achieved by symbol-rate optimization (SRO) and digital backpropagation (DBP).
• To investigate the interplay between SRO, DBP, SCI, and nonlinear phase noise (NLPN) and their impact on transmission performance.

Main Methods:

• Experimental demonstration of SRO in a 31-channel WDM transmission system.
• Comparative analysis of DBP versus single-carrier (SC) transmission gains.
• Investigation of SCI mitigation by DBP and its effect on SRO.
• Analysis of nonlinear phase noise (NLPN) impact and symbol-rate dependence.
• Evaluation of carrier phase estimation (CPE) for NLPN mitigation.

Main Results:

• Symbol-rate optimization (SRO) achieved a maximum reach gain of approximately 9% in MSC-PM-16QAM transmission.
• Digital backpropagation (DBP) provided gains comparable to SRO when compared to single-carrier (SC) transmission.
• DBP effectively reduced self-channel interference (SCI), weakening the SRO phenomenon.
• The combined effect of SRO and DBP yielded only an additional 4% reach gain due to experimental DBP limitations.
• Nonlinear phase noise (NLPN) was found to be symbol-rate dependent, impacting transmission performance.

Conclusions:

• Symbol-rate optimization offers significant reach enhancement for MSC-PM-16QAM systems.
• While DBP mitigates SCI and enhances performance, its combination with SRO yields limited additional gains due to practical limitations.
• Further research into advanced NLPN mitigation techniques beyond standard CPE is necessary to fully exploit the potential of high-capacity optical transmission systems.