Modified phase-conjugate twin wave schemes for fiber nonlinearity mitigation

Area of Science:

• Optical Communications
• Nonlinear Optics
• Signal Processing

Background:

• Conventional phase-conjugate twin wave (PCTW) schemes mitigate fiber nonlinear distortions but halve spectral efficiency (SE).
• There is a need for methods that improve SE without sacrificing nonlinear distortion mitigation.

Purpose of the Study:

• To enhance spectral efficiency (SE) in phase-conjugate twin wave (PCTW) systems.
• To maintain nonlinear distortion suppression capabilities while increasing data transmission rates.

Main Methods:

• Modulating one conjugated signal with additional bits to improve SE.
• Employing error correction coding for redundancy in the additional bits to overcome performance bottlenecks.
• Simulating a 25-Gbaud polarization-division-multiplexed quadrature phase shift keying (PDM-QPSK) system over 15,200 km.

Main Results:

• The proposed scheme increases normalized SE from 50% to 80% for similar performance compared to conventional PCTW.
• Information in additional bits becomes the primary performance limiter, addressed by error correction coding.
• The concept is applicable to higher-level modulation formats.

Conclusions:

• The novel PCTW scheme significantly enhances SE while preserving nonlinear distortion mitigation.
• Error correction coding is crucial for overcoming performance limitations introduced by increased SE.
• This approach offers a promising solution for high-capacity optical communication systems.