A nonlinearity-tolerant frequency domain root M-shaped pulse for coherent optical communication systems

Area of Science:

• Optical Communications
• Signal Processing
• Photonics

Background:

• Intra-channel nonlinearity and intersymbol interference (ISI) limit transmission reach in dispersion unmanaged optical systems.
• Existing pulse shaping techniques like root raised cosine (RRC) and root optimized pulse (ROP) have limitations in mitigating these effects.

Purpose of the Study:

• To derive and experimentally validate a new frequency domain root M-shaped pulse (RMP) for nonlinearity-tolerant and ISI-free optical transmissions.
• To evaluate the performance enhancement offered by the RMP in terms of transmission reach compared to existing pulse shapes.

Main Methods:

• Derivation of closed-form expressions for the RMP based on the relationship between pulse shaping and intra-channel nonlinearity.
• Experimental demonstration of the RMP in single-channel 56 Gb/s polarization-division-multiplexed quadrature phase-shift keying (PDM-QPSK) and 128 Gb/s PDM-16QAM systems.
• Experimental evaluation in a dense wavelength-division multiplexing (DWDM) 504 Gb/s PDM-QPSK transmission system.
• Comparative analysis of transmission reach extension against RRC and ROP pulses.
• Experimental study of narrow filtering effect tolerance for RMP, RRC, and ROP.

Main Results:

• The RMP extends transmission reach by 33% (vs. RRC) and 17% (vs. ROP) for a 56 Gb/s PDM-QPSK system at a roll-off factor of 1.
• For a 128 Gb/s PDM-16QAM system, the RMP extends reach by 44% (vs. RRC) and 18% (vs. ROP).
• Reach increases of 30% (vs. RRC) and 13% (vs. ROP) are observed for a 504 Gb/s DWDM PDM-QPSK system.

Conclusions:

• The frequency domain RMP is an effective solution for nonlinearity-tolerant and ISI-free optical transmission in dispersion unmanaged systems.
• The RMP offers significant improvements in transmission reach across various high-speed modulation formats and system configurations.
• The RMP demonstrates comparable or superior tolerance to narrow filtering effects compared to conventional pulses.