On the multipath interference mitigation for high-speed IM-DD transmissions with Nyquist subcarrier modulation

Area of Science:

• Optical Communications
• Signal Processing

Background:

• High-speed intensity modulation direct detection (IM-DD) systems suffer performance degradation from multipath interference (MPI).
• Higher-order modulation formats exacerbate MPI effects, limiting transmission performance.

Purpose of the Study:

• To propose and demonstrate Nyquist subcarrier modulation (Nyquist-SCM) as an MPI-resistant format.
• To experimentally compare the MPI tolerance of Nyquist-SCM 16QAM with PAM-4 signals.

Main Methods:

• Experimental transmission of 56 Gbit/s PAM-4 and Nyquist-SCM 16QAM signals over 2 km of standard single-mode fiber (SSMF).
• Utilized a C-band semiconductor laser with a 1.7 MHz linewidth.
• Evaluated performance based on the KP4-FEC threshold (BER = 2 × 10^-4).

Main Results:

• Nyquist-SCM 16QAM demonstrated a 4 dB enhanced MPI tolerance compared to PAM-4.
• Even with advanced MPI mitigation techniques for PAM-4, Nyquist-SCM 16QAM maintained a 1 dB advantage.
• The study highlights the inherent MPI resilience of the Nyquist-SCM format.

Conclusions:

• Nyquist-SCM is a promising modulation format for mitigating MPI in high-speed optical IM-DD systems.
• This format offers a significant advantage over PAM-4, especially in challenging transmission environments.
• The findings pave the way for more robust and higher-performance optical communication systems.