Enhanced 4D-OFDM optical communication systems with color-coded constellations and probability constellation shaping

Area of Science:

• Optical communications
• Signal processing
• Information theory

Background:

• Orthogonal Frequency Division Multiplexing (OFDM) is crucial for high-speed optical transmission.
• Enhancing constellation mapping is key to improving data rates and receiver sensitivity.
• Current methods face limitations in spectral efficiency and error performance.

Purpose of the Study:

• To introduce a novel four-dimensional probability constellation mapping for OFDM optical transmission.
• To amalgamate geometric and probability shaping with color coding for enhanced Constellation Figure of Merit (CFM).
• To evaluate the performance gains in receiver sensitivity and error rate.

Main Methods:

• Development of a four-dimensional constellation structure using color coding.
• Implementation of a two-dimensional inverse fast Fourier transform (2D-IFFT) based OFDM system.
• Experimental transmission of signals over a 2 km seven-core optical fiber.

Main Results:

• Successful transmission of OFDM signals at 51.49 Gb/s over a 2 km seven-core fiber.
• Achieved receiver sensitivity gains of 0.85 dB, 1.33 dB, and 1.83 dB compared to traditional 4D, 3D-OFDM, and 2D-OFDM.
• Demonstrated a 1.36 dB receiver sensitivity gain over uniform distribution constellations at 4.4 bits/symbol entropy.

Conclusions:

• The proposed color-coded four-dimensional constellation significantly enhances receiver sensitivity and error performance.
• The system shows promising prospects for future short-distance optical communication applications.
• The combined geometric and probability shaping approach effectively improves CFM.