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

Abstract

The present work introduces a four-dimensional probability constellation mapping OFDM optical transmission system based on a two-dimensional inverse fast Fourier transform (2D-IFFT). A four-dimensional constellation structure employing color coding is designed, amalgamating geometric shaping with probability shaping to enhance the constellation figure of merit (CFM). Successful transmission of OFDM signals at 51.49 Gb/s is achieved over a 2 km seven-core optical fiber, validating the performance of the proposed constellation diagram. Under the conditions of multicore multiplexing and a bit error rate of 3.8 × 10−3, the receiver sensitivity of the OFDM signals mapped with the proposed color-coded four-dimensional constellation exhibits gains of 0.8 dB, 1.33 dB, and 1.83 dB compared to traditional four-dimensional constellations, 3D-OFDM, and 2D-OFDM modulation, respectively. Furthermore, under an entropy value of 4.4 bits/symbol, a receiver sensitivity gain of 1.36 dB is attained compared to a uniform distribution constellation, indicating the favorable error performance of this scheme with promising prospects for short-distance communication in the future.