Experimental Demonstration of Multidimensional Voronoi Constellation With Two-Level Coding for Four-Core Fiber Transmission

Multidimensional (MD) geometric shaping is an effective approach for achieving spectral efficiency gains in optical communication systems. MD formats also support the joint transmission across different cores of multi-core fibers (MCFs), enabling higher performance improvements through joint decoding. As a structured geometric shaping method, MD Voronoi constellations (VCs) allow low-complexity encoding and decoding without the need for look-up tables, offering superior performance over quadrature amplitude modulation (QAM) formats in terms of bit error rate and mutual information. Moreover, MD VCs can be combined with multilevel coding (MLC) schemes to achieve higher shaping gains after soft-decision (SD) decoding. In this paper, the performance of 16-dimensional VCs with MLC is experimentally demonstrated over a 50 km four-core weakly-coupled MCF transmission system. Compared to 16QAM with bit-interleaved coded modulation at the outer HD-FEC BER threshold of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ 4.5\times 10^{-3}$</tex-math></inline-formula>, VCs achieve a 6 dB reduction in the required launch power and extend the operating range by 17 dB.