Experimental demonstration of Vandermonde-structured generalized Frank sequence division multiplexing on a 1.8  Tb/s comb-based DSCM-coherent PON system

We propose a novel, to our knowledge, Vandermonde-structured generalized Frank sequence division multiplexing (VGFDM) scheme. The widely used discrete Fourier transform structure can be seen as the special case of our scheme. The VGFDM framework reduces the peak-to-average power ratio (PAPR), without spectral efficiency loss, and creates a uniform signal-to-noise ratio across the user and subcarrier levels. The proposed VGFDM-based digital subcarrier multiplexing passive optical network (DSCM-PON) not only achieves fast Fourier transform (FFT)-like computational complexity due to its unique structure but also dispenses with the additional inverse FFT/FFT modules required in precoding-based orthogonal frequency division multiplexing (OFDM)-PON systems. Proposed schemes redistribute impairment/noise such that grouped subcarriers exhibit similar effective SNR, thereby eliminating the need for per-subcarrier adaptive loading and enabling the use of a single encoder-decoder pair for the entire system. Experimental results from a 1.8 Tb/s optical frequency comb-based coherent DSCM-PON show a 10.8% improvement in generalized mutual information (GMI) compared to the conventional DSCM baseline with neither VGFDM nor entropy loading (EL) under the same baud rate and digital signal processing configuration, demonstrating its potential for practical high-capacity access networks. The scheme substantially reduces the complexity of the optimization algorithm, which is experimentally validated in a multi-user frequency division multiplexing PON system where maximizing the total GMI is achieved while lowering the algorithmic complexity from O(N 2 ) to O(1).