Experimental Comparison of Cap and Cup Probabilistically Shaped PAM for O-Band IM/DD Transmission System

Abstract

For 200Gbit/s net rates, uniform PAM-4, 6 and 8 are experimentally compared against probabilistic shaped PAM-8 cap and cup variants. In back-to-back and 20km measurements, cap shaped 80GBd PAM-8 outperforms 72GBd PAM-8 and 83GBd PAM-6 by up to 3.50dB and 0.8dB in receiver sensitivity, respectively.

Revisiting Probabilistic Constellation Shaping in Unamplified Coherent Optical Links

“…However, PCS can be achieved through a wide range of probability distribution functions (PDF). A particularly interesting PDF is the reverse MB (rMB) distribution, which is achieved by substituting the exponential argument with its symmetric in [2, (4)], and can still be implemented through probabilistic amplitude shaping (PAS) [5]. By implementing an rMB-based PCS, we can take advantage of the data rate flexibility, while reducing the impact of the increased PAPR inherent to MB-based PCS, since higher probability is allocated at higher-amplitude symbols.…”

“…By implementing an rMB-based PCS, we can take advantage of the data rate flexibility, while reducing the impact of the increased PAPR inherent to MB-based PCS, since higher probability is allocated at higher-amplitude symbols. In [5], both MB and rMB distributions are experimentally compared in an optically pre-amplified IM-DD system, and [6] demonstrates a gain of 0.05 bits/channel use in 4-PAM with an optimized PCS targeted at unamplified IM-DD systems. The question then remains on whether PCS achieved through a rMB distribution can indeed be beneficial to unamplified coherent optical systems.…”

Probabilistically Shaped PAM-8 Transmission With Simplified Volterra Equalizer

“…In comparison with PAM-4 signals, PAM-8 signals can carry more information at the expense of more complicated digital signal processing (DSP), and probabilistic shaping (PS) and nonlinear equalizers were exploited to enhance the robustness of PAM-8 signals [9][10][11][12][13][14]. Furthermore, when the modulation amplitude is increased to PAM-16, the nonlinear equalization becomes more challenging for compensating the critical nonlinear impairments caused by the electro-optical components in the nonlinear operating region [15][16][17].…”

“…However, it is significant for future large-capacity IDC to investigate the PAM-8 and PAM-16 schemes. After the probabilistically shaped PAM-8 (PS-PAM-8) system has been first experimentally demonstrated, several state-of-the-art works have been reported to show the outperformance of PS-PAM-8 signals [9][10][11][12]. Furthermore, a probabilistic amplitude shaping (PAS) scheme was proposed by integrating PS and forward error correction (FEC) to combine the distribution matcher (DM) with the systematic encoder of binary low-density parity-check (LDPC) codes [18,19].…”