Multidimensional optical modulation (MOM) is one of the promising techniques for spectrally efficient optical access network transmissions. However, inter -dimensional interference (IDI) in MOM limits the signal-to-interference-plus-noise ratio (SINR) giving trade-off between each dimension. In this paper, we pro-pose IDI-tolerant four-dimensional (4-D) set-partitioning quadrature amplitude modulation with M-ary differential phase shift keying (SP-QAM-MDPSK) based on direct-detection (DD) systems. We compared the proposed scheme with QAM-MDPSK without set-partitioning and experimentally demonstrate SP-16QAM-16DPSK over 20-km single-mode fiber, results in nearly 3 dB signal-to-noise ratio (SNR) gain at 3 x 10- 2 symbol error rate (SER) compared to 16QAM-4DPSK, which shows that SP-QAM-MDPSK is tolerant to the possible IDI.
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