Non-Orthogonal DMT Enabled by Iterative ICI Cancellation Algorithm for Bandwidth-Limited IM/DD Optical Systems

In this paper, non-orthogonal discrete multi-tone (NO-DMT) is proposed for improving the performance of bandwidth-limited intensity-modulation and direct-detection (IM/DD) optical systems. The bandwidth of NO-DMT signal can be compressed to alleviate high-frequency distortions. Meanwhile, the adaptive bit and power loading in the NO-DMT can make full use of the SNR on each subcarrier. However, inter-carrier interference (ICI) is induced by the bandwidth compression, which significantly degrades the performance of NO-DMT. Therefore, we propose an iterative ICI cancellation algorithm for the NO-DMT, which is applicable to the large number of subcarrier and high-order modulation. For verifying the feasibility of the proposed scheme, a 50 Gbit/s NO-DMT system is experimentally demonstrated using 10 G-class optics at center wavelength of 1370 nm. Due to the limited bandwidth of the devices and the large chromatic dispersion at the wavelength of 1370 nm, the overall 10 dB bandwidth of the system is only approximately 10 GHz. Owing to the robustness to high-frequency distortions, the NO-DMT has 3 dB higher receiver sensitivity compared to DMT at the BER of $1.0\times 10^{-2}$ . Thanks to the full use of SNR, the adaptive bit and power loading in NO-DMT improves approximately 6 dB receiver sensitivity. In conclusion, NO-DMT has the potential for application in bandwidth-limited IM/DD optical systems.