The coherent reception of intensity modulated signal has beenrecently widely investigated, in which the signal is recovered by the envelopdetection. High linewidth tolerance is achieved with such scheme. However,strong optical carrier exists during the transmission, which degrades theoptical power efficiency.

Professor Wei Li, Dr. Cai Li with the Wuhan National Lab for Optoelectronics, Huazhong University of Science and Technology and Dr. Rong Hu, with the State Key Laboratory of Optical Communication Technologies and Networks proposed a novel fading-free transmission of PDM-DMT signal over long-reach SSMF using digital carrier regeneration.

In this paper, an efficient modulation scheme fordiscrete multi-tone (DMT) signal is proposed based on the Mach-Zehndermodulator (MZM). Different from the traditional intensity modulation, theproposed method employs both intensity and phase domain. Thus, the opticalcarrier power can be greatly reduced by adjusting the bias of MZM aroundthe null point. By employing coherent detection and digital carrierregeneration (DCR), the carrier suppressed DMT signal can be recoveredusing envelop detection. No carrier frequency or phase estimation isrequired. Numerical investigations are made to demonstrate the feasibility, inwhich significant improvements are found for the proposed DCR method,showing great tolerance against laser linewidth and carrier power reduction.Finally, a 124-Gb/s transmission of polarization-division multiplexed DMT(PDM-DMT) signal is demonstrated over 100-km SSMF, with only −8 dBoptical carrier to signal power ratio (CSPR).

The paper was published at Optics Express (Vol. 24, No. 2, pp. 817-824, 2016) and this work was supported by the National Natural Science Foundation of China (Grant No.61505154).