Abstract
High-baud-rate coherent optical system is essential to support the ever-increasing demand for high-speed applications. Owing to the recent progress in advanced modulation formats, over 1 Tb/s single-carrier data transmission has been achieved in the laboratory, and its commercial application is envisioned in the near future. This paper presented the trend of increasing baud rate and utilizing high-order quadrature-amplitude modulation (QAM), and several enabling technologies in the coherent optical communication systems. We first discussed recent progress of high-order QAM system and digital signal processing technology. Furthermore, we compared the transmission performance of three different ultrahigh-order QAM formats. The paper then reviewed the commonly used methods of achieving over 100 GBaud optically modulated signals. Besides, five attractive modulators and their corresponding modulation structures are illustrated. Key performance parameters including electrode length, 3-dB bandwidth, half-wave voltage, extinction ratio and optical loss are also compared. Finally, the trade-off between the baud rate and QAM orders in implementing high-speed systems are investigated in simulations. The results show that for the coming 800 GbE or 1.6 TbE, PDM-64-QAM might be an idea choice by considering the trade-off between the link reach and required system bandwidth. By adopting the latest probabilistic shaping technology, higher-order QAM signals, such as PS PDM-256-QAM, could be favorable for long reach applications while using extra system bandwidth.
Highlights
In this review, we have surveyed the recent progress of the enabling technologies in high-baud-rate coherent optical communication systems
High-order quadratureamplitude modulation (QAM) signals with various advanced digital signal processing (DSP) algorithms have the great potential for achieving high-speed systems
Plasmonic modulator shows great potential in large bandwidth, but the loss introduced by conversion between surface plasmon polariton (SPP) and light is the problem need to be solved urgently
Summary
The material and structure choices of the modulators are becoming the key parts to realize high-baud-rate coherent optical communication systems. In practice, due to the limited ENOB and bandwidth of the DACs, the performance still gets worse for high-baud-rate coherent optical communication systems with a given QAM order. The generated QAM order depends on the bit resolution of DACs. With Nyquist pulse shaping, a SC PDM-16-QAM signal up to 127.9 GBd was well synthesized and transmitted over 3000 km, achieving a record 1 Tb/s line rate [31]. Architectures of different high-baud-rate high-order QAM generation schemes: (a) All-ETDM, (b) High-speed DAC, (c) Multiple spectral slices synthesis multiplexing and (d) DBI. 100 GBd 32-QAM signal employing all-silicon modulator was successful generated, achieving a net data rate of 416.7 Gb/s with pre-compensation and Rx-side DSP [49]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
