This paper reviews the development and latest research progress of large-capacity optical transmission systems. Theoretical and experimental studies have shown that due to the limitations of the fiber nonlinear effect and the amplifier bandwidth, communication capacity is close to the limit of single-mode fiber transmission. Therefore, on the one hand, the development of optical fiber communication needs to overcome the bottleneck of high-speed electrical devices in single carrier transmission. So this paper investigates the multi-carrier generation schemes like orthogonal frequency division multiplexing (OFDM) technology or Nyquist wavelength division multiplexing (Nyquist-WDM) technology, which can improve spectrum efficiency and increase channel capacity to achieve Pbit/s rate or even higher. On the other hand,we study from the perspective of the optical fiber itself how to take full advantage of the spatial dimension of the fiber in consideration of cost-effectiveness and energy efficiency. It is shown that space division multiplexing (multi-mode, multi-core) and angular momentum multiplexing (OAM) will be the focus of future research to overcome the limit of the capacity of single-mode fiber and greatly improve optical transmission capacity.

large capacity optical transmission systems  /  high spectral efficiency modulation  /  multicarrier  /  mode-division multiplexing