6.2 High-capacity scalable optical communication for future Optical Transport Network

The future penetration of long-term-evolution mobile phone services and various data cloud services will continuously accelerate the present traffic evolution. Figure 6.2.1 shows the commercial system capacity evolution of NTT´s network over the last 30 years. The transmission capacity of today´s Optical Transport Network (OTN) exceeds 1Tbit/s based on the conventional single-core singlemode fiber (SMF) at the growth rate about 1.4-to-1.5 times a year. In 10 years however, we will encounter the fundamental capacity limit of conventional SMF at around 100 Tb/s due to optical fiber nonlinearity and the limitation of allowable fiber launched power into the SMF. In this paper, the impact and future scaling of digital signal processing (DSP) on high-capacity OTN are investigated. A high-speed optical communication system with coherent detection aided by DSP ASIC, that is a digital coherent system, has great potential to change the transmission system design. This approach can enhance total commercial system capacity to more than 8 Tbit/s. Digital coherent systems will evolve to both high-speed applications and ultralow power consumption applications in the near future. Further future enhancements to the key DSP are discussed enabling 1Pb/s/fiber capacity in combination with space division multiplexing.