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The voracious demand for bandwidth — driven by internet video, cloud computing, Internet of Things, LTE and IDC, etc. — is making a bottleneck of obsolete transport networks. Since the service access data rate provided by both wireless and wireline is approaching 1,000Mbps, 100G and beyond is considered the most promising solution to meet the ever-increasing need for bandwidth.
Capacity, distance and cost are the main evaluation indexes of optical transmission system. This is being shaped by the process of maximizing the transmission capacity and distance with up-to-date technologies while lowering the cost of every bit. It is more feasible and cost-effective to improve the capacity as well as efficiency of existing networks by upgrading the optical line card with high-speed channel data rate.
The channel data rate of DWDM transport system has been upgraded from 2.5Gbps to 100Gbps in the past 20 years. Compared with 10G/40G DWDM system, the transport capacity and performance of 100G DWDM system is improved dramatically with the introduction of the advanced modulation format PM-QPSK (Polarization Multiplexing-Quadrature Phase Shift Keying) and digital coherent detection technology.
The FiberHome 100G DWDM system can provide high transmission capacity up to 9.6Tbps in C band, which can greatly enhance utilization efficiency of fiber, reducing wiring construction cost. The non-electricity relay transmission distance is more than 3000 km, which means more flexible network deployment
Since there is no need to care about CD and PMD of optical path, the cost of Dispersion Compensation Fibers (DCF) and extra power compensation amplifiers can be saved. The decreasing of the nonlinear noise means better transmission performance or longer transmission distance. What’s more, the simplified line path means decreased fault probability, and the dismissed DCF means lower propagation delay.
The goal of high-speed data rate beyond 100G is to further improve the capacity of the limitedly available bandwidth of the fiber. The key is to improve the spectrum efficiency with advanced modulation format and to improve utilization efficiency with advanced frequency multiplexing technique. It is generally recognized that 400Gbps is more practicable than 1Tbps.
Without doubt, the 400G DWDM system will carry forward the key idea of 100G to enhance spectrum efficiency with advanced modulation format, to increase receiver sensitivity and equalization capability with digital coherent detection. Moreover, multicarrier technology would be adopted to lower the bandwidth requirement of electro-optic devices.
In fact, there is always a tradeoff between transmission capacity and distance for a noise limited channel. When the channel data rate is increased to 100Gbps, the nonlinearity of the fiber, instead of dispersion, become the main distortion which limit the transmission performance.
Since the generation of fiber nonlinearity is complex and influenced by many random factors, the effective equalization mechanism is still under development. The conflict of the transport capacity and distance of 400Gbps is more noticeable due to the nonlinearity of the fiber.
With higher order QAM modulation, such as 16QAM and 64QAM, the transmission capacity and spectrum efficiency can be improved, but the transmission distance would decrease exponentially, which is not feasible for long-distance optical transmission.