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With the continuous growth in bandwidth demands from data center interconnects and 5G bearer networks, 400G Dense Wavelength Division Multiplexing systems have become core technologies in modern optical communication networks. This report systematically analyzes the key technical characteristics and main challenges of C-band transmission in 400G DWDM systems.
I. Technical Significance of C-band in 400G DWDM Systems
The C-band (1525-1565 nm) serves as the primary operating window for DWDM systems due to its low transmission loss characteristics in single-mode fiber. In 400G transmission scenarios, the C-band provides approximately 4 THz of available spectrum resources, laying the foundation for high-speed signal transmission.
II. Comparative Analysis of Key Technical Characteristics
Depending on system configuration, C-band transmission exhibits the following characteristics:
| System Configuration | Traditional C-band | Extended C-band |
| Channel Capacity | 80-96 channels | Up to 120 channels |
| Spectral Range | ~4 THz | Up to 6 THz |
| Typical Applications | Metro networks | Long-haul & submarine |
III. Analysis of Core Technical Challenges
1.Transmission Performance Challenges
●Nonlinear Effects: Kerr effect and other nonlinear impairments significantly intensify under 400G high-speed transmission
●Dispersion Management: More precise dispersion compensation schemes are required
●Signal-to-Noise Ratio Requirements: Approximately 6 dB higher compared to 100G systems
2.Key Device Challenges
●Optical Amplifiers: Extended C-band imposes higher requirements on EDFA gain flatness
●Wavelength Selective Switches: Need to support broader spectrum and finer grid adjustment
●Modulation Devices: Must support more complex modulation formats and higher bandwidth
3.System Design Challenges
●Fiber Selection: G.654.E ultra-low loss fiber becomes the preferred choice for long-distance transmission
●Power Budget: Requires precise balancing of input power for each channel
●Operational Complexity: Increased difficulty in fault localization and performance monitoring
IV. Technology Development Trends
1.Band Expansion Technology
●Evolution from traditional C-band to extended C-band
●Gradual maturation of C+L band combined transmission solutions
●Continuous optimization of spectrum utilization efficiency
2.Advanced Modulation Technologies
●Probabilistic Constellation Shaping enhances system flexibility
●Coherent reception technology becomes standard for 400G systems
●Continuous optimization of digital signal processing algorithms
3.Standardization Progress
●YD/T 3964-2021 regulates metropolitan application scenarios
●YD/T 6437-2025 supports ultra-long distance transmission
●IEEE 802.3cw defines interconnection interface standards
V. Conclusion and Outlook
C-band transmission technology serves as the critical foundation for the commercial deployment of 400G DWDM systems. By continuously optimizing optical device performance, improving system design solutions, and advancing standardization processes, current technical challenges can be effectively addressed. Looking forward, as higher-rate technologies such as 800G/1.6T evolve, C-band and its extension technologies will continue to play vital roles, providing reliable support for enhancing optical network capacity
