CWDM modules offer medium-range, cost-efficient 100G transmission over single-mode fiber, bridging the gap between short-range multimode and long-range single-mode solutions.

Overview of Fiber Types

• Single-Mode Fiber (SMF): Uses a ~9 µm core, ideal for long-distance transmission (up to 10 km or more). Supports high-speed modules above 25G efficiently, with low insertion loss and minimal modal dispersion .
• Multi-Mode Fiber (MMF): Uses ~50 µm cores, optimized for short distances (typically ≤ 500 m for 100G). Cost-effective for intra-rack or intra-building connections but suffers from signal degradation at higher speeds .
• CWDM Modules: Operate over single-mode fiber using coarse wavelength division multiplexing to transmit multiple 25G lanes on a single fiber pair, achieving medium distances (~2 km) efficiently .

100G Optical Module Comparison

Key Performance Considerations

• Distance vs. Cost: MMF is cheapest but limited in reach. PSM4 is low-cost for very short distances but consumes more fibers. CWDM4 balances cost and medium-range reach by using wavelength multiplexing on fewer fibers. LR4 is the most expensive but supports the longest distances .
• Fiber Efficiency: CWDM4 reduces fiber count (2 fibers) compared to PSM4 (8 fibers), making it more scalable for data center interconnects .
• Power Consumption: CWDM4 modules typically consume less power than LR4 due to simpler DML lasers, while LR4's EML lasers are more power-hungry .
• Scalability and Upgrade Path: CWDM4 allows easier migration from 25G/40G to 100G over existing single-mode fiber infrastructure, whereas MMF may require fiber replacement for higher speeds .
• Operational Complexity: CWDM introduces wavelength management and potential O&M overhead, while PSM4's parallel lanes are simpler to deploy but bulkier in cabling .

Summary

• Multi-Mode SFPs: Best for short, cost-sensitive intra-building links; limited for high-speed 100G deployments.
• Single-Mode SFPs: Future-proof, long-distance, suitable for metro and inter-data center links.
• CWDM4 Modules: Optimal for medium-range 100G links (~2 km), conserving fiber, balancing cost, power, and scalability.
• PSM4 Modules: Ideal for ultra-short, high-density connections where fiber count is less critical.
• LR4 Modules: Preferred for long-haul 100G links requiring maximum reach and reliability. Choosing the right module depends on distance requirements, fiber availability, cost constraints, and future scalability. CWDM4 provides a versatile middle ground between short-range multimode and long-range single-mode solutions, making it increasingly popular in modern data center interconnects .