Optical modules DR4 and SR4

SR4 modules are short-reach, multimode solutions for intra-data center links, while DR4 modules are single-mode, medium-reach solutions for inter-data center connections up to 500 meters.Overview

SR4 (Short Reach, 4 lanes) is designed for short distances, typically within a single rack or between racks in a data center. It uses multimode fiber (MMF), commonly OM3 or OM4, and transmits data over four parallel optical channels, each at 100Gbps, achieving a total of 400Gbps using PAM4 modulation. The typical reach is 30 meters on OM3 and 50 meters on OM4, with some OM5 deployments extending up to 150 meters. SR4 modules use MPO-12 APC connectors and are optimized for high-density, cost-effective deployments with low power consumption (around 4–5W per module) ( ). DR4 (Datacenter Reach, 4 lanes) is intended for medium-short distances, up to 500 meters, using single-mode fiber (SMF, OS2). Like SR4, it uses four optical channels at 100Gbps each with PAM4 modulation, but it employs DFB lasers instead of VCSELs. DR4 is suitable for inter-rack or inter-room connections within a data center, bridging dense fabrics to aggregation or spine switches. It also uses MPO-12 APC connectors for parallel single-mode transmission ( ).

Key DifferencesFeatureSR4DR4Fiber TypeMultimode (OM3/OM4/OM5)Single-mode (OS2)Maximum Distance30–50 m (OM3/OM4), up to 150 m (OM5)500 mLaser TypeVCSELDFBConnectorMPO-12 APCMPO-12 APCTypical UseIntra-rack or intra-data centerInter-rack or inter-room within data centerPower Consumption4–5 WSlightly higher than SR4CostLowerHigher due to single-mode opticsApplications

• SR4: Ideal for short, high-density connections inside racks or between adjacent racks, where cost and low power are priorities. Common in AI clusters, high-performance computing, and dense data center fabrics ( ).
• DR4: Suitable for longer intra-data center links, such as connecting aggregation switches or spine layers, where single-mode fiber is preferred for future-proofing and longer reach ( ).

Deployment Considerations

• Fiber Compatibility: SR4 requires multimode fiber; DR4 requires single-mode fiber. Using the wrong fiber type can limit reach or cause signal degradation.
• Connector Type: Both use MPO-12 APC for 400G parallel optics. Ensure patch panels and cabling support this standard.
• Power and Thermal Design: SR4 modules have lower power consumption, which is important when populating high-density switches.
• Cost vs Reach: SR4 is cheaper but limited in distance; DR4 costs more but supports longer links without re-cabling. In summary, choose SR4 for short, cost-sensitive, high-density intra-data center links, and DR4 for longer intra-data center or inter-room connections where single-mode fiber is available and future scalability is needed ( ).