What is the wavelength of a 40G optical module

40G QSFP+ SR4 modules use 850 nm, while 40G LR4 modules use four CWDM wavelengths: 1271 nm, 1291 nm, 1311 nm, and 1331 nm.

40G QSFP+ SR4 (Short-Reach) Modules

The 40GBASE-SR4 QSFP+ module is designed for short-distance transmission over multimode fiber (MMF). It uses four parallel lanes, each transmitting at a center wavelength of 850 nm. The module supports link lengths of 100 m on OM3 fiber and 150 m on OM4/OM5 fiber. It employs an MPO/MTP 12-fiber connector and is aligned with IEEE 40GBASE-SR4 specifications for high-bandwidth 40G optical links over parallel fiber lanes. SR4 modules are optimized for 40 GbE interfaces and support digital diagnostics monitoring (DDM) for operational parameters (temperature, optical power, etc.), .

40G QSFP+ LR4 (Long-Reach) Modules

The 40GBASE-LR4 QSFP+ module is intended for long-distance transmission up to 10 km over single-mode fiber (SMF). It uses four CWDM (Coarse Wavelength Division Multiplexing) channels, with central wavelengths of 1271 nm, 1291 nm, 1311 nm, and 1331 nm. Each lane carries 10 Gbps, which are multiplexed into a single 40 Gbps optical signal. The module uses duplex LC connectors and is compliant with IEEE 40GBASE-LR4 standards, enabling interoperability across compliant switches and platforms. CWDM technology allows long-distance deployment without increasing fiber count, making LR4 modules suitable for backbone and aggregation networks .

Summary

• SR4 (short-reach, multimode fiber): 4×850 nm, MPO/MTP interface, 100–150 m reach
• LR4 (long-reach, single-mode fiber): 1271 nm, 1291 nm, 1311 nm, 1331 nm, LC duplex interface, up to 10 km reach These wavelength specifications are critical for ensuring fiber compatibility, link distance, and network performance when deploying 40G optical modules.