Ethernet optical modules typically operate at wavelengths of 850 nm, 1310 nm, or 1550 nm, depending on the module type and fiber used.

Common Wavelengths by Module Type

• Short-Range (SR) Modules: Usually operate at 850 nm over multimode fiber (MMF), suitable for distances up to a few hundred meters .
• Long-Range (LR) Modules: Typically use 1310 nm over single-mode fiber (SMF), supporting distances up to 10 km or more .
• Extended Long-Range (ER) or Ultra Long-Range Modules: Often operate at 1550 nm, optimized for distances beyond 40 km .
• Wavelength Division Multiplexing (WDM) Modules: Use multiple distinct wavelengths within the same fiber. Coarse WDM (CWDM) modules have center wavelengths spaced 20 nm apart, while Dense WDM (DWDM) modules use much narrower spacing, often in the 1525–1565 nm range .

Example: QSFP28 Optical Modules

• QSFP28 SR4: Center wavelengths per lane are around 840–860 nm for short-range multimode fiber .
• QSFP28 LR4: Center wavelengths per lane are in the 1294–1310 nm range for single-mode fiber, supporting up to 10 km .

Technical Notes

• The wavelength is the optical carrier frequency used to transmit data as light pulses, with “on” representing a 1 and “off” representing a 0 .
• Selection of wavelength depends on fiber type, link distance, and network standard (e.g., 10GBASE-SR, 10GBASE-LR, 100GBASE-SR4, 100GBASE-LR4).
• Using the correct wavelength ensures signal integrity, minimal dispersion, and compatibility with existing fiber infrastructure . In summary, Ethernet optical modules operate primarily at 850 nm, 1310 nm, or 1550 nm, with WDM modules using multiple wavelengths within these bands to maximize fiber utilization. The exact wavelength depends on the module type, fiber type, and intended transmission distance.