Multimode fiber typically operates at 850 nm and 1300 nm, while single-mode fiber operates at 1310 nm and 1550 nm, with additional wavelengths used for WDM applications.

Multimode Fiber (MMF) Wavelengths

Multimode fibers have larger cores (50–62.5 µm) and support multiple light modes, which limits their transmission distance due to modal dispersion. They are optimized for short-range applications, such as data centers and LANs. The most common operating wavelengths for multimode fiber are 850 nm and 1300 nm, using LEDs or VCSELs as light sources .

• 850 nm: Ideal for short distances, low-cost LEDs, and VCSELs.
• 1300 nm: Lower attenuation than 850 nm, suitable for medium-range connections.
• OM5 fibers: Support SWDM (Short Wavelength Division Multiplexing) in the 850–950 nm range, but adoption is limited and mostly legacy .

Single-Mode Fiber (SMF) Wavelengths

Single-mode fibers have a small core (~9 µm) and transmit only one mode of light, minimizing modal dispersion. They are used for long-haul, high-speed networks. Standard wavelengths for single-mode fiber are 1310 nm and 1550 nm .

• 1310 nm: Low chromatic dispersion, suitable for medium distances.
• 1550 nm: Lowest attenuation (~0.2 dB/km), ideal for long-haul and high-bandwidth applications.
• Additional wavelengths: 1490 nm for GPON and 1625 nm for monitoring; WDM systems use ranges from 1260–1670 nm, including C-band (1530–1565 nm) for DWDM .

Wavelength Division Multiplexing (WDM)

Single-mode fiber is preferred for WDM because its small core ensures minimal crosstalk between wavelengths.

• CWDM (Coarse WDM): Uses 8–16 wavelengths (1270–1610 nm) for enterprise networks.
• DWDM (Dense WDM): Uses 40–160 closely spaced wavelengths (1530–1565 nm) for telecom backbones, enabling Tbps data rates . Multimode fiber supports limited WDM, such as SWDM on OM5, but large cores increase wavelength interference, making it less suitable for dense multiplexing .

Summary

• Multimode fiber: 850 nm and 1300 nm, short-range, LED/VCSEL sources.
• Single-mode fiber: 1310 nm and 1550 nm, long-range, laser sources, supports WDM.
• Advanced applications: WDM expands usable wavelengths, primarily on single-mode fiber for high-capacity networks. Choosing the correct fiber type and wavelength is critical for optimizing distance, bandwidth, and cost in modern optical networks .