Hardware · Cabling · Networking
Wavelength
Wavelength is the physical distance between two peaks of a wave. In networking, it refers to the wavelength of light used in fiber optic transceivers — different wavelengths travel different distances and enable WDM (multiple channels on one fiber).
Wavelength and frequency are inversely related: longer wavelength = lower frequency, shorter wavelength = higher frequency. In fiber optics, wavelength (measured in nanometers) determines how far light travels in glass before attenuating and what transceiver types are compatible.
Common fiber wavelengths
850nm (multimode) — short-range, used with VCSEL lasers in SFP+ and QSFP transceivers for data center connections up to ~300m. The most common wavelength for short inter-rack fiber.
1310nm (single-mode) — mid-range, used for campus and metro connections from hundreds of meters to ~10km.
1550nm (single-mode) — long-range, lowest attenuation in standard single-mode fiber, used for distances from 10km to 100km+.
WDM — Wavelength Division Multiplexing
Multiple wavelengths of light can travel simultaneously in a single fiber without interfering, because the wavelengths don't interact. WDM systems combine multiple wavelengths (channels) onto a single fiber pair at the transmit end and separate them at the receive end.
CWDM (Coarse WDM) — up to 18 channels spaced 20nm apart. Lower cost, shorter distances. Common for campus and metro.
DWDM (Dense WDM) — 40-96 or more channels spaced 0.8nm apart. Used for long-haul backbone and dark fiber capacity maximization — a single fiber pair can carry 400Gbps or more using DWDM.