Fiber doesn’t carry one colour of light — it carries many. Give each channel its own wavelength and a single strand can carry dozens of independent signals at once.
The “colour” of infrared light is its wavelength, measured in nanometres. Fiber’s useful range from about 1260 to 1625 nm is split into bands — O, E, S, C and L. Each band is a stretch of spectrum a system can use, and different bands suit different jobs.
Two wavelengths dominate. Around 1310 nm (O-band) glass has almost no dispersion; around 1550 nm (C-band) it has the lowest loss — and cheap optical amplifiers (EDFAs) work there, which is why long-haul and DWDM live in the C-band.
Wavelength-division multiplexing puts many channels on one fiber, each on its own colour. CWDM spaces them widely (~20 nm) for low cost and a handful of channels. DWDM packs them tightly (0.8 or 0.4 nm) for 40, 96 or more channels — the backbone of high-capacity networks.
~20 nm spacing · up to ~18 channels · low cost
0.8/0.4 nm spacing · 40–96+ channels · dense
The Fiber Optic Lab turns these concepts into hands-on instruments you can practise safely — no fragile fiber, no costly gear. Log in to the suite to try them.
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