Fibre — SM vs MM

Two fibres, two uses — and a jacket colour to tell them apart. Single-mode (SM), 9/125 µm core, yellow jacket, has minuscule attenuation and runs to 40+ km, but calls for a laser source at 1310 or 1550 nm. Multi-mode (MM), 50/125 µm core, orange (multi-mode) or aqua (OM3/OM4) jacket, reaches 300 m on OM3 and 400 m on OM4 at 10GBASE-SR, using cheaper 850 nm VCSEL optics. The two are not interoperable: a single-mode transceiver will not establish a link with a multi-mode one.