Singlemode fiber cables are typically rated for between 1 and 10 Gigabits per second over these incredible lengths. Since they're designed with outdoor use in mind, and to ensure no problems arise over that expansive length, OS2 singlemode fiber cables are also built with a unique. OS1 single mode fiber optic cables are made with a single mode fiber core, which means that they have a very small core diameter of 9 microns. This guide breaks down their technical differences, performance. Single mode fiber has a very narrow core (around 8–10 microns in diameter), so it only allows one light signal (or "mode") to pass through at a time.