The first is a relatively simple method for indoor optical fiber, through single-mode fiber and multimode fiber to identify the external color, single-mode optical fiber / cable is yellow, and red multi-mode. Including fiber optic patch cords and pigtails are the same identification method.
For outdoor fiber / cable, can generally be identified by model code, in the cable jacket on a string of characters, such as GYXTW-4-A1a, the last paragraph beginning with A on behalf of a multi-mode fiber, the B represents the beginning of a multi-mode fiber, a little more detail, said, A1a specifications on behalf of 50/125 multimode fiber, A1b specifications on behalf of 62.5/125 multimode fiber, B1.1 on behalf of non-dispersion shifted single-mode fiber, and so on.
If this approach can not identify a single-mode fiber or multimode fiber, it is only through a special device to identify, as fiber splicing machine, it will automatically recognize a single mode or multimode, single mode will show SM, multi-mode will show MM.
Of course, speaking from the other hand, single-mode fiber core diameter typically 50μm or 62.5μm, while the single-mode fiber generally only 8.3μm, this point of view the difference is quite large, but the naked eye it still has some difficulty . Note: μm for the micron code, 1μm = 1 / 1000 mm.