The basic difference
Singlemode fiber has a very small core and carries light over long distances — building-to-building and campus or outside-plant runs. Multimode fiber has a larger core and is typically used for shorter runs inside buildings and data rooms.
Identify it by jacket color
| Type | Core / cladding | Common jacket color |
|---|---|---|
| OS2 singlemode | 9/125 µm | Yellow |
| OM1 multimode | 62.5/125 µm | Orange |
| OM2 multimode | 50/125 µm | Orange |
| OM3 multimode | 50/125 µm | Aqua |
| OM4 multimode | 50/125 µm | Aqua (sometimes violet) |
| OM5 multimode | 50/125 µm | Lime green |
Connectors and polish
- LC is the most common small-form connector today; SC and ST are still found in many existing installs; MPO/MTP is used for high-density trunks.
- Blue connector bodies usually indicate UPC polish; green indicates APC (angled) polish. Never mate APC with UPC.
- Keep everything in a link the same type — don’t mix singlemode and multimode, or 50 µm and 62.5 µm multimode.
- Clean every end face before you connect it. Dirty connectors are one of the most common causes of fiber link problems.
General guidance only — always follow project specifications, manufacturer instructions and local code.