Fibre optic links fail at the connector more often than in the cable. Choosing the right connector type, and the right polish, is a matter of the equipment on each end, the fibre count and the environment. This chart compares the connector families most often met in Indian telecom, campus and data centre work.
Connector family chart
| Connector | Ferrule size | Coupling | Fibres per connector | Typical use |
|---|---|---|---|---|
| SC | 2.5 mm | Push-pull snap | 1 (duplex clips available) | Telecom patch panels, FTTH and PON equipment, enterprise backbones |
| LC | 1.25 mm | Push-pull latch | 1 (duplex clips common) | Data centre switches, SFP transceivers, high-density panels |
| ST | 2.5 mm | Bayonet twist | 1 | Older multimode campus and industrial installations |
| FC | 2.5 mm | Screw thread | 1 | Test equipment, laboratories, vibration-prone single-mode links |
| MPO | Multi-fibre ferrule | Push-pull, with alignment pins | 12 or 24 (higher counts exist) | Parallel optics, trunk cabling and ribbon cable terminations |
Polish types
The polish describes the shape of the fibre end face. It affects back reflection, which matters on single-mode links.
| Polish | End face | Housing colour (usual) | Where it is used |
|---|---|---|---|
| PC and UPC | Slightly domed, centred | Blue for UPC | General single-mode and multimode links |
| APC | Domed and cut at an angle of 8 degrees | Green | FTTH, PON and any link sensitive to reflection |
APC and UPC connectors must never be mated together. The angled and flat faces do not align, and the result is high loss and possible damage to both end faces. The housing colour is a convention, not a safeguard, so check the marking before connecting.
How to choose
- Match the equipment first. Transceivers and patch panels fix the connector type on most links. Matching the existing standard avoids adapters and extra loss.
- Use APC where reflection matters. PON networks and analogue video overlays are typical cases.
- Use LC or MPO where density matters. Both fit more fibres in the same panel space than SC.
- Keep single-mode and multimode apart. The same connector body is used for both, so label the patch cords and the panels clearly.
- Clean before every mating. A dirty end face is the commonest cause of high loss.
Connectors and the loss budget
Every mated connector pair adds loss to the link, and the loss figure used in the budget should come from the connector maker’s datasheet. The fibre optic link loss budget guide shows how to add connector, splice and cable loss together. To pick the cable itself, see the fibre optic cable selection guide, and for the fibre types APAR supplies see single-mode and multi-mode fibre.