UPC and APC connectors compared
UPC and APC are the two polishes used on single-mode connectors. Apart from the colour they look alike, but an APC connector must never be mated with a UPC one.
The difference at the end-face
A UPC connector is polished with a slight dome, so the two fibers touch head-on. An APC connector is polished at an 8° angle, so light reflected at the joint is sent into the cladding instead of back down the fiber. That gives APC a better return loss.
| Property | UPC | APC |
|---|---|---|
| End-face | 0°, domed | 8°, angled |
| Return loss usually specified | ≥ 50 dB | ≥ 60 dB |
| Connector colour | Blue | Green |
| Typical use | Ethernet and telecom equipment, data centres | FTTH and PON, RF video |
Where each is used
UPC is the usual choice on switches, routers and telecom equipment, where the transceivers tolerate some reflection. APC is the standard in FTTH and PON networks and for RF video over fiber, where reflections cause problems.
Never mate APC with UPC
An angled end-face pressed against a flat one leaves a gap and an offset between the fiber cores. The joint has high loss and the end-faces can be damaged. The colours exist to prevent this: green goes with green, blue with blue. Where APC equipment has to connect to UPC equipment, use a hybrid cord with APC at one end and UPC at the other.
What about PC?
Multimode connectors use PC polish. APC on multimode is uncommon, so check the equipment ports before ordering it.
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