What is a PC connector?
In fiber optics, PC stands for Physical Contact, a way of polishing the end of a connector's ferrule. Early fiber connectors had flat end faces that could leave a tiny air gap between two mated fibers, which caused loss and reflected light back toward the source. A PC polish gives the end face a slight dome, so the fiber cores at the center press together with no air gap.
"PC connector" isn't a connector shape. PC is a polish style, written after the connector type, as in SC/PC, FC/PC or ST/PC.
PC vs. UPC vs. APC
| PC | UPC | APC | |
|---|---|---|---|
| End face | Slightly domed, 0 degrees | Domed, 0 degrees, finer extended polish | Angled 8 degrees |
| Return loss (back reflection) | About -40 dB | About -50 dB | About -60 dB or better |
| Status | Older; largely replaced by UPC | Common for Ethernet and other data links | Common for FTTH/PON and cable TV video |
UPC is a refinement of PC: the same 0-degree domed shape with a finer polish, which cuts back reflection by roughly another 10 dB. APC angles the end face so most reflected light goes into the cladding instead of back down the core. On patch panels, blue usually marks UPC and green marks APC.
Mating rules
- PC and UPC end faces are both 0-degree domes, so they can mate with each other, though the connection is only as good as the PC side.
- Never mate PC or UPC with APC. The angled face doesn't meet a flat one properly, which causes high loss and can damage both end faces.
- Inspect and clean end faces before mating. Dust or oil on the core raises both loss and back reflection, whatever the polish.
For the CompTIA A+ exam
Core 1 (220-1201) objective 3.2 lists the ST, SC and LC fiber connectors. PC, UPC and APC aren't connector types and aren't named in the objectives; they're polish styles applied to connectors like these. If you see SC/PC or LC/UPC, the first part is the connector the exam cares about.