Fiber Connector Types — LC to MPO
The connector families in the field, decoded: ferrule size and latch mechanics (the two things that actually distinguish them), where each connector lives today, the body colors that encode fiber type and polish, and the UPC/APC rules. Connector mechanics are hardware facts; body colors follow TIA-598; return-loss figures are typical published specs.
Connector families
| Connector | Ferrule | Latch | Where it lives today |
|---|---|---|---|
| LC | 1.25 mm | Push-latch (RJ45-style tab) | The dominant connector — SFP/QSFP transceivers, high-density panels |
| SC | 2.5 mm | Push-pull snap ("stick and click") | FTTH drops and ONTs, older patch panels |
| ST | 2.5 mm | Bayonet twist-lock | Legacy premises/campus multimode |
| FC | 2.5 mm | Threaded screw-on | Test equipment and legacy telco single-mode |
| MPO / MTP | Rectangular multi-fiber (12/24-fiber rows) | Push-on / pull-off | Parallel optics (40/100/400G), pre-terminated trunks and cassettes |
| LC uniboot | 2 × 1.25 mm, one boot | Push-latch | High-density data centers — twin-fiber cable halves pathway bulk |
Body colors
| Body color | Meaning |
|---|---|
| Blue | Single-mode UPC |
| Green | Single-mode APC |
| Beige (or black) | Legacy multimode OM1/OM2 |
| Aqua | Laser-optimized multimode OM3/OM4 |
| Lime | Wideband multimode OM5 |
The one rule that costs money: green never mates blue
Every other mismatch on this page is an adapter problem; APC-to-UPC is a damage problem. The 8° ferrule contacts the dome at its edge — one mating can scar both endfaces, and the link limps with high loss until both sides are re-terminated. Where APC rules (ftth/pon, rf-over-glass and analog catv, das, reflection-sensitive systems), keep green-bodied jumpers on the truck and inspect before every mating. For which fiber the connector terminates in the first place, see the color code chart and the multimode vs singlemode comparison; for MPO trunk gender and polarity, the MPO polarity reference.
Common questions
What is the difference between LC and SC connectors?
Size and grip: LC uses a 1.25 mm ferrule with an RJ45-style push-latch and packs two fibers where one SC fits; SC uses a 2.5 mm ferrule with a push-pull snap body. LC won the density war — transceivers standardized on LC duplex — while SC survives at FTTH drops and on older panels. Adapters and hybrid cords bridge the two without splicing.
What is the difference between UPC and APC connectors?
Endface geometry. UPC (blue) is dome-polished flat-on; light reflecting at the interface travels straight back up the fiber (return loss ≈ 50 dB). APC (green) is polished at an 8° angle so reflections leave the core (≈ 60–65 dB). Insertion loss is comparable. APC is required where reflections wreck the signal: PON/FTTH, RF-over-glass and analog CATV, DAS.
Can you plug an APC connector into a UPC port?
No — never. The 8° angled ferrule meets the flat dome at the corner, producing severe loss and permanent physical damage to both endfaces. The color code exists exactly for this: green never mates to blue. In practice this bites at ISP hand-offs — a GPON ONT expecting green APC fed with a blue UPC jumper.
Is APC available for multimode fiber?
In practice, no — APC is a single-mode connector. Multimode systems tolerate reflections far better (and their VCSEL sources are less bothered), so no manufacturer offers multimode APC as a standard product. If a spec calls for "OM4 APC," query it.
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