Fibre Optic Connector Types LC vs SC, APC vs UPC, Single Mode vs Multimode
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Most fibre faults on new installations come down to a mismatch: an APC cord in a UPC port, multimode optics on single mode fibre, or an SC panel where the switch needs LC. This guide explains the main fibre optic connector types, polish types and fibre grades, and how to match them.
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A fibre optic connector terminates the end of a fibre so it can be joined to another fibre or to equipment. A precision ferrule holds the fibre in alignment, and the end face is polished so that light passes across the joint with minimum loss and back reflection. Connectors are defined by their body type (LC, SC, ST, MPO), their polish (UPC or APC) and the fibre they are fitted to.
The Main Fibre Connector Types
| Connector | Ferrule | Coupling | Typical use |
|---|---|---|---|
| LC | 1.25 mm | Push and latch | Data centres, switches, SFP and SFP+ transceivers, high-density patch panels |
| SC | 2.5 mm | Push-pull | Telecoms, FTTx, PON and exchange ODFs |
| ST | 2.5 mm | Bayonet twist | Legacy multimode campus links |
| MPO / MTP® | Multi-fibre (12 or 24) | Push-pull | Pre-terminated trunk cables and 40/100G parallel optics |
LC vs SC: which should you use?
Use LC wherever density matters or the equipment has LC ports, which covers almost all switches and SFP optics. Use SC where the network standard is SC, typically in telecoms, FTTx and PON. An LC duplex adapter takes about the same space as a single SC adapter, which is why high-density panels and switch faceplates use LC.
MPO vs MTP
MPO is the generic multi-fibre push-on connector standard. MTP® is a registered brand of MPO-compatible connector made to tighter tolerances. Both carry 12 or 24 fibres in a single ferrule, which makes them ideal for pre-terminated trunks.
APC vs UPC
UPC (blue)
Ultra Physical Contact. A flat, slightly domed end face. Return loss is typically better than 50 dB. Standard for Ethernet data links, multimode and most data centre single mode.
APC (green)
Angled Physical Contact. Polished at 8°, so reflected light leaves the core. Return loss is typically better than 60 dB. Preferred for PON, FTTx, RF video and long-haul single mode.
Never mate APC with UPC. The angled and flat faces leave an air gap, causing high loss and possible end-face damage. Match the polish across every panel, cord and adapter in the link.
Single Mode vs Multimode Fibre
| Fibre | Core / cladding | Jacket colour | Typical reach | Use |
|---|---|---|---|---|
| OS2 single mode (G.652D) | 9/125 µm | Yellow | Kilometres | Backbones, telecoms, FTTx, inter-building |
| Bend-insensitive single mode (G.657A2) | 9/125 µm | Yellow | Kilometres | Tight trays, patch panels, in-building and FTTH drops |
| OM3 multimode | 50/125 µm | Aqua | 10G to 300 m | Data centre and campus links with 850 nm optics |
| OM4 multimode | 50/125 µm | Aqua or violet | 10G to 400 m | Higher-bandwidth data centre links |
OM3 vs OM4
OM4 has higher modal bandwidth than OM3, so the same 850 nm optics reach further: 10GBASE-SR is specified to 300 m on OM3 and 400 m on OM4. Our 10GBase SFP+ 850 nm and 1000Base SFP 850 nm transceivers are multimode LC duplex optics.
What is G.657A2?
G.657A2 is bend-insensitive single mode fibre. It is backwards compatible with standard G.652D fibre but tolerates much tighter bends without extra loss, which is why many of our patch panel pigtails and fibre trunks use it.
Fibre Adapter and Connector Colour Codes
| Colour | Usually means |
|---|---|
| Blue | Single mode, UPC |
| Green | Single mode, APC |
| Aqua | Multimode OM3 (sometimes OM4) |
| Violet | Multimode OM4 |
| Beige | Multimode OM1 / OM2 |
Colour codes are a convention, not a guarantee. Always confirm the fibre type and polish on the label or datasheet.
How to Match Every Part of a Fibre Link
Start at the optic
The transceiver sets the fibre type, wavelength and connector (usually LC duplex).
Match the fibre
Single mode optics need single mode fibre; 850 nm optics need OM3 or OM4.
Match the polish
UPC or APC throughout, never mixed.
Choose the panel
Pick a fibre patch panel or ODF with matching adapters.
Clean and inspect
Clean every end face before mating; contamination is the top cause of loss.
Test
Measure insertion loss with a light source and power meter and keep the results.
Fibre Connector and Fibre Type FAQs
What is the difference between LC and SC connectors?
Both are push-in fibre connectors. LC has a 1.25 mm ferrule and a latch, half the size of SC, so it gives higher density and is used on SFP transceivers and switches. SC has a 2.5 mm ferrule and a square push-pull body and is common in telecoms and FTTx networks.
What is the difference between APC and UPC?
UPC (Ultra Physical Contact) connectors have a slightly domed, flat-faced polish and are colour-coded blue. APC (Angled Physical Contact) connectors are polished at 8°, are colour-coded green and reflect far less light back down the fibre, which is why they are preferred for PON, FTTx and RF video. They cannot be mated together.
What is the difference between single mode and multimode fibre?
Single mode fibre has a 9 µm core and carries a single path of light, so it supports long distances, from building backbones to tens of kilometres. Multimode fibre has a 50 µm core, is used with lower-cost 850 nm optics and is limited to a few hundred metres at 10G and above.
What is the difference between OM3 and OM4?
Both are 50/125 µm laser-optimised multimode fibres. OM4 has higher bandwidth, so it supports longer links: 10GBASE-SR is specified to 300 m on OM3 and 400 m on OM4. OM3 is usually aqua; OM4 is aqua or violet.
What is OS2 fibre?
OS2 is a low water peak single mode fibre category (typically ITU-T G.652D) for indoor and outdoor use over long distances. Bend-insensitive single mode fibres such as G.657A2 are compatible with G.652D and tolerate much tighter bends.
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