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Fiber Connectors

Fiber optic connectors—including the LC, ST, and SC types—require extremely precise alignment to function correctly, making them far less forgiving than standard copper Ethernet connectors.

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About this video

Fiber optic infrastructure depends on a set of standardized connector types, each designed for specific equipment and deployment scenarios. The three most commonly encountered are the LC (Lucent Connector), a compact form-factor connector widely used in high-density environments; the ST (Straight Tip), a bayonet-style connector common in older enterprise and campus installations; and the SC (Subscriber Connector), a push-pull design frequently found in telecommunications and data center environments. Connectors are also classified as simplex, carrying a single fiber, or duplex, bundling two fibers into one housing to support simultaneous send and receive paths. Precision is the defining challenge of fiber optic connectivity. Because light must travel through a glass or plastic core measured in microns, even minor misalignment at a connection point will degrade or completely block signal transmission. This makes fiber connector tolerances significantly tighter than those of copper Ethernet terminations. Two polishing standards address how mating end-faces make contact: UPC (Ultra Physical Contact) uses a perpendicular polish for a direct flat-to-flat connection, while APC (Angled Physical Contact) uses an eight-degree angle to minimize back-reflection and insertion loss. Because of these precision requirements, fiber connectors are typically factory-terminated or installed by trained technicians rather than field-fabricated, in sharp contrast to the DIY approach common with copper RJ45 terminations.

What you'll learn

What's covered

Fiber Optic Connectors

Aligned to

CompTIA Network+
1.5 Compare and contrast transmission media and transceivers.
CompTIA A+ Core 1
3.1 Explain basic cable types and their connectors, features, and purposes.
Cisco CCNA
1.3 Compare physical interface and cabling types
Cisco CCST Networking
3.1 Identify cables and connectors commonly used in local area networks

Key terms

Local Connector
LC
A small form-factor fiber optic connector with a push-pull latching mechanism, widely used in SFP transceivers, patch panels, and high-density fiber installations. LC connectors have largely replaced SC connectors in modern data center and enterprise network cabling.
ST Connector
ST
The Straight Tip connector, a fiber optic connector that uses a bayonet-style twist-lock mechanism to secure the connection.
Subscriber Connector
SC
A push-pull fiber optic connector with a square form factor commonly used in single-mode and multimode fiber network installations. SC connectors are widely used in telecommunications and campus backbone cabling, though they have been largely replaced by LC connectors in high-density applications.
Simplex
A fiber optic cable or connector configuration that uses a single fiber strand to carry one-directional signal.
Duplex
A fiber optic cable or connector configuration that uses two fiber strands, typically to support simultaneous transmission and reception.
Ultra Physical Contact
UPC
A fiber optic connector polishing standard where the end-faces are polished flat and mated straight on to minimize signal loss.
Angled Physical Contact
APC
A fiber optic connector polishing standard where the end-faces are polished at an angle, reducing back-reflection and signal loss compared to UPC.

Transcript

There are a lot of different types of connectors for fiber optics. We're just going to cover a few of the more common ones.

Common fiber connectors

As you can see here, we've got the LC connector right here. This is the Lucent connector, or LC. We've got the straight tip connector, or ST. And then we've got the SC connector, or the subscriber connector. I've got the most experience with this and have seen most of it on the equipment that I've worked with out in the field.

You'll also see a simplex versus duplex. The simplex is just one of these connectors to connect in, and the duplex is two of those connectors. So those are the different types of connectors that you'll see out there.

Why connectors are tricky

Connectors are tricky because, as they come together, they have to come together exactly. It's got to be precise where it comes together. If it's off at all, that connectivity is not going to work right, and so you have to bring them together exactly right. The tolerances of this are even more so than, like, our Ethernet copper connectors.

If you've got two connectors that are coming together, let's say this is one line connecting to another line, we've got the outer jacket here that can't be off. So we've got a couple of different ways that we can do that. This is called a UPC, or ultra physical contact. And then we also have a slanted one as well that will come together at a slant, and this is called an angled physical contact. So we've got different types of ways even in how those contact. But the big key here is, once again, they have to come up exactly right.

There's a lot of people that will do their own Ethernet copper cables and put RJ45s on the ends of their cables, but you really don't see as many people making their own fiber connectors, because it's very precise.

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