If you've ever looked at a fiber optic patch cable or worked with networking equipment that uses fiber, you've probably noticed there are several different connector types — and they're not interchangeable. Plugging an SC connector into an LC port doesn't work. Even worse, mixing single-mode and multimode fiber types can damage equipment.
Here's a complete guide to fiber optic connectors: what each one looks like, where they're used, and how to choose the right one.
Why so many connector types?
Fiber optic technology evolved over decades, with different manufacturers and applications creating different connectors optimized for specific needs. Some prioritized:
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Density — fitting more connections in less space (LC, MTP)
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Reliability — secure locking mechanisms (ST, FC)
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Ease of use — push-pull simplicity (SC, LC)
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Multi-fiber connections — bundling many fibers in one connector (MTP/MPO)
The result: about 100+ different fiber connector types have existed historically, but only 5-6 are commonly used today.
The main connectors
LC Connector — The Modern Standard
The most common fiber connector in 2026.
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Size: Small Form Factor (about half the size of SC)
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Design: Push-pull with latching tab (like RJ45 Ethernet)
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Locking: Plastic clip that snaps into the port
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Duplex configurations: Usually paired (two LC connectors joined side by side for send/receive)
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Color coding: Blue (single-mode UPC), Green (single-mode APC), Beige/aqua (multimode)
Where you'll find it:
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Data center server-to-switch fiber connections
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SFP transceiver modules (almost all SFP/SFP+ optics use LC)
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Modern enterprise patch panels
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Fiber to the desk in offices
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10G/25G/40G/100G Ethernet
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Cisco, Juniper, Arista equipment
Why it won: The LC's small size doubled the port density compared to SC. A 48-port LC patch panel takes the same space as a 24-port SC panel. As data centers grew, this density became essential.
SC Connector — The Telecom Veteran
A larger square-shaped connector that was the standard before LC took over.
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Size: Larger than LC (about 9mm × 9mm)
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Design: Push-pull with no twist required
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Locking: Snap-in design holds firmly
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Duplex configurations: Usually paired with a clip
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Color coding: Blue (single-mode UPC), Green (single-mode APC), Beige (multimode)
Where you'll find it:
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Telecom installations (still very common at telecom service entry points)
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FTTH (Fiber To The Home) installations
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Older enterprise installations
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Some industrial applications
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Cable TV networks
Why it's still around: SC connectors are very reliable, easy to install (no specific orientation needed), and were the established standard for fiber-to-the-home. Many ISPs still ship modems and routers with SC connections.
ST Connector — The Old-School Bayonet
A round connector with a bayonet-style twist-lock mechanism.
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Size: Round, about 9mm diameter
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Design: Insert and twist 1/4 turn to lock
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Locking: Bayonet mount (similar to BNC for coax)
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Use: Single fiber per connector
Where you'll find it:
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Older multimode fiber installations (pre-2010)
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Industrial environments where vibration could loosen push-pull connectors
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Some legacy security camera systems
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Military and aerospace applications
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Older Ethernet equipment
Why it's declining: ST connectors require physical twisting to install, making them slow for high-density installations. The bayonet mechanism is reliable but bulky compared to LC.
You'll still encounter ST in older buildings being renovated. Adapter patch cables (ST to LC, ST to SC) are widely available to bridge old and new equipment.
FC Connector — Threaded Industrial
A threaded screw-on connector used in specific applications.
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Size: Round with threaded outer shell
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Design: Screw-on connection
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Locking: Threading provides positive lock (similar to F-type coaxial)
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Use: Single fiber
Where you'll find it:
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Test equipment (oscilloscopes, optical power meters)
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High-vibration industrial environments
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Some military applications
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Scientific instruments
The threaded design provides excellent stability but is slow to connect. Mostly seen in specialty applications where the connector might be exposed to significant vibration or where precision is critical (test labs).
MTP/MPO Connector — The Multi-Fiber Powerhouse
A larger connector containing 8, 12, 24, or even 72 fibers in one connector.
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Size: About 12mm × 6mm
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Design: Push-pull with key for orientation
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Locking: Spring-loaded latch
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Fiber count: 8, 12, 24, 32, 48, 72 per connector
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Color coding: Same as other fiber types based on fiber
Where you'll find it:
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Data center backbone connections
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40G QSFP+ optics (typically 12-fiber MTP)
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100G QSFP28 optics (12-fiber MTP for SR4)
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200G/400G QSFP-DD optics (16/24-fiber MTP)
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High-density data center patch panels
MTP vs MPO terminology: MTP is a brand name from US Conec; MPO ("Multi-fiber Push-On") is the generic name. MTP connectors are physically compatible with MPO connectors, but MTP is generally considered higher quality. In practice, they're used interchangeably.
Why it matters: With a single MPO connector, you can deliver 4 × 25G or 4 × 100G connections to a single 100G or 400G transceiver. This is essential for the bandwidth and density needs of modern data centers.
UPC vs APC polish
Beyond connector type, fiber connectors come in two polish styles that affect performance:
UPC (Ultra Physical Contact) — Domed end face polished flat. Used for most data center and enterprise applications. Color: Blue.
APC (Angled Physical Contact) — End face polished at an 8-degree angle. The angle reflects any returning light away from the fiber, dramatically reducing back-reflection. Color: Green.
Where you use which:
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UPC: Standard Ethernet, data center, enterprise networking
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APC: PON (Passive Optical Network) for fiber-to-the-home, telecom long-haul, RF over fiber, any application sensitive to back-reflection
Critical: Don't mix UPC and APC. Plugging a UPC into an APC port (or vice versa) doesn't damage the connector but causes high signal loss and can damage the polished end faces.
Single-mode vs Multimode
Underneath the connectors, the fiber itself is either:
Single-mode (OS1, OS2) — Yellow jacket. Tiny 9 μm core. Used for long distances (up to 80+ km with appropriate transceivers). Telecom, ISP last-mile, building-to-building campus.
Multimode (OM1, OM2, OM3, OM4, OM5) — Orange (OM1/OM2), Aqua (OM3/OM4), Lime green (OM5). Larger 50 or 62.5 μm core. Used for shorter distances (typically 100m to 550m). Data center, in-building, server-to-switch.
The connector type and the fiber type are independent specifications. You can have LC connectors on single-mode or multimode fiber. But ALL ENDS OF A LINK must match — if one end is single-mode, the other end must be single-mode too.
Common configurations
Data center server-to-switch (10G/25G):
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LC duplex connectors
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OM4 multimode fiber
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300m maximum distance
Data center spine connections (100G/400G):
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MTP/MPO connectors (12 or 24 fiber)
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OM4 multimode fiber
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Up to ~150m for 100G SR4
Building-to-building (1G/10G):
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LC connectors
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OS2 single-mode fiber
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Up to 10km for 1310nm optics
Fiber to the home (FTTH):
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SC or LC connectors (depends on ISP)
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OS2 single-mode fiber
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Green APC polish (required for PON technology)
Telecom carrier handoff:
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SC or LC connectors
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OS2 single-mode fiber
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Usually APC polish for distribution
Adapter cables
Mixing connector types is solved with hybrid adapter cables — for example, LC to SC hybrid patch cables that have an LC connector on one end and an SC connector on the other.
These let you connect new LC-equipped equipment to legacy SC infrastructure without rewiring. Available in single-mode and multimode versions.
Buying tips
For new installations, default to LC connectors with multimode OM4 (for short distances) or single-mode OS2 (for long distances). LC is the modern standard and will remain so for the foreseeable future.
For legacy upgrades, identify what's already installed and either match it (to avoid full recabling) or buy hybrid adapters (to bridge old and new). Many buildings still have a mix of SC and LC, with adapters everywhere.
For data centers building 100G+ infrastructure, plan for MTP/MPO from the start. The density and bandwidth requirements of modern data centers essentially require it.
At Kentek, we carry fiber optic patch cables in LC, SC, ST, and MTP configurations, in single-mode (OS2) and multimode (OM3, OM4) options, including hybrid adapter cables for connecting legacy and modern equipment.
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