The most popular fiber optic connectors, LC / ST / SC / FC

There are various types of fiber optic connectors. This article explains the most common ones (LC, SC, ST, FC) and their key differences, including simplex vs duplex, single mode vs multimode, and APC/PC/UPC types. Fiber optic connectors are critical for fiber cables. They’re categorized by factors like usage, fiber count, fiber mode, and polishing type.

1. Common Connectors

These connectors usually need an adapter panel and are used in data centers, telecom rooms, and enterprise networks.

• LC Connector: A small form factor (SFF) connector with a 1.25mm ferrule. Its compact design works well for high-density setups, making it the most widely used connector today.
• SC Connector: A push-pull snap-in connector with a square body and 2.5mm ferrule. It’s common for datacoms, telecoms, and passive optical networks, and ranks second for polarization maintaining applications.
• ST Connector: A bayonet-mount connector with a 2.5mm ceramic ferrule. It’s used for campus/building multimode networks, corporate systems, and military applications.
• FC Connector: A screw-type connector with a ceramic ferrule and metal body. It’s precise (ideal for OTDRs) but less common now, as SC/LC connectors have replaced it in most cases.
  
  

VOSCOM's fiber optic extenders usually support LC, FC, ST, SC optical connectors, Customers can choose the corresponding fiber optic interfaces according to different application scenarios.
For example, our balanced audio over fiber extender use SFP modules and thus support LC (connectors), while our contact closure over fiber, 3G-SDI fiber Extender series use built-in fiber optic modules can support LC, ST, FC connectors.

2. Simplex vs Duplex Connectors

• Simplex: For one-way signal transmission. Uses 1 fiber strand—signals go from Device A to B but not back.
• Duplex: For two-way transmission. Uses 2 fiber strands to send signals between devices in both directions.
  
  

3. Single Mode vs Multimode Connectors

• Single Mode Fiber: Carries only one light mode at a time.
• Multimode Fiber: Carries multiple light modes at once.
  
  

Most modern connectors (LC, SC, FC) work with both fiber types.

4. APC/PC/UPC Connectors (By Polishing Type)
They differ in color coding and performance (insertion loss, return loss):

• PC: Black color.
• UPC: Blue color.
• APC: Green color.