A Practical Guide to Common Fiber Optic Connector Types
In fiber optic communication systems, connectors are critical interfaces that ensure efficient and reliable light signal transmission. Their performance directly impacts insertion loss and return loss. This guide, brought to you by Shenzhen Feiyi Optoelectronics, a professional manufacturer of optical components, introduces the most widely used connector types, categorized by their ferrule design and polish type.
1. Understanding Ferrule Types: SC, LC, ST, FC
The ferrule is the precision tube that holds and aligns the fiber. Its design defines the connector’s physical form and mating mechanism.
- SC (Subscriber Connector):
- Design: A square, snap-in connector with a 2.5mm ceramic ferrule. It offers a simple push-pull latching mechanism.
- Use Case: Historically dominant in datacom and telecom networks. Common in equipment interfaces, patch panels, and single-mode applications.
- LC (Lucent Connector):
- Design: A small form-factor connector with a 1.25mm ceramic ferrule, half the size of SC. It uses a tab-style latch.
- Use Case: The current industry standard for high-density applications. Universally used in SFP/SFP+ transceivers, modern switches, routers, and data centers.
- ST (Straight Tip):
- Design: Features a round, 2.5mm ceramic ferrule and a spring-loaded, bayonet-style “twist-and-lock” coupling mechanism.
- Use Case: Primarily found in legacy multi-mode LAN, CCTV, and security systems. Its use is declining in favor of SC and LC.
- FC (Fiber Connector):
- Design: A round connector with a 2.5mm metal or ceramic ferrule and a threaded nut for secure screw-on mating.
- Use Case: Preferred in high-vibration environments, test and measurement equipment, and high-precision single-mode applications due to its robust physical connection.
2. Understanding Polish Types: PC, UPC, APC
The end-face of the ferrule is polished to an exact shape to minimize back reflection (return loss).
- PC (Physical Contact):
- Finish: A curved, domed surface that forces fibers into physical contact.
- Typical Return Loss: ~40 dB.
- Use Case: The baseline polish, largely superseded by UPC.
- UPC (Ultra Physical Contact):
- Finish: An extended, more refined spherical polish than PC, achieving better surface contact.
- Typical Return Loss: ~50 dB or higher.
- Use Case: The standard for most modern digital systems, including high-speed data, CATV, and telecom.
- APC (Angled Physical Contact):
- Finish: Features an 8-degree angled end-face. This angle reflects any back-reflected light into the cladding, virtually eliminating it.
- Typical Return Loss: ~65 dB or higher (superior to UPC/PC).
- Visual Identifier: Green-colored boot or ferrule.
- Use Case: Mandatory for analog RF/video signals (e.g., FTTx/PON) and any application where back-reflection is critical, such as with high-power lasers or in WDM systems.
3. Connector Type Comparison & Selection Guide
| Connector | Ferrule Size | Latch Mechanism | Typical Polish | Key Application & Notes |
|---|---|---|---|---|
| SC/APC | 2.5mm | Push-Pull | APC (Green) | FTTx/PON networks, WDM systems, analog video. |
| SC/PC or SC/UPC | 2.5mm | Push-Pull | UPC (Blue) | Legacy datacom, patch panels, single-mode links. |
| LC/UPC | 1.25mm | Tab Latch | UPC (Blue) | Modern high-density networks, SFP modules, data centers. |
| LC/APC | 1.25mm | Tab Latch | APC (Green) | High-density FTTx OLT/ONT, sensitive WDM/EDFA systems. |
| ST/PC | 2.5mm | Bayonet Twist | UPC (Blue) | Legacy multi-mode LAN, CCTV, security systems. |
| FC/UPC | 2.5mm | Screw Thread | UPC (Blue) | Test equipment, laser modules, high-vibration environments. |
| FC/APC | 2.5mm | Screw Thread | APC (Green) | High-precision test & measurement, RF over fiber. Feiyi OEO supplies related high-stability optical components for such systems. |
Selection Rule of Thumb:
- Choose the Ferrule (SC/LC/FC/ST) based on your equipment port (e.g., LC for switches) and density requirements.
- Choose the Polish (UPC/APC) based on the signal type:
- Use APC (Green) for analog signals, RF video (CATV), and FTTx/PON.
- Use UPC (Blue) for standard digital data transmission (Ethernet, SDI).
Important: APC and UPC connectors are not compatible. Mating them will cause permanent damage to the ferrules due to the angled vs. flat contact. Always ensure polish types match.
About Shenzhen Feiyi Optoelectronics
Shenzhen Feiyi Optoelectronics Communication Co., Ltd. is a professional manufacturer of precision optical passive components, polarization-maintaining devices, and integrated optical chips. We support the infrastructure described above with reliable components. Visit our website to learn more about our solutions: https://www.feiyi-oeo.com/