The acronyms LC vs. SC vs. ST vs. FC refer to the most common types of optical connectors in FTTH applications and data networks. As for the PC/UPC/APC terminology, it refers to the type of polishing applied to the optical terminal (ferrule) which makes possible laser light pulses to cross through two optical fibers. Understanding these types is critical for network performance in fiber optic installations.
Then, for example, a typical FTTH pigtail with an SC/APC connector is referring to an SC connector with an APC polishing.
What Are SC, LC, FC, and ST Fiber Optic Connectors?
FC Connector Overview
“FC” stands for Ferrule Connector.
A brief history: It was the first optical connector using a ceramic ferrule, developed by Nippon Telephone and Telegraph. Its use is becoming less common in favor of SC and LC connectors.
Features:
- Screwed fitting (vibration-resistant)
- Common in OTDRs and CATV
- Insertion loss: 0.3 dB
Optical features: For single mode fibers.
ST Connector Overview
“ST” stands for: Straight Tip.
A brief history: Developed in the USA by AT&T and used in professional environments such as corporate networks as well as the military field.
Features:
- Bayonet-style twist-lock coupling (BNC-type)
- Robust design for harsh environments
Optical features: For multimode fibers. Losses about 0.25 dB.
LC Connector Overview
“LC” stands for “lucent connector” or “little connector.”
A brief history: Developed by Lucent Technologies and released in 1997.
Features:
- Push-pull latch (RJ45-style)
- 50% smaller than SC connectors
- Dominates modern high-density installations
Optical features: For single-mode and multimode fibers. Losses of 0.10 dB.
SC Connector
“SC” stands for: Subscriber Connector or Square Connector.
A brief history: Developed by Nippon Telegraph and Telephone, it has become the most popular because of its decreasing production costs.
Features:
- Simple push-pull design
- Low-cost manufacturing
- Standard for passive optical networks (PON)
Optical features: For single mode and multimode fibers. Losses of 0.25 dB
| Connector | Size | Coupling | Insertion Loss | Primary Fiber | Top Application |
|---|---|---|---|---|---|
| LC | Smallest | Push-pull | ≤0.10 dB | Both | High-density FTTH |
| SC | Medium | Push-pull | ≤0.25 dB | Both | PON terminal blocks |
| FC | Medium | Threaded | ≤0.30 dB | Single-mode | OTDR test equipment |
| ST | Large | Bayonet | ≤0.25 dB | Multimode | Industrial networks |
PC vs UPC vs APC Polishing: Key Differences
PC: Physical Contact. The ferrule is beveled and finished in a plain surface. This avoids empty spaces between the ferrules of the connectors being coupled and achieves insertion losses among -30 dB and -40 dB. Its use is increasingly falling out.
UPC: Ultra Physical contact. They are similar to the PC connectors, allowing decreasing return losses to a margin between -40 and -55 dB thanks to the sharper curve of the bevel. The current trend is using it in deadlines to allow operators to perform networks tests for example by using an OTDR.
APC: Angled Physical Contact. The ferrule ends in a plain, 8 degree angled surface making it the connector that achieves a best optical link because it cuts down the return losses up the -60 dB thus allowing increasing the number of users in single mode fibers. For this reason, combined to its constantly decreasing manufacturing costs, APC has become the most used polishing type.
FAQ: Fiber Connector Selection
Q: Why is APC required for FTTH?
A: APC’s 8° angle achieves ≤-60dB return loss, preventing reflected light from disrupting sensitive GPON/XPON transceivers.
Q: Can I mix UPC and APC connectors?
A: Never. Mismatch causes ≥20dB loss and permanent equipment damage. Always match colors (blue=UPC, green=APC).
Q: Which connector is best for data centers?
A: LC dominates due to high port density. Use LC/UPC for multimode and LC/APC for single-mode DWDM links.
Q: Are ST connectors still relevant?
A: Primarily in legacy multimode systems (e.g., campus backbone). Not recommended for new FTTH deployments.
【Edited in August 2025】
