SC LC ST FC connectors, what is the difference?

Maybe FC, ST, SC, and LC are the most popular types of fiber connectors you may come across, besides the Multiple fiber connector. They’re widely used in modern-day telecommunication networks.  Though they’re commonly seen, you may not know their strengths and weaknesses. Today we’d like to elucidate this question.

Overview of FC, ST, SC, and LC

FC stands for “ferrule connector” or “fiber channel,” designed by JP NTT, aiming to use in high-vibration environments. It is a round threaded connector, using a 2.5 mm ferrule around with a stainless-steel housing, applied in datacom, telecommunications, measurement equipment, and singlemode lasers.

ST refers to the “Straight Tip,” designed by AT&T in the late 1980s, using a half-twist bayonet mount to hold a long cylindrical 2.5 mm spring-loaded ferrule. Due to its ease to plug and unplug and low cost, it was widely used in campus, enterprise, and military multimode networks. It was once the most popular connector for multimode networks till 2005, but it isn’t compatible with APC, greatly limiting its usage.

FC and ST fiber connectors are both phasing out in favor of SC and LC.

SC stands for “Subscriber Connector,” also known as “Square Connector.” Developed by JP NTT in the mid-1980s, SC uses a snap-in push/pull coupling mechanism with a 2.5 mm ferrule. It has excellent performance and fast deployment; therefore, it has gained popularity and is widely used in single-mode fiber optic cable, analog CATV, GPON, and GBIC.

LC is the acronym for Lucent Connector, named after its designer Lucent Technologies. LC features a push/pull coupling mechanism with a latch. As a Small Form Factor (SFF) member, it is commonly referred to as the “little connector.” The main draw of LC lies in its 1.25 mm ferrule, half the size of the ferrule of FC, ST, and SC, which reduces its footprint by 50% of FC, ST, and SC. That’s why LC is widely used in high-density environments. Rivaling SC at present, LC is most likely to be the long-run winner.

FC vs. ST vs. SC vs. LC: the difference

We could classify these four types of connectors in dimensions, history, performance, coupling type, cost, and ease of use. First, let’s talk about their sizes.

Name	Mating Cycles	Coupling mechanism	Ferrule diameter	Standard	Cost	Ease of use	Application Features
FC	500	screw	2.5 mm	IEC 61754-13	High	**	Datacom, telecom, measurement equipment. obsolete
ST	500	bayonet	2.5 mm	IEC 61754-2	low	**	Multimode, rarely singlemode; APC not compatible
SC	1000	Snap-in (push/pull)	2.5 mm	IEC 61754-4	low	****	Datacom and telecom applications, such as GBICs, PON, etc. extremely common
LC	500	snap	1.25 mm	IEC 61754-20	A little Higher than SC	***	High-density connections, SFP+/ SFP28, QSFP+ or QSFP28, etc. extremely common

Standard Size: FC, ST, SC vs. SFF: LC

These three all use the 2.5 mm ferrules, yet LC uses a 1.25 mm ferrule, so generally, we could divide them by dimension. The Standard size fiber connectors refer to these connectors which have a normal size, like FC, ST, and SC; On the contrary, the SFF refers to these connectors which have a smaller size, initially designed to satisfy the need for large fiber count applications, like LC. LC is only half FC, ST, and SC size, which means it could provide twice the density of connections as FC, ST, and SC, giving it huge popularity.

Respective advantage

FC is ideally suitable for high-vibration environments due to its threaded screw-on design, commonly used in military applications.

ST is extremely easy to use and has a low cost, commonly used in security and industrial applications.

SC and LC provide nearly the same insertion and return losses, both extremely popular.

SC is low-cost, simple, and durable.

LC is well established due to its compact size, excellent performance, and reliability. It is perfect for high-density environments, such as data centers and service provider networks.

Coupling type

FC is tightened by screwing using a threaded collet.

ST features a bayonet mount.

SC features an easy-to-use push and pull mechanism.

LC features a pull/pull with a latch design.

Repeatability

SC has 1000 mating cycles, while the other three have 500 mating cycles.

Cost

Compared with SC and LC, FC and ST cost higher due to their complex design and are more difficult to use.

Compared with SC, LC costs a little higher. But the economy of scale is expected to reduce their price gap.

Ease of use

SC is the easiest one to use, while LC is the second-best. ST and FC both are not handy to use.