LC vs SC vs ST vs FC: Fiber Connector Types Compared

Why Fiber Has So Many Connector Types

Unlike copper, where RJ45 has been dominant for decades, fiber optic networking developed across multiple eras and multiple industries. Each generation of equipment introduced a new connector that solved the problems of the previous generation -- smaller footprint, faster installation, higher density, better vibration resistance, lower insertion loss. The result is an installed base that includes everything from 1980s ST connectors in factory floors to 2020s LC connectors in 400Gb data center spines.

For a field technician, the practical implication is that you will encounter all four of these connectors -- often in the same building. A modern enterprise might have LC in the data center, SC at the FTTH demarcation, ST in legacy floor distribution, and FC in the carrier handoff cabinet. Knowing which is which, what they pair with, and how to terminate or splice each type is part of the job.

LC (Lucent Connector)

The LC connector was developed by Lucent Technologies in the mid-1990s and has become the dominant fiber connector in modern installations. Its small form factor (SFF) design uses a 1.25mm ceramic ferrule -- half the diameter of the 2.5mm SC and ST ferrules. This allows two LC connectors to occupy the same panel space as one SC connector, doubling the port density of patch panels and switch faceplates.

Key Characteristics

• Ferrule diameter: 1.25mm ceramic (zirconia)
• Latching mechanism: RJ45-style push-pull latch
• Form factor: Small form factor (SFF), approximately half the size of SC
• Polish types: Available in UPC (blue) and APC (green)
• Duplex configuration: Standard duplex clip pairs two LC connectors with consistent polarity
• Insertion loss: Typical 0.1-0.3 dB for factory-terminated patch cords
• Return loss: -50 dB or better (UPC), -65 dB or better (APC)

Where LC Dominates

LC is the standard connector for data center switching, server networking, transceivers (SFP/SFP+/SFP28/QSFP+/QSFP28/QSFP-DD), enterprise structured cabling, and any application where port density on a faceplate or patch panel matters. Every major vendor's high-speed Ethernet transceiver uses LC ports. If you are working on 10G, 25G, 40G, 100G, or 400G fiber inside a building, the connectors at both ends are almost certainly LC.

LC is also used in FTTH central office equipment, particularly for OLT line cards where high port density is essential. ONT and subscriber-side equipment more commonly uses SC, but the central office is increasingly LC. Browse our LC/UPC duplex patch cords and LC/APC jumpers for typical data center and PON applications.

SC (Subscriber Connector)

The SC connector, originally developed by NTT in Japan, uses a 2.5mm ceramic ferrule and a square-profile push-pull plastic housing. The "SC" name has been variously translated as Subscriber Connector, Standard Connector, and Square Connector -- all of which appear in vendor documentation. Whatever you call it, SC is the standard FTTH connector and is ubiquitous in outside plant and access network equipment.

Key Characteristics

• Ferrule diameter: 2.5mm ceramic (zirconia)
• Latching mechanism: Push-pull, no twist required
• Form factor: Square profile, approximately twice the footprint of LC
• Polish types: Available in UPC (blue) and APC (green)
• Insertion loss: Typical 0.1-0.3 dB
• Return loss: -50 dB or better (UPC), -65 dB or better (APC)

Where SC Dominates

SC is the universal connector for FTTH ONTs (optical network terminals), GPON/XGS-PON splitters, fiber distribution hubs, and outside plant terminations. The 2.5mm ferrule is more tolerant of contamination and rough handling than the smaller LC, which matters for technicians working in pedestals, splice trailers, and aerial drop boxes. The simple push-pull engagement also makes SC fast to mate without requiring fine motor control.

SC/APC (green) is the dominant variant in PON deployments because the angled polish prevents back-reflection problems on PON's bidirectional fiber. SC/UPC (blue) is used for data and test applications. See our SC/APC simplex jumpers for typical FTTH installations and SC/APC to LC/APC adapters for connecting central office LC equipment to SC outside plant.

For a deeper dive on the polish difference, see our guide to SC/APC vs SC/UPC connectors.

ST (Straight Tip)

The ST connector was developed by AT&T in the 1980s and was the dominant multimode connector through the 1990s. It uses a 2.5mm ceramic ferrule and a bayonet-style locking mechanism -- the connector is inserted, twisted a quarter turn, and locks into place. The bayonet design provides positive engagement that resists vibration and accidental disconnection.

Key Characteristics

• Ferrule diameter: 2.5mm ceramic
• Latching mechanism: Bayonet-style with quarter-turn lock
• Form factor: Round profile with metal coupling nut
• Polish types: Almost exclusively PC or UPC (multimode rarely needs APC)
• Insertion loss: Typical 0.25-0.5 dB
• Common fiber type: Multimode (OM1, OM2)

Where ST Persists

ST is rarely specified for new installations. The connector is bulky, the bayonet locking is slower to mate than push-pull, and the supported fiber types are typically legacy multimode grades. However, ST connectors remain installed and operational in:

• Older buildings and campuses: Multimode plants installed in the 1990s and early 2000s commonly used ST. Many of these are still in service.
• Industrial and factory installations: The vibration-resistant bayonet lock is valued in environments where push-pull connectors might be jostled loose.
• Military and government: MIL-STD specifications and legacy government infrastructure include ST in many specs.
• Educational and medical facilities: Universities, hospitals, and labs with long-running fiber plants often have substantial ST infrastructure.

If you encounter an ST plant, the practical question is whether to maintain it or migrate. Migration to LC or SC requires either re-terminating the existing fiber (possible if the cable supports the speeds you need) or pulling new cable. Maintaining an ST plant requires keeping ST patch cords, pigtails, and adapter sleeves in stock, which is increasingly a niche supply chain.

FC (Ferrule Connector)

The FC connector was developed by NTT in the 1980s and uses a 2.5mm ceramic ferrule with a threaded screw-on coupling nut. The threaded coupling provides extremely positive engagement and is highly resistant to vibration. FC was once the dominant single-mode connector for telecom carrier networks but has been largely displaced by SC in access applications and LC in modern equipment.

Key Characteristics

• Ferrule diameter: 2.5mm ceramic
• Latching mechanism: Threaded screw-on coupling (rotating nut)
• Form factor: Round profile with knurled metal coupling nut
• Polish types: Available in PC, UPC, and APC
• Insertion loss: Typical 0.2-0.4 dB
• Common fiber type: Single-mode

Where FC Persists

FC connectors remain common in specific application niches:

• CATV headends: Cable TV systems with RF over fiber overlays use FC/APC connectors heavily because the threaded coupling and angled polish provide a very stable, low-back-reflection connection.
• DWDM and laboratory equipment: Test labs, photonics research, and DWDM measurement systems often use FC connectors because the threaded coupling holds rigidly through repeated mating cycles.
• Optical test equipment: Many older OTDRs, optical spectrum analyzers, and tunable lasers use FC ports. Adapter cables (FC-to-LC, FC-to-SC) are commonly stocked in test toolkits.
• Legacy telecom: Carrier central offices built before the SC transition still have substantial FC plant.

The downside of FC is the time it takes to mate -- threading a connector is significantly slower than the push-pull engagement of LC or SC. In high-density panels, the rotation also requires clearance space that LC and SC do not. New installations rarely specify FC.

Head-to-Head Comparison

How to Choose Between Them

For a new installation, the connector choice is usually driven by what equipment you are connecting to:

• Connecting to a switch, server, or transceiver? LC. Every modern transceiver uses LC.
• Terminating an FTTH drop or splitter? SC/APC. The PON ecosystem is built around SC/APC.
• Migrating an existing ST plant? If the multimode fiber is OM1 or OM2 and the speeds are 1Gb or below, maintain ST until a planned cable replacement. If you need 10Gb or higher, plan a fiber replacement (likely with single-mode and LC).
• Working with CATV or older lab equipment? Plan for FC/APC patch cords and FC-to-LC hybrid adapters in your toolkit.

For mixed environments, hybrid patch cords (LC-to-SC, LC-to-FC, SC-to-FC) and hybrid adapters bridge the form factors. Hybrid adapters internally adapt the mechanical housing while passing the fiber through unchanged. They add a small amount of insertion loss compared to a clean factory connection but are often the most practical solution.

Identifying Connectors in the Field

If you arrive at a job site and need to identify what is in front of you, the visual cues are straightforward:

• LC: Small, plastic, RJ45-like latch on top. Often duplex with two connectors paired by a clip.
• SC: Square plastic housing, push-pull, no rotation. Often single but sometimes duplex.
• ST: Round metal nut that you twist a quarter turn. Bayonet pin visible on the side.
• FC: Round metal nut that you screw on (multiple full rotations). Knurled grip on the nut.

The color tells you the polish type: green = APC, blue = UPC, beige or black = PC (typically multimode). After identifying the connector, inspect the ferrule under a fiber inspection microscope before mating to verify the endface is clean. Contamination is the leading cause of connector loss and damage. For LC connectors specifically, the LC/APC male inspection tip and LC/APC female inspection tip let you inspect both the patch cord and the bulkhead adapter side. For routine cleaning, see our fiber connector cleaning guide.

Related Reading

• SC/APC vs SC/UPC Connectors -- understanding the polish difference that applies across all connector form factors.
• Single-Mode vs Multimode Fiber -- the fiber type drives many connector decisions.
• How to Clean Fiber Connectors -- proper cleaning technique for LC, SC, ST, and FC.