Fiber Optic Connectors: Identification Guide

Data Center

Last Updated on July 19, 2022 by Josh Mahan

As fiber optic technology has developed over the years, many companies have introduced different fiber optic connectors. However, with over 100 fiber optic connectors available, identifying the correct one can be tricky.

Do you have a fiber optic connector that you need to correctly identify so you can either replace it or find the correct adapter to use?

We’ve put together this guide on some of the industry leaders and most popular types of fiber optics connectors available to help you identify them quickly and accurately.

Related: What Are Data Center Operations?


Types of Fiber Optic Connectors

We’ve compiled a list of some of the most popular and common fiber optic connectors used over the years in the telecommunications industry. They go from legacy connectors from when fiber optics were introduced to today’s cutting-edge fiber technology

ST Connector

ST Connector

ST connectors were one of the first types of connectors widely used in fiber optic networking. The “Straight Tip” or ST connector was created by AT&T and uses a 2.5mm ferrule. 

The 32.5mm ferrule means that the ST can be matched and mixed with ESON, FDDI, FC, and SC connectors using a hybrid adapter. In addition, a half-twist bayonet-style lock helps the connector stay in place.

ST connectors are typically used with a multi-mode cable. However, they are gradually being replaced by multi-fiber connectors like the MTP and LC. 

ST-type connectors can be plugged and unplugged from fiber optic cables quickly and easily. The average insertion loss is 0.25dB.

SC Connector

SC Connector

SC connectors are snap-in connectors developed in Japan by the telecommunications company NTT. SC  stands for either “Standard Connector or Subscriber Connector.”

You can use the SC connector with either single-mode or multi-mode fiber optic cables. Along with ST Connectors, multi-fiber connectors are slowly replacing SC connectors in fiber optic cabling.

The SC connector has a 2.5mm ferrule. It is attached with a push-pull mechanism that allows easy insertion and removal. As a result, SC connectors are typically more straightforward to use in tight spaces than ST twist-style ones.

Two square-shaped SC connectors are often attached with a plastic clip to create a duplex connection. SC connectors are inexpensive, durable, and simple to use. SC connectors have a typical insertion loss of 0.25 dB.

FC Connector

FC Connector

For many years FC was one of the most popular single-mode connectors. It uses a 2.5 mm ferrule, but some early models use ceramic inside stainless steel ferrules. 

The FC connector screws on tightly, but you must ensure the key is aligned in the slot properly before tightening. The FC Connector has generally been replaced by SC and LC connectors.

The typical insertion loss for matching FC connections is 0.3 dB.

LC Connector

LC Fiber Connector

The LC connector, or Lucent Connector, was invented by Lucent Technologies. The LC connector is around half of the size of the SC connector type. 

The LC connector’s 1.25mm ferrule and retaining tab mechanism give it a small form factor, similar to the RJ-45 or phone connector. LC connectors are used in deployments with a high density of fibers terminating in a confined area. 

The body of an LC connector is square-shaped like SC connectors. A plastic clip commonly attaches two LC connectors to create a duplex connection. 

You can use LC connectors with both single-mode and multi-mode fiber cables. The typical insertion loss of matching LC connectors is 0.25 dB.

LX-5 Fiber Connector

LX-5 Fiber Connector

The LX-5 fiber connector is very similar to the LC connector, except it has a shutter over the end of the fiber. 

10G-CX4 Connector

10G-CX-4 Connector

The 10G-CX4 was the first 10G copper standard to be published. The 10G-CX4 connector provides low latency, low cost, and low power. However, its larger form factor uses much bulkier cables than modern single-lane SFP+ standard connectors.

Copper cables that use the 10G-CX4 connectors have a shorter maximum range of up to 15 meters compared to fiber or 10GBASE-T cables.

Infiniband (4x) Connector 

Infiniband 4X Connector

The 4x connector got its name for its ability to support four aggregated data links. The 4x connector is often used on Infiniband cables and is called the “Infiniband Connector.”

Infiniband is a high-bandwidth I/O communication technology frequently deployed in data centers, high-performance computing applications, and server clusters

Infiniband cables appear identical to 10G-CX4 cables. However, you cannot use Infiniband cables for 10G-CX4 applications.

MTRJ Connector

MTRJ Fiber Connector

Corning and AMP/Tyco invented the Mechanical Transfer-Registered Jack (MTRJ) connector. The MTRJ is a duplex-style connector that resembles the RJ-style modular jack. It has a tab locking mechanism, a plastic body, and a ferrule. 

The ferrule technology that MTRJ connectors use is the same as Multi-fiber Termination Push-on (MTP) connectors. In addition, the MTJR connector comes in both male and female versions that use pins for alignment

Both female and male versions of the MTRJ connector use alignment pins. MTRJs are available in both single-mode and multi-mode versions. MTRJ connectors that are matched have a 0.25dB insertion loss for single-mode fiber and 0.35dB loss for multi-mode fiber. 

MTP/MPO Connector

MTP/MPO Fiber Connector

The MTP connector, manufactured by US Conec, is an improved version of the MPO connector designed by NTT

The MTP connector can terminate up to 12 strands of fiber in one ferrule and is locked into place by a push-on/pull-off fastener. Also, a pair of metal guide pins extend from the connector’s front.

You can use single-mode and multi-mode cables with MTP/MPO  fiber connectors. Singlemode MTP/MPO connectors use an angled ferrule to ensure minimal reflection. In contrast, multi-mode MTP/MPO connectors have a flat ferrule.

MTP/MPO assemblies are mainly used in backbone, breakout, and cross-connect applications. Matched MTP/MPO connectors have a loss insertion of 0.25 dB.

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RJ-45 Connector

RJ-45 Connector

The RJ-45, also known as the “Registered Jack-45” connector, is an eight-wire connector. The RJ-45 connector primarily connects devices on an Ethernet LAN. 

RJ-45 connectors look like the RJ-11 connectors used to wire telephones but are larger.

RJ-45 connectors are not fiber optic connectors. However, they are the standard connector for CATx Ethernet cables. CATx cables connect a network switch to a patch panel or connect a computer’s network interface controller to a data port.

D4 Connector

D4 Fiber Connector

The D4 connector uses a screw-on mechanism and has a 2.0mm ferrule. It’s an older generation connector that is keyed and spring-loaded. The key stops opposing ferrule ends from rubbing together while pairing. Thanks to its smaller size, multiple D4 connectors can be loaded into a fiber distribution frame.

NEC specified the D4 connector for use on all of their equipment interfaces. The NEC D4 was likely the first connector to use hybrid ceramic and stainless or ceramic steel ferrules. It was popular in telecommunications networks in the late ’80s and early ’90s and is still in use today.

ESCON Connector

ESCON Connector

IBM invented the Enterprise Systems Connection (ESCON) in the ’90s to connect their main-frame computers to external devices, like disk storage drives and tape drives. 

The ESCON connector is an optical fiber, half-duplex, and serial interface connector. It has a 2.5mm ferrule and mates with adapters to SC and ST connectors. However, ESCON connectors have been mainly replaced by much faster fiber channel connectors (FICON).

OptiJack Connector

OptiJack Fiber Connector

The Panduit Opti-Jack is a duplex connector that uses two SC duplex ceramic ferrules, each 2.5mm in diameter. The ferrules are aligned using conventional split-sleeve mechanical techniques and are independently spring-loaded.

The Opti-Jack is the same size as an RJ-45 connector and comes in both male and female variants. The connector’s latch is designed like the industry-standard RJ-45 wall jack. 

It supports duplex jumper cables, couplers, and adapters. Opti-jack transceivers aren’t widely used.

FDDI Connector

FDDI Fiber Connector

The FDDI, or Fiber Distributed Data Interface, is a LAN standard for transmitting data. The point where fiber optic cables terminate is the FDDI connector, also known as the MIC (Media Interface Connector). 

An FDDI connector has two ferrules inside a large plastic housing and utilizes a squeeze-tab latch. FDDI connectors can be mated to ST or SC connectors using adapters.

FDDI provides optical standards of 100 Mbit/s for the transmission of data. AN FDDI can be used in a local area network, extended up to 120 miles (200KM), and support thousands of users.

MU Connector

MU Fiber Connector

Multi-Termination Unibody Connector (MU) looks like a smaller version of an SC connector type. MU connectors are SFF connectors produced by NTT. They are used more frequently in Japan than in the United States.

MUs have a ceramic ferrule of 1.25mm, about half the size of a standard SC connector’s ferrule. 

Zirconia split-sleeves with smaller diameters support duplex couplers, adapters, and similar jumper cable applications.

MUs use a self-retention mechanism similar in design to a push-pull SC latch. This latch allows for blind mating inside a printed circuit board backplane. Unfortunately, it is not yet possible to purchase transceivers with an MU interface. However, some development work has been started in this area.

Volition Fiber Connector


Volition, made by 3M, is a slim duplex connector that does not have a ferrule. Instead, it uses a v-groove to align fiber, much like a splice. It comes in plug and jack versions. However, only jacks field terminates.

Related: 8 Data Center Trends Changing the Industry 2022

Bionic Connector

Bionic Fiber Connector

ALT Text: Bionic Fiber Connector (

The Bionic connector was one of the first connectors used in fiber-optic communications. The tapering sleeve that fixes onto the fiber optic connector can quickly identify this connector. The narrowing end allows the sleeve to be placed on the connector snugly. 

The connection is secured by guided rings that come complete with caps. The caps fit over the ferrule and screw onto the threaded sleeve.

E2000 Connector

E2000 Fiber Connector

Telecommunications networks use  E2000 connectors commonly today. A spring-loaded shutter protects the ferrule from scratches, dust, and dirt. 

In addition, the monobloc ceramic ferrule eliminates the issues due to the coefficient of expansion. 

The connector is used in many broadband applications such as Fiber CATV, Fiber to the  Home  (FTTH), Fiber to the Desk (FTTD), and telecommunications networking. 

Senko CS Connector

Senko CS Connector

The Senko CS is a Very Small Form Factor (VSFF) connector. It allows you to double the density in patch panels compared to an LC duplex. As a result, it can provide better airflow and add more room for cable management within a rack. 

The unique push-pull tab allows for better usability in high-density applications. The connector accepts up to 2.0/3.0mm duplex fiber. QSFP-DD and OSFP have adopted the connector, and COBO, Standardized by TIA.

US Conec MDC Connector

US Conec MDS Fiber Connector

The MDC is a two-fiber connector manufactured with a 1.25mm ferrule used by standard LC connectors. Three port MDC adapters fit directly into panel openings for duplex LC adapters, tripling the fiber density.  

The format will support up to four single MDC cables in a QSFP footprint and two single MDC cables in an SFP footprint. Inserting or extracting the MDS is done with a simple push or pull.

3M Expanded Beam Connector

3M Expanded Beam Connector

The 3M Expanded Beam connector’s technology rescues sensitivity to dust. Its ferrule is designed to support up to 12 fibers and comes in single-mode and multi-mode versions. 

It has a hermaphroditic design that eliminates the need for female and male connectors. It is simple to connect and disconnect from equipment.

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The Past, Present, and Future of Fiber Optic Connectors

As the thirst for high-speed data and communications continues to grow, the demand for smaller, faster fiber optic connectors that can quickly carry incredible amounts of data around the world will continue.

As with any technology, what was once cutting edge will someday become obsolete. This evolution holds with fiber optic connectors as new technology will continue to be invented, and innovations will phase out legacy equipment.

Quickly identifying the type of fiber optic connector you are looking at can save you time and money from choosing the wrong adapter or connector when replacing or updating your system.

Related: Data Center Cabling Best Practice Guide

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