Choosing Fiber Connectors

Fiber Connector Types

Selecting Fiber Optic Connectors

There are many different types of fiber optic connector, so choosing the correct one can be confusing. Think of it this way: if terminating RG6 coax you could use an F, RCA, or BNC connector depending on your installation requirements. Similarly, choosing the right type of fiber optic connector depends on the equipment and type of optical fiber you are installing. Adapters are available, but it is always easiest to determine both fiber type and connector style ahead of time. In this article, we’ll discuss some common types of fiber optic connectors.

Types of Fiber Optic Connector

There are quite a few different styles of connectors. In the USA for networking and audio/video, the three most popular styles are LC, SC, and ST. LC and SC tend to be the most commonly used styles. Today, ST connectors are seeing more limited usage.

LC Connectors

LC Multimode
LC Multimode

A Lucent connector (LC) is a connector with a 1.25 mm ferrule, half the size of an SC or ST connector. LC connectors are frequently used as their small footprint makes them ideal for high-density installations. Similarly, SFP (small form-factorable pluggable) modules and fiber optic extenders often require these connectors, although this varies by manufacturer. LC connectors, again, are smaller in size and feature a clip design.


SC Connectors

SC Multimode
SC Multimode

A 2.5 mm snap-in connector. This was the first connector chosen for the TIA-568 standard and is a snap-in connector that latches with a simple push-pull motion. SC connectors, as noted above, are larger than LC connectors. SC connectors are used with some styles of fiber optic extenders, although LC tends to be more common.


ST Connectors

ST Connector
ST Connector

A ST connectors is a 2.5 mm AT&T™-designed connector. It has a bayonet mount and a long cylindrical ferrule to hold the fiber. Most ferrules are ceramic, but some are metal or plastic.


Choosing a Connector

Connector style is determined by the equipment that the fiber cable will be plugged into, as well as the type of fiber you are using. If you know what equipment you will be using, you will be able to determine which style of connector to install. As noted above, LC connectors are a common choice for high-density installations and almost exclusively used in network applications.

Fiber connectors are designed specifically for the type of fiber you are using.

Single mode uses a 9/125 connector, which refers to the core and cladding diameter of the optical fiber (i.e. core of 9 µm and cladding of 125 µm).

Multimode fibers require either a 50/125 µm (OM2/OM3/OM4) or 62.5/125 (OM1) connector. For more information on the difference between single mode and multimode fibers, visit our article.

Polish Type

Connectors are available with differently polished endfaces, which impact the connector’s level of return loss (back reflection). Single mode connectors are available either as a UPC (Ultra Physical Contact) or an APC (Angled Physical Contact/Angled Polish Connector).

UPC connectors are most commonly installed. These connectors have a slightly domed endface. For identification, single mode UPC connectors are colored blue.

APC connectors feature an 8 degree angle at the endface. This decreases their return loss. However, APC connectors have very specific applications (GPON, FTTx, etc.) and used only when equipment requires them. APC connectors are commonly used by service providers, or for very long distance transmission. For identification, APC connectors are colored green.

Due to the angle of an APC connector, it cannot be mated to a UPC connector. These connector types are not interchangeable, so it is very important to verify whether your installation requires UPC or APC connectors.

Color Coding

Connectors are color-coded to identify multimode connectors and single mode APC or single mode UPC connectors.  Note that color coding conventions vary by manufacturer, so always make sure to double check your cables and connectors.  The general guidelines are: 

  • Aqua: 50/125 Multimode (OM3/OM4, also compatible with OM2 fibers)
  • Blue: Single mode UPC
  • Green: Single mode APC
  • Beige, although this is variable: 62.5/125 Multimode (OM1)
  • Black: 50/125 Multimode OM2 (varies by manufacturer)

Again, color coding can have some variation, so it is important to always double check the connector’s specifications.  For example, Cleerline SSF™ pre-terminated Duplex 50/125 Multimode OM2/OM3/OM4 Patch Cables have beige connectors. 

Changing Connector Type

SC Duplex Coupler
SC Duplex Coupler

If you have a SC-style connector installed and find that you need LC instead, you can purchase a SC-SC coupler, then purchase a pre-terminated SC to LC patch cable. This is a very common solution. Adapters are also available LC-LC or LC-SC.

Patch cables can be purchased with all various configurations (SC-SC, SC-LC, etc.). Again, the type of equipment you are installing will determine your connector needs. Various adapters and patch cable configurations can be utilized to connect fiber optic-based equipment.


The Bottom Line

LC Duplex Coupler.
LC Duplex Coupler – note that two LC connectors fit in the same space as one SC

To choose the correct fiber connector, here are some points to consider:

  1. Do the electronics you are connecting to require LC, SC, or ST connectors?
  2. Are you installing single mode or multimode fiber? If multimode, what is the grade (OM2/OM3/OM4)?
  3. If you are installing single mode fiber, the most common connector type will be UPC (blue). UPC is the default if there is no indication that APC is required. If your equipment specifically requires APC (green), you must install all angled polish connectors.  

Remember, always check the requirements of your installation before purchasing fiber optic connectors.

Learn how to install Cleerline SSF™ mechanical splice connectors on SSF™ fiber by watching one of our short instructional videos.

Connector Guide

Download your printable copy of the Connector Selection Guide, including all the information in this article plus additional networking examples and images.