Choosing Fiber Connectors

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 a 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 SC or ST connector. LC connectors are frequently used as their small footprint makes them ideal for high-density installations. Similarly, these connectors are often required for SFP (small form-factorable pluggable) modules and fiber optic extenders, 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 exclusive 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 impacts the connector’s level of return loss (back reflection). Single mode connectors are available either as a UPC (Ultra Physical Contact) or APC (Angled Physical Contact/Angled Polish Connector).

UPC connectors are most commonly installed. These connectors have an endface which is slightly domed. For identification, 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. 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.

  • Aqua: 50/125 Multimode (OM2/OM3/OM4)
  • Blue: Single mode UPC
  • Green: Single mode APC
  • Typically beige, although this is variable: 62.5/125 Multimode (OM1)

Color coding can have some variation, so it is important to always double check the connector’s specifications.

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. There are also various adapters and patch cable configurations that 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. Are you installing single mode or multimode fiber? If multimode, what is the grade (OM2/OM3/OM4)?
  2. Will the electronics you are connecting to require LC, SC, or ST connectors?
  3. If you are installing single mode fiber, the most common connector type will be UPC (blue). Does your installation require APC connectors (green)? If these are not specified, we recommend UPC.

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