Cleerline Technology Group

October 14, 2021 - Choosing fiber connector type depends on the equipment in use.  What do you do, however, in situations where you do not know the requirements? If facing a switch, SFP, or other item and not sure of the connector type, there are a few steps you can take.

Get the Details

First, check with the item's manufacturer or look up the part number via your preferred search engine.  Most manufacturers will list connection requirements on the item's product page, or in a related specification download (make sure to look for links to PDF specification documents). We try to make information like this very clear on our SFPs and media extension items.

If on a site and looking at an unfamiliar switch, it's possible the ports will be labeled, or information may be included on a label elsewhere on the item.  

SFP modules will often notate "LC" and "SC" on the item label to indicate connector type.  Additionally, SFP modules may be printed with wavelength information to indicate single mode or multimode fiber requirements.  For example, look for wavelength measurements like 850nm or 1300nm (multimode) or 1330nm and 1550nm (single mode).  For more information on wavelength and other abbreviations, check out our article on choosing SFP modules. 

If no information is available, looking at the switch's ports themselves should help you.  While this probably won't give you a definitive answer on whether a single mode or multimode connector is required, you should be able to narrow down the connector style.

What Do the Ports Look Like?

SFP Slots

A fiber-enabled device with about a ½ inch (13 mm) wide open port space labeled "SFP" (or unlabeled) has an open SFP slot.  SFPs are hot-pluggable, swappable modules, providing the greatest flexibility in connection.  Frequently, SFP-accepting devices are also flexible with regards to fiber type, but again, check for wavelength information or check with the manufacturer.

Fiber-enabled items without open SFP slots most likely accept LC, SC, or ST connectors, and the size or shape of the port will help show this.

Connectors

For installations in the United States, you are most likely to be dealing with LC, SC, or ST connections (with SC and LC connectors being more likely).

ST Connectors

Out of those options, ST connectors are easiest to recognize because of their round barrels.  (For integrators working internationally, note that FC connectors are also round.) 

LC & SC Connectors

LC and SC connectors, on the other hand, both have ports that are more rectangular in shape.  The main differences with these connectors are that 1) LC clips are about half the width of SC connectors and 2) LC connectors have tabs.

Since LC connectors are smaller, they tend to be more common on switches, SFPs, and other electronics. (Two LC ports fit at the end of average SFP modules.)  Port openings tend to be around 3/16 inch (5 mm) wide. 

The most noticeable characteristic of LC ports is that one side is shaped like a short "t" or plus sign.  This allows each LC connector's tab to fit the opening. 

SC connectors, on the other hand, fit a more rectangular port.  There is no extra space for a tab.  Instead, SC ports have a slot cut into one side to accommodate the raised key on the connector itself.  (The key keeps connectors from being installed incorrectly.) 

SC clips, again, are wider than LC, at about 3/8 inch (10 mm) wide.  Only one SC connector will fit in the same space as two LC connectors.

MTP/MPO Connectors

Items destined for high-volume installations, like data centers, may require MTP (MPO) connections.  These ports are slightly wider than SC connections, but generally not as tall.  The center of the port will either have two prongs (male) or two openings (female).  When dealing with MTP connections, polarity tends to be especially important, so check the installation details before trying to find a compatible cable.

Single Mode or Multimode and UPC or APC?

Make sure that your link cables, connectors, and electronics all use the same type of fiber.  Using an SFP rated for multimode? Your connectors and patch cables also need to be multimode, or you need to plan a transition from single mode to multimode within your system (which requires additional equipment).  In any case, single mode connectors will not work on multimode fiber, and multimode connectors will not work on single mode fiber.

Again, the best ways of determining required fiber type are to a) check with the manufacturer or b) find indicators on the item itself. 

In some cases, ports may be color-coded to indicate fiber type.  Feedthrough adapters by themselves or in adapter plates are usually color-coded for multimode (aqua), single mode UPC (blue), or single mode APC (green).  We recommend conforming to the color-coding or manufacturer's recommendation on feedthrough adapter type (i.e. use a multimode feedthrough with multimode fiber).  While in a pinch a multimode feedthrough may work with single mode fiber and vice versa, it is better to avoid confusion.

Single mode equipment may require either UPC (ultra polished) or APC (angle polished) connectors. This should be clearly indicated by the equipment in use.  In the majority of cases, UPC connectors are required.  APC connectors are need for specific applications, like GPON or FTTx, and are often called for by service providers.