What You Need to Know About Fiber Connectors for AV

Bob Ferguson

Over the past year or two, I’ve received more calls and emails about fiber support for AV systems than ever before. And many of the questions are about fiber connectors.


Bandwidth and distance for audio and, in particular, video are always increasing to support formats like 4K and 8K. An uncompressed, ultra-high definition 4K video signal requires a bandwidth of more than 10 Gb/s.


Because copper cable isn’t always able to transmit the higher data rates that come along with this technology, designers are now turning to fiber to provide connectivity for the AV formats of today and tomorrow.


4 Basic Fiber Connector Options for AV


While there are hundreds of fiber connectors, the AV world typically makes use of four types for terminations. (There are a few types of specialty connectors as well, but these connectors are not typically field terminated.)


These four connectors—each available in singlemode and multimode fiber—will cover the vast majority of audio and video installations:


  1. STs (straight tips): These legacy connectors have maintained a foothold in the broadcast market even though they disappeared from traditional networks. They offer robustness not found in other connectors. Locking bayonet pins give you firm connections like those found on BNC connectors. Typically, coupling and connector housing modules are made from metal, which makes them much stronger than the plastics found in some newer connectors. The downside is that STs take up lots of space, which is sacrificed for reliable AV installation.

  3. SCs (subscriber connectors): These connectors are push-on/pull-off for convenience. They’re also available in simplex (single connector) and duplex (two connector) versions, making them very convenient since the vast majority of fiber uses one fiber to send and one fiber to receive signals.

  5. LCs (lucent connectors): These connectors feature a release tab similar to an RJ45 plug. These have quickly become the most popular LAN connector on the market. They won the small form factor battle (two connectors terminated within the space of an RJ45 jack). This makes them an ideal termination for SFP modules in network switches. As fiber counts grow, density has become an issue; these connectors have a firm hold in the market. Like SCs, they’re available in simplex and duplex versions.

  7. MPOs (multi-fiber push-on) connectors: Sometimes called MTP connectors by other manufacturers, these connectors take fiber density to the next level. They each feature one row of 12 fibers. You can stack rows to get 24 and 36 fibers per connector—but stacking often proves to be more of a hassle than it’s worth. MPO connectors are much harder to field terminate, usually requiring fiber ribbonization. They’re also more complex when it comes to correctly laying out polarity (connecting transmitters to receivers). In addition, they’re one of the few fiber connectors that has gender pins and keying tabs. MPO connectors are often chosen because they support easy plug-and-play cabling; they also offer extreme bandwidth.


Using couplers, fiber connectors connect fibers face to face with one another. The connectors we listed above have physical contact between the fiber ends. Most of these ends have a small convex point to ensure that the very center touches. For singlemode connectors, this is often referenced as UPC or ultra-physical contact.


Reflection and loss vary by connector type and termination method. Have you ever noticed a green connector before? These are APC (angled physical contact) connectors and known as an exception to UPC; the endface is polished at 8 degrees. Instead of reflecting light straight back down a cable, it’s reflexed at an angle. This can be critical in some AV applications, especially if you’re sending and receiving signals in both directions on the same fiber.


Belden offers APC connectors in singlemode LC and SC versions (bright green in color). Other connector colors are:


  • UPC singlemode: blue
  • OM1 andOM2 multimode: black and beige
  • OM3 and OM4 multimode: aqua and erika violet
  • OM5 multimode: lime green


It's possible to use more than one type of connector on a single project, but we recommend sticking with just one type and adjusting patch cords to fit different equipment requirements.


For example: If all fibers coming into a rack’s fiber enclosure use SC connectors but your application requires ST connectors, then you should purchase SC-to-ST patch cords for both ends. 


Terminating Fiber Connectors for AV


Now that you understand connector types, let’s talk about putting connectors on the ends of fiber.


There are four options here as well. The fast and easiest option is to use a pre-terminated fiber from the factory. The connectors are installed on the fiber and the entire link is tested. Because pre-terminated fiber is made to your specifications, you need to know the length ahead of time. Cost and lead time can also be a little higher as compared to other options.


The hardest and most complex approach to termination is puck and polish (I recommend avoiding this unless you’re an expert). This process requires polishing the end of the glass using an abrasive paper.


This leaves the last two options: mechanical and fusion connectors. Both have factory-polished tips for good loss. Mechanical connectors clamp fiber ends securely together and use index matching gel to connect them. Fusion connectors join fiber ends by melting the glass with the connector or pigtail end. Fusion connectors offer the best optical performance and temperature stability, so we recommend using them whenever possible.


In addition to these four termination options, the AV industry also occasionally uses specialty fiber connectors, which need adaptation in order to be terminated in the field.


Neutrik offers a fiber connector with an XLR body called opticalCON®. The panel side of these connectors holds an LC or MPO insert, which allows them to be field terminated. The connector on the patch cable—which is the cable from panel to actual equipment—requires special factory termination from an assembly shop.   


Similarly, SMPTE 311 connectors for broadcast camera applications are too complex to field terminate, so there are several options available to splice them directly into your system or use a field-terminated connector for panel ends.


As fiber becomes more popular, I’m sure we will see even more options develop. If you’re still not sure which connector is right for you, then give Belden a call. We would be happy to learn more about your project and guide you toward the right solution. We can even demonstrate our FiberExpress Fusion Splicer, which supports consistent, reliable and high-quality terminations for single fiber splice-on connectors and pigtail splicing.