The two most prolific connector types that have gained a significant market hold are the SC connector and LC connector. These connectors are self-orienting (more on that in a moment), snap in, and resilient for a variety of connections. The LC connector is the reigning king of the transceiver interfaces due to its small size, which allows multiple connections in little space. In the legacy space, you’ll encounter FC and ST connectors, both of which use screw on coupling sleeves. A newer kid on the block is the MPO connector that allows many (commonly 12 or 24) fiber connections in the space of about two LC connectors. It is important to note that with more fibers in a connector, the lane orientation on each side is really important per application.
Polished to Perfection (and Specification)
The whole purpose of these connectors is to allow signals to pass from one fiber end-face to another in a way that is reliable, has low loss, and is simple.
Multimode fibers have a larger core and are more tolerant of an air gap between the end-faces, so the granddaddy of the styles, the flat fiber connector, works out (most of the time). The larger the end-face, the more likely that imperfections will widen that gap. When dealing with the very tiny (9µm) core of single mode fiber, that gap is a problem.
The flat fiber connector has evolved into a style that allowed direct physical contact called, you could probably guess, the PC connector. These are polished with beveled edges to mitigate the effects of surface imperfections and get a tight connection. This also reduces signal reflection. When light passes through different media, some light is bounced back towards the source. This is reflection. By pressing glass to glass with as little air between the surfaces as possible, reflection is minimized.
The PC connector was refined by making the bevel more severe and increasing the meticulousness of the polishing. This successor is called the Ultra Physical Connector. The tighter connections result in less signal loss and less reflection, which is why this connector is still used prolifically today.
With so much progress being made to perfect the contact between the two fibers, a new style was developed to tackle reflection issues that still lingered. The aptly named Angled Physical Connector is keyed so that the contact between he fibers is not perpendicular to the signal. This is so that whatever reflection there is does not point straight back down the fiber and instead ricochets of the core walls to diminish it’s effect.
Judging a Book by It’s Cover
All of the modern connectors can be made in the UPC or APC style. And with all of these connectors being orientation keyed, lining up the angles when connecting them is automatic. The danger comes from trying to connect the UPC to the APC styles, which will result in creating an uneven gap between them. To avoid this accident, the connectors largely follow a color scheme where the UPC styles are blue and the APC are green. It’s a crazy world though, so customizations are out there. Mind your connector types!
Bonus trivia: Even though barrel connectors for mating jumpers together come in a variety of colors, as long as the jumpers that are mating are the same connector format they will fit correctly.
As we conclude this three part series, you should have a better feel for the character of fiber optic cables and jumpers available. After just a little time applying this knowledge, you’ll be able to quickly identify most characteristics of a fiber at a glance.