How to Tell Different Types of Connectors?

Fiber optic connectors terminate the ends of fiber optic cable jumpers, either single mode or multimode fiber jumpers, and enable quicker connection and disconnection than splicing. They adopt the mechanical optical means for cross connecting fibers and linking to fiber optic transmission equipment. Fiber optic connectors are the most widely used optical passive components in fiber optical transmission, optical distribution frame, optical test instruments and instrument panels. There are numerous types of fiber optic connectors available today. Generally, we can divide fiber optic connectors into various types according to different standards. This paper will introduce three methods for the classification of fiber connectors according to fiber core size, connector structure, and end face preparation.

Fiber Core Size

According to the fiber core size, fiber optic connectors can be divided into common silicon-based single-mode and multimode optical fiber connectors. As the name implies, the single-mode connector is connected with SM (single-mode) patch cable with a relatively narrow diameter, through which only one mode will propagate typically 1310 or 1550 nm. While the multimode optical fiber connector is used for MM (multimode) cable which has a little bit bigger diameter, with common diameters in the 50 or 62.5 microns. Besides, some fiber optic connectors can be both single mode and multimode types. For example, LC connectors can be used with single-mode and multimode fiber-optic cables.

Connector Structure

Since 1980s, various manufacturers have developed a dozen types of fiber optic connectors. A fiber connector mainly includes a dust cap, connector housing, ferrule, crimp eyelet and boot bare buffer, etc. The mechanical design varies a lot among different connector types, thus we can get various connectors, such as FC, SC, ST, LC, MT, etc. For example, SC connector is built around a long cylindrical 2.5 mm diameter ferrule. A 124 to 127 µm diameter high precision hole is drilled in the center of the ferrule, where stripped bare fiber is inserted through and usually bonded by epoxy or adhesive. The end of the fiber is at the end of the ferrule, where it typically is polished smooth. While ST connector, simplex only, is twist-on mechanism. It is the most popular connector for multimode fiber optic LAN applications with a long 2.5 mm diameter ferrule. It mates with a interconnection adapter and is latched into place by twisting to engage a spring-loaded bayonet socket.

End Face Preparation

The connector end face preparation can determine what the connector return loss, known as back reflection, will be. Minimizing back reflection can provide high-speed and analog fiber optic links. In accordance with connector end face preparation, the connectors can be classified into PC polish, UPC/SPC polish, and APC polish connectors. PC polish connectors are typically polished with a slight curvature when the connectors are mated the fibers touch only at their cores. UPC polish types, improvement to the PC connectors, refer to the radius of the end face polishing administered to the ferrule, the precision tube used to hold a fiber in place for alignment. APC connectors have a curved end face which is angled at an industry-standard eight degrees. Only APC connectors can consistently achieve return losses of 60 dB. The following picture demonstrates their difference.

Conclusion

Fiber optic connector manufacturers offer various kinds of fiber optic connectors, including FC connectors, LC connectors, SC connectors, ST connectors, etc. Choosing the suitable fiber optic connector for any installation not only provides perfect performance for your job, but also saves time. Next time when you make a selection of fiber optic connectors, this article may give you a general idea of how to choose them.