Knowing Fiber Optic Connectors

An optical fiber connector terminates the end of an optical fiber cable. Its purpose is to allow quicker connection and disconnection of fiber cables than manual splicing. Simple enough concept. The problem is there are about 100 different types of fiber connectors available on the market today. Do you know the best one for your application?

Fiber connectors mechanically couple and align the cores of fibers so light can pass. The best ones lose very little light due to reflection or misalignment of the fibers. If you want a standard for fiber connectors, forget it.

Due to the polishing and tuning procedures that may be incorporated into optical connector manufacturing, connectors are often assembled onto optical fiber in a supplier’s manufacturing facility. This, however, can also be done in the field.

Optical fiber connectors are used in a wide range of applications beyond broadcast facilities. Most connectors are spring-loaded, so the fiber faces are pressed together when the connectors are mated. The resulting glass-to-glass or plastic-to-plastic contact eliminates signal losses that would be caused by an air gap between the joined fibers.

Performance of optical fiber connectors is quantified by insertion loss and return loss. Measurements of these parameters are now defined in IEC standard 61753-1. The standard gives five grades for insertion loss from A (best) to D (worst), and M for multimode. The other parameter is return loss, with grades from one (best) to five (worst).

A variety of optical fiber connectors are available, but SC and LC connectors are the most common types of connectors on the market. Typical connectors are rated for 500–1,000 mating cycles. The main differences among types of connectors are dimensions and methods of mechanical coupling. Generally, organizations will standardize on one kind of connector, depending on the application and equipment they use.

This is where it gets complicated. Equipment used in a stationary indoor rack needs a different connector from highly mobile, frequently used gear on mobile broadcast rigs. In such mobile settings, protective enclosures are often used around the connector. These fall into two broad categories: hermetic (sealed) and free-breathing.

Hermetic cases prevent entry of moisture and air but, lacking ventilation, can become hot if exposed to sunlight or other sources of heat. Free-breathing enclosures, on the other hand, allow ventilation, but can also admit moisture, insects and airborne contaminants. Selection of the correct housing depends on the cable and connector type, the location and environmental factors.

Thanks to Camplex, the fiber cable manufacturer, here are the most popular fiber connector types:

ST Straight Tip.

ST Straight Tip.

ST STRAIGHT TIP
Popular in broadcast and other media facilities, this connector is also used by the military, in buildings and on campuses. The round design features a twist on/twist off bayonet lock with an alignment key to prevent rotation of the ceramic 2.5mm ferrule. The ferrule is a component (usually a rigid tube) used to align and protect the stripped end of a fiber.

SMPTE 304M

SMPTE 304M

SMPTE 304M
Used in high definition broadcast applications and harsh environments. This connector conforms to SMPTE standards for HD broadcasting. The push on/pull off self-latching hybrid connectors include fiber, power and low voltage signal.

LC Lucent

LC Lucent

LC LUCENT CONNECTOR
This connector is popular for Ethernet, IT and with high density hardware. Its small form factor, square connector features a 1.25mm ferrule and a retaining push/pull latch. It is ideal for densely populated racks and panels.

Neutrik opticalCON

Neutrik opticalCON

Neutrik opticalCON
Used in mobile and rugged outside settings. The metal round enclosure features a shutter system to protect the connector from dirt and damage. It is waterproof to IP safety standards and compatible to conventional LC connectors.

SC SUBSCRIBER

SC SUBSCRIBER

SC SUBSCRIBER/STANDARD CONNECTOR
Popular in data centers, PON, CATV and MADI installations. This square connector with a 2.5mm ceramic ferrule features a push on/pull off latching design to reduce fiber and end-face damage during connections.

MTP

MTP

MTP by USCONEC
Popular for high bandwith, high density indoor applications. MTPs provide integrated multifiber connection for up to 72 optical fibers in a single ferrule when locked into place with the push/pull lock mechanism. The gender can be easily changed.

There are dozens more types of connectors. Research is required to find the best for a given application.

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