SC, ST, LC, FC, FDDI, SMA, D4, MT-RJ, Bionic...
Fiber Optic Connector Guide Before one can choose the proper fiber connector, it is important to understand some of the basic terminology and make-up of the connectors. THE CONNECTOR
A Connector
is a device used to provide a semi-permanent link between two optical fibers. Connectors must be able to maintain good optical contact between the fibers at the connector interfaces. In theory, only the cross sectional face of the two fibers need to touch, hence the term
Physical Contact (PC)
connector is used. The basic components of a connector include the body, the ferrule, the barrel (coupling nut), and the boot. The body
is the physical shell of the connector, which houses the mechanism used to secure the fiber to the connector. The ferrule is the long cylinder-like piece, which extends from the body and provides protection and alignment of the fiber. Ferrules can be made of composite materials, stainless steel, or ceramic. These material types provide for a wide range in cost and performance values. The
barrel
is the plastic or metal screw applicator, which provides the method of attaching some connector types (FC, SMA, D4, Bionic) to their mating couplers. And finally there is the boot, the small plastic strain relief that provides protection for
the fiber entering the rear of the connector body. Key performance values in connectors include Insertion Loss
, Reflectance, Core Alignment (Apex Offset), and End Face Polishing. Insertion Loss
is the measure of reduction in signal caused by inserting a component, such as a connector, into the optical pathway. Insertion loss is measured in decibels (dB), with a lower dB reading having better performance standards, i.e. (0.10dB) is better than (0.20dB). Reflectance is the measurement of light reflected from the cleaved or polished fiber end at the glass/air interface. Reflectance is expressed in dB relative to the incident signal. This value is important because some systems are sensitive to light reflecting back into them. Similar terms are
back reflection and optical return
loss. Again a lower reading is better, i.e. (-50dB) is better than (-40dB). Alignment
of the fiber cores is extremely important when connectorizing two fibers. One of the basic differences between multimode and singlemode connectors is the degree of tolerance in core alignment. With singlemode core diameters approaching 8um, accurate core alignment is imperative. Finally there is
End Face Polishing. The End Face of the
connector refers to the circular cross-section of the fiber where light is emitted and received. By proper polishing of the connector, the geometrical properties of the endface can be enhanced to provide
optimum fiber coupling. As connectors get worn, scarred, or contaminated, these geometric properties change resulting in increased attenuation and loss of signal strength. To improve upon the physical
performance values at the connection point, there are several options to choose from. One of the best ways to provide ultimate connector performance is to terminate the fiber with factory connectorized pigtails. A pigtail is nothing more than a factory
terminated connector with a short piece of fiber that can be fusion or mechanically spliced onto the fiber cable. Another method is by selecting high performance polishing techniques and/or utilizing Angled
Physical Contact (APC) connectors. Obviously not all connectors are created equal. Beside field termination polishing, which has been a tried and true method of terminating fiber, there are various grades of
polished connectors available from the factory. Typical field terminated PC connectors will have a reflectance of (< -35dB) while an
Ultra Physical Contact (UPC)
connector will have a reflectance value approaching (<-55dB). Lastly by introducing a small angle to the end face, the reflectance properties of the connector can be improved to (<-65dB). Generally PC connectors have a flat 90-degree edge to them. With
APC connectors, a slight 8-degree angle
is introduced to the end face allowing improved performance at the fiber/air interface. However, when working with this type of connector, extreme care must be taken in properly aligning the fibers in any
electronics and/or adapters. Even though these connectors are keyed, they still may require a little 'jiggle and wiggle' before the matching connectors align with each other. Many times, an installer has
thought connector alignment was successful only to find the power loss too great until they were wiggled into position. Another word of caution would be about the actual cut of the angle. Though manufactures
have now standardized on the 8-degree angle, there are still some old systems out there that use a different degree of cut. Be careful to match the angles of the connectors and equipment. COLOR CODE
The generally accepted color code for connector bodies and/or boots is: Beige for multimode fiber, Blue for singlemode fiber, and Green for APC (angled) connectors. |
