|
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.
|
