CHOOSING THE CORRECT CONNECTOR | UNDERSTANDING FIBER CONNECTIONS
With more than 100 fiber optic connector styles and types available today, the right choice for a particular application can often be difficult to figure out. Design and performance of both the optical fibers and connectors has become more sophisticated over the years. Today’s fiber connectors provide end-to-end solutions that cover a wide range of applications and, in many cases, can be easily terminated in the field.
Some early fiber optic connectors, used in telephone central offices, such as AT&T’s single mode Biconic and D4 style connectors were terminated with heat-cured epoxy adhesive and polished, at the factory, onto single mode optical fibers. They were used to connect high speed digital outside plant (OSP) fiber links.
These connectors have threaded nuts that tighten onto threaded equipment port receptacles. In the case of the D4 and FC, built-in keys provide repeatable optical coupling when mated to other FC/PC and FC/UPC bulkhead mounted connectors or to single mode laser equipment receptacles.
In addition, the SMA and AMP Optimate style connectors were some of the key industry fiber connector solutions for digital communications data links at the time. Those were soon followed up by the popular ST bayonet-style connector that is still often used today.
And, this is now...
The LC (SFF - Small Form Factor) and MPO connector are popular today for applications in data centers and building networks because of their small size and ability to provide high density patching and connectivity. Optical transceivers for most switches either have LC duplex ports, or use 12 or 24-Fiber MPO ports when employing parallel optical links for 40gbps or 100gbps speeds.
So, how do we determine the right connector?
First - define the application.
It is important to determine where the connectors are being used. Figure out what type of communication equipment is being connected at each end of the link, and what the data rates, distances and numbers of connections are for the network. That will determine the optical signal power loss budget , and the loss performance the fiber connectors need to meet.
Consult the standards requirements which can also help define the cable and connector types. For instance, connectors in the data center should meet the requirements of ANSI/TIA, and also meet the FOCIS standard defining the approved connector footprint(s) and ensuring intermatability. The standards can often point to a particular connector design and help quantify the key parameters of maximum Insertion loss and minimum return loss performance. Standards can also provide insights into the type of equipment necessary for the application:
Once the application is defined, the active equipment’s optical transceiver modules and bulkhead receptacles are also determined. This selection usually sets the types of adapters and connectors that will be selected for connecting the transceivers and the backbone and patching fiber cables and harnesses. At this point, it will become evident whether or not pre-terminated cables can be used. For example, in some instances if MPO connectors are specified, a pre-terminated cable can be selected. For splicing applications, connectors do not need to be installed the field, since factory terminated pigtails, and the splice connector, are fusion spliced directly onto the fiber cables.
Second - Describe the operating environment - How can the connectors be applied to the cable?
There are a number of ways a fiber optic connector can be terminated to fiber optic cables. Take a look at the type of fiber and cable construction you are planning to work with in the application. The best way to select a particular connector is by looking at the operating environment where it is going to be used. Harsher environments usually make field termination more difficult and demand the use of heat-cured epoxy. Factory terminated fiber patch cords are polished, for instance.
What is the connector life and performance expectancy?
Epoxy terminated fiber connectors provide a lifetime of performance and are backed by manufacturer’s warranties. The gel in pre-polished connectors has been used for years in telecommunications splicing for a 40-year life.
The ferrule end-face polish and finishes dictate the type of performance that a connector can achieve. The higher loss and reflections encountered with the SMA connector flat polish is virtually eliminated today with PC radius polishes.
Choosing the right fiber optic connector requires proper planning and attention to detail to achieve the best possible fiber link performance in the field. Careful consideration and definition of the application and the environment for the connector will help to determine the best connector solution for the application.
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