Adapt your dissimilar connectors

Barbara E. Thompson

Fiber-optic hybrid adapters are mechanical termination devices that enable alignment of two dissimilar connectors. Installers can reterminate dissimilar connectors with standard couplings and hybrid cables, but this means extra cable and couplings are needed. Hybrid adapters replace these interconnect alternatives with one component.

For new systems, installers will normally use one connector type throughout the network for ease of testing, maintenance and administration. Hybrid adapters are necessary in retrofits, however, because of the many types of fiber connectors that have already been installed.

According to Steven Walls, operations manager of the data division at Comlink Corp. (Marlborough, MA), "A large percentage of the products today are coming through with ST connectors; however, future products are moving toward SC connectors. Your backbone cable will still be ST to ST," he explains, "but any equipment that you install after that will be interfaced with a hybrid. For example, if you buy a product with an SC connector, you will need an SC-to-ST hybrid adapter, or jumper."

Design and features

Available in many styles and configurations, adapters are offered for all types of optical connectors in male-to-female, male-to-male, female-to-male and female-to-female versions. Hybrid adapters can have flange, plug-in (sometimes known as snap-in) or threaded connections.

"A lot of the electronics require mini-BNCs; for example, the 8230 IBM local area network scenario with fiber inserts," says Joe Mattice, operations manager of the Lastar Group, a division of Cables to Go (Dayton, OH).

"And you don`t want to order a patch cable that has two different ends on it. You need to have adapters that can convert the ST to SMA or ST to mini-BNC in the IBM world," he adds. "The key is to have available adapters in all the different configurations that you might run into."

The inner shell of a hybrid adapter can be manufactured from ceramic, which is the highest quality, metal, which can be several different alloys, or plastic. Ceramic and metal can be used for singlemode and multimode applications, whereas composite or engineered plastic inserts are used mainly for multimode.

"The insert material (sleeve) for the ST adapter is available in ceramic, metal and plastic," says Martin Curran, marketing manager for fiber-optic joining point at Siecor Corp. (Keller, TX). "But because of the physical design of the SC adapter, only ceramic and metal inserts are currently offered."

Standard Connector Types

The International Standards Organization, the International Electrotechnical Commission and the Telecommunications Industry Association have endorsed the SC connector, which can be duplexed. The ST, however, is widely used in data communications and the telephone industry. The SC and ST are similar in that they are built around a cylindrical ferrule that holds the fiber, and they mate with an interconnection adapter.

Donna Ballast, communications analyst at the University of Texas at Austin, and author of Cabling Installation & Maintenance`s "Ask Donna" column, explains the use of ST/SC adapters (December 1994, page 46): "The hybrid adapter is mentioned in Annex F of the EIA/TIA-568A for the user with an installed base of ST connectors who wants to retrofit the site. Replacing the ST couplers with a hybrid eliminates having to cut off the existing ST connectors and reterminating the fiber with SC connectors. The ST/SC coupler was not intended to be used in new placements."

The FC is a screw-on connector with the same ferrule size as the ST and SC, but cannot be used as a module in duplex connectors. The FDDI connector, also a ferrule-based connector, was developed for duplex connections in local area networks. It is keyed so that it can be installed in only one polarity to prevent the reversal of transmit and receive fibers.

Connectors such as SMA, mini-BNC and D4 look like the ST, while others, such as the biconic and the EC, have a different construction. Hybrid adapters make it possible to interconnect all of these different types of connectors.