Choosing Transmission Equipment

Choosing transmission equipment is the next step in designing a fiber optic network. This step usually will be a cooperative venture involving the customer, who knows which types of data they need to communicate; the designer and installer; and the manufacturers of transmission equipment. Transmission equipment and the cable plant are tightly interrelated. The distance and bandwidth will help determine the fiber type necessary, and that will dictate the optical interfaces on the cable plant. The ease of choosing equipment may depend on the type of communications equipment needed.

Telecom has been standardized on fiber optics for 30 years now, so manufacturers have plenty of experience building and installing equipment. Most telecom equipment uses industry conventions and will be available for short links (usually metropolitan networks, perhaps up to 20 to 30 km), long distance, and really long distance, such as undersea runs. All run on single-mode fiber, but may specify different types of single-mode.

Most CATV links are AM (analog) systems based on special linear lasers called distributed feedback (DFB) lasers using either 1,310 nm or 1,550 nm operating on regular single-mode fibers. As CATV moves to digital transmission, it will use technology more like telecom, which is already all digital.

The choices become more complex when it comes to data and CCTV because the applications are varied and standards may not exist. In addition, equipment may not be available with fiber optic transmission options, requiring conversion from copper ports to fiber using devices called media converters.

In computer networks, the Ethernet standards, created by the IEEE 802.3 committee, are fully standardized. You can read the standards and see how far each equipment option can transmit over different types of fiber, choosing the one that meets your needs. Most network hardware, such as switches or routers, are available with optional fiber optic interfaces, but personal computers generally come with only unshielded twisted-pair copper interfaces that require media converters. Media converters will allow the choice of media appropriate for the customer application, allowing use with multimode or single-mode fiber and may even offer transceiver options for the distance that must be covered by the link. An Internet search for “fiber optic media converters” will provide you with dozens of sources of these inexpensive devices.

Closed-circuit television (CCTV) is a similar application. More cameras now come with fiber interfaces, since many CCTV systems are in such locations as big buildings, airports or areas where the distances exceed the capability of coax transmission. If not, video media converters, usually available from the same vendors as the Ethernet media converters, are readily available and also inexpensive. Again, choose converters that meet the link requirements set by the customer application, which in the case of video would include distance and functions to allow video links to carry control signals to the camera for pan, zoom and tilt and for sending video back to a central location.

What about industrial data links? Many factories use fiber optics for its immunity to electromagnetic interference. But industrial links may use proprietary means to send data converted from old copper standards like RS-232, the ancient serial interface once available on every PC; SCADA, popular in the utility industry; or even simple relay closures. Many companies that build these control links offer fiber optic interfaces themselves in response to customer requests. Some of these links have been available for decades, as industrial applications were some of the first premises uses of fiber optics, dating back to before 1980.

Whatever the application, it is important for the end-user and the cabling contractor to discuss the actual application with the manufacturer of the transmission hardware to ensure getting the proper equipment. While the telecom and CATV applications are set and the data (Ethernet) applications are covered by standards, it is our experience that not all manufacturers specify their products in exactly the same way.

I recently worked with a company in the industrial marketplace that offered about 15 different fiber optic products, mainly media converters for its control equipment. However, those 15 products had been designed by at least a dozen different engineers, not all of whom were familiar with fiber optics, especially fiber jargon and specifications. As a result, one could not compare the products to make a choice or design them into a network based on specifications. Until we trained their design, sales and applications engineers and created guidelines for product applications, the company suffered from problems in customer application.

The only way to make sure you are choosing the proper transmission equipment is to make absolutely certain the customer and equipment vendor—and you—communicate clearly what you are planning to do.

HAYES is a VDV writer and educator and the president of The Fiber Optic Association. Find him at



About the Author

Jim Hayes

Fiber Optics Columnist and Contributing Editor
Jim Hayes is a VDV writer and trainer and the president of The Fiber Optic Association. Find him at .

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