Technical advances move singlemode fiber to the marketplace

With the exception of incremental improvements in quality, ease of use, and performance, singlemode optical fiber has remained relatively stable since it was introduced about a decade ago. Manufacturers in the cabling industry agree that singlemode fiber is a well-proven medium used in an established cabling system.

Jun 1st, 1997

Technical advances move singlemode fiber to the marketplace

Lynn T. Haber

With the exception of incremental improvements in quality, ease of use, and performance, singlemode optical fiber has remained relatively stable since it was introduced about a decade ago. Manufacturers in the cabling industry agree that singlemode fiber is a well-proven medium used in an established cabling system.

Available from a number of vendors, singlemode fiber is less expensive than multimode by approximately $0.40 to $0.50 per foot. The electronics, however, can cost two to five times as much as that for multimode. This is partly because singlemode depends on more-costly lasers, whereas multimode uses light-emitting diode (led) technology.

With little difference between the two fiber cable types in terms of handling and installation, cabling contractors say the biggest thing singlemode fiber has going against it from the customer`s viewpoint is cost. "If the cost of a singlemode fiber system came down, I definitely think customers would consider it," says Brian Ballard, sales engineer for Clawson Communications, a cabling installation firm in Greenwood, IN.

In fact, as customers begin to talk about Gigabit Ethernet, interest in singlemode fiber will increase. "When we present singlemode fiber to our customers, they`re definitely more receptive than they were a couple of years ago," says Paul Kopera, senior marketing manager for structured cabling systems at Anixter International, a distributor based in Skokie, IL. "More and more, customers can see the value of singlemode fiber."

Hybrid cable an option

Manufacturers selling hybrid cable containing both singlemode and multimode fiber say that the loose-tube type of hybrid cable is most commonly installed. In this construction, the different fiber types are placed in different buffer tubes or bundles within the same cable. According to Allen Dixon, product specialist at Siecor Corp. (Hickory, NC), the loose-tube construction provides easy access to individual fibers without disturbing any others.

Some vendors also sell hybrid cable with a central-tube design. This design places all fibers, usually 6 to 12 per bundle, in a central tube and separates them by binder thread. "To access any fiber in a central-tube design, all fibers are exposed," explains Dixon. The main reason installers use the central-tube design, he adds, is because they sometimes need a smaller diameter of hybrid cable.

Singlemode fiber in the interbuilding backbone has already become a given in the industry, and networking trends suggest that the future deployment of singlemode fiber in short-haul applications is all but certain. Industry analysts also suggest that cabling installers should stay attuned to advances in singlemode technology.

Anixter`s Kopera, for instance, suggests that singlemode fiber will have a bigger role in premises wiring when the centralized networking architecture recently approved by the Telecommunications Industry Association (tia-- Arlington, VA) in one of its telecommunications systems bulletins becomes a more popular cabling method, overshadowing the traditional star-wiring configuration. He anticipates that this increased interest in centralized cabling will be apparent when Gigabit Ethernet is used in the riser. "I also expect that the industry will look at singlemode in the horizontal," he adds.

A benefit of the centralized cabling scheme is that it requires fewer expensive electronic devices than star-wiring: Fiber-optic cable can be run for longer distances than copper wires, and electronics are no longer needed in the telecommunications closets on each floor.

Less expensive lasers on the way

However, the high cost of singlemode electronics is still a concern to the industry. Another limitation of singlemode fiber is the space that its connectors consume in the hub. The good news is that manufacturers are tackling both the cost and footprint issues.

Several vendors, for example, are working on a less expensive laser for use with singlemode fiber. Prototype products using vertical-cavity surface-emitting laser (vcsel) technology are already on the market. vcsels are being designed for use with both singlemode and multimode fiber.

Hewlett-Packard Co. (Palo Alto, CA), for instance, is shipping its vcsel-based product to original equipment manufacturers for evaluation, according to Northe Osbrink, technical editor with the company`s Optical Components Group.

Hewlett-Packard`s current transceiver product targets the multimode market for Gigabit Ethernet, adds Osbrink, although it is also suitable for singlemode fiber. "It`s important to maximize the investment users have already made," he says.

led technology has bandwidth limitations, so there is strong industry interest in a low-cost multimode laser that can achieve higher bandwidths. Osbrink suggests that, when dealing with a cabling situation requiring 600 megabits per second to a gigabit-per-second rate at 500 meters or more, it is time to move to the new 850-nanometer vcsel technology.

Next-generation connectors

There is also work in progress to develop the next-generation connector for singlemode optical fiber. In fact, the Fibre Channel Association met in February in San Jose, CA, to discuss specifications.

As optical fiber moves deeper into the campus and building, reaching the desktop for high-bandwidth applications, the need for a high-density connector becomes more obvious. This is because the only way to fit more transceivers on a network card and increase the number of users who can be served is to shrink the size of the connector and reduce the amount of real estate it takes up.

Compared to users of copper cabling, users of optical fiber today pay a penalty, in that a limited number can connect to a hub; copper can accommodate many more users in the same amount of real estate. "If you want to do fiber-to-the-desk, which means you`re now talking about adding hundreds of lines, you have to be able to shrink the size of the connectors," says Bryan Gregory, product marketing manager of optoelectronic devices at Molex Inc. (Lisle, IL).

Singlemode fiber has a long future ahead of it, but ongoing industry developments will show the role it will play in the network. This leads Kopera to conclude that the time has arrived for cabling installers to introduce their customers to singlemode fiber. "Customers should know about singlemode fiber when preparing their communications infrastructure plans," he says.

Industry experts agree that singlemode fiber is no more difficult to work with than multimode fiber. However, singlemode fiber requires a different set of tools, and laser-based systems require additional safety precautions. Also, technological advances will continue to make fiber easier to handle. Advances in mass-fusion splicer technology, for example, make it simpler than ever for installers to work with singlemode fiber, since mass-fusion splicing does not require as much precision. q

Lynn T. Haber is a freelance writer specializing in networking and telecommunications issues.

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