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The force of fiber.


Fiber-optic systems currently carry crystal-clear telephone messages over thousands of miles, move razor sharp, high-definition video across the studio and across town, and carry computer data over far-flung networks at blinding speeds. Still, many security managers stand on the sideline, interested but skeptical.

Why? "It's the way of the future, but not for now." "It's too complicated to bother with." And the familiar, bottom-line response: "We can't afford it." Here's news: Fiber optics offers a cost-effective, superior-quality, flexible, upgradable solution for a wide variety of security applications - and is available now. "We can't afford it" should be "We can't afford not to have it."

The total CCTV and access control market, of which security is the major component, had worldwide sales of more than $1 billion in 1989. About $180 million of this was for system inter-connect equipment. And fiber-optic equipment, far from being a distant, futuristic solution, has already captured about 15 percent of that interconnect market - $27 million in 1989. As security and other professionals learn the advantages of fiber optics, the trend becomes clear: 50 percent of the total CCTV interconnect market is expected to be handled by fiber optics.

Ease of use. Many potential users are intimidated by the new technology. They expect to have to wade through confusing new terms, skills, and equipment. But for the majority of applications, the fiber-optic component of the system is essentially transparent. Cameras and monitors connect to the fiber-optic link with familiar electrical connectors. Connectorized fiber cables, smaller and lighter than their coax counterparts, connect the fiber-optic transmitters and receivers.

A user needn't understand fiber-optic technology to operate a fiber-optic system. Nevertheless, a brief description of the principles behind the technology may be helpful.

Optical fiber works by transmitting light. The fiber itself, usually made of glass, is composed of a core surrounded by cladding. Because the core has a higher refractive index than the cladding, the fiber exhibits total internal reflection - that is, all the light is confined to the core. That is how the narrow fiber, housed in an easy-to-handle cable, can carry light around a corner or over long distances.

An electrical signal, say from a CCTV camera, enters a fiber-optic transmitter. The signal drives a light-emitting diode or laser diode. The output of the diode is light (usually in the infrared region), which varies in intensity with the input signal. The signal, now carried by light, travels down the optical fiber to the fiber-optic receiver.

The detector in this receiver, either an avalanche photodiode or a positive intrinsic negative photodiode, reverses the process of the transmitter, converting the signal from light back to electricity. The output of the receiver then feeds into the intended destination, such as a CCTV monitor. Although the complexity increases with the sophistication of the system, the basics remain the same for every fiber-optic link.

Distance advantage. One of the major advantages of fiber-optic cable over coaxial, twisted-pair, or other metallic cables is that it can transmit signals over especially long distances. With video, for example, using metallic cable, one must install a line amplifier every 1,000 feet to get a usable picture at the other end. By contrast, some fibers can transmit a studio-quality video signal 30 miles or more without using any line or signal amplification whatsoever.

In addition, fiber eliminates the need to adjust video transmission equipment to account for differences in cable length. Picture quality is always noticeably uneven when 10 or more monitors are lined up in the control center of a large installation. While video line amplifiers are designed to drive coaxial cables with a nominal impedance of 75 ohms, the actual impedance of the cable is a function of its length. As cable length increases, so does its capacitance.

That capacitance increase degrades high-frequency response in metallic cables longer than 50 or 100 feet, thereby affecting the picture's contrast, dynamic range, and color. An equalization process may be able to boost the high-frequency signal, but that process requires knowledge of the cable's length and attenuation characteristics. High-frequency compensation is much harder when metallic cables run over 1,000 feet and is totally impractical for cable runs longer than 3,000 feet.

Fiber-optic cable eliminates that problem. Since signals are transmitted in the form of light, the length of the cable has no analogous effect on its effective impedance.

Another factor in fiber's superior long-distance transmission is its ability to carry high bandwidth. Metallic wires of any kind have an upper limit to the frequency of the signals they can carry as electronic current. Beyond that limit, usually in the microwave spectrum, expensive and unwieldy tubular wave-guides are required.

Optical fibers, by contrast, have no such bandwidth restrictions, nor do they exhibit any of the propagation delays associated with electron flow through a conductor. In theory, light carried by these fibers is slowed by just one millisecond every 186 miles!

Security and EMI. When information quality and security are a priority. fiber is the absolute choice. Metallic wires use electromagnetic signal propagation methods, which generate fluctuations outside the conductor. These fluctuations carry the same information as the conductor itself; therefore, an outsider with access to the wire could listen in by means of magnetic flux gathering.

Optical fiber eliminates that possibility. Electromagnetic fields, in the form of light, are confined within the glass fiber, making it impossible to listen in - via magnetic flux gathering - on the communications carried by a fiber. If an intruder attempted to listen in by cutting into the fiber, a prohibitive signal loss would result and the user of the communications channel would easily detect the intrusion.

This feature of fiber is undoubtedly a must to the military. The authors' company has provided fiber-optic links for the surveillance of US Air Force bases and nuclear missile silos overseas, as well as for the security of US naval bases and submarine pens.

The flip side of the tapping problem is electromagnetic interference (EMI). Electromagnetic interference makes the installation of communications networks in electric utilities, nuclear power plants, and transportation facilities, among other locations, very difficult. Magnetic field lines generate or induce an electrical current as they run across a conductor, thereby producing a magnetic field that changes with the current flow. Stray magnetic fields can induce a current in any wire exposed to them. The result is a noisy signal and distortion that looks like snow and hum bars on the monitor.

Any metallic conductor, including coaxial cable, is susceptible to the problem. Optical fiber, on the other hand, is immune to EMI. Signals are carried by light, not current, and no metallic conductors are present, only glass.

Thus fiber-optic cables that avoid metal in their design should be chosen for EMI applications. An example of such an application is the Department of Energy's Oak Ridge Nuclear Facility. MERET Optical Communications, the authors' company, is supplying fiber-optic links to Martin Marietta, the main contractor for the facility's communications system. The multipoint system includes CCTV, badge readers, and door lock links.

Choosing a nonmetallic, fiber-optic cable eliminates other problems as well for electric utilities and power plants. Ground loops may exist over long runs of metallic cables. Stray currents caused by these differences in potential can introduce noise into the system and, if large enough, even damage components. In addition, metallic cables outdoors are susceptible to being hit by lightning, which can cause power surges that destroy components.

A final, related problem most often occurs in oil refineries and chemical plants. Hot, corrosive, and poisonous environments present the biggest challenge to most communications media. Explosions sometimes occur in such environments, and almost all of them are caused by a spark or overheated equipment around the workplace. Using metallic cable to transmit an electric signal in an oil refinery or chemical plant, where the air is contaminated with explosive vapors, is just too dangerous. Nonmetallic, fiber-optic cable makes communications possible even in those environments.

Signal quality. A security communications system depends on the quality of its signals. Fiber optics has earned a reputation for its superior signal quality.

The primary component of a CCTV security link is video, which is usually carried as an analog signal. Analog signals need to be reproduced accurately for good-quality communications. However, EMI and ground loops can introduce noise into a system that uses metallic cables, as can the repeaters used in long-distance links. Optical fiber averts these sources of noise. Moreover, because fiber, unlike coax, does not exhibit the problem of impedance varying with distance, that effect on picture quality is eliminated.

Video is a bandwidth-intensive medium. That makes fiber, with its enormous bandwidth capabilities, a natural choice. The attenuation of signals carried by coax rises sharply with bandwidth. With fiber, on the other hand, transmission signal loss is relatively independent of bandwidth.

Fiber also allows for higher-resolution signal to be sent. More and more high-level security applications are using high-resolution monitors, whose bandwiths are handled easily by fiber-optic systems.

Flexibility and upgradability. Security communications systems, of course, are often more than just video. Pan, tilt, and zoom control may be required for the camera. Audio links may be desired.

Handling a variety of signals is a feature of the flexibility of fiber optics. Multiple-fiber cables - smaller, lighter, and more flexible than their coax counterparts - carry the various signals over individual fibers. The long-haul user, on the other hand, may take advantage of fiber's huge bandwidth capacity and opt to multiplex several signals onto a single fiber.

Remote or local switching of several adjacent peripherals, along with the ability to transmit their signals over a single fiber, is an advantage only fiber offers. Frequency or amplitude modulation, electrical multiplexing of signals (FDM, or frequency division multiplexing), and multiplexing of lightwave signals (WDM, or wavelength division multiplexing) are all options for long distance transmission of high-quality signals overfiber.

Flexibility in packaging is also available to fiber-optic system users. Choices range from a transmitter that fits in the camera housing itself to a multislot chassis holding several multichannel cards. These chassis, housing cards for a variety of signals, can be rack-mounted in the control room. Stand-alone chassis, along with recievers that fit within a monitor, round out the packaging options.

Fiber-optics systems are easy to upgrade. Users often choose to lay fiber-optic cable that has more fibers than the system currently needs. That is an inexpensive way to allow for additional cameras and monitors or voice or data signals - to be added later without laying more cable. Should a higher-resolution monitor be desired, the large bandwidth capacity of the fiber also allows for upgrading the video bandwidth capability with new transmitters and recievers. Multiplexing additional signals over the same fiber is another way to upgrade a system; fiber's bandwidth capacity also offers that advantage over coax.

Cost. The deciding factor in convincing security professionals to go with fiber optics may well be affordability. Ever since the beginning, fiber optics has been considered an exotic medium that, while superior to coaxial or other metallic wires, simply costs too much. Cost certainly has been a major drawback and one of the main reasons fiber optics did not find its way sooner into the closed-circuit television, cable television, medical, high-resolution, and computer interconnection markets.

By contrast, the telecommunications industry endorsed the use of fiber as far back as the early 1970s. Because of the huge number of subscribers and fiber's ability to move vast amounts of information to many points, fiber has long been a cost-effective solution for telecommunications.

The price of a new technology often takes some time to come down. That has certainly been the case with computers, videocassette recorders, and other now affordable products. A computer in the late 1970s or even the early 1980s cost at least 10 times the price of one today; the computer also had less capacity and a slower processing speed than today's model.

With huge leaps in technology, better and more efficient manufacturing techniques, and a vast market that views fiber optics as the way to go, costs have decreased to the point where fiber optics is affordable, feasible, and in most cases the only alternative for connecting peripherals of any type.

For a comparison of the costs of coax and fiber, see the accompanying box. Although the analysis was done for multichannel TV, it illustrates the issues involved in the cost of coax and fiber links.

A final word. For years, engineers and users alike have dreamed of being able to send real-time images, data, and other information over long distances and at the highest quality. Fiber optics has brought us a giant step closer to reaching that goal.

The range of applications is wide: from high-definition television links to workstation extensions, from cable television subscriber loops to air traffic control systems. A project may range from the simplest commercial link to outer space: Providing space-qualified fiber-optic links for the NASA Space Station Freedom is perhaps the most intriguing application yet for the author's company.

In the security field, other fiber-optic applications the authors' company has been involved in include fiber-optic links for the Bay Area Rapid Transit System, the I-90 route in Washington State, and the Coronado Bay Bridge in San Diego. Many others, big and small, are handled every day by fiber-optic manufacturers.

For the security professional, the time has come for fiber optics to become the preferred medium of communications. Potential computer users were won over in the '70s and '80s once they had a little hands-on use. A fiber-optic manufacturer, dealer, or system integrator can analyze the user's requirements and supply a demonstration unit that shows the unique capabilities of the fiber-optic solution.

About the Authors. . .Chris P. Cladis is product manager for CCTV and access control fiber-optic interconnect products. Mitch Frishman is an applications engineer and technical writer. Both work for MERET Optical Communications Inc., an AMOCO company based in Santa Monica, CA.
COPYRIGHT 1990 American Society for Industrial Security
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1990 Gale, Cengage Learning. All rights reserved.

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Title Annotation:fiber-optic technology in security systems
Author:Cladis, Chris P.; Frishman, Mitch
Publication:Security Management
Date:Oct 1, 1990
Previous Article:Residence hall security 101.
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