Nowhere are the advantages of fiber optics—low loss, high bandwidth and immunity to electrical interference—more important than in security systems, especially surveillance cameras. As crime and terrorism have become more worrisome around the world, a major deterrent has been continuous monitoring of public places like streets, airports or subways looking for suspicious behavior and recording actions to deter or capture perpetrators.
Utility companies use cameras to watch the perimeter of power plants and substations. Sea- and airports are fully covered with cameras. Roadways are monitored by video cameras 24/7 for traffic control, and many are accessible over the Web for drivers who want to know what to expect when they hit the freeway. You can even see what conditions are like on ski trails with Webcams in parks. Most of these applications are made possible by optical fiber cable connections.
Video monitoring and recording are not new, having been used in retail and banking for many years. But monitoring of public spaces has become widespread only in the last few years, a result of new technologies applied to video systems. Connecting a camera inside a small building is easily done with a coax cable, and recording can be done on videotape.
But coax cable has a limited distance capability, about 1,000 feet (300 meters), and storing and scanning videotape can be tedious. Surveillance camera recording has moved to PC-based systems with mass storage, allowing easy access to video footage, and image processing software allows identifying and tracking objects. The use of fiber optic cables has allowed virtually unlimited range for cameras, centralizing recording and monitoring functions for convenience.
How pervasive is video monitoring for security? The United Kingdom probably holds the record for installed video cameras with an estimated 4 million surveillance cameras. A person going to and from work and walking out to lunch in London may be recorded on as many as 4,000 cameras per day. These cameras helped identify the terrorists who attacked a London subway in 2005. Lower Manhattan already has several thousand cameras in Greenwich Village and Soho alone. Most office buildings have surveillance cameras inside and out. On a visit to Las Vegas recently, I counted 45 cameras in the ceiling of the gaming floor of one casino, not so much looking for criminals as cheaters. Wherever you are, look up. You may find you’re on a camera.
Connecting video cameras with fiber is quite easy. Many manufacturers offer cameras with direct fiber optic connections. Inexpensive adapters allow conversion of the analog or digital electrical signals from the cameras to optical signals. These signals can be transmitted over multimode fiber for several kilometers in premises applications and single-mode fiber for longer distances in municipal or transportation applications. Control of pan/zoom/tilt of the cameras can be controlled by signals sent in the opposite direction on the same fiber or a second fiber.
Where many cameras are used in an area but monitored remotely, multiple cameras can be multiplexed on a single fiber, or a multifiber cable can be used. A cable containing dozens of fibers is smaller than a single coax cable, simplifying runs in areas such as airports or subways, where cables are run in conduits. Cameras also can be digitized for transmission longer distances, multiplexing or formatted as Internet protocol (IP) for Web monitoring.
Recently, reports have appeared that encourage unshielded twisted pair (UTP) copper cabling for video and local area networks (LANs). UTP has less distance capability than coax, even when the highest bandwidth Category 6 is used. While it may be convenient in some cases to use UTP in a structured cabling system for surveillance cameras, the distance limitation can be a big problem if cameras are located in places where computers are not.
Besides connecting video cameras, fiber can be used either for connecting other security devices or as a sensor. Almost any security device, such as intrusion alarms, can be connected on fiber using adapters called media converters. Depending on the remoteness of the device, media converters using multimode or single-mode fibers can be used.
Fiber is sensitive to stress, which causes optical loss at the point of stress—a characteristic normally reduced by cable design, but it can be used as a sensor by exposing it directly to stress. For example, fiber can be woven into a fence where it will be stressed if someone tries to climb or cut the fence. It can be buried in gravel where weight on the surface will stress the fiber and create loss. More than 20 years ago, we developed perimeter alarms that could determine the location and approximate weight of the intruder, distinguishing a person from a vehicle, for example. Unlike copper-based systems, a fiber intrusion alarm is undetectable, making it difficult, if not impossible, to find and disable.
Design and installation
One of the reasons fiber has become so popular for surveillance cameras is the familiarity of contractors with fiber optics and its installation processes. Cameras use the same types of fiber, multimode (50/125 micron or 62.5/125 micron) or single-mode and the same connectors (generally ST or SC) that are used in other fiber optic systems. If spare fibers are available, video may be sent over the same cables that carry LAN, telco or CATV signals. Thus, in a corporate network or utility power generation facility, for example, currently installed cabling may be available for security system usage.
While fiber optic cable is hard to tap and impossible to jam (see sidebar), it is possible to disrupt links by simply cutting the cable. Therefore, most security systems run fiber optic cables in conduit, usually metal, for protection.
Pulling fiber in conduit is not difficult, but does require following some basic guidelines. Remember to pull fiber optic cable only by the strength members, not the jacket. Properly attached, premises fiber cable can be pulled at tensions of up to 200 pounds. Pulls should go through only two 90-degree bends at a single pull, and the bend radius should be greater than 20 times the cable diameter.
If pulling tension is high due to friction in the conduit, use a suitable lubricant, which means compatible with the jacket of the fiber cable and the conduit. Different lubricants are needed for outdoor and indoor usage, since indoor lubricants are designed not to drip out of conduit. Special dedicated lubricants for fiber cable are available, and lubricant manufacturers should be consulted for advice on choosing and using these lubricants.
Not following these installation guidelines can cause serious problems. For example, an installer on an airport project pulled a cable through a long distance and a large number of 90-degree turns without lubricant. When the fibers were tested with a LED test source and power meter, all had higher than expected loss at 850 nm, but some had an even higher loss at 1,300 nm. Remember that fiber shows higher stress losses at longer wavelengths, so the higher loss at 1,300 nm showed the cable had been overstressed during installation, probably affecting its long-term reliability. Replacement was the only reasonable fix.
You may be able to run power for the equipment in the same conduit as the fiber according to most codes. Check the local inspectors for clarification on this issue. Custom composite cables with power conductors and fibers are an option worth considering if a large number of systems is being installed. EC
HAYES is a VDV writer and educator and the president of The Fiber Optic Association. Find him at www.jimhayes.com.