More Fiber for Video Diet
Why Fiber?If you look at all the benefits optical fiber offers such as bandwidth to carry multiple signals, transmission distance, immunity from outside interference, life span, labor and installation costs, ability to transmit different types of signals over the same fiber and future expansion capabilities, optical fiber is the most cost-effective medium available, offers John Nave, design center
engineer, International Fiber Systems, Newtonn, Conn.
With most typical modern, moderate-sized facilities heading in the direction of integration, it is imperative that multiple electronic systems, including fire and burglar alarms, access control, closed-circuit television (CCTV), audio systems, telephones, lighting system controls and heating, ventilation, air conditioning (HVAC) systems will not be compromised. “Just push up one of your ceiling tiles and look at the number of cables running in the ceiling. Fiber can replace most of this while providing more versatility and better signal quality at a lower cost. Today’s technology allows a wide range of signal combinations to be combined multiplexed onto a single fiber, and can also permit two-way, or duplex transmission of multiple signals,” says Darren Nicholson, vice president of marketing, GE Interlogix/Fiber Options. Today’s high-performance CCTV systems require greater reliability and more throughput, that is, getting more signals from the camera end to the monitor end, over greater distances, and in harsher environments. The fiber optic transmission system preserves the quality of video signal and provides a high level of security. Fiber optics transmit at higher bandwidths, have lower losses and operate at distances five times greater than coaxial cable.
Secure TransmissionsNicholson further states that optical fiber is as tamper-proof as a communications medium can be. Since fiber is a dielectric, it does not radiate electromagnetic pulses, radiation or other energy that can be detected. This makes the fiber/cable difficult to find and methods to tap into fiber create a substantial system signal loss. “It would then take a great amount of effort and skill to splice a separate line into an existing fiber and draw any sort of communication from it. Considering that this must take place in the field with a previously installed and running system, it becomes virtually impossible to accomplish,” says Terry McBride, president, Infinova, Monmouth Junction, N.J.
There are no metallic conductors to induce crosstalk into the system. Power influence is nonaffecting, and security breaches of communications are very difficult due to the complexities of tapping optical fiber. Strength members add mechanical strength to the fiber. During installation, the strength members handle the tensile stresses applied to the cable so that the fiber is not damaged. The most common strength members are of Kevlar aramid yarn, steel and fiberglass epoxy rods. And, “because fiber is typically glass, it is not capable of emitting magnetic or electric fields that can be detected without breaking into the fiber itself. As long as a fiber is monitored for signal interruption, the integrity of a fiber can never be compromised,” says Nave.
The dielectric nature of the glass from which optical fiber is manufactured prevents all electro-magnetic interference (EMI) from degrading the optical signal in the fiber. Combine EMI immunity with optical attenuation coefficients that are typically less than 3.5 dB/km—some fiber even less than 0.2 dB/km—and even under adverse EMI conditions, optical fiber can generally maintain better signal quality over longer distances than any other transmission medium. There are no short circuits with fiber, because fiber is glass and does not carry electrical current, radiate energy, or product heart or sparks, the data is kept within the fiber medium. The large signal-carrying capacity of optical fibers makes it possible to provide not only many more signals, but also much more sophisticated signals than could ever be handled by a comparable amount of copper wire. A fiber optic system can accommodate multiple CCTV cameras, saving in electrical installation costs. Fiber optic cable preserves the integrity of the signal. Signals carried over copper cables are permeable to electromagnetic interference (EMI), which can degrade the signal. Signals carried on glass fiber are completely immune to EMI, no matter what the environment.
Fiber is a widely accepted method of transmitting video, audio and data signals for the following reasons:
• Radio frequency interference (RFI) and electromagnetic interference are eliminated and protection from lightning and ground loops is gained.
• No signal radiation. Optical fiber eliminates cross talk or electrical shorts.
• Fiber optic transmission offers very high bandwidth that is ideal for moving large volumes of audio, video and data signals simultaneously.
• Fiber cables are difficult to tap, making very secure communications possible.
Two stands of fiber can carry more information than a bundle of copper wires four inches in diameter.
• Installation flexibility
Optical fiber offers flexible installation options within the National Electrical Code (NEC).
• System upgrades and changes are easily accomplished.
Upgrading the channel-carrying capacity and type of signal is as easy as changing the fiber optic transmitter and receiver on each end.
And, most copper systems have a very fast degradation curve. The longer a copper path, the more the quality of the video and the integrity of data will degrade. With typical analog transmission equipment over fiber, this curve is very slow. With digital over fiber equipment, the curve disappears, and the video can be delivered perfectly up to the distance rating of the fiber equipment in use. This is typically in the kilometer range for multimode fiber, and up to 100 kilometers with single mode fiber. In addition, fiber provides a measure of electrical isolation for equipment. The isolation fiber provides prevents this from spreading to the interior monitoring equipment via a copper direct connection.
Digital vs. AnalogReprinted from the “Why Digital? The Advantages of Digital Transmission over Fiber” EduGuide from Communications Specialties, Hauppauge, N.Y., there are a new generation of products that employ pure digital signaling to transmit analog information. Another advantage of digital systems over their analog predecessors is their ability to regenerate a transmitted signal without incurring any additional degradation to the original baseband video, audio or data signal. This is accomplished by using a repeater. As light travels through a length of fiber, its optical power gradually attenuates. Eventually, not enough light remains to be detected by a receiver. By placing a repeater on the fiber at a point prior to where the light diminishes too much to be detected, the repeater can regenerate and restore the digital signal to its original form. This regenerated signal is then launched again on the same wavelength, with the same optical power found at the original transmission point. It is important to note that the baseband video, audio or data signal is never actually recovered in a repeater; only the data stream representing the original signal or signals is processed. In this manner, the quality of the original baseband signal is not degraded, regardless of how many times the signal is repeated and over how great a distance. Digital systems allow for the transmission of more information over a single fiber, thus minimizing the required quantity of cable. This advantage is particularly evident in applications requiring the transmission of disparate signal types, such as video with audio, or audio with data. Using analog technology, this same signal transmission would most likely require two systems, or at least two fibers, for separate transmission of video and audio signals.
Digital requires no adjustments in the installation process. There is no possibility for the system to require retuning or adjustments. The user is likely to spend less time troubleshooting because the digital design makes it immune to interference, crosstalk and drifting.
What’s in StoreAccording to Nhu Dang, IFS product manager, International Fiber Systems, coarse wavelength division multiplexing (CWDM) is an all fiber, bi-directional multiplexer and demultiplexer and is designed for integrating large numbers of multiple channels for applications such as light rail and high-volume optical communication networks. The CWDM allows two, four or eight wavelengths (channels) traveling into one single-mode fiber cable and the demultiplexer module can separate two, four or eight wavelengths on the other end. The unique and highly integrated design offers a very low insertion loss while high channel isolation allows fiber optic modules to operate independently of protocols and data types.
“The main focus of many fiber optic trends is providing greater numbers of video, audio and data channels over fewer fibers,” says McBride. While a single coaxial cable has the capacity to transmit only a single channel of base-band video, a single strand of fiber in combination with the different types of fiber optic transmission equipment available can carry as many as 32 individual video signals a distance of 40 miles. Utilizing that same single fiber, depending on the need, video, audio and data signals can be transmitted on that single optical fiber. In the short term and a very simple installation, for example, a four-camera CCTV system, the initial transmission medium, equipment and installation costs are very similar between coaxial cable and fiber.
Another major trend is the progression toward digitally encoded transmission, rather than standard FM.