Fiber optic transmission systems provide a substantial number of well known benefits. Fiber offers speed and security, and is not subject to the abnormalities suffered by RF. With the rapid conversion over to digital signal processing and digital to digital system architectures, the speed and bandwidth available from fiber can be fully exploited.
Fiber optics in security applications today is much different than when it originated in the mid-80s, as a black-box technology: signals were connected to the fiber transmitter over copper, converted to light, transmitted over glass fiber, then reconverted to electrical signals by the receiver and output over copper. Most development during the first ten years was focused on increasing the types of signals supported and increasing the number of signals transmitted over one fiber. Troubleshooting a system used to frequently require high experience levels and expensive test equipment.
Security Dealer's Technical Editor Tim O'Leary taps Fiber Option's Jerry Jacobsen to shed some (laser generated) light on the new developments at one of the companies leading the way in fiber technology.
What is the difference between single mode and multimode fiber?
JJ: Multimode fiber has a wider core (most common is 62.5 microns), whereas single-mode fiber is 8.3 microns. "Mode" means "light path" in simple terms, and multimode fiber allows a burst of light to take a wide range of different paths to the receiver, some rays reflecting many times, some reflecting few times. This causes the original sharp pulse to arrive at the receiver somewhat spread out. In single-mode fiber, only one path is available, and a signal does not experience the spreading effect. At some distance in multimode, beam spreading will cause the signal to be undecipherable at the receiver. Since there is no beam spreading in single-mode, the operating distance can be much greater. The bandwidth in each is affected in the same way.
SD: An important issue
when designing fiber optic distribution systems is the "optical budget"
which refers to the maximum amount of signal loss which can be tolerated by
the various system elements. It is somewhat analogous to signal-to-noise ratio,
a term used in analog? Does fiber mode type have any affect on the optical budget?
JJ: No, everything else being equal, it doesn't. However, the same optical budget produces much different operating distances: a 13 db multimode unit yields 5.2 km and a single-mode unit yields 32 km.
SD: Is it correct that
the 712D-4 enables sending receiving digital data over fiber and the data device
port connects via copper to the 712D?
JJ: Each 712D connects to other 712D units by fiber. A data device, such as an access card reader, connects to the 712D with copper.
SD: Many CCTV systems
utilize analog devices, does Fiber Options offer A/D or D/A converters?
JJ: Yes. We have an extensive line of products for converting analog video or audio to digital formats for transmission. The A/D and D/A converters are built in.
SD: Fiber Options products
offer built-in diagnostics to help isolate the sources of problems. Can you
explain how they work?
JJ: These diagnostic aids are in the form of colored LEDs, which show if the transmitter is receiving a good signal, if the condition of the fiber, and if the output electrical signal was good. In units supporting multiple signal types, such as video, audio and data, there may be several LEDs. The new diagnostic systems are incorporated in a new brand of fiber products called Omega, and consist of three types of diagnostics: more extensive LED displays covering more aspects of the system in which the fiber equipment is incorporated; built-in video, audio, and data generators to permit testing a fiber link without connecting it to any other device. Loop-back testing is provided where appropriate; and on-screen displays to show the status of video inputs at the transmitter to the system operator at the receiver end. The new diagnostics now provide information not only about the fiber units themselves but also a great deal of information about any devices connected to the fiber links. Fiber Options calls it Status Monitoring And Reliability Test System, or SMARTS.