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Fiber Optics In the Home

Aug 1, 1999 12:00 PM, Irwin Math


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Fiber-optic technology is well known in telecommunications, local area networks, the CCTV security marketplace and in many Intelligent Transportation System (ITS) highway projects. Even CATV (cable) distribution to various local feed points within a residential community is now routine for fiber. Where fiber has not made a major inroad, however, is in the region that encompasses the area directly to and within the average home. Here, CAT X copper wire cable still reins supreme. The increase in demand for bandwidth for a wide range of consumer-oriented services to come that will fall within this region, however, could dramatically influence the amount of fiber-optic cable used in residential applications.

Two of the most important attributes of fiber-optic cable that make it a candidate for wiring within the home are its inherent immunity to electrical noise and the wide available bandwidth as compared to copper wire. Both of these features will be of great importance as consumer-related high-speed technology develops. To achieve even a measure of these features for copper wire requires extensive shielding and careful manufacturing techniques to ensure uniform characteristics at high frequencies along with low losses.

In the case of noise immunity, when installing fiber-optic cable in the home, the contractor does not have to be particularly concerned with the exact route the cable will take; rather, he can install it via the most convenient path. Running a fiber cable in close proximity (or even tie-wrapped where electrical codes permit) to a power line will not result in induced 60 Hz hum or other AC line interference nor create any situation where the integrity of the power line is compromised. Having a cable immersed in a pool of water after a heavy rainstorm will not result in short circuits or grounds, nor will it interfere with existing signals traveling through the fiber. In addition, although a broken fiber-optic cable will result in a loss of signal, it will not create any electrical safety or potential fire hazard.

The copper wire route, on the other hand, requires a separate path as far from a power line as possible. Even when this is done, the cable is still susceptible to short circuits and hum pickup, can create a safety hazard when broken, and requiresextensive equalization in the form of special drivers and receivers when increased bandwidth is required.

With regard to bandwidth, the hundreds of MHz per km available on inexpensive multimode fiber (or GHz per km for the similarly priced single-mode version) will allow a multitude of live action HDTV cable channels, ultra high-speed Internet access (in excess of T-1 data rates) and live full-motion video telephones to share a single optical conductor that could, if desired, easily be routed from room to room. Because light travels in both directions within a fiber, even two-way communications are easy. In fact, the only drawback to the use of fiber-optic technology today is the electronic interfaces that are required (and their additional cost), but that will change as fiber-optic interfaces begin to appear on consumer products.

To convert electrical signals to and from light for transmission in a fiber-optic system requires an optical transmitter and receiver. These devices are similar to external computer modems in size, function and complexity and range in cost - a few hundred dollars for simple, single channel devices to several thousand dollars for a multiplexed, multi-signal device. Most of these take the form of small, self-contained modules that can be mounted anywhere convenient or in standard 19 inch (483 mm) rack-mountable card cages. Power is usually derived directly from the AC line or from small plug-in wall adapters. In a CCTV security system, for example, an individual transmitter module would be mounted at each video camera with all receivers mounted at a single monitoring location along with some sort of switch and monitor. In a high-end audio or video distribution system within a home, a head-end would consist of a group of transmitters at one location driving separate individual receivers in each room that signals were desired. Such a system could eliminate extraneous noise pickup from various appliances around the house and could result in snow-free pictures coupled with noise-free CD-quality audio. Not only would a room dedicated to a home entertainment center provide true movie theater quality, but every room could, in essence, also become a mini-theater.

Today, common household A-V systems are normally interconnected by means of copper wire, both twisted-shielded pair and coaxial. The connections are easily made with simple and inexpensive connectors or terminal blocks. The video quality is not always perfect, and the sound is sometimes prone to interference, but the results are acceptable. The equipment exists today, however, to do the job with fiber optics if one is not too concerned with costs. An A-V transmitter/receiver set capable of transmitting and receiving high-quality baseband video and line-level stereo audio pushes the cost to $1,400. Remember, this is with existing equipment. In the near future, it is not unreasonable to expect to have an optical port on a videodisc or CD player, especially when the signals to be distributed are digitally encoded video and audio at data rates in the hundreds of megabits. When that occurs, prices will drop. It is important to realize that even though installing a fiber-optic system using currently available transmission systems is more expensive than installing a copper wire infrastructure in today's home, as technology progresses, the electronic transmitters and receivers can always be upgraded. The fiber-optic cable in the walls cannot be changed as easily, but because it is capable of operating in the GHz range, there is little risk of obsolescence.

As a result, the sound and video contractor of today would do well to learn about fiber optics and how it will (and for that matter does) apply to future business. In fact, it is an even better idea to gain some hands-on experience with such systems, even if it is just for a simple security link.



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