Use Existing Fiber-Optic Links for Physical Security
April 1, 2008
The “dark” or “unlit” fiber-optic cables within buildings are ideally suited for the connection of physical security cameras, access control, intercoms and other devices. They provide high bandwidth capability, immunity to radio frequency interference (RFI) and electromagnetic interference (EMI) and can carry signals much farther than comparable copper cabling.
These unused fibers typically are installed between network closets. When fiber links are planned, it is common for excess fiber strands to be pulled between communication closets.
Network planners often recommend that spare fiber strands be installed for three primary reasons. First, the cost of individual fiber strands is quite low, so putting in extra strands has little impact on the price of an installation.
Secondly, during installation, it is possible to break a fiber, so having spares in the cable provides some insurance that enough usable fibers will be available after the installation is complete.
The third reason is that having additional spare fibers in the communications network future-proofs the installation, because the spare fibers can be used for virtually any communication application, such as networking, telephony, serial communications and other uses.
When planning an installation, security integrators always should ask whether any existing unused fiber strands could be incorporated into the physical security cabling system. If the answer is affirmative, the security company must verify the type, quality and lengths of fiber links to be used, and the style of connectors installed on each end of the link.
Fiber-optic cabling is available in two basic types â€” multimode and single-mode. Multimode fiber has a core size of either 62.5 or 50 microns and commonly is found providing connections between telecommunications closets within a building or campus.
Multimode is preferable for most physical security applications, because it uses either low-cost LEDs or cheap lasers for transmission and is easier to terminate and test. The drawback to multimode is that it has a distance limitation of three to four miles.
Single-mode fiber has a core size of 7 to 10 microns, and typically is used for long distances of more than 50 miles in high-bandwidth applications, such as telephone company connections. In most cases, the fiber links within a building will be multimode, although it would not be unusual to find a mix of multimode and single-mode within a client’s network infrastructure.
The quality of a particular fiber link can be tested in a variety of ways. (Please visit www.sdmmag.com and type “Turn Dark Fiber into Light Work” in the search at the top of the home page to read this article).
A simple no-go test is to shine a flashlight directly into the connector on one end of a fiber link and see if the light comes out the other end. If no light does, that fiber link is in need of repair before it can be used. The important thing for security integrators to remember is that a particular fiber link being fully operational is not guaranteed, and that it must be tested before an installation is sold to a client.
The overall length of the fiber is not critical unless the installation is so large that the maximum usable distance of multimode fiber (from three miles to four miles) might be exceeded. It is important to know the distance of a particular fiber link so a proper “optical budget” calculation can be achieved.
To find the distance of a fiber link, examine the cabling at both ends. Stamped on the jacket will be “foot marker” numbers, usually placed on the cable every three feet by the manufacturer. Subtracting the lower value at one end of the cable from the higher value at the other end will yield the length of the fiber link.
Fiber connectors are available in several common styles, such as ST (round) and SC (square) types. Be sure to verify the style of connectors used, because devices for interfacing physical security equipment to fiber-optic links usually can be ordered with either the ST or SC connector. A smaller square connector called an LC is gaining in popularity.
Various adapters can be purchased to convert connections, such as connecting an ST-equipped video fiber encoder to an SC connector on a network fiber patch panel.
Smart security integration companies will actively look for the availability of dark fibers in potential installation sites. Using these fibers can substantially reduce installation costs that can directly translate into increased system sales.