Fiber Can Enrich Your Installation Diet
One technology that has been able to ride the Convergence Wave on both sides is fiber optics. Fiber has been used as a high bandwidth backbone media for networks for many years. On the physical security side, we have been very comfortable using fiber to send large amounts of video over long distances, utilizing the “dark” fiber the network guys didn’t need.
However, even now there are those out there who are still unfamiliar with the technology behind fiber-optic equipment and its many uses.
How Fiber Is Constructed
Fiber-optic cable can be made either from glass or plastic. However, you generally don’t find plastic fiber in either the security or network industries. Plastic fiber mostly exists in lighting systems or in some home theater applications.
Light is modulated and sent along a piece of glass, giving us our path for data. This light is received at the opposite end and converted back to electronic impulses.
The cable itself is made up of several components. At the very center is the core. The core is the actual piece of glass that the light travels down. We’ll look more at the light itself in a moment.
Surrounding the core is the cladding. The cladding is basically a mirrored surface, generally also made from glass, that keeps the light traveling down the core, reflecting it back in if it tries to stray out, such as what occurs at the apex of a bend in the cable. No matter how focused a beam of light is, there will always be some scattering of light particles, especially over long distances. The cladding helps maintain that focus.
Between the cladding and the outer jacket is a piece of material known as the buffer. The buffer provides strength and protection for the core and cladding, which can be smaller than the diameter of a human hair. Inside the buffer, the core/cladding combination can float loosely, or be tightly held by the buffer itself. Some fiber-optic cables also have a Kevlar strength member that provides reinforcement when the cable needs to be pulled in.
The outer jacket is the final piece of the puzzle. Just like with other types of cable, this jacket can be made of PVC or Plenum-rated materials, for use in air handling spaces and other locations governed by Plenum standards.
2 Types Are Multi, Single Mode
Optical fiber cable generally falls into two main categories, multimode and single mode. The difference between the two is basically the number of paths the light has to travel.
Multimode cable utilizes multiple paths of light. The light pulses are timed differently as they are generated and arrive at their destination at different times. This allows multiple signals to travel on the same cable. In multimode transmission equipment, the light is generated by a high-power LED. This light immediately begins bouncing down the core, reflected back by the cladding. The light continues bouncing down the glass until it is received at the other end.
In single mode cable, the light is generated by a laser. This provides a very focused, single path of light. This light travels down the center of the core with minimal scatter or bouncing. Single mode cable provides greater bandwidth and is capable of longer distances than multimode.
The difference between single mode and multimode is crucial when selecting fiber. The transmission equipment is not interchangeable, and single mode cable and equipment is generally more expensive. For installations within a building, multimode is usually sufficient. For campus or metropolitan applications, single mode is probably the only option.
Another important difference between single and multimode cable is the size. Fiber-optic cable size is stated in microns. As a reference, an average human hair is approximately 100 microns in diameter. Multimode fiber is most popularly used in one of two sizes — 50 microns or 62.5 microns. Single mode cable is much smaller, usually only 8 microns.
When you read the specs for a piece of fiber, the size will be shown as two numbers, i.e. 62.5/125 microns fiber. The first number is the diameter of the core, and the second number is the diameter of the buffer. Single mode will be something like 8/125 microns, but the numbers represent the same components. It is crucial the size be known when the connectors are purchased; again, single and multimode equipment is not interchangeable.
Making the Right Connections
Speaking of fiber connectors, there are several different ones to choose from. For the purposes of this column, we’re going to focus on two specific types: ST and SC connectors. Interestingly, each enjoys its own popularity on each side of the convergence wave.
The traditional security integrator is generally more familiar with the ST connector. It is a bayonet-style connector that uses a twist-lock, much like a BNC on coax.
On the network side, the SC connector is more popular. It is a square, plastic connector that pushes straight in. The SC is nice for high-density applications, as they are easy to insert and remove, and the square shape allows connectors to be placed right next to each other.
It has been true in the past that connectorizing fiber cable is a highly specialized skill requiring a great deal of training to perform correctly. Now, however, universal crimp-on connectors are becoming more prevalent in the market. Where the process used to include cleaving the cable and polishing each end, the new connectors provide a much easier installation process, similar to connectorizing other types of cable. Some connectors are filled with an optically sensitive gel that compensates for small variations in the alignment between the cable end and the center of the connector.
Tips for Working Well, Safely
As thin as a fiber-optic core is, it can be remarkably resilient. With all the components surrounding the core, fiber is not quite as fragile as some people assume. There are some rules, though, for dealing with fiber that will ensure a solid installation.
The most important one, in my opinion, is not to exceed the bend radius of the fiber. Bending a fiber-optic cable beyond the radius it is designed for is the easiest way to compromise the integrity of the fiber. Even if the fiber looks solid, microscopic cracks in the cladding will allow light to escape, and reduce the available amount of light at the receiver, compromising the signal. There are visible light testers that can show locations along the fiber jacket where light is escaping.
Another important factor to remember when handling fiber is to not exceed the recommended pull strength. Pulling a fiber-optic cable with more weight than it can handle will also inflict cracks into the core and cladding, again, allowing light to escape.
It also needs to be mentioned that there are very real safety considerations when working with fiber.
As we mentioned above, single mode fiber-optic cable is 8 microns in diameter, much smaller than a hair. Always wear gloves when handling all fiber cable. If a piece were to break off and get into your skin, it is plenty small enough to work its way into a blood vessel, and possibly cause problems locally. In some cases it may even be possible for the fiber shard to travel to the heart.
Another safety practice to heed is never look into the end of a fiber-optic cable to see if it is working. Fiber light is generally in the IR range (meaning you can’t see it anyway) and in some cases, such as with a laser, the light can permanently damage your eyes. There are visible light testers and adaptors for standard multimeters that can be used to test the integrity of fiber. Don’t use your eyes.
Once you get past the basics, it will soon become evident that fiber-optic cable is a very versatile addition to your t
oolkit. While other technologies might be approaching fiber in terms of distance, the sheer bandwidth available on a single piece of glass much smaller than a human hair is still a very impressive achievement.
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