When using fiber connectivity within a network infrastructure, the digital signals sent by network devices are converted into light beams, sent across the fiber link, and converted back into digital signals on the other side. One of the major advantages of using this approach instead of other technologies (e.g., RF signals) is that nobody can easily tap into that connection without being noticed. However, if this does happen, the intruder can be easily identified by monitoring systems because the signal will drop significantly. The major advantages of using fiber cabling include the following:
- It offers high transfer rates (more than 10Gbps)
- It operates over long distances (up to 100 km)
- It is immune to radio interference
Fiber signals experience very slow degradation, so fiber connections can be used over very long distances, unlike copper connectivity. Fiber cabling is also immune to radio interference that can come from microwaves, wireless networks, mobile phones, or other devices (because light signals do not interfere with radio signals). For these reasons, fiber cabling is recommended in industrial environments that are electrically noisy.
Fiber connections can operate based on two technologies:
- Multi-mode fiber
- Single-mode fiber
| Note: There is a direct compatibility requirement between the type of fiber used and the type of device interface/transceiver in which you plug the fiber. You cannot use single-mode fibers with multi-mode transceivers or multi-mode fibers with single-mode transceivers.
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Multi-mode fiber technology involves the light beam travelling across multiple paths inside the fiber, bouncing off the fiber walls, as presented in Figure 14.1 below. This technology is called multi-mode because the light beam can travel in “multiple modes” across the cable.
Figure 14.1 – Multi-Mode Fiber
Multi-mode fiber is often used for communication over short distances, either inside a building or outside if the distance is less than 2 km. If you try to use it on longer distances, you will experience signal degradation because of the light beams that bounce off the fiber walls. Because the light does not have to travel over very long distances, multi-mode fiber connections can use inexpensive light sources based on LED technologies, unlike the case with single-mode fibers. Using inexpensive components allows you to keep the cost down for multi-mode fiber infrastructures.
While multi-mode fiber allows the light to travel on multiple paths, the main characteristic of single-mode fiber is that it offers a single light path across the fiber, as shown in Figure 14.2 below:
Figure 14.2 – Single-Mode Fiber
When using a single-mode fiber, the light follows a direct path (a “single mode”) to the destination, without the light beam bouncing off the cable walls like in the case with multi-mode fiber. Single-mode fiber is generally used for communications over very long distances (up to 100 km). Communication can even exceed 100 km, but in that case you would have to use special devices to regenerate the signal.
The light source in single-mode fiber is more expensive than in the case of multi-mode fiber because laser beams are used instead of LED sources. Laser beams offer a very strong light that can reach the other side of the cable, even over long distances, without major attenuation. Because of this, equipment using single-mode fiber will be a lot more expensive than equipment using multi-mode fiber. In addition, the actual single-mode fiber cables are more expensive than multi-mode fiber cables because the core of the fiber must be manufactured with different technologies in order to be very thin. For this reason, single-mode fiber is generally used only in special cases and not over short distances.