Since the first commercial installation of a fibre-optic system in 1977, the applications of optical fibre communications have increased rapidly. Here we’ll discuss the basics behind fibre optic cable, its benefits over copper cable and the most common types of fibre optic cable.
THE BASICS OF FIBRE OPTIC CABLE
The fibre-optic system is similar to the copper wire system that fibre-optics is replacing, but the difference is that fibre-optics use light pulses to transmit information down fibre lines instead of using electronic pulses to transmit information down copper lines.
The components in a fibre-optic chain
If we look at the components in a fibre-optic chain, it will give us a better understanding of how the system works in conjunction with wire-based systems;
At one end of the system is a transmitter, which is the place of origin for information coming on to fibre-optic lines. The transmitter accepts coded electronic pulse information coming from copper wire. It then processes and translates that information into equivalently coded light pulses. A light-emitting diode (LED) or an injection-laser diode (ILD) can be used for generating the light pulses.
Using a lens, the light pulses are funnelled into the fibre-optic medium where they travel down the cable. The light (near infrared) is most often 850nm for shorter distances and 1,300nm for longer distances on Multi-mode fibre and 1300nm for single-mode fibre and 1,500nm is used for longer distances.
Think of a fibre cable like a very long cardboard roll (such as the inside roll of paper towel) that is coated with a mirror on the inside. If you shine a flashlight in one end you can see light come out at the far end – even if it’s been bent around a corner.
Total internal reflection
Light pulses move easily down the fibre-optic line because of a principle known as total internal reflection. This principle states that when the angle of incidence exceeds a critical value, light cannot get out of the glass; instead, the light bounces back in. When this principle is applied to the construction of the fibre-optic strand, it is possible to transmit information down fibre lines in the form of light pulses. The core must be a very clear and pure material for the light or in most cases near infrared light (850nm, 1300nm and 1500nm).
The core can be plastic (used for very short distances) but most are made from glass. Glass optical fibres are almost always made from pure silica, but some other materials, such as fluorozirconate, fluoroaluminate, and chalcogenide glasses, are used for longer-wavelength infrared applications.
THE ADVANTAGES OF FIBRE OPTIC CABLE
- Fibre optic networks can operate at high speeds – up to gigabits per second.
- A large bandwidth allows for a large carrying capacity.
- Signals can be transmitted further without needing to be amplified.
- Greater resistance to electromagnetic noise such as radios, motors or other nearby cables.
- Fibre optic cables cost much less to maintain.
WHO WOULD BENEFIT FROM SWITCHING TO FIBRE OPTIC CABLE?
Telephone companies began early on, replacing their old copper wire systems with optical fibre lines. Today’s telephone companies use optical fibre throughout their system as the backbone architecture and as the long-distance connection between city phone systems.
Cable television services, college and university campuses, office buildings, industrial plants, and electric utility companies are some other examples of system users who would also benefit from fibre optic cable.
Also, power companies are an emerging group that have begun to utilize fibre-optics in their communication systems. Most power utilities already have fibre-optic communication systems in use for monitoring their power grid systems.
WHAT ARE THE DIFFERENT TYPES OF FIBRE OPTIC CABLE?
There are three main types of fibre optic cable:
1. Singlemode: single path through the fibre
Singlemode cable is a single strand of glass fibre with a diameter of 8.3 to 10 microns that has one mode of transmission. It has a relatively narrow diameter, through which only one mode will propagate (typically 1310 or 1550nm). It carries a higher bandwidth than multimode fibre, but requires a light source with a narrow spectral width.
Singlemode fibre is used in many applications where data is sent at multi-frequency (WDM Wave-Division-Multiplexing) so only one cable is needed- (single-mode on one single fibre). It gives you a higher transmission rate and up to 50 times more distance than multimode, but it also costs more. Single-mode fibre has a much smaller core than multimode. The small core and single light-wave virtually eliminate any distortion that could result from overlapping light pulses, providing the least signal attenuation and the highest transmission speeds of any fibre cable type.
Singlemode optical fibre is an optical fibre in which only the lowest order bound mode can propagate at the wavelength of interest typically 1300 to 1320nm. It’s also known as mono-mode optical fibre, singlemode fibre, singlemode optical waveguide and uni-mode fibre.
2. Multimode: multiple paths through the fibre
Multimode fibre has a little bit bigger diameter, with common diameters in the 50-to-100 micron range for the light carry component. In most applications in which Multi-mode fibre is used, 2 fibres are used (WDM is not normally used on multi-mode fibre).
Multimode fibre gives you high bandwidth at high speeds (10 to 100MBS – to 275m to 2km) over medium distances. Light waves are dispersed into numerous paths, or modes, as they travel through the cable’s core typically 850 or 1300nm. Typical multimode fibre core diameters are 50, 62.5, and 100 micrometers. However, in long cable runs (greater than 3000 feet [914.4 meters), multiple paths of light can cause signal distortion at the receiving end, resulting in an unclear and incomplete data transmission, so designers now call for single mode fibre in new applications using Gigabit and beyond.
3. Plastic optical fibre (POF)
POF is a newer plastic-based cable which promises performance similar to glass cable on very short runs, but at a lower cost.
CORE Cabling provides customized expert fibre optic cable installation services. Feel free to contact us to discuss any questions you may have about our fibre optic services and we’d be happy to help.
