The Advantages of Fibre Optics

Fiber Optics: Light-Wave Communication

Mathew Geraghty 0647712

Wednesday, 11:30am

ENG-1P03, Prof. D. Jones

Guest Lecture #3, Yaser Haddara

Fiber Optics: Light-Wave Communication

It's the Best to be at the Speed of Light

It is general knowledge that nothing can travel faster than the speed of light, not even Superman. But, no one ever said that the idea of hitching a ride on top of a wave of light is entirely impossible. Granted it is not possible for you or me to get a piggyback from a photon, but for electrical information it is another story. This is where the theory of fiber optics comes in. Fiber optics, by definition, is the science of using light as a means for transferring light by using very fine, flexible glass fibers. By its definition alone you can tell that fiber optics is something huge in the world of communication. It has revolutionized our thoughts of a speedy transfer. The process of a fiber optics system is actually rather simple. It all begins when an electrical signal is converted into light. This light is transmitted through the fiber to another location and converted back into an electrical signal for the receiver. The input signal can be in digital form (on or off) or analog form (video, sound, etc). Digital modulation is far more popular because it allows for greater transmission distances with the same power as analog modulation. A typical system has five major points: the encoder, the light source (transmitter), the optical fiber, the light receiver, and the decoder. The encoder converts the signal to a format that is useful to the transmitter, and the transmitter then converts this signal into a light pulse. This light pulse is guided down the cable to the light receiver, where it is converted to an electrical current corresponding to the intensity of the transmitted light; the signal is now decoded and is a replica of the original. ("Introduction to Fiber Optics," 2005) Optical fiber provides a low-loss path for the light to follow from the light source to the detector. They are most often made from ultrapure glass, but can also be made out of plastic and silica fiber. Silica fibers are most often used when high power lasers and sensors are involved, such as laser-surgery. Plastic fibers are used for very short data links because inexpensive light sources may be used. (Freudenrich, 2004) Because of its design and its unique utilization of light, compared to conventional copper wiring, it is simply the better technology.

Why, you might ask, are fiber optics cables better than conventional copper wiring technology? The first answer to this question is that because fiber optics uses light as their medium of transmission, the rate of transfer fiber optics is very fast, literally transmitting information at the speed of light to vast distances. A fiber optics network operates at 2.5 gigabits per second, as opposed to the 155 megabit per second transfer rate for copper wire. Along with this great speed comes an extremely large bandwidth. Bandwidth is the range of frequencies that can carry information from one point to another. For copper wires, the bandwidth available for information transmission extends from 108 to 109 Hz. With bandwidths of up to 1010 Hz, optical fibers are able to transmit a greater volume of information. (Palais, 1998) Whether this information is in the form of video, sound, or data, it can be easily conveyed using fiber optics. This larger bandwidth is very useful because each day the demand for bandwidth is growing; the technology that utilizes bandwidth is becoming more and more popular. In order to compensate for this increase in demand, companies need a way to increase the supply of bandwidth for these consumers, and fiber optics is an excellent way to accomplish this.

You would think that in order to provide larger bandwidths the cables would have to be rather large, correct? This simply is not the case. The fiber optical cable is far smaller than conventional wire cables. An individual fiber is roughly the size of a human hair, one tenth of a millimeter. Even after the protective coating is added, the fiber cable is still smaller than a copper wire. For example, an optical fiber that is about a quarter inch diameter carries the same amount of information as a three inch bundle of 900 pairs of copper wiring. (Green, 1993) Not only are fiber optics cables smaller in size, they also weigh much less than conventional copper wiring. Copper wiring weighing 208 pounds would be replaced by an eight pound cable of optical fiber. Many groups of people can benefit from this. For example, because air and space vehicles are prolific users of wires, replacing bulky metal wires with fiber optics cables increases reliability, and by reducing the overall weight, helps to lower fuel consumption. Along with the reduction in size and weight, a longer life span is predicted for fiber optics: 20 to 30 years, compared to 12 to 15 years for conventional cable. Because fiber optic cables are made of glass or plastic as opposed to metal, they have a high tolerance to temperatures as well as to corrosion. (Meardon, 1993) These longer lasting, more durable cables will help decrease the need for maintenance, and in turn lowers costs for the consumer.

A problem with copper wiring is that they simply do not function properly, if at all, when they are near sources of interference. Optic fiber cables, on the other hand, are excellent at rejecting radio-frequency and electromagnetic interference. Radio-frequency interference refers to interference caused by radio and television stations, radar, and other signals that originate from electronic equipment. Electromagnetic interference includes these radio-frequency examples, as well as interference caused by nature (such as lightning), and other electromagnetic wave emitting systems, such as electrified railway tracks. Because of this remarkable characteristic, it is possible to place optical cables in areas that copper wires are not effective in, such as near, or in contact with, high voltage electrical equipment and power lines. Also, fiber optic cables are insulated and never have current flowing through them. As a result, they will not cause interference problems if many are installed in the same place. (Palais, 1992)

With these great advantages comes a major disadvantage: cost. Some types of fiber optic cables are