One growing application of optical fibres is in communication. Because the information-carrying capacity of a signal increases with frequency, the use of laser light offers many advantages. Fibre-optic laser systems are being used in communications networks. Many long-haul fibre communications networks for both transcontinental connections and, through undersea cables, international connections are in operation. One advantage of optical fibre systems is the long distances that can be maintained before signal repeaters are needed to regenerate signals. These are currently separated by about 100 km (about 62 mi), compared to about 1.5 km (about 1 mi) for electrical systems. Newly developed optical fiber amplifiers can extend this distance even farther. Telephone-transmission method uses fibre-optic cable, which is made of bundles of optical fibres, long strands of specially made glass encased in a protective coating. Optical fibres transmit energy in the form of light pulses. The technology is similar to that of the coaxial cable, except that the optical fibres can handle tens of thousands of conversations simultaneously.
Multimode fibre is commonly used as the "backbone" to carry signals between the hubs of Local Area Networks (LAN’s) from where copper coaxial cable takes the data to the desktop. Fibre links to the desktop, however, are also common. Cable Televisions in the home tend to use optical fibre because of its very low power consumption. Closed circuit television(CCTV) security systems use optical fibre because of its inherent security, as well as its other advantages. Many advances have been made in recent years in the use of Optical Fibres as sensors. Gas concentration, chemical concentration, pressure, temperature, and rate of rotation can all be sensed using optical fibre. Optical fibres are also being used in a wide variety of sensing devices, ranging from thermometers to gyroscopes. The potential of their applications in this field is nearly unlimited, because the light sent through them is sensitive to many environmental changes, including pressure, sound waves, and strain, as well as heat and motion. The fibres can be especially useful where electrical effects could make ordinary wiring useless, less accurate, or even hazardous. Fibres have also been developed to carry high-power laser beams for cutting and drilling.
Optical fibres are well suited for medical use. They can be made in extremely thin, flexible strands for insertion into the blood vessels, lungs, and other hollow parts of the body. Optical fibres are used in a number of instruments that enable doctors to view internal body parts without having to perform surgery. Surgical lasers and devices for measuring temperature or pressure also use optical fibres. Arthroscopy is the technique of using an arthroscope to examine a joint of the body. An arthroscope is a straight, tube like instrument with a series of lenses and optical-fibre bundles. It comes in sizes from 2 to 5 millimetres in diameter. It can be inserted into a joint through a small incision. A light transmitted by the optical fibres to the tip of the arthroscope illuminates the joint. Using an arthroscope, a doctor can thoroughly examine a patient's joint and perform certain surgical operations. Doctors use arthroscopy mainly on shoulder, elbow, hip, and knee joints. The problem most commonly treated by arthroscopy is torn cartilage in the knee. The doctor diagnoses this problem by looking into the knee joint through the arthroscope. Then the cartilage is removed with other instruments through a second incision. The main advantage of arthroscopic surgery is that the operation can be performed through a small incision at the joint. As a result, a patient can sometimes have the surgery and leave the hospital the same day. Also, the patient experiences a minimum amount of discomfort, and healing time is much shorter than for other methods of surgery.
The simplest application of optical fibers is the transmission of light to locations otherwise hard to reach, for example, the bore of a dentist's drill. Also, bundles of several thousand very thin fibers assembled precisely side by side and optically polished at their ends, can be used to transmit images. Each point of the image projected on one face of the bundle is reproduced at the other end of the bundle, reconstituting the image, which can be observed through a magnifier. Image transmission by optical fibres is widely used in medical instruments for viewing inside the human body and for laser surgery, in facsimile systems, in phototypesetting, in computer graphics, and in many other applications.
