F i b r e O p t i c s
Fibre optics is an emerging form of technology that uses minute fibres of glass or plastic to transmit light. The light source and method of delivery can be modified to transmit computer data, such as images and sound, or simply luminescent light. In recent years, the advancement of fibre optic technology has increased greatly. Many of these advancements, along with an explanation of the technology and societal implications will be discussed within this essay.
Figure1 Fibre Structure
Fibre optics is a method used to transmit information via light pulses along very fine fibres of glass or plastic. Plastic is not commonly used due to it's incapacity for extreme pureness. Optical fibres consist of a glass core, roughly fifty micrometers in diameter, surrounded by a glass "optical cladding" giving an outside diameter of about 120 micrometers. See Figure1 for an overview of an optical fibre.
Total Internal Reflection
Optical fibres rely upon Total Internal Reflection (TIR) to achieve reliable results through minimal light loss. If TIR did not occur, light loss would rapidly result in signal loss and optical fibres would have the capacity to carry signals only a few feet rather than many miles. The angle eA in Figure2 is called the Acceptance Angle. Any light entering the fibre at less than this angle will meet the cladding at an angle greater than eC. If light meets the inner surface of the cladding (the core-cladding interface) at greater than or equal to eC, TIR occurs. All the energy in the ray of light is thus reflected back into the core and none escapes into the cladding. The ray then crosses to the other side of the core, and because the fibre is more or less straight, the ray will meet the cladding at an angle which causes TIR to again occur. This pattern continues until the ray meets the end of the fibre.
Figure2 Propagation of Light in a Fibre
The development of fibre optics has taken many years of testing and research by numerous academic institutions and corporations, and as such, no single person has been named the inventor. Development of optical fibres began in the 1960's with the advent of the laser as a source of coherent light. At first, long transmission distances were hindered by impure glass which caused signal corruption. Arriving in the 1970's were techniques for very pure glass which corrected this problem and popularised this new form of transmission. By 1980, developments in semi-conductor light sources and detectors founded world wide installation of optical fibres within telecommunication's backbone networks.
Fibre Optic Technology Advancements
Fibre optics are unique amongst many other optical technologies in that they are relatively new and rapidly improving. For instance, advances in connector technology have allowed cheaper and more effective splicing of 2 fibres. Previously, splicing of two fibres was the largest cost in the installation of a fibre optic network, since expensive equipment and expert precision is required to minimise signal loss. Now, splices are of better quality at a fraction of the previous cost. Figure3 diplays common difficulties incurred during splicing that leads to signal loss.
Figure3 Common Difficulties Incurred During Splicing
Optical Fibres vs Copper Wire
Some reasons why optical fibres are preffered over copper wires in transmissions lines:
- optical fibres carry signals with much less energy loss than copper cables
- optical fibres are much lighter and thinner than copper cables with same bandwidth
- optical fibres are immune to electromagnetic interference, and can be safely routed through explosive or flammable atmospheres without risk of ignition
- optical fibres are very secure, meaning difficult to get information from undetected
- optical fibres require expensive precision splicing and measurement equipment
- optical fibres require additional training of personnel
- optical fibres are more expensive per meter than copper wires, although optical fibre systems carry much more bandwith over longer distances with fewer expensive repeaters required
Due to the extremely high bandwidth that optical fibres possess, fibre optic networks are being implemented all over the world at an alarming rate. These networks connect computers, telephones, video cameras and much more. Fibre optic systems are now being heavily implemented within medical fields to get images or video from within virtually any part of the body. Listed below are just some of the fantastic opportunities that fibre optic networks have made available:
Telecommunications optical fibres are now the standard for point-to-point cable links between telephone substations
Large Area Networks multimode optical fibre is commonly used as the "backbone" to carry signals between the hubs and LANs from where copper coaxial cable takes it to the desktop
Cable TV Optical fibres are beginning to be used due to low power consumption
CCTV Closed Circuit Television security systems use optical fibres because of it's inherent "man in the middle" security
Optical Fibre Sensors Gas concentration, chemical concentration, pressure, temperature, and rate of rotation can all be sensed using optical fibres
Medicine Brilliant images inside our bodies have been captured via optical fibres.
Optical fibres used in medicine and as sensors are at the cutting edge of technology. Amongst the most intriguing is determining the concentrations of chemicals within a substance. This same technology is also used to detect concentrations of specific components in blood such as total protein, cholestrol, urea, and uric acid. This is done by making use of a evanescent waves.
The idea of TIR is easily explained using the model of light as millions of infinitesimally thin rays. Unfortunately this is not entirely true. Light is, in fact, a wave motion, meaning it propogates through glass or any transparent medium in the form of electromagnetic waves, which have a tendency to spread out as they travel. Because of this characteristic, some of the energy of light waves in the core of the fibre does actually penetrate into the cladding for a very short distance. This thin penetration of light into the cladding is called the evanescent wave.
In a single mode fibre, there is always a layer of light energy surrounding the core whenever light is travelling along the fibre. If a lot of evanescent energy is absorbed by the cladding, then energy will be drawn out of the core to replace it. When the cladding is removed and replaced by a sample to be tested, the sample becomes in direct contact with the evanescent wave. A sensor is designed where energy is absorbed from the evanescent wave in the presence of certain chemicals. If the chemicals are not present, then the evanescent energy is not absorbed. By choosing the correct wavelengths, we can quickly measure the concentrations of specific components of blood. When the component concentration is high, the energy received at the end of the fibre is low, and vice-versa. These sensors are critical to doctors in the diagnosis of certain disease conditions. Fibre optic sensors give results quickly without the need to send samples away to an analytical laboratory.
Fibre optics are part of an industry that is changing the way we do things today. Tomorrow will bring even further advancements in medicine, telecommunications, and security. Although no one can tell the future, everyone should bet on optical fibres playing a major role in whatever the future may bring.
Comments This is a good essay. 98% Grade 12 Enhanced Physics. The picture descriptions are still there but no pictures, sorry gotta find em yourself.