The Nature and Propagation of Light
In order to understand how the light propagates across the optical fiber, it is important to understand the nature of light and how it propagates.
The Nature of Light
The scientists were confused about what light really is. Three main theories were evolved to understand what is light.
1- Light as rays
"In the classical physics that many of us learned at school, light consisted of "rays” that could be reflected and refracted through mirrors and prisms etc. This is a good description as far as it goes but it cannot explain many of the phenomena we make use of in optical communications" (Dutton, 1998, p. 15). Dutton (1998) illustrates that this theory cannot clarify the diffraction or interference phenomena in light.
2- Light as photons
"In many contexts light behaves as though it consists of tiny particles called “photons”. There are a number of phenomena that the wave model of light can't explain. The best known of these is the “photoelectric effect” (Dutton, 1998, p. 15).
3- Light as electromagnetic waves
"In the context of optical communications, most of the time it will be found that the best way of regarding light is to think of it as an electromagnetic wave. In this view it is no different from a radio wave except that the wavelength is much shorter" (Dutton, 1998, p. 15). According to Dutton (1998), the electromagnetic wave consists of electric field and magnetic field as shown in figure 1.
Figure 1: The electric field and magnetic field
Principles of Light Propagation
According to Brunel University (2007), the light is the visible light that its wavelength ranges from approximately 400 to 700 nm." However, as will be shown, the propagation characteristics of optical fibers dictate ...
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...index of the core is uniform throughout and undergoes an abrupt or step change at the core cladding boundary. The light ray propagating through the fiber are in the form of meridional rays which will cross the fiber axis during every reflection at the core cladding boundary and are propagating in a zig-zag manner as shown in figure 3a". (Arumugam, 2001, p.851).
• The multi-mode graded index fiber
"In the graded index fiber, the refractive index of the core is made to vary in the parabolic manner such that the maximum value of refractive index is at the center of the core. The light rays propagating through it are in the form of skew rays or helical rays which will not cross the fiber axis at any time and are propagating around the fiber axis in a helical (or) spiral manner as shown in figure 3b". (Arumugam, 2001, p.851).
Figure 3: Different types of optical fibers
through space. This theory came to life when Heinrich Hertz created those waves and seven
Electromagnetic waves are waves that can propagate even though there is no medium. A magnetic field that changes with time can generate an electric field that also changes with time, and an electric field that changes with time can also produce a magnetic field. If the process is continuous it will produce a magnetic field and electric field continuously. If these magnetic fields and electric fields simultaneously propagate (spread) in space in all directions then this is a symptom of the wave. Such a wave is called an electromagnetic wave because it consists of an electric field and a magnetic field that travels in space.
The author tells of how waves are effected by quantum mechanic. He also discusses the fact that electromagnetic radiation, or photons, are actually particles and waves. He continues to discuss how matter particles are also matter, but because of their h bar, is so small, the effects are not seen. Green concludes the quantum mechanics discussion by talking about the uncertainty principle.Chapter 5: The need for a New Theory: General Relativity vs.
Nature of wave: It is an electromagnetic wave as it does not necessarily require a medium for p...
Williams, B. 1999. A History of Light and Lighting. [online] Available at: http://www.mts.net/~william5/history/hol.htm [Accessed: 5 Jan 2014].
X-rays and gamma ray photons are part of the electromagnetic spectrum. The twin nature of electromagnetic radiation is used to justify the wave and its behavior. A photon is a bundle of energy that can be identified by the equation E = hv. Where h is the planks constant and v is the frequency. The frequency is equal to the speed of light 3x10 8 divided by the wavelength. Therefore, high-energy radiations have a short wavelength and a high frequency.
Refraction occurs when light travels from one medium crosses a boundary and enters another medium of different properties. For example, light traveling from air to water. The amount of refraction (or bending) can be calculated using Snell's Law.
In 1801 Thomas Young provided some very strong evidence to support the wave nature of light, he placed a monochromatic light in front of a screen with two slits cut into it, and observed an interference pattern, only possible if light was a wave. In 1965 Richard Feynman came up with a thought-experiment that was similar to Young’s experiment. In Feynman’s double-slit experiment, a chosen material is fired at a wall which has two small slits that can be opened and closed at will – some of the material gets blocked and some passes through the slits, depending on which ones are open.
The index of refraction is defined as the speed of light in vacuum divided by the speed of light in the medium. In this experiment, the index of refraction for the perspex is 1.50. Snell's Law relates the indices of refraction of the two media to the directions of propagation in terms of the angles to the normal. It refers to the relationship between the different angles of light as it passes from one transparent medium to another. When light passes from one transparent medium to another, it bends according to Snell's law which states: [IMAGE] where: n1 is the refractive index of the medium the light is leaving, n2 is the refractive index of the medium the light is entering, sin 2 is the is the incident angle between the light ray and the normal to the medium to medium interface, sin 1 is the refractive angle between the light ray and the normal to the medium to medium interface.
Masters, Barry R. "Albert Einstein and the Nature of Light." 2010. Optics and Photonics News. The Optical Society. Article. 31 March 2014. .
Spring, K. R., & Davidson, M. W. (2016, 05 17). Light: Particle or a Wave? Retrieved from Physics of Light and Color: http://micro.magnet.fsu.edu/primer/lightandcolor/particleorwave.html
Now in order to understand how lights is able to be refracted in different angles, it is important to understand the Snell’s Law which states that, the refractive angle always depend on the refractive index of both media. Now, the refractive index keeps on changing depending on the wavelength of the light passing through. Light, as we know, it is a wave that has different wavelength. Each wavelength represents a different color. Thus, different colors will have different refractive index when passed through the same media. It is important to note that light is normally refracted twice when it travels through a prism, first on its way in, and when it is going back.
The concept of fiber optics is simple, yet it provides so many potentialities in the world of technology. Presently the world relies on fiber optical technology for its data and communications systems. The consumer can converse on the telephone and hear voices with clarity, as well as send and receive information on the Internet with ease. However, there still lay a sea of possibilities in this area of technology that has not yet been discovered.
The electromagnetic spectrum is a range of different types of radiations, this is energy that travels and spreads out as it goes. This range involves more than just visible light- small portion of the spectrum detected by the human eye- it goes beyond what the human eye cannot see. The two most important characteristics of the spectrum are wavelength and frequency. The electromagnetic spectrum can be divided into three different parts: the theory of visible light, the range of the electromagnetic spectrum, and how it benefits mankind.
Refraction is a process that occurs when light travels between media of different optical density. Light travels at a speed of roughly 3.0 × 108ms-1 in a vacuum. A vacuum has a refractive index n=1.00. The speed at which the light is travelling will decrease as it moves into differently optically