1. Fiber-Optics Chad Richmond Aaron Parker Billy Spies Fiber

2. 2 Optical Media How data is transmitted over fiber-optics. The light used in optical fiber networks is one type of electromagnetic energy. When an electric charge moves back and forth, or accelerates, a type of energy called electromagnetic energy is produced. This energy in the form of waves can travel through a vacuum, the air, and through some materials like glass. This is how data is transmitted through optical cable. 1.To understand how optical media work, we have to look at light first. ----------------------------------------------------------------------------------------------------------

3. How Data Is Carried Light waves Reflection When a ray of light (the incident ray) strikes the shiny surface of a flat piece of glass, some of the light energy in the ray is reflected. Ideally, all the light needs to be reflected. Refraction When a light strikes the interface between two transparent materials, the light divides into two parts. Part of the light ray is reflected back into the first substance, with the angle of reflection equaling the angle of incidence. The remaining energy in the light ray crosses the interface and enters into the second substance. This is called “refraction”. ----------------------------------------------------------------------------------------------------------

4. Applying Light A light ray that is being turned on and off to send data (1s and 0s) into an optical fiber must stay inside the fiber until it reaches the far end. The ray must not refract into the material wrapped around the outside of the fiber. The refraction would cause the loss of part of the light energy of the ray. A design must be achieved for the fiber that will make the outside surface of the fiber act like a mirror to the light ray moving through the fiber. If any light ray that tries to move out through the side of the fiber were reflected back into the fiber at an angle that sends it towards the far end of the fiber, this would be a good "pipeline" or "wave guide" for the light waves. Light can only travel through a piece of fiber if it meets these conditions: Transmitted light must hit the core and the outer jacket at an angle < 90° or < “critical angle”. The inner core of a piece of fiber must have an index of refraction greater than that of the outer casing (cladding). ----------------------------------------------------------------------------------------------------------

5. Applying Light (pt 2)  Achieving the second condition we just mentioned in a piece of fiber, “the index of refraction” part, is easy. Glass already has a greater index, is cheap, and is an ideal reflector/refractor, so they use glass probably 100% of the time.  The first condition, or “the angle of incidence”, brings us to something called “modes” of fiber. Now, we’ve heard of multi- mode fiber and single-mode fiber, but just what is a mode? ---------------------------------------------------------------------------------------------------------- Modes A mode is, by definition, the pathway that a blip of light takes to travel from the origin point, or Chad’s flashlight which we saw earlier, to the destination, which was represented by Parks. There are two different types of modes: 1. Single-Mode Fiber and 2. Multi-Mode Fiber

6. Types of Modes ----------------------------------------------------------------------------------------------------------

7. Transmission ---------------------------------------------------------------------------------------------------------- “Okay, so we understand how the light can go through the fiber, and the different types of fiber, but we still don’t know how it understands what the light is saying!” How it transmits light: 1. The transmitter receives electrical impulses from a router, switch, or hub. 2.Then, the transmitter converts the 1s and 0s to their equivalent light impulses. For example, a ‘0’ might be a darker pulse then a ‘1’, which would be a brighter impulse How it receives light: 1.The receiver on the other end of the fiber-optic cable acts like a photovoltaic cell: when light hits it, electricity is created; much like the solar cell on most calculators. First, an impulse of light must be detected by the receiver, then it determines the intensity of the light and then converts that into the appropriate voltages and sends them off as 1s and 0s again. Flashlight Lab

8. Loss of Data ---------------------------------------------------------------------------------------------------------- Problems with Data Transmission Fiber-optic cable is not affected by the sources of external noise that cause problems on copper media because external light cannot enter the fiber except at the transmitter end. The cladding is covered by a buffer and an outer jacket that stops light from entering or leaving the cable. 1.) Although fiber is the best of all the transmission media at carrying large amounts of data over long distances, fiber is not without problems. When light travels through fiber, some of the light energy is lost. The farther a light signal travels through a fiber, the more the signal loses strength. This attenuation of the signal is due to several factors involving the nature of fiber itself. The most important factor is scattering. The scattering of light in a fiber is caused by microscopic non-uniformity (distortions) in the fiber that reflects and scatters some of the light energy. 2.) Absorption is another cause of light energy loss. When a light ray strikes some types of chemical impurities in a fiber, the impurities absorb part of the energy. This light energy is converted to a small amount of heat energy. Absorption makes the light signal a little dimmer. 3.) Another factor that causes attenuation of the light signal is manufacturing irregularities or roughness in the core-to-cladding boundary. Power is lost from the light signal because of the less than perfect total internal reflection in that rough area of the fiber. Any microscopic imperfections in the thickness or symmetry of the fiber will cut down on total internal reflection and the cladding will absorb some light energy. 4.) Dispersion of a light flash also limits transmission distances on a fiber. Dispersion is the technical term for the spreading of pulses of light as they travel down the fiber. 4 Main Causes of Lost Data 1.Light scattering 2.Absorption of data 3.Cable irregularities 4.Dispersion of light

9. Pros and Cons ---------------------------------------------------------------------------------------------------------- Pros of using Optical Fiber 1.Transmits much more data faster. 2.Fiber tends to lose much less data then copper or wireless media. 3.The size of fiber media are smaller then copper media. 4.The distances fiber can be transmitted over is much greater then other media. 5.Fiber-optics use light to carry data, which is one of the more easy medium to carry information Cons of using Optical Fiber 1.More fragile then copper or wireless media. 2.Fiber can be expensive; the cladding and glass pipelines break a lot, resulting in constant maintenance. 3.Fiber can only go so far until signal dispersion renders a signal unusable.