Fiber optic HUNG NGUYEN PHUONG THAN

History of Fiber Optics John Tyndall demonstration in 1870 In 1870, John Tyndall, using a jet of water that flowed from one container to another and a beam of light, demonstrated that light used internal reflection to follow a specific path. As water poured out through the spout of the first container, Tyndall directed a beam of sunlight at the path of the water. The light followed a zigzag path inside the curved path of the water. This idea know as total internal reflection. This idea is the basic of fiber optic. Total Internal reflection is the basic idea of fiber optic

History of Fiber optics During 1930, other ideas were developed with this fiber optic such as transmitting images through a fiber. During the 1960s, Lasers were introduced as efficient light sources In 1970s All glass fibers experienced excessive optical loss, the loss of the light signal as it traveled the fiber limiting transmission distance. This motivated the scientists to develop glass fibers that include a separating glass coating. The innermost region was used to transmit the light, while the glass coating prevented the light from leaking out of the core by reflecting the light within the boundaries of the core. Today, you can find fiber optics used in variety of applications such as medical environment to the broadcasting industry. It is used to transmit voice, television, images and data signals through small flexible threads of glass or plastic.

Several applications of fiber optic Configuration of a Fiber Optic Sensor System

Total internal Reflection Total internal reflection only takes place when both of the following two conditions are met: the light is in the more dense medium and approaching the less dense medium. the angle of incidence is greater than the so-called critical angle.

Source and transmitters A basic fiber optic communications system consists of three basic elements: Fiber media Light sources Light detector

There are three types of fiber optic cable commonly used Fiber media Optical fibers are the actual media that guides the light There are three types of fiber optic cable commonly used Step-index Multimode fiber Single mode: Diameter of 8.3 to 10 microns., fairly narrow diameter -It will propagate typically 1310 or 1550nm -higher transmission rate (up to 50 times more distance than multimode) -Cost more than multimode. Step-index Multimode fiber -made of glass fibers. -diameter in the 50 to 100 micron range -multiple paths of light can cause signal distortion at the receiving end, result in unclear or incomplete data transmission. Plastic optic fiber -POF is strong and very difficult to bend. -POF is not suitable for long-distance transmission -POF transmits very little infrared light -It can used for cold lighting or lighting displays of artwork Single Mode Plastic optic fiber

Optical fiber transmits light Optical fiber transmits light. But, what prevents the light from escaping from the fiber? when you looking straight down into clear lake you can see its bottom. However, when you view it at an angle and look off into the distance, the distance scenery is reflected upside down. This is caused by the difference in the index of refraction between the water and air. It is the same with the optical fiber, the optical fiber has 2 structures similar to water and air. The area where light is transmitted is called the core, and the external area is called the lad.

How Does fiber optic transmit light When light enters the area between 2 difference materials it will produce two different indexes of refraction. The light will either entirely reflected or a portion of it will be refracted depending on the angle. If the light can be kept at an angle where it is entirely reflected, it will become trapped inside and transmitted along the fiber.

The loss of fiber optic Material obsorption Material Scattering Waveguide scattering Fiber bending Fiber coupling loss

A Light Sources ILD (injection laser diode) LED (Light emitting diode) -A light sources, there are two types used today are LED (light emitting diode) and ILD (injection laser diode) -ILD have a higher output potential and coupling efficiency, they are suited for long distance transmissions. -LED have a lower bandwidth, or information capacity than ILD ILD (injection laser diode) LED (Light emitting diode)

Detectors Detector is the receiving end of a fiber optic link. There are two kinds of Detectors PIN (Positive Intrinsic Negative) APD (Avalanche photo diodes) There are two types of detectors are positive intrinsic negative(PIN) and avalanche photo diodes (APD). A PIN can be operational with voltage as low as 5v The APD require a large bias between 100v to 300v PIN APD

Idea of Modulation When sending information by an optical fiber, the information must be encoded or transformed somehow into information that capable of being transmitted through a fiber. The signal needs to be modulated. There are two types of modulation Analog and digital.

The advantages of fiber optic over wire cable Thinner Higher carrying capacity Less signal degradation Light signal Low power Flexible Non-flammable Lightweight

Disadvantage of fiber optic over copper wire cable Optical fiber is more expensive per meter than copper Optical fiber can not be join together as easily as copper cable. It requires training and expensive splicing and measurement equipment.

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References http://electronics.howstuffworks.com/fiber-optic7.htm http://www.commspecial.com/fiberguide.htm http://www.thefoa.org/ http://www.fiber-optics.info/fiber-history.htm