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OPTOELECTRONIC COMMUNICATIONS EKT 442 1 MEETING • LECTURE • LABORATORY : 3 HOURS : 2 HOURS LECTURER Assoc. Prof. Dr. Syed Alwee Aljunid 017-5872667 [email protected] 2 Textbook • John Wilson and John Hawkes “Optoelectronics: An Introduction, 3nd Ed.” Prentice Hall, 1998. 3 References • • • Joseph C. Palais “Fiber Optic Communications, 5th Ed.” Prentice Hall, 2005. Ghatak and Thyagarajan“ An introduction to Fiber Optics”, Cambridge University Press, 1998. John. M. Senoir “Optical Fiber Communication: Principle and Practise, 2nd Ed. ”, Prentice Hall, 1993. 4 Assessment • Final Exam = 50 % • Coursework = 50 % – Assignments/Quiz = 10 % – Tests = 10 % – Labs/Tutorials = 30 % 5 Syllabus: 1. 2. 3. 4. 5. 6. 7. Light Properties Fundamentals of Fiber Optic Optical Components/Devices Light Sources Light Detectors, Noise and Detection Optical Amplifiers System Design 6 Chapter 1.0 Light Properties 7 Contents a) b) c) d) Electromagnetic radiation Frequency and wavelength of light Refraction of light Polarization of light 8 Electromagnetic radiation 9 Wavelength range of electromagnetic transmission Wavelength 3000km 102 30km 103 104 300m 105 106 NF range analog phone 3m 107 108 HF range AM radio TV & FM radio 3cm 109 0.3mm 1010 1011 1012 1013 Microwaves range mobile phone 3 mm 30nm 1014 1015 Optical range microwave oven 0.3nm 1016 1017 1018 Frequency [Hz] X / gamma range X-rays 10 Wavelength range of optical transmission wavelength nm 1800 1600 1400 1200 1000 2x1014 Radar range Laser range 800 600 400 3x1014 Infrared range 1. Optical window 2. Optical window 3. Optical window 200 1x1015 Frequency Hz Visible range 5x1014 Ultraviolet range 850 nm 1300 nm 1550 nm 11 Electromagnetic radiation Gamma rays, • highest-frequency electromagnetic energy • emitted by certain radioactive materials and also originate in outer space. • tremendous penetrating ability and able to pass through three meters of concrete! 12 Electromagnetic radiation X-rays • frequency just above ultraviolet • powerful enough to pass easily through many materials including soft tissues of animals. • This has led to the extensive use of X-rays in medicine to investigate textures in the human body. 13 Electromagnetic radiation Ultraviolet radiation • frequencies just above those of visible light • these rays have enough energy to kill living cells and cause tremendous tissue damage. • sun is a constant source of ultraviolet radiation • small doses of this light can promote the production of vitamin D and tan the skin. • Too much ultraviolet radiation can lead to serious sunburn. • Ultraviolet light is used extensively in scientific instruments to probe various systems, and it is also important in astronomical observations of the solar system, galaxy, and other parts of the universe. 14 Electromagnetic radiation Infrared radiation • This type of radiation is associated with the thermal region where visible light is not necessarily present. • For example, the human body does not emit visible light but it does emit infrared radiation which is felt as heat. • Almost all objects emit infrared rays, depending on the temperature of the object. Warmer objects emit more infrared radiation than cooler objects. • Common uses for infrared radiation are night vision scopes, electronic detectors, sensors in satellites and airplanes, and in astronomy 15 Electromagnetic radiation Microwave • The energy spectrum of microwaves has been utilized in oven technology where the wavelength is tuned to frequencies that are readily absorbed by water molecules in food causing them to absorb energy and release heat as they vibrate. • Microwaves are the highest frequency radio waves and are emitted by the Earth, buildings, cars, planes, and other large objects. • Short wavelength microwaves are the basis for RADAR, which stands for radio detecting and ranging, a technique used in locating large objects and calculating their speed and distance. 16 Electromagnetic radiation Radio • well known for their ability to transmit radio and television signals. • wide spectrum of electromagnetic radiation • Radio waves used in communication usually consist of two types of transmissions: amplitude modulated (AM) waves that vary in the amplitude of the wavelengths and frequency modulated (FM) waves that vary in wavelength frequency. FM radio waves are shorter in length than AM waves and tend to be blocked by large objects such as houses, buildings, and tunnels. AM waves are longer than FM waves and can be bent around these large objects to improve reception. 17 Electromagnetic radiation Visible light • comprises only a tiny portion of the entire electromagnetic spectrum of radiation. • The wavelengths that we are able to see lie between 400 and 700 nanometers in length. 18 Electromagnetic radiation Visible Light Wavelength and Perceived Color Wavelength Range (nanometers) Perceived Color 340-400 Near Ultraviolet (UV; Invisible) 400-430 Violet 430-500 Blue 500-560 Green 560-620 Yellow to Orange 620-700 Orange to Red Over 700 Near Infrared (IR; Invisible) 19 Frequency and wavelength of light electrons moving in orbits around the nucleus of an atom are arranged in different energy levels within their electron clouds. 20 Frequency and wavelength of light These electrons can absorb additional energy from outside sources of electromagnetic radiation, which results in their promotion to a higher energy level or electron cloud. 21 Frequency and wavelength of light higher energies are associated with shorter wavelengths and lower energies are associated with higher wavelengths 22 Light propagation Water tank Expected way of the light Light source Effective way of the light Total reflection at the boundary water-air 23 Speed of light Vacuum Milan 1 Millisecond Zuric h Glas Milan 1,5 Millisecond Speed of light in vacuum: C0 = 299’793 km/sec. Speed of light in glass: Cglass = 200’000 km/sec. Zurich 24 Wavelength / Frequency 1 Sek. f Wavelength (nm) covered distance of a wave during one period (oscillation) Frequency t Frequency (Hz) Number of oscillations (period per second) Wavelength 25 Frequency and wavelength of light Relationship between wavelength and frequency of light n = c/l Where: c is the speed of light n is the frequency of the light in hertz (Hz) l is the wavelength of the light in meters wavelength of light in inversely proportional to the frequency 26 Frequency and wavelength of light relationship between the energy of a photon and it's frequency E=h n E = h (c/ l) Where: E is the energy in kiloJoules per mole h is Planck's constant with a value of 6.626 x10-34 Joule-seconds per particle energy of a photon is directly proportional to its frequency and inversely proportional to its wavelength 27 Frequency and wavelength of light Conclusion • Very high-frequency electromagnetic radiation such a gamma rays, x-rays, and ultraviolet light possess very short wavelengths and a great deal of energy. • On the other hand, lower frequency radiation such as visible, infrared, microwave, and radio waves have correspondingly greater wavelengths with lower frequencies and energy. 28 Nature of light 29 Nature of light 30 Nature of light 31 Nature of light 32 Nature of light 33 Reflection Perpendicular to division line Division line Light path Light path Division line Light reflection Total reflection Perpendicular to division line 34 Light propagation in glass fiber Optical thinner Medium (n2) Light refraction Border ray Optical denser Medium (n1) Total reflection Light source 35 Reflection of light 36 Refraction of light Refraction (or bending of the light) occurs as light passes from a one medium to another when there is a difference in the index of refraction between the two materials, and is responsible for a variety of familiar phenomena such as the apparent distortion of objects partially submerged in water. When light passes from a less dense medium (such as air) to a more dense medium (such as water), the speed of the wave decreases. 37 Refraction of light Refractive index is defined as the relative speed at which light moves through a material with respect to its speed in a vacuum. By convention, the refractive index of a vacuum is defined as having a value of 1.0. The index of refraction, N (or n), of other transparent materials is defined through the equation: Material Refractive Index Air 1.0003 Water 1.33 Glycerin 1.47 Immersion Oil 1.515 Glass 1.52 Flint 1.66 Zircon 1.92 Diamond 2.42 Lead Sulfide 3.91 38 Refraction of light When light passes through a medium of high refractive index into a medium of lower refractive index, the incident angle of the light waves becomes an important factor. If the incident angle increases past a specific value (dependent upon the refractive index of the two media), it will reach a point where the angle is so large that no light is refracted into the medium of lower refractive index, 39 Refraction of light This phenomenon takes place when the angle of refraction (angle r in Figure 4) becomes equal to 90 degrees and Snell's law reduces to: When the critical angle is exceeded for a particular wave, it exhibits total reflection back into the medium. 40 Refraction of light Another important feature of light refraction, is that the wavelength of light has an impact on the amount of refraction in the same material. The amount of refraction is inversely proportional to the wavelength.. Thus, shorter wavelength visible light is refracted at a greater angle than longer wavelength light. White light is composed of all the colors in the visible spectrum. When this light is passed through a glass prism, the white light is dispersed into its component colors in a manner that is dependent upon the individual wavelengths 41 Polarization of light 42 Diffraction of light 43 Difraction of light 44 Difraction of light 45 Polarization of light 46 Polarization of light 47 Polarization of light 48 Polarization of light 49 Brewster’s(Critical) angle 50 Thank You 51