Optical ceramics


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Optical ceramics

  2. 2. contents- Introduction- General structures and properties- Case study : fiber optics- Introduction- Optical Fiber & Communications System- Modes and materials- Optical fibers processing- Applications- Applications- Conclusions and References
  3. 3. Introduction
  4. 4. Optical ceramics Materials with special light reflecting,transmitting or other optical propertiesinclude a wide range of glass compositions,glass ceramics, and selected ceramics. Classification: Transparent ceramics : glass, optical fibers,opticalswitches, laser amplifiers and lenses… Glass coloring Luminessence ceramics…
  5. 5. OPTICAL PROPERTIES OF CERAMICS-REFRACTIONLight that is transmitted from onemedium into another, undergoesrefraction.Refractive index, (n) of a material isthe ratio of the speed of light in avacuum (c = 3 x 108 m/s) to the speedof light in that material.n = c/v5
  7. 7. OPTICAL PROPERTIES OF CERAMICSCallister, W., D., (2007), Materials Science And Engineering, 7th Edition,730.04.2013
  8. 8. OPTICAL PROPERTIES OF CERAMICSABSORPTION•Color in ceramicsMost dielectric ceramics andglasses are colorless.By adding transition metals(TM)Ti, V, Cr, Mn, Fe, Co, NiCarter, C., B., Norton, M., G., Ceramic Materials Science And Engineering,8
  9. 9. Case study: fiber optics(optical fibers )
  10. 10. Introduction An optical fiber is essentially awaveguide for light It consists of a core andcladding that surrounds thecore The index of refraction of thecladding is less than that ofthe core, causing rays of lightleaving the core to berefracted back into the core A light-emitting diode (LED)or laser diode (LD) can beused for the source
  11. 11. Optical Fiber &Communications System
  12. 12. Optical Fibers It has little mechanical strength, so it must beenclosed in a protective jacket Often, two or more fibers are enclosed in the samecable for increased bandwidth and redundancy in caseone of the fibers breaks It is also easier to build a full-duplex system using twofibers, one for transmission in each direction- Fiber optics ( optical fibers) is a flexible, transparentfiber made of glass (silica) or plastic, slightly thickerthan a human hair. It functions as a waveguide, or“light pipe”,to transmit light between the two endsof the fiber
  13. 13. Types of Fiber Both types of fiber described earlier are known as step-index fibers becausethe index of refraction changes radically between the core and the cladding Graded-index fiber is a compromise multimode fiber, but the index ofrefraction gradually decreases away from the center of the core Graded-index fiber has less dispersion than a multimode step-index fiber
  14. 14. Why are fiber-optic systems revolutionizingtelecommunications?Compared to conventional metal wire(copper wire), optical fibers are……….
  15. 15. Less costSeveral miles of optical cable can be madecheaper than equivalent lengths of copperwire. This saves your provider (cable TV,Internet) and you money.
  16. 16. Smaller-ThinnerOptical fibers can be drawn to smallerdiameters than copper wire.
  17. 17. Higher carrying capacityBecause optical fibers are thinner than copperwires, more fibers can be bundled into a given-diameter cable than copper wires. This allowsmore phone lines to go over the same cable ormore channels to come through the cable to yourtv.
  18. 18. Less Signal Degradation- The loss of signal in optical fiber is lessthan in copper wire, so there is far less“bleeding” on the lines.
  19. 19. Light signalsUnlike electrical signals in copper wires, lightsignals from one fiber do not interfere with thoseof other fibers in the same cable. This meansclearer phone conversations or TV reception.
  20. 20. Low power RequirementBecause signals in optical fibers degrade less,lower-power transmitters can be used instead ofthe high-voltage electrical transmitters neededfor copper wires. Again, this saves your providerand you money.
  21. 21. Digital signalsOptical fibers are ideally suited for carryingdigital information, which is especially useful incomputer networks.
  22. 22. Non-flammableBecause no electricity is passed throughoptical fibers, there is no fire hazard.
  23. 23. LightweightAn optical cable weighs less than a comparablecopper wire cable. Fiber-optic cables take up lessspace in the ground.
  24. 24. how do we make an opticalfiber? Materials : glass (silica) or plastic Making optical fibers requires thefollowing steps: Making a preform glass cylinder Drawing the fibers from thepreform Testing the fibers
  25. 25. Making a preform glass cylinder Purifying silica Mine sand (raw silica) React with chlorine to produce SiCl4 and other metalsfrom the impurities in the sand (FeCl3, etc.) Heat this mixture (essentially distilling) Collect SiCl4 vapors only Condense the pure SiCl4 vapors
  26. 26. modified chemical vapordeposition (MCVD). Prepare a silica tube (glass extrusion). Heat the tube Inject SiCl4 and O2 into the tube At the heated portion, the SiCl4 is oxidizedThe lathe turns continuously to make an evencoating and consistent blank UItra pure SiO2 is deposited on the inner wallsof the tube Draw the tube through the furnace, continuouslycoating the inner walls. SiO2 particles deposit and sinter along thetube, leaving a hollow core [for now].2224 2ClSiOOSiCl heat
  27. 27. modified chemical vapordeposition (MCVD).
  28. 28.  This technique can be used to manufacture very longfibres (50 km). It is used for both step-index and graded-index fibres.Plasma-Enhanced Modified Chemical VapourDeposition (PMCVD)
  29. 29. Fiber drawing and protecting Anneal the multiwalled tube to the glass softening temperature. The tube and inner coating collapse to a solid, multilayered rod. Fire the rod at an even higher temperature softening it further. Draw the fiber through a nozzle, thinning the fiber dramatically. Core diameters from <5 to 500 um are used. Polymer coatings must also be applied. Fibers are finally bundled.
  30. 30. Fiber drawing- The tip of the preform is heated toabout 2000 oC in a furnace.- As the glass softens, a thin strandof softened glass falls by gravityand cools down.- As the fiber is drawn its diameter isconstantly monitored- A plastic coating is then applied tothe fiber, before it touches anycomponents.- The fiber is then wrapped around aspool.
  31. 31. Continuous production Fibers are drawn at 30 to 60feet per second. Multiple polymer coatingsmay be applied Thermoplastic (buffer) Aramid (strength) PVC of fluoride co-polymer Spools of up to severalkilometers are wound.2000 C
  32. 32. Fiber optic diameter Plastic fiber has a core diameter of upto 900 micrometer. 20-30 feet max length. Easy to work with. Cheap. Glass fibers have cores from 8 to 62.5micrometer across. Connecting two fibers end-to-end isthe hardest par—requires amicroscope or an automaticconnection of some kind.
  33. 33. Fiber testing Fibers must generally pass the following tests Tensile strength greater than 100,000 lb/in2 Dimensional tolerance Temperature dependence Optical properties
  34. 34. Importance of Fiber Purity This complicated procedure is necessary due to the incredible sensitivity ofoptical fiber communications to impurities and flaws. Fiber optics only became a reality in 1970, when Corning figured out how tomake fiber optics with less than 99% loss/km. Light transmission through 1 km of fiber drops to 1% of the input intensity ifthere are only: 2 Co atoms per billion 20 Fe atoms per billion 50 Cu atoms per billion Transmission in modern fibers is still limited to: 60 to 75 percent/km for light with a wavelength of 850 nm. Transmission losses <1% have been achieved over >3000 miles.
  35. 35. Repeating Stations Repeating stations are generally placed at regular distancesalong a fiber network to detect and amplify the signals since losswill occur over km, or hundreds of km, of fiber. When light drops to 95% of transmission, a repeating stationis required. Since the cost of the repeaters is high compared to fiber,tremendous effort goes into making pure, flaw free opticalfibers. Repeating stations today are generally 100 km apart for majorfiber bundles (trans-oceanic, etc).http://www.telebyteusa.com/foprimer/foch2.htm
  36. 36. disadvantages difficult to install and test optical fibers fiber is a less familiar technology andrequires skills Fibers can be damaged easily if bent toomuch fiber interfaces cost more than electricalinterfaces
  37. 37. Future fiber optic manufacturing? Why bother purifying Si and the trouble of making pureand flaw-free fiber optics when a spider does it naturally?http://www.newscientist.com/article.ns?id=dn3522
  38. 38. APPLICATIONS- Optical fiber communication :telecommunicationand computer networking- Fiber optic sensors ( removesensing )- Other uses…
  39. 39. Optical fiber communication
  40. 40. Fiber optic sensing systems (opticalsensors )Two types :-Intrinsic sensor : the sensors are internal or embedded into thefibers-Extrinsic sensors : the transducer is external to the fiber
  41. 41. how the environmental signal isdetected Informations (in terms ofintensity, phase, frequency,polarization, spectral content,etc.) are printed into the lightbeam and is carried through theoptical fiber to an optical and/orelectronic processor.The environmental signal isperceived by the fiber optic itself( as the light modulator )-intrinsic sensor can be classifiedas a distributed sensor, since itallows the measurement to takeplace in any point along the opticfiber.
  42. 42. Properties of Fiber OpticSensing - Highly sensitive (more than other technologies) - Configuration versatility - point and distributed configurations possible - Dielectric construction (can be used with high voltages, high temperatures,and stressed environments) -Wide dynamic range - Multiplexing capabilities - Freedom from electromagnetic interface (fibers carry no current) - Chemically passive - Provide real-time feedback - Resistant to corrosion - Multi point measurement (intrinsic sensors) or specific location sensing(extrinsic sensors)
  43. 43.  -Ability to measure a wide range of different properties (wide rangeof applications) - High resistance to extreme environments due to their robustnessand immunity to both electromagnetic and radio frequencyinterference (intrinsic sensors). -They do not conduct electricity which means that themeasurements are not easily affected by external causes (intrinsicsensors). - Extremely small size - Remotely powered -Ability to measure direct physical strain. - Sensors can placed upon the optic fiber
  44. 44. Input and Output Input: Light beam that carries the information Output:-Extrinsic: 1. encoder plates/disks: linear and angular position 2. Evanescence: temperature, strain 3. reflection and transmission: pressure, flow, damage 4. Laser Doppler velocimetry: flow measurement 5. total internal reflection: liquid level, pressure 6. absorption Band edge: temperature 7. Gratings: Pressure,Acoustics, vibrations 8. Photo elastics effects: pressure, acceleration, vibration, rotatory, position. 9. Fluorescence: temperature, viscosity, chemical analysis. 10. Pyrometers: temperature.- Intrinsic: 1. Microbends sensors: strain, pressure, vibration. 2. blackbody sensors: temperature 3. interferometryc sensors: rotation acceleration, acoustics, magnetic fileds,electric fields, strain, temperature, pressure, current.
  45. 45. Uses of Fiber optic sensingsystems testing machinery monitoring conditions in bridges or windturbines. used for industrial automation, biomedical technologies for digitaldiagnostic imagery, Endoscopy… military, space, and automotive applications.
  46. 46. Example: Uses of Fiber opticsensing systems in Endoscopy
  47. 47. SUMMARY Optical Fiber Processing Initial tube CVD of core Sintering and annealing coating applications
  48. 48. references Callister, W., D., (2007), Materials Science And Engineering, 7thEdition, http://www.laserfocusworld.com/articles/2011/01/medical-applications-of-fiber-optics-optical-fiber-sees-growth-as-medical-sensors.html http://en.wikipedia.org/wiki/Optical_fiber http://www.ofsoptics.com/fiber/ http://www.madehow.com/Volume-1/Optical-Fiber.html#b [4] John Crisp, Barry Elliott, Introduction to Fiber Optics, 3rdedition, Newnes, 2005 http://www.fiberopticproducts.com/ http://www.fiber-optics.info/ ………………………..