2. Chapter 24 Fiber Optics and Lasers

3. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives State the advantages and disadvantages of fiber-optic systems. Explain light theory. Explain causes of light energy losses in fiber-optic systems.

4. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Objectives Explain the transmission of light as data. Explain how light is received and changed into data. Explain how lasers operate. List safety precautions to be taken when working with lasers.

5. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Fiber Optics Nature of light Cable construction Attenuation Splices and connectors Transmitters Receivers Troubleshooting

6. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Why Fiber Optics? Small and lightweight Resist corrosion and water Provide data security Immune to electromagnetic interference Safety from fire and explosion Wide bandwidth

7. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Weight and Size 1/10 th the weight of traditional copper wiring systems Aircraft and ships can carry more cargo with fiber-optic cables Smaller diameter than conventional systems

8. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Corrosion and Water Resistance Glass and plastic are resistant to most corrosives Water has no effect on the light conduction capabilities Fiber-optic cables that run under oceans are expected to last

9. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Security Fiber optics cannot be tapped into without being detected Cut made into the cables affects the light signal Far more secure than copper cable

10. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Immunity to Electromagnetic Energy Fiber optics conduct light instead of electricity Do not need to be shielded to prevent electromagnetic interference Can withstand electromagnetic field of a nuclear explosion

11. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Safety Fiber optics can be installed anywhere without fear of electrical sparks Light can be transmitted through fiber optics in place of other lamps Safer and cheaper than conventional electrical lamps

12. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Bandwidth Light transmits at a higher frequency than electrical signals More signals can be transmitted at once Fiber optics can handle higher frequencies without losing conduction capabilities, like copper cables

13. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. The Nature of Light Theories of light –Light as a wave –Light as a particle Photons

14. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Cable Construction Cladding Buffers Plenum areasPlenum (Siecor Corporation, Hickory, NC)

15. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Attenuation Scattering Dispersion Extrinsic losses

16. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Scattering Always some impure material in the corecore –Causes light to reflect Longer cables have more signal loss Glass cores are better than plastic

17. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Dispersion Longer fiber-optic cables have more dispersion Receivers equipped with a digital gate can reshape the signal

18. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Extrinsic Loss Fiber-optic cables have minimum radius of bend Attenuation results when radius is exceeded Splices, couplings, and connectors are main reasons for transition signal losses

19. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Splices and Connectors Glass cores must be cleaved Extremely sharp cutters must be used on plastic cores Splicing is used to transfer light directly to next cable or connector Fusion splices

20. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Splices and Connectors (Cont.) Fresnel reflection loss –Minimized by use of sealing material with a refraction index close to index of core material Temporary splices might be needed Pigtail splices

21. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Fiber-Optic Transmitters LEDs or laser diodeslaser diodes Signal can be AM amplitude modulated or pulse modulated

22. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Fiber-Optic Receivers Use photodiodes to convert light energy back to electrical energy –Avalanche photodiodes –PIN diodesPIN diodes –Phototransistors and photodarlingtons

23. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Troubleshooting Fiber-Optic Systems Two components needed –Light transmitter –Light receiver Optical time domain reflectors (OTDRs)

24. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review Why are fiber-optic cables resistant to corrosion? The glass or plastic cores are resistant to corrosives

25. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review What will happen to a fiber-optic cable if a cut is made into it? The transmission of the signal is completely disrupted

26. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review Why is the bandwidth of fiber-optic cables so much better than copper cables? Because light is transmitted at a much higher frequency than electrical signals

27. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review What are the two theories of light based on? Light as a wave and light as a particle

28. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review What is a photon? A quantum of radiant energy

29. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review What part of the fiber-optic cable keeps the light wave contained to the glass or plastic? The cladding

30. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review What are the units of attenuation? Decibels (dB) or decibels per kilometer (dB/km)

31. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review What is the loss of signal strength due to impurities in the core material called? Scattering

32. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review What causes extrinsic losses? Physical factors outside the normal core

33. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review What causes a fresnel reflection loss? Differences in the refraction of two different materials joined together

34. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review What are fiber-optic transmitters typically made of? LEDs or laser diodes

35. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review What are the two basic components needed to troubleshoot fiber-optic systems? A light transmitter and a light receiver

36. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Lasers Coherent light –In phaseIn phase Incoherent light –Not in phase

37. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Laser Construction Light source –Strobe lamp –Ruby tube Reflective surface Emission of radiation Lasing

38. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Types of Lasers Ruby lasers –Light is pulsed, instead of continuous –Might use a liquid-nitrogen cooling system –Used for welding and cutting hard materials Gas lasers –Gas ionizes and produces light –Used in medical field –Used for cutting and drilling metal

39. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Laser Applications Construction Medicine Supermarket checkout counters CD players

40. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Lasers in Construction Used for measuring distances and alignment Used as surveying instruments Used as levels

41. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Lasers in Medicine Used to perform many types of surgery Low level light helps vision Can view the inside of a patient Can be directed to the surgical area Used for angioplasty

42. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Lasers at Supermarket Checkout Counters Nd:YAG lasers Laser system used to identify product codes Light shines on a rotating mirrored surface Light flashes through glass top Black bars in bar code absorb light

43. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Lasers in CD Players Beam directed through optical lens Photoreceiver receives beam from CD and converts it to electrical impulses Tiny pits are recorded sound pattern Digital impulses are converted to analog signals

44. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Other Uses of Lasers Private industry Government Education Military

45. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Damage from Lasers Can be minimal and cause only temporary irritation Can do irreversible damage to the eye The light from the laser does not have to be in the visible spectrum to do damage Eye protection should be worn at all times

46. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Laser Classifications Classified by –Maximum possible output during normal operation –Beam width Class I Class II Class III Class IV

47. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Night Vision Devices Infrared light sources enhance available light Photocathodes Microchannel plates (MCPs) CCDs Intensifier tubes

48. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review What does the acronym laser represent? Light amplification by stimulated emission of radiation

49. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review What is light consisting of all the same wavelength called? Coherent light

50. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review What is used to produce a ruby laser? A manufactured ruby consisting of an aluminum oxide compound and chromium

51. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Review What three kinds of gases might be used in a gas laser? Helium-neon, carbon dioxide (CO 2 ), or argon

52. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. For Discussion Discuss what other mediums could be used to transmit data. List causes for the greatest signal loss in a typical fiber-optic installation. How might laser light transmit a voice?

53. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Glossary Attenuation –A decrease in amplitude or intensity. Buffer –A type of amplifier placed between the oscillator and the power amplifier to isolate them from the load.

54. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Glossary Cladding –A layer that keeps the light wave contained to the core of a fiber-optic cable. Coherent light –Light consisting of waves that are all the same length.

55. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Glossary Core –Medium for the movement or transfer of the light energy in a fiber-optic cable. Dispersion –Distortion of an optical signal caused by light waves arriving at the termination point at different times.

56. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Glossary Emission of radiation –The escape of light through the small hole in the reflective material at one end of a laser tube. Extrinsic loss –A loss caused by physical factors outside the normal core of fiber-optic cable, such as bends, splices, and connectors.

57. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Glossary Fiber optics –The controlled transmission of light as a signal. Fresnel reflection loss –Loss occurring when two different fiber-optic materials, with different refraction properties, are joined.

58. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Glossary Fusion splice –Joining two fiber-optic cores, using heat to fuse or melt the materials together. Gas laser –A laser in which the resonant cavity is filled with a gas such as helium-neon, CO 2 (carbon dioxide), or argon.

59. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Glossary In phase –The quality of light having all the same wavelength. Incoherent light –Light consisting of many different wavelengths.

60. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Glossary Laser –Acronym for Light Amplification by Stimulated Emission of Radiation. A highly intense beam of coherent light, not necessarily visible. Laser diode –A type of fiber-optic transmitter that produces a beam of light that carries the signal.

61. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Glossary Lasing –Basic operating principle behind the laser. Light must reach a certain level to produce the stimulation of more photons. Nd:YAG laser –Uses yttrium aluminum garnet for the laser medium.

62. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Glossary Optical time domain reflector (OTDR) –A special piece of fiber-optic test equipment that can trace and record attenuation of a fiber-optic cable. Photon –Quantum of radiant energy.

63. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Glossary Pigtail splice –A factory-made connection on one end of a short piece of fiber-optic cable. PIN diode –Three layers of the diode: positive, intrinsic, and negative. It has a wider intrinsic layer (depletion layer) than the photodiode.

64. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Glossary Plenum –Space above a drop ceiling or under a raised floor in a building. It is used as part of the air- conditioning duct system and to run cables. Ruby laser –Laser that uses a manufactured ruby consisting of an aluminum oxide compound and chromium.

65. © Goodheart-Willcox Co., Inc.Permission granted to reproduce for educational use only. Glossary Scattering –The loss of signal strength due to impurities in the core material.