Chapter 24

2. Chapter 24 Fiber Optics and Lasers

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

4. 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. Permission granted to reproduce for educational use only.

5. Fiber Optics • Nature of light • Cable construction • Attenuation • Splices and connectors • Transmitters • Receivers • Troubleshooting Permission granted to reproduce for educational use only.

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

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

8. 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 Permission granted to reproduce for educational use only.

9. 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 Permission granted to reproduce for educational use only.

10. 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 Permission granted to reproduce for educational use only.

11. 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 Permission granted to reproduce for educational use only.

12. 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 Permission granted to reproduce for educational use only.

13. The Nature of Light • Theories of light • Light as a wave • Light as a particle • Photons Permission granted to reproduce for educational use only.

14. Cable Construction • Cladding • Buffers • Plenum areas (Siecor Corporation, Hickory, NC) Permission granted to reproduce for educational use only.

15. Attenuation • Scattering • Dispersion • Extrinsic losses Permission granted to reproduce for educational use only.

16. Scattering • Always some impure material in the core • Causes light to reflect • Longer cables have more signal loss • Glass cores are better than plastic Permission granted to reproduce for educational use only.

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

18. 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 Permission granted to reproduce for educational use only.

19. 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 Permission granted to reproduce for educational use only.

20. 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 Permission granted to reproduce for educational use only.

21. Fiber-Optic Transmitters • LEDs or laser diodes • Signal can be AM amplitude modulated or pulse modulated Permission granted to reproduce for educational use only.

22. Fiber-Optic Receivers • Use photodiodes to convert light energy back to electrical energy • Avalanche photodiodes • PIN diodes • Phototransistors and photodarlingtons Permission granted to reproduce for educational use only.

23. Troubleshooting Fiber-Optic Systems • Two components needed • Light transmitter • Light receiver • Optical time domain reflectors (OTDRs) Permission granted to reproduce for educational use only.

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

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

26. 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 Permission granted to reproduce for educational use only.

27. Review What are the two theories of light based on? Light as a wave and light as a particle Permission granted to reproduce for educational use only.

28. Review What is a photon? A quantum of radiant energy Permission granted to reproduce for educational use only.

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

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

31. Review What is the loss of signal strength due to impurities in the core material called? Scattering Permission granted to reproduce for educational use only.

32. Review What causes extrinsic losses? Physical factors outside the normal core Permission granted to reproduce for educational use only.

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

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

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

36. Lasers • Coherent light • In phase • Incoherent light • Not in phase Permission granted to reproduce for educational use only.

37. Laser Construction • Light source • Strobe lamp • Ruby tube • Reflective surface • Emission of radiation • Lasing Permission granted to reproduce for educational use only.

38. 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 Permission granted to reproduce for educational use only.

39. Laser Applications • Construction • Medicine • Supermarket checkout counters • CD players Permission granted to reproduce for educational use only.

40. Lasers in Construction • Used for measuring distances and alignment • Used as surveying instruments • Used as levels Permission granted to reproduce for educational use only.

41. 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 Permission granted to reproduce for educational use only.

42. 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 Permission granted to reproduce for educational use only.

43. 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 Permission granted to reproduce for educational use only.

44. Other Uses of Lasers • Private industry • Government • Education • Military Permission granted to reproduce for educational use only.

45. 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 Permission granted to reproduce for educational use only.

46. Laser Classifications • Classified by • Maximum possible output during normal operation • Beam width • Class I • Class II • Class III • Class IV Permission granted to reproduce for educational use only.

47. Night Vision Devices • Infrared light sources enhance available light • Photocathodes • Microchannel plates (MCPs) • CCDs • Intensifier tubes Permission granted to reproduce for educational use only.

48. Review What does the acronym laser represent? Light amplification by stimulated emission of radiation Permission granted to reproduce for educational use only.

49. Review What is light consisting of all the same wavelength called? Coherent light Permission granted to reproduce for educational use only.

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