COMMUNICATIONS ENGINEERING PART 11FIBER OPTICS

Multiple Choice: Encircle the letter that corresponds to your answer.

1. A transparent material along which we can transmit light is called:

a. a fiber opticb. a flashlightc. an optic fiberd. a xenon bulb

2. A simple fiber optic system would consist of:

a. a light source, an optic fiber and a photo-electric cellb. a laser, an optic fiber and an LEDc. a copper coaxial cable, a laser and a photo-electric celld. an LED, a cathode ray tube and a light source

3. Optic fiber is normally made from:

a. coherent glass and xenonb. copperc. waterd. silica glass or plastic

4. It is not true that:

a. endoscopes use coherent bundles of fibersb. silica glass is used because of its clarityc. photocell converts light into electric currentd. plastic fiber is normally used for long distance

communications

5. The number of fibers in a typical endoscope is about:

a. 1870b. 300c. 50,000d. 60

6. The speed of light in a transparent material:

a. is always the same regardless of the material chosenb. is never greater than the speed of light in free spacec. increases if the light enters a material with a higher

refractive indexd. is slowed down by a factor of a million within the first 60

meters

7. A ray of light in a transparent material of refractive index 1.5 is approaching a material with a refractive index of 1.48. At the boundary, the critical angle is:

a. 90b. 9.4c. 75.2d. 80.6

8. If a ray of light approaches a material with a greater refractive index:

a. The angle of incidence will be greater than the angle of refraction

b. TIR will always occurc. The speed of the light will increase immediately as it

crosses the boundaryd. The angle of refraction will be greater than the angle of

incidence

9. If a light ray crosses the boundary between two materials with different refractive indices:

a. no refraction would take place if the angle of incidence was 0

b. refraction will always occurc. the speed of the light will not change if the incident ray is

traveling along the normald. the speed of light never changes

10. The common windows used in fiber optic communications are centered on wavelengths of:

a. 300 nm, 1550 nm and 850 nmb. 850 nm, 1500 nm and 1300 nmc. 1350 nm, 1500 nm and 850 nmd. 800 nm, 1300 nm and 1550 nm

11. A wavelength of 660 nm is often used for visible light transmission. The frequency of this light in free space would be:

a. 660 x 109 Hzb. 4.5 x 1014 Hzc. 300 x 108 Hzd. 45 x 1012 Hz

12. In free space, light travels at approximately:

a. 180,000 ms-1

b. 3 x 109 ms-1

c. 300 ms-1

d. 0.3 meters per nanosecond

13. The window with the longest wavelength operates at a wavelength of approximately:

a. 850 nmb. 1550 mc. 1350 nmd. 1.55 m

14. The 850 nm window remains popular because it:

a. uses visible light and this allows plastic fibers to be usedb. the fiber is less expensive to install and has lower losses

than any other windowsc. the system is less expensive and easier to installd. allows higher data transmission rates

15. No material could have a refractive index of:

a. 1.5b. 1.3c. 1.1

d. 0.9

16. As the meridional ray is propagated along the optic fiber it:

a. travels in a sort of spiral shapeb. stays in the center of the fiberc. passes repeatedly through the center of the cored. is reflected off the the inside surface of the primary

buffer. This is called TIR

17. If the refractive index of the core of an optic fiber was 1.47 and that of the cladding was 1.44, the cone of acceptance would have an angle of approximately:

a. 17.19b. 72.82c. 78.4d. 34.36

18. An active fiber detector:

a. is used to prevent accidental exposure to invisible lightb. is a communication system used during installationc. detects movement of fiber in security systemsd. can be used to weigh objects

19. If light leaves a material of refractive index 1.45 and crosses an abrupt into a material of refractive index 1.0, the Fresnel loss would be:

a. 0.346 dBb. 0.149 dBc. 1.613 dBd. 3 dB

20. Absorption loss is caused by:

a. insufficient stirring of the ingredients during manufactureb. changes in the density of the fiber due to uneven rates of

coolingc. microscopic cracks in the cladding which allow leakage

of the vacuum in the cored. impurities in the fiber

21. Rayleigh scatter is most severe:

a. in light with a short wavelengthb. in blue light on the Earth and black light on the moonc. in low frequency lightd. at sunset

22. Bending losses:

a. always result in breakage of the fiberb. can be caused by microbends and macrobendsc. are used to detect the length of fiber on a drumd. are caused by the difference in the operating

temperature of the core compared with the cladding on active fibers

23. Dispersion:

a. causes the core to spread out and get wider as the pulse is transmitted along the fiber

b. results in the wavelength of the light increasing along the fiber

c. is the lengthening of light pulses as they travel down the fiber

d. cannot occur with a laser light source

24. An SI MM fiber has a core of 62.5 m diameter and a numerical aperture of 0.2424. The number of modes that would occur using a light of wavelength of 865 nm would be:

a. 1b. 378c. 1513.78d. 1513

25. Intramodal dispersion:

a. only occurs in multimode fiberb. is also called chromatic dispersionc. does not occur in multimode fiberd. could not occur in an all plastic fiber

26. If the wavelength of the transmitted light were to be decreased, the number of modes would:

a. increaseb. decreasec. remain the samed. halve in a graded index fiber

27. The refractive index of a GI fiber

a. is at its highest value at the center of the coreb. is usually higher in the cladding than in the corec. increases as we move away from the center of the cored. has a value of 4 instead of the 2 common in step index

fibers

28. A cable containing both optic fiber and copper conductors is called:

a. an armored cableb. a dehydrated cablec. tight jacketed cabled. a hybrid cable

29. LSOH means low smoke:

a. zero halogenb. zero heatc. optic fibers of hybrid designd. or heat

30. Spiral galvanized wires are sometimes added to a cable to:

a. conduct electricityb. allow the cable to stretch more to relieve stressc. improve crush resistanced. allow the fibers to be upgraded as necessary

31. Blown fiber allows:

a. easy removal of the fibers to clean the ductsb. the diameter of the fiber to be increased by filling it with

compressed airc. easy removal of any water in the fiberd. easy replacement of any damaged fiber

32. Within buildings:

a. both tight buffered and loose jacketed cables are usedb. only loose jacketed cables are usedc. only armored cables can be usedd. only tight buffered cables are used

33. If light is launched from a fiber with a core diameter of 50 m into a fiber of core 62.5 m diameter, the loss would be:

a. +1.9 dBb. zeroc. –1.9 dBd. 16.8 dB

34. Cleaving is the process of:

a. removing the cladding before connecting fibers togetherb. cutting the end of the fiber in preparation for connecting

two fibersc. cleaning the surface of optic fibersd. inspecting fibers for flaws

35. A tang is most likely to give rise to:

a. increased values of NAb. eccentricityc. excessive amplificationd. gap loss

36. The core of a typical monomode fiber would have a diameter of:

a. 50 mb. 50 nmc. 8 md. 1 mm

37. Stripping off the primary buffer can be achieved by:

a. chemical or mechanical meansb. cleaving the buffer offc. isopropyl alcohold. brushing on index matching gel then wiping off with lint

free cloth

38. Too much overfeed whilst splicing will cause:

a. waistingb. a bubble being formed due to air being trapped inside

the fiberc. a bulge in the fiberd. runback

39. The main fusing arc is likely to have a duration of:

a. 15 sb. 62.5 nsc. 10-20 minutesd. less than a second

40. PAS stands for:

a. position adjustment systemb. profile alignment standardc. plane alignment systemd. profile alignment system

41. For viewing the splicing process, a CCD camera is preferable to a microscope because:

a. higher magnification can be achievedb. better resolution is possiblec. there is no risk of eye damaged. a CCD camera can operate at very low light levels

42. A splice protector:

a. provides more flexibility at the mechanical jointb. is not needed inside an enclosurec. protects against unauthorized copying of datad. provides mechanical protection to the fusion splice

43. The three basic designs used for mechanical splices are:

a. vee-groove, bent tube and precision holeb. vee-groove, PAS and LIDc. fusion splice, mechanical splice and enclosuresd. UV curing epoxy, index matching gel and isopropyl

alcohol

44. A typical value for the insertion loss for a mechanical splice is:

a. –50 dBb. 0.2 dBc. 12 mmd. 3 dB

45. Mechanical splices have the advantage that they:

a. are easily mistaken for splice protectorsb. have lower losses than fusion splicesc. are quick and easy to fitd. are waterproof

46. An elastomeric splice:

a. has losses which are about one thousandth of a fusion splice

b. uses a flexible plastic to align the fibersc. is based upon the bent tube principled. cannot be re-used

47. Some designs of mechanical splice can be easily mistaken for:

a. an enclosureb. a PAS splicerc. a splice protectord. an all plastic fiber

48. Two fibers can be joined by:

a. two adapters plugged into each end of a connectorb. a bare fiber connectorc. two connectors and one adapterd. a single connector

49. A connector with a keyed ferrule and secured by a screw thread is likely to be an:

a. SCb. FCPCc. STPCd. SMA 906

50. A PC finish:

a. reduces both the return loss and the insertion lossb. makes physical contact but damages the end of the fiberc. is the result of polishing on a hard surfaced. is the result of using an incorrect dolly

51. A full length Delrin sleeve:

a. converts the ferrule of an SMA 905 connector to be compatible with the SMA 906

b. can be used instead of an adapterc. is a popular choice of connector with cable television

companiesd. reduces the insertion loss of SMA 906 connectors

52. During polishing of a silica fiber, final inspection reveals a large scratch running right across the fiber. A likely cause of this is:

a. contamination of the final lapping film with some coarse grit from a previous stage of the polishing

b. using diamond lapping film instead of aluminum oxide film

c. using the wrong dollyd. water laying on the surface of the fiber. Simply wipe it

off with lint-free tissue

53. A 4 x 4 coupler would have a total of:

a. 16 portsb. 4 portsc. 9 portsd. 8 ports

54. The main advantage of using a star coupler to connect a large number of terminals is that:

a. more cable would be used and hence system reliability would increase

b. the power loss is lower than would be the case if tee couplers were to be used

c. higher levels of data errors could be toleratedd. less cable is used

55. Coupling ratio is also known as:

a. directional lossb. coupling lossc. splitting ratiod. directivity ratio

56. The output connection which carries the highest power level is the:

a. tap portb. power portc. stard. throughput port

57. The safest type of laser is referred to as:

a. infraredb. class 1c. pulsedd. class 4

58. A typical value for the spectral width of a laser is:

a. 1310 nmb. 3 nmc. 850 nmd. 30 nm

59. An APD:

a. can produce visible light as well as infrared light at 850 nm, 1300 nm and 1550 nm

b. has good electrical output in low light conditionsc. has a lower dynamic range than a PIN dioded. is cheaper than a PIN diode

60. LEDs are not used as the light source for high speed telecommunications because of their:

a. higher costb. poor reliabilityc. inability to provide a visible light outputd. slow switching speed and higher spectral width

61. A typical value of tr for a laser would be:

a. 3.5 nsb. 3 nmc. 90%d. 0.3 ns

62. For contract purposes, test equipment should:

a. have a valid certificate of calibrationb. be left switched on at all timesc. be powered by internal batteriesd. be manufactured by the same company as produced the

fiber

63. Light sources often include a tone output. This enables:

a. the length of the fiber to be calculatedb. our eyes to see the infrared light more easilyc. longer fibers to be testedd. easy identification of the fiber being tested

64. For detailed examination of a very short length of optic fiber cable, the OTDR should use the:

a. shortest possible wavelengthb. shortest possible pulsewidthc. longest available pulsewidthd. highest available power

65. The averaging facility of an OTDR can be switched off:

a. to provide a real time responseb. to remove noise and clean up the display of informationc. to allow the peak power to be usedd. if simultaneous measurements on more than one fiber

system are required

66. Reducing the length of a multimode fiber would:

a. decrease the transmitter rise timeb. decrease the system bandwidthc. increase the bandwidth of the systemd. increase the system rise time

67. Changing the spectral width of the light source would affect the:

a. fiber bandwidth in a singlemode systemb. system bandwidth of a multimode system but not a

singlemode onec. aging lossesd. number of likely repairs

68. If the transmitter and the receiver rise times were 0.5 ns and 1.5 ns respectively, and the fiber rise time was 25 ps, the system rise time would be approximately:

a. 25.05 nsb. 1.42 nsc. 1.58 nsd. 5.19 ns

69. If the dispersion figure for a singlemode fiber is known to be 44 ps, the bandwidth of the fiber would be:

a. 10 GHzb. 7.95 GHzc. 100 MHzd. 795 MHz

70. The following are the advantages of optical fiber system except

a. greater capacityb. crosstalk immunityc. safer to handle d. lower initial cost of installation

71. Plastic fibers have the following advantages over glass fiber except

a. flexibility b. ease of installationc. ruggednessd. low attenuation

72. This explains how a light may react when it meets the interface of two transmission materials that have different indices of refraction.

a. Huygen's Law b. Nyquist's Theorem c. Len's Law d. Snell's Law

73. In optical fibers

a. the core and cladding have the same index of refractionb. the core and cladding have the same area c. the core surrounds the cladding d. the cladding surround the core

74. A type of fiber whereby light rays take many paths between the source and the receiver

a. monomode b. multimode c. single mode d. step Index

75. A figure of merit used to measure the light gathering or light collection ability of the optical fiber.

a. acceptance angle b. numerical aperture c. acceptance core d. critical angle

76. The Basic Optical Fiber Communication System consist of the following except

a. optical sourceb. photodetector c. transmission medium d. 48 volts power supply

77. Optical fibers can be made out of

a. glassb. plastic c. combination of glass and plastic d. any of these

78. In ____________ , the core has index of refraction that changes continuously from the center to the outside

a. step index fiberb. graded index fiber c. monomoded. multimode

79. The following are causes of attenuation and loss of optical power within the fiber except

a. microbending loss b. connector loss c. splicing loss d. ohmic loss

80. For a signal to be propagated through the optical fiber, the angle of incidence should be __________ the critical angle.

a. greater thanb. less thanc. equal tod. none of these

81. Scattering loss is caused by:

a. insufficient stirring of the ingredients during manufactureb. changes in the density of the fiber due to uneven rates of

coolingc. microscopic cracks in the cladding which allow leakage

of the vacuum in the cored. impurities in the fiber

82. Cleaving is the process of

a. removing the cladding before connecting fibers togetherb. cutting the end of the fiber in preparation for connecting

two fibersc. cleaning the surface of optic fibersd. inspecting fibers for flaws

83. The following are light detectors in Fiber Optic Communications System except

a. ILDb. PIN diodec. APDd. NOTA

84. The following are the three distinct regions of an optical fiber except

a. coreb. claddingc. jacketd. coating

85. Which of the following combinations is impossible for optical fibers

a. plastic core and claddingb. glass core and claddingc. plastic core and glass claddingd. glass core and plastic cladding

86. The scientist who coined the term “fiber optics”

a. H.H. Hopkinsb. C.W. Hanselc. N.S. Kapanyd. A.C. Van Heel

87. That dielectric material of an optical fiber surrounding the core

a. claddingb. armorc. shieldd. cover

88. Approximately what is the frequency limit of the optical fiber?

a. 20 GHzb. 1 MHzc. 100 MHzd. 40 MHz

89. A single fiber can handle as many voice channels as

a. a pair of copper conductorsb. a 1500 pair cablec. a 500 pair cabled. a 1000 pair cable

90. An incident ray can be defined as

a. a light ray reflected from a flat surfaceb. a light ray directed toward a surfacec. a diffused light rayd. a light ray that happens periodically

91. It is made from semiconductor material such as aluminum-gallium-arsenide or gallium-arsenide-phosphide.

a. APDb. Injection laser diodec. Light emitting dioded. Positive-intrinsic-negative

92. An absorption loss caused by valence electrons in the silica material from which fibers are manufactured.

a. ultraviolet absorptionb. ion resonance absorptionc. modal dispersiond. infrared absorption

93. The loss in signal power as light travels down a fiber is

a. attenuationb. scatteringc. propagationd. absorption

94. An object farther from a converging lens than its focal point always has an __________ image.

a. invertedb. virtualc. smaller sized. the same in size

95. The refractive index number is

a. a number which compares the transparency of a material with that of air

b. a number assigned by the manufacturer to the fiber in question

c. a number which determines the core diameterd. a term for describing core elasticity

96. The mechanical splice is best suited for

a. quicker installation under ideal conditionsb. minimum attenuation lossesc. field service conditionsd. situations in which cost of equipment is not a factor

97. The cladding which surrounds the core

a. is used to reduce optical interferenceb. is used to protect the fiberc. acts to help guide the light in the cored. ensures that the refractive index remains constant

98. The different angles of entry of light into an optical fiber when the diameter of the core is many times the wavelength of the light transmitted is known as __________.

a. refractionb. emitterc. moded. sensor

99. Proposed the use of a clad glass fiber as a dielectric waveguide

a. Kao and Keckb. Karpon and Keckc. Bockham and Kaod. Karpon and Brockham

100. The wavelength of light has no role in

a. polarizationb. interferencec. diffractiond. resolving power