Test answers for Fiber Optics Test 2015

69 Answered Test Questions:

1. For a step index fiber, relationship between numerical aperture (NA) and coupling efficiency (ηc) is ________.

Answers:

• a

• b

• c

• d

2. Mirrors are placed in LASER optical sources to maintain conditions for ________.

Answers:

• incoherence

• amplification

• modulation

• coherence

3. Optical bandwidth (OB) relates to electrical bandwidth (EB) when

Answers:

• OB<EB

• OB=EB

• OB>EB

• OB≥EB

4. What is the thermal noise current it in a resistor R expressed in its mean square value?

where, K is Boltzmann's constant, T is absolute temperature and B is the bandwidth

Answers:

• a

• b

• c

• d

5. For a profile parameter (α)=1, the profile shape of refractive index for a graded index fiber will be _______.

Answers:

• triangular

• parabolic

• step

• circular

6. The rays which travel in a helical path through an optical fiber are called ______.

Answers:

• refracted rays

• reflected rays

• infra-red rays

• skew rays

7. Dark spot defects (DSD's) occur in:

Answers:

• Non-semiconductor LASER

• Fiber LASER

• Glass fiber LASER

• Injection LASER

8. What happens when dispersion occurs?

Answers:

• Output transmitted pulse broadens

• Output transmitted pulse shortens

• Output transmitted pulse gets completely eliminated

• None of the above

9. Silicon reach through avalanche photodiodes has _______.

Answers:

• maximum absorption of photons

• maximum absorption of electrons

• maximum quantum efficiency

• minimum noise

10. The vapor-phase deposition technique is used to produce _______.

Answers:

• fiber-rich glasses

• silica-rich glasses

• oxide-rich glasses

• carbonate-rich glasses

11. Scattering losses happen due to:

Answers:

• a rise in temperature

• imperfections in glass manufacturing process

• humidity

• bending of fiber

12. Graded-index fibers have:

Answers:

• a constant refractive index in the core

• a variable refractive index in the cladding

• a variable refractive index in the core

• None of these

13. Dispersion in optical fibers causes distortion in _______.

Answers:

• analog signals only

• digital signals only

• both analog and digital signals

• infra-red signals only

14. The LASER is a/an

Answers:

• incoherent device

• switching device

• threshold device

• incandescent device

15. SONET is _________.

Answers:

• Scattered optical network

• Synchronous optical network

• Stable optical network

• Silicon optical network

16. In p-i-n photodiodes "i" stands for:

Answers:

• Internal

• Intrinsic

• Impurity

• None of the above

17. Dispersion is the lowest in a________.

Answers:

• Multimode step-index fiber

• Multimode graded-index fiber

• Single-mode step-index fiber

• Silicon fiber

18. Superluminescent LED's are preferred because of _______.

Answers:

• large spectral linewidth

• a directional output beam

• low output power

• small size

19. Total internal reflection takes place at angles ________.

Answers:

• greater than the critical angle

• less than the critical angle

• equal to the critical angle

• None of the above

20. LED is more suitable for analog transmission because of its _______.

Answers:

• linearity

• bandwidth (spectrum)

• modulation property

• output power

21. When optical power is incident on the photo detector during the 0 bit period, then the system is said to exhibit _______.

Answers:

• a non-zero extinction ratio

• a zero extinction ratio

• an infinity extinction ratio

• an infinity absorption ratio

22. Which of the following is a fiber dispersion measurement method?

Answers:

• Time domain measurement

• Interferometric method

• Refracted near field method

• Reflected near field method

23. Germanium photodiodes are generally not preferred in the optical fiber system because of _________.

Answers:

• large current gain

• large voltage gain

• temperature dependence

• large dark current

24. Which one of the following is a type of non-linear scattering?

Answers:

• Stimulated Raman scattering (SRS)

• Rayleigh scattering

• Mie scattering

• Ultraviolet scattering

25. Refer to the figure above.

The critical angle at the core cladding interface is given by:

Answers:

• a

• b

• c

• d

26. Intersymbol interference (ISI) in optical fibers occurs due to ______.

Answers:

• refraction

• scattering

• bending

• dispersion

27. Near-field scanning method is used to measure:

Answers:

• Fiber attenuation

• Fiber dispersion

• Fiber numerical aperture

• Fiber refractive index profile

28. Which phenomenon does not let light rays escape an optical fiber?

Answers:

• Total internal reflection

• Total internal refraction

• Total internal diffraction

• Total internal attenuation

29. Quantum efficiency (η) is defined as

Answers:

• a

• b

• c

• d

30. Which of the following is an Optical System Design Software?

Answers:

• MATLAB

• COMSIM

• Photonic Transmission Design Suite (PTDS)

• ORCAD

31. COBRA (commutateur optique binaire rapide) is an ________.

Answers:

• optical fiber

• optical source

• optical detector

• optical switch

32. For a multimode optical graded index fiber, the profile parameter (α) will be equal to:

Answers:

• ∞

• Zero

• 1

• 2

33. What would the optical return loss (ORL) be defined as when r-fresnal reflection occurs at a fiber-air interface?

Answers:

• ORL= -10log10r

• ORL= -20log10r

• ORL= -30log10r

• ORL= -10loger

34. When microwave frequency rather than radio frequency subcarriers are employed, the strategy is usually referred to as ______.

Answers:

• Time division multiplexing

• Frequency division multiplexing

• Code-division multiplexing

• Subcarrier multiplexing (SCM)

35. FDDI can support a data rate of

Answers:

• 10 Mbps

• 10 Gbps

• 100 Mbps

• 1000 Mbps

36. Numerical aperture (NA) is related to the refractive indexes of core (n1) and cladding (n2) when,

Answers:

• a

• b

• c

• d

37. What does TPON stand for?

Answers:

• Telephony on a pure optical network

• Telephony on a plastic optical network

• Telephony on a polarized optical network

• Telephony on a passive optical network

38. Light emitting diodes (LED's) are:

Answers:

• Monochromatic incoherent sources

• Monochromatic coherent sources

• Incandescent light sources

• None of the above

39. A multimode graded index fiber exhibits total pulse broadening of 0.2 µsec over a distance of 10Km. Estimate the maximum possible bandwidth assuming that there is no inter-symbol interference.

Answers:

• 5 MHZ

• 2.5 MHZ

• 10 MHZ

• 1 MHZ

40. Homodyne detection is used for _______.

Answers:

• incoherent systems

• incandescent systems

• coherent systems

• analog systems

41. Avalanche photodiodes are ________.

Answers:

• less sensitive than simple photodiodes

• more sensitive than simple photodiodes

• cheaper than simple photodiodes

• less complex in structure than simple photodiodes

42. Hydrogen absorption by optical fiber causes _______.

Answers:

• an increase in efficiency

• a decrease in optical fiber losses

• no effect

• an increase in optical fiber losses

43. For an ideal photo detector, the absorption coefficient must be ______.

Answers:

• low

• zero

• one

• large

44. Rayleigh scattering is a ________.

Answers:

• non-linear scattering

• differential scattering

• cumulative scattering

• linear scattering

45. FDDI is _______.

Answers:

• Fiber dual data interface

• Fiber distributed data interface

• Fiber dual data interchange

• Fiber distributed data interchange

46. Macro bending losses in optical fibers can be reduced by designing the fibers with ________.

Answers:

• a smaller refractive index difference

• a fiber glass

• a silica glass

• a larger refractive index difference

47. Metallic impurities are eliminated from optical fiber by:

Answers:

• Vapor axial deposition (VAD) method

• Modified chemical vapor deposition (MCVD)method

• Vapor-phase oxidation method

• Plasma-activated chemical vapor deposition (PCVD)method

48. The information carrying capacity of optical fibers is in the range of:

Answers:

• MHZ

• mHZ

• GHZ

• µHZ

49. The first generation optical fibers are fabricated from:

Answers:

• Silica

• Oxides

• Gallium aluminum arsenide alloys

• Plastic

50. The Nd:YAG LASER is a/an_______.

Answers:

• non semiconductor laser

• semiconductor laser

• injection laser

• directional laser

51. Optical time domain reflectometry (OTDR) is a/an ________.

Answers:

• attenuation measurement technique

• refractive index measurement technique

• field measurement technique

• core diameter measurement technique

52. What is the relationship between refractive index (n1) of core and refractive index (n2) of cladding for an optical fiber?

Answers:

• n1 < n2

• n1 = n2

• n1 < n2

• n1 > n2

53. SOLITON is a/an ______.

Answers:

• type of optical fiber

• optical source

• optical detector

• pulse traveling in optical fiber

54. What is signal attenuation in an optical fiber where P1=Input power and P0=Output power

Answers:

• a

• b

• c

• None of the above

55. Index optical fibers are sometimes referred to as:

Answers:

• Homogenous core fibers

• Heterogeneous core fibers

• Long fibers

• Short fibers

56. IEEE 802.5 is a/an ________.

Answers:

• Ethernet

• Token bus

• Token ring

• Token star

57. The cutback technique is a/an _______.

Answers:

• attenuation measurement technique

• refractive index measurement technique

• impurity measurement technique

• frequency measurement technique

58. The refractive index is defined as the ratio of ____________.

Answers:

• the velocity of light in a vacuum to the velocity of light in the medium

• the velocity of light in the medium to the velocity of sound in a vacuum

• the velocity of light in the medium to the velocity of light in a vacuum

59. The population inversion phenomenon in optical sources occurs when _________.

Answers:

• the population of atoms in the upper energy level is greater than in the lower energy level

• the population of atoms in the lower energy level is greater than in the upper energy level

• the population of atoms in the upper and lower energy levels is equal

• None of the above

60. Intermodal dispersion is less in a __________.

Answers:

• Multimode step index fiber

• Multimode graded index fiber

• Single mode step index fiber

• Single mode graded index fiber

61. The fiber gyroscope is an ______.

Answers:

• Intrinsic fiber sensor

• Interferometer fiber sensor

• Extrinsic fiber sensor

• Extinction fiber sensor

62. One polarization maintaining fiber operates at a wavelength of 1.5 µm and has a beat length of 0.6mm. Its modal birefringence is given by _______.

Answers:

• 1.5 x 10-3

• 3.5 x 10-3

• 2.5 x 10-3

• 4.5 x 10-3

63. The output power of a LASER is greater than that of a LED because of _____.

Answers:

• stimulated emission

• spontaneous emission

• straight emission

• None of the above

64. Dispersion is low in the __________.

Answers:

• Multimode step index fiber

• Single mode step index fiber

• Two mode step index fiber

• None of the above

65. Surface emitter LEDs have high radiance because _______.

Answers:

• a hemisphere of n type GaAs is formed around a diffused p-type region

• of p-type diffusion into the n-type substrate

• it restricts the emission to a small active region

• of n-type diffusion into the p-type substrate

66. LASER stands for:

Answers:

• Light amplification by spontaneous emission of radiation

• Light amplification by stimulated emission of radiation

• Light amplification by straight emission of radiation

• None of the above

67. Dark line defects (DLDs) occur when:

Answers:

• non-radiative electron-hole recombination occurs

• mobile impurities are displaced into the active region of LASER

• all modes are not stabilized

• all modes are not polarized

68. Germanium avalanche photodiodes can be used for _______.

Answers:

• longer wavelength operation

• shorter wavelength operation

• low output power operation

• minimum noise operation

69. Which of the following is a characteristic of an injection LASER?

Answers:

• Frequency Chirp

• Amplification

• Frequency modulation

• Output power