Coaching Materials in Fiber Optics Part 1 | ECE Board Exam

(Last Updated On: February 10, 2020)

Coaching Materials in Fiber Optics

This is the Coaching materials in Fiber Optics Part 1 as one topic in ECE Board Exam taken from various sources including but not limited to past Board Examination Questions in Electronic System and Technologies (EST), Communications Books, Journals and other Communications References. This particular Coaching Notes in Communications Engineering has random Questions and Answers in random topics. Make sure to familiarize this review notes to increase the chance of passing the ECE Board Exam.

Fiber Optics Coaching Materials Part 1

1. Fiber optics is coined by

NS Kapany

2. What are three means of producing light?

Mechanical, electrical and chemical

3. What is the smallest unit of radiant energy?

A photon

4. What unit is used to measure the different wavelengths of light?

Angstrom unit

5. What are the three primary colors of light?

Red, green and blue

6. What are the three secondary colors of light?

Magenta, yellow and cyan

7. A substance that transmits light but through which an object cannot be seen clearly is known as what kind of substance?


8. What type of wave motion is represented by motion of water?

Transverse-wave motion

9. A substance that transmits almost all of the light waves falling upon it is known as what type of substance?


10. A substance that is unable to transmit any light waves is known as what type of substance?


11. What is the law of reflection

The law of reflection states that the angle of incidence is equal to the angle of reflection

12. When a wave is reflected from a surface, energy is reflected. When is the reflection of energy greatest?

When the wave is nearly parallel to the reflecting surface

13. When is the reflection energy the least?

When the wave is perpendicular to the reflecting surface

14. Light waves obey what law?

The law of reflection

15. A light wave enters a sheet of glass at a perfect right angle to the surface. Is the majority of the wave reflected, refracted, transmitted or absorbed?


16. When light strikes a white piece of paper, the light is reflected in all directions. What do you call this scattering of light


17. What is the basic optical-material property relevant to optical fiber light transmission?

The index of refraction

18. What name is given to the angle where total internal reflection occurs?

Critical angle of incidence

19. List the three parts of optical fiber

Core, cladding and coating or buffer

20. Light transmission along an optical fiber is described by two theories. Which theory is used to approximate light acceptance and guiding properties of an optical fiber?

The ray theory

21. Light rays that passes thru the longitudinal axis at the fiber core are called

meridional rays

22. Meridional rays are classified as either bound or unbound rays. Bound rays propagate through the fiber according to what property?

Total internal reflection

23. What mechanisms in fiber waveguides weaken and distort the optical signals?

Scattering, absorption and dispersion

24. How can loss be reduced during construction (or fabrication) of optical fibers?

By removing the impurities from the optical fiber

25. What fiber property does numerical aperture (NA) measure?

NA measures the light-gathering ability of the optical fiber

26. Skew rays and meridional rays define different acceptance angles. Which acceptance angle is larger, the skew ray angle or the meridional ray angle?

Skew ray angle

27. The mode theory uses electromagnetic wave behavior to describe the propagation of light along the fiber. What is the set of guided electromagnetic waves called?

Modes of fiber

28. Modes that are bound at one wavelength may not exist at longer wavelengths. What is the wavelength at which a mode ceases to be bound is called?

Cutoff wavelength

29. What type of optical fiber operates below cutoff wavelength?

Multimode fiber

30. The fiber’s normalized frequency (V) determines how many modes a fiber can support. As the value of V increases, will the number of modes supported by the fiber increase or decrease?


31. The number of modes propagated in a multimode fiber depends on the core size and numerical aperture (NA). If the core size and the NA decrease, will the number of modes propagated increase of decrease?


32. What is the main loss mechanism between ultraviolet and infrared absorption regions?

Rayleigh scattering

33. Name the two types of intramodal, or chromatic, dispersion. Material dispersion and waveguide dispersion

34. Which dispersion mechanism (material or waveguide) is a function of the sine of the fiber’s core relative to the waveguide operation?

Waveguide dispersion

35. Modes of light pulse that enter the fiber at one time exit the fiber at different times. This condition causes the light pulse to spread. What is this condition called?

Modal dispersion

36. The reflective index of a fiber core is uniform and undergoes an abrupt change at the core-cladding boundary. Is this fiber a step-index or graded-index fiber?


37. What happens to the fundamental mode as the operating wavelength becomes longer than the single mode cutoff wavelength?

The fundamental mode becomes increasingly lossy

38. Give two reasons why optical fiber manufacturers depart from the traditional circular core cladding, low-loss glass fiber design?

To increase performance and reduce cost

39. Why do cable manufactures introduce a controlled twist to the stacked ribbons during the cabling process?

To minimize fiber stress when the cable is bent

40. Which fiber optic component (splice, connector, or coupler) makes a permanent connection in a distributed system?


41. What are the main causes of coupling loss?

Poor fiber end preparation and poor fiber alignment

42. When the axes of two connected fibers are no longer in parallel, the two connected fibers are in what kind of misalignment?

Angular misalignment

43. Which are more sensitive to alignment errors, single mode or multimode fibers?

Single mode

44. Quality fiber-end preparation is essential for proper system operation. What property must an optical fiber-end face have to ensure proper fiber connection?

Be flat, smooth, and perpendicular to the fiber axis

45. What is the basic fiber cleaving technique for preparing optical fibers for coupling?


46. Fiber splicing is divided into two broad categories that describe the techniques used for fiber splicing. What are they?

Mechanical and fusion splicing

47. What fiber property directly affects splice-loss in fusion splicing?

The angles and quality of the two fiber-end faces

48. What is a short discharge of electric current that prepares the fiber ends for fusion is called?


49. Do small core distortions formed by arc fusion’s self-alignment mechanism have more of an affect on light propagating through multimode or single mode fibers?

Single mode fibers

50. Which is the more critical parameter in maintaining total insertion loss below the required level, fiber alignment of fiber mismatch?

Fiber alignment

51. Fiber optic connectors can reduce system performance by increasing what two types of noise?

Modal and reflection

52. Which type of fiber optic connector (butt-jointed or expanded beam) brings the prepared ends of two optical fibers into contact?

Butt-jointed connectors

53. Is coupling loss from fiber separation and lateral misalignment more critical in expanded beam or butt-jointed connectors?

Butt-jointed connectors

54. Is coupling loss from angular misalignment more critical in expanded beam or butt-jointed connectors?

Expanded beam connectors

55. Which type of optical splitter (Y-coupler or T-coupler) splits only a small amount of power from the input fiber to one of the output fibers?


56. What two properties of the launch condition may affect multimode fiber attenuation measurements?

Launch spot size and angular distribution

57. Does underfilling a multimode optical fiber excite mainly high-order of low-order modes?

Low-order modes

58. A mode filter is a device that attenuates specific modes propagating in the core of an optical fiber. What mode propagating along single mode fibers do mode filters eliminate?

Second-order mode

59. What are the two most common types of mode filters?

Free-form loop and mandrel wrap

60. The cutoff wavelength of matched-clad and depressed-clad single mode fibers varies according to the fiber’s radius of curvature and length. The cutoff wavelength of which single mode fiber type is more sensitive to length?


61. What determines the range of wavelengths over which meaningful data is obtained for calculating the chromatic dispersion?

The wavelength range of the optical source(s) used

62. Near-filed power distributions describe the emitted power per unit are in the near-field region. Describe the near-field region.

The near-field region is the region close to the fiber0end face

63. How is the core diameter defined?

The core diameter is define as the diameter at which the near-filed intensity is 2.5 percent of the maximum intensity

64. Far-field power distributions describe the emitted power per unit area as a function of angle theta in the far-field region. Describe the far-field region.

The far-field region is the region far from the fiber-end face

65. Will fiber coupling loss generally increase of decrease if the mode field diameter of a single mode fiber is decreased?


66. In multimode fibers, how do fiber joints increase fiber attenuation following the joint?

By disturbing the fiber’s mode power distribution (MPD)

67. Reflectance is given as what ration?

The ratio of reflected optical power to incident optical power

68. When is an OTDR recommended for conducting field measurements on installed optical fibers or links?

When installed optical fiber cables or links are 50 meters or more in length

69. An OTDR measure the fraction of light that is reflected back from the fiber or link under test. What causes light to be reflected back into the OTDR?

Rayleigh scattering and Fresnel reflection

70. What is a temporary or permanent local deviation of the OTDR signal in the upward of downward direction called?

A point defect

71. Why is dead-zone fiber placed between the test fiber and OTDR when conducting attenuation measurements?

To reduce the effect of the initial reflection at the OTDR

72. The amount of backscattered optical power at each point depends on what two properties?

Forward optical power and backscatter capture coefficient

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