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Unit 3: Fiber Optics - Practice Quiz

PHY110 — Engineering Physics 50 Questions
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1 What is the fundamental physical principle behind the propagation of light in an optical fiber?

A. Refraction
B. Diffraction
C. Total Internal Reflection
D. Polarization

2 In an optical fiber, what is the relationship between the refractive index of the core () and the refractive index of the cladding ()?

A.
B.
C.
D.

3 Which component of the optical fiber provides mechanical strength and protects the core-cladding structure?

A. Buffer Coating / Jacket
B. Cladding
C. Acceptance Cone
D. Core

4 The critical angle at the core-cladding interface is given by which formula?

A.
B.
C.
D.

5 What is the 'Acceptance Angle' of an optical fiber?

A. The angle at which light reflects inside the core
B. The critical angle of the core-cladding interface
C. The maximum angle of incidence at the input end for which light is propagated
D. The angle of refraction inside the cladding

6 The Numerical Aperture (NA) of a fiber is a measure of its:

A. Attenuation capability
B. Core diameter
C. Light gathering power
D. Dispersion limit

7 Which of the following is the correct formula for Numerical Aperture (NA) assuming air () is the launch medium?

A.
B.
C.
D.

8 The Relative Refractive Index Difference () is defined as:

A.
B.
C.
D.

9 How is the Numerical Aperture (NA) related to the Relative Refractive Index Difference ()?

A.
B.
C.
D.

10 If the refractive index of the core is 1.50 and the cladding is 1.48, what is the Numerical Aperture (approximate)?

A. 0.344
B. 0.244
C. 0.144
D. 0.02

11 The V-number (or normalized frequency) determines:

A. The speed of light in the fiber
B. The attenuation of the fiber
C. The number of modes the fiber can support
D. The tensile strength of the fiber

12 What is the formula for the V-number?

A.
B.
C.
D.

13 What is the condition for a Step Index fiber to be Single Mode?

A.
B.
C.
D.

14 Approximately how many modes () travel in a Step Index Multimode fiber if is large?

A.
B.
C.
D.

15 Approximately how many modes () travel in a Graded Index (parabolic profile) Multimode fiber?

A.
B.
C.
D.

16 In a Step Index fiber, the refractive index:

A. Is constant throughout the core and cladding
B. Increases continuously from the axis to the cladding
C. Is constant in the core and changes abruptly at the cladding boundary
D. Decreases continuously from the axis to the cladding

17 In a Graded Index (GRIN) fiber, the light rays travel in:

A. Only along the axis
B. Sinusoidal or helical paths
C. Square waves
D. Straight lines zig-zagging

18 Why are Graded Index fibers preferred over Step Index Multimode fibers for higher bandwidth applications?

A. They are cheaper to manufacture
B. They have a larger numerical aperture
C. They significantly reduce intermodal dispersion
D. They have higher attenuation

19 What is the typical core diameter of a Single Mode Fiber (SMF)?

A. 200 m
B. 8 - 10 m
C. 50 m
D. 1 mm

20 Attenuation in an optical fiber is usually expressed in:

A. Watts
B. Volts/m
C. dB/km
D. Decibels (dB)

21 If the input power is and output power is over a length , the attenuation (in dB/km) is calculated as:

A.
B.
C.
D.

22 Rayleigh scattering loss is inversely proportional to:

A.
B.
C.
D.

23 Which of the following causes Intrinsic Absorption in optical fibers?

A. Iron impurities
B. OH ions (water peaks)
C. Electronic transitions in the UV region and atomic vibrations in the IR region
D. Microbending

24 The peak absorption around 1.38 m in silica fibers is primarily caused by:

A. Macrobending
B. OH (hydroxyl) ions
C. Rayleigh Scattering
D. Transition metals

25 Microbending loss is caused by:

A. Microscopic irregularities in the fiber geometry or pressure from cabling
B. Absorption by impurities
C. Large radius bends in the fiber cable installation
D. Scattering by atomic defects

26 Which type of dispersion is dominant in Single Mode Fibers?

A. Intermodal Dispersion
B. Polarization Mode Dispersion only
C. Intramodal (Chromatic) Dispersion
D. Modal Noise

27 Material dispersion arises because:

A. Light rays take different paths
B. The refractive index of the glass varies with wavelength
C. The core diameter varies along the length
D. The cladding index is higher than the core index

28 What is the primary advantage of operating at the 1550 nm wavelength window?

A. Highest V-number
B. Minimum attenuation
C. Maximum scattering
D. Zero dispersion

29 Intermodal dispersion leads to:

A. Wavelength shifting
B. Pulse broadening
C. Increased NA
D. Signal strengthening

30 Which rays propagate through the fiber axis without reflecting?

A. Skew rays
B. Meridional rays
C. Evanescent waves
D. Axial rays

31 Skew rays are rays that:

A. Follow a helical path and never intersect the fiber axis
B. Are reflected back to the source
C. Travel only in the cladding
D. Intersect the fiber axis

32 Why is an optical fiber considered a 'Dielectric Waveguide'?

A. It is made of non-conducting (insulating) materials like glass/plastic
B. It requires a dielectric coating to function
C. It uses magnetic fields to guide light
D. It conducts electricity

33 If the fractional refractive index change and , what is ?

A. 1.0
B. 1.490
C. 1.515
D. 1.485

34 Macrobending loss can be reduced by:

A. Increasing the Numerical Aperture (NA)
B. Using a lower frequency light
C. Decreasing the refractive index difference
D. Increasing the core radius

35 What is the unit of the V-number?

A. Dimensionless
B. Degrees
C. Hertz
D. Meters

36 Waveguide dispersion depends primarily on:

A. The material composition only
B. The cable jacket material
C. The purity of the silica
D. The fiber diameter and refractive index profile relative to wavelength

37 Which window of optical communication is typically around 850 nm?

A. Fourth window
B. Third window
C. Second window
D. First window

38 What is the phenomenon responsible for the 'Zero Dispersion Wavelength'?

A. Material dispersion and Waveguide dispersion cancel each other out
B. Refractive index becomes 1
C. TIR stops occurring
D. Attenuation is zero

39 In the context of fiber optics, what does 'Modes' refer to?

A. Allowed paths for light propagation solving the wave equation
B. Different colors of light
C. The number of fibers in a cable
D. The speed settings of the laser

40 If a fiber has an acceptance angle of , light entering at will:

A. Refract into the cladding and be lost
B. Undergo total internal reflection
C. Travel faster than the other rays
D. Be guided efficiently

41 For a Multimode Step Index fiber, if the core radius is doubled, the number of modes increases by a factor of:

A. It remains the same
B. 4
C. 2
D. 8

42 The refractive index profile of a Graded Index fiber is typically:

A. Hyperbolic
B. Exponential
C. Linear
D. Parabolic

43 Which of the following is NOT a source of loss in optical fibers?

A. Absorption
B. Rayleigh Scattering
C. Total Internal Reflection
D. Bending

44 Which fiber type has the largest information-carrying capacity (Bandwidth)?

A. Multimode Step Index
B. Plastic Optical Fiber
C. Multimode Graded Index
D. Single Mode Step Index

45 The cone of acceptance is the solid angle formed by rotating the:

A. Brewster angle
B. Acceptance angle
C. Critical angle
D. Refraction angle

46 If light travels from air () into a fiber core (), the maximum value of NA is theoretically:

A. 1.5
B. 0.5
C. 1.0
D. Infinity

47 Why are optical fibers immune to Electromagnetic Interference (EMI)?

A. The frequency is too low
B. They are shielded by copper
C. The cladding reflects the EMI
D. Light photons are electrically neutral

48 Calculate the acceptance angle if the Numerical Aperture is 0.5 and the medium is air.

A.
B.
C.
D.

49 As the wavelength of light increases, the V-number of the fiber:

A. Increases
B. Remains constant
C. Decreases
D. Becomes zero

50 Dispersion is usually measured in units of:

A. nm/km
B. dB/km
C. Hz
D. ps/(nmkm)
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