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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. Total Internal Reflection
B. Diffraction
C. Refraction
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. Cladding
B. Buffer Coating / Jacket
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 maximum angle of incidence at the input end for which light is propagated
B. The critical angle of the core-cladding interface
C. The angle of refraction inside the cladding
D. The angle at which light reflects inside the core

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

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

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. 0.244
B. 0.344
C. 0.144
D. 0.02

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

A. The attenuation of the fiber
B. The speed of light in 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. Decreases continuously from the axis to the cladding
C. Is constant in the core and changes abruptly at the cladding boundary
D. Increases 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. Straight lines zig-zagging
C. Sinusoidal or helical paths
D. Square waves

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 have higher attenuation
D. They significantly reduce intermodal dispersion

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

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

20 Attenuation in an optical fiber is usually expressed in:

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

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

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

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

25 Microbending loss is caused by:

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

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

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

27 Material dispersion arises because:

A. The core diameter varies along the length
B. The refractive index of the glass varies with wavelength
C. Light rays take different paths
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. Zero dispersion
D. Maximum scattering

29 Intermodal dispersion leads to:

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

30 Which rays propagate through the fiber axis without reflecting?

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

31 Skew rays are rays that:

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

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

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

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

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

34 Macrobending loss can be reduced by:

A. Using a lower frequency light
B. Increasing the Numerical Aperture (NA)
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 fiber diameter and refractive index profile relative to wavelength
C. The cable jacket material
D. The purity of the silica

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

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

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

A. TIR stops occurring
B. Material dispersion and Waveguide dispersion cancel each other out
C. Refractive index becomes 1
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. The speed settings of the laser
C. The number of fibers in a cable
D. Different colors of light

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

A. Refract into the cladding and be lost
B. Travel faster than the other rays
C. Undergo total internal reflection
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. 8
B. It remains the same
C. 2
D. 4

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

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

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

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

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

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

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

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

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

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

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

A. The cladding reflects the EMI
B. They are shielded by copper
C. The frequency is too low
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. Decreases
B. Increases
C. Becomes zero
D. Remains constant

50 Dispersion is usually measured in units of:

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