# Fiber Numerical Aperture and Fiber Diameter Measurements MCQ’s

This set of Optical Communication Multiple Choice Questions & Answers (MCQs) focuses on “Fiber Numerical Aperture and Fiber Diameter Measurements”.

1. The numerical aperture for a step index fiber is sine angle of the ____________
a) Efficient angle
b) Aperture
c) Acceptance angle
d) Attenuation

2. The calculations of the numerical aperture from a refractive index data are less accurate for the graded index fibers than for step index fibers.
a) False
b) True

3. The ____________ affects the light gathering capacity and the normalized frequency of the fiber.
a) Numerical aperture
b) Amplitude modulation
c) Responsivity
d) Quantum efficiency

4. The shadow velocity is given by 0.4 μm μs-1 and shadow pulse of width 300 μs is registered at an instant by the photodetector. Determine the outer diameter of the optical fiber in μm.
a) 100 μm
b) 120 μm
c) 140 μm
d) 90 μm

5. Far field pattern measurements with regard to multimode fibers are dependent on the _____________ of the fiber.
a) Amplitude
b) Frequency
c) Diameter
d) Length

6. During the fiber drawing process, the fiber outer diameter is maintained constant to within ________
a) 2%
b) 1%
c) 5%
d) 10%

7. Which of the following is a non-contacting optical method of on-line diameter measurement?
a) Brussels’s method
b) Velocity differentiator method
c) Photo detector method
d) Image projection method

8. The screen is positioned 10 cm from the fiber end face. When illuminated from a wide angled visible source the measured output pattern size is 6.2 cm. Calculate the approximate numerical aperture of the fiber.
a) 0.21
b) 0.30
c) 0.9
d) 1.21

9. What is the minimum value of accuracy in diameter is needed to avoid radiation losses in the fiber?
a) 0.1%
b) 0.2%
c) 0.3%
d) 0.03%

10. The shadow method is used for measurement of the outer diameter of an optical fiber. The apparatus employs a rotating mirror with an angular velocity of 4 rad/s which is located at 10 cm from the photo detector. Compute the shadow velocity.
a) 0.1 μm μs-1
b) 0.4 μm μs-1
c) 0.87 μm μs-1
d) 1 μm μs-1

11. The techniques used to determine the refractive index profile can also be used to determine the core diameter.
a) True
b) False

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