250+ TOP MCQs on Optical Fiber Cables and Answers

Optical Communications Multiple Choice Questions on ” Optical Fiber Cables”.

1. When optical fibers are to be installed in a working environment, the most important parameter to be considered is?
a) Transmission property of the fiber
b) Mechanical property of the fiber
c) Core cladding ratio of the fiber
d) Numerical aperture of the fiber
Answer: b
Explanation: Nowadays, optical fibers are used alternatively to electric transmission lines. They are installed safely and maintained in all environments including underground areas. This requires mechanical strengthening of fibers in order to ensure proper transmission.

2. It is not important to cover these optical fibers required for transmission.
a) True
b) False
Answer: b
Explanation: Unprotected optical fibers have number of losses regarding its strength and durability. Bare glass fibers are brittle and have small cross-section area that makes them highly susceptible to damages while handling and maintenance. Thus, to improve tensile strength, optical fibers should be covered by surrounding them with number of protective layers.

3. Optical fibers for communication use are mostly fabricated from ___________
a) Plastic
b) Silica or multicomponent glass
c) Ceramics
d) Copper
Answer: b
Explanation: Silica or a compound of glass are brittle and have almost perfect elasticity until reaching their breaking point. Strength of these materials is high. Thus, optical fibers are fabricated from these materials.

4. An Si-O bond with a Young’s modulus of 9*10¹⁰Nm^-1 have an elliptical crack of depth 7nm. The surface energy is 2.29 J. Estimate fracture stress for silica fiber.
a) 4.32*10⁹Nm^-1
b) 6.32*10⁹Nm^-1
c) 5.2*10⁹Nm^-1
d) 3*10⁹Nm^-1
Answer: a
Explanation: For an elliptical crack, the fracture stress is given by-
S_f = (2Eγ_p/πC)^1/2
Where S_f = fracture stress
γ_p = surface energy
C = depth of crack.

5. Calculate percentage strain at break for a Si-O bond with a fracture strength of 3.52*10¹⁰Nm^-1 and Young’s modulus of 9 *10⁹Nm^-1.
a) 3.1 %
b) 2.8 %
c) 4.5 %
d) 3.9 %
Answer: d
Explanation: Young’s modulus is given by-
E = Stress/Strain
To calculate strain from the above formula, we have to divide stress by Young’s modulus. Therefore, Strain = Stress/E.

6. Stress corrosion must be considered while designing and testing optical fiber cables.
a) True
b) False
Answer: a
Explanation: Stress corrosion means growth of flaws due to stress and water. This occurs as a result of molecular bonds at the tip of crack being attacked by water. Hence, it is important to have a protection against water to avoid stress corrosion.

7. Which statistics are used for calculations of strengths of optical fibers?
a) Edwin statistics
b) Newton statistics
c) Wei-bull statistics
d) Gamma statistics
Answer: c
Explanation: Calculations of strengths are conducted using Wei-bull statistics in case of optical fibers. It describes the strength behavior of a system that is dependent on the weakest link of the system. The Wei-bull statistics gives the probability of failure of the optical fiber at a given strength.

8. What does n denotes in the equation given below, if v_c is the crack velocity; A is the constant for the fiber material and KI is the strength intensity factor?

v_c = AK_Iⁿ

a) Refractive index
b) Stress corrosion susceptibility
c) Strain
d) Young’s modulus
Answer: b
Explanation: The above equation allows estimation of the time to failure of a fiber under stress corrosion conditions. The constant n is called as stress corrosion susceptibility. It is typically in the range of 15 to 50 for a glass.