# Optical Communications Questions and Answers – Fiber Refractive Index Profile Measurements

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This set of Optical Communications Questions and Answers for Campus interviews focuses on “Fiber Refractive Index Profile Measurements”.

1. The detailed knowledge of the refractive index profile predicts the __________ of the fiber.
a) Nodal response
b) Variation in frequency
c) Impulse response
d) Amplitude

Explanation: Refractive index profile plays an important role in characterizing the properties of optical fibers. These properties include numerical aperture, intermodal response and number of modes propagating in the fiber. This makes the impulse response of the fiber.

2. ______________ of the fiber is strongly dependent on the refractive index profile.
a) Amplitude
b) Tuning frequency
c) Diameter
d) Information carrying capacity

Explanation: Information carrying capacity is strongly dependent on the refractive index profile same as that of the impulse response of the fiber. These characteristics predict the dispersion in the fiber.

3. ______________ is required in case of graded index fibers.
a) High amplitude
b) High frequency
c) High impulse response
d) Optimum profile

Explanation: In case of graded index fibers, it is essential that the fiber manufacturer is able to produce particular profiles with higher accuracy. This profile is known as optimum profile as it minimizes the dispersion rate.

4. _______________ have been widely used to determine the refractive index profiles of optical fibers.
a) Interference microscopes
b) Gyro meters
c) Mode-diameter device
d) Tunable microscopes

Explanation: Interference microscopes are used to determine the refractive index profiles of the fibers. These microscopes use an index matching technique to determine the index profiles.

5. Which of the following is not an interference microscope?
a) Gerry Buzynski
b) Michelson
c) Mach-Zehnder
d) L.G. Cohen

Explanation: Mach-Zehnder and Michelson are the widely used interference microscopes. L.G.Cohen reused a modification of the Mach-Zehnder.

6. What stands for x in the given equation?

`δn = qλ/x`

a) Displacement
b) Thickness
c) Constant
d) Coefficient of refraction

Explanation: The given equation is an equation for the difference in the refractive index which is denoted by δn. q is the fringe shift, λ is the wavelength and x is the thickness of the fiber slab.

7. The ________ method gives an accurate measurement of the refractive index profile.
a) Slab
b) Biometric
c) GSLB
d) Tuning

Explanation: The slab method gives an accurate measurement of the refractive index profile. Also, there are some drawbacks to it. The computation of individual points is somewhat tedious unless an automated technique is used.

8. Which of the following is the main drawback of the slab technique?
a) Efficiency
b) Amplitude
c) Time
d) Accuracy

Explanation: The main drawback of the slab method is the time required to prepare the fiber slab. There are some interferometry methods which require no sample preparation.

9. ________________ method is used to measure the nonlinear refractive index of the silica fiber.
a) Grating
b) Non-linear
c) Silica-refraction
d) IGA

Explanation: IGA is abbreviated as induced-grating autocorrelation. This method requires no slab preparation and involves electro-optic effect where measuring the electric field autocorrelation function determines the refractive index of the optical fiber.

10. Near field scanning method provides a rapid method for acquiring the refractive index profile.
a) True
b) False

Explanation: The near field scanning method provides no time lag for slab preparation, thus it is not time bound. Hence, it is accurate and rapid mode of measuring refractive index profile.

Sanfoundry Global Education & Learning Series – Optical Communications.

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