Optical Communications Questions and Answers Part-1

1. The ratio of speed of light in air to the speed of light in another medium is called as _________
a) Reflection index
b) Dielectric constant
c) Speed factor
d) Refraction index

Answer: d
Explanation: When a ray travels from one medium to another, the ray incident from a light source is called as incident ray. In passing through, the speed varies. The ratio of the speed of incident and the refracted ray in different medium is called refractive index.

2. The light sources used in fibre optics communication are ____________
a) Phototransistors
b) LED’s and Lasers
c) Incandescent
d) Xenon lights

Answer: b
Explanation: LED’s and Lasers are the light sources used in optical communication.

3. Who proposed the idea of transmission of light via dielectric waveguide structure?
a) Albert Einstein
b) Christian Huygens
c) Hondros and debye
d) Karpon and Bockham

Answer: c
Explanation: It was in the beginning of 20th century where Hondros and debye theoretical and experimental study demonstrated that information can be transferred as a form of light through a dielectric waveguide.

4. What is refraction?
a) Bending of light waves
b) Reflection of light waves
c) Refraction of light waves
d) Diffusion of light waves

Answer: a
Explanation: Unlike reflection, refraction involves penetration of a light wave from one medium to another. While penetrating, as it passes through another medium it gets deviated at some angle.

5. When a ray of light enters one medium from another medium, which quality will not change?
a) Wavelength
b) Direction
c) Frequency
d) Speed

Answer: c
Explanation: The electric and the magnetic field have to remain continuous at the refractive index boundary. If the frequency is changed, the light at the boundary would change its phase and the fields won’t match. In order to match the field, frequency won’t change.

6. Who proposed the use of clad waveguide structure?
a) Kao and Hockham
b) Edward Appleton
c) James Maxwell
d) Schriever

Answer: a
Explanation: The invention of clad waveguide structure raised the eyebrows of the scientists. The proposals by Kao and Hockham proved beneficial leading in utilization of optical fibre as a communication medium.

7. The ________ ray passes through the axis of the fiber core.
a) Refracted
b) Reflected
c) Shew
d) Meridional

Answer: d
Explanation: When a light ray is passed through a perfect optical fiber, any discontinuities at the core cladding interface would result in refraction rather than total internal reflection. Such light ray passes through the axis of fiber core and is called as meridional ray. This principle is used while stating the fundamental transmission properties of optical fiber.

8. What is the numerical aperture of the fiber if the angle of acceptance is 16 degree?
a) 0.36
b) 0.20
c) 0.50
d) 0.27

Answer: d
Explanation: The numerical aperture of a fiber is related to the angle of acceptance as follows:
NA = sin Ѳa
Where NA = numerical aperture
Ѳ = acceptance angle.

9. Which law gives the relationship between refractive index of the dielectric?
a) Huygen’s Law
b) Law of refraction (Snell’s Law)
c) Law of reflection
d) Millman’s Law

Answer: b
Explanation: Snell’s Law of refraction states that the angle of incidence Ø1 and refraction Ø2 are related to each other and to refractive index of the dielectrics.
It is given by n1sinØ1 = n2sinØ2
where n1 and n2 are the refractive indices of two mediums. Ø1 and Ø2 are angles of incidence and refraction.

10. Light incident on fibers of angles________the acceptance angle do not propagate into the fiber.
a) Equal to
b) Less than and equal to
c) Greater than
d) Less than

Answer: c
Explanation: Acceptance angle is the maximum angle at which light may enter into the fiber in order to be propagated. Hence the light incident on the fiber is less than the acceptance angle, the light will propagate in the fiber and will be lost by radiation.