## 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

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

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

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

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

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

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

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

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