# Optical Communications Questions and Answers – Ray Theory Transmission

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This set of Optical Communications Multiple Choice Questions & Answers (MCQs) focuses on “Ray Theory Transmission”.

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

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.

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

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.

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

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.

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

Explanation: LED’s and Lasers are the light sources used in optical communication. During the working process of optical signals they are both supposed to be switched on and of rapidly and accurately enough to transmit the signal. Also they transmit light further with fewer errors.

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

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.

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

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.

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

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

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

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.

Sanfoundry Global Education & Learning Series – Optical Communications. 