EC2402-OPTICAL COMMUNICTION AND NETWORKING
VII SEM. ECE
EC2402- OPTICAL COMMUNICATION AND NETWORKING
TWO MARKS QUESTIONS AND ANSWERS
UNIT I - Introduction
Optical fiber is made up of glass. Because of the impurities present with the
1. What are the limitations of optical fiber communication systems?
fiber
It is costly.
It results in absorption, which leads to loss of light in the optical fiber.
Maximum limitation of the bandwidth of the signals can be carried by the
fiber due to spreading of pulse.
2. What is the necessity of cladding for an optical fiber?
To avoid leakage of light from the fiber
The necessity of cladding for an optical fiber is
To avoid mechanical strength for the fiber
To protect core from scratches and other mechanical damages.
3. List the advantages of mono-mode fiber.
No internal dispersion
The advantages of mono-mode fiber are
Information capacity of single mode fiber is large.
4. Define - Acceptance Angle
The maximum angle Фmax with which a ray of light can enter rough the entrance
end of the fibre and still be totally internally reflected is called acceptance angle
of the fiber.
5. List the uses of optical fiber.
The uses of optical fibers are as follows
To act as light source at the inaccessible places
To transmit the optical images. (example: endoscopy)To act as sensors
to do mechanical, electrical and magnetic measurements
To transmit the information which are in the form of coded signals
of the telephone communications, computer data etc.
Prepared by A.Devasena., Associate Professor / Dept. Of ECE Page 1
, EC2402-OPTICAL COMMUNICTION AND NETWORKING
VII SEM. ECE
6. List the disadvantages of mono-mode fiber.
The disadvantages of mono-mode fiber are
Launching of light into single mode and joining of two fibers are very
difficult.
Fabrication is very difficult and so that fiber is so costly.
7. What is the principle used in the working of fibers as light guides?
The phenomenon of total internal reflection is used to guide the light
in the optical fiber. To get total reflection, the ray should travel from denser
region rarer region i.e. from core to clad region. Of the fiber and the angle of
incidence in the denser medium should be greater than the critical angle of
that medium.
8. Define- Refraction
When light travels from air medium to glass medium, bending of light
may occur.
This is called refraction.
9. What is critical angle?
When we increase the incident angle with respect to normal, at some incident
angle, the dielectric of surface and φ2 becomes 90 and such incident angle is called
critical angle.
10. What is Snell’s law?
The relationship at the interface is called Snell’s Law. It is given by the
equation
n1sinφ1 = n2sinφ2
11. What is meant by mode coupling?
The effect of coupling energy from one mode to another mode is known as mode
coupling. The cause of mode coupling is due to waveguide perturbations such as
deviations Of the fiber axis from straightness variations in the core diameter,
irregularities at the Core- cladding interface and refractive index variations.
Prepared by A.Devasena., Associate Professor / Dept. Of ECE Page 2
, EC2402-OPTICAL COMMUNICTION AND NETWORKING
VII SEM. ECE
12. What is V number of a fiber?
Normalized frequency or V number is a dimensionless parameter and represent
the relationship among three design parameters variables of the fiber viz core radius a,
relative refractive index Δ and the operating wavelength λ.
It is expressed as V = (2*π* Numerical aperture(a)) / λ
13. Compare Ray optics and wave optics.
Ray optics Wave optics
It is used to represent the It is used to analyze mode
light propagation theory
It is used to study reflection It is used to analyze
and refraction of light diffraction and interference of
light waves
14. Differentiate between mono-mode fiber and multi-mode fiber.
Mono-mode fiber Multi-mode fiber
Only one ray passes through the More than one ray passes
fiber through fiber at a time.
Coupling efficiency is less. Coupling efficiency is
large.
LED is not suitable for single mode LED is suitable for multi-
fiber. mode fiber
Intermodal dispersion is not Intermodal dispersion is
present. present
Fabricating single mode fiber is Fabricating multi-mode
difficult. fiber is easy.
15. What is meant by linearly polarized mode?
The field components HE, EH, TE, TM forms linearly polarized modes. Linearly
polarized Modes are labeled LPjm where j and m are integers designation mode solutions.
16. What are the three windows of optical communications?
The three wavelengths 850nm, 1300nm, and 1500nm are three optical
windows of optical communication system. Since only at this wavelength silica
fiber loss is minimum.
Prepared by A.Devasena., Associate Professor / Dept. Of ECE Page 3
, EC2402-OPTICAL COMMUNICTION AND NETWORKING
VII SEM. ECE
17. Define – Fiber Optic system
Fiber optic system is nothing but a fiber-optic cable is essentially light
pipe that is used to carry a light beam from one place to another.
18. What are the advantages of graded index fiber?
The advantages of graded index fiber are
It provides higher bandwidth.
It exhibits less intermodal dispersion because the different group velocities
of the mode tend to be normalized by the index grading.
19. What is step index fiber?
Step index fiber is a cylindrical waveguide that has the central core with
uniform refractive index n1 surrounded by outer cladding with refractive index of
n2. The refractive index of the core is constant and is larger than the refractive
index of the cladding. It makes a step change at the core cladding interface.
20. Why step index single mode fiber preferred for long distance
communication?
The step index single mode fiber is preferred for long distance
communication because
They exhibit higher transmission bandwidth because of low fiber losses.
They have superior transmission quality because of the absence of the
model noise.
The installation of single mode fiber is easy and will not require any fiber
replacement over twenty plus years.
21. Define- Birefringence
Manufactured optical fibers have imperfections such as asymmetrical
lateral stresses, non - circular cores and variations in refractive index profiles.
These imperfections break the circular symmetry of the ideal fiber and lift the
degeneracy of the two modes. These modes propagate with different phase
velocity and it is called as fiber birefringence.
Prepared by A.Devasena., Associate Professor / Dept. Of ECE Page 4
VII SEM. ECE
EC2402- OPTICAL COMMUNICATION AND NETWORKING
TWO MARKS QUESTIONS AND ANSWERS
UNIT I - Introduction
Optical fiber is made up of glass. Because of the impurities present with the
1. What are the limitations of optical fiber communication systems?
fiber
It is costly.
It results in absorption, which leads to loss of light in the optical fiber.
Maximum limitation of the bandwidth of the signals can be carried by the
fiber due to spreading of pulse.
2. What is the necessity of cladding for an optical fiber?
To avoid leakage of light from the fiber
The necessity of cladding for an optical fiber is
To avoid mechanical strength for the fiber
To protect core from scratches and other mechanical damages.
3. List the advantages of mono-mode fiber.
No internal dispersion
The advantages of mono-mode fiber are
Information capacity of single mode fiber is large.
4. Define - Acceptance Angle
The maximum angle Фmax with which a ray of light can enter rough the entrance
end of the fibre and still be totally internally reflected is called acceptance angle
of the fiber.
5. List the uses of optical fiber.
The uses of optical fibers are as follows
To act as light source at the inaccessible places
To transmit the optical images. (example: endoscopy)To act as sensors
to do mechanical, electrical and magnetic measurements
To transmit the information which are in the form of coded signals
of the telephone communications, computer data etc.
Prepared by A.Devasena., Associate Professor / Dept. Of ECE Page 1
, EC2402-OPTICAL COMMUNICTION AND NETWORKING
VII SEM. ECE
6. List the disadvantages of mono-mode fiber.
The disadvantages of mono-mode fiber are
Launching of light into single mode and joining of two fibers are very
difficult.
Fabrication is very difficult and so that fiber is so costly.
7. What is the principle used in the working of fibers as light guides?
The phenomenon of total internal reflection is used to guide the light
in the optical fiber. To get total reflection, the ray should travel from denser
region rarer region i.e. from core to clad region. Of the fiber and the angle of
incidence in the denser medium should be greater than the critical angle of
that medium.
8. Define- Refraction
When light travels from air medium to glass medium, bending of light
may occur.
This is called refraction.
9. What is critical angle?
When we increase the incident angle with respect to normal, at some incident
angle, the dielectric of surface and φ2 becomes 90 and such incident angle is called
critical angle.
10. What is Snell’s law?
The relationship at the interface is called Snell’s Law. It is given by the
equation
n1sinφ1 = n2sinφ2
11. What is meant by mode coupling?
The effect of coupling energy from one mode to another mode is known as mode
coupling. The cause of mode coupling is due to waveguide perturbations such as
deviations Of the fiber axis from straightness variations in the core diameter,
irregularities at the Core- cladding interface and refractive index variations.
Prepared by A.Devasena., Associate Professor / Dept. Of ECE Page 2
, EC2402-OPTICAL COMMUNICTION AND NETWORKING
VII SEM. ECE
12. What is V number of a fiber?
Normalized frequency or V number is a dimensionless parameter and represent
the relationship among three design parameters variables of the fiber viz core radius a,
relative refractive index Δ and the operating wavelength λ.
It is expressed as V = (2*π* Numerical aperture(a)) / λ
13. Compare Ray optics and wave optics.
Ray optics Wave optics
It is used to represent the It is used to analyze mode
light propagation theory
It is used to study reflection It is used to analyze
and refraction of light diffraction and interference of
light waves
14. Differentiate between mono-mode fiber and multi-mode fiber.
Mono-mode fiber Multi-mode fiber
Only one ray passes through the More than one ray passes
fiber through fiber at a time.
Coupling efficiency is less. Coupling efficiency is
large.
LED is not suitable for single mode LED is suitable for multi-
fiber. mode fiber
Intermodal dispersion is not Intermodal dispersion is
present. present
Fabricating single mode fiber is Fabricating multi-mode
difficult. fiber is easy.
15. What is meant by linearly polarized mode?
The field components HE, EH, TE, TM forms linearly polarized modes. Linearly
polarized Modes are labeled LPjm where j and m are integers designation mode solutions.
16. What are the three windows of optical communications?
The three wavelengths 850nm, 1300nm, and 1500nm are three optical
windows of optical communication system. Since only at this wavelength silica
fiber loss is minimum.
Prepared by A.Devasena., Associate Professor / Dept. Of ECE Page 3
, EC2402-OPTICAL COMMUNICTION AND NETWORKING
VII SEM. ECE
17. Define – Fiber Optic system
Fiber optic system is nothing but a fiber-optic cable is essentially light
pipe that is used to carry a light beam from one place to another.
18. What are the advantages of graded index fiber?
The advantages of graded index fiber are
It provides higher bandwidth.
It exhibits less intermodal dispersion because the different group velocities
of the mode tend to be normalized by the index grading.
19. What is step index fiber?
Step index fiber is a cylindrical waveguide that has the central core with
uniform refractive index n1 surrounded by outer cladding with refractive index of
n2. The refractive index of the core is constant and is larger than the refractive
index of the cladding. It makes a step change at the core cladding interface.
20. Why step index single mode fiber preferred for long distance
communication?
The step index single mode fiber is preferred for long distance
communication because
They exhibit higher transmission bandwidth because of low fiber losses.
They have superior transmission quality because of the absence of the
model noise.
The installation of single mode fiber is easy and will not require any fiber
replacement over twenty plus years.
21. Define- Birefringence
Manufactured optical fibers have imperfections such as asymmetrical
lateral stresses, non - circular cores and variations in refractive index profiles.
These imperfections break the circular symmetry of the ideal fiber and lift the
degeneracy of the two modes. These modes propagate with different phase
velocity and it is called as fiber birefringence.
Prepared by A.Devasena., Associate Professor / Dept. Of ECE Page 4
