61. ________ is also called as intermodal dispersion.
Waveguide Dispersion
Material Dispersion
Polarization mode Dispersion
Chromatic Dispersion
Answer:4. Chromatic Dispersion
Explanation:
Intramodal dispersion is also called chromatic dispersion because it depends on the range of wavelengths transmitted by a fiber.
Chromatic dispersion is the sum of two components: waveguide dispersion and material dispersion.
Unlike intermodal dispersion, chromatic dispersion can be positive or negative.
When material dispersion, which is always negative, is added to waveguide dispersion, the total can be positive or negative.
The two components of chromatic dispersion can also cancel each other, yielding zero dispersion.
62. What is pulse dispersion per unit length if for a graded-index fiber, 0.1μs pulse broadening is seen over a distance of 13 km?
6.12ns/km
7.69ns/km
10.29ns/km
8.23ns/km
Answer: 2. 7.69ns/km
Explanation:
Dispersion is the spreading out of light pulses as they travel along with fiber. It occurs because the speed of light through a fiber depends on its wavelength and the propagation mode.
In its simplest sense, dispersion measures pulse spreading per unit distance in nanoseconds or picoseconds per kilometer. Total pulse spreading, Δt, is
Δt = Dispersion × Distance
Given
Pulse Broading = 0.1 μs = 0.1 × 10-6
Distance = 13 km
Dispersion = (0.1 × 10-6)/13 = 7.69 ns/km.
63. A multimode graded-index fiber exhibits a total pulse broadening of 0.15μs over a distance of 16 km. Estimate the maximum possible bandwidth, assuming no intersymbol interference.
4.6 MHz
3.9 MHz
3.3 MHz
4.2 MHz
Answer:3. 3.3 MHz
Explanation:
The digital bit rate and pulse duration are always inversely proportional to each other.
$B_{T}<\frac{1}{2\tau }$
Where
BT = bit rate
2Γ = duration of pulse.
$B_{T} = \frac{1}{2\times0.15\times 10^{-6} }$
BT = 3.3 MHz
64. The optical source used in fiber is an injection laser with a relative spectral width σλ/λ of 0.0011 at a wavelength of 0.70μm. Estimate the RMS spectral width.
1.2 nm
1.3 nm
0.77 nm
0.98 nm
Answer:3. 0.77 nm
Explanation:
λRMS is the RMS spectral width of the source, in nm (the RMS spectral width is the standard deviation of the curve of power density versus wavelength)
The relative spectral width σλ/λ= 0.01 is given. The RMS spectral width can be calculated as follows:
Given
Wavelength = 0.70μm = 0.70 × 10-6
σλ/λ = 0.0011
σλ = 0.0011λ
= 0.0011 × 0.70 × 10-6
= 0.77 nm.
65. Dispersion is measured in the unit of time in ______
Second
Nanosecond
Picosecond
Both 2 and 3
Answer:4. Both 2 and 3
Explanation:
Dispersion is the spreading out of light pulses as they travel along with fiber. It occurs because the speed of light through a fiber depends on its wavelength and the propagation mode.
Dispersion is measured in the unit of time either in nanoseconds or picoseconds. The total dispersion produced by the fiber depends directly on its length. So, dispersion is typically measured in nanoseconds per kilometer (ns/km).
66. Which one of the following optical phenomena gives evidence that light waves are transverse?
Rectilinear propagation of light
Polarization of light
Diffraction of light
Interference of light
Answer.2. Polarization of light
Explanation:-
Light is a transverse, electromagnetic wave that can be seen by the typical human.
The wave nature of light was first illustrated through experiments on diffraction and interference.
Like all electromagnetic waves, light can travel through a vacuum.
The transverse nature of light can be demonstrated through polarization.
The phenomenon of the restriction of the vibrations of light waves in a particular plane perpendicular to the direction of the propagation of wave motion is called polarization.
Polarization explains the wave nature of light, as light waves are polarized in a particular plane.
The longitudinal waves cannot to be polarized. So, transverse wave can only be polarized. Hence, polarization of light proves the transverse nature of light.
67. The phenomenon of polarization shows that light has _____ nature.
Particle
Transverse
Longitudinal
Dual
Answer.2. Transverse
Explanation:-
Polarization is a process by which unpolarised light is transformed into polarized light. Polarisation tells about the transverse wave nature of light, as the light wave is polarised in a particular plane. The longitudinal waves cannot be polarised. Only transverse waves can be polarized. So, by the phenomenon of polarization, light shows transverse nature.
68. The phenomenon of polarization CANNOT occur in _________.
Radio waves
x-rays
Acoustic waves
Visible light waves
Answer.3. Acoustic waves
Explanation:-
Transverse waves can be polarized because their vibrations can potentially occur in all directions perpendicular to the direction of travel. It is, therefore, possible to confine the vibrations to a single plane. Transverse waves: The wave in which the movement of the particles is at right angles to the motion of the energy is called a transverse wave. Light is an example of a transverse wave.
Longitudinal wave: The wave in which the movement of the particles is parallel to the motion of the energy is called a longitudinal wave. A sound wave is an example of a longitudinal wave. Longitudinal waves cannot be plane polarised because the direction of vibration and direction of propagation is the same.
Radio waves, x-rays, and visible light waves come under the EM waves category. Hence they can be polarized.
Sound waves (acoustic waves) are longitudinal waves hence cannot be polarized
69. _______ fiber does not maintain the polarization state of the light input.
Cylindrical Optical Fiber
Plastic Optical Fiber
Coaxial Fiber
Glass Fiber
Answer.1. Cylindrical Optical Fiber
Explanation:-
Cylindrical optical fibers do not generally maintain the polarization state of the light input for more than a few meters, and hence, for many applications involving optical fiber transmission some form of intensity modulation of the optical source is utilized. The optical signal is thus detected by a photodiode which is insensitive to optical polarization or phase of the lightwave within the fiber.
70. Transverse nature of light is examined by:
Dispersion
Scattering
Diffraction
Polarization
Answer.4. Polarization
Explanation:-
Only transverse waves can be plane polarised because their vibration is perpendicular to the direction of energy travel – you can therefore have this vibration at different orientations. Longitudinal waves cannot be plane polarised because the direction of vibration and direction of propagation are the same.
