81. Nonlinear effects which are defined by the intensity-dependent refractive index of the fiber are called as ________
a) Scattering effects
b) Kerr effects
c) Raman effects
d) Tomlinson effects
Answer.2.
Explanation:-
Nonlinear propagation effects can be divided into two categories: the scattering effect and the Kerr effect.
The scattering effect includes the phenomena in which a propagating field photon is scattered by some material alteration caused by the field itself.
Kerr effect includes all the phenomena due to the dependence of the real part of dielectric susceptibility on the field.
Nonlinear effects which are defined by the intensity-dependent refractive index of the fiber are called as Kerr effects
82. The ______ effects in optical fibers are large.
Linear
Non-Linear
Polarization
Scattering
Answer.2. Non-Linear
Explanation:-
Normally light waves or photons transmitted through a fiber have little interaction with each other and are not changed by their passage through the fiber (except for absorption and scattering).
However, there are exceptions arising from the interactions between light waves and the material transmitting them, which can affect optical signals. These processes generally are called nonlinear effects because their strength typically depends on the square (or some higher power) of intensity rather than simply on the amount of light present.
83. The nonlinear effects are weak at _______.
High Power
High Bandwidth
Low Bandwidth
Low Power
Answer.4. Low Power
Explanation:-
Normally light waves or photons transmitted through a fiber have little interaction with each other and are not changed by their passage through the fiber (except for absorption and scattering).
However, there are exceptions arising from the interactions between light waves and the material transmitting them, which can affect optical signals. These processes generally are called nonlinear effects because their strength typically depends on the square (or some higher power) of intensity rather than simply on the amount of light present.
This means that nonlinear effects are weak at low powers, but can become much stronger when light reaches high intensities. This can occur either when the power is increased, or when it is concentrated in a small area—such as the core of an optical fiber.
84. The types of nonlinear effects seen in optical fibers are?
a) One
b) Two
c) Three
d) Four
Answer.2.
Explanation:-
Nonlinear propagation effects can be divided into two categories: the scattering effect and the Kerr effect.
The scattering effect includes the phenomena in which a propagating field photon is scattered by some material alteration caused by the field itself.
Kerr effect includes all the phenomena due to the dependence of the real part of dielectric susceptibility on the field.
85. _________ results from a case of nonlinear dispersion compensation in which the nonlinear chirp caused by self-phase modulation balances postpones, the temporal broadening induced by group velocity delay.
a) Four-wave mixing
b) Phase modulation
c) Soliton propagation
d) Raman scattering
Answer.3. Soliton propagation
Explanation:-
In optics, the term soliton is used to refer to any optical field that does not change during propagation because of a delicate balance between nonlinear and linear effects in the medium.
Soliton propagation results from a special case of nonlinear dispersion compensation in which the nonlinear chirp is caused by SPM balances, and hence, postpones, the temporal broadening induced by group velocity delay (GVD).
Although both of these phenomena limit the propagation distance that can be achieved when acting independently, if balanced at the necessary critical pulse intensity they enable the pulse to propagate without any distortion (i.e., its shape is self-maintaining) as a soliton.
86. Which of the following is not related to Kerr’s effects?
a) Self-phase modulation
b) cross-phase modulation
c) Four-wave mixing
d) Stimulated Raman Scattering
Answer.4.
Explanation:-
The Kerr effect is a phenomenon in which the refractive index of material changes because of an applied electrical field, and the change in the refractive index is proportional to the square of the applied electric field.
Stimulated Raman Scattering is related to scattering.
The Kerr effect is caused by incoherent interaction between the molecule’s external orbitals and the traveling field.
87. When three-wave components co-propagate at angular frequency w1, w2, w3, then a new wave is generated at frequency w4, which is given by?
a) w4 = w1 – w2 – w3
b) w4 = w1 + w2 + w3
c) w4 = w1 + w2 – w3
d) w4 = w1 – w2 + w3
Answer.3. w4 = w1 + w2 – w3
Explanation:-
Four-wave mixing (FWM) is an intermodulation phenomenon in nonlinear optics, whereby interactions between two or three wavelengths produce two or one new wavelengths. It is similar to the third-order intercept point in electrical systems.
FWM occurs when the light of three different wavelengths is launched into a fiber, giving rise to a new wave (know as an idler), the wavelength of which does not coincide with any of the others.
This type of frequency mixing is called four-wave mixing. This frequency combination is problematic for multichannel optical communication as they become phase-matched if the channel wavelengths are near to zero-dispersion wavelengths.
When three-wave components co-propagate at angular frequency w1, w2, w3, then a new wave is generated at frequency w4, which is
w4 = w1 + w2 – w3
88. Linear scattering effects are _______ in nature.
a) Elastic
b) Non-Elastic
c) Mechanical
d) Electrical
Answer.1. Elastic
Explanation:-
Non-linear scattering (i.e. Rayleigh), is said to be elastic because the scattered wave has the same frequency as the incident wave. Nonlinear scattering processes are clearly inelastic. A schematic of the spectrum was obtained from these inelastic scattering processes.
89. What is different in the case of cross-phase modulation from self-phase modulation?
a) Overlapping but same pulses
b) Overlapping but distinguishable pulses
c) Non-overlapping and same pulses
d) Non-overlapping but distinguishable pulses
Answer.2. Overlapping but distinguishable pulses
Explanation:-
Self-phase modulation (SPM) and cross-phase modulation (XPM, or CPM) are two of the most important nonlinear effects in optical telecommunications. Both effects lead to a phase alteration of the pulses and are frequently called carrier-induced phase modulation (CIP).
In cross-phase modulation, variation in the intensity of one pulse width modulates the refractive index of the fiber which causes phase modulation of the overlapping phases. In self-phase modulation, this phase modulation broadens the pulse spectrum.
90. Which thing is more dominant in making a fiber function as a bidirectional optical amplifier?
a) Core material
b) Pump source
c) Cladding material
d) Diameter of fiber
Answer.2. Pump source
Explanation:-
For a typical fiber, a pump power of around one watt in 100 m of fiber results in a Raman gain of about a factor of 2.
Brillouin gain is always greater than Raman gain. It exists for light propagation in opposite direction to the pump source. Also, Brillouin frequency shifts and gain bandwidth are much smaller than Raman. Raman amplification occurs for light propagating in either direction.
Hence, with a suitable pump source, a fiber can function as a relatively high gain, broad bandwidth, bidirectional optical amplifier.
