Non-Linear Effects in Optical Fiber Questions and Answers || Optical Fiber Non-Linear Effect MCQ

Optical Fiber, Electronics MCQ / March 15, 2022

1. Nonlinear effects which are defined by the intensity-dependent refractive index of the fiber are called as ________

  1. a) Scattering effects
  2. b) Kerr effects
  3. c) Raman effects
  4. 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

 

2. The ______ effects in optical fibers are large.

  1. Linear
  2. Non-Linear
  3. Polarization
  4. 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.

 

3. The nonlinear effects are weak at _______.

  1. High Power
  2. High Bandwidth
  3. Low Bandwidth
  4. 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.

 

4. The types of nonlinear effects seen in optical fibers are?

  1. a) One
  2. b) Two
  3. c) Three
  4. 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.

 

5. _________ 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.

  1. a) Four-wave mixing
  2. b) Phase modulation
  3. c) Soliton propagation
  4. 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.

 

6. Which of the following is not related to Kerr’s effects?

  1. a) Self-phase modulation
  2. b) cross-phase modulation
  3. c) Four-wave mixing
  4. 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.

 

7. 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?

  1. a) w4 = w1 – w2 – w3
  2. b) w4 = w1 + w2 + w3
  3. c) w4 = w1 + w2 – w3
  4. 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

 

8. 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.

 

9. What is different in the case of cross-phase modulation from self-phase modulation?

  1. a) Overlapping but same pulses
  2. b) Overlapping but distinguishable pulses
  3. c) Non-overlapping and same pulses
  4. 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.

 

10. Which thing is more dominant in making a fiber function as a bidirectional optical amplifier?

  1. a) Core material
  2. b) Pump source
  3. c) Cladding material
  4. 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.

 

11. The beating between light at different frequencies or wavelengths in multichannel fiber transmission causes ________

  1. a) Attenuation
  2. b) Amplitude modulation of channels
  3. c) Phase modulation of channels
  4. d) Loss in transmission

Answer.3. Phase modulation of channels

Explanation:-

  • The beating between light at different frequencies or wavelengths in multichannel fiber transmission causes phase modulation of the channels and hence the generation of modulation sidebands at new frequencies which are termed four-wave mixing (FWM).
  • 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
  • This frequency combination can be problematic for multichannel optical communications as they can become phase-matched if the channel wavelengths are close to the zero-dispersion wavelength.
  • FWM is therefore one of a broad class of harmonic mixing or harmonic generation processes in which two or more waves combine to generate waves at a different frequency that is the sum (or difference) of the signals that are mixed.

 

12. _________ semiconductor laser sources generally have broader bandwidths.

  1. a) Injection
  2. b) Pulsed
  3. c) Solid-state
  4. d) Silicon hybrid

Answer.2. 

Explanation:-

Pulsed lasers are lasers that emit light not in a continuous mode, but rather in the form of optical pulses (light flashes). Pulsed semiconductor lasers have broader bandwidths. Therefore, these sources prove to be inefficient pump sources. They prove inefficient, especially for the narrow gain spectrum.

 

13. ________ modulation causes modifications to the pulse spectrum.

  1. Pulse
  2. Phase
  3. Self-phase
  4. Self-pulse

Answer.3. Self-phase

Explanation:-

Self-phase modulation refers to the phenomenon in which a laser beam propagating in a medium interacts with the medium and imposes a phase modulation on itself. In the case of a pulsed laser input, the temporal variation of the laser intensity leads to an SPM in time.

Self-phase modulation can broaden the frequency spectrum of the pulse as the time-varying phase creates a time-varying frequency.

 

14. Self-phase modulation can be used for _____________

  1. a) Enhancing the core diameter
  2. b) Wavelength shifting
  3. c) Decreasing the attenuation
  4. d) Reducing the losses in the fiber

Answer.2. Wavelength shifting

Explanation:-

  • Self-phase modulation refers to the phenomenon in which a laser beam propagating in a medium interacts with the medium and imposes a phase modulation on itself. In the case of a pulsed laser input, the temporal variation of the laser intensity leads to an SPM in time.
  • Self-phase modulation can broaden the frequency spectrum of the pulse as the time-varying phase creates a time-varying frequency.
  •  Self-phase modulation is related to phase change. It imposes a positive frequency sweep on the pulse which in turn enables wavelength or frequency shifting.

 

15. ________ occurs when signal power reaches a level sufficient to generate tiny acoustic vibrations in the glass.

  1. Wavelength shifting
  2. Brillouin scattering
  3. Linear Scattering
  4. Non-linear Scattering

Answer.2. Wavelength shifting

Explanation:-

  • Stimulated Brillouin scattering occurs when signal power reaches a level sufficient to generate tiny acoustic vibrations in the glass. This can occur at powers as low as a few milliwatts in single-mode fiber.
  • Acoustic waves change the density of a material and thus alter its refractive index. The resulting refractive-index fluctuations can scatter light, called Brillouin scattering. Since the light wave being scattered itself generates the acoustic waves, the process is called stimulated Brillouin scattering. It can occur when only a single channel is transmitted.

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