11. _______ losses are caused by deviations of the core as measured from the axis of the fiber.
Micro Bend
Macro Bend
Sharp Bend
Twisting Pair
Answer:2. Macro Bend
Explanation:
Macrobends are bends having a large radius of curvature relative to the fiber diameter. Macro-bend losses are caused by deviations of the core as measured from the axis of the fiber. These irregularities are caused during the manufacturing procedures and should not be confused with micro-bends.
12. Optical fibers suffer ______ losses at bends or curves on their paths.
Bandwidth Losses
Scattering Losses
Radiation Losses
None of the above
Answer: 3. Hondros and debye
Explanation:
Optical fibers suffer radiation losses at bends or curves on their paths.
This is due to the energy in the evanescent field at the bend exceeding the velocity of light in the cladding and hence the guidance mechanism is inhibited, which causes light energy to be radiated from the fiber.
The part of the mode which is on the outside of the bend is required to travel faster than that on the inside so that a wavefront perpendicular to the direction of propagation is maintained.
Hence, part of the mode in the cladding needs to travel faster than the velocity of light in that medium.
13. ______ losses occur when a wave interacts with a particle in a way that removes energy in the directional propagating wave and transfers it to other directions.
Bandwidth Losses
Scattering losses
Radiation Losses
Bend Losses
Answer:2. Scattering losses
Explanation:
Scattering losses occur when a wave interacts with a particle in a way that removes energy in the directional propagating wave and transfers it to other directions. The light isn’t absorbed, just sent in another direction. However, the distinction between scattering and absorption doesn’t matter much because the light is lost from the fiber in either case.
14. How the potential macro bending losses can be reduced in the case of multimode fiber?
By designing fibers with large relative refractive index differences
By maintaining direction of propagation
By reducing the bend
By operating at larger wavelengths
Answer:1. By designing fibers with large relative refractive index differences
Explanation:
Macrobends are bends having a large radius of curvature relative to the fiber diameter. Macro-bend losses are caused by deviations of the core as measured from the axis of the fiber.
It is possible to reduce the sensitivity to macro-bending losses by resorting to particular refractive index profiles. Losses are inversely proportional to refractive index differences.
15. The type of scattering losses in optical fiber are
Linear Scattering
Non-Linear Scattering
Both 1 and 2
None of the above
Answer: 3. Hondros and debye
Explanation:
There are two main types of scattering: linear scattering and nonlinear scattering.
For linear scattering, the amount of light power that is transferred from a wave is proportional to the power in the wave. It is characterized by having no change in frequency in the scattered wave.
Nonlinear scattering is accompanied by a frequency shift of the scattered light. Nonlinear scattering is caused by high values of the electric field within the fiber (modest to the high amount of optical power). Nonlinear scattering causes significant power to be scattered in the forward, backward, or sideways directions.
16. __________ in glass arise from microscopic variations in the material density, from compositional fluctuations.
Bandwidth Losses
Scattering Losses
Radiation Losses
All of the above
Answer:2. Scattering Losses
Explanation:
Scattering losses in glass arise from microscopic variations in the material density, from compositional fluctuations, and from structural inhomogeneities or defects occurring during fiber manufacture.
Scattering the common source of attenuation in optical fibers is the loss of optical energy due to molecular imperfections or lack of optical purity in the fiber due to the manufacturing process and form the basic structure of the fiber.
17. Rayleigh scattering and Mie scattering are the types of ________
a) Linear scattering losses
b) Non-linear scattering losses
c) Fiber bends losses
d) Splicing losses
Answer:1. Linear scattering losses
Explanation:
For linear scattering, the amount of light power that is transferred from a wave is proportional to the power in the wave. It is characterized by having no change in frequency in the scattered wave.
Linear scattering processes are further classified into Rayleigh and Mie scattering which is related to the losses in glass arising from microscopic variations in the material density, from compositional fluctuations, and from structural inhomogeneities or defects occurring during fiber manufacture.
18. Stimulated Raman scattering may have an optical power threshold of maybe three orders of magnitude ________
a) Lower than Brillouin threshold
b) Higher than Brillouin threshold
c) Same as Brillouin threshold
d) Higher than Rayleigh threshold
Answer:2. Higher than Brillouin threshold
Explanation:
Stimulated Raman scattering (SRS) is an important nonlinear process that can turn optical fibers into broadband Raman amplifiers and tunable Raman lasers. It can also severely limit the performance of multichannel lightwave systems by transferring energy from one channel to the neighboring channels.
Stimulated Raman scattering (SRS) is similar to SBS except that a high-frequency optical phonon rather than an acoustic phonon is generated in the scattering process. Also, SRS can occur in both the forward and backward directions in optical fiber and may have an optical power threshold of up to three orders of magnitude higher than the Brillouin threshold in a particular fiber.
19. Dominant intrinsic loss mechanism in low absorption window between ultraviolet and infrared absorption tails is _________
a) Mie scattering
b) Rayleigh scattering
c) Stimulated Raman scattering
d) Stimulated Brillouin scattering
Answer:2. Rayleigh scattering
Explanation:
Rayleigh scattering results from light interacting with inhomogeneities in the medium that ‘are much smaller than the wavelength of the light.
Rayleigh scattering is the dominant intrinsic loss mechanism in the low absorption window, which is in between the UV and IR absorption tails. Rayleigh scattering is caused when material anomalies within the fiber material are 1/10 of the diameter (or less) of the operating wavelength.
20. The Rayleigh scattering is ______ to the wavelength.
Directly Proportional
Inversely Proportional
Equal
None of the above
Answer:2. Inversely Proportional
Explanation:
Rayleigh scattering is due to small localized changes in the refractive index of the core and the cladding material.
In commercial fibers operating between 700 nm and 1600 nm wavelength, the main source of loss is called Rayleigh scattering.
Rayleigh scattering is the main loss mechanism between the ultraviolet and infrared regions. Loss caused by Rayleigh scattering is proportional to the fourth power of the wavelength (1/λ4).
As the wavelength increases, the loss caused by Rayleigh scattering decreases. Rayleigh scatter is most severe in light with a short wavelength.
