1. Which of the following statements best explain the concept of material absorption?
A loss mechanism related to the material composition and fabrication of fiber
A transmission loss for optical fibers
Results in attenuation of transmitted light
Causes of transfer of optical power
Answer: 1. A loss mechanism related to the material composition and fabrication of fiber
Explanation:
Material absorption is a loss mechanism related to the material composition and fiber fabrication process. This results in the dissipation of some of the transmitted optical power as heat in the waveguide. Absorption is classified into two basic categories: Intrinsic and extrinsic.
2. The type of absorption loss in an optical fiber are
Intrinsic
Extrinsic
Both 1 and 2
None of the above
Answer: 3. Both 1 and 2
Explanation:
Absorption is a loss mechanism. It may be intrinsic, extrinsic, and also caused by atomic defects.
Intrinsic Absorption:- It is caused due to the interaction of free electrons within the fiber material and the light wavelength. The lightwave propagation covers a wide wavelength spectrum, from UV to IR. This spectrum interacts differently with the atoms of the fiber material.
Extrinsic Absorption:- It is mainly due to the impurities injected into the optical fiber mix during the fabrication process. The metal ions are the most undesirable impurity in an optical fiber mix because the presence of metal ions influence and alter the transmission properties of the fiber. This results in the loss of optical power. The metal-ion contaminant in the fiber mix should not exceed one part per billion (pp.
3. ______ is caused due to the interaction of free electrons within the fiber material and the light wavelength.
Extrinsic Absorption
Intrinsic Absorption
Radiation
None of the above
Answer: 2. Intrinsic Absorption
Explanation:
Intrinsic Absorption is caused due to the interaction of free electrons within the fiber material and the light wavelength. The lightwave propagation covers a wide wavelength spectrum, from UV to IR. This spectrum interacts differently with the atoms of the fiber material.
4. ________ is caused due to the impurities injected into the optical fiber mix during the fabrication process.
Extrinsic Absorption
Intrinsic Absorption
Radiation
None of the above
Answer: 1. Extrinsic Absorption
Explanation:
Extrinsic Absorption is mainly due to the impurities injected into the optical fiber mix during the fabrication process. The metal ions are the most undesirable impurity in an optical fiber mix because the presence of metal ions influence and alter the transmission properties of the fiber. This results in the loss of optical power. The metal-ion contaminant in the fiber mix should not exceed one part per billion (pp.
5. Absorption losses due to atomic defects mainly include _______
Radiation
Missing molecules, oxygen defects in glass
Impurities in fiber material
Interaction with other components of core
Answer:2. Missing molecules, oxygen defects in glass
Explanation:
Absorption loss is a part of the transmission loss caused by the dissipation or conversion of electrical, electromagnetic, or acoustic energy into other forms of energy as a result of its interaction with a material medium.
Atomic defects are imperfections in the atomic structure of fiber material. e.g. Missing molecules high-density clusters of atom group’s oxygen defects in the glass structure.
These imperfections in the atomic structure include absorption by the presence of the above defects. The atomic structure includes the nucleus, molecules, protons, etc. Atomic defects thus contribute towards the loss of molecules, oxygen, etc.
6. The absorption losses is significantly increased due to an increase in ______
Ionization Radiation
Reflection
Refraction
Scattering of light
Answer:1. Ionization Radiation
Explanation:
Usually, the absorption losses due to the atomic effects are negligible compared to the other two absorption effects – intrinsic and extrinsic absorption. However, if the fiber is exposed to ionizing radiation, this absorption might become significant.
Radiation damages a material by changing its internal structure. The damage effects depend on the energy of the ionizing rays or particles, the fluence (i.e., particles per square centimeter), and the radiation flux.
7. The effects of intrinsic absorption can be minimized by ________
Ionization
Radiation
Suitable choice of core and cladding components
Melting
Answer: 3. Suitable choice of core and cladding components
Explanation:
Intrinsic Absorption is caused due to the interaction of free electrons within the fiber material and the light wavelength. The lightwave propagation covers a wide wavelength spectrum, from UV to IR. This spectrum interacts differently with the atoms of the fiber material.
Intrinsic absorption is caused by the interaction of light with one or more components of the glass i.e. core. Thus, the intrinsic absorption can be minimized by carefully choosing both the core and the cladding composition.
For example, some non-oxide glasses such as fluorides and chlorides give less attenuation to longer wavelength transmissions (upto 50 µm) compared with oxide glasses.
8. ______ causes significant losses in fiber.
Sharp Bend
Micro Bend
Both 1 and 2
None of the above
Answer: 3. Both 1 and 2
Explanation:
Sharp Bend and Micro Bend cause significant losses in fiber.
Bending the fiber also causes attenuation. Bending losses are caused by micro bends and macro bends.
A sharp bend in fiber can cause significant losses as well as the possibility of mechanical failure. The bend in the short length of the fiber causes higher losses.
Micro-bends are small microscopic bends of the fiber axis that occur mainly when a fiber is cabled.
Micro bend-loss results from small variations or bumps in the core-to-cladding interface.
Macrobends are bends having a large radius of curvature relative to the fiber diameter.
Macrobend 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 microbends.
9. Which of the following is not a metallic impurity found in glass in extrinsic absorption?
Fe2+
Fe3+
Cu
Si
Answer:4. Si
Explanation:
Extrinsic Absorption is mainly due to the impurities injected into the optical fiber mix during the fabrication process.
During the preparation of optical fibers, the presence of transition metal impurities like Cr3+, Cu2+, Fe2+, Fe3+, Ni2+, etc. may cause attenuation loss.
In the optical fibers, prepared by melting techniques, extrinsic absorption can be observed. It is caused by transition metal element impurities. In all these options, Si is a constituent of glass and it cannot be considered as an impurity to glass itself.
10. ________ losses are caused by small discontinuities or imperfections in the fiber.
Micro Bend
Macro Bend
Sharp Bend
Twisting Pair
Answer:1. Micro Bend
Explanation:
Micro bend losses are caused by small discontinuities or imperfections in the fiber.
Uneven coating applications and improper cabling procedures increase micro bend loss. External forces are also a source of micro bends.
An external force deforms the cabled jacket surrounding the fiber but causes only a small bend in the fiber.
Micro bends change the path that propagates modes. Micro bend loss increases attenuation because low-order modes become coupled with high-order modes that are naturally lossy (causing an appreciable loss).
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. Radiation Losses
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.
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.
