This set of Optical Communications Questions and Answers for Experienced people focuses on “Preparation of Optical Fibers – Liquid Phase Techniques”.
1. What is a fundamental necessity in the fabrication of fibers for light transmission?
a) Same refractive index for both core and cladding
b) Pump source
c) Material composition of fiber
d) Variation of refractive index inside the optical fiber
Explanation: For fabrication of fibers, two different transparent materials to light over a wavelength range of 0.8 to 1.7μm are required. Fiber should exhibit low attenuation, absorption and scattering losses. The variation of refractive indices in a fiber is a necessity for fiber fabrication.
2. Which materials are unsuitable for the fabrication of graded index fiber?
b) Mono-crystalline structures
c) Amorphous material
d) Silica based material
Explanation: In case of graded index fiber, it is essential that the refractive index of the material is varied by suitable doping with another compatible material. These two materials should have mutual solubility over a wide range of concentration. This is achieved only in glass-like-materials.
3. How many different categories are available for the methods of preparing optical glasses?
Explanation: The methods of preparing optical glasses are divided into two categories. One is the conventional glass refining technique and other is vapor-phase-deposition method.
4. What is the first stage in liquid-phase-technique?
a) Preparation of ultra-pure material powders
b) Melting of materials
Explanation: In liquid-phase-technique melting, the first stage includes the preparation of ultra-pure material powders. These are usually oxides or carbonates which decomposes during glass melting.
5. Which processes are involved in the purification stage in liquid-phase-technique?
a) Filtration, Co-precipitation, Re-crystallization
b) Decomposition, Filtration, Drying
c) Doping, Drying, Decomposition
d) Filtration, Drying, Doping
Explanation: The compounds such as oxides and carbonates are formed during the glass melting. The purification accounts for a large proportion of material cost. These compounds are commercially available. The purification involves filtration, co-precipitation, re-crystallization and drying.
6. At what temperature range, does the melting of multi components glass systems takes place?
a) 100-300 degree Celsius
b) 600-800 degree Celsius
c) 900-1300 degree Celsius
d) 1500-1800 degree Celsius
Explanation: The glass materials in the powdered form and have relatively low melting point. Thus, the glass materials are melted at relatively low temperatures in the range of 900-1300 degrees Celsius.
7. Fiber drawing using preform was useful for the production of graded index fibers.
Explanation: A technique for producing fine optical fiber waveguides is to make a preform using the rod in the tube process. This technique was useful for the production of step-index fibers with large core diameters. In this technique, achievement of low attenuation is not critical as there is a danger of including bubbles at the core-cladding interface.
8. The minute perturbations and impurities in the fiber drawing process using preform technique can result in very high losses of _____________
a) Between 500 and 1000 dB/km
b) Between 100 and 300 dB/km
c) Between 1200 and 1600 dB/km
d) More than 2000 dB/km
Explanation: The minute perturbations and impurities in the fiber include formations of bubbles and involvement of particulate matter. The losses due to such impurities can be between 500 and 1000 dB/km.
9. The liquid-phase melting technique is used for the production of fibers ___________
a) With a core diameter of 50μm
b) With a core diameter less than 100μm
c) With a core diameter more than 200μm
d) With a core diameter of 100μm
Explanation: The multicomponent glass fibers prepared continuously by liquid-phase melting technique have losses in the range of 5 and 20 dB/km at a wavelength of 0.85μm. This method is thus used for preparation of fibers with a large core diameter. Also this technique is used for the continuous production of fibers.
10. Graded index fibers produced by liquid-phase melting techniques are less dispersive than step-index fibers.
Explanation: Liquid-phase melting technique does not offer optimum parabolic profile fibers. This parabolic profile yields minimum pulse dispersion. Graded index fibers prepared using liquid-phase melting techniques are less dispersive but do not have the bandwidth-length products of optimum profile fibers.
Sanfoundry Global Education & Learning Series – Optical Communications.
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