This set of Optical Communications Multiple Choice Questions & Answers (MCQs) focuses on “Vapor – Phase Deposition Techniques”.
1. Which of the following is not a technique for fabrication of glass fibers?
a) Vapor phase oxidation method
b) Direct melt method
c) Lave ring method
d) Chemical vapor deposition technique
Explanation: Lave ring method refers to the deposition of a crystalline layer on a substrate. All the other methods, except lave ring method, refer to the optical fiber fabrication.
2. _____________ technique is method of preparing extremely pure optical glasses.
a) Liquid phase (melting)
b) Radio frequency induction
c) Optical attenuation
d) Vapor Phase Deposition (VPD)
Explanation: Vapor Phase Deposition techniques are used to prepare silica-rich glasses. These glasses exhibit highest transparency and optimal optical properties.
3. Which of the following materials is not used as a starting material in vapor-phase deposition technique?
Explanation: In vapor-phase deposition technique, starting materials are volatile organic compounds. These materials are distilled to reduce the concentration of transition metal impurities. B2O3 is used as a dopant.
4. P2O5 is used as a _____________
b) Starting material
c) Cladding glass
d) Core glass
Explanation: P2O5 is a non silica material. Dopants are formed from non silica materials so that refractive index modification is achieved. Other dopants include Ti O2, Ge O2etc.
5. How many types of vapor-phase deposition techniques are present?
Explanation: Vapor-phase deposition techniques are divided into two types. The two types are flame hydrolysis and chemical vapor deposition (CVD). Further, these two types are subdivided into two more sections.
6.___________ uses flame hydrolysis stems from work on soot processes which were used to prepare the fiber with losses below 20 dB/km.
a) Outside vapor phase oxidation
b) Chemical vapor deposition
c) Liquid phase melting
Explanation: Outside vapor phase oxidation is a type of vapor flame hydrolysis. It was originally developed by Hyde. In this process, the glass composition is deposited from a ‘soot’ generated by hydrolyzing the halide vapors in an oxygen-hydrogen flame.
7. Complete the given reaction
SiCl4+ 2H2O→ SiO2+ ______
Explanation: SiCl4is a starting material used in vapour-phase deposition technique. Dopants are added to the starting material in presence of heat to give glass compound. In the above reaction SiO2 (solid compound) along with 4HCl(gas) is obtained.
8. In modified chemical vapor deposition, vapor phase reactant such as _________ pass through a hot zone.
a) Halide and oxygen
b) Halide and hydrogen
c) Halide and silica
d) Hydroxides and oxygen
Explanation: Halide and oxygen are passed through the hot zone during chemical vapor deposition. Glass particles formed during this travel are deposited on the walls of silica tube which are moved back and forth allowing the particles to deposit layer by layer.
9. _________ is the stimulation of oxide formation by means of non-isothermal plasma maintained at low pressure in a microwave cavity surrounding the tube.
a) Outside Vapor Phase Oxidation (OVPO)
b) Vapor Axial Deposition (VAD)
c) Modified Chemical Vapor Deposition (MCVD)
d) Plasma-activated Chemical Vapor Deposition (PCVD)
Explanation: PCVD method was first developed by Cuppers and Koenig’s. It involves a plasma-induced chemical vapor deposition inside a silica tube. It is different from MCVD process as it involves stimulation of oxide formation by means of non-isothermal plasma.
10. Only graded index fibers are made with the help of vapor-phase deposition techniques. State whether true or false.
Explanation: Vapor phase deposition techniques are used for preparation of both step-index and graded index fibers. These techniques provide fibers with low attenuation losses. Also, it gives similar performance for the fabrication of both single mode and multimode fibers.
11. Modified Chemical Vapor Deposition (MCVD) process is also called as an inside vapor phase oxidation (IVPD) technique. State whether the given statement is true or false.
Explanation: MCVD process was developed by Bell Telephone Laboratories and Southampton University, UK. It is called as inside vapor phase oxidation (IVPO) as it takes place inside the silica tube at the temperatures between 1400 and 1600 degree Celsius.
Sanfoundry Global Education & Learning Series – Optical Communications.
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