Optical Fibre Preform

MCVD process refers to the improved chemical vapor deposition method, which is composed of two process steps of deposition and melt shrinkage (rod forming). Deposition is to heat the high-quality quartz reaction tube prepared in advance with hydrogen oxygen flame, use high-purity oxygen as carrier gas, put a certain proportion of high-purity SiCl4 and GeCl4 into the quartz reaction tube, and react to generate SiO2 and GeO2 molecular small particles, which are deposited on the inner wall of the quartz reaction tube according to the principle of thermophoresis. Melt shrinkage is to melt and shrink the deposited hollow quartz glass tube into a solid optical fiber preform by introducing chlorine gas. The process is flexible in operation, can accurately control the flow of raw materials and the number of deposition layers, and can produce optical fiber preforms with fine refractive index profile, which is conducive to the control of optical fiber performance.

VAD process refers to the axial vapor deposition method. The process is to vaporize the raw material under the heating condition of hydrogen oxygen flame, and hydrolyze in the flame to generate SiO2 and GeO2 particles. These particles are deposited on the axial initial rod, and the refractive index distribution is adjusted by controlling the deposition temperature, speed, gas flow rate, injection structure and other factors. After dehydration and sintering, the water molecules and hydroxyl radicals in the core area of the preform are removed to form a transparent preform core. This process has the advantages of high deposition speed and efficiency, not easy to mix impurities, small eccentricity of core and cladding and good economy.

OVD process refers to the vapor deposition method outside the tube. Similar to VAD principle, raw materials are gasified under the heating condition of hydrogen and oxygen flame, and hydrolysis reaction occurs in the flame to generate particles. These particles are deposited on the outer surface of the initial rod. After reaching a certain size and removing the initial rod, the hollow preform is dehydrated and sintered to form a transparent solid preform. The advantages of this process are that the process is easy to control, the production efficiency is high, and it is suitable for manufacturing large-size optical fiber preforms.

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