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Optical fiber coatings for telecommunications: Viscoelasticity of polymeric coatings and characterization of hermetical carbon coatings
|關鍵字:||光纖;Optical fiber;黏彈性;碳密封鍍層;Viscoelasticity;Hermetical carbon coating||出版社:||材料工程學系所||摘要:||
第三，探討退火效應對以電漿輔助化學氣相沉積法製備碳密封鍍層光纖性質的影響。使用甲烷和氫氣當前驅物，退火溫度是100、200、300、400和500 °C。結果顯示，隨著退火溫度的上升，碳膜厚度和缺陷含量降低，但是結構有序程度和石墨微晶的數量增加。當退火溫度超過300 °C時，碳膜獲得足夠的熱能造成大量的氫和碳氫化合物逸出，導致碳膜轉變為石墨化結構。此外，由水氣抵抗能力和低溫所引起碳膜的剝落和脫落，發現碳膜在退火溫度300 °C下有最佳的碳密封鍍層光纖。
第四，探討沉積溫度效應對以熱化學氣相沉積法製備碳密封鍍層光纖性質的影響。使用甲烷當前驅物，沉積溫度為900、925、950、975和1000 °C。結果顯示，隨著沉積溫度的上升，碳膜的沉積速率和電阻率增加，但是碳膜的有序程度、微晶尺寸和楊氏模數降低。此外，水氣抵抗能力和觀察碳膜低溫表面形態，發現碳膜在沉積溫度950 °C下有最佳的碳密封鍍層光纖。
最後，以熱化學氣相沉積法製備碳鍍層光纖，去探討圓錐狀顆粒在碳鍍層光纖上的成長。使用甲烷當前驅物，在沉積溫度950 °C下，探討不同碳膜厚度對圓錐狀顆粒的影響。以及，固定厚度下，探討沉積溫度為925、950、975、1000和1025 °C對圓錐狀顆粒的影響。結果顯示，隨著厚度和沉積溫度的增加，光纖上的圓錐狀顆粒尺寸變大和數量增加，但是在石英玻片上並無明顯改變。此外，碳膜的有序程度隨著厚度的增加而降低，但是隨著沉積溫度的增加而增加。圓錐狀顆粒成長在光纖上，主要是光纖有很小的橫截面表面積。並且提出降低在碳膜表面上圓錐狀顆粒的方法。
This dissertation is to investigate the viscoelasticty of polymeric coatings and characterization of hermetical carbon coatings used as the optical fiber coatings for telecommunications.
First, to prevent the delamination of polymeric coatings from glass fibers, temperature cycling induced interfacial-shear-stress between the glass fiber and primary coating should be always smaller than its interfacial shear strength in a long time. The method for the prevention of the long-term delamination of polymeric coatings from glass fibers is as follows. The thickness of the primary coating can be increased if the spring constant of the optical fiber is selected to prevent low temperature microbending of the glass fiber. Meanwhile, Poisson's ratio of the primary coating should be selected to be very close to 0.5. Alternatively, the relaxation time of the primary coating and secondary coating should be increased, but Young's modulus of the primary coating as well as the thermal expansion coefficient of the secondary coating should be decreased. Meanwhile, the thickness and Young's modulus of the secondary coating should be decreased if the strength of the secondary coating is satisfied.
Second, the viscoelastic behavior of polymer used as the optical fiber coating is experimentally studied by the tensile test and dynamic mechanical analysis. It is shown that the viscoelastic behavior of polymeric coatings can be modeled by the four-parameter materials. A four-parameter material consists of two springs and two dashpots, in which the spring and dashpot represent the elastic and viscous behavior, respectively. The viscoelastic parameters of the four-parameter materials can be determined from the tensile test and dynamic mechanical analysis, and the method is proposed. The viscoelastic behavior of polymeric coatings is very important to understand the long-term stresses in optical fibers. An application example using the four-parameter model to evaluate the effect of polymeric coatings on the fiber's static fatigue is illustrated. It is depicted that the cross-sectional area, Young's modulus, and relaxation time of the secondary coating should be increased to minimize the static fatigue of optical fibers. Furthermore, the four-parameter model of polymeric coatings should be adopted to experimentally verify the effect of polymeric coatings on the long-term performance of optical fibers, such as static fatigue and microbending losses.
Thirdly, the effects of annealing on the properties of hermetically carbon-coated optical fibers are investigated. The hermetically carbon-coated optical fibers are prepared by the plasma enhanced chemical vapor deposition method using methane and hydrogen as the precursor gases. The annealing temperatures are selected at 100, 200, 300, 400 and 500 °C, respectively. The thickness, optical band gap, and microstructure of carbon films are measured. Meanwhile, the water-repellency and low-temperature surface morphology of carbon-coated optical fibers are evaluated. The results indicate that the thickness and defect content of the carbon films decrease with increasing the annealing temperature, while the degree of structure order and the amount of microcrystalline graphite in the carbon films increase. When the annealing temperature is over 300 °C, the carbon films acquire enough thermal energy to cause a great amount of hydrogen and hydrocarbon to be released, and the carbon films transform to the graphitelike structure. Additionally, based on the evaluation of water-repellency and low temperature-induced break or delamination of carbon films, it is found that the carbon film annealed at 300 °C is the best one for use as the hermetic optical fiber coating.
Fourthly, the effects of deposition temperature on the properties of hermetically carbon-coated optical fibers are investigated. Hermetically carbon-coated optical fibers are prepared by thermal chemical vapor deposition using methane as the precursor gas. The deposition temperatures are 900, 925, 950, 975 and 1000 °C. The deposition rate, microstructure, electrical resistivity and Young's modulus of the carbon films are measured. The water-repellency and low-temperature surface morphology of carbon-coated optical fibers are elucidated. The results indicate that the deposition rate and electrical resistivity of the carbon films increase with the deposition temperature, while the degree of ordering, the nano-crystallite size and the Young's modulus of the carbon film decrease. Additionally, the water-repellency and low-temperature surface morphology of the carbon films show that the carbon film that is deposited at a temperature of 950 °C is the best for use in hermetical optical fiber coating.
Finally, the growth of conical particles in carbon films deposited on silica glass substrates prepared by thermal chemical vapor deposition is investigated. The carbon coatings of optical fibers are prepared by the thermal chemical vapor deposition using the methane as the precursor gas. The thickness of carbon films at the deposition temperature of 950 °C is controlled by the different deposition time. Besides, the carbon films with the same thickness are deposited at deposition temperatures of 925, 950, 975, 1000 and 1025 °C. The results show that the size or number of conical particles in carbon films deposited on the silica glass fiber increases with the carbon film thickness and deposition temperature, which is strictly larger than that deposited on the silica glass plate. In addition, the order of the carbon films decreases with the coating thickness, while increases with deposition temperature. The growth of conical particles on the silica glass fiber is mainly due to the small cross-sectional area of the silica glass fiber. The method to minimize conical particles in carbon films is also proposed.
|Appears in Collections:||材料科學與工程學系|
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