Method to prevent cracks in optical fiber preforms and optical fiber preforms obtained thereby

The present disclosure provides optical fiber preforms formed from core canes having large core-clad ratio, intermediate core-cladding assemblies, and methods for making the preforms and core claddingassemblies. The preforms are made with capped core canes. The capping material has a coefficient of thermal expansion less than the coefficient of thermal expansion of the core cane and more closelymatched to or lower than the coefficient of thermal expansion of the surrounding cladding monolith in a cane-in-soot process. Presence of the cap reduces stresses that arise from differential thermalexpansion of the core cane and cladding materials and leads to preforms having low defect concentration and low probability of failure during subsequent thermal processing steps. 本公开提供了从具有大的纤芯-包层比的芯棒形成的光纤预成形件，提供了中间体纤芯-包层组件，以及制造该预成形件和纤芯包层组件的方法。预成形件是由封端芯棒制造的。封端材料的热膨胀系数小于芯棒的热膨胀系数，并且与烟炱内的坯棒工艺中的围绕的烟炱包层单体件的热膨胀系数更为紧密匹配或者低于其。封端的存在降低了由于芯棒与包层材料的不同热膨胀所引起的应力，并且得到的预成形件具有低缺陷浓度和后续热加工步骤期间低的失效概率。