低损耗单模锗酸盐玻璃光纤的制备与性质研究

Germanate glasses, i.e. GeO2-based oxide glasses, have relatively low phonon energy of ~900 cm-1 and an infrared window with cut-off wavelength over 5μm, which are regarded as a potential candidate for 2~3μm mid-IR fiber lasers. To investigate transmission and optical properties at mid-IR region, water-free or extremely low water contained germanate glass fibers are required. The main research contents include the following parts: To further decrease phonon energy and widen infrared transmission window, heavy metal-oxide is necessary to be co-doped into GeO2 base. Referring to the fabrication technologies of silica fiber, modified chemical vapor deposition (MCVD) system and heavy-metal chelate vapor doping technique (CPDT) are used to fabricate germanate glass fiber preforms. During MCVD processes, Cl2 gas is used to remove rest water and OH- groups in order to dramatically decrease fiber loss at 2~5μm. To achieve small core/clad ration, ‘mother preform’ with a 4-10 mm core was elongated into a fiber cane with a certain diameter, inserted into a thick jacketing tube. And we finally seal them into a final preform with a design core/clad ratio. Single-mode germanate glass fiber with low background loss of ≤20dB/km was drawn in an inert atmosphere and coated with normal UV-curing polymer, and its mid-IR optical properties was systemically measured and investigated.

以氧化锗GeO2为主体的锗酸盐玻璃具有较低的声子能量（~900 cm-1），其红外截止波长大于5μm，是2~3μm中红外光纤激光材料与传输介质的潜在候选者。为研究锗酸盐玻璃光纤在中红外区域的传输性能和综合光学性质，需要制备无水的（或极低水分的）低损耗锗酸盐玻璃光纤。主要研究内容包括：选择合适的重金属氧化物构建锗酸盐玻璃体系，进一步降低声子能量来拓展其红外透过窗口；借鉴成熟的石英光纤制造技术，利用改进型气相沉积系统MCVD结合重金属螯合物气相掺杂系统CPDT来制备低损耗锗酸盐玻璃光纤预制棒；MCVD工艺过程中利用氯气去除玻璃中残留的水分与羟基OH-以减少2~5μm的吸收损耗，对“母棒”预制棒进行延伸、切割、套管、塌缩等工艺流程来获得较小芯/包比的预制棒。在惰性气体保护条件下优化拉丝工艺技术，制备低损耗（≤20dB/km）单模锗酸盐玻璃光纤，并测试锗酸盐光纤在中红外波段的综合光学性质。

2~3µm激光器在激光医疗、气体探测等民用领域和红外干扰等军用领域均有着广泛的应用。锗酸盐玻璃（主要成分GeO2，声子能量～900cm-1）是最有可能成为2~3μm光纤激光主体材料的选项之一。然而，传统玻璃制备工艺很难获得超低水分或羟基OH-含量的锗酸盐玻璃，因此几乎无法打开锗酸盐玻璃光纤的中红外“窗口”。.在青年基金项目51602295的大力支持下，我们项目组选择GeO2-Al2O3作为锗酸盐玻璃的主体组分，并引入铟、镧等重金属离子，以拓展其红外透过窗口；利用改进型气相沉积系统MCVD结合重金属螯合物气相掺杂系统CPDT，对锗酸盐玻璃光纤预制棒进行制备；制备过程中引入氯气，降低玻璃中残留的水分与羟基OH-以减少2~3μm的吸收损耗。对“母棒”预制棒进行延伸、切割、套管、塌缩等工艺流程获得较小芯/包比的预制棒。在惰性气体保护条件下，成功拉制锗酸盐玻璃光纤，并测试锗酸盐光纤的透过光谱，背景损耗等特性。.基于CPDT螯合物全气相掺杂装置与MCVD系统，成功制备了阶跃型与肩膀型的两类型光纤预制棒。阶跃型预制棒主要是GeO2含量为52%(52%GeO2-SIF)与GeO2含量为92%(92%GeO2-SIF)的锗酸盐预制棒。在肩膀型预制棒(72%GeO2-PSIF)制备过程中，纤芯中成功掺杂重金属La，从而制备了纤芯组分为(GeO2-SiO2-La2O3-Al2O3)，肩膀层组分为锗硅酸盐(GeO2-SiO2)的预制棒，其中纤芯部GeO2含量为72%。采用截断法对三类光纤传输损耗进行测试：92%GeO2-SIF光纤在1.3μm与1.55μm损耗分别为99dB/km，42dB/km；72%GeO2-PSIF光纤在1.3μm与1.55μm损耗分别为52dB/km，39dB/km。 52%GeO2-PSIF光纤在1.3μm与1.55μm损耗分别为9.2dB/km，4dB/km。92%GeO2-SIF与72%GeO2-PSIF光纤的红外截止波长拓展至2.7μm。同时，三种光纤都没有观察到在1.38μm处的水峰。.本项目研究结果表明MCVD系统结合CPDT掺杂法是一套能制备锗酸盐光纤预制棒的全气相玻璃材料合成工艺路线，并成功消除了锗酸盐玻璃光纤中水分，将锗酸盐玻璃的红外截止波长拓展至2.7μm，成功地打开锗酸盐玻璃体系的红外窗口。