硫系玻璃的光致改性与微光子学器件研究

【作者】 张启明；

【导师】 徐雷；

【作者基本信息】 复旦大学 ， 光学， 2010， 博士

【摘要】 硫系玻璃材料由于具有高折射率、宽红外透明窗口、极高的光学非线性,以及丰富的光敏性如光致相变、光致聚合和光致暗化等性质,是重要的光学材料,在非线性集成光学器件、高密度光存储和生物光子学上有巨大的应用潜力。本文围绕着如何提升硫系玻璃的光学性质及制备微纳光子学结构和器件开展了系列研究工作。首先,我们利用中心波长为780 nm飞秒激光与波长为579 nm连续激光对As2S3玻璃进行了照射,研究超短脉冲双光子激发和亚带隙的连续激光激发引发材料的不同光学性质(线性和非线性光学性质)改变。接着,我们利用了中心波长为800 nm飞秒激光对硫系玻璃的不同作用(包括激光表面烧蚀,激光内部破坏和激光诱导选择性腐蚀),在As2S3体材料玻璃上制作了不同的微纳光子学结构。最后,我们成功制作出硫系玻璃的微纳光纤,并将微纳光纤转移到硅基片上形成掩埋型波导,成功制备了高Q微谐振腔等不同类型的微纳光子学器件,并实现了窄带滤波、超连续光产生等不同的功能。本论文的创新点主要有以下几点：1.通过飞秒激光与连续激光实现了对As2S3硫系玻璃非线性折射率的调节,其中飞秒激光能增强非线性折射率最高达50%,而连续激光能减弱非线性折射率最高达60%。我们对其变化的原因进行了讨论。提出了两种激光产生了不同的缺陷,飞秒激光产生的变价对缺陷能增强样品三阶光学非线性系数,而亚带隙连续激光产生的同极键缺陷则会降低其三阶光学非线性系数。2.我们利用了飞秒激光对硫系玻璃的不同作用在As2S3体材料玻璃制作了不同的微纳光子学结构。利用飞秒激光对材料的表面烧蚀,在多脉冲照射情况下产生周期为180 nm的纳米光栅,在单脉冲照射下产生直径为200 nm的纳米洞结构。并通过系列的实验验证了产生纳米光栅的理论。指出在硫系玻璃内,激光诱导等离子体的非均匀生长可能是产生纳米光栅的主要原因。研究了飞秒激光暗化后材料在有机胺类溶液的选择性腐蚀效应,制作出宽为2.5μm的微管。3.制作出的基板上的掩埋型硫系玻璃微纳光子学器件。通过熔融拉锥方法制作出直径最小可达200 nm的As2S3玻璃光纤,并成功地将微纳光纤掩埋于聚合物SU8胶中并固定并保护在硅基板上。制作出低传输损耗的波导与高Q值的结形微腔。利用532 nm连续激光的照射,实现了结形微腔共振波长的调节,调节范围约1.5 nm。通过中心波长在1560 nm的飞秒激光泵浦直径为1μmm长度为7 cm的直波导,在脉冲能量为2 nJ的情况下,实现了光谱宽度为500 nm的激光超连续展宽。更多还原

【Abstract】 Chalcogenide glasses, which possess high refractive index, wide transparent window and ultrahigh optical nonlinearity and rich photo-induced effects, such as phase changing, photopolymerization, and photodarkening upon light exposure, are very important optical materials. These glasses are excellent candidates for diverse applications including nonlinear and reconfigurable photonic chip devices, high density optical data storage, and biophotonic devices. In this thesis, we focused our research on how to improve the optical properties of chalcogenide glasses and fabrication of micro/nano structures and devices.Firstly, As2S3 glasses were exposed by femtosecond (fs) laser at 780 nm and continuous wave (CW) laser at 579 nm. The different changes in linear and nonlinear optical properties induced by the two-photon excitation of short pulse laser and sub-bandgap excitation of CW laser were also studied. Secondly, we used different laser-glass interactions (laser ablation, laser induced damaging inside material and laser induced selective etching) induced by fs laser at 800 nm to fabricate varieties of photonic structures in As2S3 bulk glasses. Thirdly, we successfully fabricated chalcogenide micro/nano fibers and transferred them on silicon chips to form buried optical waveguides. Different kinds of functions, such as narrow band filtering and super continuum generation, were demonstrated as well.The main achievements of this thesis are as follows:1. The third order optical nonlinearity of As2S3 glasses was tuned by fs laser and CW laser. The fs laser could enhance the nonlinear refractive index up to 50%, while the CW laser could suppress the nonlinear refractive index down to 60%. Then we discussed the origins of the changes induced by the lasers. We point out that two lasers induce different kinds of defects. The fs laser could induce valence alternation pairs to enhance the third order nonlinearity and the CW sub-bandgap laser could induce homopolar bonds to decrease the third order nonlinearity.2. We used different laser-glass interactions in As2S3 bulk glasses to fabricate varieties of photonic structures. By using laser ablations, nanogratings with a period of 180 nm were realized by multi-pulse irradiation, and nanoholes as small as 200 nm in diameter were fabricated by single pulse irradiation. The theories of generation of nanogratings were verified by series of experiments. We point out that the irregular growth of laser induced plasmas could be the main reason for the generation of nanogratings in chalcogenide glasses. And we studied the selective etching of chalcogenide glasses after laser irradiation and produced 2.5-μm-width micro channels.3. We have fabricated on-chip buried chalcogenide micro/nano photonic devices. Nano fibers in diameters of 200 nm were drawn by fiber tapering method. The fibers were then mounted on silicon chip and protected by polymers (SU8). On-chip low optical loss waveguides and high-Q micro knot resonators were fabricated. The post tuning in a range of about 1.5 nm of micro knot resonators were demonstrated by irradiation of CW laser at 532 nm as well. By pumping with an fs laser at 1560 nm in pulse energy of 2 nJ, supercontinuum generation with bandwidth of 500 nm was achieved in a 1-μm-wide 7-cm-long chalcogenide waveguide.更多还原