【作者】 李宇航；

【导师】 童利民； Guillaume Vienne；

【作者基本信息】 浙江大学 ， 光学工程， 2008， 博士

【摘要】 与电子器件相似,微型化也是光子器件的发展趋势之一。微纳光子器件通过在波长和亚波长尺度上对光的操控,实现各种各样的功能。微纳光波导是微纳光子器件的基本结构单元,是目前光子学领域的研究热点之一。微纳光纤是一种典型的微纳光波导,因制备简单、损耗低而受到越来越多的关注。微纳光纤的突出特点之一是周围的倏逝场可以很强,本文首先研究了微纳光纤的模场特性。本文用氧化硅徼纳光纤模场的解析解,在线偏振和圆偏振输入光情况下分别讨论了微纳光纤内部及周围的电场和能量的分布,以及氧化硅微纳光纤的色散特性。两根微纳光纤通过倏逝波耦合可形成微型耦合器,这是研制微纳光纤器件非常有用的一个特性。文中用微扰理论模型从物理上探讨了微纳光纤间的倏逝波耦合机理,并通过3D-FDTD方法用数值计算实例分析了微纳光纤倏逝波耦合器的特性。本文的工作以氧化硅微纳光纤和玻璃微纳光纤的制备方法为基础,研究重点为基于倏逝场的微纳光纤器件,包括共振型和干涉型两种。共振型器件以微纳光纤结型谐振腔和环形激光器为代表,其中对微纳光纤环形激光器的理论建模分析是共振型器件的重点内容。基于耦合区的耦合波方程和激光工作物质的速率方程,文中给出了三能级系统和四能级系统的激射条件、阈值泵浦功率和量子效率的解析表达式。研究表明,若能实现泵浦光的谐振,则能大大降低泵浦的阈值功率,增加泵浦吸收,从而增加激光器的量子效率。此外,还研究了泵浦光谐振时的耦合损耗和微环直径对泵浦闽值和量子效率的影响。研究发现,采用大吸收截面和高掺杂材料制作微纳光纤环形激光器,可以实现直径约几十微米的低阈值、高效率的微型激光器。这些理论分析对微纳光纤环形激光器和其他微激光器的制作和特性分析具有一定的指导意义。在干涉型器件部分,详细研究了基于微纳光纤耦合器的微型Mach-Zehnder干涉仪的实验制作过程和光学特性表征。通过在光学显微镜下的微纳操作,我们可以方便地在低折射率衬底上制作不同分束比的耦合器。基于3 dB耦合器,可以方便的制作氧化硅和玻璃微纳光纤Mach-Zehnder干涉仪,器件尺寸在几十微米到几百微米。通过仔细调节耦合器的长度,干涉对比度可以达到10 dB,通过微纳操作,还可以自由调节干涉仪两臂的程差,从而改变干涉仪的自由光谱区。制作方便、结构紧凑,程差可调,且便于与光纤系统相连,这些特性使得微纳光纤Mach-zehnder干涉仪有可能用在传感器,光调制器等微光子学器件中。更多还原

【Abstract】 Similar to their electronic counterparts, photonic devices also show the trend for miniaturization. Micro- or nanophotonic devices, which manipulate light on the wavelength or subwavelength scale, demonstrate various impressive functions. Micro-or nanoscale waveguides are one of the fundamental building blocks for micro- or nanophotonic devices, and are hot topics in current photonics research. Being one of the typical micro or nanoscale waveguides, micro- or nanofiber （MNF）, featured with simple fabrication and low loss, is attracting more and more attentions.One of the outstanding properties of MNFs is their possibilities to offer high fraction of evanescent fields. In the thesis, we first investigate the mode field properties of MNFs. Using analytical expressions of the mode fields of silica MNFs, we study the electric field and energy distribution, both inside and outside the silica MNFs with linear and circular polarization. Besides, we also investigate the diameter-dependent waveguide dispersions in MNFs.Two MNFs can form a micro coupler by means of side-by-side evanescent coupling, which is very helpful for building MNF devices. The mechanism of evanescent coupling of MNFs are investigated using perturbation model, and the behavior of an evanescent coupler is numerically investigated using a 3D-FDTD method.Started with the taper-drawing fabrication of MNFs from silica fibers and bulk glasses, the thesis puts its emphasis on resonance and interference MNF devices based on evanescent coupling. In resonance devices, MNF knot resonators and microring lasers are investigated. The main efforts are made on the theoretical modeling of MNF ring lasers, which is based on ring resonator equations at the coupling region and rate equations for active materials. Analytical expressions are given for lasing condition, pump threshold and quantum efficiency for three-level and four-level transitions in Er³⁺ and Yb³⁺ doped glasses. It shows that pump resonance can significantly reduce the threshold, increase the pump absorption, and thus greatly increase the quantum efficiency. Besides, we also study the effect of the coupling loss and the ring size at the pump resonance. It is found that highly doped MNFs with large absorption cross sections will facilitate low-threshold, high quantum efficiency microring lasers with ring diameters down to tens of micrometers. These results may offer valuable reference to the realization of MNF-based ring lasers or other kind of microlasers.In the section of interference MNF devices, we present the fabrication and optical characterization of MNF Mach-Zehnder interferometers in detail. By means of micromanipulation under an optical microscope, miniature MNF couplers with different splitting ratios can be easily constructed. Based on two MNF couplers, silica and glass MNF Mach-Zehnder interferometers are assembled, with typical dimensions of tens to hundreds of micrometers. The extinction ratio can reach 10 dB by finely adjusting the coupler length. Besides, the path-length differences can be tuned by micromanipulation, and thus the free spectrum range can be easily adjusted. By virtue of its easy fabrication, compact size, tunability and convenient integration with fiber system, MNF Mach-Zehnder interferometers are promising to find applications in sensors, optical modulators and other miniature photonic devices.更多还原