【作者】 孙雪铮；

【导师】 顾培夫； 刘旭；

【作者基本信息】 浙江大学 ， 光学工程， 2008， 博士

【摘要】 薄膜中的超棱镜效应为光学薄膜开拓了新的应用领域,它使得倾斜放置的光学薄膜可以从空间上将不同波长的电磁波进行分离,因此薄膜超棱镜结构可用作类如棱镜、光栅的空间色散器件。而基于超棱镜效应的光学薄膜色散器件可以获得远远超过传统色散器件的空间解复用效果,且在尺寸、集成度、稳定性、可靠性和成本等方面优势明显,被认为是新一代低成本的光通讯波分复用器件。本课题研究了多种光学薄膜中的超棱镜效应并进行了相关测试,主要涉及以下几个内容:1.超棱镜效应相关的模拟计算。在深入分析实现前人工作的基础上,针对其局限性,提出了几种新的超棱镜效应相关计算的方法。首先,鉴于群延迟是色散系统中的一个重要因子,提出了一种基于多镜理论计算多腔级联滤波器群延迟的方法,从而大大简化了多腔器件群延迟的计算和优化工作。接着,在以往研究者提出的超棱镜效应计算方法——时空色散正比法的基础上,首次引入了应用于其他领域的稳态位相法和高斯频谱展开法计算模拟了超棱镜效应。与时空色散正比法相比,稳态位相法更为简单、准确;而高斯频谱展开法不但可以适用于更广泛的场合:如不同分布的入射光、不同结构的膜系等,而且可以更为精确地分析薄膜内部的电磁场分布,从而方便地解释各种伴随发生的物理现象:如光斑分裂效应、波形畸变效应等。2.设计了几种新型的可调谐和多通道薄膜超棱镜器件,并进行了实际测试。为了适应光通信领域中密集波分复用(DWDM)系统的需求,设计并优化了几种典型的薄膜超棱镜系统,包括利用角度调谐的薄膜法布里—珀罗滤光片和液晶法布里—珀罗滤光片中的超棱镜效应,实现了可调谐的空间解复用器件;然后设计了一种在常规反射膜堆两端添加厚度递减反射膜堆的薄膜结构,实现了多通道的空间解复用效果;最后基于铌酸锶钡Gires-Tournois薄膜干涉滤光片的电光效应设计了一种新型的空间色散位移随入射波长呈台阶状分布的超棱镜结构,改善了线性空间位移的不足,得到了在信道中心附近有一定波长漂移容差的“类台阶”空间位移特性。事实证明这种结构还可以用于色散补偿系统,并举例对50GHz的薄膜滤光片进行了色散补偿。这几种薄膜结构与已有的设计相比要简单很多,制备方便,本文实际制备了其中两种器件,并搭建了薄膜超棱镜测试装置对色散效应进行了测试。3.提出了一种新型的薄膜窄带反射滤光片结构,并测试了其超棱镜效应。针对显示、摄像、激光等经常使用反射系统的领域设计了一种薄膜反射滤光片,可以实现高的峰值反射率、窄的带宽及高的截止深度。相对于传统透射滤光片来说,这种反射滤光片对结构对称性要求不高,制备方便,本文实际制备出的反射滤光片与理论设计极为接近。对此结构的超棱镜效应测试发现,这种结构相对于常用的高反膜、透射滤光片等,反射能量利用率可以提高到两倍以上,且基本不降低色散效果。最后将光子晶体理论引入这种结构,实现了多通道反射滤光片的设计并进行了制备。4.首次测试出了光学薄膜中负色散位移效应,并给出了相关的分析讨论。负的空间位移效应意味着光束产生了逆传播方向的移动,尝试了使用波形畸变和超光速两种理论对这种效应进行了解释。分析了脉冲光经过产生负位移薄膜后的分布情况,试图在空间上的色散位移正负与时间上的快慢光效应之间建立一种联系,这种联系将为快慢光效应的测试提供一条低成本的捷径。将正负空间位移效应相结合,本文还设计了一种增强的超棱镜效应,从而实现更宽的色散范围和更大的色散位移。5.搭建了超棱镜效应相关测试系统。为了更好地对超棱镜效应进行测试,本文先后两次搭建了微位移测试平台,尤其是最后采用的“光学薄膜光栅”超色散测试系统,采用精密可调的单色系统、小光束准直系统以及精密光斑位置检测系统,实现高灵敏度、高精度的反射光斑及透射光斑的位置检测,为超分辨色散器件的研究奠定了基础。同时,鉴于位相特性在色散系统中的重要性,本文还搭建了基于迈克尔逊的白光干涉系统进行薄膜的位相测试,并实际测试了单层薄膜的位相信息。这个装置不仅可以应用在超棱镜效应的测试中,同时在飞秒、通信、成像等多种需要位相信息的领域中都起着至关重要的作用。最后,本文对整个课题的工作进行了总结,提出了今后需要进一步研究和发展的方向。更多还原

【Abstract】 Superprism effect opens new application to optical thin films, the thin film superprism can spatially separate light with different wavelengths when obliquely placed. It means the thin film superprism can be used as the spatial dispersion device, just as prisms and gratings. Moreover, compared with these conventional dispersion devices, much better spatially demultiplexing effect can be obtained by using the thin film superprism, meanwhile, their small size, integrativity, stability and low cost lead them as the precursor in wavelength demultiplexing field in optical communication system. The research is focus on simulation and corresponding measurement on superprism effect in various of optical thin films. The main contents in this paper are as follows:1. Simulation and calculation on superprism effect. After analyzing the limits of the works presented by predecessor, some new methods on superprism effect and relative calculation are proposed. Firstly, as group delay is a significant ingredient in dispersion system, a novel method based on multi-mirror theory for calculating group delay of multi-cavities filters is presented to simplify the calculation and optimization. Besides the calculation on superprism effect (proportionality technique between temporal and spatial dispersion) proposed by previous works, introducing stationary-phase theory and Gaussian angular spectrum method, which usually used in other fields, to simulate the superprism effect in thin films. Compared with the proportionality technique between temporal and spatial dispersion, the stationary-phase theory is simpler and more accurate. While Gaussian angular spectrum method can not only apply to more situation, such as different profiles of incident light, different thin film structure, but also explain some complex physical phenomena, just as beam splitting effect, beam distortion effect an so on.2. Design and measurement on some novel tunable and multichannel thin film superprism devices. To adapt to the requirement of dense wavelength demultiplexing (DWDM) system in optical communication field, design and optimize some typical superprism thin film systems, including utilizing the superprism effect in Fabry-Perot filter with tunable incident angle and liquid crystal Fabry-Perot filter to realize the tunable spatially demultiplexing effect; then a novel struture of conventional high reflectance (HR) coating sandwiched between two thickness-tapered period thin film stacks is designed to be used as the multichannel spatial demultiplexer; At last, based on the electro-optic property in strontium barium niobate Gires- Tournois interferometer, a novel superprism structure is designed to obtain the step-like spatially dispersive shift with the incident wavelengths. The step-like shift can overcome the limits of linear shift and allow some drifts in the central wavelength of the output channel. This sturcture can also be used in dispersion compenesation system, a compensator to the 50GHz thin film filter is designed as the example. Compared with the prior work, these thin film structures are much simpler for depostion, we fabrication two structures of them, and establish the measurement setup to test the spatial dispersion effect in thin film superprism.3. A novel narrow-band thin film reflection filter is designed and fabricated, and its superprism effect is also studied. A novel thin film reflection filter with hight peak reflectance, narrow bandwidth and deep cutoff is designed for display, colorful, special photography, laser and some other fields which are inclined to reflection system. The requirement on symmetry for reflection filter is not as strict as the conventional transmission filter, so it is much easier for fabrication, and we get approximate agreement between design and depostion. Moreover, we also measure the superprism effect in this filter, compared to the high reflectance coatings and transmission filter, it demonstrate that this structure can double the reflective energy efficiency without decreasing dispersive ability. Ultimately, photonic crystal theroy is introduced to design multichannel reflection filters.4. A dramatic negative spatial shift effect is tested in optical thin film for the first time, analysis and discussion are given on this phenomenon. Negative spatial shift means the beam shift against the propagation direction. We introduce the theroy of beam distortion and superluminal effect to explain this phenomenon. The distribution of the pulse propagate through thin film superprism is analyzed, the relationship between spatially positive/ negative dispersive shift phenomena and temporally fast/ slow light effect is tried to estabilished. This relation may supply a short cut for fast and slow light measurement. Combining the negative and positive shift phenomena, we also frame an enhanced superprism effect to get wider dispersive band and larger dispersive shift.5. Relative measurement setups are built. We establish measurement twice on micro shift for testing superprism effect. And the "thin film gratings" measurement, which we adopt finally, has critically tunable monochroic system, collimated system and exact system for spot detection, realizing detect the micrometer-level shift of reflective and transmissive spots with high sensitivity and precision, and is useful for studies on dispersive device with high resolution. Moreover, owing to the importance of phase properties in dispersion system, we also build a white-light Michelson interferometer to measure the phase properties of thin films. Phase information of single layer is tested in this research. This setup can be not only used to measure superprism effect, but also useful for femtosecond, communication, imaging and some other fields.At last, a summary of this paper is included and the prospect of this research is also given.更多还原