Active controllable optical phase shifters employing the localized particle plasmon resonance in the near infrared of n-doped metal oxide nanoparticles

传统的氧化还原电致变色(EC)材料具有通过电化学势控制EC膜的光吸收的能力。尽管Kramers-Kronig关系预测这种效应伴随着通过薄膜的波的光学相移，但由于所提到的强吸收，在很宽的光谱范围内很难检测到这种相移。因此，本项目的目标是研究和主动控制利用具有电容EC效应的无机氮掺杂金属氧化物纳米颗粒(NP)的光学相移。它们在近红外的窄带内表现出强吸收的局域粒子等离子体共振(LSP)，并伴随着几乎整个光学范围内的光学相移。通过使用一种简化的有效介质方法(Bruggeman模型)计算了TiO2NP薄膜的折射率和吸收系数，在理论上成功地证明了我们相移概念的这一基本思想。在实验中，EC薄膜中的自由电子密度将通过允许相移连续变化的外部电压来改变。这一跨学科项目一方面需要金属氧化物NP的化学合成方面的专门知识，包括尺寸和掺杂水平的控制以及用于模板印刷的浆料的制备。另一方面，将这些NP材料作为薄膜集成到微细加工的EC电极中需要专业知识。这也涉及到理论建模、光电化学表征以及概念的应用和论证。申请者的互补专业知识在最近的BMBF项目中得到了成功的展示。在该项目中，我们将确定相移能力的光谱范围以及它与化学材料组成、掺杂水平和NP尺寸的关系。为了表征LSP在近红外的共振和光学响应，我们将进行UV-Vis-NIR光谱和光谱椭偏测量。相移能力将用空间分辨率迈克尔逊干涉仪对一组离散的波长进行研究。这些实验数据将进一步用于材料和器件的综合理论建模。金属氧化物NP电极的相移能力将通过两组不同的实验得到验证：基于微结构位相光栅的光学相位调制器(离散的衍射角和可控制的强度)和创新的控制极角和方位角的连续光束稳束系统。这需要对电势分布进行广泛的有限元模拟，并计算与材料相关的空间分辨相变。

Conventional redoxactive electrochromic (EC) materials have the capability to control the optical absorption of an EC film by means of an electrochemical potential. Although the Kramers-Kronig relations predict that this effect is accompanied by an optical phase shift for a wave passing through the film, it is hard to detect the phase shift over a broad spectral range because of the strong absorption mentioned. Therefore, the goals of this project are the investigation and active control of the optical phase shift employing inorganic n-doped metal oxide nanoparticles (NP) with capacitive EC effect. They exhibit a localized particle plasmon resonance (LSP) with strong absorption in a narrow band in the near infrared accompanied by an optical phase shift over almost the complete optical range with low absorption. This basic idea of our phase shifting concept was successfully proven in theory by evaluating the refractive index and absorption coefficient of a TiO2 NP film using a simplifying effective media approach (Bruggeman model). In the experiment the free electron density in the EC film will be varied by means of an external voltage allowing a continuous variation of the phase shift. This interdisciplinary project demands on one hand the expertise of the chemical synthesis of metal oxide NP including the control of size and doping level and the preparation of pastes for stencil printing. On the other hand, it requires the expertise to integrate these NP materials as thin film into microfabricated EC electrodes. This also involves the theoretical modeling, optoelectrochemical characterization and the application and proof of concept. The complementary expertise of the applicants has been successfully demonstrated in a recent BMBF project. In the project we will determine the spectral range of the phase shifting capability and its dependence on the chemical material composition, doping level and NP size. For the characterization of the LSP resonance in the near infrared and the optical response, we will perform UV-Vis-NIR spectroscopy and spectral ellipsometry. The phase shifting capability will be investigated for a discrete set of wavelengths with a spatially resolving Michelson interferometer. These experimental data are further used for a comprehensive theoretical modelling of materials and devices.The phase shifting capability of the metal oxide NP electrodes will be proven in two different sets of experiments: an optical phase modulator based on a microstructured phase grating (discrete set of diffraction angles and controllable intensity) and an innovative continuous beam stearing system controlling the polar and azimuthal angle. This requires an extensive FEM simulation of the potential distribution and the calculation of the spatially resolved resultant material-related phase change.