Switchable materials with nanoplasmonics for optical applications

该提案是在光束与可切换和可调节的材料（如二氧化钒（VO2）和等离子体纳米粒子）相互作用的领域。我的部分研究将这些材料与纳米颗粒结合起来，或者使用纳米尺度的模式来改变其特性。在所研究的材料中，VO2特别有趣的是，它在加热几十摄氏度时就能从介电态转变为金属态。这种相变伴随着折射率和吸收系数的巨大变化，使得光学控制成为可能，在光子器件和超材料中具有潜在的应用前景。这项研究的目的不是了解这些化合物的生长、制造和其他材料科学方面，而是了解它们与激光和其他光束的相互作用，以利用这些效应用于各种光子应用。其中一个主要项目旨在精确控制与VO2薄膜相互作用的激光束的相位：该材料有望用于薄至100纳米或更小的相位调制设备。光相位控制、调制和移位是光子学的核心目标之一，在干涉测量、光脉冲延迟/提前和快/慢光等领域有着广泛的应用。我们最近观察到，在我们实验室特定条件下生长的VO2薄膜在800-1600 nm范围内的特定波长表现出一个有趣的特性：在相变期间，光束的相位发生了变化，同时保持光束的其他特性不变，包括偏振和振幅。最近，我们使用了一种高灵敏度的相位测量技术（由我们的团队开发）来通过薄膜看到精确相位可调的证据。这一效应的研究和应用将是我们未来几年的一个研究课题，因为它表明了在极短距离内进行相位控制的可能性。每单位距离的相移比电光材料（如Pockels电池）和液晶通常实现的相移大几个数量级。它开启了集成光学器件高度小型化的可能性。然而，在这些应用程序成为可能之前，我们仍然需要调查问题的许多方面。例如，该效应的波长可调节性和输入偏振的影响必须进行理论建模和实验验证。另一个研究方向是通过将金属纳米颗粒掺入可切换材料中来增强和调整材料的性能。金纳米粒子表现出等离子体共振，可以通过调整这些粒子的大小来调节波长，从而增加光学吸收。关于VO2，金纳米粒子特别有趣，因为它们的共振发生在可见光谱中：与处于金属状态的VO2相比，它们在近红外波段的吸收较弱。因此，纳米粒子可以用来增强光泵浦和光感应开关的材料使用可见激光束。与合作者，材料科学专家，我们打算创造具有这种特性的混合材料，并充分表征它们的光子应用。对于加拿大来说，该研究项目将对培养光学和光子学等重要经济领域的高素质人才产生积极影响。此外，由于该项目的应用性质，与工业界的合作将是可能的，具有新设备商业化的潜力。

The proposal is in the area of optical beams interacting with switchable and adjustable materials such as vanadium dioxide (VO2) and plasmonic nanoparticles. Parts of my research combine these materials with nanoparticles or uses nanometer-scale patterns to modify the properties. Among the studied materials, VO2 is especially interesting for its ability to change from a dielectric state to a metallic state when heated by only tens of degrees centigrade. This phase transition is accompanied with large changes in refractive indices and absorption coefficients, making optical control possible, with potential applications to photonic devices and metamaterials. This research is not aimed at understanding the growth, fabrication and other such material science aspects of these compounds, but rather understanding their interaction with lasers and other optical beams to exploit these effects for various photonic applications. One of the lead projects aims at controlling accurately the phase of a laser beam that is interacting with a thin film of VO2: the material shows promises for phase modulating devices as thin as 100 nanometers or less. Optical phase control, modulation and shifting is one of the central goals of photonics, with widespread applications in areas like interferometry, optical pulse delay/advance and fast/slow light. We have recently observed that films of VO2 grown under certain conditions in our laboratory exhibit an interesting property at specific wavelengths in the 800-1600 nm range: during phase transition, the phase of the optical beam is changed while keeping the other properties of the beam intact, including polarization and amplitude. Recently, we used a highly sensitive phase measurement technique (developed by our group) to see evidences of accurate phase adjustability through the film. Studies and applications of this effect will be for us a topic of research in the next few years, because it suggests the possibility of phase control over extremely short distances. The phase shift per unit of distance travelled is orders of magnitudes larger than what is typically achieved with eletro-optic materials (e.g. Pockels cells) and liquid crystals. It opens the possibility of highly miniaturized devices for integrated optics, among others. However, there are still many aspects of the problem we need to investigate before these applications are made possible. For example, the wavelength adjustability of the effect and the influence of input polarization have to be theoretically modeled and verified experimentally. Another axis of research involves the enhancement and tailoring of the properties of switchable materials by incorporating metal nanoparticles into them. Gold nanoparticles exhibit plasmon resonances that increase optical absorption at wavelengths that can be tuned by adjusting the size of these particles. With respect to VO2, gold nanoparticles are especially interesting because their resonances occur in the visible spectrum: their absoption in the near infrared is weak compared to that of the VO2 in its metallic state. As a result, nanoparticles can be used to enhance optical pumping and optically-induced switching of the material using visible laser beams. With collaborators, experts in material science, we intend to create hybrid materials with such properties and fully characterize them for photonic applications. For Canada, this research program will have a positive impact by training highly qualified personnel in the economically important areas of optics and photonics. Morover, partnership with industry will be possible because of the applied nature of the project, with potential for new device commercialization.