Coupled periodic nanowaveguides for the generation of photon pairs

集成光学的核心挑战之一是引导光场的空间和光谱特性的完全控制。波导场的空间分布通常是通过几个波导之间的倏逝波能量交换耦合来控制的。虽然这种方法是很好理解的，但它通常使用非常相似的低色散波导来实现。另一方面，强色散能够实现光谱控制，并且通常在波导芯与周围介质之间具有大折射率对比的单个纳米尺寸波导中实现，通过由具有大折射率对比度的结构化和非结构化双波导形成耦合波导系统，我们期望同时实现远距离控制，传播场的空间和光谱特性。因此，我们将周期性结构波导用于色散控制的有利特性与耦合波导系统用于空间控制的固有可能性相结合。此外，这种系统的非常不同的耦合波导另外提高了控制光传播的可能性，通过解锁新的自由度，这个项目的目的是建立一个基本的理解，如何耦合周期性的耦合波导的属性取决于它们的参数，例如，波导的大小，周期的结构或系统的整体对称性。作为一个相关的应用案例，我们将研究在锂氧化物中制造的耦合周期性双光子波导中通过自发参量下转换产生具有可剪裁特性的光子对。所产生的双光子量子态的光谱和空间特性敏感地依赖于生成结构的相应特性，从而打开了通过结构设计来控制它们的可能性。在这个项目中，我们计划实现可调谐光谱和纠缠的光子对源，以及实现特定时间波形所需的复杂光谱轮廓的双光子态。此外，我们还将展示空间工程双光子源，例如，允许产生的光子的确定性分离或根据其光谱特性的路由。通过完成这个项目，我们将引入一种新型的结构集成光学，并将提供耦合和纳米尺度上的周期性结构的相互作用的理解。最后，该项目将为量子光学开辟新的前景，因为实验上可用的光态种类繁多。

One of the central challenges of integrated optics is the complete control of the spatial and spectral properties of guided optical fields. The spatial distribution of guided fields is usually controlled by coupling of several waveguides using evanescent energy exchange between them. Although this approach is well understood, it is usually implemented using very similar waveguides with low dispersion. Strong dispersion, on the other hand, enables spectral control and is usually achieved in single nanosized waveguides with a large refractive index contrast between wave-guiding core and the surrounding media, which additionally may be periodically structured to introduce resonances in the dispersion.By forming coupled waveguide systems from structured and unstructured nanowaveguides with large refractive index contrast we aspire to simultaneously enable far reaching control of the spatial and spectral properties of the propagating fields. Thus, we are combining the favorable properties of periodically structured waveguides for dispersion control with the inherent possibilities of coupled waveguide systems for spatial control. Furthermore, such systems of very different coupled waveguides additionally enhance the possibilities for controlling light propagation by unlocking new degrees of freedom.The aim of this project is to establish a fundamental understanding of how the properties of such coupled periodic nanowaveguides depend on their parameters, e.g. the size of the waveguides, period of the structuring or overall symmetry of the system. Such insight will enable the systematic design of coupled periodic nanowaveguides for specific purposes.As a relevant application case we will study the generation of photon pairs with tailorable properties by spontaneous parametric down-conversion in coupled periodic nanowaveguides manufactured in lithium niobate. The spectral and spatial properties of the generated two-photon quantum states sensitively depend on the respective properties of the generating structures, opening up the possibility for controlling them by the structure design. In this project we plan to realize sources for photon pairs with tunable spectrum and entanglement as well as two-photon states with complex spectral profile needed to realize specific temporal waveforms. Furthermore, we will demonstrate spatially engineered two-photon sources, allowing for e.g. the deterministic separation of the generated photons or the routing depending on their spectral properties.By completing this project, we will introduce a new type of structure to integrated optics and will deliver an understanding of the interplay of coupling and periodic structuring on the nanoscale. Finally, the project will open up new perspectives for quantum optics due to a larger variety of experimentally available light states.