Coupled periodic nanowaveguides for the generation of photon pairs

集成光学的核心挑战之一是完全控制引导光场的空间和光谱特性。引导场的空间分布通常是通过几个波导之间的倏逝能量交换耦合来控制的。虽然这种方法很容易理解，但它通常使用非常相似的低色散波导来实现。另一方面，强色散使光谱控制成为可能，通常在单纳米波导中实现，波导核心和周围介质之间的折射率对比度很大，另外，这些介质可以周期性地结构以引入色散中的共振。通过将具有大折射率对比度的结构和非结构纳米波导形成耦合波导系统，我们希望同时实现对传播场的空间和光谱特性的深远控制。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，这种不同耦合波导的系统通过解锁新的自由度，增加了控制光传播的可能性。这个项目的目的是建立一个基本的理解，这种耦合周期纳米波导的特性是如何依赖于它们的参数的，例如波导的大小，结构周期或系统的整体对称性。这种见解将使耦合周期纳米波导的系统设计用于特定目的。作为一个相关的应用案例，我们将研究在铌酸锂制造的耦合周期纳米波导中通过自发参数下转换产生具有定制性质的光子对。生成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各自特性，从而开辟了通过结构设计来控制它们的可能性。在本项目中，我们计划实现具有可调谐光谱和纠缠的光子对的源，以及实现特定时间波形所需的具有复杂光谱轮廓的双光子态。此外，我们将展示空间工程双光子源，允许例如产生的光子的确定性分离或路由取决于它们的光谱特性。通过完成这个项目，我们将为集成光学引入一种新型的结构，并将在纳米尺度上理解耦合和周期结构的相互作用。最后，该项目将为量子光学开辟新的视角，因为有更多种类的实验可用光态。

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.