Light cages meet metasurfaces: On-chip twisted light applications enabled by direct laser writing

同时具有自旋角动量和轨道角动量的扭转(手征)光由于其独特的物理性质和应用，是一个非常热门的研究领域。从波导学的角度来看，扭曲的光纤表现出令人着迷的现象，如螺旋布洛赫模或强圆二向色性。然而，所获得的扭转速率相当小，仅导致对模式形成的微小微扰型影响。从波前整形的角度来看，几何亚表面能够控制轨道角动量状态，但在多路复用的情况下往往会受到严重的串扰。最近引入的一种复杂光子结构的实现方法是使用直接激光写入(DLW)的3D纳米打印，这为波导和亚表面提供了独特的优势。在这里，新型的片上空芯波导，即所谓的光笼和具有额外高度自由度的亚表面已经被应用人员联合展示。拟议的项目旨在探索光与纳米打印的扭曲光子结构相互作用的产生、引导和操纵，包括光笼、手性亚表面及其组合。该项目的目的是(I)了解光在扭曲光笼内传播并通过手性亚表面控制的性质，(Ii)释放DLW实现扭曲功能光子结构的潜力，以及(Iii)评估手性亚表面和扭曲光笼的组合是否会导致一个新的光子平台，以达到以前无法达到的物理和应用。举几个例子，DLW主要使光笼具有极高的扭转率和未探索的几何形状。对于超表面，高度自由度不仅提供了对几何形状的完全控制，而且还提供了对传播相位的完全控制，因此，通过复杂的形状也使得本质上具有手性的单胞成为可能。对我们的工作同样重要的是，DLW允许在单个制造步骤中直接实现变形表面接口的扭曲光笼。总体而言，该项目将揭示关于光与扭曲光子结构相互作用的产生、引导和操纵的新物理。在本项目范围内评估的潜在应用将包括手性分子芯片上传感、OAM辅助多路传输或原子磁测量。

Due to its unique properties in terms of physics and applications, twisted (chiral) light with both spin and orbital angular momentum is a highly topical field of research. From a waveguide perspective, twisted optical fibers exhibit fascinating phenomena such as helical Bloch modes or strong circular dichroism. Twisting rates achieved, however, are rather small, only leading to a small perturbative-type influence on mode formation. From the perspective of wavefront shaping, geometric metasurfaces enable control over orbital angular momentum states, yet often suffer from significant cross talk for example in a context of multiplexing.A recently introduced implementation approach for sophisticated photonic structures is 3D nanoprinting using Direct Laser Writing (DLW), offering unique advantages for waveguides and metasurfaces. Here, novel on-chip hollow-core waveguides - so-called light cages - and metasurfaces with access to the additional height degree of freedom have been jointly demonstrated by the applicants.The proposed project targets to explore the generation, guidance and manipulation of light interacting with nanoprinted twisted photonic structures including light cages, chiral metasurfaces and their combination. The project aims to (i) understand the properties of light propagating inside twisted light cages and controlled via chiral metasurfaces, (ii) unlock the potential of DLW to realise twisted functional photonic structures, and (iii) to evaluate whether the combination of chiral metasurfaces and twisted light cages results in a novel photonic platform to reach previously inaccessible physics and applications. To give some examples, DLW principally enables light cages with exceptionally high twist rates and unexplored geometries. For metasurfaces, the height degree of freedom offers full control not only over geometric but also over the propagation phase and therefore the complex amplitude, and via sophisticated shapes also enables intrinsically chiral unit cells. Equally important for our work, DLW allows for direct implementation of metasurface-interfaced twisted light cages in a single fabrication step.Overall, the project will uncover novel physics concerning generation, guidance and manipulation of light interacting with twisted photonic structures. Potential applications that are evaluated within the context of this project will include chiral molecular on-chip sensing, OAM-assisted multiplexing or atomic magnetometry.