Uncovering the role of cladding complexity by understanding light scattering for improved hollow core waveguide functionality

• Applicant: Professor Dr. Markus A. Schmidt
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: since 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 315131181

Hollow-core waveguides (HCWs) are at the forefront of photonics research and offer distinct advantages over their solid-core counterparts. Significant progress has been made in hollow-core fibers (HCFs), particularly in telecommunications, while the portfolio of HCWs in on-chip photonics is much smaller. Guiding light in HCWs generally requires complex microstructured claddings to compensate for the lack of total internal reflection. Currently, understanding HCW-guidance relies heavily on mode calculations, which are critical for complex microstructured claddings due to excessive simulation times and inability to specifically reveal cladding characteristics. In planar photonics, extensive research has been directed towards the analysis of scattering processes in nano- and micro-structured media, allowing desirable tuning of transmission and reflection properties. In the preceding project, a mathematical model was introduced that links the modal properties of HCWs to the scattering properties of the cladding. One unique aspect of the model is the independence of the cladding transmission calculations from the core mode, making it possible to understand and optimize light guidance in HCWs from a light scattering perspective, which has received very little attention to date. Based on these aspects, this project investigates how light guidance in HCWs can be understood from the perspective of the light scattering properties of the cladding, thus linking planar photonics with HCWs. Using the aforementioned mathematical model, the properties of HCW cladding will be studied and optimized without considering the core, allowing (i) to investigate the specific properties of the cladding, (ii) to optimize the cladding properties via computational optimization, and (iii) to transfer well-established nano- and microphotonic effects to HCWs. Two waveguide platforms - nanoprinted light cages and HCFs - will be used to enable (i) large-scale parameter sweeps, (ii) unconventional cladding geometries, and (iii) potentially ultra-low-loss waveguiding. One focus is to optimise HCWs and in particular light cage for the mid-IR to investigate their potential for spectroscopic applications. In summary, this research-oriented project will explore HCWs from new and previously unconsidered perspectives using an unconventional approach. It will uncover unexplored physical principles and enable computational optimisation that could lead to innovative HCWs with tailored properties for various applications in telecommunications, life sciences or quantum technology.

• DFG Programme: Research Grants
• International Connection: Australia
• Cooperation Partner: Professor Dr. Christopher Poulton