arXiv subjects

Oliver Kuster

Publications and source records attributed to Oliver Kuster.

5 recordsLinked to original sources

arXiv2026

Fabrication-Aware Inverse Design of Nanophotonic Devices for 3D Laser-Nanoprinting

Advances in 3D laser-nanoprinting enable us to fabricate 3D nanophotonic devices with a wide range of functionalities on demand. By exploiting all three spatial dimensions, an enormous design space becomes available for these nanophotonic devices. However, such an immense design space is impossible to explore efficiently by intuition alone, especially when designing free-form nanophotonic devices. Density- based topology optimization offers a natural tool for 3D nanophotonic design by allowing the efficient design of devices with millions of degrees of freedom. Traditional density-based topology optimization relies on heuristic measures to account for limitations imposed by the fabrication method. Indeed, the fabrication method is rarely considered as part of the forward model in the design pipeline. In this work, we introduce an inverse design method that explicitly models the direct-laser-writing process used in 3D nanoprinting. Incorporating a differentiable formulation of the direct-laser-writing model allows us to design 3D nanophotonic devices within the experimentally available design space and to precompensate for fabrication-specific effects. Optimizing inside the experimentally available design space ensures that the constraints we put on the optimization are given by our parametrization of the fabrication method and not by heuristic methods, which might over- or underconstrain the optimization problem. Furthermore, modeling the 3D laser-nanoprinting process explicitly allows us to not only take fabrication-specific effects, such as the proximity effect, into account but also enables the optimization to actively make use of these fabrication-specific effects to increase the functionality of the device.

physics.optics↗

arXiv2025

Gradient-based optimization of scatterer arrangements based on the T-matrix method

The demand for inverse design is increasing as the ability to fabricate sub-10 nm features expands the design space by orders of magnitude. Efficient inverse design benefits from differentiable models of light-structure interaction. While traditional full-wave solvers based on finite differences, finite elements, or Fourier modal methods have already been presented for that purpose, a dedicated tool adapted for performing multiple scattering simulations is still lacking. To overcome this limitation, we provide a multiple-scattering framework compatible to automatic differentiation, suitable for treating periodic and non-periodic arrangements of scatterers. It yields exact gradients regarding geometric and positional parameters in finite clusters and infinite metasurfaces. In this work, we use spheres as the elementary building blocks to demonstrate the framework's capabilities as a standalone tool. However, the framework is adaptable to arbitrarily shaped scatterers, provided the individual T-matrices are calculated using differentiable full-wave Maxwell solvers. Since the gradients are obtained simultaneously in a single backward pass, the framework is well-suited for moderately dimensional problems. It is also possible to combine multiple performance goals into a single objective function. The versatility of our method is illustrated in proof-of-concept examples that focus on various aspects of Kerker-type physics. In the first example, a finite cluster of scatterers is optimized in order to reach a high forward-to-backward scattering ratio, and we show experimental feasibility of the designs. In the second example, a metasurface made from multiple scatterers in each unit cell is designed to maximize the reflectance contrast between orthogonal linear polarizations of the incident light. We make the framework publicly available at https://github.com/tfp-photonics/dreams.

physics.optics↗

arXiv2025

A three-dimensional polarization-insensitive grating coupler tailored for 3D nanoprinting

Efficiently coupling light from optical fibers into photonic integrated circuits is a key step toward practical photonic devices. While a notable coupling can be achieved by out of plane couplers such as grating couplers, their basic planar geometry typically tends to be sensitive to the polarization of light. This is partly due to the fact that the design spaces of such grating structures typically fabricated with techniques such as electron beam lithography are only two dimensional with a simple extrusion into the vertical dimension. This makes it challenging to optimize for both polarizations simultaneously, as performance typically degrades when trying to achieve high efficiency in both. As a result, conventional approaches either suffer from increased losses or require additional filtering components to account for different polarizations. In this work, we present a fully three dimensional, polarization insensitive grating coupler which has a highly efficient simulated coupling efficiency of over 80% in both polarizations. This performance matches that of state of the art couplers that are performant for one polarization only. This comes at the cost of a moderately larger size due to the lower refractive index materials typically available in 3D nanoprinting. Our design method uses density based topology optimization with a multi objective approach that combines electromagnetic simulations with a fictitious heat conduction model acting as a soft constraint to promote structural integrity. This ensures that the designed structures are feasible for fabrication. Our work opens new possibilities for robust 3D photonic devices, enabling advanced integration, fabrication, and applications across next generation photonics and electronics.

physics.optics↗

arXiv2025

Inverse Design of 3D Nanophotonic Devices with Structural Integrity Using Auxiliary Thermal Solvers

3D additive manufacturing enables the fabrication of nanophotonic structures with subwavelength features that control light across macroscopic scales. Gradient-based optimization offers an efficient approach to design these complex and non-intuitive structures. However, expanding this methodology from 2D to 3D introduces complexities, such as the need for structural integrity and connectivity. This work introduces a multi-objective optimization method to address these challenges in 3D nanophotonic designs. Our method combines electromagnetic simulations with an auxiliary heat-diffusion solver to ensure continuous material and void connectivity. By modeling material regions as heat sources and boundaries as heat sinks, we optimize the structure to minimize the total temperature, thereby penalizing disconnected regions that cannot dissipate thermal loads. Alongside the optical response, this heat metric becomes part of our objective function. We demonstrate the utility of our algorithm by designing two 3D nanophotonic devices. The first is a focusing element. The second is a waveguide junction, which connects two incoming waveguides for two different wavelengths into two outgoing waveguides, which are rotated by 90{\deg} to the incoming waveguides. Our approach offers a design pipeline that generates digital blueprints for fabricable nanophotonic materials, paving the way for practical 3D nanoprinting applications.

physics.optics↗

arXiv2024

Inverse Design of Polaritonic Devices

Polaritons, arising from the strong coupling between excitons and photons within microcavities, hold promise for optoelectronic and all-optical devices. They have found applications in various domains, including low-threshold lasers and quantum information processing. To realize complex functionalities, non-intuitive designs for polaritonic devices are required. In this contribution, we use finite-difference time-domain simulations of the dissipative Gross-Pitaevskii equation, written in a differentiable manner, and combine it with an adjoint formulation. Such a method allows us to use topology optimization to engineer the potential landscape experienced by polariton condensates to tailor its characteristics on demand. The potential directly translates to a blueprint for a functional device, and various fabrication and optical control techniques can experimentally realize it. We inverse-design a selection of polaritonic devices, i.e., a structure that spatially shapes the polaritons into a flat-top distribution, a metalens that focuses a polariton, and a nonlinearly activated isolator. The functionalities are preserved when employing realistic fabrication constraints such as minimum feature size and discretization of the potential. Our results demonstrate the utility of inverse design techniques for polaritonic devices, providing a stepping stone toward future research in optimizing systems with complex light-matter interactions.

physics.optics↗