Directional emission of white light via selective amplification of photon recycling and Bayesian optimization of multi-layer thin films

Abstract

Over the last decades, light-emitting diodes (LED) have replaced common light bulbs in almost every application, from flashlights in smartphones to automotive headlights. Illuminating nightly streets requires LEDs to emit a light spectrum that is perceived as pure white by the human eye. The power associated with such a white light spectrum is not only distributed over the contributing wavelengths but also over the angles of vision. For many applications, the usable light rays are required to exit the LED in forward direction, namely under small angles to the perpendicular. In this work, we demonstrate that a specifically designed multi-layer thin film on top of a white LED increases the power of pure white light emitted in forward direction. Therefore, the deduced multi-objective optimization problem is reformulated via a real-valued physics-guided objective function that represents the hierarchical structure of our engineering problem. Variants of Bayesian optimization are employed to maximize this non-deterministic objective function based on ray tracing simulations. Eventually, the investigation of optical properties of suitable multi-layer thin films allowed to identify the mechanism behind the increased directionality of white light: angle and wavelength selective filtering causes the multi-layer thin film to play ping pong with rays of light.

Merging automatic differentiation and the adjoint method for photonic inverse design

“…Consequently, most optimization algorithms can be categorized as either global or local optimization. Global optimization techniques for photonic optimization include evolutionary algorithms [2] and Bayesian optimization techniques [3,4]. Although global optima are typically preferred over local optima, these algorithms face significant limitations in terms of their applicability and scalability.…”

Investigation of inverse design of multilayer thin-films with conditional invertible neural networks

“…Application examples are vertical-cavity surface-emitting lasers [14,15], anti-reflection coatings [16] and wavelength demultiplexers [17]. Recently, they were successfully employed to enhance the directionality of a white LED while maintaining the desired color temperature [18]. Designing multilayer thin-films [19][20][21] has long been a task in the nanophotonics community, and sophisticated techniques have been developed to synthesize thin-films that exhibit the desired optical properties, as the problem becomes computationally intractable when using simple combinatorics, since the number of possible thin-film designs scales exponentially with the number of layers.…”

Bayesian optimisation for efficient material discovery: a mini review

“…4 BO has been successfully applied to many materials science problems. Some recent applications include drug design, 7,8 lithium-ion battery optimisation, 9,10 optical material design, [11][12][13] optimisation of thermoelectric properties 14 and energy predictions of materials. 15,16 It has also been applied to optimise operational conditions such as heating conditions 17 and equipment configurations.…”