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Optical micro-resonators have broad applications. They are used, for example, to enhance light���matter interactions in optical sensors or as model systems for investigating fundamental physical mechanisms in cavity quantum electrodynamics. Coupling two or more micro-cavities is particularly interesting as it enlarges the design freedom and the field of application. In this context, achieving tunability of the coupling strength and hence the inter-cavity gap is of utmost importance for adjusting the properties of the coupled micro-resonator system. In this paper, we report on a novel coupling approach that allows highly precise tuning of the coupling gap of polymeric micro-resonators that are fabricated side by side on a common substrate. We structure goblet-shaped whispering-gallery-mode resonators on an elastic silicone-based polymer substrate by direct laser writing. The silicone substrate is mechanically stretched in order to exploit the lateral shrinkage to reduce the coupling gap. Incorporating a laser dye into the micro-resonators transforms the cavities into micro-lasers that can be pumped optically. We have investigated the lasing emission by micro-photoluminescence spectroscopy, focusing on the spatial localization of the modes. Our results demonstrate the formation of photonic molecules consisting of two or even three resonators, for which the coupling strengths and hence the lasing performance can be precisely tuned. Flexibility and tunability are key elements in future photonics, making our approach interesting for various photonic applications. For instance, as our coupling approach can also be extended to larger cavity arrays, it might serve as a platform for tunable coupled-resonator optical waveguide devices.

Whispering gallery mode (WGM) resonators made from dielectrics like glass or polymers have outstanding optical properties like huge cavity quality (Q) factors which can be achieved on scales compatible with on-chip integration. However, tunability of these resonances is typically difficult to achieve or not suitable for robust device applications. We report here on the fabrication of polymeric micro-goblet WGM resonators with an optically controlled and stable reversible tunability over a large spectral range. This tunability is achieved by integration of photo-responsive liquid crystalline elastomers (LCEs) into micro-goblet cavities. The optical response of the elastomer allows reshaping the goblet by employing low pump power, leading to a fully reversible tuning of the modes. The structure can be realistically implemented in on-chip devices, combining the ultra-high Q factors, typical of WGM resonators, with reliable, optical tunability. This result serves as an example of how light can control light, by invoking a physical reshaping of the structure. This way of optical tuning creates interesting possibilities for all-optical control in circuits, enabling interaction between signal and control beams and the realization of self-tuning cavities.

The research area of photonics deals with all kinds of optical systems used for the generation, manipulation, detection, etc. of signals of light. To be able to compete with modern-day electronics, these systems need to be fabricated from cheap materials on a chip scale using scalable processes. This work introduces a novel all-polymeric and chip-scale platform for such photonic devices. The optical functionality of these devices is based on whispering gallery modes. Additionally, a tunability of at least one optical key characteristic of these systems is aimed for. To achieve this objective, a flexible elastomer that responds to various external stimuli (like heat or illumination) has been incorporated into the all-polymeric building blocks. Thus, certain optical characteristics of these devices can be reversibly controlled via a change of their geometrical properties. The present work deals with the design, fabrication, and characterization of these tunable and all-polymeric photonic systems. At first, the fundamental concept of whispering gallery modes as well as their investigation using fiber-transmission spectroscopy are recapitulated. Afterwards, several novel and scalable fabrication processes of all-polymeric tunable photonic systems are introduced. Finally, two exemplary devices are presented and the tunability of their optical key features is demonstrated in detail.

Perovskite solar cells are the new hope of next-generation photovoltaic concepts for sustainable energy generation. Regarding their favorable optoelectronic properties, bound electron-hole pairs (so-called excitons) play a significant role and are thoroughly investigated utilizing various spectroscopic methods. Moreover, bandgap instabilities caused by segregation effects in mixed perovskites are analyzed in detail using electroreflectance spectroscopy and structural characterization techniques.