Electrical Multi-wavelength Control in Chiral Liquid Crystal Elastomers for Tunable Photonic Applications

Abstract

Periodic arrangement of nanoscale dielectric structures generates a photonic bandgap that blocks certain light wavelengths, resulting in structural color when reflected wavelengths are within the visible spectrum. Particularly, soft material- based structural-colored materials with stimuli-responsive characteristics have attracted significant research interest due to their potential for maximizing wavelength tunability. Among these materials, chiral liquid crystal elastomers are distinguished by their vibrant structural colors, broad wavelength tuning range, and simple fabrication through self-assembled periodic helical structures. By altering this periodic helical structure, the wavelength position of the structural color can be precisely adjusted. These stimuli-responsive materials are promising for reconfigurable photonic elements in applications such as information displays, tunable filters, biomedical sensors, and photonic skins. However, despite numerous previous research efforts, there are still many technical breakthroughs required for practical device applications including impractical triggering methods, low degree of freedom in wavelength tuning, and limitations to single-color tuning. In this thesis, key technologies to enhance the practicality and functionality of wavelength-tunable photonic elements based on structural-colored materials are studied. Firstly, an electrical wavelength control method was developed by integrating electroactive soft actuators with structural-colored materials to enhance compatibility with existing electro-optical devices. Secondly, to increase the degree of freedom in wavelength tunability, multi-modal soft actuators were developed, enabling bidirectional wavelength tuning in both longer and shorter wavelength directions. Thirdly, to achieve comprehensive capabilities beyond single-color tuning, a method for simultaneous multi-color control was proposed through the heterogeneous materials design. These technical breakthroughs are expected to significantly enhance the functionality of existing wavelength-tunable structural color-based photonic devices and can be applied as key technologies for utilizing structural-colored materials in more practical photonic applications.