Plasmonic Color Filters for Industrial Applications

Abstract

Light can strongly interact with metallic nanostructures, leading to resonant excitation of the confined electrons. This results in a strong near-field enhancement with subwavelength confinement. The resonance condition can be controlled by the material, shape and surrounding of the metal nanostructures. Thus, this so-called field of plasmonics holds great potential for applications in photonics. Besides biosensing, novel applications are scarce though, not only due to challenges in the up-scaling process, but also because of expense of material, design complexity and sensitivity of the structures in ambient conditions. Furthermore, intrinsic losses impede the implementation compared to competing alternatives. This thesis describes the development and realization of color filters based on plasmonic structures. The structures are tailored for intriguing applications and their large-scale manufacturing. Specifically the variability of plasmonic color filters is exploited and applied. This precisely controllable change of color appearance can be essential for applications such as optical security or imaging systems, for which first realizations are presented here. In particular, color filters are investigated, which strongly change their optical appearance with the angle of incidence. Additionally, a given color is only visible from one tilt direction. This unique feature makes these color filters highly attractive for optical security applications. Further, the high sensitivity to the surrounding material can be utilized; a position dependent modification of the color filters can be achieved by inkjet printing of transparent inks with different refractive indices. Additionally, a different set of plasmonic color filters are studied, which can be precisely controlled with the incident polarization while having almost angle-independent optical properties. This renders them ideal for camera filters, where a large-field-of-view is desired. By controlling the optical properties of the filters, a plasmonic multispectral imaging device is demonstrated. Overall, the used fabrication methods and materials are compatible with large-scale and cost-efficient manufacturing methods. Thus this thesis may help paving the way for everyday products based on plasmonics.