Theoretical And Experimental Study Of Angle-insensitive Plasmonic Colour Filters

Surface plasmon polaritons (SPPs) has been the focus in various fields due to its extraordinary ability to manipulate light beyond the optical diffraction limit. As one of its promising applications in image sensors, displays, digital photography, and projectors, SP-based plasmonic colour filters featured by metallic periodic nanostructures have been considerably studied owing to their distinct merits, e.g., durable under high temperature and ultraviolet radiation, ease of fabrication, and high resolution over conventional colour filters, which generally consist of chemical pigments or dyes. Despite these advantages of plasmonic colour filters, several issues such as transmission, colour pureness, polarization dependency, angle sensitiveness, cost effectiveness and ease of large scale fabrication have to be dealt properly in order to bring them into commercial applications. As an effort of this thesis, with the understanding of the theory of surface plasmon polaritons, we designed and studied novel nanostructures through both finite difference time domain simulation and nanofabrication methods, aiming to improve the overall performance of plasmonic colour filters.Firstly, we carried out a systematical study on the effect of duty cycle on the spectral performance in one-dimensional Ag grating nanostructure deposited on a glass substrate with different film thicknesses and periods. It is revealed in the simulation that the transmission minimum could be tuned within a limited wavelength range by varying the duty cycle, since too large or too small duty cycle are detrimental for the transmission spectrum and therefore the colour pureness. The optical measurements of experimentally fabricated samples validate our simulation. Furthermore, investigation of localized surface plasmon resonance (LSPR) and propagation surface plasmon resonance (PSPR) indicates that LSPR played a major role in tuning the colour, and the effects of PSPR will degrade the optical performance of the grating as colour filters when duty cycle is large enough to excite it with a high probability. This work provided guidance to designing duty cycle of metallic nanostructures for plasmonic colour filters.Secondly, based on the facts that plasmonic colour filters using periodic metallic nanostructures are intrinsically sensitive to incident angles as a result of momentum matching conditions supported by diffraction in periodic nanostructures, we reported an angle-insensitive plasmonic colour filter that consists of two-dimensional randomly distributed ultrathin silver nanodisks (40 nm, thicker than the skin depth of silver film in the visible regime) on a glass substrate. Through structural periodicity elimination, the proposed plasmonic color filter works via LSPR and thus enables both polarization independence and excellent angle-insensitive (up to 60°) performance. By optimizing structural parameters, randomly and nearly uniformly distributed nanodisks were produced and uncoupled LSPR between nanodisks were guaranteed, which is crucial for the reproducibility and stability of the color filter. In addition, a palette of colors across the visible region was obtained with the proposed color filters by simply varying the diameter of nanodisks, exhibiting a promising and robust applicability in digital imaging and sensing industries.Finally, the thesis works were summarized and future works were expected.