Design and use of guided mode resonance filters for refractive index sensing

摘要

This Ph.D. thesis is concerned with the design and use of guided mode resonance filters (GMRF) for applications in refractive index sensing. GMRFs are optical nanostructures capable of efficiently and resonantly reflecting a narrow wavelength interval of incident broad band light. They combine a diffractive element with a waveguiding element, and it is the coupling between diffracted light and quasi guided modes that gives rise to the resonant response.The linewidth of the resonance can be tuned by the material and geometrical configuration of the device. The resonance wavelength is highly sensitive to changes in refractive index that occur within the region overlapped by the quasi guided mode, and GMRFs are thus well suited for optical sensing and tunable filter applications. They produce a polarization dependent response and can be optically characterized in both reflection and transmission.The structures investigated in this thesis were fabricated in a process based on nanoreplication, in which the surface of a polymer was patterned with a structured master, cured with ultra-violet light and coated with a high refractive index material. The masters were defined using electron beam lithography, a lift-off process, and reactive ion etching. After an introduction to the history and principles of GMRFs, the thesis describes the state-of-the-art of relevant research in the field, covers the necessary theoretical background required to understand their operation, and discusses the fabrication and characterization methods used. The thesis furthermore includes three journal articles. The first concerns an iterative computational model for the analytical prediction of the wavelengths at which resonances will occur, which is beneficial for e.g. device sensitivity optimization. The second paper discusses an all-polymer GMRF, which exhibits narrow resonance linewidths and a low detection limit, made by rapid and inexpensive fabrication methods. The third paper presents a novel method for measuring the refractive index dispersion of liquids using an array of GMRFs of different periods.