2014

Hiltunen, Marianne

Slot waveguide is a specific light-guiding structure with a property to enhance the optical field in a nanometer scale void of low refractive index (RI) material embedded between higher RI material rails. Typically, slot waveguides have been fabricated from high refractive index inorganic dielectrics or semiconductors, such as silicon or silicon nitride, and they operate in the near infrared (NIR) wavelength region. The slot waveguide structure enables strong light-ambient interaction, a property that is preferred, for instance, in integrated optical sensors utilizing the change of the refractive index as the sensing transduction signal. In this thesis; the characteristic properties of slot waveguides were studied as regards their usage in polymer platforms. The polymers are transparent in the visible and NIR wavelength region. In this work, the operation of the polymer slot waveguide was demonstrated for both visible and NIR wavelengths by using Young interferometer devices. For the device fabrication, the ultraviolet (UV) assisted nanoimprint moulding method was utilized. The emphasis was to demonstrate that the high performance slot waveguide sensor configuration is attainable with a simple low-cost fabrication method, enabling usage as disposable sensors. The bulk refractive index (RI) response of the slot waveguide-based Young interferometer was characterized with glucose - deionized water solutions. With this arrangement, an ambient RI change of 6.4*10-6 was measured. In the slot Young interferometer structure, both waveguide arms of the interferometer detect the bulk RI changes of the ambient material. This novel structure was proved to effectively compensate for thermo-optic originated response drift while maintaining high sensitivity against bulk RI change.