Embedded metallic grating and photonic crystal based scanning probes for subwavelength near-field light confinement
Near-field light confinement on scanning probe is the backbone technology for near-field imaging with subwavelength resolution that overcomes the diffraction limit by exploiting the properties of evanescent waves. The fusion of the photonics and the latest nanofabrication technology creates emerging frontier for near-field light confinement research with new design approach. The propagation of light can now be controlled by periodical structure at subwavelength scale with low loss in the artificially synthesized dielectric material. New light propagation patterns can now be implemented in subwavelength structure, such as directional free space light focus grating coupler, photonic bandgap material like photonic crystal by permitting light propagation at certain wavelength while prohibiting light outside of bandgap, and nano-slot light resonator for increased light-matter interaction at nanometer scale. Advances in this research area will have tremendous impact on electromagnetic modeling and biomedical technology for probe based subwavelength optical detection. My doctoral research focused on investigating highly efficient, nanofabrication compatible directional light coupling structure and near-field subwavelength light focus through photonic crystal material. The distinct significance of this research was placed on exploitation of the embedded metallic grating coupler of high free space directivity and subwavelength light processing circuit of enhanced near-field transmission rate, the two most dominating basic elements of the scanning optical imaging system. First, I designed a compact elliptical grating coupler based on embedded noble metal such as gold or silver that efficiently interconnects free space with dielectric rectangular waveguide. The dense system integration capability shows the application potential for on-chip interfacing subwavelength light processing circuits and near-field fluorescent biosensors with far-field detection of superb radiation directivity and coupling efficiency. Second, a novel all-dielectric light confinement probe designed by slotted photonic crystal waveguide provides a light confinement mechanism on the lateral plane. The resonating nano-cavities and the λ/4 nano-slot are used to enlarge the light throughput while as the nano-slot waveguide provides single subwavelength center lobe. The impetus of this research is the growing interests by near-field imaging researchers to obtain a low loss visible light confinement probe designs through mass production.