Nano-photonic signal processing structures
Waveguide and scattering structures with features which are small relative to the wavelength offer opportunities for compact optical signal processing, as would be important in imaging, sensing, and communication. Irregular structures comprised of conductors and/or dielectrics have a large number of degrees of freedom and can be designed to achieve near-field transformations. At optical frequencies, metal-insulator structures provide waveguide opportunities for small-scale photonic components, field enhancement, important in spectroscopy, enhanced coupling through apertures, and optical waveguides. A multi-resolution technique is used to synthesize two-dimensional irregular diffractive elements having dimension of only several wavelengths. A direct binary search procedure is used to achieve subwavelength near-field focusing, power splitting, wave length division multiplexing, and polarization beam splitting. Surface-enhanced Raman scattering, which occurs in small recessed metallic-walled structures, is studied by numerical simulation and explained using an analytical propagating waveguide mode model which appears to describe the basic physics. The increase in the Raman dipole moment is due to an enhanced field, which is shown to occur because of resonance in a waveguide mode. Enhanced transmission through a small slots or circular apertures in conducting films is studied. Using an analytic model, the transmission characteristics are described and low loss propagation in specific wavelength regions is shown. A metallic nanoparticle chain with resonant gaps is shown to be a good waveguide. The influence of geometry and material properties is demonstrated.
Webb, Purdue University.
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