Invited Paper
Metal Optics for Nanophotonics Applications

This paper presents recent research results that emphasize use of metals to achieve (1) optical field localization to increase the interaction cross section with biomolecules for biomedical sensing for healthcare and (2) the most compact footprint for photonic light emitters and nanolasers for on chip communications. As specific example of our most recent research in optical field localization for biomedical sensing, we present nanoscale engineered optical field localization nanostructures that super-localize the incident electromagnetic field to “hotspots” with a spatial full width at half maximum (FWHM) area of 2 nm² and a local field enhancement of 200-400. The nanostructure exhibits field localization in a very large spectral range in the near infrared with a spectral FWHM bandwidth ≥900 nm. Furthermore, it is possible to introduce defects into its circular symmetry to tailor its polarization response and allow for selective excitation to achieve reconfigurable hotspots.

For construction of compact nanolasers and light emitters we incorporate metals to reduce the size of the resonator in all 3-D. The modes in such 3-D cavities can be grouped into two main categories: (i) surface bound (that is, surface plasmon polariton (SPP)) resonant modes and (ii) conventional resonant modes within the metal cavity. Although highly confined, the plasmonic modes are lossy and the lasing gain threshold for such cavities can be very large. However, the negative permittivity of metals enables them to act as efficient mirrors, leading to the second class of metallo-dielectric cavity modes, which can be viewed as lossy approximations of the modes in a perfectly conducting metal resonator. In this type of cavity it is possible to achieve higher Q factors and lower lasing gain thresholds, albeit at the expense of reduced mode confinement. Specifically, we describe two types of metal-dielectric 3-D resonators: (a) a composite metal-dielectric-semiconductor cavity where the low index dielectric acts as a shield to reduce the loss into the metal and (b) a coaxial resonator that supports a TEM-like mode which has no cut-off and the physical size of the cavity can be infinitely scaled down in lateral dimensions.

fainman@ece.ucsd.edu