title: Radiation engineering of optical antennas for maximum field enhancement.
abstract: Optical antennas have generated much interest in recent years due to their ability to focus optical energy beyond the diffraction limit, benefiting a broad range of applications such as sensitive photodetection, magnetic storage, and surface-enhanced Raman spectroscopy. To achieve the maximum field enhancement for an optical antenna, parameters such as the antenna dimensions, loading conditions, and coupling efficiency have been previously studied. Here, we present a framework, based on coupled-mode theory, to achieve maximum field enhancement in optical antennas through optimization of optical antennas' radiation characteristics. We demonstrate that the optimum condition is achieved when the radiation quality factor (Q(rad)) of optical antennas is matched to their absorption quality factor (Q(abs)). We achieve this condition experimentally by fabricating the optical antennas on a dielectric (SiO(2)) coated ground plane (metal substrate) and controlling the antenna radiation through optimizing the dielectric thickness. The dielectric thickness at which the matching condition occurs is approximately half of the quarter-wavelength thickness, typically used to achieve constructive interference, and leads to ∼20% higher field enhancement relative to a quarter-wavelength thick dielectric layer.
authors.affiliation: Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, California 94720, United States.
authors.forename: Tae Joon
authors.initials: TJ
authors.lastname: Seok
authors.forename: Arash
authors.initials: A
authors.lastname: Jamshidi
authors.forename: Myungki
authors.initials: M
authors.lastname: Kim
authors.forename: Scott
authors.initials: S
authors.lastname: Dhuey
authors.forename: Amit
authors.initials: A
authors.lastname: Lakhani
authors.forename: Hyuck
authors.initials: H
authors.lastname: Choo
authors.forename: Peter James
authors.initials: PJ
authors.lastname: Schuck
authors.forename: Stefano
authors.initials: S
authors.lastname: Cabrini
authors.forename: Adam M
authors.initials: AM
authors.lastname: Schwartzberg
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Bokor
authors.forename: Eli
authors.initials: E
authors.lastname: Yablonovitch
authors.forename: Ming C
authors.initials: MC
authors.lastname: Wu
mesh_terms: D049329:Nanostructures / Q000737:chemistry; D036103:Nanotechnology; D055095:Optics and Photonics; D010316:Particle Size; D012822:Silicon Dioxide / Q000737:chemistry; D013499:Surface Properties
chemical_list: D012822:Silicon Dioxide