G. J. Lee

Resonant coupling of surface plasmons to radiation modes by use of dielectric gratings

Efficient outcoupling of surface-plasma waves to radiation modes by use of dielectric diffraction gratings on a flat metallic surface is discussed. The dielectric gratings, which have a surface-relief structure with only several tens of nanometers in peak-to-trough height on a flat metal surface, can efficiently extract radiation modes propagating in free space from the surface-plasmon modes. An outcoupling efficiency of 50% is estimated with the rigorous coupled-wave diffraction theory, and it is confirmed by the experiment.

Surface-plasmon photonic band gaps in dielectric gratings on a flat metal surface

Photonic band gaps created by Bragg scattering of the surface plasmon polaritons are observed from dielectric grating structures on a flat metal surface. Observation results that directly image the band gaps are confirmed by the well-known numerical calculation method of diffraction, the rigorous coupled-wave analysis method. A numerical model based on the plane wave expansion method is also developed for estimation of the surface-plasmon band-gap characteristics in our dielectric-on-metal system. Consistency among the results of the band structures obtained from the experiment and the two numerical methods is achieved.

Magneto-optical enhancement through gyrotropic gratings

Diffracted magneto-optical (MO) effects are numerically investigated for one-dimensional lossy gyrotropic gratings in the zeroth and the first orders for the polar magnetization by utilizing the rigorous coupled-wave approach implemented as an Airy-like internal-reflection series. The simulated Kerr spectra agree well with the experimental ones. The dependence of the MO Kerr enhancement on the grating depth in the first-order diffraction, compared with that in the zeroth one, is illustrated, and the diffracted MO Faraday effect is theoretically investigated as well. Such a MO enhancement through the gyrotropic gratings is superior to the conventional MO devices and magneto-photonic crystals. The potential applications are also suggested.

Arbitrary structuring of two-dimensional photonic crystals by use of phase-only Fourier gratings

The computer-generated holography technique is applied to the structuring of two-dimensional (2D) photonic crystals with inherently embedded arbitrary defects. The technique uses phase-only Fourier gratings as a generator of spot arrays in the focal plane, such that a single exposure produces a 2D array of focused spots with desired defects or modifications in the lattice structure. We demonstrate several types of large-area 2D lattice structures with square, hexagonal, or hybrid lattices embedded with point and (or) line defects. Scanning the Fourier plane in the depth direction throughout multiphoton polymerization media allows 3D lattices with stacked defect layers to be formed.

Photonic Band Gaps for Surface Plasmon Modes in Dielectric Gratings on a Flat Metal Surface

For dielectric gratings on a flat metal surface, photonic band gaps created by Brags scattering of surface plasmon polaritons are observed. The observation result that directly images this gap is compared with that predicted by a numerical model based on a plane wave expansion. Consistency between the experimental and numerical results is also confirmed by comparison with the well-known calculation method of diffraction, the rigorous coupled wave analysis method.

Diffracted magneto-optical Kerr effect in one-dimensional magnetic gratings

One-dimensional Co2MnSi magnetic gratings were fabricated with a significant ease by using the interference pattern of two femtosecond-laser beams which resulted in a selective-area annealing of the as-deposited Co2MnSi film. The longitudinal Kerr rotation of the negative first-order diffracted beam was nearly 30 times larger than that of the zeroth-order one in a sample fabricated with the optimal conditions. The enhancement strongly depends on the grating depth, which varies with the number of laser shots, confirming the theoretical result that the magneto-optical Kerr-effect enhancement is reduced as the grating depth increases.

Enhancement of magneto-optical properties of a magnetic grating

The magneto-optical properties of one-dimensional magnetic grating structure of Co2MnSi film were investigated. By using the interference pattern of two femtosecond laser beams, a selective-area annealing of as-deposited Co2MnSi film was achieved and one-dimensional magnetic grating structures were fabricated. The longitudinal Kerr rotations of the zeroth- and the first-order diffracted beams were measured. The longitudinal Kerr rotation of the first-order diffracted beam is nearly 18 times larger than that of the zeroth-order beam.

Subwavelength Focusing of Light From a Metallic Slit Surrounded by Grooves with Chirped Period

Extraordinary phenomena related to the transmission of light via metallic films with subwavelength holes and grooves are known to be due to resonant excitation and interference of surface waves. These waves make various surface structures to have optically effective responses. Further, a related study subject involves the control of light transmitted from a single hole or slit by surrounding it with diffractive structures. This paper reports on the effects of controlling light with a periodic groove structure with Fresnel-type chirping. In Fresnel-type chirping, diffracted surface waves are coherently converged into a focus, and it is designed considering the conditions of constructive interference and angular spectrum optimization under the assumption that the surface waves are composite diffracted evanescent waves with a well-defined in-plane wavenumber. The focusing ability of the chirped periodic structures is confirmed experimentally by two-beam attenuated total reflection coupling. Critical factors for achieving subwavelength foci and bounds on size of focal spots are discussed in terms of the simulation, which uses the FDTD algorithm.

Tunable Wavelength Filters Based on Long-Range Surface-Plasmon-Polariton waveguides

We design and fabricate a novel tunable wavelength filter, which utilizes long-range surface plasmon-polaritons excited along nm-thick-metal strips. A gold metal strip, with cm length, 20 nm thickness, and 5m width, is embedded in thick thermo-optic Polymer films supported by a silicon wafer. A dielectric Bragg grating structure is Placed on the metal strip, so that transmission signals at telecom wavelength are selected by thermal effect of the thermo-optic polymer. High extinction ratio of 25 dB and total insertion loss of 25 dB/cm can be measured by single-mode coupling of optical fibers. We also verify that wavelength tuning of the long-range surface plasmon-polariton filters can be achieved by electric current directly applied to the metal-strip waveguides.

Direct measurement of surface plasmon bandgaps in dielectric gratings on a flat metal surface

We have observed experimentally photonic band gap in dispersion curves of SPPs excited at a 1-D dielectric lattice structure on a flat metal surface. The observation result is compared with theoretical result by using of the well-known calculation method of diffraction, rigorous coupled wave analysis method.