Jaewoong Yoon

Critical coupling in dissipative surface-plasmon resonators with multiple ports

We theoretically investigate resonant absorption in a multiple-port surface-plasmon polaritons (SPP) resonator near the condition of critical coupling at which internal loss is comparable to radiation coupling. We show that total absorption is obtainable in a multiple-port system by properly configuring multiple coherent lightwaves at the condition of critical coupling. We further derive analytic expressions for the partial absorbance at each port, the total absorbance, and their sum rule, which provide a non-perturbing method to probe coupling characteristics of highly localized optical modes. Rigorous simulation results modeling a surface-plasmon resonance grating in the multiple-order diffraction regime show excellent agreements with the analytic expressions.

Mapping Surface-Plasmon Polaritons and Cavity Modes in Extraordinary Optical Transmission

Transmission of light through periodic metal films with intensity considerably exceeding that predicted by aperture theory is referred to as extraordinary optical transmission (EOT). The mechanisms responsible for this effect have been investigated intensively during the past decade. Here, we show an elegant method of visualizing the operative physical mechanisms for model resonance systems. By numerically mapping the resonance loci, modal and plasmonic mechanisms emerge clearly with delineated regions of dominance. Thus, the photonic transmission resonances are parametrically correlated with localized electromagnetic fields forming pure surface-plasmon polaritons (SPPs), coexisting plasmonic and cavity-mode (CM) states, and pure CMs. This mapping method renders a consistent picture of the transitions between photonic states in terms of key parameters. It shows how the TM1 CM seamlessly morphs into the odd SPP mode as the film thickness diminishes. Similarly, the TM0 mode converts to the even SPP mode. At the intersection of these mode curves, an EOT-free gap forms due to their interaction. On account of a reflection phase shift of a slit-guided mode, an abrupt transition of the resonance loci in the SPP/CM region is observed.

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.

Extraction efficiency of highly confined surface plasmon-polaritons to far-field radiation: an upper limit

We propose a unique method determining an upper limit of extraction efficiency of the surface plasmon-polaritons (SPPs), E(SP), which are highly confined on a corrugated metal surface. The method is based on measurement of the spectral bandwidth of a grating-induced absorption spectrum as a function of metal dielectric constant. After finding the fact that E(SP) exhibits an extremely linear relationship with the collision frequency Gamma of metal over a SPP band below the surface plasmon frequency, an upper limit of E(SP) can be determined by an asymptotic estimation as Gamma-->0 for total decay rates of the confined SPPs. Our method based on the bandwidth measurement is inherently free from the ambiguity and underestimation difficulties pertaining to the previous prism-coupling approaches for E(SP) estimation. It will also be quite applicable for evaluating SPP-mediated light-emitting diodes (LEDs) of which total external efficiency is dominantly restricted by the upper limit of E(SP). Especially for the case when SPP excitation probability approaches unity, the proposed method would excellently figure out the maximum realizable external efficiency of SPP-mediated LEDs.

Leaky-mode resonance photonics: an applications platform

Resonant leaky modes can be induced on dielectric, semiconductor, and metallic periodic layers patterned in one or two dimensions. In this paper, we summarize their physical basis and present their applicability in photonic devices and systems. The fundamental amplitude and phase response of this device class is presented by computed examples for TE and TM polarizations for lightly and heavily spatially modulated gratings. A summary of potential applications is provided followed by discussion of representative examples. In particular, we present a resonant polarizer enabled by a single periodic silicon layer operating across 200-nm bandwidth at normal incidence. Guided-mode resonance (GMR) biosensor technology is presented in which the dual-polarization capability of the fundamental resonance effect is applied to determine two unknowns in a biodetection experiment. In principle, using polarization and modal diversity, simultaneously collected data sets can be used to determine several relevant parameters in each channel of the sensor system; these results exemplify this unique capability of GMR sensor technology. Applying the GMR phase, we show an example of a half-wave retarder design operating across a 50-nm bandwidth at λ~1550 nm. Experimental results using a metal/dielectric design show that surface-plasmon resonance and leaky-mode resonance can coexist in the same device; the experimental results fit well with theoretical simulations.

Long-range surface plasmon polaritons on asymmetric double-electrode structures

An asymmetric double-electrode structure composed of metal strips separated by a dielectric core layer, all on a metal slab, is proposed as a long-range surface plasmon-polariton (LR-SPP) waveguide. LR-SPP modes on asymmetric structures, including straight, S-bended, and Y-branched strips, are found by far-field measurement to be consistent with theoretical estimates. The proposed structure is inherently free from a symmetry requirement on dielectric constants between the core and cladding materials, therefore, an asymmetric double-electrode waveguide which substitutes a nonlinear medium or biofluid for the core dielectric may be essential to realization of SPP nonlinear devices or biosensors in a long-range manner.

Guided-mode resonant coherent light absorbers.

We present a new class of coherent perfect absorbers based on guided-mode resonance in thin semiconductor films. Using particle-swarm optimization methods, we design a thin-film amorphous silicon grating that maximizes coherent modulation of the absorbance. The optimized device exhibits a maximum scattering power of ∼94% and a power absorption limit approaching 100% at the 1550-nm wavelength.

Experimental observation of leaky modes and plasmons in a hybrid resonance element

We provide experimental evidence of a hybrid photonic device supporting simultaneously surface-plasmon polaritons and resonant leaky modes. A fabricated metallo-dielectric structure exhibits a pronounced plasmonic resonance at 799u2009nm wavelength and a modal resonance at 669u2009nm in transverse magnetic polarization. In transverse electric polarization, a weak modal resonance appears at 725u2009nm wavelength. We identify the corresponding modes by computing the attendant internal field distributions. Numerically computed spectra are in good agreement with our measurements. Since traditional modal and plasmonic devices find many uses, their hybrid versions may enable the extension of their applicability.

Flat-top surface plasmon-polariton modes guided by double-electrode structures

We characterize the frequency dependence of symmetrically-coupled long-range surface plasmon-polaritons (sc-LRSPPs) excited on double-electrode slab waveguides composed of five layers of insulator(I) and metal(M) stacked in order of IMIMI. When the core insulator has a refractive-index larger than the cladding ones, there is no cut-off core-thickness(D) for sc-LRSPP modes in all frequency range likely for modes in a conventional dielectric slab waveguide. At a specific frequency of ωc which depends on the index difference of insulator layers and the thickness of metal, the sc-LRSPP modes are non-dispersive at all for change in D. Furthermore, regardless of D alteration, the modes at ω = ω(c) consistently maintain a perfect flat-top profile in the core region and identical decay tails in the cladding. The sc-LRSPP modes with these prominent characteristics may excite an active medium sandwiched in between the metal layers very uniformly, therefore it will be interesting to implement such a non-dispersive flat-top mode for nonlinear applications of SPP waveguides.

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.