Sang Soon Oh

Line-defect-induced bending and splitting of self-collimated beams in two-dimensional photonic crystals

We show that line defects can give rise to the bending and splitting of self-collimated beams in two-dimensional photonic crystals from the equifrequency contour calculations and the finite-difference time-domain simulations. The power ratio between two split self-collimated beams can be controlled systematically by varying the radii of rods or holes in the line defect. We also show that the bending and controllable splitting of self-collimated beams can be useful in steering the flow of light in photonic crystal integrated light circuits.

Tunable 3D Extended Self‐Assembled Gold Metamaterials with Enhanced Light Transmission

The optical properties of metamaterials made by block copolymer self-assembly are tuned by structural and environmental variations. The plasma frequency red-shifts with increasing lattice constant and blue-shifts as the network filling fraction increases. Infiltration with dielectric liquids leads also to a red-shift of the plasma edge. A 300 nm-thick slab of gyroid-structured gold has a remarkable transmission of 20%.

On the Origin of Chirality in Nanoplasmonic Gyroid Metamaterials

Metallic single gyroids, a new class of self-assembled nanoplasmonic metamaterials, are analyzed on the basis of a tri-helical metamaterial model. The physical mechanisms underlying the chiral optical behavior of the nanoplasmonic single gyroid are identified and it is shown that the optical chirality in this metallic structure is primarily determined by structural chirality and the connectivity of helices along the main cubic axes.

Two-Dimensional TiO2 Inverse Opal with a Closed Top Surface Structure for Enhanced Light Extraction from Polymer Light-Emitting Diodes

The authors thank Prof. H. Y. Park, Korea Advanced Institute of Science and Technology, and Dr. C.-S. Kee, Advanced Photonics Research Institute, for assistance with the FDTD simulations. This work was supported by an ERC grant of the National Research Foundation of Korea NRF) funded by the Korea Ministry of Education, Science and Technology (MEST) (No. R11–2007-045–01002-0(2009)).

Duplexer using microwave photonic band gap structure

We propose a frequency selective duplexer using microwave photonic band gap (PBG) structures. It uses two different PBGs to control the propagation of electromagnetic waves in the microwave region. In this structure, an additional narrow reflection band appears in the transmission spectrum when the PBG structure is not properly located relative to the T junction. By considering multiple reflections, it is proved that this additional reflection band in each PBG structure results from the interference between the input wave and the reflected wave from the other PBG structure. An effective way to prevent this interference effect is also discussed.

A tri-helical model for nanoplasmonic gyroid metamaterials

Metallic gyroid metamaterials are formed by a combination of nanoplasmonic helices leading to unique and complex optical characteristics. To unravel this inherent complexity we set up an analytic tri-helical metamaterial model that reveals the underlying physical properties. This analytic tri-helical model is complete in the sense that it is only dependent on the structures geometric and material parameters. It allows us to elucidate the characteristic transverse and longitudinal modes of the metal nano-gyroid as well as explain the surprisingly small optical chirality of gyroid metamaterials that is observed in experiments. We argue that this behaviour originates from the interconnection of multiple helices of opposing handedness.

Chiral metamaterials: enhancement and control of optical activity and circular dichroism

The control of the optical activity and ellipticity of a medium has drawn considerable attention due to the recent developments in metamaterial design techniques and a deeper understanding of the light matter interaction in composite metallic structures. Indeed, recently proposed designs of metaatoms have enabled the realisation of materials with unprecedented chiral optical properties e.g. strong optical activity, broadband optical activity, and nondispersive zero ellipticity. Combining chiral metamaterials with nonlinear materials has opened up new possibilities in the field of nonlinear chirality as well as provided the foundation for switchable chiral devices. Furthermore, chirality together with hyperbolicity can be used to realise new exciting materials such as photonic topological insulators. In this review, we will outline the fundamental principles of chiral metamaterials and report on recent progress in providing the foundations for promising applications of switchable chiral metamaterials.

Photonic band gaps and defect modes of polymer photonic crystal slabs

We show from the photonic band calculation and the finite difference time domain simulation that polymer photonic crystal slabs with a triangular array of air holes can exhibit complete photonic band gaps for transverse electric-like modes. A line defect introduced in the polymer photonic crystal slab can create guided modes which are useful in implementing low loss waveguides. We also show that thermal nanoimprint lithography is an attractive way to pattern the triangular array of air holes with high aspect ratio, which is a necessary step in the realization of the polymer photonic crystal slab.

Optical Activity Enhanced by Strong Inter-molecular Coupling in Planar Chiral Metamaterials

The polarization of light can be rotated in materials with an absence of molecular or structural mirror symmetry. While this rotating ability is normally rather weak in naturally occurring chiral materials, artificial chiral metamaterials have demonstrated extraordinary rotational ability by engineering intra-molecular couplings. However, while in general, chiral metamaterials can exhibit strong rotatory power at or around resonances, they convert linearly polarized waves into elliptically polarized ones. Here, we demonstrate that strong inter-molecular coupling through a small gap between adjacent chiral metamolecules can lead to a broadband enhanced rotating ability with pure rotation of linearly polarized electromagnetic waves. Strong inter-molecular coupling leads to nearly identical behaviour in magnitude, but engenders substantial difference in phase between transmitted left and right-handed waves.

Self-collimation phenomena of surface waves in structured perfect electric conductors and metal surfaces

We demonstrate that surface waves in structured perfect electric conductor surfaces can be self-collimated using the finite-difference time-domain method. The self-collimation frequency is obtained from the equi-frequency contours of a perfect electric conductor patterned with an array of square holes. The field patterns of the self-collimated surface wave, obtained using the periodic boundary conditions, show that the surface waves propagate with almost no spreading. We also show that self-collimation phenomena can be observed for the hybrid surface plasmon waves in structured metal surfaces using the finite-difference time-domain method with the Drude model. It is shown that for a structured silver surface the self-collimation can be achieved at the frequencies in the infrared region.