Dawoon Choi

Optical beam focusing with a metal slit array arranged along a semicircular surface and its optimization with a genetic algorithm

A metal slit array arranged along a semicircular surface achieving subwavelength optical beam focusing along the lateral direction is proposed. Taking into consideration surface plasmon polaritons that pass through a metal slit array, we design the array with a curvature. By use of a genetic algorithm, the size of the metal slit and the corresponding curvature are to be determined. Based on our metal slit array configuration, the full width at half-maximum can be achieved on a subwavelength scale.

Airy Beam Excitation Using a Subwavelength Metallic Slit Array

A novel method for launching an Airy wave packet based on a metallic slit array with stepped-height is proposed. By appropriately adjusting the amplitude and phase of the transmittance from the metallic slit array, the Airy beam can be launched in a compact area. The method can be used in various applications, such as particle tweezing and trapping, without the need for any optical components or bulky structure.

Metallic-Grating-Based Interconnector Between Surface Plasmon Polariton Waveguides

A metallic-grating-based interconnection scheme that interconnects two waveguide layers of surface plasmon polaritons (SPPs) is presented. We designed a diffraction grating for radiating light from the SPPs into free space or a homogeneous medium. An efficient receiver grating for receiving the light into SPPs is also explored. Using the well-established finite-element method, the appropriate grating geometry parameters are found. The directional interconnection efficiency is 32.4% for the best case in our numerical analysis.

Formation of photoluminescent germanium nanostructures by femtosecond laser processing on bulk germanium: role of ambient gases.

We present preparation of Ge nanostructures formed using by femtosecond laser pulse and origin of visible photoluminescence (PL) properties. High intensity of incident laser energy gives rise to make oxidized layer to surface of Ge nanoparticle after irradiation. Moreover, size dependent Raman shift and PL spectrums are observed with different fluences and various process surroundings. It is noted that the oxidation of Ge nanoparticle formed ambient surroundings plays an important role of photoluminescence.

Generation of finite power Airy beams via initial field modulation

We investigate the finite power Airy beams generated by finite extent input beams such as a Gaussian beam, a uniform beam of finite extent, and an inverse Gaussian beam. Each has different propagation behavior: A finite Airy beam generated by a uniform input beam keeps its Airy profile much longer than the conventional finite Airy beam. Also, an inverse Gaussian beam generates a finite Airy beam with a good bent focusing in free space. In this paper, the analysis and experimental results of finite Airy beams are presented.

Tunable subwavelength hot spot of dipole nanostructure based on VO 2 phase transition

We propose a novel approach to generate and tune a hot spot in a dipole nanostructure of vanadium dioxide (VO2) laid on a gold (Au) substrate. By inducing a phase transition of the VO2, the spatial and spectral distributions of the hot spot generated in the feed gap of the dipole can be tuned. Our numerical simulation based on a finite-element method shows a strong intensity enhancement difference and tunability near the wavelength of 678 nm, where the hot spot shows 172-fold intensity enhancement when VO2 is in the semiconductor phase. The physical mechanisms of forming the hot spots at the two-different phases are discussed. Based on our analysis, the effects of geometric parameters in our dipole structure are investigated with an aim of enhancing the intensity and the tunability. We hope that the proposed nanostructure opens up a practical approach for the tunable near-field nano-photonic devices.

Holographic Reconstruction of Finite Airy Beams with Self-Healed and Multiplexed Features

To generate finite-power Airy beams, a novel holographic method is proposed. We record the interference pattern between an Airy beam (signal beam) and plane wave (reference beam) on a photopolymer, then decode the hologram by illuminating with the reference beam. The reconstructed beams still present the non-diffraction, acceleration, and self-healing features of optical Airy beams. In addition, angular multiplexing of two Airy beams with opposite acceleration directions is presented.

Airy beam manipulation based on the metallic slit array

New Airy beam manipulation method based on the metallic slit array is presented. By controlling the phases and intensities of the transmitted lights from each subwavelength metallic slit via the variations of the parameters such as widths, heights, positions, and numbers of the slits, the overall phase and intensity distributions of the transmitted light are designed to mimic that of Airy beam. The proposed method can effectively produce the Airy wave packet in microscale without any spatial light modulator (SLM) and lens. The numerical result and considerations on the design method to make compact structure to generate the Airy wave packet will be presented.

Surface plasmon polariton power divider using metallic gratings

We propose a dividing method of the power of surface plasmon polariton (SPP) propagating along a metal film based on metallic gratings. By placing gratings on the top and under the bottom of the metallic film and varying the off-set distance, grating height, and filling factor, the power of SPP can be divided with specific ratios.

Holographic generation of non-diffractive beams

An Airy beam is a non-diffractive wave which propagates along a ballistic trajectory without any external force. Although it is impossible to implement ideal Airy beams because they carry infinite power, so-called finite Airy beams can be achieved by tailoring infinite side lobes with an aperture function and they have similar propagating characteristics with those of ideal Airy beams. The finite Airy beam can be optically generated by several ways: the optical Fourier transform system with imposing cubic phase to a broad Gaussian beam, nonlinear generation of Airy beams, curved plasma channel generation, and electron beam generation. In this presentation, a holographic generation of the finite Airy beams will be discussed. The finite Airy beams can be generated in virtue of holographic technique by ‘reading’ a hologram which is recorded by the interference between a finite Airy beam generated by the optical Fourier transform and a reference plane wave. Moreover, this method can exploit the unique features of holography itself such as successful reconstruction with the imperfect incidence of reference beam, reconstruction of phase-conjugated signal beam, and multiplexing, which can shed more light on the characteristics of finite Airy beams. This method has an advantage in that once holograms are recorded in the photopolymer, a bulky optics such as the SLM and lenses are not necessary to generate Airy beams. In addition, multiple Airy beams can be stored and reconstructed simultaneously or individually.