Se-Guen Park

Self-imaging phenomena in multi-mode photonic crystal line-defect waveguides: application to wavelength de-multiplexing

We show that the self-imaging principle still holds true in multimode photonic crystal (PhC) line-defect waveguides just as it does in conventional multi-mode waveguides. To observe the images reproduced by this self-imaging phenomenon, the finite-difference time-domain computation is performed on a multi-mode PhC line-defect waveguide that supports five guided modes. From the computed result, the reproduced images are identified and their positions along the propagation axis are theoretically described by self-imaging conditions which are derived from guided mode propagation analysis. We report a good agreement between the computational simulation and the theoretical description. As a possible application of our work, a photonic crystal 1-to-2 wavelength demultiplexer is designed and its performance is numerically verified. This approach can be extended to novel designs of PhC devices.

Nanofocusing of light using three-dimensional plasmonic mode conversion.

Efficient nanofocusing of light into a gap plasmon waveguide using three-dimensional mode conversion in a strip plasmonic directional coupler is proposed. Unlike conventional nanofocusing using tapering structures, a plasmonic directional coupler converts E(z)-type odd mode energy into E(y)-type gap plasmon mode by controlling phase mismatch and gap spacing. The simulation result shows the maximum electric field intensity increases up to 58.1 times the input intensity, and 17.3% of the light is focused on the nano gap region.

The effect of KOH and KOH/IPA etching on the surface roughness of the silicon mold to be used for polymer waveguide imprinting

We reports on an experimental result on a wet chemical etching of silicon for the fabrication of a mold template to be used in the embossing of optical waveguide. The silicon wafers we etched with its sidewall inclined to 45° and vertical to the bottom by using the anisotropic etching characteristics of the crystalline silicon. The results show that the surface roughness of the etched (100) and (110) planes is very much dependent on the etching condition such as the etchant concentration and etching temperature. The etched surface roughness is reduced by about 10 times from 34.5nm to 3.05nm in the (100) plane etching by changing the etching condition from 10M KOH solution at 80°C to 18M KOH solution at 40°C. For the (110) plane, the etched roughness is reduced dramatically from 115.75nm to 9.05nm by changing the etching condition from IPA saturated 5M KOH solution at 80°C to 1.25M KOH at 40°C.

Characterization and optimization of residual layer thickness during UV imprint process for singlemode waveguide fabrication

We report on the fabrication and characterization of a residual layer resulting from UV imprinting of singlemode optical waveguide. We have measured the residual thickness formed from the imprinting process for several-um-size singlemode waveguide fabrication using the parameters of the imprinting pressure, dropped volume, and viscosity of the used polymer. We found that the residual layer thickness is dependent on both the initial polymer volume and process pressure and the initial polymer volume is more critical than process pressure. Viscosity of polymer also affects the residual layer thickness, the lowest residual layer thickness of 29nm is achieved with nano-imprinting resin, 0.3uL volume, and imprint pressure more than 20bar. Even with optical resin, the residual layer thickness of 60nm is achieved with 0.3uL volume and imprinting pressure of 30bar.

Design of micro-ring optical sensors and circuitsfor integration on optical printed circuit boards (O-PCBs)

We report on the design of micro-ring resonator optical sensors for integration on what we call optical printed circuit boards (O-PCBs). The objective is to realize application-specific O-PCBs, either on hard board or on flexible board, by integrating micro/nano-scale optical sensors for compact, light-weight, low-energy, high-speed, intelligent, and environmentally friendly processing of information. The O-PCBs consist of two-dimensional planar arrays of micro/nano-scale optical wires, circuits and devices that are interconnected and integrated to perform the functions of sensing and then storing, transporting, processing, switching, routing and distributing optical signals that have been collected by means of sensors. For fabrication, the polymer and organic optical wires and waveguides are first fabricated on a board and are used to interconnect and integrate sensors and other micro/ nano-scale photonic devices. Here, in our study, we focus on the sensors based on the micro-ring structures. We designed bio-sensors using silicon based micro-ring resonator. We investigate the characteristics such as sensitivity and selectivity (or quality factor) of micro-ring resonator for their use in bio-sensing application. We performed simulation studies on the quality factor of micro-ring resonators by varying the radius of the ring resonators and the separation between adjacent waveguides. We introduce the effective coupling coefficient as a realistic value to describe the strength of the coupling in micro-ring resonators.