Shin-Won Kang

High-sensitivity temperature sensor using a side-polished single-mode fiber covered with the polymer planar waveguide

A temperature sensor based on evanescent field coupling between a single-mode side-polished fiber and a polymer planar waveguide was demonstrated. Due to thermooptic effects of a polymer planar waveguide, the resonance wavelength of the device is very sensitive to ambient temperature. Two kinds of polymers were used as planar waveguide materials. Fabricated sensors have a sensitivity of 0.37 nm C and 0.71 nm C, respectively. We also measured the thermooptic coefficient of employed polymer approximately.

Highly sensitive nano-porous lattice biosensor based on localized surface plasmon resonance and interference

We propose a design for a highly sensitive biosensor based on nanostructured anodized aluminum oxide (AAO) substrates. A gold-deposited AAO substrate exhibits both optical interference and localized surface plasmon resonance (LSPR). In our sensor, application of these disparate optical properties overcomes problems of limited sensitivity, selectivity, and dynamic range seen in similar biosensors. We fabricated uniform periodic nanopore lattice AAO templates by two-step anodizing and assessed their suitability for application in biosensors by characterizing the change in optical response on addition of biomolecules to the AAO template. To determine the suitability of such structures for biosensing applications, we immobilized a layer of C-reactive protein (CRP) antibody on a gold coating atop an AAO template. We then applied a CRP antigen (Ag) atop the immobilized antibody (Ab) layer. The shift in reflectance is interpreted as being caused by the change in refractive index with membrane thickness. Our results confirm that our proposed AAO-based biosensor is highly selective toward detection of CRP antigen, and can measure a change in CRP antigen concentration of 1 fg/ml. This method can provide a simple, fast, and sensitive analysis for protein detection in real-time.

Efficient visible-light-driven photocatalytic degradation of nitrophenol by using graphene-encapsulated TiO2 nanowires

In this work, a new hybrid nanocatalyst, namely titanium dioxide (TiO2) composite nanowires, encapsulated with graphene (G) and palladium nanoparticles (Pd NPs) (designated as G-Pd@TiO2-CNWs), was prepared. In preparing the nanowires, a combination of electrospinning and hydrothermal approaches was employed. The visible-light-driven photocatalytic performance of G-Pd@TiO2-CNWs was investigated using the reduction of 4-nitrophenol (4-NP) as a model reaction. The results showed that G-Pd@TiO2-CNWs converted nearly 100% of 4-NP under visible light irradiation. The reaction kinetics of the photocatalytic reduction of 4-NP was studied by UV-vis spectrophotometry and the apparent rate constant was determined and compared with those for other supported TiO2 catalysts. Furthermore, the spent G-Pd@TiO2-CNWs could be recovered by simple centrifugation and reused. The work is expected to shed new light on the development of G-incorporated hybrid nanostructures for harvesting light energy and on the development of new photocatalysts for the removal of environmental pollutants.

Polarizing properties of optical coupler composed of single mode side-polished fiber and multimode metal-clad planar waveguide

Abstract We report the experimental results for the polarizing properties of an optical coupler made of a single mode side-polished fiber and multimode metal-clad planar waveguide. The experimental results show that the large birefringence of a metal-clad planar waveguide facilitates the effective separation of TE and TM polarization in the spectral domain. Furthermore, through proper control of the planar waveguide parameters, the coupler can be used as either a TE-pass or TM-pass polarizer within a large spectral window (>130 nm). We present an approximated analytical method to calculate resonant wavelengths and demonstrate its validity experimentally.

Nondestructive defect inspection for LCDs using optical coherence tomography

In this study, we used optical coherence tomography (OCT) to perform nondestructive inspection of liquid crystal display (LCD) for defects. By using OCT, we obtain tomograms and two-dimensional images of LCD panels. Based on these images, we construct three-dimensional images of the LCD panel and confirm the three-dimensional shape and vertical location of eventual defects with in the LCD panel. This nondestructive and effective defect-inspection method for LCD using OCT that gives direct results and is applicable for detecting defects in flat panel or flexible displays.

Nanostructures in biosensor-a review

In the 21(st) century, it is widely recognized that along with information technology (IT) and biotechnology (BT), nanotechnology (NT) will be a key field of science that will drive future developments. NT is expected to allow innovations in industrial fields such as electrical and electronics, biochemistry, environment, energy, as well as materials science by enabling the control and operation of materials at the atomic and molecular levels. In particular, the application of NT in the field of biochemistry is now enabling the realization of previously unachievable objectives.This review discusses the growth, synthesis, and biocompatible functionalization of each materials, with an emphasis on 1D nanomaterials such as CNTs, inorganic nanowires (made of Si, metals, etc.), and conducting polymer nanowires, along with 0D nanomaterials such as nanoparticles. This review also investigates the sensing principle and features of nanobiosensors made using the abovementioned materials and introduce various types of biosensors with nanostructure 0-D and 1-D. Finally, the review discusses future research objectives and research directions in the field of nanotechnology.

Controllable in-line UV sensor using a side-polished fiber coupler with photofunctional polymer

A novel ultraviolet (UV) sensor using evanescent field coupling between single-mode-polished fiber and photochromic dye-dispersed polymer waveguide was demonstrated. It was found that resonance wavelength shifts occurred due to variations in the refractive index of the photochromic dye-dispersed polymer waveguide relative to UV intensities. A spiroxazine dye was chosen as the overlay material because of its photochromic isomerization induced by UV irradiation. The wavelength responses of these sensors by UV exposure power were measured 0.18 and 0.25 nm/mW when UV was exposed for 5 and 10 s, respectively. The recovery time for the sensor was independent of UV exposure power, and 80% recovery time was shown 90 s.

Fiber-optic multi-sensor array for detection of low concentration volatile organic compounds

In this paper, we proposed a new type high sensitive volatile organic compounds (VOCs) gas sensor array that is based on the pulse width modulation technique. Four different types of solvatochromic dyes and two different types of polymers, were used to make the five different types of sensing membranes. These were deposited on the five side-polished optical fibers by a spin coater to make the five different sensing elements of the array. In order to ascertain the effectiveness of the sensors, five VOC gases were tested. Finally, principal component analysis (PCA) has been used to discriminates different types of VOCs.

A PDMS-Coated Optical Fiber Bragg Grating Sensor for Enhancing Temperature Sensitivity

We proposed a poly-dimethylsiloxane (PDMS)-coated fiber Bragg grating (FBG) temperature sensor for enhancing temperature sensitivity. By embedding the bare FBG in a temperature-sensitive elastomeric polymer, the temperature sensitivity of the proposed structure could be effectively improved by 4.2 times higher than those of the conventional bare-type FBG sensors due to the high thermal expansion coefficient of the PDMS. We analyzed the temperature-sensitivity enhancement effect with the increased Bragg wavelength shift in our structure and dependence on the temperature sensitivity with respect to the cross-section area of the PDMS.

Photoinduced refractive index change of self-assembled spiroxazaine monolayer based on surface plasmon resonance

Abstract The self-assembly of a photochromic, spiroxazine-containing alkanethiol monolayer on a gold surface is described. Contact angle measurements confirm the presence of a hydrophilic surface in the self-assembled monolayer. Atomic force microscopy (AFM) images and measurements confirm that this monolayer was formed by stepwise chemical assembly. Evidence for self-assembled monolayer-photochromism was gathered from UV–visible spectral evaluation before and after irradiation at 366 nm. Surface plasmon resonance (SPR) revealed that a resonance angle change of 0.13° which corresponded to a refractive index change, Δ n , of 0.0034.