Tae Un Kim

Extremely small multimode-interference coupled triangular resonator with sharp angle of incidence

Novel triangular ring resonators combining extremely small multimode-interference (MMI) coupler, low loss total internal reflection (TIR) mirrors, and semiconductor optical amplifiers are reported for the first time. The MMI length of 90 microm is among the shortest reported. The incidence angle of the TIR mirror inside the resonator is 22 degrees. A free-spectral range of approximately 2 nm is observed near 1550 nm along with an on-off ratio of 17 dB. The triangular resonators with a sharp angle are very attractive components due to their promise of compact size and high levels of integration. Therefore, large numbers of resonators can be integrated on a chip to increase functionality in future optical wavelength division multiplexing system.

The Effect of Au/Ag Bimetallic Thin-Films on Surface Plasmon Resonance Properties Comparing with Those of Au and Ag Single Thin-Films

The surface plasmon resonance (SPR) properties of Au/Ag bimetallic thin-film nanostructures were investigated to improve the chemical stability and the figure of merit (FOM) in the SPR sensors. The SPR characteristics such as resonance angle, extinction ratio, and full width half maximum (FWHM) were calculated by the simulation of the finite-difference time-domain method and were measured using the laser with a 632.8 nm wavelength in the Kretschmann-Raether configuration. The measured resonance angle, extinction ratio, FWHM of Au(20 nm)/Ag(20 nm) thin-film nanostructure were found to be 44°, 0.8, and 1.4°, respectively. The FOM values were determined to be 56.9 for Au/Ag bimetallic thin-film, 47.9 for Au(50 nm) single thin-film, and 89.1 for Ag(50 nm) single thin-film. Also the sensitivity values were about 53.5, 57.0, and 57.8°/RIU for Au(50 nm), Ag(50 nm), and Au(20 nm)/Ag(20 nm) thin-film nanostructures in the SPR sensors, respectively. The SPR properties of Au/Ag bimetallic thin-film nanostructures were compared with those of the Au and Ag single thin-film nanostructures.

Integrated Refractometric Sensor Utilizing a Triangular Ring Resonator Combined With SPR

In this letter, a triangular resonator-based surface plasmon resonance (SPR) sensor that uses total internal reflection (TIR) mirrors to provide SPR excitation for the detection of refractive index (RI) change is proposed and first demonstrated using SoI substrate without any gain medium. The fabricated triangular resonator sensor with a 35-nm-thick Au film on a TIR mirror shows an output power increment of 1.2 dB and a sensitivity of 102 nm/RIU, while that nonmetallic layer on a TIR mirror shows 30 nm/RIU. The sensitivity enhancement is attributed to a phase change in the SPR resulting in a large shift of the resonance peak. This configuration provides significant advantages by increasing the sensitivity of the RI sensor even with the extremely small sensing area of the SPR mirror.

Bidirectional Lasing Characteristics of Rectangular Ring Laser with Three-Guide Coupler

The lasing characteristics of three-guide coupled rectangular ring laser containing active and passive sections were investigated numerically and experimentally. The rectangular laser cavity consists of four low-loss total internal reflection mirrors and an output coupler made from three passive coupled waveguides. The laser having active section lengths of 350 µm and total cavity lengths of 780 µm was fabricated. The lasing threshold current in the clockwise circulating direction is approximately 35 mA, while that in the counterclockwise circulating direction is around 40 mA under continuous wave operation. The lasing characteristics are bidirectional operation of the single mode with a side mode suppression ratio better than 27 dB.

Mechanism of photonic crystal and waveguide effects in ZnO nanorods

Two different shaped ZnO nanorods were grown on ZnO buffered Al2O3 substrate by laser interference lithography and hydrothermal method. The light waveguide within ZnO nano rod and photonic crystal effects in arrayed ZnO nanorods was calculated by 3D-finite dimension time domain(3D-FDTD) programs. The ZnO photonic crystal effect and number of modes of ZnO nanorod was governed by arrangement and shape of ZnO nanorod, respectively.

Structural and optical properties of TiO2 thin films annealed in O2 and N2 gases flow

Titanium dioxide (TiO2) thin films were prepared by ion-assisted electron-beam deposition on glass at room temperature and were annealed by rapid thermal annealing in O2 and N2 gas flow. TiO2 thin films annealed in N2 gas flow are (110) rutile phase and (101) anatase phase, but in O2 gas flow are (110) rutile phase. The optical band gaps of the TiO2 thin films are increased to 3.281 eV with annealing treatment of 300 ~ 500 °C in O2 gas flow and to 3.271 eV in N2 gas flow. However, the band gap begins to decrease to 3.277 eV at the annealing temperature of 600 °C in O2 gas flow and to 3.257 eV in N2 gas flow, respectively.

Optical Characteristics of Double Layered Plasmonic Structure Using Nanopatterning Process

A double layered plasmonic device based on transferring technique with polystyrene nano-beads is analyzed and demonstrated to increase the sensing characteristics of plasmonic sensor system. The double layered plasmonic devices are calculated using the three-dimensional finite-difference time-domain method for the width and thickness of the nano-hole structures. The double layered plasmonic devices with different diameters of the Au nano-hole are fabricated by transferring method with commercially available chloromethyl latex with a diameter of 0.42 μm. The optimum sensing characteristic of the proposed plasmonic device is obtained with the film and the hole thickness of 15 and 15 nm in the 246 nm wide nano-hole size. The best sensitivity of the proposed plasmonic sensor is 67.7 degree/RIU when the sensitivity of the conventional plasmonic sensor is 42.2 degree/RIU.

Biosensing characteristics of InAs nanowire transistors grown by MOCVD

We demonstrated the ion-sensitive field-effect transistors (IS-FETs) based on nanowires (NWs) with different diameters and doping concentrations to obtain the high sensitivity and various applications. The growth of the catalyst-free InAs NWs was carried out using a horizontal reactor MOCVD system (AIXTRON Inc.). A p-type Si (111) wafer (ρ = 1 -10 Ω-cm) was prepared for the NW growth. Here, NWs with diameters of around 50 ~ 150 nm were grown and the doping concentration also was changed around x±1016~18 /cm2. IS-FETs with the grown InAs NWs were fabricated using the photolithography and the lift-off process. The gas sensing characteristics have been investigated through studying the gate response of the NW conductance in different ambient conditions.

Sensing characteristics of plasmonic structure based on transferring process of polystyrene nano-beads

We analyzed and demonstrated the double layered metallic nano-structures using polystyrene lift-off process on the conventional surface plasmon resonance (SPR) sensor to enhance the sensitivity of an SPR surface. The double layered plasmonic structures are optimized using the three-dimensional finite-difference time-domain method for the width, thickness, and period of the polystyrene beads. The thickness of the metal film and the metallic nano-hole is 20 and 20 nm in the 305 nm wide nano-hole size, respectively. The double layered metallic nano-structures are fabricated with monolayer polystyrene beads of chloromethyl latex 4% w/v 0.4 μm. The sensitivities of the conventional SPR sensor and the double layered plasmonic sensor are obtained to 42.2 and 60 degree/RIU, respectively. The SPR devices are also applied to the lead ion sensor. The resonance shifts of SPR sensors with and without a poly(vinyl chloride) membrane are 1328 RU and 788 RU from 10-5 M to 10-2 M concentration, respectively.

Plasmonic characteristics of metallic nano-ring structures

We proposed and demonstrated the metallic nano-ring structure using polystyrene lift-off process to enhance the sensitivity of an SPR surface. The double layered SPR structures are optimized using the finite-difference time-domain method for the width, thickness, and period of the polystyrene beads. The optimum thickness of the metal film and the metallic nano-ring is 30 and 20 nm in the 214 nm wide nano-hole size, respectively. The metallic nano-ring structures are fabricated with monolayer polystyrene beads of 400 nm wide. The various metallic nano-ring structures have been obtained by transferring method. The sensitivities of the conventional SPR sensor and the metallic nano-ring structures are obtained to 42.2 and 52.1 degree/RIU, respectively.