Hang Ju Ko

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.

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.

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.

Vanadium Oxide Microbolometer Using ZnO Sandwich Layer

Optical, electrical and structural properties of VOx/ZnO/VOx thin film are studied. The VOx/ZnO/VOx multilayer is deposited by using a radio frequency (RF) sputtering system. The VOx/ZnO/VOx thin film shows the high temperature coefficient of resistance (TCR) of ?3.12%/℃ and the low sheet resistance of about 80 kΩ/sq at room temperature. The responsivity and detectivity of the bolometer are measured as a function of modulation frequency.

A fabrication and characterictics of microbolometer detectors using VOx/ZnO/VOx multilayer thin film processing

In this work, a novel fabrication method for VOx-ZnO multilayers with mixed phase of the VO2 and V2O3 through the diffusion of oxygen by annealing at low temperature is presented. A stable sandwich structure of a VOx/ZnO/VOx multilayer was deposited at room temperature, through the oxygen gas flow rate, by RF sputtering system, and the mixed phase was formed through oxygen diffusion by annealing at O2 atmosphere. The results show that the single phase like multilayer formed by this process has a high TCR of more than -2.5%/K and low resistance of about 100 kohm at room temperature. XRD results for the as-deposited VOx/ZnO/VOx multilayer.

Structural characteristics of ternary In(x)Ga(1-x)As nanowires on Si (111) grown via Au-catalyzed VLS.

We have characterized the structural properties of the ternary In(x)Ga(1-x)As nanowires (NWs) grown on silicon (Si) substrates using metalorganic chemical vapor deposition (MOCVD). Au catalyzed vapor-liquid-solid (VLS) mode was used for the NW growth. The density of the In(x)Ga(1-x)As NW array grown under optimized condition exceeds 1 x 10(8)/cm2. X-ray diffraction (XRD) spectra confirm the In composition (x = 0.9-0.3) of the In(x)Ga(1-x)As nanowires which bandgap energy can cover the entire near-infrared (NIR) range. Massive stacking faults and twin planes were observed but no misfit dislocation was found along the NWs as confirmed by transmission electron microscopy (TEM). The energy-dispersive X-ray spectroscopy (EDS) analysis shows the gradual variation of In composition along the NW.

Optical properties in InGaAs quantum dots on SiO2-patterned vicinal (001) GaAs substrate

We studied the energy states in In0.8Ga0.2As SAQDs (self-assembled quantum dots) which depended on W(001) and the misorientation angle of the substrate. Starting materials used in this study were SiO2-patterend exact and 5 degree - off (001) GaAs substrates. In0.8Ga0.2As SAQDs had only ground state emissions for SiO2-patterned exact (001) GaAs substrate, whereas those had ground and excited state emissions for SiO2-patterned 5 degree-off (001) GaAs substrate. These results suggest that discrete nature of the density of states in SAQDs was improved by using SiO2-patterned vicinal (001) GaAs substrate with higher misorientation angle of substrate.

Optical characteristics of surface plasmon resonance based on ZnO and metallic nanograting structures

We proposed the grating coupled surface plasmon resonance (GC-SPR) sensors using ZnO and metallic nanograting structures to enhance the sensitivity of an SPR sensor. The GC-SPR sensors were analyzed using the finitedifference time-domain method. The optimum resonance angles of 49 and 55.5 degrees are obtained in the 150 nm wide grating structure with a period of 300 nm for the ZnO thickness of 30 and 50 nm, respectively. Here, an enhanced evanescent field is obtained due to the surface plasmon on the edge of the bandgap when the ZnO and metallic grating structures are used to excite the surface plasmon.

Triangular ring resonator incorporating total internal reflection mirror and compact multimode interference coupler

We report fabrication and measurements on novel triangular ring resonators with extremely small multimode interference couplers and total internal reflection mirrors. Free spectral range and on-off ratio are 256 GHz and 14 dB respectively.

Nano pattering by double expose hologram lithography and ZnO nanoscale photonic crystal

We present spot and mesh patterns formed with same photo-resist by using ultra-violet laser holographic lithography. The ZnO nano crystal was deposited on patterned Si substrate by hydrothermal method.