J. Y. Chang

Growth of single-phase In2Se3 by using metal organic chemical vapor deposition with dual-source precursors

Single-phase γ-In2Se3 thin films have been prepared by the metal organic chemical vapor deposition technique using dual-source precursors, trimethylindium, and hydrogen selenide to obtain a different VI/III ratio by independent adjustment of the precursors’ flow rate. 2in Si(111) and Si(100) wafers are used as substrates. The films have been characterized by x-ray diffraction and scanning electron microscopy. The single-phase γ-In2Se3 films can be grown on both Si(111) and Si(100) substrates. The optical properties of the films have been studied by photoluminescence measurements. Strong exciton emissions were observed at around 2.14eV at 20K. The band gap of γ-In2Se3 at room temperature is estimated at approximately 1.93eV.

Transmission enhancement through a trench-surrounded nano metallic slit by bump reflectors

We propose using a pair of bumps bordering the conventional trench-surrounded metal nano slit in order to confine the surface waves and further enhance the slit transmission. The bump height of 1.mum is larger than the depth of penetration on air side of the surface waves. The reflectivity of such bumps is larger than 95%. A very large slit transmission, which is 50% of the energy of the incident beam impinging on the entire size 13.mum of the trench-surrounded slit structure, is obtained through the metallic slit of 50nm width and 400nm depth. The bumps enhance the transmission by 1.75 fold.

Electro-optic narrowband multi-wavelength filter in aperiodically poled lithium niobate

We report on an iterative design scheme for and the first experimental demonstration of active narrowband multi-wavelength filters based on aperiodically poled lithium niobate crystals. A simultaneous transmission of 8 wavelengths, each with a ~0.45-nm linewidth and nearly 100% peak transmittance, was achieved in such a device. The transmission spectrum of this device can be tuned by temperature at a rate of ~0.65 nm/ degrees C.

Spectral narrowing and manipulation in an optical parametric oscillator using periodically poled lithium niobate electro-optic polarization-mode converters.

We report a unique spectral narrowing and manipulation technique in an optical parametric oscillator (OPO) realized by an integrated periodically poled lithium niobate comprising an optical parametric gain medium sandwiched by two electro-optic polarization-mode converters (EO PMCs). We achieved a manipulation of the gain spectrum of the OPO via EO and/or temperature control of the EO PMCs, in which we obtained single to multiple signal spectral peaks from the OPO with a spectral width reduced by up to 10 times and peak intensity increased by up to 6 times in comparison with the original signal. Fast EO tuning of the narrowed signal spectral peak has also been demonstrated.

Monolithically integrated multi-wavelength filter and second harmonic generator in aperiodically poled lithium niobate

We report on the design and experimental characterization of aperiodically poled lithium niobate (APLN) crystals for use in monolithically integrated dual nonlinear-optical devices. A cascade and a single aperiodic-domain-structure designs based on simulated annealing method were constructed in LiNbO(3) to simultaneously perform as 4-channel electro-optically active (EOA) filters and 4-channel frequency doublers in the telecom band. We found that we could obtain a 2.44-fold enhancement in second-harmonic-generation conversion efficiency and a 2.4-time reduction in filter transmission bandwidth with the single APLN device over the cascade one when the same device length of 2 cm and the EOA field of 1027 V/mm were used.

Photorefractive effect in hydrogen-reduced BaTiO3

Abstract Optical and photorefractive properties of hydrogen-reduced BaTiO3 are investigated. Hydrogen-reduction induced a broad optical absorption around 620 nm. From two beam coupling, the electrooptic gain is highly dependent on intensity, with electrons being the major carriers. When the annealing temperature increases, the electrooptic gain decreases, though the trap density increases. From light-induced erasure decay measurement, the response time has a little change with intensity at low intensity, though it is much faster than that of the as-grown sample. These properties can be attributed to high dark conductivity of the reduced sample. The dark conductivity increases about three orders after hydrogen-reduction. It is about 6.6 × 10 −11 1/( cm Ω) for the reduced sample, compared with 2.3 × 10 −14 1/( cm Ω) for the as-grown.

The optical and photorefractive properties of reduced Rh-doped BaTiO3 at wavelength of 514 nm

Abstract Optical and photorefractive properties of reduced Rh-doped barium titanate are reported. Reduction eliminates energy levels of Rh +4 and Rh +5 , and induces an absorption around 480 nm, which has a large light-induced transparency of ∼4 cm −1 . After reduction, the speed increases by a factor of 30 though the electrooptic gain decreases by a factor of 1.6. In addition, it induces an increase of dark conductivity by three orders.

Wavelength dependence of carrier-type in reduced BaTiO3:Rh

We report that in BaTiO3:Rh the carrier-type depends not only on the postprocessing condition but also on the incident wavelength in two beam coupling. Carriers are the holes for the as-grown sample, and change to electrons for the sample reduced in the atmosphere of 10−14 atm oxygen partial pressure. However, for the sample reduced in the atmosphere of 10−10 atm oxygen partial pressure, the carrier is an electron for the incident wavelength of 514 nm, and a hole for 633 nm. Its absorption, photoinduced absorption, and two beam coupling are investigated and discussed.

Fabricating a silicon microlens mold by ICP dry etching

In this paper, a silicon mold, with spherical/aspherical concave microlens arrays, was made by using ICP dry etching technique. A PMMA microlens was molded by using this mold and then tested by SEM, Dektakprofiler and etc.

Characterization of 380nm UV-LEDs grown on free-standing GaN by atmospheric-pressure metal-organic chemical vapor deposition

We reported the defects and optical characterizations of the ultraviolet light-emitting diodes grown on free-standing GaN substrate (FS-GaN) and sapphire. Cross-sectional transmission electron microscopy (TEM) images showed that the total defect densities of grown UV LEDs on FS-GaN and sapphire including edge, screw and mixed type were 3.6×106 cm-2 and 5.5×108 cm-2. When substrate of UV LEDs was changed from sapphire to FS-GaN, it can be clearly found that the crystallography of GaN epilayers was drastically different from that GaN epilayers on sapphire. Besides, the microstructures or indium clustering can be not observed at UV LEDs on FS-GaN from TEM measurement. The internal quantum efficiency of UVLEDs on FS-GaN and sapphire were 34.8 % and 39.4 % respectively, which attributed to indium clustering in multi-layers quantum wells (MQWs) of UV LEDs on sapphire. The relationship between indiumclustering and efficiency droop were investigated by temperature-dependent electroluminescence (TDEL) measurements.