Hyun-Woo Song

High-finesse AlxOy/AlGaAs nonabsorbing optical cavity

We report the measured finesse value of ∼390 in nonabsorbing AlxOy/AlGaAs cavities. The nonabsorbing cavity consisting of a bottom AlxOy/AlGaAs distributed Bragg reflector (DBR), an AlxOy spacer layer, and a top AlxOy/AlGaAs DBR is prepared by a wet-oxidation process. The measured resonance linewidth agrees well with that of calculation, indicating very small overall losses in the cavity. The wet-oxidation process does not seem to degrade the interface of the epitaxial layers significantly. The lower bound of maximum achievable reflectivity from the AlxOy DBR is estimated to be >99.95%, assuming an average interface roughness of about 0.6 nm. The maximum achievable finesse of this type of cavity is expected to be larger than that of the all-epitaxial counterpart assuming the same roughness.

Fabrication Method of Densely Spaced 1.55 µm Multiple-Wavelength Vertical-Cavity Surface-Emitting Laser Array Structure for the Application of Dense Wavelength Division Multiplexing

We demonstrate a very precise cavity-mode control scheme in a 1.55 µm multiple-wavelength vertical-cavity surface-emitting laser (VCSEL) array. For the precise control of the cavity mode, selective wet etchings of InP and InAlGaAs superlattice tuning layers are investigated using HCl/H2O and H3PO4/H2O2/H2O solution systems, respectively. The average calibrated cavity-mode spacing between channels for the fabricated eight-channel full VCSEL array structure is approximately 0.9 nm, which agrees well with the calculated value of 0.8 nm.

Optical Monitoring of Tumors in BALB/c Nude Mice Using Optical Coherence Tomography

We report a method for optical monitoring of tumors in an animal model using optical coherence tomography (OCT). In a spectral domain OCT system, a superluminescent diode light source with a full width of 66 nm at half maximum and peak wavelength of 950 nm was used to take images having an axial resolution of 6.8 μ m. Cancer cells of PC-3 were cultured and inoculated into the hypodermis of auricle tissues in BALB/c nude mice. We observed tumor formation and growth at the injection region of cancer cells in vivo and obtained the images of tumor mass center and sparse circumferences. On the 5 th day from an inoculation of cancer cells, histological images of the tumor region using cross-sectional slicing and dye staining of specimens were taken in order to confirm the correlation with the high resolution OCT images. The OCT image of tumor mass compared with normal tissues was analyzed using its A-scan data so as to obtain a tissue attenuation rate which increases according to tumor growth.

Continuous wave operation of MOCVD grown 1.55 /spl mu/m buried tunnel junction VCSELs

We demonstrate continuous wave operation of MOCVD-grown 1.55 /spl mu/m buried tunnel junction VCSELs at room temperature. This buried tunnel junction VCSEL structure is prepared by MOCVD twofold epitaxial growth. The threshold current and emission wavelength for a 10 /spl mu/m-diameter device are 3.5 mA and 1552 nm, respectively.

Ultrasensitive formaldehyde gas sensors based on a hollow assembly and its 3-dimensional network formation of single-crystalline Co3O4 nanoparticles

The detection of formaldehyde at a very low concentration is a significant research topic, because of its harmful impact on human health. In this current study, we have fabricated a hierarchical structure by the reasonable assembly of single-crystalline Co3O4 nanoparticles. A hollow morphology using sacrificial ZnO spheres could make a three-dimensional conducting network in a solid state. The resulting structure was quite active for formaldehyde sensing, and the detection limit was 50 ppb, which was nearly close to the record-high value among the other semiconducting materials. Such superior properties were attributed to the regular, hierarchically assembled structures with a small crystalline domain size, a thin hollow morphology with a large surface area, and a three-dimensional conductive network with a narrow diameter. We think that this hierarchical assembly can show great potential as a platform for improving human health through the monitoring of indoor environments.

1.1 mW Single-Mode Output Power of All-Monolithic 1.3 µm InAlGaAs/InP Vertical Cavity Surface Emitting Lasers Grown by Metal Organic Chemical Vapor Deposition

We present all-monolithic InAlGaAs/InP vertical cavity surface emitting lasers (VCSELs) emitting wavelength of 1.3 µm grown by metal organic chemical vapor deposition (MOCVD). The devices with tunnel junction (TJ) and the air-gap aperture showed the performances as high as output power of 1.1 mW and as low as threshold current of 1.9 mA operating in single-mode at room temperature. We obtained the emitting transverse wavelength of 1333.1 nm with side mode suppression ratio (SMSR) of 40 dB, the continuous wave (CW) operation of temperature over 80°C, and modulation bandwidth exceeding 2.5 Gbit/s.

Long wavelength VCSEL using ion-implantation and dielectric mirror

We proposed a new type of 1550 nm VCSEL incorporating proton implantation and a dielectric mirror. Even though it suffers from poor heat removal rate, it could be a promising structure since the structure and fabrication scheme rely on stable material and well-established processing techniques. The fabricated laser operates under pulsed conditions emitting at 1550 nm. The use of flip-chip bonding and good choice of dielectric material may improve the overall laser performance.

Plastic extended optical-path-length absorbance Detection Microchip For On-Chip Prostate Specific antigen (PSA) quantification

This paper reports a new polymer extended optical-path-length absorbance-based detecting device for quantification of free PSA for point-of-care testing. The plastic COC device was fabricated using the polymer micromachining protocols, including multi-stage silicon molder, replica-molding and photolithographic protocols. The plastic-based microdevice incorporated with optical functions including micromirrors with minimum dead volume and a huge extended optical path length of 2 mm, which is the dimension in enzyme-linked immunosorbent assay (ELISA). We demonstrated the quantitative detection of free PSA, a prostate cancer biomarker, in range of 1~10 ng/ml on microchip with a 3 mul-volume chamber after positive and negative control tests.

1.5 μm InAlGaAs/InP VCSELs with Al2O3 Embedded Apertures

We report InAlGaAs VCSELs with Al₂O₃ embedded apertures. Using atomic layer deposition, the current confinement apertures are fabricated by depositing of Al₂O ₃ on air-gap surfaces of undercut apertures, 1.57mum VCSELs showing the output power of over 1 mW and direct modulation at 4 Gbit/s are reported using these apertures

1.55-/spl mu/m bottom-emitting InAlGaAs VCSELs with Al/sub 2/O/sub 3//a-Si thin-film pairs as a top mirror

We demonstrate a 1.55-/spl mu/m InAlGaAs/InP vertical-cavity surface-emitting laser grown by metal-organic chemical vapor deposition. AI/sub 2/O/sub 3/-Si thin-film pairs and InAlGaAs/InAlAs epitaxial layers are used as a top mirror and a bottom-side output coupler, respectively. Direct modulation characteristics through single mode fiber are reported in the speed of 2.5 Gbit/s.