Akihiro Matsutani

Strong enhancement of light extraction efficiency in GaInAsP 2-D-arranged microcolumns

This paper experimentally demonstrates the strong enhancement of light extraction efficiency in two-dimensionally arranged microcolumns. They were designed like a honeycomb photonic crystal and fabricated into GaInAsP-InP wafers by using the inductively coupled plasma etching. For the laterally directed light passing through the microcolumns, peculiar transmission characteristics were observed, which could be explained by the Bragg reflection theory, namely, the photonic bandgap (PBG). The measurement of spontaneous lifetime showed that the internal efficiency in the microcolumns was reduced by the surface recombination at sidewalls. In contrast, the light extraction efficiency evaluated from the measured photoluminescence intensity, and the internal efficiency was more than ten times that for a planar wafer. This was thought to be due to the expanded escape cone of internal light by the low effective refractive index, and also due to the strong diffraction and scattering of laterally directed light, which corresponds to the second-order Bragg condition. Such effects are expected not only in photonic crystals but also in some disordered structures. We expect this structure to allow a high-efficiency light-emitting diode (LED), since electronic elements needed for current injection devices can be added independently of the effects.

Modeling and Fabrication of Hollow Optical Waveguide for Photonic Integrated Circuits

We present the design and fabrication of hollow optical waveguides with highly reflective mirrors on the guiding walls of waveguides. We demonstrate the possibility of polarization-insensitive and low-loss slab waveguides by loading properly designed dielectric multilayer mirrors. We also propose a novel three-dimensional (3D) hollow waveguide with an etched groove structure for confining light in a lateral direction. We also predict that the propagation constant is independent of the ambient temperature, resulting in temperature-insensitive photonic waveguide devices such as optical filters and grating optical demultiplexers. We fabricate slab and 3D hollow optical waveguides with Au coating and present their propagation characteristics. The propagation loss of a slab waveguide was 1–2 dB/cm and 3–4 dB/cm for transverse electric (TE) and transverse magnetic (TM) modes, respectively. We also suggest the possibility of low-loss 3D hollow waveguides.

Lasing characteristics of low-threshold oxide confinement InGaAs-GaAlAs vertical-cavity surface-emitting lasers

Some lasing characteristics of index-guided InGaAs-GaAlAs vertical-cavity surface-emitting lasers (VCSELs) with a native oxide confinement structure, which produced a low threshold current of 70 /spl mu/A, are presented. It was found that nonradiative recombination was reduced and the estimated surface recombination velocity was almost negligible. The oxidation process was uniform to produce low threshold devices while the oxidation rate was dependent on the doping or composition of DBRs.<<ETX>>

Hollow Optical Waveguide for Temperature-Insensitive Photonic Integrated Circuits.

We propose a hollow optical waveguide with metal coating or dielectric multilayer coating to achieve sufficient reflectivity at guiding walls. Low-loss and polarization-insensitive propagation characteristics are predicted. The propagation constant is independent of the temperature, resulting in temperature-insensitive photonic waveguide devices, such as optical filters and grating optical demultiplexers. We demonstrate a hollow optical waveguide with metal-coated walls on a GaAs substrate, which was fabricated using dry etching. The propagation loss including the coupling loss with an input fiber was 2.6 dB/cm and 7.3 dB/cm for transverse electric (TE) mode and transverse magnetic (TM) mode, respectively.

Vertical and Smooth Etching of InP by Cl2/Xe Inductively Coupled Plasma

We have demonstrated anisotropic and smooth etching of InP by an inductively coupled plasma (ICP) using Cl2/Xe at high substrate temperatures. We investigated the etching characteristics by varying the substrate temperature, gas pressure, Cl2 flow rate and rf power. Vertical and smooth dry etching of InP was achieved under a low dc bias of -80 V. The ICP etching process is an effective low-damage dry-etching technique for microfabrication of InP-based optoelectronic devices.

Effect of radical fluorination on mono- and bi-layer graphene in Ar/F2 plasma

Fluorinated graphene has the possibility to achieve unique properties and functions in graphene. We propose a highly controlled fluorination method utilizing fluorine radicals in Ar/F2 plasma. To suppress ion bombardments and improve the reaction with fluorine radicals on graphene, the substrate was placed “face down” in the plasma chamber. Although monolayer graphene was more reactive than bilayer, fluorination of bilayer reached the level of ID/IG ∼ 0.5 in Raman D peak intensity at 532 nm excitation. Annealing fluorinated samples proved reversibility of radical fluorination for both mono- and bi-layer graphenes. X-ray photoelectron spectroscopy showed the existence of carbon-fluorine bonding.

Data transmission over single-mode fiber by using 1.2-μm uncooled GaInAs-GaAs laser for Gb/s local area network

We demonstrate 2-Gb/s data transmission through a 5-km-long standard single-mode fiber by using a GaAs-based 1.2-/spl mu/m GaInAs-GaAs quantum well laser. The fabricated laser exhibits a high characteristic temperature of 140 K. The results indicate the possibility of Gigabit/s local area networks (LANs) using uncooled lasers (possibly surface-emitting lasers) operating at a 1.2-/spl mu/m wavelength band.

An over 10-Gb/s transmission experiment using a p-type delta-doped InGaAs-GaAs quantum-well vertical-cavity surface-emitting laser

We have fabricated a p-type delta-doped InGaAs-GaAs quantum-well (QW) vertical-cavity surface-emitting laser (VCSEL) with a low-resistance GaAs-AlAs distributed Bragg reflector (DBR). The threshold was as low as 700 /spl mu/A for 10/spl times/10 /spl mu/m/sup 2/ devices. A penalty-free 10-Gb/s transmission experiment with a 100-m-long multimode fiber was performed using fabricated VCSELs. The modulation speed was up to 12 Gb/s, which was limited by an RC constant. Further threshold reduction and high-speed operation can be expected by controlling the doping concentration in p-type delta-doped layers.

Highly angular dependent high-contrast grating mirror and its application for transverse-mode control of VCSELs

We report on the design and fabrication of a highly angular dependent high contrast grating (HCG) mirror. The modeling and experiment on amorphous-Si/SiO2 HCG clearly show the large angular dependence of reflectivity, which enables single transverse-mode operations of large-area VCSELs. We fabricate 980 nm VCSELs with the angular dependent HCG functioning as a spatial frequency filter. We obtained the single transverse mode operation of the fabricated device in contrast to conventional VCSELs with semiconductor multilayer mirrors

Novel phase-tunable three-dimensional hollow waveguides with variable air core

We propose novel micromachined tunable waveguide devices based on hollow optical waveguides. The combination of hollow waveguides and mechanical movable elements gives us a large change in a propagation constant of guided waves in a hollow waveguides. We fabricated a three-dimensional (3-D) hollow waveguide and experimentally demonstrated the change of the propagation constant in the 3-D hollow waveguide with a variable air core. We observed the wavelength shift of 1.8 nm in a hollow waveguide resonator with a displacement of 6 /spl mu/m in an air core.