Takashi Tokuda

Coherent two-dimensional lasing action in surface-emitting laser with triangular-lattice photonic crystal structure

Lasing action of a surface-emitting laser with a two-dimensional photonic crystal structure is investigated. The photonic crystal has a triangular-lattice structure composed of InP and air holes, which is integrated with an InGaAsP/InP multiple-quantum-well active layer by a wafer fusion technique. Uniform two-dimensional lasing oscillation based on the coupling of light propagating in six equivalent Γ−X directions is successfully observed, where the wavelength of the active layer is designed to match the folded (second-order) Γ point of the Γ−X direction. The very narrow divergence angle of far field pattern and/or the lasing spectrum, which is considered to reflect the two-dimensional stop band, also indicate that the lasing oscillation occurs coherently.

COMPOSITIONAL INHOMOGENEITY AND IMMISCIBILITY OF A GAINN TERNARY ALLOY

Compositional inhomogeneity in a GaInN ternary alloy layer is investigated. A theoretical estimation of the interaction parameter based on the delta lattice parameter suggests that the immiscibility of InN in a nitride alloy is very strong. We investigate the compositional splitting and the existence of InN inclusion in the GaInN epilayer grown on sapphire (0001) substrates. The mechanism of compositional inhomogeneity is discussed.

Implantable CMOS Biomedical Devices

The results of recent research on our implantable CMOS biomedical devices are reviewed. Topics include retinal prosthesis devices and deep-brain implantation devices for small animals. Fundamental device structures and characteristics as well as in vivo experiments are presented.

Design of Chiral Bifunctional Quaternary Phosphonium Bromide Catalysts Possessing an Amide Moiety

Novel bifunctional quaternary phosphonium bromides possessing an amide moiety were designed for the highly enantioselective sulfenylation and chlorination of β-ketoesters under base-free phase-transfer conditions. The tuning of an amide moiety of the catalyst was crucial to achieve high reactivity and enantioselectivity.

CMOS-Based Multichip Networked Flexible Retinal Stimulator Designed for Image-Based Retinal Prosthesis

We propose and characterize a CMOS LSI-based neural stimulator for retinal prosthesis technology. The stimulator is based upon a multichip architecture in which small-sized CMOS stimulators named ldquounit chipsrdquo are organized on a flexible substrate. We designed a unit chip with an on-chip stimulator and light-sensing circuitry. We verified that all the functions implemented on the unit chip worked correctly and that an organized unit chip can be used as a retinal stimulator with multisite image-based patterned stimulation. We also demonstrated light-controlled retinal stimulation for the first time in an in vivo animal experiment on a rabbits retina.

Catalytic Asymmetric Synthesis of 3,3′‐Diaryloxindoles as Triarylmethanes with a Chiral All‐Carbon Quaternary Center: Phase‐Transfer‐Catalyzed SNAr Reaction

Catalytic asymmetric synthesis of unsymmetrical triarylmethanes with a chiral all-carbon quaternary center was achieved by using a chiral bifunctional quaternary phosphonium bromide catalyst in the S(N)Ar reaction of 3-aryloxindoles under phase-transfer conditions. The presence of a urea moiety in the chiral phase-transfer catalyst was important for obtaining high enantioselectivity in this reaction.

One-chip sensing device (biomedical photonic LSI) enabled to assess hippocampal steep and gradual up-regulated proteolytic activities

We developed an implantable one-chip biofluoroimaging device (termed biomedical photonic LSI; BpLSI) which enabled real-time molecular imaging with conventional electrophysiology in vivo in deep brain areas. The multimodal LSI enabled long-term sequential imaging of the fluorescence emitted by proteolysis-linked fluorogenic substrate. Using the BpLSI, we observed a process of stimulation-dependent modulation at synapse with multi-site (16 x 19 pixel) in widespread area and a high-speed video rate, and found that the gradual up-regulated proteolytic activity in a wide range of hippocampal CA1 area and the steep activity in local area, indicating that the proteolysis system is a basis for the fixation of long-term potentiation in post-excited synapses in the hippocampus. Mathematical data analysis confirmed the direct involvement of functional proteolysis for neural plasticity.

Silicon LSI-based smart stimulators for retinal prosthesis

In this article, the authors report on a retinal prosthesis smart stimulator that is biocompatible and fully compatible with a standard large-scale-integration (LSI) structure and that provides high-stimulation efficiency. Our stimulator is based on multimicrochip architecture. The stimulator has been specifically developed for retinal prostheses, but it could be applied to other neuroscience and clinical neuroengineering fields

Efficient approach for the design of effective chiral quaternary phosphonium salts in asymmetric conjugate additions

An efficient approach for the design of chiral quaternary phosphonium bromides as chiral phase-transfer catalysts was demonstrated. A catalyst library of phosphonium salts with various structures was readily constructed using commercially available chiral phosphines as catalyst precursors, and an optimized catalyst was successfully applied to highly enantioselective conjugate additions under base-free phase-transfer conditions with low catalyst loading.

Real time in vivo imaging and measurement of serine protease activity in the mouse hippocampus using a dedicated complementary metal-oxide semiconductor imaging device.

The aim of the present study is to demonstrate the application of complementary metal-oxide semiconductor (CMOS) imaging technology for studying the mouse brain. By using a dedicated CMOS image sensor, we have successfully imaged and measured brain serine protease activity in vivo, in real-time, and for an extended period of time. We have developed a biofluorescence imaging device by packaging the CMOS image sensor which enabled on-chip imaging configuration. In this configuration, no optics are required whereby an excitation filter is applied onto the sensor to replace the filter cube block found in conventional fluorescence microscopes. The fully packaged device measures 350 microm thick x 2.7 mm wide, consists of an array of 176 x 144 pixels, and is small enough for measurement inside a single hemisphere of the mouse brain, while still providing sufficient imaging resolution. In the experiment, intraperitoneally injected kainic acid induced upregulation of serine protease activity in the brain. These events were captured in real time by imaging and measuring the fluorescence from a fluorogenic substrate that detected this activity. The entire device, which weighs less than 1% of the body weight of the mouse, holds promise for studying freely moving animals.