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 $\mathrm{\Gamma -X}$ directions is successfully observed, where the wavelength of the active layer is designed to match the folded (second-order) Γ point of the $\mathrm{\Gamma -X}$ 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 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.

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.

In this work, we present a simple complementary metal-oxide semiconductor (CMOS)-controlled photovoltaic power-transfer platform that is suitable for very small (less than or equal to 1–2 mm) electronic devices such as implantable health-care devices or distributed nodes for the Internet of Things. We designed a 1.25 mm × 1.25 mm CMOS power receiver chip that contains integrated photovoltaic cells. We characterized the CMOS-integrated power receiver and successfully demonstrated blue light-emitting diode (LED) operation powered by infrared light. Then, we integrated the CMOS chip and a few off-chip components into a 1-mm³ implantable optogenetic stimulator, and demonstrated the operation of the device.

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 rabbit's retina.

In this study, we demonstrate a polarization sensitive pixel for a complementary metal-oxide-semiconductor (CMOS) image sensor based on 65-nm standard CMOS technology. Using such a deep-submicron CMOS technology, it is possible to design fine metal patterns smaller than the wavelengths of visible light by using a metal wire layer. We designed and fabricated a metal wire grid polarizer on a 20 × 20 μm² pixel for image sensor. An extinction ratio of 19.7 dB was observed at a wavelength 750 nm.