Daisuke Inoue

Sub-milliampere threshold operation of butt-jointed built-in membrane DFB laser bonded on Si substrate

We fabricated GaInAsP/InP waveguide-integrated lateral-current-injection (LCI) membrane distributed feedback (DFB) lasers on a Si substrate by using benzocyclobutene (BCB) adhesive bonding for on-chip optical interconnection. The integration ofa butt-jointed built-in (BJB) GaInAsP passive waveguide was performed by organometallic vapor-phase epitaxy (OMVPE).By introducing a strongly index-coupled DFB structure with a 50-µm-long cavity, a threshold current of 230 µA was achieved for a stripe width of 0.8 µm under room-temperature continuous-wave (RT-CW) conditions. The maximum output power of 32 µW was obtained. The lasing wavelength and submode suppression ratio (SMSR) were 1534 nm and 28 dB, respectively, at a bias current of 1.2 mA.

Room-temperature continuous-wave operation of membrane distributed-reflector laser

In this paper, we report on the first ever demonstration of a continuous-wave operation of an injection-type membrane distributed-reflector (DR) laser at room temperature. A threshold current of 250 µA was obtained with a stripe width of 0.7 µm, a DFB region length of 30 µm, and a DBR region length of 90 µm. An external differential quantum efficiency of 11% with a light output ratio between the front and the rear of 6.7 was obtained at the front waveguide.

Room-temperature continuous-wave operation of GaInAsP/InP lateral-current-injection membrane laser bonded on Si substrate

We successfully demonstrated room-temperature continuous-wave (RT-CW) operation of a lateral-current-injection (LCI) GaInAsP/InP membrane Fabry–Perot laser by benzocyclobutene (BCB) adhesive bonding on a Si substrate for the first time. Our results include, for example, a threshold current of 2.5 mA and an external differential quantum efficiency of 22% per facet were obtained for a stripe width of 0.7 µm and a cavity length of 350 µm. From measurements of the differential quantum efficiency as a function of the cavity length, an internal quantum efficiency of 75% and a waveguide loss of 42 cm−1 were obtained.

Experimental and Theoretical Considerations of Polarization Field Direction in Semipolar InGaN/GaN Quantum Wells

The polarization-related electric field in semipolar {1122} InGaN/GaN quantum wells (QWs) is investigated. Experimentally, the direction and magnitude of the electric field are determined by bias-dependent photoluminescence. Using both (1122) and the reverse (1122) QWs enables the electric field direction, which indicates that the polarization direction flips between the polar (0001) plane and semipolar (1122) plane, to be reliably determined. Lattice distortion due to lattice mismatch, which is the origin of the polarization effect, is theoretically assessed by the valence force field model, and the analysis supports the experimental result.

Low-bias current 10 Gbit/s direct modulation of GaInAsP/InP membrane DFB laser on silicon.

Low-power consumption directly-modulated lasers are a key device for on-chip optical interconnection. We fabricated a GaInAsP/InP membrane DFB laser that exhibited a low-threshold current of 0.21 mA and single-mode operation with a sub-mode suppression ratio of 47 dB at a bias current of 2 mA. A high modulation efficiency of 11 GHz/mA1/2 was obtained. A 10 Gbit/s direct modulation using a non-return-to-zero 231-1 pseudo-random bit sequence signal was performed with a bias current of 1 mA, which is the lowest bias current ever reported for direct modulation of a DFB laser. A bit-error rate of 10-9 was successfully achieved.

High-modulation efficiency operation of GaInAsP/InP membrane distributed feedback laser on Si substrate

The direct modulation characteristics of a membrane distributed feedback (DFB) laser on a silicon substrate were investigated. Enhancement of the optical confinement factor in the membrane structure facilitates the fabrication of a strongly index-coupled (κ(I) = 1500 cm(-1)) DFB laser with the cavity length of 80 µm and a threshold current of 270 µA. Small-signal modulation measurements yielded a -3dB bandwidth of 9.5 GHz at 1.03-mA bias current, with modulation efficiency of 9.9 GHz/mA(1/2), which is, to the best of our knowledge, the highest value among those reported for DFB lasers.

Identification and characterization of an insulin receptor substrate 4-interacting protein in rat brain: Implications for longevity

The hypothalamus is organized as a collection of distinct, autonomously active nuclei that regulate discrete functions, such as feeding activity and metabolism. We used suppression subtractive hybridization (SSH) to identify genes that are enriched in the hypothalamus of the rat brain. We screened a subtractive library of 160 clones, and 4 genes that were predominantly expressed in the hypothalamus, compared to other brain regions. The mRNA for a member of the WD-repeat family of proteins, WDR6, was abundantly expressed in the hypothalamus, and we found that WDR6 interacted with insulin receptor substrate 4 (IRS-4) in the rat brain. Interestingly, WDR6 gene expression in the hypothalamic arcuate nucleus was decreased by caloric restriction, and in growth hormone (GH)-antisense transgenic rats, both of which are associated with an increased life span. Insulin-like growth factor (IGF)-I and insulin treatment increased WDR6 gene expression in mouse hypothalamus-derived GT1-7 cells. Our results might suggest that WDR6 participates in insulin/IGF-I signaling and the regulation of feeding behavior and longevity in the brain.

Structural and electrical properties of poly-SiGe thin films prepared by reactive thermal CVD

Abstract Polycrystalline thin films of Si × Ge (0.95≥×≥0.05, poly-SiGe) were prepared on SiO 2 and glass substrates by thermal chemical vapor deposition (CVD) from Si 2 H 6 and GeF 4 at 450°C. The Ge-rich films had a high crystallinity owing to the direct nucleation of crystallites on the substrates. The crystallinity of Si-rich films, however, depended on the growth rate, and the direct nucleation was achieved at smaller growth rates, leading to improvement of the crystallinity. All the films were p-type regardless of film composition, whose carrier concentration decreased from 10 18 cm −3 to 10 12 cm −3 , and the Hall mobility from 100 cm 2 /Vs to 1 cm 2 /Vs with an increase in the Si content in the films. The Hall mobility was improved up to 8 cm 2 /Vs in the film prepared at a growth rate of 3.6 nm/min.

High crystallinity poly-SixGe1-x at 450°C on amorphous substrates

The composition variation and strutural properties of poly-SiGe thin films prepared by Reactive Thermal chemical vapor deposition (CVD) with Si2H6 and GeF4 were investigated. Deposition of the films at 450° C was carried out with various gas flow ratios of Si2H6 to GeF4 on amorphous substrates such as glass plates and oxidized silicon wafers. The structural profiles of films were characterized by X-ray diffraction (XRD) and Raman scattering spectroscopies, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). All films show high crystallinity and (220) prefered orientation. The mole fractions of Si in the Six Ge1-x films were estimated to be from 0.95 to 0.05 for x, using Vegards law for the XRD peaks. Crystallinity in the Si-rich films was affected by growth rate and was greatly improved at lower growth rates. TEM observation revealed that high crystallinity was well established, even in poly- Si0.95Ge0.05 film, owing to direct polycrystalline layer growth on the substrate surface.

Monolithic Integration of Membrane-Based Butt-Jointed Built-in DFB Lasers and p-i-n Photodiodes Bonded on Si Substrate

We demonstrate a monolithic integration of lateral-current-injection (LCI)-type membrane-based distributed-feedback (DFB) lasers and p-i-n-photodiodes (PDs) using a butt-jointed built-in (BJB) structure bonded on a Si substrate using benzocyclobutene. The BJB structure to be integrated to the membrane optical devices was prepared by organometallic vapor-phase epitaxy. A threshold current of 280 μA was obtained under a room-temperature continuous-wave condition by adopting a strongly index-coupled DFB laser with a surface grating structure and a λ/4-shift region. A low dark current of 0.8 nA was obtained with the p-i-n-PD at a bias voltage of -1 V, and its photocurrent property coincided with the light output property of the membrane DFB laser.