III-V/SOI heterogeneous photonic integrated devices for optical interconnection in LSI

金沢大学理工研究域電子情報学系InP-based photonic devices on SOI substrate using bonding technologies were demonstrated. Direct bonding and BCB bonding enable us to realize high optical confinement DFB lasers and other devices for intra/inter-chip connection in Si LSI circuit. Low threshold optical pumped membrane lasers and CW-operation of lateral current injection lasers with thin lateral cladding lasers were realized. ©2009 IEEE

GaInAsP/InP membrane lasers for optical interconnects

In this paper, the state-of-the art of long-wavelength GaInAsP/InP membrane semiconductor lasers, one of the most promising candidate light sources for optical interconnects and on-chip optical wiring between large-scale integrated circuits, is described. After an extensive review of research activities focused on laser preparation on either Si or Si-on-insulator substrate, the findings of our recent research activities on low power consumption lasers are presented. Specifically, our interest was set on the low-damage fabrication of strongly index-coupled grating, which is generally opted forDFB and distributed reflector (DR) lasers consisting of wire-like active regions, as well as of high index-contrast membrane waveguides. A submilliampere threshold current and a differential quantum efficiency close to 50 from the front facet were achieved in the case of the DR laser. On the other hand, a lateral current injection (LCI) structure, which can be combined with the membrane laser, was adopted for the realization of an injection-type membrane laser. The successful continuous wave operation of LCI lasers, prepared on a semiinsulating InP substrate, was achieved with moderately low threshold current at room temperature. © 2011 IEEE

The Distance to the Galactic Center Derived From Infrared Photometry of Bulge Red Clump Stars

On the basis of the near infrared observations of bulge red clump stars near the Galactic center, we have determined the galactocentric distance to be R_0 = 7.52 +- 0.10 (stat) +- 0.35 (sys) kpc. We observed the red clump stars at |l| < 1.0 deg and 0.7 deg < |b| < 1.0 deg with the IRSF 1.4 m telescope and the SIRIUS camera in the H and Ks bands. After extinction and population corrections, we obtained (m - M)_0 = 14.38 +- 0.03 (stat) +- 0.10 (sys). The statistical error is dominated by the uncertainty of the intrinsic local red clump stars' luminosity. The systematic error is estimated to be +- 0.10 including uncertainties in extinction and population correction, zero-point of photometry, and the fitting of the luminosity function of the red clump stars. Our result, R_0 = 7.52 kpc, is in excellent agreement with the distance determined geometrically with the star orbiting the massive black hole in the Galactic center. The recent result based on the spatial distribution of globular clusters is also consistent with our result. In addition, our study exhibits that the distance determination to the Galactic center with the red clump stars, even if the error of the population correction is taken into account, can achieve an uncertainty of about 5%, which is almost the same level as that in recent geometrical determinations.Comment: 14 pages, 4 figures, accepted by Ap

Interstellar Extinction Law in the J, H, and Ks Bands toward the Galactic Center

We have determined the ratios of total to selective extinction in the near-infrared bands (J, H, Ks) toward the Galactic center from the observations of the region |l| < 2.0deg and 0.5deg < |b| < 1.0deg with the IRSF telescope and the SIRIUS camera. Using the positions of red clump stars in color-magnitude diagrams as a tracer of the extinction and reddening, we determine the average of the ratios of total to selective extinction to be A(Ks)/E(H-Ks) = 1.44+-0.01, A(Ks)/E(J-Ks) = 0.494+-0.006, and A(H)/E(J-H) = 1.42+-0.02, which are significantly smaller than those obtained in previous studies. From these ratios, we estimate that A(J) : A(H) : A(Ks) = 1 : 0.573+-0.009 : 0.331+-0.004 and E(J-H)/E(H-Ks) = 1.72+-0.04, and we find that the power law A(lambda) \propto lambda^{-1.99+-0.02} is a good approximation over these wavelengths. Moreover, we find a small variation in A(Ks)/E(H-Ks) across our survey. This suggests that the infrared extinction law changes from one line of sight to another, and the so-called ``universality'' does not necessarily hold in the infrared wavelengths.Comment: 18 pages, 9 figures, Accepted for publication in the Ap

Lateral current injection GaInAsP/InP laser on semi-insulating substrate for membrane-based photonic circuits

金沢大学理工研究域電子情報学系A room-temperature pulsed operation was demonstrated using lateral current injection-type lasers composed of a 400-nm-thick GaInAsP core layer with compressively strained 5 quantum wells. A threshold current of 105 mA and corresponding density of 1.3 kA/cm2 (260 A/cm2 per well) were obtained with the stripe width of 5.4 μm and the cavity length of 1.47 mm. A fundamental transverse mode operation was obtained with the narrower stripe device of 2.0 μm and the cavity length of 805 μm, while the threshold current and corresponding density were 49 mA and 3.0 kA/cm 2, respectively. © 2009 Optical Society of America

Herbig Ae/Be Stars in the Magellanic Bridge

We have found Herbig Ae/Be star candidates in the western region of the Magellanic Bridge. Using the near infrared camera SIRIUS and the 1.4 m telescope IRSF, we surveyed about 3.0 deg x 1.3 deg (24 deg < RA < 36 deg, -75 deg < Dec. < -73.7 deg) in the J, H, and Ks bands. On the basis of colors and magnitudes, about 200 Herbig Ae/Be star candidates are selected. Considering the contaminations by miscellaneous sources such as foreground stars and early-type dwarfs in the Magellanic Bridge, we estimate that about 80 (about 40%) of the candidates are likely to be Herbig Ae/Be stars. We also found one concentration of the candidates at the young star cluster NGC 796, strongly suggesting the existence of pre-main-sequence (PMS) stars in the Magellanic Bridge. This is the first detection of PMS star candidates in the Magellanic Bridge, and if they are genuine PMS stars, this could be direct evidence of recent star formation. However, the estimate of the number of Herbig Ae/Be stars depends on the fraction of classical Be stars, and thus a more precise determination of the Be star fraction or observations to differentiate between the Herbig Ae/Be stars and classical Be stars are required.Comment: 22 pages, 6 figures. Accepted for publication in Ap

Eukaryotic ribosomal protein RPS25 interacts with the conserved loop region in a dicistroviral intergenic internal ribosome entry site

The intergenic region-internal ribosome entry site (IGR-IRES) of dicistroviruses binds to 40S ribosomal subunits in the absence of eukaryotic initiation factors (eIFs). Although the conserved loop sequences in dicistroviral IGR-IRES elements are protected from chemical modifications in the presence of the 40S subunit, molecular components in the 40S subunit, which interacts with the loop sequences in the IRES, have not been identified. Here, a chemical crosslinking study using 4-thiouridine-labeled IGR-IRES revealed interactions of the IGR-IRES with several 40S proteins but not with the 18S rRNA. The strongest crosslinking signal was identified for ribosomal protein S25 (rpS25). rpS25 is known to be a neighbor of rpS5, which has been shown to interact with a related IGR-IRES by cryo-electron microscopy. Crosslinking analysis with site-directed mutants showed that nucleotides UU(6089–6090), which are located in the loop region in conserved domain 2b in the IRES, appear to interact with rpS25. rpS25 is specific to eukaryotes, which explains why there is no recognition of the IGR-IRES by prokaryotic ribosomes. Although the idea that the IGR-IRES element may be a relict of a primitive translation system has been postulated, our experimental data suggest that the IRES has adapted to eukaryotic ribosomal proteins

Near-Infrared Imaging Polarimetry of the Serpens Cloud Core: Magnetic Field Structure, Outflows, and Inflows in A Cluster Forming Clump

We made deep NIR imaging polarimetry toward the Serpens cloud core. The polarization vector maps enable us to newly detect 24 small IR reflection nebulae with YSOs. Polarization measurements of NIR point sources indicate an hourglass-shaped magnetic field, of which symmetry axis is nearly perpendicular to the elongation of the C18O (J=1-0) or submillimeter continuum emission. The bright part of C18O (J=1-0), submillimeter continuum cores as well as many class 0/I objects are located just toward the constriction region of the hourglass-shaped magnetic field. Applying the CF method, the magnetic field strength was estimated to be ~100 muG, suggesting that the ambient region of the Serpens cloud core is moderately magnetically supercritical. These suggest that the Serpens cloud core first contracted along the magnetic field to be an elongated cloud, which is perpendicular to the magnetic field, and that then the central part contracted cross the magnetic field due to the high density in the central region of the cloud core, where star formation is actively continuing. Comparison of this magnetic field with the previous observations of molecular gas and large-scale outflows suggests a possibility that the cloud dynamics is controlled by the magnetic field, protostellar outflows and gravitational inflows. This appears to be in good agreement with the outflow-driven turbulence model and implies the importance of the magnetic field to continuous star formation in the center region of the cluster forming region.Comment: 36 pages, 11 figures, 2 tables, accepted for publication in the Astrophysical Journa