A novel GaInNAs-GaAs quantum-well structure for long-wavelengthsemiconductor lasers

We propose a novel quantum-well (QW) structure for GaInNAs-GaAs lasers that can emit 1.3 μm or longer wavelength light. The idea is insertion of lattice-matched GaInNAs intermediate layers between well and barrier, which is effective for elongating the emission wavelength and reducing well thickness. It is shown that 1.3-μm emission is achievable by using the proposed GaInNAs-GaAs QW with a well thickness thinner than that of conventional rectangular GaInNAs QWs. This structure will relax the design limitation of strained GaInNAs layers     

Therapeutic effects of beclomethasone dipropionate enemas on colon damage of inflammatory bowel disease model rats]

The effects of beclomethasone dipropionate (BDP) enemas on ulcerative colitis were investigated by administrating BDP enemas to Fischer male rats with an inflammatory bowel disease induced by 2,4,6-trinitrobenzensulfonic acid (TNB). After administration of a TNB ethanol solution to rats, diarrhea and melena were found in all rats, and the wet tissue weights of the colons in the rats increased by erosion and thickness of epithelial mucous membranes with edema. BDP enemas were administered to the rats one time a day at a dose of 20 or 50 micrograms of BDP for 4 or 11 days from the day 3 after TNB treatment, respectively. After dosing of BDP, the rate of rats developing diarrhea and melena decreased more with time in comparison with that of BDP-free rats, and the symptoms of all rats developing the diseases were improved on the day 4 after administration of a dose of 50 micrograms of BDP. A dose dependent recovery in the wet tissue weights and scores of damages, and the myeloperoxidase (MPO) activity in the tissue were found at the early days (until the day 4). However, their measurements on the day 11 at each dose of BDP were not different from those of control rats significantly, as the damages in the colons of the control rats were recovered naturally with time. In conclusion, the clinical usefulness of BDP enemas was supported by elucidating the dose dependent effect of BDP at the early days in the model rats with an inflammatory bowel disease induced by TNB.     

Microstructure and hydrogen desorption characteristics of hydrogenated ScH2–MBn (M = Mg and Ca) systems synthesized by mechanical milling

The mixtures of scandium hydride ScH₂ and metal boride MB_n, which is MgB₂ or CaB₆, were hydrogenated by mechanical milling under hydrogen pressure at room temperature. ScH₂–MgB₂ and ScH₂–CaB₆ desorbed 3.4 and 2.3 mass% of H₂, respectively, with peaks below 300 °C. The results of synchrotron radiation X-ray powder diffraction and X-ray absorption spectroscopy at the Sc K-edge indicated that ScB₂ was produced by milling. Fourier-transform infrared spectroscopy suggested that hydrogen was stored as B–H bonds in the as-milled samples. Nuclear magnetic resonance spectroscopy clarified the presence of metal borohydrides M(BH₄)₂ (M = Mg and Ca) in the as-milled ScH₂–MB_n mixtures. These results indicate that M(BH₄)₂ is synthesized by milling the ScH₂–MB_n mixtures under hydrogen pressure at room temperature, and hydrogen was desorbed from M(BH₄)₂. The by-products of M(BH₄)₂ are MgH₂ in the M = Mg case, which was observed by transmission electron microscopy, and ScB₂ in both cases.     

Topology optimization for thermal conductors considering design-dependent effects,including heat conduction and convection

In structural designs considering thermal loading, in addition to heat conduction within the structure, the heat convection upon the structure’s surface can significantly influence optimal design configurations. In this paper, we focus on the influence of design-dependent effects upon heat convection and internal heat generation for optimal designs developed using a topology optimization scheme. The method for extracting the structural boundaries for heat convection loads is constructed using a Hat function, and heat convection shape dependencies are taken into account in the heat transfer coefficient using a surrogate model. Several numerical examples are presented to confirm the usefulness of the proposed method.     

Multi-oxide layer structure for single-mode operation invertical-cavity surface-emitting lasers

We propose a novel vertical-cavity surface emitting laser (VCSEL) with Al(Ga)As multi-oxide layer (MOX) structure for the purpose of enlarging window aperture maintaining single transverse mode operation. We have fabricated an InGaAs-GaAs VCSEL with the proposed MOX structure formed on GaAs (311)B substrate. We have performed a numerical simulation to investigate single-mode behavior of the proposed structure and showed a possibility of single-mode VCSEL's with a large active area. We have fabricated an 11-μm current aperture 960-nm wavelength VCSEL with this MOX structure. The threshold current and voltage were 1.0 mA and 2.0 V, respectively, which are comparable to those of conventional oxide VCSELs. In 8-μm aperture, single-mode operation was maintained with a driving current up to four times the threshold     

Consideration on threshold current density of GaInAsP/InP surface emitting junction lasers

The oscillation condition of the GaInAsP/InP surface emitting (SE) junction laser (lambda = 1.3mum) is examined. Theoretical calculations indicate that reflectivity of the mirrors of a Fabry-Perot resonator is necessary to be 95 percent for a reasonably low threshold current density. Then, we have fabricated a new structure for SE laser and compared its threshold current density with the theoretical estimation. In order to maintain the necessary reflectivity without deteriorating the ohmic contact, we adopted a ring electrode where the reflecting mirror is separated from thep-side electrode. The threshold current was reduced down to 35 mA at 77 K which is 70 percent of the early experiment. The threshold current density was estimated to be 5 kA/ cm². The estimated reflectivity was 80-85 percent. The operating temperature has been raised to -21°C (252 K). The temperature dependence of the threshold current near room temperature suggests that room temperature operation of GaInAsP/InP SE lasers is possible by increasing the reflectivity of mirrors and current confinement.     

Frequency chirping of external modulation and its reduction

A general formula is given for frequency chirping of external intensity loss modulation which is caused by phase modulation due to an accompanied refractive index change. It can be reduced by optimising the optical modulation waveform, and a related ultimate bandwidth of such small chirping single-mode fibre transmission will be presented.