Search

Both high-beam-quality and high-power operation of InGaN laser array are realized by lateral-corrugated waveguides (LCWG) with reduced higher-order transverse modes. In our proposed structure, the number of higher-order modes supported by the waveguide and scattered by the LCWG is smaller than that of a conventional LCWG, which suppresses the deterioration of quantum efficiency. This contributes to high-power operation for laser processing, since the maximum output power of an array is sensitive to the efficiency. Even at 55 W from a single InGaN array chip, averaged lateral beam-quality factor of 4.9 is successfully obtained for individual emissions in the array.

Both high-beam-quality and high-power operation of InGaN laser diodes are realized by lateral corrugated waveguides with reduced higher-order transverse modes. As a result, lateral beam-quality factor is reduced from 8.8 (straight waveguide) to 3.8 even at a continuous-wave output power of 2.1 W.

A smile-suppressed high-power InGaN laser array has been developed for a high beam quality material processing light source. The smile effect becomes apparent especially in InGaN laser array with large chip curvature due to lattice mismatch of epitaxial growth layers. To reduce the smile, periodic grooves are introduced to the epitaxial layers for removing the origin of strain. It also enables a two-dimensional strain management of remaining epitaxial layers. This technology improves the chip curvature within micron range, i.e. as small as 0.3 μm in a 9 mm-width InGaN laser array. We have successfully realized reducing the smile to 0.4 μm without degrading the laser light output characteristics.

High-power over 7W is presented in a single-emitting GaN diode laser with optical-loss suppressed waveguide structure. Here, thick undoped optical waveguide eliminates undesired light leakage to the absorbing p-cladding layer and thus leads the device to a high slope efficiency operation. The diode laser pumped white spotlight illuminator achieves a luminous efficiency 51.3 lm/W at a flux of 861 lm.

We propose optical-loss suppressed thick-optical-waveguide (TOW) InGaN laser diodes (LDs) without operatingvoltage increase. A record high continuous-wave (CW) output of 7.2W for a single-emitting InGaN LD is achieved without thermal peak-out in the light-current curve. The TOW enables to confine major part of the propagating light into a transparent undoped region, and thus significantly reduces the optical-loss. An electron-overflow-suppression (EOS) layer placed between the waveguide layer and a p-cladding layer plays an important role to reduce the operating voltage after introduction of the undoped TOW layer. We executed a self-consisted calculation of voltage-current characteristics taking into account Schrodinger and Poisson equations in conjunction with a carrier continuity equation. The calculation result indicates possible presence of conductivity-modulation in the waveguide filled with electrons reflected backward by the EOS layer and holes injected from the p-type cladding layer. We successfully demonstrated the optical-loss suppressed operation resulting in the slope efficiency (SE) increase from 2.0W/A to 2.5W/A. It is noted that the operating voltage of the TOW LD is nearly identical to the conventional LD thanks to the above conductivitymodulation phenomenon. The presented result suggests that our TOW structure can overcome the optical-loss drawback of the InGaN LDs, and hence will lead them to the applications requiring high wattage light sources.

We report on continuous wave lasing characteristics of GaN vertical cavity surface emitting lasers (VCSELs). The VCSEL operates at room temperature under current injection by using highly reflective distributed Bragg reflectors (DBRs) made up of transparent ${\rm ZrO}_{2}$ and ${\rm SiO}_{2}$ film stacks. Together with high reflectivity and the wide stop band of the DBR, the long cavity of 6 $\mu{\rm m}$ allows multimode lasing oscillation with narrow mode spacing of 2.9 nm. In addition, a short cavity structure of 2 $\mu{\rm m}$ is fabricated and shows quasi-single mode operation. The spacing of the lasing modes shows a clear dependence of the actual cavity lengths with fairly good agreement to theory taking account of the refractive index dispersion.

High-power InGaN-based laser diodes (LDs) are expected as light-sources of various high-power applications. The catastrophic-optical-damage (COD) is a major failure mechanism to limit the output power, where optical absorption at a light-emitting facet causes an irreversible damage to the LDs. In this paper, a window structure in InGaN-based LDs to suppress the COD is demonstrated for the first time. The structure is formed by the metal organic chemical vapor deposition growth over a recess placed besides of the ridge-waveguide. The In composition in the quantum well which is corresponding to the bandgap energy is reduced by controlling the local tilt angle at the sidewall of the recess. Thus, the formed window structure eliminates undesired optical absorption at the cleaved facet so that extremely high light output power over 2 W in narrow-stripe ridge-waveguide InGaN-based blue-violet LDs is achieved without any CODs.

High concentration (more than 1 × 1018 cm−3) of hydrogen atoms remaining in Mg-doped GaN epitaxial layers grown by metalorganic chemical vapor deposition even after conventional annealing in N2 ambient could induce degradation in GaN-based devices containing Mg-doped layers. In this study, by annealing Mg-doped nitrides in NF3 ambient, we successfully reduced residual hydrogen below mid-1017 cm−3, which is much smaller than by N2 annealing. NF3 annealing enhances outdiffusion of hydrogen from the bulk, which is possibly because the nitrogen and fluorine radicals decomposed from NF3 accelerate desorption of hydrogen adatoms from the surface. The proposed method for Mg activation would improve the reliability of GaN-based light-emitting diodes and laser diodes.

We report on the photoluminescence (PL) and lasing characteristics of GaInNAs/GaAsP strain-compensated quantum wells (QWs) as a function of the amount of strain-compensation. The PL intensity of GaInNAs/GaAs(P) QWs was increased by increasing both the thickness and phosphorous (P) content of GaAsP strain-compensation layers. It was also shown that strain compensation is beneficial for increasing of the number of GaInNAs QWs. The threshold current densities of lasers were improved by introducing strain compensation.

We have studied photoluminescence (PL) properties of GaInNAs quantum wells (QWs) which have GaInAs intermediate layers (IML) inserted at the GaInNAs/GaAs heterointerfaces. Lasing characteristics of the laser using IML are also investigated. We point out that the total amount of nitrogen (N) in the GaInNAs QW could be reduced by using the GaInAs IML while maintaining the emission wavelength. We also found that the optical quality of the GaInNAs IML QWs depends on both the N composition and the total amount of N incorporated in the QW. Due to the reduced total amount of N, an IML QW evidently exhibited a better PL property than a conventional rectangular potential QW. No deterioration in lasing characteristics was observed for GaInNAs lasers using GaInAs IML. The GaInAs IML structure with an appropriate design is expected to lead to improved lasing characteristics of GaInNAs lasers.

We report on design and lasing characteristics of GaN vertical-cavity surface-emitting lasers (VCSELs) with an elongated cavity for use in uniform elements of a two-dimensional (2D) laser array. Calculations of VCSELs with the elongated cavity taking into account the wavelength dispersion of the refractive index show that the transverse mode spacing can be significantly narrower than the gain spectrum with a small tradeoff of the differential quantum efficiency. The result clearly shows that the elongated cavity is robust against the thermally induced peakshift of the gain spectrum, and thus preferable for use in elements of density packed laser array for which uniform operation of each element is crucial. The VCSEL with the elongated cavity fabricated by the wafer thinning technique operates under current injection by using highly reflective distributed Bragg reflectors (DBRs) made of transparent ZrO 2 and SiO 2 film stacks. Together with high reflectivity and wide stop band of the DBR, the elongated cavity of 6 μm (36λ) allows multimode lasing oscillation with a mode spacing of 2.9 nm, which is one order of magnitude narrower than the gain spectrum. In addition, we demonstrate a 5x5 GaN VCSEL array.

In this study, we demonstrate a highly strained 1.2 µm GaInAs/GaAs quantum well laser which may be used in high-speed local area networks. Edge emitting lasers with either a GaInP or AlGaAs cladding layer have been fabricated. We have achieved a threshold current density as low as 170 A/cm2 for GaInP-cladding-layer lasers and a high characteristic temperature T 0 as high as 211 K from 30°C to 120°C for AlGaAs-cladding-layer lasers. The material gain coefficient g 0 was estimated to be 1550 cm-1 which is comparable to that of 0.98 µm GaInAs lasers. A preliminary lifetime test under heatsink-free CW condition was carried out, which shows no notable degradation after 300 h. We also demonstrated an AlAs oxide confinement laser in a 1.2 µm wavelength band.

In this paper we experimentally determined the critical layer thickness for highly strained 1.2-μm GaInAs/GaAs quantum wells of good crystal quality. The dependence of the critical layer thickness on the indium content indicates that the observed quality degradation is caused by a growth mode transition. This is also supported by transmission electron microscopy measurements. We discuss the possibility of extending the wavelength of highly strained GaInAs/GaAs quantum wells toward 1.3 μm by delaying the growth mode transition. As a first step, a wavelength extension to 1.225 μm is achieved by using the presented technique.

Proposes two new structures, the GaInAs-GaInNAs intermediate layer (IML) and the GaInN/sub x/As graded wells, which show better optical properties than the commonly used GaInNAs-GaAs rectangular quantum-wells. A 1240-nm emitting IML laser has been achieved with a low-threshold current density (200 A/cm/sup 2//well) and a relatively high characteristic temperature (T/sub o/=100 K). The IML structure is very promising for long wavelength GaAs-based laser applications.

We investigate the effect of the sequence of gas flows at heterointerfaces on optical quality of GaInNAs/GaAs quantum wells grown by metalorganic chemical vapor deposition (MOCVD). We point out that the degradation mechanism of photoluminescence of GaInNAs grown by MOCVD method is categorized in two types. One is the formation of a GaNAs layer at the heterointerface which causes both increase of emission wavelength and degradation of crystal quality. The other is generation of nonradiative centers induced by incorporation of nitrogen (N). The insertion of a GaInAs layer to the GaInNAs/GaAs heterointerface is proposed to overcome these degradation mechanisms. A GaInAs intermediate layer is effective to suppress the GaNAs formation and to reduce the total GaInNAs thickness.

High power operation of GaN-based superluminescent diodes is demonstrated with the emission wavelength of 405nm. Reducing the reflectivity and the optical density at the front facet by the waveguide structure enables high output power of 200mW.

High power over 2W free from catastrophic-optical-damage is achieved in InGaN-based lasers with epitaxially-formed window structure. Epitaxial growth over a recess reduces the In composition which eliminates the undesired optical absorption only at the facet.

A novel GaN-based surface-emitting laser was realized by utilizing total internal reflection (TIR) by an inclined mirror formed at one end of the horizontal cavity of an edge-emitting laser. The inclined mirror was fabricated by focused ion beam (FIB) etching. The mirror was inclined by 45° with respect to the surface normal. The guided light propagating along the horizontal-cavity is reflected at the mirror to the surface normal. We analyzed optical losses in the laser. To increase the external quantum efficiency, removal of an FIB-damaged layer and precise control of the mirror angle are important. Argon-milling was applied to the FIB-etched surface to remove the FIB-damaged layer which causes an optical loss. The fabricated device with the stripe width of 8 µm and the cavity length of 600 μm lased at 390 nm with a threshold current of 260 mA. Surface-emission was obtained with beam divergence angles of 24.0° and 6.2°, corresponding to perpendicular and parallel to the junction plane, respectively. The presented surface-emitting laser is suitable to form high-power GaN-based 2D laser arrays.

The effect of current annealing for GaInNAs laser characteristics was investigated and compared with that of thermal annealing. It was found that the threshold current density was largely reduced by the current annealing and became comparable level as thermal annealing. The wavelength shift after current annealing was small contrary to the thermal annealing showing large blue shift. From the experimental result, we indicated that the annealing effects of the threshold current reduction and wavelength shift depends on different mechanisms.

We found that lasing wavelength, threshold and efficiency of GaInNAs/GaAsP strain-compensated lasers depends on the P content in GaAsP barrier layer. For a P content of 11%, we obtained improved threshold and efficiency compared with GaAs barrier.

We report on GaInNAs intermediate layer (IML) structures for improving the lasing characteristics of GaInNAs quantum well (QW) lasers. Either lattice-matched or strained (∼0.65%) GaInNAs IMLs were inserted at GaInNAs/GaAs interfaces. The elongation of the emission wavelength of IML QW structure was observed while maintaining the photoluminescence (PL) emission efficiency in comparison with that of the GaAs barrier QW structure. The elongation of the lasing wavelength of GaInNAs QW lasers without a threshold penalty was also demonstrated by employing a GaInNAs IML. The IML QW exhibited a reduction in the amount of the wavelength blue shift due to postgrowth thermal annealing.

We have investigated the growth temperature dependence of the optical property change induced by a thermal annealing for a GaInNAs/GaAs quantum well grown by metalorganic chemical vapor deposition. We found that the wavelength blue shift induced by the thermal annealing of GaInNAs strongly depends on the growth temperature. The emission wavelength blue shift significantly decreased at growth temperatures lower than 500/spl deg/C. The obtained result will be useful for improving the performance of GaInNAs lasers especially for vertical-cavity surface-emitting lasers.

We investigated the effect of the gas flow sequence of dimethylhydrazine (DMHy) at heterointerfaces on the optical quality of GaInNAs/GaAs grown by metalorganic chemical vapor deposition (MOCVD). We point out that the photoluminescence (PL) degradation of GaInNAs grown by MOCVD can be categorized into two types. One is the formation of a GaNAs layer at the interface which causes both an unexpected wavelength extension and degradation of crystal quality. Another is introduction of non-radiative centers by N incorporation itself. To overcome these degradation mechanisms, the insertion of GaInAs to the GaInNAs/GaAs heterointerface is proposed. A GaInAs intermediate layer (IML) suppresses GaNAs formation and improve the optical quality of GaInNAs QWs.

We have achieved the lowest threshold current density of 340 A/cm/sup 2/ with a high characteristic temperature of over 200 K in 1.25 /spl mu/m GaInNAs/GaAs lasers grown by MOCVD. A threshold current density per well of 170 A/cm/sup 2/ is the record low value for 1.2/spl sim/1.3 /spl mu/m GaInNAs lasers.

We investigated the crystal quality dependence of GaInNAs/GaAs quantum wells (QWs) on the growth rate for metalorganic chemical vapor deposition (MOCVD). GaInNAs QWs were grown under different growth rates of 0.15, 0.2, 0.6 and 1 /spl mu/m/h. At a growth rate of 0.2 /spl mu/m/h, GaInNAs QWs showed the smallest degradation on photoluminescence (PL) for elongating the wavelength by increasing nitrogen (N) composition. GaInNAs QW stripe lasers, which employ a GaInNAs double QWs (DQWs) active layer grown at the optimized growth rate, exhibits a threshold current density of 340 A/cm/sup 2/, which is the lowest for MOCVD grown GaInNAs lasers ever reported.

Background The leading cause of death in chronic renal dialysis patients is cardiovascular disease. As the number of dialysis patients increases, we are encountering more patients with severe ischemic heart disease requiring coronary intervention. Methods A retrospective analysis was performed of the short- and long-term clinical results in 23 coronary artery bypass grafting patients and 20 coronary angioplasty patients undergoing chronic renal dialysis. Results Among coronary bypass grafting patients, there were no hospital deaths. The graft patency rate was 100% for arterial grafts. There were four late deaths and four cardiac events. In coronary angioplasty patients, the lesion success rate was 76%. There were no hospital deaths and three major complications. The restenosis rate was 70%. There were two late deaths and 14 cardiac events. The 5-year cardiac event-free rate was 70% in coronary bypass grafting patients, significantly better than 18% in coronary angioplasty patients (p Conclusions Coronary artery bypass grafting in chronic renal dialysis patients can be accomplished with a better short- and long-term outcome than coronary angioplasty, through an intensive perioperative dialysis program and extensive use of arterial grafts.

A metal organic chemical vapour deposition grown GaInNAs quantum well laser emitting at 1.25 /spl mu/m is reported. The lowest threshold current density obtained by 50 /spl mu/m wide stripe lasers was 340 A/cm/sup 2/ for a cavity length of 1420 /spl mu/m. Which is almost comparable to the lowest value reported for GaInNAs lasers grown by molecular beam epitaxy. The threshold current density per well was 170 A/cm/sup 2/, which is the lowest threshold value reported to date.

Out of 636 patients with acute myocardial infarction (AMI) admitted to our institution, 183 patients enrolled in our non-supervised home exercise program immediately after their discharge from the hospital. The first 40 patients were randomized to control and training group, while the remaining 143 patients were included in the training group. Before and after the trial, all patients underwent cardiopulmonary exercise testing; submaximal graded treadmill exercise test with the application of expiratory gas analysis. In the training group, patients performed 2 km walk-jog exercise everyday for 1 month, keeping their heart rate (HR) at 90-100% of that in the anaerobic threshold. HR during exercise was monitored by patients themselves, using HR-meter. The anaerobic threshold significantly increased in the training group; while control group had no significant changes. VO2 and HR significantly increased at the same Borg's indices. Psychological improvement was also obtained in the training group compared to control group. It is concluded that non-supervised home exercise program is effective and easily applicable in the convalescent phase of AMI.

A quality improvement of the III–V dilute nitride semiconductor alloy, GaInNAs, grown by metalorganic chemical vapor deposition (MOCVD) on a GaAs substrate is reported for 1.3 µm-wavelength lasers. GaInNAs wafers were grown at various growth temperatures, V/III ratios, and growth rates. The photoluminescence (PL) efficiency of GaInNAs/GaAs quantum wells (QWs) was increased by lowering the growth temperature and increasing the V/III ratio in the growth conditions conventionally used for nitrogen (N)-free GaInAs/GaAs QW growth. These conditions are important for realizing high PL efficiency because they prevent the inhomogeneity of the immiscible alloy of GaInNAs. It was also observed that the optimal window for the growth temperature, V/III ratio, and growth rate for the GaInNAs is narrower than that of N-free GaInAs QWs. After careful optimization of the growth conditions, GaInNAs/GaAs QW lasers with various emission wavelengths were fabricated. Low-threshold current densities of 0.17 kA/cm2/well, 0.18 kA/cm2/well, and 0.44 kA/cm2/well are obtained for emission wavelengths of 1.25 µm, 1.30 µm, and 1.34 µm, respectively. The results obtained for growth conditions and lasing characteristics are useful in further improving 1.3 µm or longer wavelength GaInNAs lasers grown by MOCVD.

We report on the lasing characteristics of low-threshold long-wavelength GaInNAs double quantum well (DQW) lasers grown by metalorganic chemical vapor deposition (MOCVD). We have achieved a threshold current density of 450 A/cm2 for a 1.28-µm-emitting laser. This is the lowest value for 1.3-µm-range GaInNAs lasers grown by MOCVD. We also observed high characteristic temperatures (T 0) of 210 K and 130 K for 1.25 µm and 1.28 µm lasers, respectively. In addition, we investigated the gradual change in lasing characteristics under pulsed operation. The blue shift of an emission wavelength and a threshold current reduction were observed, which is similar to that observed in the thermal annealing of GaInNAs.

GaInNAs/GaAs quantum wells with indium compositions of up to 39% were grown by metalorganic chemical vapor deposition under different growth rates. We found that the growth rate (∼1 µm/h) critically affects the optical quality of GaInNAs/GaAs quantum wells and that a low growth rate (∼0.2 µm/h) is preferable for increasing nitrogen compositions.

We have demonstrated a highly strained GaInAs/GaAs double quantum well laser operating at nearly 1.2 µm with AlGaAs cladding layers for the first time. Our previously reported high characteristic temperature of 150 K was improved to 202 K for a 410-µm-long broad-area GaInAs/GaAs/AlGaAs laser in the temperature range from 30°C to 70°C. The threshold current density of this laser was as low as 370 A/cm2.

An autopsy case of cerebro-hepato-renal syndrome of Zellweger, which occurred in a 14-year-old Japanese girl, is reported. The autopsy revealed widely distributed cystic changes in addition to renal blastema of both kidneys, and the liver was cirrhotic. The case was complicated by anomalies such as high forehead, strabismus, and partial defect of chorioidea. So far there have been only 10 reported cases of cerebro-hepato-renal syndrome of Zellweger in Japan.

The substrate specificity of human endo-beta-N-acetylglucosaminidase was studied by using the homogenate of cultured skin fibroblasts of fucosidosis patients as an enzyme source. The results indicate that biantennary complex type asparagine-linked sugar chains as well as high mannose type sugar chains are cleaved by the enzyme action. None of the sugar chains with a fucosyl residue on the proximal N-acetylglucosamine of their N,N'-diacetylchitobiose moieties was cleaved. These results proved enzymatically the mechanism of production of oligosaccharides detected in the urine of various exoglycosidase deficiencies.

1983年世界保健機構により「心血管疾患の動向と決定因子の多国間モニタリング」計画が立案され,これに呼応してわが国でも「冠動脈疾患患者の登録追跡システム開発」研究が始まった.今回われわれはその研究の一つである急性心筋梗塞症診断基準を作成し,その精度に関して自験例を用いて検討した.診断感度は99%と満足すべきものであり,この基準は急性心筋梗塞症の診断登録に有用であると考えられた.