High-temperature continuous-wave operation of directly grown InAs/GaAs quantum dot lasers on on-axis Si (001).

Laser devices for silicon photonics are expected to be implemented in an integrated environment to complement CMOS devices. For this reason, quantum dot (QD) lasers with excellent thermal properties have been considered as strong candidates for Si photonics light sources. The direct growth of QD lasers on Si (001) on-axis substrates has been garnering attention owing to the possibility of monolithic integration on a CMOS-compatible wafer. In this paper, we report on the high-temperature (over 100°C) continuous-wave operation of an InAs/GaAs QD laser directly grown on on-axis Si (001) substrates through the use of only molecular beam epitaxy.

All MBE grown InAs/GaAs quantum dot lasers on on-axis Si (001).

Directly grown III-V quantum dot (QD) laser on on-axis Si (001) is a good candidate for achieving monolithically integrated Si photonics light source. Nowadays, laser structures containing high quality InAs / GaAs QD are generally grown by molecular beam epitaxy (MBE). However, the buffer layer between the on-axis Si (001) substrate and the laser structure are usually grown by metal-organic chemical vapor deposition (MOCVD). In this paper, we demonstrate all MBE grown high-quality InAs/GaAs QD lasers on on-axis Si (001) substrates without using patterning and intermediate layers of foreign material.

Thresholdless quantum dot nanolaser.

Thresholdless lasing is an outstanding challenge in laser science and is achievable only in devices having near unity quantum efficiency even when not lasing. Such lasers are expected to exhibit featureless linear light output curves. However, such thresholdless behavior hinders identification of the laser transition, triggering a long-lasting argument on how to identify the lasing. Here, we demonstrate thresholdless lasing in a semiconductor quantum dot nanolaser with a photonic crystal nanocavity. We employ cavity resonant excitation for enabling the thresholdless operation via focused carrier injection into high cavity field regions. Under conventional (above bandgap) excitation, the same nanolaser exhibits a typical thresholded lasing transition, thereby facilitating a systematic comparison between the thresholdless and thresholded laser transitions in the single device. Our approach enables a clear verification of the thresholdless lasing and reveals core elements for its realization using quantum dots, paving the way to the development of ultimately energy-efficient nanolasers.

Direct Observation of Two-Step Photon Absorption in an InAs/GaAs Single Quantum Dot for the Operation of Intermediate-Band Solar Cells.

We present the first direct observation of two-step photon absorption in an InAs/GaAs single quantum dot (QD) using photocurrent spectroscopy with two lasers. The sharp peaks of the photocurrent are shifted due to the quantum confined Stark effect, indicating that the photocurrent from a single QD is obtained. In addition, the intensity of the peaks depends on the power of the secondary laser. These results reveal the direct demonstration of the two-step photon absorption in a single QD. This is an essential result for both the fundamental operation and the realization of ultrahigh solar-electricity energy conversion in quantum dot intermediate-band solar cells.

Nanocavity-based self-frequency conversion laser.

Self-frequency conversion (SFC), where both laser oscillation and nonlinear frequency conversion occurs in the same laser crystal, has been used to efficiently extend the operational wavelength of lasers. Downsizing of the cavity mode volume (V) and increasing the quality factor (Q) could lead to a more efficient conversion process, mediated by enhanced n-th order nonlinearities that generally scale as (Q/V)(n). Here, we demonstrate nanocavity-based SFC by utilizing photonic crystal nanocavity quantum dot lasers. The high Q and small V supported in semiconductor-based nanocavities facilitate efficient SFC to generate visible light, even with only a few photons present in the laser cavity. The combined broadband quantum dot gain and small device footprint enables the monolithic integration of 26 different-color nanolasers (spanning 493-627 nm) within a micro-scale region. These nanolasers provide a new platform for studying few-photon nonlinear optics, and for realizing full-color lasers on a single semiconductor chip.

1.3 µm InAs/GaAs quantum dot lasers on Si rib structures with current injection across direct-bonded GaAs/Si heterointerfaces.

An InAs/GaAs quantum dot laser on a Si rib structure has been demonstrated. The double heterostructure laser structure grown on a GaAs substrate is layer-transferred onto a patterned Si substrate by GaAs/Si direct wafer bonding without oxide or metal mediation. This Fabry-Perot laser operates with current injection through the GaAs/Si rib interface and exhibits InAs quantum dot ground state lasing at 1.28 µm at room temperature, with a threshold current density of 480 A cm(-2).

Comparison of the Importance and Prioritization of Information Communicated to Consumers by Experts Regarding Food Safety.

Key topics related to risk communication and food safety were investigated by three different expert groups. In this study, the Delphi method was used to systematically and iteratively aggregate experts' opinions, and the topics to be communicated to consumers were expressed and prioritized. The opinions of three groups, consisting of 26 members of the expert committee (EC) from the Food Safety Commission of Japan (FSCJ), 29 local government officials (LGOs) from their respective food safety departments, and 25 food safety monitors (FSM) appointed by the FSCJ, were obtained in the period of June through September 2017. "Safety and security concept" was identified and ranked high in all groups. This topic identified "Zero-risk" demand of consumers without understanding risks as the reverse side of safety. The EC group prioritized additional issues, such as "concept of risk" and "safety costs and relevant risk management". The LGO and FSM groups prioritized specific hazard items for food poisoning and preventive measures. With regard to the so-called "health foods", the EC and LGO groups indicated insufficient transmission of scientific evidence from the government to consumers, and the FSM group indicated insufficient understanding by consumers of the food labeling system for health and nutrition. Because consumers do not fully understand all concepts of food safety, governments are encouraged to disseminate the probability of risk and the knowledge of risk reduction directly to the consumers by using simple and easy-to-understand terms.

Coherently driven semiconductor quantum dot at a telecommunication wavelength.

We proposed and demonstrate use of optical driving pulses at a telecommunication wavelength for exciton-based quantum gate operation. The exciton in a self-assembled quantum dot is coherently manipulated at 1.3 microm through Rabi oscillation. The telecom-band exciton-qubit system incorporates standard optical fibers and fiber optic devices. The coherent manipulation of the two-level system compatible with flexible and stable fiber network paves the way toward practical optical implementation of quantum information processing devices.

Room temperature continuous-wave lasing in photonic crystal nanocavity.

We demonstrate room temperature continuous-wave laser operation at 1.3 mum in a photonic crystal nanocavity with InAs/GaAs self-assembled quantum dots by optical pumping. By analyzing a coupled rate equation and the experimental light-light characteristic plot, we evaluate the spontaneous emission coupling factor of the laser to be ~ 0.22. Three-dimensional carrier confinement and a low transparent carrier density due to volume effect in a quantum dot system play important roles in the cw laser operation at room temperature as well as a high quality factor photonic crystal nanocavity.

[Practice of the low back pain treatment by acupuncture and moxibustion].

In oriental medicine, not only the local pathological state but also disharmony within the body and the stagnation of Ki are examined. For this purpose, diagnoses in modern western medicine are also used as references. The pathological condition is evaluated by the 4 diagnostic methods as original methods of oriental medicine, treatment points are decided, and acupuncture and moxibustion are performed. If meridians and reactive points that appear with Ki stagnation impairing natural healing ability can be determined, not only low back pain but also symptoms such as constipation disappear, resulting in harmony of the body and improvement in constitutional symptoms.

III-V/Si hybrid photonic devices by direct fusion bonding.

Monolithic integration of III-V compound semiconductors on silicon is highly sought after for high-speed, low-power-consumption silicon photonics and low-cost, light-weight photovoltaics. Here we present a GaAs/Si direct fusion bonding technique to provide highly conductive and transparent heterojunctions by heterointerfacial band engineering in relation to doping concentrations. Metal- and oxide-free GaAs/Si ohmic heterojunctions have been formed at 300°C; sufficiently low to inhibit active material degradation. We have demonstrated 1.3 µm InAs/GaAs quantum dot lasers on Si substrates with the lowest threshold current density of any laser on Si to date, and AlGaAs/Si dual-junction solar cells, by p-GaAs/p-Si and p-GaAs/n-Si bonding, respectively. Our direct semiconductor bonding technique opens up a new pathway for realizing ultrahigh efficiency multijunction solar cells with ideal bandgap combinations that are free from lattice-match restrictions required in conventional heteroepitaxy, as well as enabling the creation of novel high performance and practical optoelectronic devices by III-V/Si hybrid integration.