Superconducting nanowire single-photon detectors (SSPDs) are sensitive to wavelengths from ultra-violet to mid-infrared, and SSPD systems with detection efficiencies of over 90 % at telecom wavelengths are commercially available. The development of an SSPD with higher detection efficiency, lower noise, a higher counting rate, and a larger detection area is currently underway for a wide range of applications. A higher counting rate and larger detection area can be achieved with a multi-pixel SSPD, but the signal readout from a multi-pixel SSPD is challenging due to the limited number of readout cables. This article presents recent research trends in SSPDs including their signal readout technology from multi-pixel arrays.
High-field lasers will bring great benefits to the cutting edge of science and technology. 30 years ago, the progress of a chip-type computer “Microprocessor” stimulated “micro-solid-state photonics” in the field of solid-state lasers. Recent progress of these photonics has been demonstrated to offer tremendous effects in downsizing powerful lasers. Additionally, this tiny integrated laser holds promise for the future of high-field laser-based ablation, shock waves, laser ignition, and nonlinear optics including THz wave generation. The extremely high-brightness lasers will open up new areas in science, such as laser driven electron accelerators for table-top XFEL, and innovations in the field of industrial, bio-medical, and safety applications including infrastructure maintenance.
Thermal emission control based on material absorption and photonic resonance is demonstrated. Narrowband thermal emitters in the mid-infrared range are realized using intersub-band transitions and photonic crystals, which show 12 times higher peak power compared to the blackbody reference under the same input power conditions. Near-infrared wavelength selective emitters are realized using Si-based rod-type photonic crystals, and a thermophotovoltaic system comprised of a Si thermal emitter and InGaAs photovoltaic cells is demonstrated. A high heat to electricity conversion efficiency of 11.2 % is obtained, which is 1.65 times higher than the previously reported record value (6.8 %).
GaN-on-diamond high electron mobility transistors (GoD HEMTs) were fabricated by surface-activated room-temperature bonding. A monocrystalline diamond substrate and polycrystalline diamond substrate were finely polished using mechanical polishing techniques and novel polishing techniques utilizing catalytic reactions, respectively. GaN-HEMTs removed from a Si substrate were bonded to the finely-polished diamond substrates. A cross-sectional transmission electron microscope (TEM) image showed that the GaN-HEMTs and diamond substrate were well-bonded with a few-nm-thick interface layer. Measured drain current (Id) - drain voltage (Vd) curves implied that GaN-HEMTs were successfully transferred on the diamond substrate and HEMT performance was improved due to effective heat dissipation via the diamond with high thermal conductivity. Two-dimensional temperature mapping measurements revealed that fabricated GoD-HEMTs had very improved heat dissipation performance.
Spin wave devices have attracted much interest as a candidate for a post-CMOS device. XNOR, AND, and OR gates using a forward volume spin wave propagating in yttrium iron garnet (YIG) films were demonstrated. YIG films with a thicknesses on the order of 10 µm and 10 nm were used for the millimeter-size, and micrometer-size spin wave devices, respectively. These devices used spin wave attenuators to suppress reflected and scattered spin waves.
Inorganic semiconductors tend to fail in a brittle manner when subjected to an external force. Such poor mechanical properties limit their application range. Recently, we report extraordinary plasticity in an inorganic semiconductor, ZnS in darkness. Room-temperature deformation tests of ZnS were performed under varying light conditions. ZnS crystals immediately fractured when they deformed under light. On the other hand, it was found that ZnS crystals can be plastically deformed up to a plastic strain of 45 % in darkness. In addition, the optical band-gap of the deformed ZnS was decreased by 0.6 eV. These results suggest that dislocations in ZnS become extremely mobile in darkness and that multiplied dislocations can affect the optical band-gap over the whole crystal.
In order to predict inland flooding due to the frequent sudden rainfall in recent years, it is important to measure the sewerage water level, which cannot be visually confirmed, unlike the river water level, in real time. An energy harvesting device (thermoelectric conversion element) is installed in the sewer manhole to measure the water level of the sewer in real time, which was not possible before. By reducing the power consumption of the network, we have succeeded in developing and commercializing a real-time monitoring system that can store water level data in the cloud while operating the sensor for more than 5 years without replacing the battery. We will explain the development technology.