Polarization- and angle-independent, dual-band metasurface thermal emitter was developed. The metasurface emits radiation at 4.26 μm and 3.95 μm, conventionally used for CO2 sensing. The metasurface is based on a planar Au/Al2O3/Au structure, in which orthogonal rectangular Au patches are arrayed alternately, and generates nearly perfect blackbody radiation with an emittance as high as 0.97. The metasurface is integrated on a resistive heater mounted on a SiN membrane, so that the infrared waves are produced by applying a voltage. The metasurface emitter was incorporated into an actual CO2 sensing system and was demonstrated to reduce the electric power needed by about 30% compared with a conventional blackbody emitter by suppressing unnecessary radiation.

We have demonstrated thermal emission of linearly polarized and narrow-band midinfrared waves from subwavelength gratings of narrow and deep rectangular cavities engraved on a Au surface. 100-nm-wide and 1000-nm-deep, high-aspect trenches were accurately manufactured by inversion from master molds. Organ pipe resonance of surface plasmons in the cavities exhibits a Lorentzian emission peak centered at 2.5–5.5μm. The maximum emittance reaches 0.90 and the peak width Δλ∕λ is as narrow as 0.13–0.23. This simple emitter is expected to play a key role in the infrared sensing technologies for analyzing our environment.

We have demonstrated that orthogonally polarized two-color infrared waves thermally emitted from gratings integrated onto a single Au chip open a way for simple and efficient chemical analysis. Each component grating is made of high-aspect cavities with a width on the order of 100nm and a depth close to 1μm, and generates linearly polarized and narrow-band midinfrared light by the organ pipe resonance of surface plasmons. Effectiveness of the integrated grating emitters for nondispersive infrared analysis has been shown on the basis of a model experiment for determining the concentration of a specific chemical compound in liquids.

There is a great demand for the highly accurate and reliable arrangement of micro objects smaller than 100 p in order to construct micro devices. Since micro objects tend to adhere to other objects by electrostatic force, it is possible to pick them up easily by contact with a needle tip instead of grasping by tweezers. On the other hand, it is difficult to place them on a substrate. To solve this problem, we have proposed a handling method by controlling the contact face area, i.e. picking up the object by contact with the center of the tool-tip plane, and placing it by contact with the edge and also inclining the tool. However, it is difficult to execute this operation by manual control, because it requires delicate movement by the manipulator, in order not to break the object or flip it away. In this study, we automate this pick-andplace operation by visual and force control. Moreover, to arrange micro objects with high accuracy and reliability, all necessary functions such as calibration, object search, and positioning are integrated, and an automatic handling system is constructed. We successfully demonstrated a completely automatic arrangement of several micro objects of 30 pn in diameter under SEM monitoring.

Optical patch antennas sandwiching dielectrics between metal layers have been used as deep subwavelength building blocks of metasurfaces for perfect absorbers and thermal emitters. However, for applications of these metasurfaces for optoelectronic devices, wiring to each electrically isolated antenna is indispensable for biasing and current flow. Here we show that geometrically engineered metallic wires interconnecting the antennas can function to synchronize the optical phases for promoting coherent resonance, not only as electrical conductors. Antennas connected with optimally folded wires are applied to intersubband infrared photodetectors with a single 4-nm-thick quantum well, and a polarization-independent external quantum efficiency as high as 61% (responsivity 3.3 A W −1 , peak wavelength 6.7 μm) at 78 K, even extending to room temperature, is demonstrated. Applications of synchronously wired antennas are not limited to photodetectors, but are expected to serve as a fundamental architecture of arrayed subwavelength resonators for optoelectronic devices such as emitters and modulators.

The micromanipulation technique in a scanning electron microscope (SEM) has been attracting interest as a technique to produce microstructures such as three-dimensional photonic crystals or advanced high-density electronic circuits. However, it is difficult to fabricate a large-scale structure or to conduct a systematic experiment using numbers of structures, as long as we rely on manually operated micromanipulation. In this study, we constructed an automatic system which arranges 10-μm-sized microspheres into a given two-dimensional pattern in a SEM. The spheres are picked up by touching with the center of the planar tip of a probe (needle), and placed on the substrate by moving the contact point to the edge of the tip and inclining the probe. The positions of the probe and the spheres are visually recognized from the SEM image from above and the optical microscope image from the side. The generalized Hough transform, which can robustly detect arbitrary shape from the edge fragments, is employed for the image recognition. Contact force information obtained by a force sensor with a resolution of 14 μN is also utilized for the control. Completely automatic rearrangement of randomly sprinkled metal spheres with a diameter of 30 μm into arbitrary patterns was successfully demonstrated. Autonomous micromanipulation technique under the observation of a SEM would contribute not merely to laboratories but also to the opto-electronics industry.

AbstractThe integration of quantum well infrared photodetectors with plasmonic cavities has allowed for demonstration of sensitive photodetectors in the mid-infrared up to room-temperature operating conditions. However, clear guidelines for optimizing device structure for these detectors have not been developed. Using simple stripe cavity detectors as a model system, we clarify the fundamental factors that improve photodetector performance. By etching semiconductor material between the stripes, the cavity resonance wavelength was expected to blue-shift, and the electric field was predicted to strongly increase, resulting in higher responsivity than unetched stripe detectors. Contrary to our predictions, etched stripe detectors showed lower responsivities, indicating surface effects at the sidewalls and reduced absorption. Nevertheless, etching led to higher detectivity due to significantly reduced detector dark current. These results suggest that etched structures are the superior photodetector design, and that appropriate sidewall surface treatments could further improve device performance. Finally, through polarization and incidence angle dependence measurements of the stripe detectors, we clarify how the design of previously demonstrated wired patch antennas led to improved device performance. These results are widely applicable for cavity designs over a broad range of wavelengths within the infrared, and can serve as a roadmap for improving next-generation infrared photodetectors.

Packaged dual-band metasurface thermal emitters integrated with a resistive membrane heater were manufactured by ultraviolet (UV) nanoimprint lithography followed by monolayer lift-off based on a soluble UV resist, which is mass-producible and cost-effective. The emitters were applied to infrared CO2 sensing. In this planar Au/Al2O3/Au metasurface emitter, orthogonal rectangular Au patches are arrayed alternately and exhibit nearly perfect blackbody emission at 4.26 and 3.95 μm necessary for CO2 monitoring at the electric power reduced by 31%. The results demonstrate that metasurface infrared thermal emitters are almost ready for commercialization.