Masaharu Hyodo

Fabrication of Nano-Antennas for Superconducting Infrared Detectors

To improve the response performance of superconducting infrared detectors, we have developed a fabrication process for nano-antennas. A nano-antenna consists of a dipole antenna, and a superconducting thin film strip placed in the antennas center. By measuring the transition temperature of the superconducting strips, we confirmed that their superconductivity maintained a good condition after the nano-antenna fabrication process. We also evaluated nano-antenna characteristics using Fourier transform infrared spectroscopy. The evaluated antenna length and width were respectively set at around 2400 nm and 400 nm, and the antennas were placed at intervals of several micrometers around the area of 1 mm2 . In an evaluation of spectral transmission characteristics, clear absorption caused by antenna effects was observed at around 1400 cm-1. High polarization dependencies were also observed.

Fabrication of Superconducting Mid-Infrared Photodetectors With Dipole Nanoantennas

We have proposed using nanoantennas with superconducting detector to improve the response performance of infrared detectors. Dipole nanoantennas that have an NbN load resistance were fabricated to evaluate the antenna properties. By using electromagnetic simulation, the antenna length was set at 2400 nm for the operation around 7-μm wavelength. The antennas were evaluated by using Fourier transform infrared spectroscopy. In an evaluation of spectral transmission characteristics, clear absorption caused by antenna effects was observed at around 1400 cm-1. The results of the simulation qualitatively agreed with the results of the experiment. The antenna effective area was also evaluated, and the area was estimated to be approximately 5.4 μm2 at 1420 cm-1. We have fabricated a prototype of midinfrared (MIR) photodetectors that were formed with 45 dipole antennas with an NbN strip. The antennas were placed within an area of 20 × 20 μm2, and they were connected by bias line in series. By the irradiation of MIR (λ = 4.9 μm) light, the responses with high polarization dependence values caused by antenna effect were observed.

Study of Midinfrared Superconducting Detector With Phased-Array Nanoslot Antenna

To improve the response performance of superconducting infrared detectors, we propose using a photonic antenna with a microdetector in conjunction with a nanostructure. In this paper, we report on the evaluated properties of a slot antenna and microstrip lines for the design of a midinfrared detector with a phased-array nanoslot antenna. We also explain the fabrication process for the detector. The antenna and microstrip line were designed for operation at a wave center near 5 μm. By measuring spectral reflectance characteristics, clear absorption by the antenna and the microstrip resonator was observed. To evaluate the validity of our process, we fabricated a midinfrared detector, which has structures composed of slot antennas and microstrip lines. We confirmed that the superconductivity of the superconducting detector was generally maintained in good condition after the fabrication process of midinfrared detectors.

Discrimination of absorption variations in two layered structure by using angular distribution of diffuse reflected light

A novel technique that is capable of discriminating absorption variations by measuring angular distribution of diffuse reflected light is presented for semi-infinite two-layered isotropic diffusive media. By using Monte-Carlo simulation, it was found that, in principle, the technique is useful to discriminate absorption variations caused in individual layers. This capability was validated in terms of partial path length as well as spatial sensitivity distribution.

Characterization of coherence-or-power selectable operation of an external-cavity semiconductor diode laser

The properties of the coherence-or-power selectable operation of an external-cavity semiconductor diode laser through the control of intracavity polarization states have been characterized in detail. In our technique, a diffraction grating and a reflector functioned as a polarization-dependent output coupler, such that the portion of light fed back to the gain medium was readily controlled by rotating the intracavity polarization axis, which resulted in the selectable operation of either a high degree of coherence or a high power for the laser output. We could continuously sweep the correlation widths over a range of approximately one order of magnitude, as well as four-fold output powers by simply rotating the intracavity half-wave plate. We also demonstrated experiments on optical phase locking, using two independent coherence-or-power selectable lasers.