Development of high sensitive superconducting detectors for terahertz spectral imaging

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We have investigated fabrication of terahertz wave detectors of YBa_2Cu_3O_7 (YBCO) grain boundary Josephson junctions integrating with various types of antenna and their sensing properties from 0.1 to 4.2 THz. The detector with a planar log-periodic antenna (LPA) indicated the RF coupling loss of about -26dB. We revealed that an impedance miss-matching loss was a dominant part of the RF coupling loss. A detector with a coplanar waveguide-fed slot dipole array (SDA) instead of LPA indicated an improvement in the RF coupling loss of about 20dB. The detector with SDA achieved the sensitivity of 1,400 (V/W).We carried out numerical simulations on radiation properties of SDA by the FDTD method and revealed that low radiation impedance of SDA have contributed the improvement in the sensitivity. For further improvement in the impedance miss-matching loss, intrinsic Josephson junctions in which many junctions are connected in series is one of candidates as sensing elements with higher impedances.Although detectors with resonance antenna replaced LPA have narrow band widths, we have found that the slot dipole shows the relative band width of about 50% at 0.2 THz resonance by numerical simulations.