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Applied Physics Letters

Mixing at terahertz frequency band using YBa2Cu3O7−δ bicrystal Josephson junctions

J. Chen, Hiroaki Myoren, K. Nakajima, Takashi Yamashita, Peiheng Wu

Published Aug 4, 1997• 35 citations
Publisher

Abstract

Using high-Tc Josephson junctions made of YBa2Cu3O7−δ deposited across MgO bicrystal boundary, at terahertz (THz) frequency band, we demonstrated both fundamental and harmonic mixing. Radiation from a far-infrared laser was coupled to the junction, which was integrated with a planar bow-tie antenna, via an extended hyperhemispherical silicon lens. Fundamental mixing manifested itself in the junction’s dc current–voltage (I–V) curve as a third Shapiro step in addition to those two induced by the THz laser lines from a slightly misaligned resonator. In harmonic mixing between a THz laser line and a microwave local oscillator, the highest harmonic number we could get was 490 with a signal-to-noise ratio of 9 dB at the intermediate frequency.

DOI
10.1063/1.119836

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Applied Physics Letters•Nov 6, 2000•23 citations
Using high-Tc Josephson junctions made of YBa2Cu3O7−δ deposited across MgO bicrystal boundary, at terahertz (THz) frequency band, we demonstrated both fundamental and harmonic mixing. Radiation from a far-infrared laser was coupled to the junction, which was integrated with a planar bow-tie antenna, via an extended hyperhemispherical silicon lens. Fundamental mixing manifested itself in the junction’s dc current–voltage (I–V) curve as a third Shapiro step in addition to those two induced by the THz laser lines from a slightly misaligned resonator. In harmonic mixing between a THz laser line and a microwave local oscillator, the highest harmonic number we could get was 490 with a signal-to-noise ratio of 9 dB at the intermediate frequency.
High temperature superconducting (HTS) Josephson junction (JJ) mixers are attractive candidates in receivers for terahertz (THz) communication due to their high sensitivity, wide bandwidth, low local oscillator (LO) power requirement and high harmonic numbers. The required LO frequencies and the cost can be greatly reduced when harmonic signals can be detected at high orders (more than 100). In this paper, up to 114thharmonic mixings is presented in a HTS bicrystal YBa2Cu3O7-δ(YBCO) JJ harmonic mixer coupled with a bowtie loaded meander antenna at 0.21 THz. HTS JJs will be promising high-order harmonic mixers for THz practical applications on reception or detection at THz bands.
The high-frequency response of bicrystal YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// Josephson junctions for far infrared laser irradiation is presented. The junctions on silicon and MgO substrates exhibit a remarkable first order Shapiro step for the methanol line at 1.76 THz. dV/dI measurements reveal several steps corresponding to the methanol lines at 1.48, 1.76 and 2.53 THz. The line width of Josephson oscillation at these frequencies is estimated from the width of the Shapiro steps. It is suggested that the excess shot noise broadens the line width.
A high-temperature superconducting (HTS) terahertz (THz) heterodyne mixer based on a thin-film antenna-coupled YBa2Cu3O7-xstep-edge Josephson junction is presented. The frequency down-conversion from 0.6 THz to an intermediate frequency (IF) of 2 GHz was achieved using high-order harmonic mixing of a local oscillator (LO), thus removing the need to use a second THz source as the LO pumping source. The DC and RF characteristics of the harmonic mixer as well as the relationship of the IF output power versus the harmonic number were experimentally studied and compared with simulated results. Most of our measurements were made at 40 K, but we also observed stable harmonic mixing at 77 K which we believe has not been reported previously in HTS junction mixers.
We report on the mixing properties of high-T, superconductor (HTS) Josephson junctions. Direct radiation and heterodyne mixing experiments in the frequency range 78 GHz-119 GHz have been performed using YBa 2Cu30 7_ x (YBCO) step-edge junctions (SEJ) and bicrystal junctions (BO) on LaA10 3 and MgO substrates. Under external radiation our junctions showed harmonic phase synchronization (Shapiro steps) up to 1.88 THz. Junctions with current voltage characteristics (PVC) dose to predictions of the resistively shunted junction model (RSJ) were mounted into a heterodyne mixing setup. Under the radiation of two monochromatic signals we obtained conversion efficiencies around -14 dB in the 11 GHz intermediate frequency (IF) band. In the fundamental mixing regime we observed response at IF at working temperatures up to 72K. We demonstrated the operation of HTS Josephson junctions in the self-mixing mode. The experimental results are in good agreement with simulations using the RSJ model.
Two high-Tc superconducting (HTS) YBa2Cu3O7-δ(YBCO) grain boundary (GB) Josephson junctions in series as a harmonic mixer is investigated. The research shows that the mixer consisting of two series YBCO Josephson junctions has a larger harmonic number than that with only one junction in heterodyne mixing at zero-voltage bias. One of the advantages of the series-Josephson-junction mixer is that the total critical current is improved without sacrificing the sensitivity of the junctions in the array that makes the mixer easier to get more microwave induced-steps required by larger harmonic number. Furthermore, the underdamped YBCO GB series-Josephson-junction mixer operated at zero-bias voltage, where the zero-order Shapiro step exists, achieves mutual phase locking of the junctions in the array, resulting in an excellent mixing performance. Thus, the series-underdamp-Josephson-junction mixer with zero bias is predominant and compact in terahertz (THz) application due to its excellent performance and no dc bias supply.
We prepared Josephson junctions made of YBa2Cu3O7 on symmetric 24° LaAlO3 bicrystal substrates. For better coupling of high-frequency radiation, we structured the contacts with logarithmic-periodic antennas made of YBa2Cu3O7. Characterization was done by measuring the voltage–current characteristics to determine the critical current IC, the normal-state resistance RN, the noise parameter Γ, and the Stewart–McCumber parameter βC as predicted by the resistively and capactively shunted junction model (RCSJ). The junctions showed excellent RCSJ-like behavior with ICRN products of up to 2.0 mV at 10 K and 220 μV at 77 K. To demonstrate the possibility to detect high-frequency radiation up to the THz regime, we used the Josephson junction as a detector for radiation from a far-infrared laser and we reconstructed the spectra by Hilbert spectroscopy.