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

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.

High-Tc superconducting Josephson mixers for terahertz heterodyne detection

“…The dc voltage V dc and the volt-ageṼ ðf LO Þ at the LO frequency are obtained by FFT analysis of the time dependent voltage V(t). The matrix elements Z ij are then calculated from V dc ,Ṽ ðf LO Þ and their derivatives with respect to I dc and I LO , according to expressions (6), (9), and (10). The results are plotted in Fig.…”

“…First realizations of mixers with high-T c superconductors, which were mainly based on grain-boundary or ramp edge junctions, 10-13 produced promising results including the demonstration of mixing beyond 1THz. 10 However, the development was slowed down by the difficulty to build a junction technology sufficiently reliable to fabricate complex devices. In recent years, a new approach based on ion irradiation has been developed to fabricate Josephson junctions with high temperature superconductors.…”

Wideband frequency metrology using high temperature superconducting Josephson junctions

“…It is difficult to use a commercial power meter to get single mode operation of the laser. However, using HTS Josephson junctions, it will be an easy job; so long as the power output is large enough to induce visible Shapiro steps on the -curves [12], we can check its frequencies in the real time and optimize the operating mode to a single one. For some lines with output power not large enough to induce Shapiro steps, the above-mentioned video detection can still be used to detect spectral lines; which, in turn, is used for monitoring the laser during its adjustments.…”

Magnetically enhanced terahertz response of Josephson junctions

“…By the mid 1990's, measurements of the subterahertz (sub-THz) response of highJosephson junctions were reported [1]- [3]. Recently, we also published experimental [4], [5] and numerical simulation [6] results on the THz response of high-Josephson junctions. We demonstrated the direct response and harmonic mixing operation at frequencies as high as 2.525 THz in a wide temperature range up to 70 K. Our results are attractive for spectroscopy applications in submillimeter-wave band.…”