THz mixing properties of YBa 2Cu 3O 7−δ grain boundary Josephson junctions on bicrystal substrates

Abstract

Using high- T c grain boundary Josephson junctions (GBJJs) made of YBa 2Cu 3O 7−δ (YBCO) deposited across MgO bicrystal boundary, at TeraHertz (THz) waveband we successfully demonstrated both fundamental and harmonic frequency mixing. Radiation from a far-infrared (FIR) 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 (IF). The IF output ( P IF) depended strongly on the bias voltage, the local oscillator power level, the harmonic number ( N), etc.