Josephson Flux Flow Research Articles

Phase locking of 270-440 GHz Josephson flux flow oscillators

External phase locking of a Josephson flux flow oscillator (FFO) to a 10 MHz reference oscillator is demonstrated experimentally in the frequency range 270-440 GHz. A linewidth as low as 1 Hz (as determined by the resolution bandwidth of the spectrum analyser) has been measured. This linewidth is far below the fundamental level given by shot and thermal noise of the free-running tunnel junction. The combination of narrow linewidth, wide band tunability and low noise is important for spectral radio astronomy applications.

Design and fabrication of Cherenkov flux-flow oscillator

The Josephson Flux-Flow Oscillator (FFO) has been used as an on chip local oscillator at frequencies up to 650 GHz. The FFO linewidth of about 1 MHz was measured in the resonant regime V<915 /spl mu/V for niobium-aluminum oxide-niobium tunnel junctions, while considerably larger values were reported at higher voltages. To overcome this fundamental linewidth broadening we propose a novel on chip Cherenkov radiation flux-flow oscillator (CRFFO). It consists of a long Josephson junction and a superconducting slow wave transmission line that modifies essentially the junction dispersion relation. Two SIS detectors are connected both to the long Josephson junction and the transmission line to evaluate available microwave power. The output power coming both from the long junction and the transmission line is estimated at different bias conditions.

Integrated sub-MM wave receivers

The concept of a fully integrated superconducting receiver looks very attractive for sub-mm space astronomy where low weight, power consumption and volume are required. The possibility to integrate on a few chips the different planar components: a SIS mixer, a superconducting local oscillator (LO), an intermediate frequency amplifier followed by superconducting circuits for digitizing and processing of down converted signals, is discussed. A first implementation of a real integrated quasioptical receiver for frequencies up to 500 GHz is described. The one-chip receiver comprises a double dipole antenna, parallel biased SIS array mixer and Josephson Flux Flow Oscillator (FFO) with matching circuits. The results of extensive investigations of the integrated receiver as well as design and investigation of novel superconducting elements are presented. >

Resonant steps due to Josephson flux-flow in long YBa 2Cu 3O 7 bicrystal junctions

Resonant steps due to viscous Josephson flux-flow were observed in the current-voltage characteristics of long YBa 2Cu 3O 7−δ bicrystal junctions. With an applied dc magnetic field of 0.20 to 0.55 Gauss, the step voltage could be linearly tuned from about 0.4 to 2 mV for a 30 μm long, 0–32° [001]-tilt junction at 16K. From the linear dependence of the step voltage with the applied field, we extract 1) the ratio between the barrier thickness and the relative dielectric constant t/ε r=2.9 A ̊ and 2) the quasiparticle loss α=1.3, at 16K.