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Revue de Physique Appliquée

Harmonic mixing with Josephson point contacts

Jean–Michel Lourtioz, Robert Adde, G. Vernet, J.C. Hénaux

Published Jan 1, 1977• 3 citations
Publisher

Abstract

Experiments are described in which Josephson point contacts were used to generate and mix harmonics (up to the 96th) of microwave klystrons with the radiation from an HCN laser at 891 GHz. A qualitative analysis of mixing of two external radiations in a Josephson junction is given in order to understand the existence of mixing components independent of the Josephson oscillation frequency and linewidth. The spectral analysis of the HCN laser shows the importance of the microwave source spectral purity when frequency multiplication by large factors is considered.

DOI
10.1051/rphysap:01977001203048700

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The performance of Nb-Nb point-contact Josephson junction mixers was investigated experimentally with signals from a 891 GHz laser. The local oscillator (LO) was provided by the appropriate junction-generated harmonic of either a 74 or 99 GHz klystron. The intermediate frequency (IF) power varied linearly with signal power for signals less than 10 −5 to 10 −6 W. The optimum conversion loss (from 891 GHz to the IF) was not significantly different for the two klystron frequencies used: the lowest useful conversion loss for the whole mixing system including the signal input matching loss, was 42 (±3) dB. This is 10 dB greater than that observed with a 891 GHz laser LO and the same junction apparatus. Conversion loss of the mixer element alone was independent of IF with the latter varied up to 1·2 GHz. The noise at the output of the IF system was usually dominated by that of the transistor preamplifier with a noise temperature of about 500 K. Thus the input signal necessary to give a signal-to-noise ratio of one at the IF was equivalent to 10 −16 W Hz −1 of IF bandwidth. This mixing system, which can be significantly improved, forms the basis of a fully tunable heterodyne receiver for the submillimetre region.

Journal of Physics D Applied Physics•Sep 21, 1974•11 citations
Experiments are described in which Josephson point contacts were used to generate and mix harmonics (up to the 96th) of microwave klystrons with the radiation from an HCN laser at 891 GHz. A qualitative analysis of mixing of two external radiations in a Josephson junction is given in order to understand the existence of mixing components independent of the Josephson oscillation frequency and linewidth. The spectral analysis of the HCN laser shows the importance of the microwave source spectral purity when frequency multiplication by large factors is considered.
Experiments are described in which simple and relatively reliable point-contact Josephson junctions were used to generate and mix harmonics (up to the 50th) of microwave klystron frequencies with emissions from a hydrogen cyanide laser operating at 891 GHz. Data are presented illustrating the variation of the intermediate frequency signal with DC bias current through the junction and incident radiation power levels, and the results compared, where possible, with a simple qualitative theory of Josephson mixing. Details are also given of experiments in which such a mixer was used to phase-lock a klystron to the laser, enabling the laser frequency to be accurately and continuously monitored.
Signals near 1 GHz were multiplied in frequency by up to 825 times and mixed with the hydrogen cyanide laser frequency at 891 GHz in point-contact Josephson junctions. The 1 GHz signals were generated by direct multiplication from a 120 MHz quartz-crystal oscillator, and no microwave transfer oscillator was needed. The maximum IF output powers obtained in these and other harmonic mixing experiments (using the same laser) were found to agree quite well with a simple theory which predicts a limit proportional to the square of the frequency being multiplied in the Josephson junction. This provides a criterion for determining the lowest frequency at which to begin multiplication in a Josephson device.
In an extension of earlier work, the response of niobium-niobium point-contact Josephson junctions to radiation from hydrogen cyanide and deuterium cyanide lasers has been studied. Constant voltage steps corresponding to the 805, 891 and 964 GHz lines from a HCN laser have been observed as well as steps corresponding to the frequency mixtures of all these lines. In addition, subharmonic and harmonics of `mixed-frequency' steps have also been observed. The first observation of Josephson step structure corresponding to the 1540 and 1578 GHz emissions of a DCN laser is reported.
The performance of Nb-Nb point-contact Josephson junction mixers was investigated experimentally with signals from a 891 GHz laser. The local oscillator (LO) was provided by the appropriate junction-generated harmonic of either a 74 or 99 GHz klystron. The intermediate frequency (IF) power varied linearly with signal power for signals less than 10 −5 to 10 −6 W. The optimum conversion loss (from 891 GHz to the IF) was not significantly different for the two klystron frequencies used: the lowest useful conversion loss for the whole mixing system including the signal input matching loss, was 42 (±3) dB. This is 10 dB greater than that observed with a 891 GHz laser LO and the same junction apparatus. Conversion loss of the mixer element alone was independent of IF with the latter varied up to 1·2 GHz. The noise at the output of the IF system was usually dominated by that of the transistor preamplifier with a noise temperature of about 500 K. Thus the input signal necessary to give a signal-to-noise ratio of one at the IF was equivalent to 10 −16 W Hz −1 of IF bandwidth. This mixing system, which can be significantly improved, forms the basis of a fully tunable heterodyne receiver for the submillimetre region.