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Soviet Journal of Quantum Electronics

Frequency multiplication using superconducting weak links

Nikolai G. Basov, É. M. Belenov, Сергей Иванович Веденеев, M A Gubin, G. P. Motulevich, V V Nikitin, M G Perevalov, В. А. Степанов, Alexander V. Uskov

Published Feb 28, 1978• 0 citations
Publisher

Abstract

An investigation was made of the mechanism of generation of oscillation modes in a resonator excited by a Josephson point junction or bridge. On the basis of a system of Maxwell's equations and material equations in the Fokker–Planck approximation expressions were derived for the amplitudes of the fundamental-frequency harmonics and for the number of harmonics with comparable amplitudes. It was shown that with an appropriate choice of junction parameters and excitation frequency, the number of harmonics may be ~103, the harmonics in this case falling within the optical band. Detailed experimental investigations were made of the nonlinear high-frequency properties of a superconducting niobium–niobium point junction in an external microwave field. Different operating conditions with frequency multiplication by the point junction were studied. Theory and experiment were compared. It was found that for frequency multiplication in the submillimeter band, a superconducting point junction operating under nonequilibrium conditions is potentially more useful than a conventional Josephson point junction.

DOI
10.1070/qe1978v008n02abeh008484

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The Josephson frequency conversion in the millimeter and submillimeter wave region is studied with superconducting Nb-Nb point contact junctions at 4.2 K, using the contact both as the local oscillator and the mixer with intermediate frequencies of 0.1 and 9.2 GHz. Frequency conversion signals are only detected in the latter case with a microwave receiver at 9.2 GHz in a range of Josephson frequencies between 145 and 1 600 GHz. The experiments with intermediate frequency fi of 0.1 GHz indicate for this small value of f i that the observed signals are not related to frequency conversion but noise effects. An analysis of the frequency conversion mechanism in a Josephson junction operated as an oscillator-mixer is proposed which includes the noise effects and also the feedback effects induced in a junction driven by a constant current source. We have then investigated the noise properties up to 450 GHz of superconducting point-contacts using the junction as an oscillator-mixer where the Josephson current is mixed with harmonics of an externally applied signal. The emitted intermediate frequency is detected at 9.2 GHz and its linewidth is measured. In the very high frequency range the dc quasiparticle current dominates in a Josephson weak-link and we compare the corresponding theoretical linewidth calculated by Scalapino with our experimental results.

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M. V. Danileǐko, V. E. Derkach, A. M. Kostyshin +2 more

Recently there has been a marked upsurge in interest in the construction of multipliers and mixers for the SHF and IR regions. Of special interest in this respect are Josephson junctions fabricated from high-temperature superconductors. The present paper reports the results of experimental investigations of superconducting point junctions (SPJ) fabricated from the high-temperature superconductor Nb3Sn, and operating in regimes of frequency multiplication and mixing in the SHF spectral region. A controllable Nb3Sn Nb3 Sn SPJ that could be adjusted after being immersed in liquid helium was used in the experiments. The method of preparation of the SPJ was the same as the one that was employed in Ref. 1. The assembled experimental setup allowed the SPJ to be irradiated with three-centimeter and four-millimeter microwaves separately and simultaneously. The current-voltage characteristics (CVO) of the (tuned) SPJ were registered on an oscillograph and then recorded automatically at different DHF-power levels. The differential resistance RD = dU/dl of the junction as a function of mixing voltage UO was recorded with the aid of a lock-in amplifier2 co nstructed by us. All the measurements were carried out at the liquid-helium temperature. The SPJ in question had the following parameters: the critical current Ic = 0.1–2.5 rnA and the resistance in the normal state Rn = 0.1–10 Ω. When the SPJ was subjected to 8.9- and 87-GHz radiation separately, the CVC exhibited current steps at voltages corresponding to the fundamental frequency and the harmonics of the external radiation, as well as a sub harmonic structure. The multiplication of the fundamental frequency to 1 THz was recorded in the case of the irradiation of the SPJ by an 8.9–GHz signal and the registration of the dependence of RD on the mixing voltage U0. This differential CVC exhibited a subharmonic structure near the fundamental frequency at low SHF-power levels and near this frequency and its harmonics at higher levels. When the SPJ was irradiated by 87-GHz signals, the multiplication of the fundamental frequency of the signals to 2.2 THz was recorded on the differential CVC. The SHF-power dependence of the harmonics and subharmonics had an oscillatory character. The mechanism underlying the formation of the sub harmonic structure on the CVC of the SPJ can be explained if we take account of the effect of the action of the Josephson self-radiation on the junction itself.3 It should be noted that the manifestation of the Josephson properties in the frequency range ∼1 · 1012 Hz was observed for a SPJ with high Ic and Rn ⩾ 1 Ω. When the Nb3Sn–Nb3Sn SPJ was irradiated by two signals with frequencies 87 and 8.9 GHz simultaneously, there appeared near the steps for the 87-GHz signal , as the power of the 8.9-GHz signal was increased, steps corresponding to signals with frequencies equal to combinations of the two frequencies, i.e., (87m ± 8.9k)-Ghz combination steps appeared on the eve. Thus, the first experimental investigations of the multiplication and mixing of signals by Nb3Sn-Nb3Sn SPJ have shown that such SPJ operate quite well in regimes of mixing and multiplication of external SHF radiation.

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Abstract : The term 'Josephson effects' refers to a number of unusual properties of current flow through a barrier or weak link between two superconductors. Such a structure--called a Josephson junction--gives rise to frequency conversion effects that suggest its use as an oscillator-mixer in the millimeter and submillimeter region. Such a device would offer high sensitivity, broad bandwidth, tunability, and, in certain modes of operation, the possibility of conversion gain. These frequency conversion effects were observed in the range of 100 GHz to 600 GHz and beyond. The junctions were driven by a 75 GHz or 25 GHz klystron while coupled either to a coaxial cavity resonant at 20 GHz or to a resonance at about 500 GHz associated with the junction structure. Lines in the junction voltage-current characteristic were observed which demonstrated that, at certain values of junction bias, power at the rf--or its harmonics--was converted to power at the resonance frequency. An explanation of the experiment is given together with the necessary background, which provides the basis for a discussion of such operational considerations as upper frequency limit, sensitivity, temperature of operation, and saturation behavior at high signal levels. (Author)

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Josephson junction as F-band mixer-multiplier

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Properties of a niobium-niobium Josephson superconducting point contact (SPC) used as a mixer-multiplier have been investigated experimentally. Conversion of a microwave signal with frequency fs= 127 GHz into a signal with the intermediate frequency fif= 8.6 GHz has been obtained using heterodyne generators with frequencies fh= 136.68, 45, and 6.8 GHz, so that fif= nfh1,2,3 ....20- fswhere n = 1.2, 3.20 are heterodyne harmonics produced in the SPC. Dependences of the conversion efficiency (ηn) on the bias voltage, the heterodyne power and the heterodyne harmonics have been measured. In the case of the second and the twentieth harmonics, the best value of η20/η2was 0.25. This value is essentially higher than that obtained for the usual (conventional) semiconducting mixer. Performed experiments have demonstrated the perspective of utilization of SPC as a mixer-multiplier in millimeter and submillimeter wavebands.

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Josephson harmonic mixing and internal oscillation-mixing in YBCO superconducting weak link at liquid nitrogen temperatures

Jiming Song, Peiheng Wu, Qilin Cheng +5 more

Using a superconducting weak link (bridge) made of YBCO, the authors have successfully observed Josephson harmonic mixing between a local oscillation (LO) at X band and a signal at Ka band. Specifically, fourth-order harmonic mixing between 35.47 GHz and 8.843 GHz was observed. For a given signal level, the IF (intermediate frequency) responses depended strongly on both LO level and DC voltage bias across the junction. For zero bias, there is still IF output which is characteristic of even-order harmonic mixing. When the LO power level is such that the zero voltage current is suppressed to the second zero, the IF responses are maximum if the junction is biased between the zeroth and first steps induced by the LO. Also studied is the internal oscillation-mixing. An incoming signal at either X or Ka band gives rise to IF signal peaks if the junction is biased at voltages such that the corresponding internal Josephson frequencies are equal to, or harmonics of, the incoming signal frequency.>

IEEE Transactions on Magnetics•Mar 1, 1989•9 citations
An investigation was made of the mechanism of generation of oscillation modes in a resonator excited by a Josephson point junction or bridge. On the basis of a system of Maxwell's equations and material equations in the Fokker–Planck approximation expressions were derived for the amplitudes of the fundamental-frequency harmonics and for the number of harmonics with comparable amplitudes. It was shown that with an appropriate choice of junction parameters and excitation frequency, the number of harmonics may be ~103, the harmonics in this case falling within the optical band. Detailed experimental investigations were made of the nonlinear high-frequency properties of a superconducting niobium–niobium point junction in an external microwave field. Different operating conditions with frequency multiplication by the point junction were studied. Theory and experiment were compared. It was found that for frequency multiplication in the submillimeter band, a superconducting point junction operating under nonequilibrium conditions is potentially more useful than a conventional Josephson point junction.
The Josephson frequency conversion in the millimeter and submillimeter wave region is studied with superconducting Nb-Nb point contact junctions at 4.2 K, using the contact both as the local oscillator and the mixer with intermediate frequencies of 0.1 and 9.2 GHz. Frequency conversion signals are only detected in the latter case with a microwave receiver at 9.2 GHz in a range of Josephson frequencies between 145 and 1 600 GHz. The experiments with intermediate frequency fi of 0.1 GHz indicate for this small value of f i that the observed signals are not related to frequency conversion but noise effects. An analysis of the frequency conversion mechanism in a Josephson junction operated as an oscillator-mixer is proposed which includes the noise effects and also the feedback effects induced in a junction driven by a constant current source. We have then investigated the noise properties up to 450 GHz of superconducting point-contacts using the junction as an oscillator-mixer where the Josephson current is mixed with harmonics of an externally applied signal. The emitted intermediate frequency is detected at 9.2 GHz and its linewidth is measured. In the very high frequency range the dc quasiparticle current dominates in a Josephson weak-link and we compare the corresponding theoretical linewidth calculated by Scalapino with our experimental results.
Recently there has been a marked upsurge in interest in the construction of multipliers and mixers for the SHF and IR regions. Of special interest in this respect are Josephson junctions fabricated from high-temperature superconductors. The present paper reports the results of experimental investigations of superconducting point junctions (SPJ) fabricated from the high-temperature superconductor Nb3Sn, and operating in regimes of frequency multiplication and mixing in the SHF spectral region. A controllable Nb3Sn Nb3 Sn SPJ that could be adjusted after being immersed in liquid helium was used in the experiments. The method of preparation of the SPJ was the same as the one that was employed in Ref. 1. The assembled experimental setup allowed the SPJ to be irradiated with three-centimeter and four-millimeter microwaves separately and simultaneously. The current-voltage characteristics (CVO) of the (tuned) SPJ were registered on an oscillograph and then recorded automatically at different DHF-power levels. The differential resistance RD = dU/dl of the junction as a function of mixing voltage UO was recorded with the aid of a lock-in amplifier2 co nstructed by us. All the measurements were carried out at the liquid-helium temperature. The SPJ in question had the following parameters: the critical current Ic = 0.1–2.5 rnA and the resistance in the normal state Rn = 0.1–10 Ω. When the SPJ was subjected to 8.9- and 87-GHz radiation separately, the CVC exhibited current steps at voltages corresponding to the fundamental frequency and the harmonics of the external radiation, as well as a sub harmonic structure. The multiplication of the fundamental frequency to 1 THz was recorded in the case of the irradiation of the SPJ by an 8.9–GHz signal and the registration of the dependence of RD on the mixing voltage U0. This differential CVC exhibited a subharmonic structure near the fundamental frequency at low SHF-power levels and near this frequency and its harmonics at higher levels. When the SPJ was irradiated by 87-GHz signals, the multiplication of the fundamental frequency of the signals to 2.2 THz was recorded on the differential CVC. The SHF-power dependence of the harmonics and subharmonics had an oscillatory character. The mechanism underlying the formation of the sub harmonic structure on the CVC of the SPJ can be explained if we take account of the effect of the action of the Josephson self-radiation on the junction itself.3 It should be noted that the manifestation of the Josephson properties in the frequency range ∼1 · 1012 Hz was observed for a SPJ with high Ic and Rn ⩾ 1 Ω. When the Nb3Sn–Nb3Sn SPJ was irradiated by two signals with frequencies 87 and 8.9 GHz simultaneously, there appeared near the steps for the 87-GHz signal , as the power of the 8.9-GHz signal was increased, steps corresponding to signals with frequencies equal to combinations of the two frequencies, i.e., (87m ± 8.9k)-Ghz combination steps appeared on the eve. Thus, the first experimental investigations of the multiplication and mixing of signals by Nb3Sn-Nb3Sn SPJ have shown that such SPJ operate quite well in regimes of mixing and multiplication of external SHF radiation.
An experimental investigation was made of superconducting point contacts (SPC's), made of the hightemperature superconductor Nb 3 Sn, in external microwave fields. It was found that under nonequilibrium conditions these SPC's had a high degree of nonlinearity which made it possible to observe current steps corresponding to harmonics of the external radiation frequency at voltages exceeding the limiting value for these SPC's. Maximum frequency multiplication up to 4.2 × 10 12 Hz was recorded for an 8.9 × 10 9 Hz signal and up to 5 × 10 12 Hz for a 7.8 × 10 10 Hz signal. Investigations were made of the subharmonic structure of the current-voltage characteristics of SPC's in external microwave fields. Mixing of the microwave radiation with the contact self-radiation was observed experimentally at gap singularities.
Abstract : The term 'Josephson effects' refers to a number of unusual properties of current flow through a barrier or weak link between two superconductors. Such a structure--called a Josephson junction--gives rise to frequency conversion effects that suggest its use as an oscillator-mixer in the millimeter and submillimeter region. Such a device would offer high sensitivity, broad bandwidth, tunability, and, in certain modes of operation, the possibility of conversion gain. These frequency conversion effects were observed in the range of 100 GHz to 600 GHz and beyond. The junctions were driven by a 75 GHz or 25 GHz klystron while coupled either to a coaxial cavity resonant at 20 GHz or to a resonance at about 500 GHz associated with the junction structure. Lines in the junction voltage-current characteristic were observed which demonstrated that, at certain values of junction bias, power at the rf--or its harmonics--was converted to power at the resonance frequency. An explanation of the experiment is given together with the necessary background, which provides the basis for a discussion of such operational considerations as upper frequency limit, sensitivity, temperature of operation, and saturation behavior at high signal levels. (Author)
Properties of a niobium-niobium Josephson superconducting point contact (SPC) used as a mixer-multiplier have been investigated experimentally. Conversion of a microwave signal with frequency fs= 127 GHz into a signal with the intermediate frequency fif= 8.6 GHz has been obtained using heterodyne generators with frequencies fh= 136.68, 45, and 6.8 GHz, so that fif= nfh1,2,3 ....20- fswhere n = 1.2, 3.20 are heterodyne harmonics produced in the SPC. Dependences of the conversion efficiency (ηn) on the bias voltage, the heterodyne power and the heterodyne harmonics have been measured. In the case of the second and the twentieth harmonics, the best value of η20/η2was 0.25. This value is essentially higher than that obtained for the usual (conventional) semiconducting mixer. Performed experiments have demonstrated the perspective of utilization of SPC as a mixer-multiplier in millimeter and submillimeter wavebands.
Using a superconducting weak link (bridge) made of YBCO, the authors have successfully observed Josephson harmonic mixing between a local oscillation (LO) at X band and a signal at Ka band. Specifically, fourth-order harmonic mixing between 35.47 GHz and 8.843 GHz was observed. For a given signal level, the IF (intermediate frequency) responses depended strongly on both LO level and DC voltage bias across the junction. For zero bias, there is still IF output which is characteristic of even-order harmonic mixing. When the LO power level is such that the zero voltage current is suppressed to the second zero, the IF responses are maximum if the junction is biased between the zeroth and first steps induced by the LO. Also studied is the internal oscillation-mixing. An incoming signal at either X or Ka band gives rise to IF signal peaks if the junction is biased at voltages such that the corresponding internal Josephson frequencies are equal to, or harmonics of, the incoming signal frequency.>