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AIP conference proceedings

Differential heterodyne frequency conversion at 0.4 mm wavelength

B. T. Ulrich, Rob W. van der Heijden, J. M. V. Verschueren

Published Jan 1, 1978• 0 citations
Publisher

Abstract

A Josephson‐effect differential heterodyne receiver converts a variable signal frequency fS, near a fixed local oscillator fL, to a fixed intermediate frequency fI=fS−fL−fQ, by mixing between fD=fS−fL and a voltage‐tunable variable quantum oscillation fQ=2eV/h provided by a double‐junction resistive interferometer. At fL−0.7 THz provided by a far infrared formic acid laser, with fS=fL+fD provided by a Doppler shift, power conversion efficienciesηQ from fDγfI up to 0.2 were observed. Linewidths of the quantum oscillation δfQ∠ (2kBT/πL)1/2 (2eR/h) down to ∠0.5 Hz were observed for R=3.3×10−9Ω interferometer resistance, and L∠10−9 H interferometer inductance, demonstrating an intrinsic frequency resolution of 1 in 1012 at high conversion efficiency for the technique.

DOI
10.1063/1.31350

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Le Journal de Physique Colloques•Aug 1, 1978•0 citations

Heterodyne reception at 891 GHz using a Josephson harmonic mixer and a microwave local oscillator

T. G. Blaney, D. J. E. Knight

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

Direct heterodyne detection of 245-GHz radiation using the internal narrowband oscillations of a resistive dc SQUID

J. M. V. Verschueren, A. A. Uiterwaal, Rob W. van der Heijden +1 more

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Frequency conversion in Josephson junctions with comparable intrinsic and thermal energies

A. V. Snezhko, Yu. Ya. Divin

We have studied Josephson junctions with intrinsic energy ħIc/2e (Ic being the critical current) comparable to thermal energy kT and examined their potential for electromagnetic signal conversion. In this case, moderate thermal fluctuations are sufficient to destroy Josephson oscillations but do not entirely suppress the Josephson dynamics. We have numerically calculated the DC I–V curves, their derivatives dnV/dIn, and the DC and harmonic voltage responses Vn of such Josephson junctions to the AC currents Iωsinωt. We have found that Josephson junction with γ = 2ekT/ħIc ≥ 0.5 is a nonlinear resistance at frequencies ω below characteristic Josephson frequency ωc = 2eIcRn/ħ and all current biases I0. Frequency conversion in such junctions occurs due to the classical mechanism on the nonlinearity of the DC I–V characteristics at low signal frequencies. With increasing the signal frequencies to the characteristic Josephson frequency ωc = 2eIcRn/ħ and higher, the Josephson mechanism by frequency modulation of the Josephson current gradually replaces the classical one. The classical conversion mechanism demonstrates higher conversion efficiencies than the Josephson mechanism, although it operates within a narrower bandwidth. At zero DC bias i0 and in the range of γ-values from 0.1 to 2, we have found odd harmonics Vn emerging from low signal currents. Zero-bias values of the third harmonic V3 maximize at 0.18IcRn for JJs with γ = 0.5 and Iω = 2.5Ic. Based on these findings and high-Tc Josephson junctions, a family of low-noise square-law detectors, harmonic multipliers, and linear heterodyne receivers can be developed for emerging terahertz applications.

Journal of Applied Physics•Jul 8, 2025•0 citations

Frequency conversion with superconducting point contacts operating as oscillator-mixers and its application to the measurement of the linewidth of the Josephson current at very high frequency

G. Vernet, Robert Adde

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.

Revue de Physique Appliquée•Jan 1, 1974•3 citations

Linewidth of a resistively shunted high-temperature-superconductor Josephson heterodyne oscillator

J.C. Macfarlane, L. Hao, D.A. Peden +1 more

High-temperature-superconducting (HTS) resistively shunted superconducting quantum interference devices, consisting of two yttrium–barium–copper–oxide (YBCO) grain boundary junctions shunted by gold-film resistors of ∼20 μΩ, have been prepared and characterized at temperatures from 17 to 74 K. The small value and stability of the resistor allows narrow-band heterodyne oscillations to be generated between the Josephson oscillations in the individual junctions. The frequency can be precisely controlled in accordance with the ac Josephson effect by adjustment of an external current applied to the YBCO–Au–YBCO shunt resistor, and the linewidth is determined in principle only by Johnson noise in the resistor. Off-chip detection and spectral analysis of the heterodyne signal generated in this way has not been previously reported. Measurements of the signal power (∼nW), the tunability of the center frequency from 5 to 50 MHz, the frequency stability and the linewidth of the heterodyne Josephson oscillation are described. Although linewidth broadening due to nonthermal fluctuations is observed, the linewidth of ∼30 kHz at T=17 K, at a center frequency of 24 MHz, is believed to be the narrowest reported for Josephson oscillations in an HTS device of this type.

Applied Physics Letters•Mar 27, 2000•14 citations
A Josephson‐effect differential heterodyne receiver converts a variable signal frequency fS, near a fixed local oscillator fL, to a fixed intermediate frequency fI=fS−fL−fQ, by mixing between fD=fS−fL and a voltage‐tunable variable quantum oscillation fQ=2eV/h provided by a double‐junction resistive interferometer. At fL−0.7 THz provided by a far infrared formic acid laser, with fS=fL+fD provided by a Doppler shift, power conversion efficienciesηQ from fDγfI up to 0.2 were observed. Linewidths of the quantum oscillation δfQ∠ (2kBT/πL)1/2 (2eR/h) down to ∠0.5 Hz were observed for R=3.3×10−9Ω interferometer resistance, and L∠10−9 H interferometer inductance, demonstrating an intrinsic frequency resolution of 1 in 1012 at high conversion efficiency for the technique.
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.
We have studied Josephson junctions with intrinsic energy ħIc/2e (Ic being the critical current) comparable to thermal energy kT and examined their potential for electromagnetic signal conversion. In this case, moderate thermal fluctuations are sufficient to destroy Josephson oscillations but do not entirely suppress the Josephson dynamics. We have numerically calculated the DC I–V curves, their derivatives dnV/dIn, and the DC and harmonic voltage responses Vn of such Josephson junctions to the AC currents Iωsinωt. We have found that Josephson junction with γ = 2ekT/ħIc ≥ 0.5 is a nonlinear resistance at frequencies ω below characteristic Josephson frequency ωc = 2eIcRn/ħ and all current biases I0. Frequency conversion in such junctions occurs due to the classical mechanism on the nonlinearity of the DC I–V characteristics at low signal frequencies. With increasing the signal frequencies to the characteristic Josephson frequency ωc = 2eIcRn/ħ and higher, the Josephson mechanism by frequency modulation of the Josephson current gradually replaces the classical one. The classical conversion mechanism demonstrates higher conversion efficiencies than the Josephson mechanism, although it operates within a narrower bandwidth. At zero DC bias i0 and in the range of γ-values from 0.1 to 2, we have found odd harmonics Vn emerging from low signal currents. Zero-bias values of the third harmonic V3 maximize at 0.18IcRn for JJs with γ = 0.5 and Iω = 2.5Ic. Based on these findings and high-Tc Josephson junctions, a family of low-noise square-law detectors, harmonic multipliers, and linear heterodyne receivers can be developed for emerging terahertz applications.
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.
High-temperature-superconducting (HTS) resistively shunted superconducting quantum interference devices, consisting of two yttrium–barium–copper–oxide (YBCO) grain boundary junctions shunted by gold-film resistors of ∼20 μΩ, have been prepared and characterized at temperatures from 17 to 74 K. The small value and stability of the resistor allows narrow-band heterodyne oscillations to be generated between the Josephson oscillations in the individual junctions. The frequency can be precisely controlled in accordance with the ac Josephson effect by adjustment of an external current applied to the YBCO–Au–YBCO shunt resistor, and the linewidth is determined in principle only by Johnson noise in the resistor. Off-chip detection and spectral analysis of the heterodyne signal generated in this way has not been previously reported. Measurements of the signal power (∼nW), the tunability of the center frequency from 5 to 50 MHz, the frequency stability and the linewidth of the heterodyne Josephson oscillation are described. Although linewidth broadening due to nonthermal fluctuations is observed, the linewidth of ∼30 kHz at T=17 K, at a center frequency of 24 MHz, is believed to be the narrowest reported for Josephson oscillations in an HTS device of this type.