Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Spectral Linewidth of Josephson Flux Flow Oscillators; influence from bias and geometry

J. Mygind, C. Mahaini

Published Jan 1, 2003• 0 citations
OpenAlex

Abstract

Presently the Josephson Flux Flow Oscillator (FFO) is the best on-chip integrated local oscillator in all-superconducting sub-millimeter wavelength receivers based on SIS mixers. Potential applications are spectral investigations in astronomy, atmospheric pollution, biophysics, etc. Theoretically, the linewidth of the emitted radiation from the FFO - as for all other Josephson oscillators - should be given by the well-known lumped junction expression containing only internal noise and quantities measured from the DC I-V characteristic. The FFO, however, differs from the other members of the Josephson oscillator family in needing also an external magnetic field bias. Several theoretical models have been proposed adding also external noise. Experimentally the linewidth may be fitted by a simple extension of the lumped junction expression including also the measured dynamic resistance of the magnetic bias current. We suggest a simple solution to this based on the assumption that the DC bias current e.g. due to geometrical asymmetries creates an additional contribution to the magnetic field in the junction.

Related papers

The Submm Wave Josephson Flux Flow Oscillator; Linewidth Measurements and Simple Theory

J. Mygind, V. P. Koshelets, Mogens R. Samuelsen +1 more

The Flux Flow Oscillator (FFO) is a long Josephson junction in which a DC bias current and a DC magnetic field maintain a unidirectional viscous flow of magnetic flux quanta. The theoretical linewidth of the electromagnetic radiation generated at the end boundary is due to internal current fluctuations as given by the usual expression for the lumped junction. Experimentally, however, the linewidth deviates significantly both in magnitude and functional dependence. We suggest a simple solution based on the assumption that the bias current creates an additional magnetic field in the junction. This is supported by linewidth measurements on FFO's subjected to different bias configurations.

IEEE Transactions on Applied Superconductivity•Jun 1, 2005•16 citations

Self-pumping effects and radiation linewidth of Josephson flux-flow oscillators

V. P. Koshelets, S. V. Shitov, А. В. Щукин +3 more

Flux-flow oscillators (FFO's) are being developed for integration with a SIS mixer for use in submillimeter wave receivers. The present work contains a detailed experimental study of the dc, microwave, and noise properties of ${\mathrm{N}\mathrm{b}\ensuremath{-}\mathrm{A}\mathrm{l}\mathrm{O}}_{x}\ensuremath{-}\mathrm{Nb}$ FFO's. A model based on the Josephson self-pumping effect is proposed for an explanation of the experimental current-voltage characteristics. A reliable technique based on harmonic mixing is used to determine the spectral linewidth of the radiation emitted by the integrated FFO's up to 600 GHz. Comprehensive measurements of the dependence of the linewidth on the dynamic resistance and the applied magnetic field have been performed. In the resonant regime a linewidth as small as 200 kHz is obtained at 450 GHz. The experimental data are compared with recent theoretical predictions.

Physical review. B, Condensed matter•Sep 1, 1997•100 citations

Linewidth and DC properties of the flux-flow oscillator with mixed inline-overlap bias

Alexander S. Sobolev, J. Mygind, V. P. Koshelets

A Flux-Flow Oscillator (FFO) is a long Josephson junction in which a unidirectional flow of magnetic flux quanta is maintained by an applied DC magnetic field and a bias current. In the overlap geometry the FFO voltage and thus its oscillation frequency is controlled independently by the (overlap) bias current and the so-called "control line" (inline) current, which creates the magnetic field at the ends of the FFO. We have studied both DC properties and the linewidth of the emitted radiation for an FFO, which can be biased in different ways; as a four current terminal object. The bias current of the mixed inline-overlap type is applied through the terminals commonly used for the "control line" current. In this configuration the bias current also contributes to the magnetic field at one of the two FFO ends. This changes the steepness of the junction's I-V characteristics and therefore the bias current dynamic resistance. The experimental FFO linewidth was found to be independent of the bias configuration and determined by the dynamic resistance of the junction with pure overlap bias current. A new method has been developed to evaluate the difference in the DC magnetic field at the ends of the junction. It may be attributed to control line redistribution caused by the impedance matching RF circuit connected to the FFO at the end where the fluxon chain annihilates and radiation is emitted. We found that the opposite end, where the fluxons enter the junction, appears to be about three times more sensitive to variations of the magnetic field than the radiating end.

Journal of Physics Conference Series•Feb 1, 2008•1 citation

Externally phase-locked flux flow oscillator for submm integrated receivers: achievements and limitations

V. P. Koshelets, S. V. Shitov, Pavel N. Dmitriev +9 more

A Josephson flux flow oscillator (FFO) is the most developed superconducting local oscillator for integration with an SIS mixer in a single-chip submm-wave receiver. Recently, using a new FFO design, a free-running linewidth /spl les/10 MHz has been measured in the frequency range up to 712 GHz, limited only by the gap frequency of Nb. This enabled us to phase lock the FFO in the frequency range 500-712 GHz where continuous frequency tuning is possible; resulting in an absolute FFO phase noise as low as -80 dBc at 707 GHz. Comprehensive measurements of the FFO radiation linewidth have been performed using an integrated SIS harmonic mixer. The influence of FFO parameters on radiation linewidth, particularly the effect of the differential resistances associated both with the bias current and the applied magnetic field has been studied in order to further optimize the FFO design. A new approach with a self-shielded FFO has been developed and experimentally tested.

IEEE Transactions on Applied Superconductivity•Jun 1, 2003•11 citations

Phase-locked Josephson flux flow local oscillator for sub-mm integrated receivers

J. Mygind, C. Mahaini, Pavel N. Dmitriev +8 more

The Josephson flux flow oscillator (FFO) has proven to be one of the best on-chip local oscillators for heterodyne detection in integrated sub-mm receivers based on SIS mixers. Nb–AlO x –Nb FFOs have been successfully tested from about 120 to 700 GHz (gap frequency of Nb) providing enough power to pump an SIS mixer (about 1 μW at 450 GHz). Both the frequency and the power of the FFO can be dc-tuned. Extensive measurements of the dependence of the free-running FFO linewidth on the differential resistances associated with both the bias current and the control-line current (applied magnetic field) have been performed. The FFO line is Lorentzian both in the resonant regime, on Fiske steps (FSs), and on the flux flow step (FFS). This indicates that internal wide-band noise is dominant. A phenomenological noise model can account for the FFO linewidth dependence on experimental parameters. The narrow free-running FFO linewidth achieved, in combination with the construction of a wide-band phase-locked loop (PLL) system, enable us to phase lock the FFO in the frequency range 490–712 GHz where continuous frequency tuning is possible.

Superconductor Science and Technology•Nov 21, 2002•1 citation

Flux-flow oscillator with anticorrelated noise on the bias current and the magnetic field

Alexander S. Sobolev, Pavel V. Kudryashov, Oleg S. Kiselev

A Flux-flow oscillator based on a long Josephson junction is a local oscillator in fully superconducting integrated receivers (SIRs). The low frequency voltage fluctuations define the free-running FFO radiation linewidth, an important parameter for employing the SIR as a submm spectrometer. The DC voltage of the oscillator is independently controlled by both the dissipative DC bias current I B and the loss-free external magnetic field at the two FFO ends. It is mainly the natural wideband current noise of the Josephson barrier, which is converted into the fluctuations of voltage by the differential resistance Rd on the current I B . We have developed and experimentally demonstrated the method for suppression of the voltage fluctuations by convey of the bias current noise into the anticorrelated noise of the magnetic field. The experiments were made with Nb/AlN/Nb FFOs, having a specially designed shunting structure at the end, where flux quanta enter the junction.

Journal of Physics Conference Series•Jun 1, 2010•0 citations
Presently the Josephson Flux Flow Oscillator (FFO) is the best on-chip integrated local oscillator in all-superconducting sub-millimeter wavelength receivers based on SIS mixers. Potential applications are spectral investigations in astronomy, atmospheric pollution, biophysics, etc. Theoretically, the linewidth of the emitted radiation from the FFO - as for all other Josephson oscillators - should be given by the well-known lumped junction expression containing only internal noise and quantities measured from the DC I-V characteristic. The FFO, however, differs from the other members of the Josephson oscillator family in needing also an external magnetic field bias. Several theoretical models have been proposed adding also external noise. Experimentally the linewidth may be fitted by a simple extension of the lumped junction expression including also the measured dynamic resistance of the magnetic bias current. We suggest a simple solution to this based on the assumption that the DC bias current e.g. due to geometrical asymmetries creates an additional contribution to the magnetic field in the junction.
The Flux Flow Oscillator (FFO) is a long Josephson junction in which a DC bias current and a DC magnetic field maintain a unidirectional viscous flow of magnetic flux quanta. The theoretical linewidth of the electromagnetic radiation generated at the end boundary is due to internal current fluctuations as given by the usual expression for the lumped junction. Experimentally, however, the linewidth deviates significantly both in magnitude and functional dependence. We suggest a simple solution based on the assumption that the bias current creates an additional magnetic field in the junction. This is supported by linewidth measurements on FFO's subjected to different bias configurations.
Flux-flow oscillators (FFO's) are being developed for integration with a SIS mixer for use in submillimeter wave receivers. The present work contains a detailed experimental study of the dc, microwave, and noise properties of ${\mathrm{N}\mathrm{b}\ensuremath{-}\mathrm{A}\mathrm{l}\mathrm{O}}_{x}\ensuremath{-}\mathrm{Nb}$ FFO's. A model based on the Josephson self-pumping effect is proposed for an explanation of the experimental current-voltage characteristics. A reliable technique based on harmonic mixing is used to determine the spectral linewidth of the radiation emitted by the integrated FFO's up to 600 GHz. Comprehensive measurements of the dependence of the linewidth on the dynamic resistance and the applied magnetic field have been performed. In the resonant regime a linewidth as small as 200 kHz is obtained at 450 GHz. The experimental data are compared with recent theoretical predictions.
A Flux-Flow Oscillator (FFO) is a long Josephson junction in which a unidirectional flow of magnetic flux quanta is maintained by an applied DC magnetic field and a bias current. In the overlap geometry the FFO voltage and thus its oscillation frequency is controlled independently by the (overlap) bias current and the so-called "control line" (inline) current, which creates the magnetic field at the ends of the FFO. We have studied both DC properties and the linewidth of the emitted radiation for an FFO, which can be biased in different ways; as a four current terminal object. The bias current of the mixed inline-overlap type is applied through the terminals commonly used for the "control line" current. In this configuration the bias current also contributes to the magnetic field at one of the two FFO ends. This changes the steepness of the junction's I-V characteristics and therefore the bias current dynamic resistance. The experimental FFO linewidth was found to be independent of the bias configuration and determined by the dynamic resistance of the junction with pure overlap bias current. A new method has been developed to evaluate the difference in the DC magnetic field at the ends of the junction. It may be attributed to control line redistribution caused by the impedance matching RF circuit connected to the FFO at the end where the fluxon chain annihilates and radiation is emitted. We found that the opposite end, where the fluxons enter the junction, appears to be about three times more sensitive to variations of the magnetic field than the radiating end.
A Josephson flux flow oscillator (FFO) is the most developed superconducting local oscillator for integration with an SIS mixer in a single-chip submm-wave receiver. Recently, using a new FFO design, a free-running linewidth /spl les/10 MHz has been measured in the frequency range up to 712 GHz, limited only by the gap frequency of Nb. This enabled us to phase lock the FFO in the frequency range 500-712 GHz where continuous frequency tuning is possible; resulting in an absolute FFO phase noise as low as -80 dBc at 707 GHz. Comprehensive measurements of the FFO radiation linewidth have been performed using an integrated SIS harmonic mixer. The influence of FFO parameters on radiation linewidth, particularly the effect of the differential resistances associated both with the bias current and the applied magnetic field has been studied in order to further optimize the FFO design. A new approach with a self-shielded FFO has been developed and experimentally tested.
The Josephson flux flow oscillator (FFO) has proven to be one of the best on-chip local oscillators for heterodyne detection in integrated sub-mm receivers based on SIS mixers. Nb–AlO x –Nb FFOs have been successfully tested from about 120 to 700 GHz (gap frequency of Nb) providing enough power to pump an SIS mixer (about 1 μW at 450 GHz). Both the frequency and the power of the FFO can be dc-tuned. Extensive measurements of the dependence of the free-running FFO linewidth on the differential resistances associated with both the bias current and the control-line current (applied magnetic field) have been performed. The FFO line is Lorentzian both in the resonant regime, on Fiske steps (FSs), and on the flux flow step (FFS). This indicates that internal wide-band noise is dominant. A phenomenological noise model can account for the FFO linewidth dependence on experimental parameters. The narrow free-running FFO linewidth achieved, in combination with the construction of a wide-band phase-locked loop (PLL) system, enable us to phase lock the FFO in the frequency range 490–712 GHz where continuous frequency tuning is possible.
A Flux-flow oscillator based on a long Josephson junction is a local oscillator in fully superconducting integrated receivers (SIRs). The low frequency voltage fluctuations define the free-running FFO radiation linewidth, an important parameter for employing the SIR as a submm spectrometer. The DC voltage of the oscillator is independently controlled by both the dissipative DC bias current I B and the loss-free external magnetic field at the two FFO ends. It is mainly the natural wideband current noise of the Josephson barrier, which is converted into the fluctuations of voltage by the differential resistance Rd on the current I B . We have developed and experimentally demonstrated the method for suppression of the voltage fluctuations by convey of the bias current noise into the anticorrelated noise of the magnetic field. The experiments were made with Nb/AlN/Nb FFOs, having a specially designed shunting structure at the end, where flux quanta enter the junction.