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Softwaretechnik-Trends

High Gain and Noise in SIS Mixers at Submillimeter Wavelengths

Michael J. Wengler, Noshir Dubash, G. Pance, Ronald Earle Miller

Published Feb 1, 1991• 0 citations
OpenAlex

Abstract

Superconducting tunnel diode (SIS) mixers are used for radio astronomy from 100 to 500 GHz. They are being considered for NASA spacebome astronomy at frequencies near 1,000 GHz. We report measurements of gain and noise in SIS mixers at 230 and 492 GHz. We measure high gain and noise associated with Josephson currents which have not been previously reported. These measurements show that Josephson currents are increasingly important as operating frequencies are raised. We discuss the techniques we use to make these measurements. Measurements made with hot and cold blackbodies are shown to be inaccurate at high frequencies. The problem is that SIS 's do not always respond linearly to the signal power incident on them. This is particularly important when 1) very broad band mixers are used and 2) Josephson effect currents are important. Both of these circumstances are present in the quasioptical SIS mixers favored for 500 GHz and higher. We use monochromatic signals to measure gain and noise to get around these problems.

Related papers

Josephson effect gain and noise in SIS mixers

Michael J. Wengler, Noshir Dubash, G. Pance +1 more

The authors report measurements of gain and noise in SIS mixers at 230 and 492 GHz. Measurements were made of relatively high gain and noise associated with Josephson currents that have not been previously reported. These measurements show that Josephson currents are increasingly important as operating frequencies are raised. The techniques used to make these measurements are discussed. Measurements made with hot and cold black-bodies are shown to be inaccurate at high frequencies. The problem is that SIS mixers do not always respond linearly to the signal power incident on them. This is particularly important when (1) very broad band mixers are used and (2) Josephson effect currents are important. Both of these circumstances are present in the quasioptical SIS mixers favored for 500 GHz and higher. Monochromatic signals were used to measure gain and noise to get around these problems.>

IEEE Transactions on Microwave Theory and Techniques•May 1, 1992•21 citations

Submillimeter receiver components using superconducting tunnel junctions

Michael J. Wengler, A. Pance, B. Liu +3 more

Superconducting tunnel diodes (SISs) are investigated for both the generation and detection of submillimeter wavelengths. For detection, heterodyne receivers using SISs are investigated. Josephson currents are found to have a large effect on SIS mixers in the submillimeter, even though their effect is less at lower frequencies. At 492 GHz, fixer conversion gain increased by 4 dB when Josephson currents are not suppressed by a magnetic field. A much higher noise is seen in this gain mode, but further investigation of this recently discovered phenomenon is warranted. For submillimeter generation, a two-dimensional array of SISs is investigated. The ac Josephson effect in the SIS is expected to deliver submillimeter power into a free-space radiation mode traveling perpendicular to the array. No experimental devices have been developed yet, but the authors show computer simulations and microwave scale model measurements of array structures.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Jul 1, 1991•0 citations

Superconducting detectors for infrared and millimeter waves

Paul L. Richards

Quasiparticle and Josephson tunneling currents in superconducting tunnel junctions provide nonlinear low-noise response up to terahertz frequencies. Many types of direct detector heterodyne mixer and parametric amplifier based on these effects have been explored. Only the SIS quasiparticle mixer has been sufficiently competitive to find significant applications. These mixers can have noise approaching the quantum limit TN = ℏω/k and gain larger than 10 dB. They are used at a number of observatories for molecular line radio astronomy at millimeter wavelengths. Similar applications at submillimeter wavelengths are beginning.

Conference on Lasers and Electro-Optics•Apr 25, 1988•0 citations

Josephson Pair Tunnelling Influence on the Performance of an SIS Mixer near its Superconducting Gap

Boon-Kok Tan, G. Yassin

We report the investigation of the influence of Josephson pair tunnelling on the sensitivity of an SIS mixer near the superconducting gap of niobium. Hot and cold load measurements were carried out from 600 GHz to 700 GHz, without completely supressing the Josephson effect. We have noticed that when measurements were made at bias points near the first Shapiro step, significantly higher values of Y-factor could be obtained with magnetic field strengths that made the Shapiro step sharper, rather then those that supressed the step. This resulted in a significant improvement in noise temperature of the mixer at those bias points. This observation is important for SIS mixers operating at frequencies near or above gap frequency (ωgap) because the warping of the second negative photon step to the positive display side, narrowing down the bias voltage interval in which measurement of the Y-factor at the first photon step could be done.

•Jan 1, 2011•2 citations

Studies of noise in Josephson-effect mixers and their potential for submillimeter heterodyne detection

Robert J. Schoelkopf

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. This thesis describes both theoretical and experimental investigations into the dynamics and noise processes of Josephson junctions, with the intent of evaluating their potential as mixers in heterodyne instruments for submillimeter-wave (i.e., the frequency range from 300 GHz to 3THz) detection. Superconducting tunnel junctions utilizing the nonlinearity due to photon-assisted tunneling of quasiparticles (SIS mixers) have become the state-of-the-art technology for sensitive heterodyne detection up to frequencies of about 700 [...]. Recent progress in the fabrication of high [...], superconductors has led to Josephson-effect devices with [...] products of up to ten millivolts, which might be suitable for mixing at frequencies of many terahertz. The key question for weighing the prospects for high-frequency Josephson mixers is that of the sensitivity which can be attained. Previous experimental work on Josephson mixing suggests the existence of an "excess" noise, which degrades the sensitivity. Theoretical modeling of mixer performance, based on the resistivelyshunted junction (RSJ) model for the dynamics of the device, also indicates the presence of larger noise than expected. The origin of this noise was not clearly understood, however, nor was its exact magnitude or expected scaling with frequency or junction characteristics known. In addition, previous experiments utilized crude devices of the point-contact type, which were unstable and thus undesirable for real applications. In the first part of this thesis research, extensive numerical simulations were performed with the RSJ model, including calculations of mixer noise and conversion efficiency. These calculations have revealed that the source of excess noise is the AC Josephson oscillations of the device, which can be completely incoherent, with a linewidth comparable to their frequency. Thus they appear as a broadband noise source. While this noise is intrinsic and unavoidable, an optimized mixer is still shown to be capable of interesting sensitivity levels, and the excess noise is expected to become relatively less important as the operating frequency is increased. Secondly, a process has been developed for the fabrication of stable, well-characterized, and reproducible Josephson devices based on resistively-shunted Nb and NbN tunnel junctions. The devices utilize submicron-area, high current-density tunnel junctions and a AuGe shunt resistor to yield completely non-hysteretic I-V curves, normal-state resistances of about [...] products of about half a millivolt. These devices should be nearly optimal for mixing at [...]. Heterodyne measurements using these junctions have been performed in a waveguide mixer mount. Receiver temperatures as low as 190 K (DSB), with -6 dB conversion efficiency, have been obtained at 100 [...], but these results are still a factor of about four higher than those predicted by the RSJ simulations. Accurate measurements of the available noise power of the junctions at the intermediate frequency of 1.5 [...] were made, and confirmed that the receivers were limited by elevated junction output noise. The deviations of the noise from theoretical predictions are shown to be caused by the nonlinear interaction of the junction with the embedding circuit. While this work points out some of the complexity introduced by the strong nonlinearity of Josephson devices, it is still expected that Josephson-effect mixers may be useful for heterodyne detection at very high frequencies.

•Nov 7, 2007•4 citations

Noise and gain in frequency mixers with NbN SIS junctions

Alexandre Karpov, B. Plathner, J. Blondel +4 more

We study noise and conversion gain in the SIS mixers with Nb/MgO/NbN junctions at the millimeter and submillimeter wavelengths in order to estimate the possibility to extent the low noise operation towards the theoretical limit of 4/spl Delta//h=2.4 THz. We present as preliminary result the lowest achieved receiver noise with NbN SIS junctions of 65 K with conversion gain of -6 dB at 162 GHz and 230 K receiver noise with conversion gain of -10 dB at 306 GHz. The junction area is 2 /spl mu/m/sup 2/ and Josephson critical current density is 1.4 KA/cm/sup 2/. The optimum R/sub N//spl omega/C of NbN junction for mixers is estimated as 600 GHz/V. In preliminary tests the junctions R/sub N//spl omega/C is 10-20 time superior to the optimum and a significant improvement of NbN SIS mixers may be expected. The noise sources in the NbN SIS junctions are studied and a possible mixer sensitivity improvement is discussed. The thermal properties of the SIS NbN are studied. The frequency limit of the low loss integrated tuning structure in NbN is estimated as at least as 1.5 THz.

IEEE Transactions on Applied Superconductivity•Jun 1, 1997•9 citations
Superconducting tunnel diode (SIS) mixers are used for radio astronomy from 100 to 500 GHz. They are being considered for NASA spacebome astronomy at frequencies near 1,000 GHz. We report measurements of gain and noise in SIS mixers at 230 and 492 GHz. We measure high gain and noise associated with Josephson currents which have not been previously reported. These measurements show that Josephson currents are increasingly important as operating frequencies are raised. We discuss the techniques we use to make these measurements. Measurements made with hot and cold blackbodies are shown to be inaccurate at high frequencies. The problem is that SIS 's do not always respond linearly to the signal power incident on them. This is particularly important when 1) very broad band mixers are used and 2) Josephson effect currents are important. Both of these circumstances are present in the quasioptical SIS mixers favored for 500 GHz and higher. We use monochromatic signals to measure gain and noise to get around these problems.
The authors report measurements of gain and noise in SIS mixers at 230 and 492 GHz. Measurements were made of relatively high gain and noise associated with Josephson currents that have not been previously reported. These measurements show that Josephson currents are increasingly important as operating frequencies are raised. The techniques used to make these measurements are discussed. Measurements made with hot and cold black-bodies are shown to be inaccurate at high frequencies. The problem is that SIS mixers do not always respond linearly to the signal power incident on them. This is particularly important when (1) very broad band mixers are used and (2) Josephson effect currents are important. Both of these circumstances are present in the quasioptical SIS mixers favored for 500 GHz and higher. Monochromatic signals were used to measure gain and noise to get around these problems.>
Superconducting tunnel diodes (SISs) are investigated for both the generation and detection of submillimeter wavelengths. For detection, heterodyne receivers using SISs are investigated. Josephson currents are found to have a large effect on SIS mixers in the submillimeter, even though their effect is less at lower frequencies. At 492 GHz, fixer conversion gain increased by 4 dB when Josephson currents are not suppressed by a magnetic field. A much higher noise is seen in this gain mode, but further investigation of this recently discovered phenomenon is warranted. For submillimeter generation, a two-dimensional array of SISs is investigated. The ac Josephson effect in the SIS is expected to deliver submillimeter power into a free-space radiation mode traveling perpendicular to the array. No experimental devices have been developed yet, but the authors show computer simulations and microwave scale model measurements of array structures.
Quasiparticle and Josephson tunneling currents in superconducting tunnel junctions provide nonlinear low-noise response up to terahertz frequencies. Many types of direct detector heterodyne mixer and parametric amplifier based on these effects have been explored. Only the SIS quasiparticle mixer has been sufficiently competitive to find significant applications. These mixers can have noise approaching the quantum limit TN = ℏω/k and gain larger than 10 dB. They are used at a number of observatories for molecular line radio astronomy at millimeter wavelengths. Similar applications at submillimeter wavelengths are beginning.
We report the investigation of the influence of Josephson pair tunnelling on the sensitivity of an SIS mixer near the superconducting gap of niobium. Hot and cold load measurements were carried out from 600 GHz to 700 GHz, without completely supressing the Josephson effect. We have noticed that when measurements were made at bias points near the first Shapiro step, significantly higher values of Y-factor could be obtained with magnetic field strengths that made the Shapiro step sharper, rather then those that supressed the step. This resulted in a significant improvement in noise temperature of the mixer at those bias points. This observation is important for SIS mixers operating at frequencies near or above gap frequency (ωgap) because the warping of the second negative photon step to the positive display side, narrowing down the bias voltage interval in which measurement of the Y-factor at the first photon step could be done.
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. This thesis describes both theoretical and experimental investigations into the dynamics and noise processes of Josephson junctions, with the intent of evaluating their potential as mixers in heterodyne instruments for submillimeter-wave (i.e., the frequency range from 300 GHz to 3THz) detection. Superconducting tunnel junctions utilizing the nonlinearity due to photon-assisted tunneling of quasiparticles (SIS mixers) have become the state-of-the-art technology for sensitive heterodyne detection up to frequencies of about 700 [...]. Recent progress in the fabrication of high [...], superconductors has led to Josephson-effect devices with [...] products of up to ten millivolts, which might be suitable for mixing at frequencies of many terahertz. The key question for weighing the prospects for high-frequency Josephson mixers is that of the sensitivity which can be attained. Previous experimental work on Josephson mixing suggests the existence of an "excess" noise, which degrades the sensitivity. Theoretical modeling of mixer performance, based on the resistivelyshunted junction (RSJ) model for the dynamics of the device, also indicates the presence of larger noise than expected. The origin of this noise was not clearly understood, however, nor was its exact magnitude or expected scaling with frequency or junction characteristics known. In addition, previous experiments utilized crude devices of the point-contact type, which were unstable and thus undesirable for real applications. In the first part of this thesis research, extensive numerical simulations were performed with the RSJ model, including calculations of mixer noise and conversion efficiency. These calculations have revealed that the source of excess noise is the AC Josephson oscillations of the device, which can be completely incoherent, with a linewidth comparable to their frequency. Thus they appear as a broadband noise source. While this noise is intrinsic and unavoidable, an optimized mixer is still shown to be capable of interesting sensitivity levels, and the excess noise is expected to become relatively less important as the operating frequency is increased. Secondly, a process has been developed for the fabrication of stable, well-characterized, and reproducible Josephson devices based on resistively-shunted Nb and NbN tunnel junctions. The devices utilize submicron-area, high current-density tunnel junctions and a AuGe shunt resistor to yield completely non-hysteretic I-V curves, normal-state resistances of about [...] products of about half a millivolt. These devices should be nearly optimal for mixing at [...]. Heterodyne measurements using these junctions have been performed in a waveguide mixer mount. Receiver temperatures as low as 190 K (DSB), with -6 dB conversion efficiency, have been obtained at 100 [...], but these results are still a factor of about four higher than those predicted by the RSJ simulations. Accurate measurements of the available noise power of the junctions at the intermediate frequency of 1.5 [...] were made, and confirmed that the receivers were limited by elevated junction output noise. The deviations of the noise from theoretical predictions are shown to be caused by the nonlinear interaction of the junction with the embedding circuit. While this work points out some of the complexity introduced by the strong nonlinearity of Josephson devices, it is still expected that Josephson-effect mixers may be useful for heterodyne detection at very high frequencies.
We study noise and conversion gain in the SIS mixers with Nb/MgO/NbN junctions at the millimeter and submillimeter wavelengths in order to estimate the possibility to extent the low noise operation towards the theoretical limit of 4/spl Delta//h=2.4 THz. We present as preliminary result the lowest achieved receiver noise with NbN SIS junctions of 65 K with conversion gain of -6 dB at 162 GHz and 230 K receiver noise with conversion gain of -10 dB at 306 GHz. The junction area is 2 /spl mu/m/sup 2/ and Josephson critical current density is 1.4 KA/cm/sup 2/. The optimum R/sub N//spl omega/C of NbN junction for mixers is estimated as 600 GHz/V. In preliminary tests the junctions R/sub N//spl omega/C is 10-20 time superior to the optimum and a significant improvement of NbN SIS mixers may be expected. The noise sources in the NbN SIS junctions are studied and a possible mixer sensitivity improvement is discussed. The thermal properties of the SIS NbN are studied. The frequency limit of the low loss integrated tuning structure in NbN is estimated as at least as 1.5 THz.