Waveguide Mixer Research Articles

Development of an SIS Mixer-Based Low-Noise Amplifier Amenable to Josephson Oscillator Pumping

We propose a low-noise and low-power-consumption microwave amplifier using superconductor-insulator-superconductor (SIS) mixers as quasi-particle frequency up- and down-converters pumped by a Josephson array oscillator in the millimeter-wave band. A proof-of-concept study of an amplifier with two W-band waveguide mixers using Nb/Al-AlOx/Nb junctions in a cascade connection demonstrated an average gain of 6 dB and a noise temperature of 12 K from nearly DC to 5 GHz. We also designed and fabricated a Josephson array oscillator at 100 GHz, which consisted of 31 overdamped Josephson junctions placed at each half-wavelength in an Nb microstrip line. The estimated output power of the oscillator was 0.2 μW at 100 GHz, which can be increased by increasing the number of the oscillator junctions. These results suggest that the proposed SIS mixer-based amplifier is suitable for on-chip integrated circuits to be implemented in large-scale multipixel SIS receivers and quantum computers.

Low-Noise Sis Receivers for New Radio-Astronomy Projects

We have developed, manufactured, and tested a waveguide mixer in the range 211–275 GHz on the basis of the superconductor–insulator–superconductor (SIS) tunnel structures. The methods of manufacturing high-quality tunnel structures on quartz substrates have been worked out. To extend the receiver band, the Nb/AlOx/Nb and Nb/AlN/NbN tunnel junctions with a high current density of up to 20 kA/cm2 are employed. The dependence of the characteristics of the receiving elements on the signal frequency is simulated for the intermediate-frequency band 4–12 GHz. The measurements demonstrate a good agreement of the input band of the receiving structures with the calculated results. The uncorrected noise temperature of the receiver amounts to 24 K at a frequency of 265 GHz, which is only two times higher than the quantum limit. The receivers under development are intended for a number of newly-built ground-based radio telescopes (“Suffa” and LLAMA), as well as for the “Millimetron” space program.

Dual color optogenetic control of neural populations using low-noise, multishank optoelectrodes

Optogenetics allows for optical manipulation of neuronal activity and has been increasingly combined with intracellular and extracellular electrophysiological recordings. Genetically-identified classes of neurons are optically manipulated, though the versatility of optogenetics would be increased if independent control of distinct neural populations could be achieved on a sufficient spatial and temporal resolution. We report a scalable multisite optoelectrode design that allows simultaneous optogenetic control of two spatially intermingled neuronal populations in vivo. We describe the design, fabrication, and assembly of low-noise, multisite/multicolor optoelectrodes. Each shank of the four-shank assembly is monolithically integrated with 8 recording sites and a dual-color waveguide mixer with a 7 × 30 μm cross-section, coupled to 405 nm and 635 nm injection laser diodes (ILDs) via gradient-index (GRIN) lenses to meet optical and thermal design requirements. To better understand noise on the recording channels generated during diode-based activation, we developed a lumped-circuit modeling approach for EMI coupling mechanisms and used it to limit artifacts to amplitudes under 100 μV upto an optical output power of 450 μW. We implanted the packaged devices into the CA1 pyramidal layer of awake mice, expressing Channelrhodopsin-2 in pyramidal cells and ChrimsonR in paravalbumin-expressing interneurons, and achieved optical excitation of each cell type using sub-mW illumination. We highlight the potential use of this technology for functional dissection of neural circuits.

Low-noise integrated balanced SIS mixer for 787–950 GHz

We developed a low-noise, compact, balanced superconductor–insulator–superconductor (SIS) mixer, operating in the 787–950 GHz radio frequency range. A waveguide mixer block was designed to integrate all the key components, such as a radio frequency (RF) 90° hybrid coupler, two identical SIS mixer chips, bias-tees, and an intermediate frequency power-combiner. The RF waveguide 90° hybrid coupler consists of branch lines with wide slots optimized by numerical simulation, for ease of fabrication. The balanced mixer was installed into a cartridge type receiver, originally developed for the Atacama Large Millimeter/submillimeter Array Band 10 (787–950 GHz). The receiver demonstrated double sideband noise temperatures of approximately 200 K for most of the band, without any correction for loss in front of the receiver. The local oscillator noise rejection ratio was estimated to be more than 15 dB within the measured frequency range.

Fiberless multicolor neural optoelectrode for in vivo circuit analysis.

Maximizing the potential of optogenetic approaches in deep brain structures of intact animals requires optical manipulation of neurons at high spatial and temporal resolutions, while simultaneously recording electrical data from those neurons. Here, we present the first fiber-less optoelectrode with a monolithically integrated optical waveguide mixer that can deliver multicolor light at a common waveguide port to achieve multicolor modulation of the same neuronal population in vivo. We demonstrate successful device implementation by achieving efficient coupling between a side-emitting injection laser diode (ILD) and a dielectric optical waveguide mixer via a gradient-index (GRIN) lens. The use of GRIN lenses attains several design features, including high optical coupling and thermal isolation between ILDs and waveguides. We validated the packaged devices in the intact brain of anesthetized mice co-expressing Channelrhodopsin-2 and Archaerhodopsin in pyramidal cells in the hippocampal CA1 region, achieving high quality recording, activation and silencing of the exact same neurons in a given local region. This fully-integrated approach demonstrates the spatial precision and scalability needed to enable independent activation and silencing of the same or different groups of neurons in dense brain regions while simultaneously recording from them, thus considerably advancing the capabilities of currently available optogenetic toolsets.

An ultra-stable optical frequency standard for telecommunication purposes based upon the 5S1/2 → 5D5/2 two-photon transition in rubidium

In this study, we report the development of a frequency standard for optical fiber communication applications based on a two-photon transition in rubidium at 385.2 THz. This standard kills two birds with one stone in the sense it is capable of providing us with two highly stable serviceable wavelengths at 778.1 and 1556.2 nm. In this system, we exploit the narrow line-width of a fiber laser emitting at 1556.2 nm in conjunction with an erbium-doped fiber amplifier to generate a sufficient second harmonic laser beam at 778.1 nm in a periodically polled lithium niobate waveguide mixer in order to probe and frequency-lock the laser to the 5S1/2 (F g = 3)–5D5/2 (F e = 5) hyperfine two-photon transition component in 85Rb. The metrological performance of the standard is evaluated with the aid of an optical frequency comb synthesizer. Allan variance measurement shows a stability of 4 × 10−12 at 1 s (limited by the comb stability), reaching a floor of 6.8 × 10−13 at 1000 s. After correction of all the major systematic frequency shifts including the light shift, the absolute frequency is found to be 385 285 142 374.0 (5.0) kHz. Moreover, the absolute frequencies of most of the hyperfine components of the 5S1/2–5D5/2 transition of the two naturally existing rubidium isotopes are measured using a femtosecond frequency comb synthesizer after stabilizing a laser on each component.

4.7-THz Superconducting Hot Electron Bolometer Waveguide Mixer

We present the first superconducting hot electron bolometer (HEB) waveguide mixer operating at 4.7 THz. The 5.5-nm-thick, 300-nm-long, and 3600-nm-wide NbN HEB microbridge is integrated into a normal metal (Au) planar circuit on a 2 $\mu$ m thick silicon substrate. This circuit is integrated in a 24 $\mu$ m $\,\times\,$ 48 $\mu$ m $\,\times\,$ 21 $\mu$ m waveguide cavity and a 14 $\mu$ m $\, \times \,$ 7 $\mu$ m $\, \times \,$ 200 $\mu$ m substrate channel, which is directly machined into a CuTe alloy block. The power spectrum of the HEB mixer, measured with a Fourier transform spectrometer, is in good agreement with the results of 3-D EM circuit simulation. Measured mixer performance shows a state-of-the-art double sideband noise temperature of 1100 K, averaged over the IF bandwidth of 0.2–3.5 GHz. The 3-dB noise roll-off is 3.5 GHz. This mixer is used in the German REceiver for Astronomy at Terahertz frequencies (GREAT) at the airborne Stratospheric Observatory for Far Infrared Astronomy (SOFIA).

High-frequency fluctuation measurements by far-infrared laser Faraday-effect polarimetry-interferometry and forward scattering system on MST.

Magnetic fluctuation-induced transport driven by global tearing modes has been measured by Faraday-effect polarimetry and interferometry (phase measurements) in the MST reversed field pinch. However, the role of small-scale broadband magnetic and density turbulence in transport remains unknown. In order to investigate broadband magnetic turbulence, we plan to upgrade the existing detector system by using planar-diode fundamental waveguide mixers optimized for high sensitivity. Initial tests indicate these mixers have ×10 sensitivity improvement compared to currently employed corner-cube Schottky-diode mixers and ×5 lower noise. Compact mixer design will allow us to resolve the wavenumbers up to k ∼ 1-2 cm(-1) for beam width w = 1.5 cm and 15 cm(-1) for beam width w = 2 mm. The system can also be used to measure the scattered signal (amplitude measurement) induced by both plasma density and magnetic fluctuations.

Superconducting mixer on the basis of a chip with one-sided conection for radio astronomy

We describe in detail the principles of designing a tunable mixer with suppression of the mirror channel for the frequency band 86–115 GHz and a mixer for the band 787–950 GHz with twochannel reception and absence of the mechanical-tuning components. The mixers are based on superconductor–insulator–superconductor tunnel superconducting junctions with normal metal (aluminum) in the tuning circuit. The two developed mixers are optimized for the one-side chip connection to the full-height rectangular waveguide, which is required for creating a submillimeterwave single-chamber balanced waveguide mixer with a wide intermediate frequency bandwidth. The input-signal reflection coefficient is below −15 dB and the loss of the signal transmission to the mixer is below 3 dB in the frequency band 787–950 GHz.

Development and testing of Band 10 receivers for the ALMA project

The production model of a dual polarization heterodyne receiver for the Atacama Large Millimeter/submillimteter Array (ALMA) telescope has been developed to operate in the 787–950GHz frequency band. The receiver uses two double sideband (DSB) waveguide mixers with Nb/AlOx/Nb tunnel junctions and NbTiN/SiO2/Al microstrip tuning circuits on quartz substrate. A terahertz time domain spectrometer was used to characterize our NbTiN film for the tuning circuit design, which revealed that the complex conductivity of the film is described by the Mattis-Bardeen theory including a finite scattering time of 15fs and a superconducting gap with a gap ratio 2Δ/kBTC∼4.0. Tens of these receivers (out of the total production number of 73) have been successfully produced, and their performance is well within the stringent ALMA requirements. The best achieved DSB receiver noise temperature is 125K, corresponding to about 3hf/kB for 4K operation. One of Band 10 receivers has successfully been installed in the ALMA antenna for a test observation.

232 THz quantum cascade laser frequency-locked to the harmonic of a microwave synthesizer source

Frequency stabilization of a THz quantum cascade laser (QCL) to the harmonic of a microwave source has been accomplished using a Schottky diode waveguide mixer designed for harmonic mixing. The 2.32 THz, 1.0 milliwatt CW QCL is coupled into the signal port of the mixer and a 110 GHz signal, derived from a harmonic of a microwave synthesizer, is coupled into the IF port. The difference frequency between the 21st harmonic of 110 GHz and the QCL is used in a discriminator to adjust the QCL bias current to stabilize the frequency. The short-term frequency jitter is reduced from 550 kHz to 4.5 kHz (FWHM) and the long-term frequency drift is eliminated. This performance is compared to that of several other THz QCL frequency stabilization techniques.

Investigation of Loading Effect on Power Performance for Planar Gunn Diodes Using Load-Pull Measurement Technique

A one-port load-pull measurement has been carried out in order to investigate the effect of loading on the RF power performance of a planar Gunn diode operating in the transit-time mode at 102 GHz. A W-band manual E-H tuner was applied between a waveguide mixer and a wafer probe to vary the load impedance on the Gunn diode. It has been found that more than 25 dB variation of output power was obtained by systematically adjusting the tuner. By de-embedding the S-parameters of the probe, E-H tuner and mixer, the relationship between RF power and load impedance for the planar Gunn diode was derived. This method is extremely useful for assisting the design of matching networks to improve power output of one-port oscillator devices.

Performance of the ALMA Band 10 SIS Receiver Prototype Model

We have developed a dual polarization prototype model of the Atacama Large Millimeter/submillimeter Array (ALMA) Band 10 (787-950 GHz) receivers. The front-end optics comprises a pair of ellipsoidal mirrors, a wire grid, and two corrugated feed horns. A waveguide mixer block is attached to each feed horn in which a mixer chip employing Nb/AlOx/Nb juncions and NbTiN/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Al microstrip tuning circuits is mounted to a WR-1.2 full-height waveguide. A local oscillator (LO) signal receiving horn and a waveguide 10-dB LO coupler are integrated in the block to provide the LO signal to the mixer chip. A fixed-tuned multiplier with a diagonal horn located at the 110-K stage is used to transmit the LO power. The LO signal is then quasi-optically coupled to the mixer receiving horn. A very wide intermediate frequency (IF) system with a bandwidth of 4-12 GHz is employed. The receiver demonstrated double sideband (DSB) noise temperatures of about 160 K (4 <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h</i> ν/ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> ) without any correction for loss in front of the receiver at the LO frequency of 834 GHz at an operating physical temperature of 4 K.

Hollow waveguide photomixing for quantum cascade laser heterodyne spectro-radiometry

An integrated optic approach, using hollow waveguides, has been evaluated for a compact, rugged, high efficiency heterodyne optical mixing circuit in the middle infrared. The approach has involved the creation of hollow waveguides and alignment features for a beam combiner component in a glass-ceramic substrate. The performance of the integrated beam combiner was tested as part of a full laser heterodyne spectro-radiometer in which a quantum cascade laser local oscillator emitting at 9.7 µm was mixed with incoherent radiation. The performance has been evaluated with both cryogenically-cooled and peltier-cooled photomixers demonstrating consistent detection limits of two and five times the shot noise limit, respectively. The hollow waveguide mixer has also shown advantages in temporal stability, laser spatial mode cleansing, and reduced sensitivity to optical feedback.

Computer-aided design of broadband single balanced waveguide mixer at K-band

In this article, computer-aided design of a broadband single balanced waveguide mixer covering full K-band (18 to 26.5 GHz) is presented. Emphasis has been given on simple design approach of the mixer using commercially available CAD (computer-aided design) tools. The mixer circuit is implemented on suspended stripline etched on soft substrate that is integrated with RF (radio frequency) and LO (local oscillator) waveguides. Conversion loss of 6-8 dB with 8.5 GHz instantaneous IF (intermediate frequency) bandwidth has been achieved with þ10 dBm LO power at 35 GHz and the RF swept from 18 to 26.5 GHz. A systematic design approach of the mixer is presented with its simulated and experimental results. V C 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:586-588, 2011; View this article at wileyonlinelibrary.com. DOI 10.1002/mop.25759

Low-Noise Waveguide-Type NbN/AlN/NbN SIS Mixers Approaching Terahertz Frequencies

In this paper, we present the development of low-noise waveguide mixers with NbN/AlN/NbN tunnel junctions at a frequency approaching 1 THz. The mixer was designed to be compatible with MgO substrate. Mixers of the presented design demonstrated much improved receiver sensitivity. This improvement is attributed to the reduction in signal dissipation in waveguide and leakage into an intermediate frequency port by adopting a full-height waveguide and an effective RF choke filter, respectively. Two types of tuning circuits, namely parallel-connected twin-junction (PCTJ) and half-wavelength self-resonance distributed junction (DJ), are designed and evaluated. Both theoretical and experimental results show that the PCTJ design is superior to the DJ design in terms of gain and sensitivity due to smaller loss in the tuning circuit.

SIS Mixer Fabrication for ALMA Band10

Band10 of the Atacama Large Millimeter Array (ALMA) is a planned heterodyne receiver covering the frequency range 790 GHz-950 GHz. The waveguide mixers are superconductor insulator superconductor (SIS) Nb/Al-AlOx/Nb junctions integrated with NbTiN/SiO2/Al tuning circuits. Our junction definition process has been greatly simplified by introducing an inductively-coupled-plasma (ICP) etcher to the fabrication. The etching process, which employs a low-pressure CF4/O2 plasma, allows to remove the entire Nb/Al-AlOx/Nb tri-layer in a single step. SIS mixers with current densities up to 10 kA/cm2 and quality factor above 15 have been fabricated with good reproducibility. Minimum receiver noise temperature, corrected for optical losses, is 210 K at 860 GHz. With the goal to further improve the performance, optimization of circuit design and fabrication technology are discussed.

Performance of Terahertz Waveguide SIS Mixers Employing Epitaxial NbN Films and Nb Junctions

We have designed, fabricated, and tested terahertz waveguide superconductor-insulator-superconductor (SIS) mixers with Nb/AlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> /Nb junctions and NbN/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Al microstriplines. The NbN ground plane used was an epitaxial film grown on a single-crystal MgO substrate. A two-junction tuning circuit, which was directly placed at the feed point of a bow-tie waveguide probe without impedance transformers, was used. A full-height waveguide, hammer-type choke filter, and zero-depth backshort were adopted for the design of the microstrip-waveguide transition structure. The Nb junctions in which the current density was 6.5 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> showed good I-V characteristics, yielding a subgap-to-normal-state resistance ratio greater than 20. The results obtained for the mixer performance showed a receiver noise temperature of 440 K (DSB) at 1 THz; the results were corrected for losses in the beam splitter and the vacuum window. A detailed analysis of the mixers suggested that the waveguide mixers composed of epitaxial NbN films and Nb junctions were effective in the terahertz band.

도파관 방향성 결합기를 갖는 60 GHz 대역 Non-Radiative Dielectric 도파관 혼합기

본 논문에서는 점 대 점 통신망으로 수요가 증가하고 있는 60 GHz 대역 무선 통신 장비의 주요 부품인 혼합기를 non-radiative dielectric 도파관으로 구현하였다. Non-radiative dielectric 도파관 혼합기의 제작에 있어서 가장 어려웠던 것이 유전체 선로 결합기의 구현이었는데, 유전체 선로를 정해진 곡율로 형상화하는 것과 정확한 간격으로 위치시키는 것이 쉽지 않기 때문이다. 이 때문에 유전체 선로 결합기를 갖는 혼합기의 경우 일정한 성능을 갖도록 제작하는 것이 매우 힘들었다. 본 논문에서는 유전체 선로 결합기를 도파관 방향성 결합기로 대체하여 가공을 통해 제작이 가능케 함으로써 결합기가 일정한 특성을 갖도록 하였다. 그 결과로 혼합기의 생산성이 획기적으로 개선되었다. 본 논문을 통해 구현된 혼합기의 설계 주파수는 RF 및 LO는 <TEX>$57{\sim}64\;GHz$</TEX>이고, IF는 <TEX>$DC{\sim}2\;GHz$</TEX>인데, LO가 10 dBm, 60 GHz인 조건에서 <TEX>$60{\sim}62\;GHz$</TEX>의 RF 입력에 대한 하향 변환 손실은 <TEX>$10{\pm}1\;dB$</TEX>로 측정되었다. In this paper, the mixer was implemented in the non-radiative dielectric waveguide that is the main component of 60 GHz band radio telecommunications equipment which a demand increases for the purpose of point-to-point communication network. As to the manufacture of the non-radiative dielectric waveguide mixer, it was the implementation of the dielectric line combiner to be most difficult. The thing which that gives shape to the curvature which is the dielectric line determined and the to place in the exact interval thing are easy. For this reason, it was very difficult to make in order to have the regular performance in the case of the mixer having the dielectric line combiner. In this paper, since the dielectric line combiner was replaced with the waveguide directional coupler and the manufacture was possible through a processing it had the characteristic that a combiner is fixed. In result, the productivity of a mixer was innovatively improved. The design frequency of the mixer implemented through this paper RF and LO are <TEX>$51{\sim}64\;GHz$</TEX>. IF Is <TEX>$DC{\sim}\;GHz2$</TEX>. The down conversion loss toward the RF input of <TEX>$60{\sim}62\;GHz$</TEX> was measured by <TEX>$10{\pm}1\;dB$</TEX> in the condition that LO is 10 dBm, 60 GHz.

Design of Balanced Mixers for ALMA Band-10

Two variants of balanced mixer employing twin-SIS structure are under development for 787-950 GHz frequency range. Easy-to-use Geometry Transformation method for modeling of superconducting microstrips is developed, compared to referenced methods and used for design of the mixers. Lens-antenna mixer is based on cross-slot antenna; it does not need any intervening optics between its lens and sub-reflector of ALMA telescope; simple yet efficient composition of lens-antenna cartridge is suggested. Compact single-chamber balanced waveguide mixer employs two SIS chips and capacitive probe for LO injection; coupling above -3 dB and signal loss below -20 dB are expected. Need in shifting of resonance frequency of twin-SIS mixer towards top of the frequency band is predicted using Tucker's theory in large-signal approximation. T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RX</sub> considerably below 200 K (DSB) is simulated using high-quality hybrid SIS junction for NbTiN/Nb - AlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> - Nb/Al for J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> = 12 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .