High Loaded Quality Factor Research Articles

Simulation framework for microwave SQUID multiplexer optimization

So far, performance prediction and optimization of microwave SQUID multiplexers have largely been based on simple approximate analytical models and experimental results. This is caused by the complexity of the underlying physics and the intricacy of operation and readout parameters. As a simplified description can never account for all potential effects occurring in a real device, we have developed a software framework to simulate the characteristics and performance of a microwave SQUID multiplexer. Our simulation framework is a powerful tool to guide understanding and optimization of microwave SQUID multiplexers and other related devices. It includes common readout schemes such as open-loop or flux ramp-modulated readout as well as the nonlinear behavior of Josephson tunnel junctions. Moreover, it accounts for the non-zero response time of superconducting microwave resonators with high loaded quality factors as well as the most significant noise contributions such as amplifier noise, resonator noise, as well as SQUID noise. This ultimately leads to a prediction of device performance that is significantly better compared to simple analytical methods. Using the simulation framework, we discuss first steps toward full microwave SQUID multiplexer optimization and highlight some other applications for which our simulation framework can be used.

Efficient acousto-optic modulation using a microring resonator on a thin-film lithium niobate-chalcogenide hybrid platform.

This Letter presents the first, to the best of our knowledge, thin-film lithium niobate-chalcogenide based microring acousto-optic modulator where an interdigital transducer and a chalcogenide strip waveguide are integrated on X-cut thin-film lithium niobate. The microring resonator exhibits a high loaded quality factor of 5 × 105. The developed hybrid acousto-optic modulator with an interaction length of 120 µm demonstrates an effective half-wave voltage of only 1.74 V, which corresponds to a voltage-length product of 0.02 V•cm. The performance of the acousto-optic modulator demonstrated on the unsuspended thin-film lithium niobate-chalcogenide waveguide platform is on par with that obtained from an acoustic cavity assisted homogeneous lithium niobate counterpart.

Continuous Wave Operation of Superconducting Accelerating Cavities With High Loaded Quality Factor

Close to 780 superconducting 1.3-GHz accelerating cavities made of bulk niobium have been installed in the European X-ray free electron laser (E-XFEL) linear accelerator. The linac can operate at a mean gradient (Eacc) of ca. 23 MV/m in the nominal short pulse (SP) operation mode with 1.4-ms pulses and a repetition rate of 10 Hz. An R&D program at Deutsches Elektronen-Synchrotron (DESY) is ongoing since 2011 on the feasibility of a continuous wave (CW) upgrade of the E-XFEL accelerator. In this publication, a modification of the low-level radio frequency (LLRF) control system to the CW mode is presented. Currently, the control system successfully stabilizes accelerating field for the SP mode. The demanding E-XFEL specifications of 0.01% for the field amplitude and 0.01° for the phase stability are required to keep the photon beam quality for all experimental stations. The proposed modification has been implemented and tested to verify the system versatility for SP and CW operation modes. The tests were conducted for a prototype E-XFEL cryomodule XM-3. As for the series cryomodules, this prototype contains eight superconducting 1.3-GHz cavities. The results presented here confirm that the same LLRF system can be used with minor software modifications for either operation mode (CW or SP). However, the CW mode requires a more complex RF-power management and more precise control, especially when cavities operate with very high loaded quality factor (Ql) of the order of 6E7. The achieved stability for such highQl is also presented and discussed.

Resonance-Based Normalization Theory for Analysis and Design of Resonant Power Converters

This paper deals with a circuit modeling approach based on a normalization procedure in order to represent the system considering resonant parameters instead of real circuit parameters. The main advantages are the attainment of generalized solutions that do not depend on specifications, which allows the design of the converter without resorting to circuit level simulations. In this work, the fundamentals and the mathematical formulation of the normalized analysis are described. Furthermore, a multi-stage Class D-E DC-DC resonant converter is analyzed without simplifying assumptions used in other methodologies, such as, high loaded quality factor and fundamental component approximation. Experimental results are shown to verify the theoretical approach.

Determination of complex permittivity of thin dielectric samples based on high-q microstrip resonance sensor

In this paper, a high quality factor microstrip resonator based on modified Minkowski fractal structure sensor is presented for determining the dielectric sample's complex permittivity. A high loaded quality factor value has been achieved by utilizing fractal structure, which is far greater than that of a typical rectangle microstrip antenna. Besides, the modified fractal radiation patch and the feeding section of the sensor result in a highly sensitive area to the tested materials. The sensing principle is implemented by detecting the electric fields perturbation of the resonator when different tested materials are placed over it. The complex permittivity change of the tested materials can be forecasted by transferring the acquired experimental relative resonant frequency shifts (Δf) and loaded QL values of the proposed sensor to a well-developed neural network system. To validate the proposed method, various standard dielectric samples including Teflon, PVC, and others are tested and analyzed. The experimental results are compared with published values with the maximum error of 4.9%.

Active suppression of microphonics detuning in high QL cavities

Operation of superconducting radio frequency (SRF) cavities with high loaded quality factors is becoming increasingly preferred for applications which involve low beam loading including energy recovery linacs (ERL). Vibration induced microphonics detuning poses a major operational bottleneck in these low bandwidth systems, adversely affecting field stability. Besides passive measures of mitigating the vibration sources, modern SRF cavities are also attached to fast tuners incorporating piezoelectric actuators. We demonstrate the narrow band active noise control algorithm for realizing active resonance control and propose a modification based on the least mean square approach to adaptively tune the control parameters and study its stability and performance. We discuss our experience of using passive mitigation techniques while commissioning the main linac cryomodule of the Cornell-BNL ERL test accelerator and report a net reduction in peak detuning by more than a factor of 2 in its unstiffened cavities. Finally, we demonstrate stable performance of our resonance control system with consistent reduction of peak microphonics detuning by almost a factor of 2 on multiple cavities.

Design of X-Cut and Z-Cut Lithium Niobate Whispering-Gallery-Mode Disk-Resonators With High Quality Factors

We demonstrate the fabrication process of millimeter-size lithium niobate (LiNbO $_3$ ) whispering-gallery-mode (WGM) disk-resonators. We fabricate both $x$ - and $z$ -cut disk-resonators, starting from commercially available LiNbO $_3$ disks with diameters of 12 mm and thicknesses of 1 mm. We characterize these two WGM resonators using a prism coupling configuration. We find that both resonators feature high loaded quality factors, in both cases higher than $10^7$ at 1550 nm. We also investigate the polarization and thermal effects in these disk-resonators. The design of high- $Q$ LiNbO $_3$ disk-resonators with different orientations using the same platform will allow for a wide variety of potential applications in nonlinear and quantum photonics.

Embedded Niobium Using PI-2611 for Superconducting Flexible Cables

ABSTRACTDense, controlled-impedance, superconducting cables with small cross-sections are desirable, especially for quantum computing applications. In this study, superconductivity properties, rf microwave response and mechanical reliability performance of embedded Nb dc cables and Nb microstrip transmission line resonators with different thicknesses of polyimide PI-2611 encapsulation layers (0, 4 and 8 μm) have been investigated. Critical temperature (Tc) and critical current (Ic) of embedded Nb dc cables are ∼ 8.2 K and ∼ 0.2 A, respectively. Embedded Nb resonators yield high loaded quality factor (QL), with values as high as 14481 at ∼ 1.2 K and at a fundamental resonance of ∼ 2 GHz. From mechanical fatigue testing, we have observed that a polyimide encapsulation layer can effectively enhance the mechanical reliability of superconducting Nb flexible cables.

Magnetically controllable silicon microring with ferrofluid cladding.

We experimentally investigate the application of magnetic fluids (MFs) on integrated silicon photonics. Using a ferrofluid-clad silicon microring resonator, we demonstrate active control of resonances by applying an external magnetic field. Relatively high loaded quality factors on the order of 6000 are achieved, despite the optical losses introduced by the magnetic nanoparticles. We demonstrate resonance shifts of 185pm in response to a 110Oe strong magnetic field, corresponding to an overall refractive index change of -3.2×10-3 for the cladding MF. The combination of MFs and integrated photonics could potentially lead to the development of magnetically controllable optical devices and ultra-compact cost-effective magnetic field sensors.

연속전류모드에서 기생손실들을 고려한 고정주파수 LCL형 컨버터 해석

This paper analyzes an LCL-type isolated dc-dc converter operating for constant output voltage in the continuous conduction mode(CCM) with resistances of parasitic losses –static drain-source on resistance of power switch, ESR of resonant network(L-C-L)-using a high loaded quality factor Q assumptions and fourier series techniques. Simple analytical expressions for performance characteristics are derived under steady-state conditions for designing and understanding the behavior of the proposed converter. The voltage-driven rectifier is analyzed, taking into account the diode threshold voltage and the diode forward resistance.BR Experimental results measured for a proposed converter at low input voltage and various load resistances show agreement to the theoretical performance predicted by the analysis within maximum 4% error. Especially in the case of low output voltages and large loads, It is been observed that introduction of both rectifier and the parasitic components of converter had considerable effect on the performance.

High-<i>Q </i>and high-order side-coupled air-mode nanobeam photonic crystal cavities in silicon

We demonstrate the design, fabrication, and characterization of side-coupled airmode nanobeam photonic crystal cavities in silicon-on-insulator platform. Results show that repeatable devices achieve similar high loaded quality factors ( $> 10^{4}$ ) and large optical energy ratio in low refractive region. The unload $Q$ -factors of the fabricated cavities are estimated to exceed $10^{5}$ . With side-coupled configuration, high transmission of through port is achieved with typical insertion loss less than 0.5 dB. Wavelength shifts of the measured resonances with respect to the designed values are observed and well explained by considering the fluctuation of etching depth. The demonstrated side-coupled airmode nanobeam photonic crystal cavities may find their applications in ultracompact integrated photonics, especially for on-chip photonic sensor, notch filter, or optical switch.

Optical nonreciprocal transmission in an asymmetric silicon photonic crystal structure

An optical nonreciprocal transmission (ONT) is realized by employing the nonlinear effects in a compact asymmetric direct-coupled nanocavity-waveguide silicon photonic crystal structure with a high loaded quality factor (QL) of 42 360 and large extinction ratio exceeding 30 dB. Applying a single step lithography and successive etching, the device can realize the ONT in an individual nanocavity, alleviating the requirement to accurately control the resonance of the cavities. A maximum nonreciprocal transmission ratio of 21.1 dB as well as a working bandwidth of 280 pm in the telecommunication band are obtained at a low input power of 76.7 μW. The calculated results by employing a nonlinear coupled-mode model are in good agreement with the experiment.

Packaged, high-Q, microsphere-resonator-based add-drop filter.

In this Letter a packaged add-drop filter composed of a silica microsphere resonator and two fiber tapers is demonstrated theoretically and experimentally. A two-step fabrication process using an UV curable polymer is shown to stabilize the microsphere resonator with a diameter of 153 μm coupled to two tapered microfibers with diameters of 1.5 μm which are used as add and drop ports. A high loaded quality factor (Q-factor) of 0.9×10(5) and a free spectral range (FSR) of about 104 pm are obtained at around 1550 nm from the microsphere for the parallel coupling tapered fibers in the add-drop configuration. This device has a range of advantages, such as ease of fabrication, low-cost, and compatibility with traditional and commercial fiber systems.

A new high-Qcompact resonator using combination of interdigital hair-pin resonator and meander-line with μ-near-zero metamaterial

In this article, a new high-loaded quality factor (QL) resonator using combination of a stepped impedance resonator-shaped hair-pin resonator, interdigital capacitor, and a meander-line with μ-near-zero (MNZ) metamaterial is suggested. An interdigital capacitor is applied to the resonator to obtain high-QL performance and MNZ characteristic for size reduction. The resonator is designed to operate at 10 GHz, and the experimental result shows the Q-factor value of 167. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1781–1785, 2014

Low phase noise oscillator using a new planar hairpin resonator for X-band applications

This article proposed a new high loaded quality factor (QL) hairpin resonator with a combination of a stepped impedance resonator and single split ring resonator and its application to low phase noise oscillator for X-band applications.A new resonator has a good characteristic of S-parameter responses. The microwave oscillator is designed at 10 GHz that exhibited a low phase noise characteristic due to the high loaded QL of the new resonator. A series feedback network is used to generate the negative resistance to make oscillation. Experimental results of the microwave oscillator show the phase noise characteristic of −103.69 dBc/Hz at 100 kHz offset with output power of 15.56 dBm. The second harmonic suppression is −32.25 dBc, which is very important in wireless communication system. The figure of merit of the fabricated oscillator is −180 dBc/Hz. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1508–1511, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27608

Design of a wide-tuning-range lithium tantalate low-phase-noise voltage-controlled oscillator

In this brief, a lithium tantalate crystal with a low capacitance ratio and a wide tuning range is used to design a Butler common-base wide-tuning-range low-phase-noise oscillator considering a reasonable compromise between seeking high loaded quality factor and maintaining oscillator output power. The formulation of is derived from analysis of the Butler oscillator circuit and calculated with MATLAB. The unloaded quality factor of the crystal utilized in the design is about 1.24 K, and the frequency of the crystal is about 10.727 MHz. In the phase noise measurement experiments, of the Butler common-base oscillator is about 33% of , and the output power is about 11 dBm. The measured phase noise level without voltage control is 145 dBc/Hz at 1 kHz, and noise floor is better than 180 dBc/Hz. The tuning ability of the prototype oscillator is tested, and voltage control ability is also tested by increasing a low-voltage varactor BB155. After increasing a varactor capacitance, the measured phase noise at 1-kHz offset and noise floor are better than 142 and 180 dBc/Hz, respectively, when voltage-controlled slope are 86.6 and 19.2 ppm/V for a control voltage range of 2-10 V. Experimental results show that the Butler common-base oscillator with a wide tuning range can realize the characteristics of low phase noise based on the reasonable compromise between seeking high and maintaining output power.

Digital base-band rf control system for the superconducting Darmstadt electron linear accelerator

The accelerating field in superconducting cavities has to be stabilized in amplitude and phase by a radio-frequency (rf) control system. Because of their high loaded quality factor superconducting cavities are very susceptible for microphonics. To meet the increased requirements with respect to accuracy, availability, and diagnostics, the previous analog rf control system of the superconducting Darmstadt electron linear accelerator S-DALINAC has been replaced by a digital rf control system. The new hardware consists of two components: An rf module that converts the signal from the cavity down to the base-band and a field-programmable gate array board including a soft CPU that carries out the signal processing steps of the control algorithm. Different algorithms are used for normal-conducting and superconducting cavities. To improve the availability of the control system, techniques for automatic firmware and software deployment have been implemented. Extensive diagnostic features provide the operator with additional information. The architecture of the rf control system as well as the functionality of its components will be presented along with measurements that characterize the performance of the system, yielding, e.g., an amplitude stabilization down to $(\ensuremath{\Delta}A/A{)}_{\mathrm{rms}}=7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ and a phase stabilization of $(\ensuremath{\Delta}\ensuremath{\phi}{)}_{\mathrm{rms}}=0.8\ifmmode^\circ\else\textdegree\fi{}$ for superconducting cavities.

Superconducting RF Metamaterials Made With Magnetically Active Planar Spirals

Superconducting metamaterials combine the advantages of low-loss, large inductance (with the addition of kinetic inductance), and extreme tunability compared to their normal metal counterparts. Therefore, they allow realization of compact designs operating at low frequencies. We have recently developed radio frequency (RF) metamaterials with a high loaded quality factor and an electrical size as small as $\sim$$\lambda$658, ($\lambda$ is the free space wavelength) by using Nb thin films. The RF metamaterial is composed of truly planar spirals patterned with lithographic techniques. Linear transmission characteristics of these metamaterials show robust Lorentzian resonant peaks in the sub- 100 MHz frequency range below the $T_c$ of Nb. Though Nb is a non-magnetic material, the circulating currents in the spirals generated by RF signals produce a strong magnetic response, which can be tuned sensitively either by temperature or magnetic field thanks to the superconducting nature of the design. We have also observed strong nonlinearity and meta-stable jumps in the transmission data with increasing RF input power until the Nb is driven into the normal state. We discuss the factors modifying the induced magnetic response from single and 1-D arrays of spirals in the light of numerical simulations.

Miniaturized superconducting metamaterials for radio frequencies

We have developed a low-loss, ultrasmall radio frequency (rf) metamaterial operating at ∼76 MHz. This miniaturized medium is made up of planar spiral elements with diameter as small as ∼λ/658 (λ is the free space wavelength), fashioned from Nb thin films on quartz substrates. The transmission data are examined below and above the superconducting transition temperature of Nb for both a single spiral and a one dimensional array. The validity of the design is tested through numerical simulations and good agreement is found. We discuss how superconductors enable such a compact design in the rf with high loaded-quality factor (in excess of 5000), which is in fact difficult to realize with ordinary metals.

A new K‐band push‐push VCO using a miniaturized hairpin resonator

AbstractIn this article, a K‐band push‐push Voltage Controlled Oscillator (VCO) is presented using a miniaturized hairpin resonator (MHR) with a higher loaded quality factor and the reduced circuit area within 50% compared to the conventional one at 9.2 GHz.The MHR combined with the GaAs MESFET varactor shows a tuning range of 140 MHz, and this voltage tunable MHR is used to compose a push‐push VCO. It provides the frequency tuning range of 71 MHz with flatness of +0.13 dB, which is increased by 31 MHz compared to the conventional VCO. The voltage controlled push‐push oscillator based on the series feedback topology is implemented on 0.54 mm‐thick Teflon substrate with a dielectric constant of 2.54. The measurement shows the output power of 1.18 dBm, the fundamental signal power suppression of −33 dBc, and phase noise performance of −86.78 dBc/Hz at 100 kHz offset. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 699–701, 2010; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/mop.25007