Frequency Tuning Research Articles

In situ Non-destructive Measurement of Josephson Junction Resistance Using Fritting Contact Technique

Abstract Conventional four-probe methods for measuring the resistance of Josephson junctions can damage superconducting thin films, making them unsuitable for frequency measurements of superconducting qubits. In this study, we present a custom probe station measurement system that employs the fritting contact technique to achieve in situ, non-destructive measurements of Josephson junction resistance. Our experimental results demonstrate that this method allows for accurate prediction of qubit frequency with an error margin of 17.2 MHz. Moreover, the fritting contact technique does not significantly affect qubit coherence time or the integrity of the superconducting film, confirming its non-destructive nature. This innovative approach provides a dependable foundation for frequency tuning and addressing frequency collision issues, thus supporting the advancement and practical deployment of superconducting quantum computing.

Simultaneous optical and RF linear frequency sweep generation using a Fourier domain mode-locked OEO with carrier-suppressed single sideband modulation.

The linear frequency swept light source is a critical device for several sensing applications, including FMCW LiDAR, with which the maximum sensing distance is determined by the coherence length of the light source and the spatial resolution is limited by the frequency scan nonlinearity. Here, we report what we believe to be a novel approach to generate highly coherent optical linear frequency sweeps (LFS) with a Fourier domain mode-locked (FDML) opto-electronic oscillator (OEO) deploying carrier suppressed single sideband (CS-SSB) modulation enabled by a dual-parallel Mach-Zehnder modulator (DP-MZM), with the coherence length determined by the fixed frequency laser used in the OEO, without the need of an expensive high-speed arbitrary waveform generator (AWG). Concurrently, a radio frequency (RF) LFS synchronized with the optical LFS is also generated with the FDML OEO. We obtained a nearly ideal optical LFS around 1550 nm with a side-mode suppression ratio of 27.4 dB, by controlling the bias point and the RF power feeding back to the DP-MZM in the OEO loop. The resulting dual optical and RF LFS' achieved a chirp rate of 27.27 MHz/µs and a frequency tuning range of 0.6 GHz, which can be extended to 142 MHz/µs and 2.0 GHz, respectively by reducing the size of the tunable ring filter circuit inside the OEO loop. By using pre-distortion method, the residual nonlinearity is reduced to 1.9881 × 10-5, and the root mean square (RMS) value of the frequency swept nonlinearity is less than 0.764 MHz. Our dual optical and RF LFS generation with a CS-SSB FDML-OEO has the advantages of long coherence length, high tuning speed, excellent frequency tuning linearity and repeatability, and potentially low cost, which can be used to make a dual optical and RF FMCW ranging system (LiDAR and RADAR) and are attractive for many applications, such as 3D sensing and autonomous driving, as well as optical frequency domain reflectometer (OFDR), and other applications requiring fast and reliable linear frequency sweeps in either optical and RF domains.

Intercalation-enhanced topological material Bi2Se3: Tuning charge carrier and phonon dynamics for advanced optoelectronic and terahertz applications

The field of topological materials (TMs) is experiencing significant advancements due to their unique surface states, which offer considerable potential for optoelectronics and terahertz (THz) applications. Intercalation in TMs can effectively modulate these surface states, thereby altering electronic and optical properties and enhancing functionalities. This approach enables the tailoring of material properties for specific applications, broadening the utility of TMs across various technological domains. This study focuses on understanding the charge carrier and phonon dynamics in bismuth selenide (Bi2Se3) intercalated with various metals (AxBi2Se3, where A = Ag, Cr, Ni, Mn, Sm, Zn). We examine carrier trapping, carrier relaxation through optical and acoustic phonons, charge recombination processes, and variations in carrier temperature with probe delay lifetimes. Additionally, we explore coherent optical phonons (COPs) in MIBS, which oscillate at THz frequencies and have potential applications in THz generation and detection. Achieving tunability in the THz frequency of COP modes is a significant challenge; however, our research establishes a correlation between optical and structural properties and the dependence of COP frequencies on effective metal intercalation. This comprehensive investigation elucidates the intricate interplay between surface carriers and phonon dynamics in intercalated TMs, highlighting promising advancements for diverse technological applications, including spintronics, optoelectronics, and THz technology.

Microwave dielectric properties, vibrational spectrum, and antenna design of a novel melilite‐type Ba2CoSi2O7 ceramic

ABSTRACTLow‐εr (the low dielectric constant) microwave dielectric ceramics play an important role in sub‐6 GHz band communication by virtue of their small signal delay. In this paper, Ba2CoSi2O7 ceramics were synthesized by the solid‐phase reaction method, and X‐ray diffraction (XRD) confirms that they belong to a new melilite structure, with C2/c (No.15) space group, and the ceramics have good microwave dielectric properties with an εr ∼ 7.37, a Q×f (Q = 1/dielectric loss, f = resonant frequency) ∼ 26,320 GHz and a TCF (the temperature coefficient of resonant frequency) ∼ −55 ppm/°C after being sintered at 1150°C, and the theoretical dielectric constants derived from the Clausius–Mosotti as well as the porosity equation, respectively, are also used to further demonstrate the low‐εr properties. Based on the group theory, the one‐dimensional integrable representations of Γacoustic (the phonon modes) and Γoptical (optical modes) of Ba2CoSi2O7 are obtained, and the internal vibrational modes of Ba2CoSi2O7 are deconstructed and the main modes of influence of the electronic polarization are analyzed in conjunction with the results of the validly fitted peaks of the 17 Raman and 25 IR tests. A microstrip Yagi antenna is also designed based on the ceramic properties, which can achieve a gain of 9.65 dBi at the center tuning frequency of 5.47 GHz, with a S11 (return loss) close to −60 dBi. Based on the above results, the Ba2CoSi2O7 ceramic is a low‐εr microwave dielectric ceramic with significant potential for communication application.

A compact SIW dual-functional design with integrated filter and self-diplexing antenna

ABSTRACT This paper proposes a compact dual-functional design (DFD) which integrates a bandpass filter (BPF) and self-diplexing antenna in a half-mode substrate-integrated waveguide (HMSIW) cavity. The design consists of four eighth-mode SIW (EMSIW) sub-cavities that are formed by etching three slots on an HMSIW cavity. Two of the sub-cavities are coupled to form a BPF with low insertion loss with a controllable transmission zero and a wide out-of-band rejection > 33 dB. In contrast, the other two sub-cavities are used to create a self-diplexing antenna with wide frequency tunability (2.8–5.0 GHz) with two additional narrow slots and high isolation (>22 dB). Detailed parametric studies confirmed that tuning of self-diplexing antenna has no significant impact on the performance of integrated BPF. An equivalent circuit model of the design is developed and validated with simulation and measurement results. The proposed design has a simple and compact structure, good isolation, and controllability, making it suitable for modern handheld wireless systems.

Advancing on-chip Kerr optical parametric oscillation towards coherent applications covering the green gap

Optical parametric oscillation (OPO) in Kerr microresonators can efficiently transfer near-infrared laser light into the visible spectrum. To date, however, chromatic dispersion has mostly limited output wavelengths to >560 nm, and robust access to the whole green light spectrum has not been demonstrated. In fact, wavelengths between 532 nm and 633 nm, commonly referred to as the “green gap”, are especially challenging to produce with conventional laser gain. Hence, there is motivation to extend the Kerr OPO wavelength range and develop reliable device designs. Here, we experimentally show how to robustly access the entire green gap with Kerr OPO in silicon nitride microrings pumped near 780 nm. Our microring geometries are optimized for green-gap emission; in particular, we introduce a dispersion engineering technique, based on partially undercutting the microring, which not only expands wavelength access but also proves robust to variations in resonator dimensions. Using just four devices, we generate >150 wavelengths evenly distributed throughout the green gap, as predicted by our dispersion simulations. Moreover, we establish the usefulness of Kerr OPO to coherent applications by demonstrating continuous frequency tuning (>50 GHz) and narrow optical linewidths (<1 MHz). Our work represents an important step in the quest to bring nonlinear nanophotonics and its advantages to the visible spectrum.

A 60 GHz low phase noise VCO with second harmonic tail extraction in 40-nm CMOS

This work presents a 60 GHz continuously adjustable mm-wave cross-coupled voltage − controlled oscillator (VCO) utilizing an innovative frequency doubling technique in 40 nm CMOS technology. The extraction of the second harmonic is performed through a transformer from the tail of the 30 GHz fundamental VCO. The primary side of the transformer serves a dual purpose, functioning both as a filter for the second harmonic and as a balun simultaneously. The circuit incorporates a MOS varactor along with a four-bit binary weighed capacitor bank to achieve coarse and fine frequency tuning respectively. Post Layout simulation results indicate that the VCO spans a broad tuning range of 12.3 GHz, covering frequencies from 52.7 to 64.98 GHz. Phase noise (PN) remains below −96.3 dBc/Hz at a 1 MHz frequency offset within all bands Power consumption, including the output stage, is 21.8 mW from a 1.1-Volt supply. The VCO provides more than −13 dBm output power in all frequency bands and occupies a chip area of 0.53 mm2.

Temperature Dependence of Electrostatic Frequency Tunability of Ultrathin Si Nanoresonators

Temperature Dependence of Electrostatic Frequency Tunability of Ultrathin Si Nanoresonators

Investigation on vibration control of TetraSpar floating offshore wind turbine

The stability of offshore wind turbines during operation is crucial, and as an emerging technology, the TetraSpar floating offshore wind turbine demonstrates commendable stability. Moreover, it can effectively reduce the levelized cost of energy (LCOE) in production and installation. However, There is relatively scarce research on its dynamic response and reliability under complex ocean conditions. To reduce the vibration response of floating offshore wind turbines in complex marine environments and improve the stability of the turbines, it is necessary to establish a fully coupled dynamic model to study the multi-field coupled dynamic response and vibration control of the turbines. In light of this, this paper establishes a multi-physical field coupled dynamic model for TetraSpar floating offshore wind turbine through an F2A coupling framework, integrating aerodynamics, servo-elasticity, hydrodynamics, and mooring dynamics. The study analyzes the vibration suppression effects of different Tuned Mass Dampers (TMDs) on the wind turbine system. Using the two main response frequencies, 0.0367Hz and 0.57Hz, in the front and rear directions of the wind turbine as the tuning frequencies for TMD. The best vibration reduction effect was achieved by comparing multiple sets of TMD with different parameters. Analysis shows that TMD can significantly reduce the standard deviation of bending moment and tension of steel bars before and after tower foundation, with maximum values of 38.76% and 73.02%, respectively. At the same time, TMDs also impose a burden on wind turbines, such as a maximum increase of 2.23% in the average values of tower base bending moment, platform pitch, and tower top longitudinal displacement, which also slightly increase under extreme sea conditions. However, compared to the significant vibration suppression effect of TMD, it can be ignored.

An ADPLL-Based GFSK Modulator with Two-Point Modulation for IoT Applications.

To establish ubiquitous and energy-efficient wireless sensor networks (WSNs), short-range Internet of Things (IoT) devices require Bluetooth low energy (BLE) technology, which functions at 2.4 GHz. This study presents a novel approach as follows: a fully integrated all-digital phase-locked loop (ADPLL)-based Gaussian frequency shift keying (GFSK) modulator incorporating two-point modulation (TPM). The modulator aims to enhance the efficiency of BLE communication in these networks. The design includes a time-to-digital converter (TDC) with the following three key features to improve linearity and time resolution: fast settling time, low dropout regulators (LDOs) that adapt to process, voltage, and temperature (PVT) variations, and interpolation assisted by an analog-to-digital converter (ADC). It features a digital controlled oscillator (DCO) with two key enhancements as follows: ΔΣ modulator dithering and hierarchical capacitive banks, which expand the frequency tuning range and improve linearity, and an integrated, fast-converging least-mean-square (LMS) algorithm for DCO gain calibration, which ensures compliance with BLE 5.0 stable modulation index (SMI) requirements. Implemented in a 28 nm CMOS process, occupying an active area of 0.33 mm2, the modulator demonstrates a wide frequency tuning range of from 2.21 to 2.58 GHz, in-band phase noise of -102.1 dBc/Hz, and FSK error of 1.42% while consuming 1.6 mW.

Effect of Electrode Montage on Frequency Tuning Properties of Air-Conducted Ocular Vestibular-Evoked Myogenic Potential.

The use of a 500 Hz tone burst over other frequencies was adopted for the clinical recording of ocular vestibular-evoked myogenic potential (oVEMP) on the basis that this stimulus frequency produces larger response amplitudes (frequency tuning) than the other frequencies. However, the possibility of reflex contamination due to a spatially displaced reference electrode from the muscle of the response origin raises questions about using an infraorbital (IO) montage. Nonetheless, the belly-tendon (BT) montage, which places both the recording electrodes over the inferior oblique muscle, increases the chances of obtaining a response with greater contribution from the inferior oblique muscle. However, whether this response continues to show the frequency tuning to 500 Hz is not known. Therefore, the present study aimed to examine the frequency tuning of oVEMP using various electrode montages. Thirty-eight young adults underwent simultaneous oVEMP recording from IO, BT, chin-referenced, and sternum-referenced electrode montages in response to 250, 500, 750, 1000, 1500, 2000, 3000, and 4000 Hz tone bursts. The frequency tuning most often coincided with a 750-Hz tone burst irrespective of the montage, with the BT montage exhibiting significantly higher response rates and larger peak to peak amplitudes than other montages (p < 0.008). Further, there was a "substantial" agreement on frequency tuning between BT and IO montages. With better response rates and response amplitudes yet similar frequency tuning to the IO montage, the BT montage can be a better option for the clinical recording of oVEMP across frequencies.

Fully tunable microwave photonic narrow bandpass filter using an on-chip dual-drive microring resonator.

We propose and experimentally demonstrate a fully tunable microwave photonic narrow bandpass filter based on phase modulation to intensity modulation (PM-IM) conversion. In the filter implementation, an on-chip dual-drive microring resonator (MRR) is a key component. This resonator leverages a multimode waveguide to enable a high Q-factor. A metallic micro-heater and a lateral PN junction are simultaneously created for resonance wavelength tuning. When one driving signal is applied to the micro-heater, a large tuning range of the resonance wavelength is resulted; when another driving signal is applied to the PN junction, a fast tuning speed of the resonance wavelength is caused. By jointly using two different tuning mechanisms, the realized microwave photonic filter features a large frequency tuning range as well as a fast tuning speed. In addition, the filter bandwidth can also be tuned. A silicon-based dual-drive high-Q racetrack MRR chip is designed, fabricated, and evaluated. By incorporating the chip in a microwave photonic filter system, a bandpass filter with a narrow bandwidth of 1.27 GHz is achieved. An ultra-wide frequency tuning range from 3 to 51 GHz, an ultra-fast tuning speed less than 0.54 ns, and a tunable bandwidth from 1.27 to 4.47 GHz is experimentally demonstrated. This fully tunable filter offers significant potential in future radar and next-generation wireless communication applications.

Comprehensive review and study for the CMOS transformer tank voltage‐controlled oscillator

AbstractThis article comprehensively reviews and studies CMOS transformer tank voltage‐controlled oscillators (VCOs) designed to improve the frequency tuning range (FTR) and minimize phase noise (PN) across a broad frequency range, particularly for mm‐wave and fifth‐generation applications. The study focuses on enhancing the performance of the oscillators to meet the demanding requirements of these advanced applications. This study thoroughly investigates and compares various strategies to increase the FTR, minimize PN, and reduce power dissipation in transformer tank VCOs. The aim is to establish fundamental guidelines for implementing transformer‐based tank VCOs. The study comprehensively reviews and analyzes the overall architecture of transformer‐based tank VCOs, presenting a detailed examination of the methods employed to enhance VCO performance. Additionally, the study illustrates the impact of the coupling factor on the VCO's performance parameters, detailing and demonstrating the overall tank circuit quality factor (Q) and resonator coupling factor (κ). A thorough understanding of PN methodology and the limitations of FTR has led to the development of innovative architectures. These include transformer‐based capacitive feedback (FB) oscillators with resistively adjusted variable inductors, as well as class‐F and inverse class‐F VCOs. These novel architectures contribute significantly to the improvement of oscillator performance.

Dispersive terahertz metasurface fed by a horn antenna for highly oriented 2D beam steering.

Highly oriented beam steering will enhance power density and field of view (FOV) in terahertz wireless links. Metasurface can be constructed by deliberate arrangement of subwavelength meta-cells to manipulate the wavefront. This paper explores a dispersive metasurface with a specific phase gradient patterned in a 2-inch aperture, allowing for collimated beamforming and two-dimensional (2D) beam steering by a combination of frequency tuning and metasurface rotation. The metasurface is directly fed by a horn antenna, ensuring a compact integration. Simulation and experiment in the 80-110 GHz band revealed that the gain band crucial for FOV and efficiency is mainly constrained by the nonlinear phase dispersion of the meta-cells. Efforts to optimize the phase linearity resulted in a more efficient metasurface with a gain of 35.7 dBi and an efficiency of 76.6% at 400 GHz. A FOV of 22.5° in the elevation was guaranteed with gain in the 325-500 GHz band (a bandwidth of 42.4%). Imaging of two scattering balls was demonstrated at a distance of 4.1 meters by using the metasurface for 2D beam steering.

Quantum paraelectric varactors for radiofrequency measurements at millikelvin temperatures

Radiofrequency reflectometry can provide fast and sensitive electrical read-out of charge and spin qubits in quantum dot devices coupled to resonant circuits. In situ frequency tuning and impedance matching of the resonator circuit using voltage-tunable capacitors (varactors) is needed to optimize read-out sensitivity, but the performance of conventional semiconductor- and ferroelectric-based varactors degrades substantially in the millikelvin temperature range relevant for solid-state quantum devices. Here we show that strontium titanate and potassium tantalate, materials which can exhibit quantum paraelectric behaviour with large field-tunable permittivity at low temperatures, can be used to make varactors with perfect impedance matching and resonator frequency tuning at 6 mK. We characterize the varactors at 6 mK in terms of their capacitance tunability, dissipative losses and magnetic field insensitivity. We use the quantum paraelectric varactors to optimize the radiofrequency read-out of carbon nanotube quantum dot devices, achieving a charge sensitivity of 4.8 μe Hz−1/2 and a capacitance sensitivity of 0.04 aF Hz−1/2.

Probing diffusive media through speckle differencing.

Temporally varying speckle patterns, produced by light-matter interaction encode valuable information about inhomogeneities embedded within a scattering medium. These speckle fluctuations arise either from the tuning of the emission frequency of a laser illuminating a static scattering medium or from the microscopic motion of scatterers within a dynamically scattering medium. In this work, we detect embedded inhomogeneities by probing static and dynamic scattering media with coherent light and leveraging the statistical distribution of temporal speckle differences. In addition, we utilize the insights from the speckle differencing paradigm, to present the first experimental results of detecting inhomogeneities embedded within a scattering medium using bio-inspired neuromorphic sensors. The proposed neuromorphic approach simplifies the optical and electronic design, and significantly reduces data throughput by capturing only the differential information in the form of 1-bit spikes.

Ultra-low frequency noise external cavity diode laser systems for quantum applications.

We present two distinct ultra-low frequency noise lasers at 729 nm with a fast frequency noise of 30 Hz2/Hz, corresponding to a Lorentzian linewidth of 0.1 kHz. The characteristics of both lasers, which are based on different types of laser diodes, are investigated using experimental and theoretical analysis with a focus on identifying the advantages and disadvantages of each type of system. Specifically, we study the differences and similarities in mode behavior while tuning frequency noise and linewidth reduction. Furthermore, we demonstrate the locking capability of these systems on medium-finesse cavities. The results provide insights into the unique operational characteristics of these ultra-low noise lasers and their potential applications in quantum technology that require high levels of control fidelity.

New millimeter-wave diagnostics to locally probe internal density and magnetic field fluctuations in National Spherical Torus Experiment-Upgrade (invited).

A set of new millimeter-wave diagnostics will deliver unique measurement capabilities for National Spherical Torus Experiment-Upgrade to address a variety of plasma instabilities believed to be important in determining thermal and particle transport, such as micro-tearing, global Alfvén eigenmodes, kinetic ballooning, trapped electron, and electron temperature gradient modes. These diagnostics include a new integrated intermediate-k Doppler backscattering (DBS) and cross-polarization scattering (CPS) system (four channels, 82.5-87GHz) to measure density and magnetic fluctuations, respectively. The system can access reasonably large normalized wavenumbers kθρs ranging from ≤0.5 to 15 (where ion sound gyroradius ρs = 1cm and kθ is the binormal density turbulence wavenumber). The system addresses the challenges for making useful DBS/CPS measurements with a remote control of launch polarization (X- or O-mode), probed wavenumber, polarization match of the launch beam with the edge magnetic field pitch angle, and beam steering of the launched beam for wave-vector alignment. In addition, a low-k DBS system consisting of eight fixed frequencies (34-52GHz) and four tunable frequencies (55-75GHz) for low-k density turbulence and fast ion physics will be located at a nearby port location. The combined systems cover the near LCFS and pedestal regions (34-52GHz), the pedestal or mid-radius (50-75GHz), and core plasmas (82.5-87GHz).

A Q-band frequency tunable Doppler backscattering (DBS) system for pedestal and scrape-off layer density fluctuation and flow measurements in the DIII-D tokamak.

We present the design and laboratory tests for a new Q-band frequency tunable Doppler backscattering (DBS) system suitable for probing poloidal wavenumber kñ = 6-8cm-1 density fluctuations and their flow velocities in the pedestal and scape-off layer (SOL) of the DIII-D tokamak. This system will provide new measurements in the increasingly important and under-diagnosed far pedestal and SOL plasma regions. These results are important for experimental transport studies and necessary for the validation of transport models, both of which are important to fusion energy research. The use of a single tunable frequency reduces the complexity and potential failure points as compared to a multichannel system. This new system utilizes a 33-50GHz tunable source and will be integrated into the current V-band DBS in DIII-D using a broadband Q- and V-band multiplexer. A full-scale mockup of the quasi-optical system was used to test and optimize the performance. These tests include beam profile measurements at different distances (and angles) from a paraboloidal focusing and steering mirror. The measurements cover the full frequency range 33-75GHz of the integrated/combined Q-V band DBS system and target a large radial coverage of the low-field side of the plasma from ρ = 1.1 to ρ = 0.5, where ρ is the normalized flux surface radial coordinate.

Multichannel information transmission via a dual-frequency point space-time coding metasurface

Space-time coding (STC) digital metasurfaces enable dynamic control of nonlinear harmonics. To achieve efficient frequency tuning and harmonic control, we propose a one-bit column-controlled temporal coding dual-frequency point STC digital metasurface. Using a field-programmable gate array (FPGA) to control diode switching, the metasurface is encoded to generate multiple target reflected harmonics as independent information transmission channels. The amplitude intensities of these harmonics are defined as independent binary symbols for transmission. The proposed space-time coding digital metasurface can achieve a phase shift of 180° in its unit structure, with reflectivities above 90% at both operating frequencies. We fabricated the designed metasurface and tested its far-field scattering experimentally. When the incident electromagnetic wave frequency is 4.63 GHz, the predicted results are essentially consistent with the experimental findings.