We demonstrate a three-dimensional fin lithium niobate (FinLN) acoustic resonator fabricated from thick lithium niobate on insulator using deep ion etching and sidewall electrode patterning. The FinLN geometry enables strong three-dimensional acoustic confinement and enhanced electromechanical coupling while maintaining a compact device footprint. The fabricated devices operate near 300 MHz and exhibit an effective electromechanical coupling coefficient of 6.2% with a mechanical quality factor of 430, in good agreement with finite-element simulations. Compared to planar surface acoustic wave resonators fabricated on the same wafer, the FinLN configuration achieves an 1.8 & times; enhancement in effective electromechanical coupling. This work establishes FinLN as a promising platform for low-cost, compact, and high-performance RF MEMS and piezo-optomechanical systems.

Superconducting quantum computers have emerged as a leading platform for next-generation computing, offering exceptional scalability and unprecedented computational speeds. However, scaling these systems to millions of qubits for practical applications poses substantial challenges, particularly due to interconnect bottlenecks. To address this challenge, extensive research has focused on developing cryogenic multiplexers that enable minimal wiring between room-temperature electronics and quantum processors. This paper investigates the viability of commercial microelectromechanical system (MEMS) switches for cryogenic multiplexers in large-scale quantum computing systems. DC and RF characteristics of the MEMS switches are evaluated at cryogenic temperatures (<10 K) through finite element simulations and experimental measurements. Our results demonstrate that MEMS switches exhibit improved on-resistance, lower operating voltage, and superior RF performance at cryogenic temperatures. In particular, an engineered gate-pulse waveform is introduced to suppress beam bouncing caused by the quasi-vacuum conditions inside the package, enabling stable dynamic operation exceeding 100 million cycles even at cryogenic temperatures. Furthermore, stable single-pole four-throw (SP4T) switching and logical operations, including NAND and NOR gates, are demonstrated at cryogenic temperatures, validating their potential for quantum computing. These results underscore the promise of MEMS switches in realizing large-scale quantum computing systems.

Spin-wave (SW) filters using single-crystal yttrium iron garnet (YIG) is an attractive technology for integration in frequency-adjustable or frequency-tunable communication systems1. However, existing SW devices do not have sufficient bandwidth for future 5G and 6G communication systems2,3, are too large or have strong spurious passbands, creating unintentional cross-channel interference. Here we report a SW ladder filter architecture requiring only a single external magnetic bias, which is enabled by modern micromachining fabrication methods capable of wafer-scale production. The filters developed in this work demonstrate loss as low as 2.54 dB, bandwidths up to 663 MHz, centre-frequency tuning over several octaves from 7.08 to 21.6 GHz and high linearity with an input-referred third-order intercept point of more than 11 dBm in the passband. The operation of the filter is also experimentally demonstrated in a frequency-tunable radio system.

Magnetostatic wave resonators based on yttrium iron garnet (YIG) are a promising technology platform for future communication filters. Such devices have demonstrated better quality factors than acoustic resonators in the 7 GHz range and above. However, the coupling coefficients of these resonators have been limited to less than 3

Ultra-low noise lasers are essential tools in various applications, including data communication, light detection and ranging (LiDAR), quantum computing and sensing, and optical metrology. Recent advances in integrated photonics, specifically the development of the ultra-low loss silicon nitride (Si3N4) platform, have allowed attaining performance that exceeds conventional legacy laser systems, including the phase noise of fiber lasers. This platform can be combined with the monolithic integration of piezoelectric materials, enabling frequency-agile low-noise lasers. However, this approach has not yet surpassed the trade-off between ultra-low frequency noise and frequency agility. Here, we overcome this challenge and demonstrate a fully integrated laser based on the Si3N4 platform with frequency noise lower than that of a fiber laser while maintaining the capability for high-speed modulation of the laser frequency. The laser achieves an output power of 30 mW with an integrated linewidth of 4.3 kHz and an intrinsic linewidth of 3 Hz, demonstrating phase noise performance that is on par with or lower than commercial fiber lasers. Frequency agility is accomplished via a monolithically integrated piezoelectric aluminum nitride micro-electro-mechanical system (MEMS) actuator, which enables a flat frequency actuation bandwidth extending up to 400 kHz. Such a MEMS device is one of the largest fabricated structures, featuring MHz-level bandwidth, which is significantly higher than the typical kHz-level bandwidth of similarly sized mm-scale MEMS devices. The chirp nonlinearity of the frequency-modulated output reaches 0.08% without any linearization or pre-distortion, making it compliant with the requirement for long-range FMCW LiDAR. This ultra-low noise and frequency-agility combination is a useful feature enabling tight laser locking for frequency metrology, fiber sensing, and coherent sensing applications. Our results demonstrate the ability of "next generation" integrated photonic circuits (beyond silicon) to exceed the performance of legacy laser systems in terms of coherence and frequency actuation.

In this paper, we present the first ultra-low-noise, self-injection locked (SIL) laser with frequency agility based on the monolithic integration of a low-loss silicon nitride (Si3N4) photonic spiral cavity with an aluminum nitride (AlN) actuator. The self-injection locking and stress-optic modulation of the optical cavity demonstrate a fully-integrated, packaged laser featuring frequency noise lower than fiber lasers (3-Hz intrinisic laser linewidth) and high-speed laser frequency modulation with flat frequency actuation bandwidth up to 400-kHz. This is achieved using piezoelectric stress-optic transduction of the entire 5-cm optical cavity, resulting in one of the largest piezoelectric structures, with an area of 19.8 square millimeters, operating at MHz level frequencies. We demonstrate pin-hole-free fabrication of the transducer devices and utilize a novel fabrication process called the “Band-Aid process” which removes unnecessary capacitance and allows for easier packaging and more robust wirebonding.

Dark matter candidates with masses around the Planck-scale are theoretically well-motivated, and it has been suggested that it might be possible to search for dark matter solely via gravitational interactions in this mass range. In this work, we explore the pathway towards searching for dark matter candidates with masses around the Planck-scale using mechanical sensors while considering realistic experimental constraints, and develop analysis techniques needed to conduct such searches. These dark matter particles are expected to leave tracks as their signature in mechanical sensor arrays, and we show that we can effectively search for such tracks using statistical approaches to track-finding. We analyze a range of possible experimental setups and compute sensitivity projections for searches for ultraheavy dark matter coupling to the Standard Model via long-range forces. We find that while a search for Planck-scale dark matter purely via gravitational couplings would be exceedingly difficult, requiring ∼ 80 dB of quantum noise reduction with a 100^3 array of devices, there is a wide range of currently unexplored dark matter candidates which can be searched for with already existing or near-term experimental platforms.

Frequency-agile lasers operating in the ultraviolet-to-blue spectral range (360-480 nm) are critical enablers for a wide range of technologies, including free-space and underwater optical communications, optical atomic clocks, and Rydberg-atom-based quantum computing platforms. Integrated photonic lasers offer a compelling platform for these applications by combining low-noise performance with fast frequency tuning in a compact, robust form factor through monolithic integration. However, realizing such lasers in the blue spectral range remains challenging due to limitations in current semiconductor materials and photonic integration techniques. Here, we report the first demonstration of a photonic integrated blue laser at around 461 nm, which simultaneously achieves frequency agility and low phase noise. This implementation is based on the hybrid integration of a gallium nitride-based laser diode, which is self-injection locked to a high-Q microresonator fabricated on a low-loss silicon nitride photonic platform with 0.4 dB/cm propagation loss. The laser exhibits a sub-30 kHz linewidth and delivers over 1 mW of optical output power. In addition, aluminum nitride piezoelectric actuators are monolithically integrated onto the photonic circuitry to enable high-speed modulation of the refractive index, and thus tuning the laser frequency. This enables mode-hop-free laser linear frequency chirps with excursions up to 900 MHz at repetition rates up to 1 MHz, with tuning nonlinearity below 2%. We showcase the potential applications of this integrated laser in underwater communication and coherent aerosol sensing experiments.

This paper reviews recent advances in the microfabrication techniques for tunable magnetostatic wave (MSW) resonators and filters. Micromachining based on ion milling, conformal metalization, and anisotropic etching of gadolinium gallium garnet (GGG) have enabled chip-scale, tunable, high performance bandstop filters, bandpass filters, and MSW resonators with a maximum f(0) center dot Q product of 9.376 x 10(13) at f(0) = 12.99 GHz with a Q-factor of 7217.

This work reports the simulation, design, and implementation of a compact MEMS switch based spatiotemporally modulated (STM) bandpass filtering isolator to improve self-interference cancellation (SIC) in underwater acoustic communication networks. Conventional ferrite circulators are unavailable in ultrasonic frequency ranges limiting SIC to techniques such as spatial cancellation and adaptive digital cancellation. This study details a sub-megahertz electronic non-magnetic filtering isolator. Compact and reliable MEMS switches in hermetically sealed glass packaging enable the periodically time varying filter circuit to be non-reciprocal. A printed circuit board (PCB) implementation shows strong agreement with spectral admittance matrix simulations with a maximum measured isolation of 15.99 dB. In conjunction with digital SIC methods, this isolator can enable in-band full duplex underwater communication, environmental sensing, and imaging.

Spinwave filters using single-crystal yttrium iron garnet are an attractive technology for integration in frequency adjustable or tunable communication systems. However, existing SW devices do not have sufficient bandwidth for future 5G and 6G communication systems, are too large, or have strong spurious passbands creating unintentional cross-channel interference. Leveraging modern micromachining fabrication methods capable of wafer-scale production, we report a SW ladder filter architecture requiring only a single external magnetic bias. The filters demonstrate loss as low as 2.54 dB, bandwidths up to 663 MHz, center frequency tuning over multiple octaves from 5.7-21.6 GHz, and high linearity with an input referred third-order intercept point over 11 dBm in the passband. The filter's operation is also experimentally demonstrated in a frequency tunable radio system.

This work investigates the p-doping effect of Nitric Oxides (NOX) annealing on transistors with a channel from a network of carbon nanotubes (CNTs), with a focus on extension doping of top-gated transistors and RF characterization. NOX annealing at 100 °C for 1 h induces oxidation in CNTs, which introduces a doping band inside the nanotube band gap near the valence band. The benefits and drawbacks of NOX annealing on the performance of back-gated (BG) CNT transistors are characterized. The doping band is beneficial in that it reduces the Schottky barrier for hole injection and increases the hole carrier concentration in the channel. However, we also note that NOX annealing deteriorates the inverse subthreshold swing (SS) and drain-induced barrier lowering (DIBL) by introducing interface traps and worsens any existing short channel effects. Our capacitance analysis confirms that the increase in source-drain and interface-trap capacitances degrades both SS and short channel effects. To circumvent the drawbacks of NOX annealing, we employ it to create extension doping regions in p-type, top-gated transistors with a scaled high-k gate oxide, leading to an increase in drain current from 5.09 to 13.95 μA at VOV = -2 V and VDS = -1 V. Because the effect of NOX annealing is limited to the extension regions and has little impact on the channel region, negative effects on the SS and DIBL are mitigated. Finally, an RF transistor is fabricated, and NOX annealing is used to enhance the cutoff frequency by approximately 10-fold.

Thin silicon nitride integrated photonics platforms rely on weakly confining waveguides and thick oxide cladding layers to enable ultra-low-optical losses on chip. Due to these favorable properties, this technology is seeing increased use in chip-scale systems tasked with manipulating and controlling classical and quantum optical systems. Phase-modulators play a crucial role in the low-noise control loops of such systems, but optically broadband phase modulators remain elusive as the same properties used to enable ultra-low-optical losses make interaction with the optical mode difficult. Here we show an unreleased and optically broadband acousto-optic modulator architecture on this platform enabled by long modulation lengths in a compact spiral structure. These devices achieve a Vπ of 8.98 V at a modulation frequency of 704 MHz across an optical bandwidth exceeding 90 nm at telecom wavelengths. We demonstrate their use as part of the control loop in an optomechanical sensing system. The authors demonstrate thin silicon nitride waveguide spirals that enable release-free phase-modulation. The presented modulators achieve a Vπ of 8.98 V with 1.13 dB of insertion loss at a modulation frequency of 704 MHz over a 90 nm optical bandwidth.

Recent decades have seen significant advancements in integrated photonics, driven by improvements in nanofabrication technology. This field has developed from integrated semiconductor lasers and low-loss waveguides to optical modulators, enabling the creation of sophisticated optical systems on a chip scale capable of performing complex functions like optical sensing, signal processing, and metrology. The tight confinement of optical modes in photonic waveguides further enhances the optical nonlinearity, leading to a variety of nonlinear optical phenomena such as optical frequency combs, second-harmonic generation, and supercontinuum generation. Active tuning of photonic circuits is crucial not only for offsetting variations caused by fabrication in large-scale integration, but also serves as a fundamental component in programmable photonic circuits. Piezoelectric actuation in photonic devices offers a low-power, high-speed solution and is essential in the design of future photonic circuits due to its compatibility with materials like Si and Si3N4, which do not exhibit electro-optic effects. Here, we provide a detailed review of the latest developments in piezoelectric tuning and modulation, by examining various piezoelectric materials, actuator designs tailored to specific applications, and the capabilities and limitations of current technologies. Additionally, we explore the extensive applications enabled by piezoelectric actuators, including tunable lasers, frequency combs, quantum transducers, and optical isolators. These innovative ways of managing photon propagation and frequency on-chip are expected to be highly sought after in the future advancements of advanced photonic chips for both classical and quantum optical information processing and computing.

Optomechanical strain sensing provides attractive opportunities for novel particle detection schemes, as well as studying stress-induced (i.e. non-radiogenic) phonon bursts, which have been demonstrated to limit the coherence times of superconducting qubits and are a suspected culprit in the low energy excesses observed by many dark matter direct detection experiments. We are investigating SiN microring optical resonator strain sensors, developed at Purdue University, for applications in fundamental particle sensing and QIS. These sensors can be embedded in the substrate upon which superconducting qubits are patterned, providing a handle to distinguish decoherence events of radiogenic origin from those due to crystal stress. In a similar way, these sensors can be operated in conjunction with superconducting detectors (e.g., MKIDs, TES) to enable multi-channel readout of particle interactions in the device substrate or serve as anticoincidence detectors, which may be required to ident ify low-energy interactions from dark matter particles down to the fermionic thermal relic mass limit of a few keV. Such sensors can potentially be used to directly observe resonant scattering processes of gamma rays (and perhaps neutrinos) where no detectable quanta are produced in the target, via the microscopic stress induced by the momentum transfer to the (fixed-in-place) crystal lattice as a whole. These strain sensors have so far found application in photonics and communications, but have yet to be adopted for HEP uses, where they can provide unique capabilities in the search for dark matter as well as understanding and improving the coherence times of superconducting qubits.

This work reports a compact temperature compensating permanent magnet assembly to provide static bias for micro-machined distributed magnetostatic forward volume wave (MSFVW) resonators. The cuboid-shaped assembly is 8.2 mm x 8.2 mm x 6.3 mm and provides strong static magnetic field to bias MSFVW resonators at a frequency of 19.65 GHz. Compensated by the bias assembly, the resonator exhibits a temperature coefficient of frequency (TCF) of -26.81 ppm/K compared to uncompensated TCF of +359 ppm/K. The temperature compensated resonator shows a quality factor of 1050 and a coupling coefficient of 4% at room temperature.

We demonstrate for the first time a frequency-modulated continuous wave photonic integrated blue laser with sub-MHz linewidth. The laser exhibits frequency excursion greater than 900 MHz at up to 1 MHz triangular chirp rate with a nonlinearity of less than 1.5%.

Recent advances in the development of ultra-low loss silicon nitride integrated photonic circuits have heralded a new generation of integrated lasers capable of reaching fiber laser coherence. However, these devices are presently based on self-injection locking of distributed feedback laser diodes, increasing both the cost and requiring tuning of laser setpoints for their operation. In contrast, turn-key legacy laser systems use reflective semiconductor optical amplifiers (RSOAs). While this scheme has been utilized for integrated photonics-based lasers, so far, no cost-effective RSOA-based integrated lasers exist that are low noise and simultaneously feature fast, mode-hop-free, and linear frequency tuning as required for frequency modulated continuous wave (FMCW) LiDAR or for laser locking in frequency metrology. Here we overcome this challenge and demonstrate a RSOA-based, frequency agile integrated laser, that can be tuned with high speed, with high linearity at low power. This is achieved using monolithic integration of piezoelectrical actuators on ultra-low loss silicon nitride photonic integrated circuits in a Vernier filter-based laser scheme. The laser operates at 1550 nm, features a 6 mW output power and a 400 Hz intrinsic laser linewidth, and allows ultrafast wavelength switching within 7 ns rise time and 75 nW power consumption. In addition, we demonstrate the suitability for FMCW LiDAR by showing laser frequency tuning over 1.5 GHz at 100 kHz triangular chirp rate with a nonlinearity of 0.25% after linearization and use the source for measuring a target scene 10 m away with a 8.5 cm distance resolution.

Coherent interconversion between microwave and optical frequencies can serve as both classical and quantum interfaces for computing, communication, and sensing. Here, we present a compact microwave-optical transducer based on monolithic integration of piezoelectric actuators atop silicon nitride photonic circuits. Such an actuator directly couples microwave signals to a high-overtone bulk acoustic resonator defined by the suspended silica cladding of the optical waveguide core, which leads to enhanced electromechanical and optomechanical couplings. At room temperature, this triply resonant piezo-optomechanical transducer achieves an off-chip photon number conversion efficiency of -48 dB over a bandwidth of 25 MHz at an input pump power of 21 dBm. The approach is scalable in manufacturing and, unlike existing electro-optic transducers, does not rely on superconducting resonators. As the transduction process is bidirectional, we further demonstrate synthesis of microwave pulses from a purely optical input. Combined with the capability of leveraging multiple acoustic modes for transduction, the present platform offers prospects for building frequency-multiplexed qubit interconnects and for microwave photonics at large.

Integrating aluminum nitride piezoelectric actuators on silicon nitride photonic circuits realizes bidirectional conversion between microwave S- and optical C-bands. On-chip generation of microwave pulses through down-conversion suggests potential as photonic interconnect for cryogenic circuits.