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Open access publications by faculty, postdocs, and graduate students in the Department of Electrical and Computer Engineering
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Item Study of phase decoherence in GeSn (8%) through measurements of the weak antilocalization effect(Journal of Applied Physics, 2024-11-18) Bradicich, Adelaide; Petluru, Priyanka; Davari, Shiva; Zhao, Haochen; Gangwal, Siddhant; Liu, Chia-You; Vasileska, Dragica; Zeng, Yuping; Churchill, Hugh; Li, Jiun-Yun; Lilly, Michael P.; Lu, Tzu-MingAlloying germanium with tin offers a means to modulate germanium’s electronic structure, enabling a greater degree of control over quantum properties such as the retention of the phase or spin of the electron wave. However, the extent to which the presence of high dopant concentrations in GeSn alters these quantum behaviors is poorly understood. Here, we investigate the role of dopant concentrations on phase coherence through measurements of the weak antilocalization (WAL) effect at temperatures between 30 mK and 10 K in p-GeSn (8%) thin films, which were doped to a series of carrier densities on the order of 1012 cm 2. Phase coherence and spin–orbit lengths were extracted from the magnetoconductivities using the 2D Hikami–Larkin–Nagaoka model. Phase coherence lengths peaked at 577, 593, and 737 nm for the low-, mid-, and high-density samples, while upper limits on the spin–orbit lengths of less than 25 nm were relatively independent of carrier density and temperature. The phase coherence lengths increased as the temperature decreased but changed only minimally with carrier density, contrary to common models of temperature-dependent inelastic scattering. Saturation of the phase coherence lengths occurred below 600 mK. Based on these findings, intrinsically generated inelastic scattering mechanisms such as two-level systems or impurity band scattering likely contribute to phase decoherence in these alloys. Our results provide insight into the inelastic scattering mechanisms of GeSn, while suggesting a need for further investigation into phase decoherence mechanisms in doped group-IV alloys.Item Real-time object detection for unmanned vehicles in Bangladesh: Dataset, implementation and evaluation(Journal of Engineering, 2024-12-04) Ali, Muhammad Liakat; Biswas, Topu; Akter, Shahin; Jawad, Mohammed Farhan; Ullah, HadaateAutomated vehicle detection within the advanced application framework of autonomous vehicles significantly enhances road safety compared to human drivers on roads and highways. However, the intelligent identification of road vehicles in a densely populated country like Bangladesh is challenging due to irregular traffic patterns, highly diverse vehicle types, a cluttered environment, and a lack of high-quality datasets. This study proposes a system that utilizes computer vision technology to identify road vehicles with greater speed and accuracy. First, the dataset was collected and organized in Roboflow to identify the 21 classes of Bangladeshi native vehicle images, along with two additional classes for people and animals. Subsequently, the You Only Look Once v5 (YOLOv5) model underwent training on the dataset. This process produced bounding boxes, which were then refined using the non-maximum suppression technique. The loss function complete intersection over union is employed to obtain the accurate regression bounding box of the vehicles. The MS COCO (Microsoft Common Objects in Context) dataset weights are included in the YOLOv5 deep learning network for transfer learning. Finally, Python TensorBoard was used to evaluate and visualize the model's performance. The model was developed and validated on the Google Colab platform. A set of experimental evaluations demonstrate that the proposed method is effective and efficient in recognizing Bangladeshi vehicles. In all test road scenarios, the proposed computer vision system for road vehicle identification achieved 95.8% accuracy and 0.3 ms processing time for 200 epochs. This research could lead to intelligent transportation systems and driverless vehicles in Bangladesh.Item Super-resolution ISAR Imaging using Off-the-grid Structured Low-rank Method(IEEE Transactions on Antennas and Propagation, 2024-11-12) Zhang, Bangjie; Xu, Gang; Xia, Xiang-Gen; Yu, Hanwen; Xing, Mengdao; Hong, WeiInverse synthetic aperture radar (ISAR) imaging relies on wideband waveform and viewing angle variation to achieve range and cross-range resolutions, respectively. To enhance the resolutions of two-dimensional (2-D) image, sparse signal processing techniques, such as compressed sensing (CS), have been applied to ISAR imaging using a sparse prior. Despite its efficiency in super-resolution imaging, the performance of CS is constrained due to the mismatch of discrete dictionary, such as Fourier transform. To address this issue, we propose a novel off-the-grid super-resolution ISAR imaging algorithm that employs a structured low-rank approach to effectively extrapolate the data bandwidth and aperture. To fully capture the low-rank property of ISAR data, the structured data model is constructed and its low-rank property is deduced to exhibit that the signal is embedded in a limited dimensional subspace. Then, the annihilating filter is derived by constructing structured data matrix to formulate the proposed structured low-rank method, termed as Off-the-grid Super-resolution using Annihilation Constraint (OSAC). Taking into account that the super-resolution imaging is highly reliant on the accuracy of annihilating filter, the optimal annihilating filter is also estimated with the updating of extrapolated ISAR data. Through iterative updates of the annihilating filter and solution of the minimization problem, the super-resolution ISAR imaging can be achieved by avoiding the discrete mismatch of conventional CS method. Due to the effective exploration of structured low-rank property, the proposed OSAC algorithm offers superior precision in scatterer location and structure interpretation of a target. Experimental results using both simulated and real data are presented to verify the enhanced performance of 2-D resolution in ISAR imaging.Item Satellites Beam Hopping Scheduling for Interference Avoidance(IEEE Journal on Selected Areas in Communications, 2024-10-10) Deng, Huimin; Ying, Kai; Feng, Daquan; Gui, Lin; He, Yuanzhi; Xia, Xiang-GenThe deployment of low earth orbit (LEO) satellites megaconstellations presents a promising way for achieving global coverage and service, attributed to their comparatively low round-trip latency and launch costs. However, this surge in LEO satellite launches exacerbates the scarcity of the limited spectrum resources. Spectrum sharing between satellite constellations and terrestrial networks and beam hopping (BH) technology emerge as viable strategies to mitigate this spectrum shortage. To enhance spectrum efficiency and avoid serious inter-system interference, we investigate the beam hopping scheduling of satellites for interference avoidance. The beam hopping scheduling of the integrated satellite-terrestrial wireless networks system is formulated as throughput-driven beam hopping (TDBH) problem and satisfaction-rate-driven beam hopping (SDBH) problem, respectively. In particular, we decompose the TDBH problem into two sub-problems by relaxation, and a genetic algorithm (GA) is introduced to handle the SDBH problem. The impact of channel conditions and traffic load intensity on the satellite system throughput is analyzed in TDBH simulation. As for SDBH optimization problem, the simulation results show that the proposed GA algorithm improves the average traffic satisfaction rate by 16.96% at least, compared with other benchmarks and suits to scenarios with different traffic demands and fading channel conditions.Item An Antiferroelectric-Coated Metal Foam Infiltrated with Liquid Metal as a Dielectric Capacitor(Energy Technology, 2024-10-07) Hanrahan, Brendan; Leff, Asher; Sesar, Alexis; Fish, Michael; Jaszewski, Samantha T.; Kropp, Jaron A.; Strnad, Nicholas; Ihlefeld, Jon F.; Lazarus, NathanNickel metal foams serve as both a substrate and bottom electrode for a dielectric capacitor using atomic-layer deposition (ALD) and a eutectic gallium–indium (EGaIn) liquid metal (LQM) counter electrode. The conformal dielectric has a composition of 6.25% Al–HfO2 in the antiferroelectric phase, confirmed with polarization versus electric field measurements. Liquid EGaIn is pressure-infiltrated within the coated foams to form the dielectric capacitor. Capacitances up to 4 μF are realized. Calorimetry of the infiltrated capacitor shows a 60 J g−1 latent heat upon melting a frozen EGaIn electrode, suggesting that the phase change can alleviate thermal deviations from pulsed power capacitor operation. Infiltrated capacitors are also shown to survive bending and freeze–thaw cycles. The metal foam–ALD dielectric–LQM capacitor shows a combined set of thermal and electrical properties not available in other classes of capacitors.Item Composition Quantification of SiGeSn Alloys Through Time-of-Flight Secondary Ion Mass Spectrometry: Calibration Methodologies and Validation With Atom Probe Tomography(IEEE Journal of Selected Topics in Quantum Electronics, 2024-09-09) Zhao, Haochen; Liu, Shang; Park, Suho; Feng, Xu; Zeng, Zhaoquan; Kolodzey, JamesTime-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) is a powerful technique for elemental compositional analysis and depth profiling of materials. However, it encounters the problem of matrix effects that hinder its application. In this work, we introduce a pioneering ToF-SIMS calibration method tailored for SixGeySnz ternary alloys. SixGe1-x and Ge1-zSnz binary alloys with known compositions are used as calibration reference samples. Through a systematic SIMS quantification study of SiGe and GeSn binary alloys, we unveil a linear correlation between secondary ion intensity ratio and composition ratio for both SiGe and GeSn binary alloys, effectively mitigating the matrix effects. Extracted relative sensitivity factor (RSF) value from SixGe1-x (0.07 < x < 0.83) and Ge1-zSnz (0.066 < z < 0.183) binary alloys are subsequently applied to those of SixGeySnz (0.011 < x < 0.113, 0.863 < y < 0.935 and 0.023 < z < 0.103) ternary alloys for elemental compositions quantification. These values are cross-checked by Atom Probe Tomography (APT) analysis, an indication of the great accuracy and reliability of as-developed ToF-SIMS calibration process. The proposed method and its reference sample selection strategy in this work provide a low-cost as well as simple-to-follow calibration route for SiGeSn composition analysis, thus driving the development of next-generation multifunctional SiGeSn-related semiconductor devices.Item Sequestration of gene products by decoys enhances precision in the timing of intracellular events(Scientific Reports, 2024-11-08) Biswas, Kuheli; Dey, Supravat; Singh, AbhyudaiExpressed gene products often interact ubiquitously with binding sites at nucleic acids and macromolecular complexes, known as decoys. The binding of transcription factors (TFs) to decoys can be crucial in controlling the stochastic dynamics of gene expression. Here, we explore the impact of decoys on the timing of intracellular events, as captured by the time taken for the levels of a given TF to reach a critical threshold level, known as the first passage time (FPT). Although nonlinearity introduced by binding makes exact mathematical analysis challenging, employing suitable approximations and reformulating FPT in terms of an alternative variable, we analytically assess the impact of decoys. The stability of the decoy-bound TFs against degradation impacts FPT statistics crucially. Decoys reduce noise in FPT, and stable decoy-bound TFs offer greater timing precision with less expression cost than their unstable counterparts. Interestingly, when both bound and free TFs decay at the same rate, decoy binding does not directly alter FPT noise. We verify these results by performing exact stochastic simulations. These results have important implications for the precise temporal scheduling of events involved in the functioning of biomolecular clocks, development processes, cell-cycle control, and cell-size homeostasis.Item 3D printer audio and vibration side channel dataset for vulnerability research in additive manufacturing security(Data in Brief, 2024-10-19) Madamopoulos, Christos; Tsoutsos, Nektarios GeorgiosThis dataset provides a comprehensive set of side channels from fused deposition modeling 3D printers in order to enable the research in the security of additive manufacturing processes against side channel attacks. These attacks exploit indirect signal emanations from physical processes to extract information about a system. Our data was collected using two different methods (iPhone app and Teensy 4.0 sensor system) on two different 3D printers (Bambu Lab P1P and A1 mini), and consists of two types of data, audio data in the form of the recording of the 3D printer's sound while printing, and vibration data in the form of the linear acceleration in the cartesian coordinates. The dataset includes data from 12 different 3D objects that cover a wide variety of movements made while 3D printing. Along with the side channels this dataset includes the source computer-aided design files of the objects, as well as .gcode and .3mf files used by the printers.Item A Moments-Based Analytical Approach for Cell Size Homeostasis(IEEE Control Systems Letters, 2024-06-07) Nieto, César; Vargas-Garcia, Cesar Augusto; Singh, AbhyudaiThis contribution explores mechanisms that regulate the dynamics of single-cell size, maintaining equilibrium around a target set point. Using the formalism of Stochastic Hybrid Systems (SHS), we consider continuous exponential growth in cell size (as determined by volume/mass/surface area). This continuous-time evolution is interspersed by cell division events that occur randomly as per a given size-dependent rate, and upon division, only one of the two daughter cells is tracked. We show that a size-independent division rate does not provide cell size homeostasis, in the sense that the variance in cell size increases unboundedly over time. Next, we consider a division rate proportional to cell size that yields the adder size control observed in several bacteria – a constant size is added on average between birth and division regardless of the newborn size. For this scenario, we obtain exact formulas for the steady-state moments (mean, variance, and skewness) of cell size. Expanding the SHS model, we explore a biologically relevant scenario where the time between successive division events is further divided into multiple discrete stages with size-dependent stage transitions. Exact moment computations demonstrate that increasing the number of stages reduces cell size variability (noise). We also find formulas considering uneven size partitioning between daughters during division, and where the division rate follows a power law of the cell size leading to deviations from adder size control. This letter provides a method for estimating model parameters from observed cell size distributions and enhances our understanding of mechanisms underlying cell size regulation.Item InP-based strain engineered InAs(Sb)/InAsPSb multiple quantum wells with tunable emission and high internal quantum efficiency enabled by Sb incorporation(APL Materials, 2024-10-07) Nguyen, P. D.; Kim, D.; Jung, H. J.; Kang, T. I.; Park, S.; Kim, J. S.; Chun, B. S.; Lee, S. J.A type I InAs(Sb)/InAsPSb strain engineered multiple quantum wells light emitting diodes system has been demonstrated. Tensile InAsPSb quantum barriers with a high degree of band offset (∆EC = 116–123 meV, ∆EV = 193–250 meV) were used to compensate for the high compressive strain of the InAs(Sb) quantum wells. The structure was grown on the n+-InAsxP1−x metamorphic buffer with a high degree of relaxation (98%), low surface roughness (0.69 nm), and low dislocation density. Through careful strain engineering design, the compressive strain of InAs(Sb) reaches 0.57%–1.52% without strain relaxation. The incorporation of Sb into the multiple quantum wells not only reduces the bandgap but also improves the interface quality by acting as an effective surfactant. Structural analysis reveals superior quality in InAsSb/InAsPSb multiple quantum wells compared to InAs/InAsPSb multiple quantum wells, demonstrating significantly reduced interface roughness and suppression of the Stranski–Krastanov growth mode. Room temperature electroluminescence measurements show a tunable emission wavelength ranging from 2.7 to 3.3 μm, accompanied by a narrow full width at half maximum value of 45 meV. Photoluminescence analysis indicates that the internal quantum efficiency of InAsSb/InAsPSb multiple quantum wells is 5.5%, which is 7 times higher than that of InAs/InAsPSb.Item Joint Beam and Power Control for Millimeter-Wave Multi-Flow Multi-Hop Networks(IEEE Communications Letters, 2024-08-16) Liu, Yanming; Mao, Haobin; Zhu, Lipeng; Xiao, Zhenyu; Xia, Xiang-GenThis letter investigates the joint beam and power control in multi-flow multi-hop networks with millimeter-wave (mmWave) directional transmissions. To guarantee fairness among multiple data flows, an optimization problem is formulated to maximize the minimum of the achievable rates for all flows by jointly optimizing three-dimensional (3D) antenna boresights and transmit powers. To address the non-convex problem, we employ the block coordinate descent (BCD) method to solve two subproblems iteratively. Specifically, each iteration involves solving the transmit power control subproblem by using successive convex approximation (SCA) techniques. Then, suboptimal antenna boresights, including the azimuth and elevation angles for multiple transmitters, are obtained by using a tailored particle swarm optimization (PSO) algorithm. The simulation results reveal the effectiveness and superiority of the proposed algorithm in enhancing the minimum end-to-end achievable rate (E2EAR) compared to the benchmark schemes.Item Beam Structured Channel Estimation for HF Skywave Massive MIMO-OFDM Communications(IEEE Transactions on Wireless Communications, 2024-08-14) Shi, Ding; Song, Linfeng; Gao, Xiqi; Wang, Jiaheng; Bengtsson, Mats; Li, Geoffrey Ye; Xia, Xiang-GenIn this paper, we investigate high frequency (HF) skywave massive multiple-input multiple-output (MIMO) communications with orthogonal frequency division multiplexing (OFDM) modulation. Based on the triple-beam (TB) based channel model and the channel sparsity in the TB domain, we propose a beam structured channel estimation (BSCE) approach. Specifically, we show that the space-frequency-time (SFT) domain estimator design for each TB domain channel element can be transformed into that of a low-dimensional TB domain estimator and the resulting SFT domain estimator is beam structured. We also present a method to select the TBs used for BSCE. Then we generalize the proposed BSCE by introducing window functions and a turbo principle to achieve a superior trade-off between complexity and performance. Furthermore, we present a low-complexity design and implementation of BSCE by exploiting the characteristics of the TB matrix. Simulation results validate the proposed theory and methods.Item An Efficient Refocusing Method for Ground Moving Targets in Multichannel SAR Imagery(IEEE Geoscience and Remote Sensing Letters, 2024-08-02) Ma, Jingtao; Xia, Xiang-Gen; Wang, Jiannan; Tao, Haihong; Liao, Guisheng; Huang, PenghuiThis letter proposes a fast Doppler parameter estimation and refocusing method for ground moving targets in a synthetic aperture radar (SAR) system. In the proposed method, after implementing the main-lobe clutter rejection by using the azimuth adaptive processing technique, the range-azimuth positions of smeared target scatterers can be obtained via the constant false alarm rate (CFAR) detection. Then, an autocorrelation function is constructed to transform a moving target signal into the time-frequency plane, where the target parameters can be precisely and efficiently estimated by applying the scaled fast Fourier transform (FFT). Finally, ground moving targets can be well refocused and relocated in a SAR imagery. Compared with the conventional methods, the target output SNR can be enlarged about 3 dB under the low SNR by using the proposed parameter estimation method.Item Transformer-Based Band Regrouping With Feature Refinement for Hyperspectral Object Tracking(IEEE Transactions on Geoscience and Remote Sensing, 2024-06-27) Wang, Hanzheng; Li, Wei; Xia, Xiang-Gen; Du, Qian; Tian, Jing; She, QingHyperspectral videos (HSVs) offer not only spatial information but also diagnostic spectral features. Due to the fact that spectral features are only related to the material of the object, this advantage can address the issue of RGB video tracking failure when the object and background are visually similar. However, the effectiveness of deep learning models is limited due to insufficient HSV training data. Existing methods tend to divide a hyperspectral image (HSI) into several three-channel false-color images to leverage the existing RGB trackers for transfer learning. Nonetheless, these methods lack adequate exploration of band interrelations and overlook correlation among objects prior to similarity calculation. In this article, a transformer-based band regrouping and feature refinement network (TBR-Net) is introduced, which is specifically tailored for hyperspectral object tracking. To maximize the potential of the RGB tracker and enhance the use of available training data, we propose a transformer-based band regrouping (TBR) method. By modeling long-range spectral dependencies, the inherent context information among bands is captured, which is subsequently utilized to reorganize bands into several false-color images. Furthermore, to combine the relationship of the template and the search (T & S) frames into a correlation calculation, a feature refinement module (FRM) is designed. The cross-attention mechanism enables mutual relation modeling, allowing similar regions to be perceived and form discriminative feature representation. As a result, a hyperspectral tracker can be efficiently trained via transfer learning to address the data insufficiency challenge, while the mutual perception between objects further enhances the tracking performance. Its effectiveness is validated by extensive benchmark experiments, which demonstrate that the TBR-Net surpasses state-of-the-art methods.Item Minimum BLER NOMA Design with Finite Blocklength(IEEE Transactions on Wireless Communications, 2024-05-29) Zhong, Tianying; Wang, Yuan; Wang, Jiaheng; Xia, Xiang-Gen; Gao, XiqiNon-orthogonal multiple access (NOMA) has been considered as a promising technology for enabling massive connectivity and achieving high spectral efficiency in future wireless communication. In the literature, most of the existing NOMA schemes are designed with the assumption of infinite blocklength, which may lead to suboptimal performance in practical communication systems. Thus, this paper investigates the downlink NOMA system with finite blocklength (FBL) transmission, namely the downlink FBL-NOMA system. We focus on developing a joint resource allocation scheme from single-channel to multi-channel systems, aiming at minimizing the average block error rate (BLER) for the downlink FBL-NOMA. Specifically, for single-channel systems, the optimal rate and power allocation scheme are derived in semi-closed form. For multi-channel systems, we conduct the convexity analysis of the minimum BLER problem and provide the optimal solution in waterfilling form for convex cases, as well as an efficient majorization-minimization (MM)-based algorithm for general cases. We also propose an efficient method to jointly optimize channel assignment, rate allocation, and power allocation for multi-channel FBL-NOMA systems. Simulation results demonstrate the superiority of the proposed designs over the existing NOMA and orthogonal multiple access (OMA) schemes in terms of reliability and efficiency.Item Distinct melanocyte subpopulations defined by stochastic expression of proliferation or maturation programs enable a rapid and sustainable pigmentation response(PLoS Biology, 2024-08-20) Aggarwal, Ayush; Nasreen, Ayesha; Sharma, Babita; Sahoo, Sarthak; Aswin, Keerthic; Faruq, Mohammed; Pandey, Rajesh; Jolly, Mohit K.; Singh, Abhyudai; Gokhale, Rajesh S.; Natarajan, Vivek T.The ultraviolet (UV) radiation triggers a pigmentation response in human skin, wherein, melanocytes rapidly activate divergent maturation and proliferation programs. Using single-cell sequencing, we demonstrate that these 2 programs are segregated in distinct subpopulations in melanocytes of human and zebrafish skin. The coexistence of these 2 cell states in cultured melanocytes suggests possible cell autonomy. Luria–Delbrück fluctuation test reveals that the initial establishment of these states is stochastic. Tracking of pigmenting cells ascertains that the stochastically acquired state is faithfully propagated in the progeny. A systemic approach combining single-cell multi-omics (RNA+ATAC) coupled to enhancer mapping with H3K27 acetylation successfully identified state-specific transcriptional networks. This comprehensive analysis led to the construction of a gene regulatory network (GRN) that under the influence of noise, establishes a bistable system of pigmentation and proliferation at the population level. This GRN recapitulates melanocyte behaviour in response to external cues that reinforce either of the states. Our work highlights that inherent stochasticity within melanocytes establishes dedicated states, and the mature state is sustained by selective enhancers mark through histone acetylation. While the initial cue triggers a proliferation response, the continued signal activates and maintains the pigmenting subpopulation via epigenetic imprinting. Thereby our study provides the basis of coexistence of distinct populations which ensures effective pigmentation response while preserving the self-renewal capacity.Item A Universal Electric Vehicle Outlet and Portable Cable for North America(World Electric Vehicle Journal, 2024-08-06) Kempton, Willett; McGee, Rodney T.; Ejzak, Garrett A.For electric vehicle (EV) charging in North America, three AC connectors are standardized, resulting in a proliferation of charging stations which can only charge one of the three types of EV. We propose a “Universal EV Outlet” that works with an EV “carry along” charging cable—one end of the cable has a connector specific to that user’s EV, the other a plug for the Universal EV Outlet. This proposal does not interfere with, nor require change to, any existing charging stations. It does not require any new types of inlets on EVs. The components are already standardized. Eight use cases are examined to illustrate the advantages, and some limitations, of the Universal EV Outlet. The use cases illustrate how this solution: resolves the problem of multiple AC charging connectors, makes today’s “EV Ready” building codes more adaptable, lowers capital and maintenance costs, creates a solution to curbside and urban charging, increases energy efficiency, enables higher power three-phase AC charging for heavy vehicles, and facilitates use of EVs for building backup power and for vehicle-to-grid. Finally, we propose a standards-based active cable used with the Universal EV Outlet, which would allow fast and secure EV identification for curbside or other shared charging locations, usable today without modifications to current EVs.Item Thermally reliable compact electro-optic modulators with a low half-wave voltage(Optics Continuum, 2024-06-11) Afsary, Noor; Alam, Md Koushik; Rasel, Md Omar Faruk; Ishigure, TakaakiRecent advancements in thin-film lithium niobate have led to the development of high-performance integrated electro-optic modulators, which are crucial for modern optical communication systems. These modulators offer tighter mode confinement, a smaller physical footprint, and reduced modulating voltages. This study presents a Mach-Zehnder modulator (MZM) on a silicon nitride-loaded lithium niobate platform using a few-mode waveguide structure. By harnessing the exceptional thermo-optic and electro-optic effects of LiNbO3, we design and simulate this modulator employing multilayer structures with the BeamPROP solver. The modulator has a length of 3.94 mm, a Vπ value of 0.96 V, and a transition temperature (Tg) of 80 °C at 1.55 µm. This proposed modulator exhibits a crosstalk of approximately -42 dB, an extinction ratio of approximately 24 dB, and a maximum transmission of -28 dB for the first-order phase shift. These findings demonstrate the significant potential of this modulator for deployment in high-speed optical communication systems, where maintaining thermal stability and optimizing energy efficiency are paramount.Item Superfluid helium ultralight dark matter detector(Physical Review D, 2024-05-10) Hirschel, M.; Vadakkumbatt, V.; Baker, N. P.; Schweizer, F. M.; Sankey, J. C.; Singh, S.; Davis, J. P.The absence of a breakthrough in directly observing dark matter (DM) through prominent large-scale detectors motivates the development of novel tabletop experiments probing more exotic regions of the parameter space. If DM contains ultralight bosonic particles, they would behave as a classical wave and could manifest through an oscillating force on baryonic matter that is coherent over ∼106 periods. Our Helium ultraLIght dark matter Optomechanical Sensor (HeLIOS) uses the high-𝑄 acoustic modes of superfluid helium-4 to resonantly amplify this signal. A superconducting reentrant microwave cavity enables sensitive optomechanical readout ultimately limited by thermal motion at millikelvin temperatures. Pressurizing the helium allows for the unique possibility of tuning the mechanical frequency to effectively broaden the DM detection bandwidth. We demonstrate the working principle of our prototype HeLIOS detector and show that future generations of HeLIOS could explore unconstrained parameter space for both scalar and vector ultralight DM after just an hour of integration time.Item Ultrawideband Modular RF Frontend Development for Photonically Enabled Imaging Receiver(IEEE Microwave and Wireless Technology Letters, 2024-05-07) Shi, Shouyuan; Wang, Fuquan; Abney, Jeremy; Aranda, Zion D.; Schneider, Garrett J.; Schuetz, Christopher; Harrity, Charles; Shreve, Kevin; Zablocki, Mathew; Dontamsetti, Samhit; Lawrence, Robert; Prather, Dennis W.This letter presents a modular-based RF frontend developed for photonically enabled phased-array systems that are capable of ultrawideband (UWB) operation from microwave to millimeter-wave (mmW) frequencies. The 1×8 modular architecture with integrated antennas, low-noise amplifiers (LNAs), and electrooptic modulators is reconfigurable and scalable to form 2-D phased arrays of any size. The developed phased-array system demonstrates the ability to process multiple wide-bandwidth RF beams simultaneously, yielding unmatched beam-bandwidth product (BBP).