arXiv subjects

Juanjuan Lu

Publications and source records attributed to Juanjuan Lu.

At least 19 recordsLinked to original sources

arXiv2026

200 mm Wafer-Scale Monolithic 3D Integration of Atomic Layer-Deposited Oxide Semiconductors

Monolithic 3D (M3D) integration offers a pathway to overcome the scaling limits of conventional silicon complementary metal-oxide-semiconductor (CMOS) technology by extending dense vertical stacking of multifunctional logic and memory devices. Here, we demonstrate wafer-scale M3D integration of three tiers of atomic-layer-deposited (ALD) indium oxide (InOx)-based devices (>100,000 fabricated), including ferroelectric, enhancement-mode, and depletion-mode field-effect transistors, on 200 mm silicon wafers. We achieve threshold voltage standard deviation as low as 0.04 V, average electron mobility up to 91.6 cm2V-1s-1, and fully functional cross-tier circuits. A four-tier 3D computing-in-memory (CIM) accelerator targeting large language model workloads is developed using a custom InOx process design kit, delivering 1.4x to 2.9x speedup and comparable energy-delay product improvements over 2D baselines. These results establish ALD InOx M3D integration as a scalable and CMOS-compatible platform for next-generation artificial intelligence hardware and advanced electronics.

physics.app-ph↗

arXiv2026

A re-entrant chip-free-space photonic interface for telecom-to-Rubidium spectroscopy

Photonic integrated circuits (PICs) generate, route, and process light with high efficiency, scalability, and functional density on a single chip. Yet the tightly confined on-chip modes can not easily access or effectively interact with atomic vapors, fluids, gain media, and biological samples. Existing approaches require bringing the medium onto the chip or into a weak, tightly confined evanescent field, which restricts the interaction volume and the range of accessible media. Here, we demonstrate a re-entrant chip-free-space interface in which a thin-film lithium niobate circuit frequency-doubles telecom light, emits the 780~nm field through a Rubidium vapor cell, and recollects the reflected probe on the same chip. This emit-interact-recollect loop resolves the saturated absorption spectrum and stabilizes the telecom laser to within $\pm 280$~kHz over 2 hours. Our study paves an route to embed external media into PICs through the re-entrant photonic interface.

physics.optics↗

arXiv2026

Modified uni-travelling-carrier photodiodes with 206 GHz bandwidth and 0.81 A/W external responsivity

The accelerating demand for wireless communication necessitates wideband, energy-efficient photonic sub-terahertz (sub-THz) sources to enable ultra-fast data transfer. However, as critical components for THz photonic mixing, photodiodes (PDs) face a fundamental trade-off between quantum efficiency and bandwidth, presenting a major obstacle to achieving high-speed performance with high optoelectronic conversion efficiency. Here, we overcome this challenge by demonstrating an InP-based, waveguide-integrated modified uni-traveling carrier photodiode (MUTC-PD) with bandwidth exceeding 200 GHz and a bandwidth-efficiency product (BEP) surpassing 130 GHz. Incorporating a spot-size converter (SSC) together with optimized electric-field distribution, balanced carrier transport, and minimized parasitic capacitance, the device achieves a 3-dB bandwidth of 206 GHz and an external responsivity of 0.81 A/W, setting a new BEP benchmark. Packaged with WR-5.1 waveguide output, it delivers radio-frequency (RF) power exceeding -5 dBm across the 127-185 GHz frequency range. As a proof of concept, we achieved a wireless transmission of 54 meters with a single-line rate of up to 120 Gbps, leveraging photonics-aided technology without requiring a low-noise amplifier (LNA). This work establishes a pathway to significantly enhance optical power budgets and reduce energy consumption, presenting a transformative step toward high-bandwidth, high-efficiency sub-THz communication systems and next-generation wireless networks.

physics.app-ph↗

arXiv2026

Magnetic-free optical mode degeneracy lifting in lithium niobate microring resonators

Breaking time-reversal symmetry in integrated photonics without magnetic fields remains a fundamental challenge. We demonstrate phonon-induced non-reciprocity through direct lifting of forward-backward mode degeneracy in microring resonators. Coherent acousto-optic coupling generates differential AC Stark shifts between counter-propagating fundamental optical modes, eliminating the need for intermodal conversion or complex photonic structures. Simple microwave excitation of integrated piezoelectric transducers provides dynamic control of non-reciprocal response, with experimentally demonstrated mode splitting exceeding twice the optical linewidth. The linear relationship between the splitting and acoustic power enables real-time reconfigurability across a wide range of optical wavelengths. This mechanism requires only simple microring resonators and fundamental optical modes, transforming non-reciprocity from a specialized technique requiring careful modal engineering to a universal, electrically-controlled functionality. Our approach establishes a new paradigm for magnetic-free optical isolation and dynamic topological photonics.

physics.optics↗

arXiv2025

Three-Octave Supercontinuum Generation Spanning from Ultraviolet in Lithium Tantalate Waveguides

We demonstrate, for the first time, supercontinuum generation spanning more than three octaves in dispersion-engineered thin-film lithium tantalate (TFLT) waveguides. Pumped by a femtosecond laser at 1560 nm, the waveguides yield a spectrum from 240 nm in the ultraviolet to beyond 2400 nm in the near-infrared. The spectral evolution is mapped from low-power harmonic generation (second- and third-harmonic) to a high-power continuum driven by soliton fission and dispersive wave emission. This first demonstration of ultrabroadband nonlinear optics in TFLT establishes it as a competitive, low-loss platform for integrated photonics, with significant potential for applications in frequency metrology and on-chip spectroscopy.

physics.optics↗

arXiv2025

Acoustically control of integrated optical microrings: from photonic molecule to Mobius strip

Microring resonators (MRRs) are fundamental building blocks of photonic integrated circuits, yet their dynamic reconfiguration has been limited to tuning refractive index or absorption. Here, we demonstrate acoustic control over optical path topology on a lithium niobate on sapphire platform. By launching gigahertz acoustic waves into a hybrid phononic-photonic waveguide, a dynamic Bragg mirror (DBM) is created within the optical path, coupling forward and backward propagating light. Employing a pair of coupled MRRs, we achieve strong coupling between supermodes of the photonic molecule with only milliwatt-level drive power, yielding a cooperativity of 2.46 per milliwatt. At higher power, DBM reflectivity up to 24% is achieved, revealing breakdowns of both the photonic molecule picture and perturbative coupled mode theory, indicating the transformation toward Mobius strip topology. Our work establishes a new dimension for controlling photonic devices, opening pathways toward fully reconfigurable photonic circuits through acoustic drive.

physics.optics↗

arXiv2025

Suspension-Free Integrated Cavity Brillouin Optomechanics on a Chip

Cavity optomechanical systems enable coherent photon-phonon interactions essential for quantum technologies, yet high-performance devices have been limited to suspended structures. Here, we overcome this limitation by demonstrating cavity Brillouin optomechanics in a suspension-free racetrack microring resonator on a lithium-niobate-on-sapphire chip, a platform that merits high stability and scalability. We demonstrate coherent coupling between telecom-band optical modes and a 9.6-GHz phonon mode, achieving a maximum cooperativity of $0.41$ and a phonon quality-factor-frequency product of $10^{13}\,\mathrm{Hz}$. The momentum-matching condition inherent to traveling-wave Brillouin interactions establishes a one-to-one mapping between optical wavelength and phonon frequency, enabling multi-channel parallel operations across nearly $300\,\mathrm{MHz}$ in phonon frequency and $40\,\mathrm{nm}$ in optical wavelength. Our suspension-free architecture provides a coherent photon-phonon interface compatible with wafer-scale integration, opening pathways toward hybrid quantum circuits that unite photonic, phononic, and superconducting components on a single chip.

physics.optics↗

arXiv2025

Multi-Channel Microwave-to-Optics Conversion Utilizing a Hybrid Photonic-Phononic Waveguide

Efficient and coherent conversion between microwave and optical signals is crucial for a wide range of applications, from quantum information processing to microwave photonics and radar systems. However, existing conversion techniques rely on cavity-enhanced interactions, which limit the bandwidth and calability. Here, we demonstrate the first multi-channel microwave-to-optics conversion by introducing a traveling-wave architecture that leverages a hybrid photonic-phononic waveguide on thin-film lithium niobate (TFLN). Our approach exploits continuous phase-matching rather than discrete resonances, enabling unprecedented operational bandwidths exceeding 40 nm in the optical domain and 250 MHz in the microwave domain. By harnessing the strong piezoelectric and photoelastic effects of TFLN, we achieve coherent conversion between 9 GHz microwave photons and 1550 nm telecom photons via traveling phonons, with an internal efficiency of 2.2% (system efficiency 2.4 *10^-4 ) at room temperature. Remarkably, we demonstrate simultaneous operation of nine conversion channels in a single device. Our converter opens up new opportunities for seamless integration of microwave and photonic technologies, enabling the quantum interface for distributed quantum computing with superconducting quantum processors, high efficient microwave signal processing, and advanced radar applications.

physics.optics↗

arXiv2025

On-chip amplification-free fCEO detection and broadband SCG in parabolically width-modulated TFLN waveguides

We demonstrate amplification-free carrier-envelope offset (fCEO) detection in parabolically width-modulated z-cut thin-film lithium niobate (TFLN) waveguide that simultaneously engineers dispersion and enhances nonlinear interactions. With 116 fs pulses at 1560 nm, the device generates more than two octaves broadband SCG spanning 600 to beyond 2400 nm, enabling spectral overlap between dispersive waves and second-harmonic generation near 780 nm for robust f-2f self-referencing. Most notably, we achieve the first fully amplification-free, on-chip fCEO detection without optical or electronic amplifiers, obtaining 34 dB SNR at 100 kHz RBW and 57 dB at 100 Hz RBW, the highest reported to date under such conditions. These results establish a new benchmark for scalable, power-efficient, self-referenced frequency combs and quantum-enabled photonic systems.

physics.optics↗

arXiv2025

Efficient and tunable frequency conversion using periodically poled thin-film lithium tantalate nanowaveguides

Thin-film lithium tantalate (TFLT) has recently emerged as a promising photonic platform for chip-scale nonlinear optics due to its weaker photorefraction, higher optical damage threshold, broader transparency window, and lower birefringence compared to that of thin-film lithium niobate. Here we develop an ultralow-loss lithium tantalate integrated photonic platform and report the first functional second harmonic generator based on high-fidelity poling of z-cut TFLT. As a result, quasi-phase matching (QPM) is performed between telecom (1550 nm) and near-visible (775 nm) wavelengths in a straight waveguide and prompts strong second-harmonic generation with a normalized efficiency of 229 %/W/$cm^2$. An absolute conversion efficiency of 5.5 % is achieved with a pump power of 700 mW. Such a second-harmonic generator exhibits stable temperature tunability (-0.44 nm/$^\circ C$) which is important for applications that require precise frequency alignment such as atomic clocks and quantum frequency conversion.

physics.optics↗

arXiv2024

On-chip Brillouin Amplifier in Suspended Lithium Niobate Nanowaveguides

Thin film lithium niobate (TFLN) has emerged as a leading material platform for integrated nonlinear photonics, enabling transformative applications such as broadband Kerr soliton microcomb and high-speed electro-optic modulation. While stimulated Brillouin scattering has been numerically proposed in TFLN, achieving sufficient gain remains challenging due to the requirement for the simultaneous low optical and mechanical losses of the device. In this work, we systematically characterize the angle-dependence of Brillouin gain coefficients in x-cut membrane-suspended TFLN nanowaveguides, taking into account the anisotropy of the photoelastic coefficients in lithium niobate. We report a Brillouin gain coefficient of 129.5 m$^{-1}$W$^{-1}$ and further demonstrate the Brillouin frequency tuning through variations in either pump frequency or chip operating temperature. Based on the suspended TFLN nanowaveguide, by optimizing the confinement of both photonic and phononic modes, we have achieved a Brillouin amplifier with a record-high gain of 8.5 dB. This result not only validates the feasibility of strong guided Brillouin interaction using suspended TFLN nanowaveguides, but also paves the way for novel on-chip sensing and signal processing applications.

physics.optics↗

arXiv2024

Symmetric Second-Harmonic Generation in Sub-wavelength Periodically Poled Thin Film Lithium Niobate

Second harmonic generation (SHG) extensively employs periodically poled nonlinear crystals through forward quasi-phase-matching to achieve efficient frequency conversion. As poling periods approach sub-micrometers, backward quasi-phase-matching has also been demonstrated, albeit by utilizing pulsed laser drives. The realization of symmetric second harmonic generation, characterized by counterpropagating pumps, however, has remained elusive despite theoretical predictions. The main challenge lies in achieving strong nonlinear coupling with poling period below half the wavelength of the second-harmonic light. The recent emergence of high-quality ferroelectric lithium niobate thin films provides an opportunity for achieving precise domain control at submicron dimensions. In this article, we demonstrate reliable control of ferroelectric domains in thin film lithium niobate waveguide with a poling period down to 370nm, thereby realizing highly efficient continuous-wave pumped symmetric SHG. This demonstration not only validates the feasibility of achieving subwavelength periodic poling on waveguides but also opens new avenues for leveraging submicron ferroelectric domain structures in integrated photonics and nonlinear optics research.

physics.optics↗

arXiv2024

Autonomous frequency locking for zero-offset microcomb

The stabilization of optical frequency comb conventionally relies on active electronic feedback loops and stable frequency references. Here, we propose a new approach for autonomous frequency locking (AFL) to generate a zero-offset frequency comb based on cooperative nonlinear optical processes in a microcavity. In a simplified few-mode system, AFL enables the concept of fractional harmonic generation as a zero-offset multi-laser reference for measuring the carrier envelope offset frequency ($f_{\mathrm{ceo}}$) of frequency combs spanning less than one octave, such as 1/3 octave. Combining with Kerr comb generation in a microcaivity, AFL is further applied to directly generate zero-$f_{\mathrm{ceo}}$ soliton comb that is robust against fluctuations in pump laser and cavity resonances. Numerical simulations validate the AFL scheme, showing good agreement with analytical prediction of the locking condition. This work presents a new pathway for exploring novel frequency locking mechanisms and technologies using integrated photonic devices, and also appeals further investigations of cooperative nonlinear optics processes in microcavities.

physics.optics↗

arXiv2024

Ultra-fast Waveguide MUTC Photodiodes over 220 GHz

We present InP-based evanescently-coupled waveguide modified uni-traveling carrier photodiodes (MUTC-PDs) exhibiting a breakthrough in bandwidth. The optimization of carrier transport and optical coupling is achieved through a detailed discussion on the design of the cliff layer and waveguide layer. Addressing the parasitic capacitance challenge, we introduce benzocyclobutene (BCB) beneath the PD electrodes, effectively overcoming the bandwidth bottleneck associated with the RC time constant. Devices with sizes of 2 * 7 um2 and 2 * 10 um2 achieve 3-dB bandwidths over 220 GHz, along with external responsivities of 0.161 A/W and 0.237 A/W, respectively. Notably, the RF output power reaches a peak of -1.69 dBm at 215 GHz for 2 * 15 um2 PDs.

physics.app-ph↗

arXiv2023

Domain control and periodic poling of epitaxial ScAlN

ScAlN is an emerging ferroelectric material that possesses large band gap, strong piezoelectricity, and holds great promises for enhanced χ^{(2)} nonliearity. In this study, we demonstrate high-fidelity ferroelectric domain switching and periodic poling of Al-polar ScAlN thin film epitaxially grown on on c-axis sapphire substrate using gallium nitride as a buffer layer. Uniform poling of ScAlN with periods ranging from 2 um to 0.4 um is realized. The ability to lithographically control the polarization of epitaxial ScAlN presents a critical advance for its further exploitation in ferroelectric storage and nonlinear optics applications.

physics.app-ph↗

arXiv2023

Two-colour dissipative solitons and breathers in microresonator second-harmonic generation

Frequency conversion of dissipative solitons associated with the generation of broadband optical frequency combs having a tooth spacing of hundreds of giga-hertz is a topical challenge holding the key to practical applications in precision spectroscopy and data processing. The work in this direction is underpinned by fundamental problems in nonlinear and quantum optics. Here, we present the dissipative two-colour bright-bright and dark-dark solitons in a quasi-phase-matched microresonator pumped for the second-harmonic generation in the near-infrared spectral range. We also found the breather states associated with the pulse front motion and collisions. The soliton regime is found to be typical in slightly phase-mismatched resonators, while the phase-matched ones reveal broader but incoherent spectra and higher-order harmonic generation. Soliton and breather effects reported here exist for the negative tilt of the resonance line, which is possible only via the dominant contribution of second-order nonlinearity.

physics.optics↗

arXiv2022

Monolithic Kerr and electro-optic hybrid microcombs

Advances in microresonator-based soliton generation promise chip-scale integration of optical frequency comb for applications spanning from time keeping to frequency synthesis. Miniaturized cavities harness Kerr nonlinearity and enable terahertz soliton repetition rates. However, such high repetition rates are not amenable to direct electronic detection. Here, we demonstrate hybrid Kerr and electro-optic microcombs using the lithium niobate thin film that exhibits both Kerr and Pockels nonlinearities. By interleaving the high-repetition-rate Kerr soliton comb with the low-repetition-rate electro-optic comb on the same waveguide, the wide Kerr soliton mode spacing is divided within a single chip, allowing for subsequent electronic detection and feedback control of the soliton repetition rate. Our work establishes an integrated electronic interface to Kerr solitons of terahertz repetition rates, paving the path towards chipscale optical-to-microwave frequency division and comb locking.

physics.optics↗

arXiv2021

A generalized 3D elastic model for nanoscale, self-assembled oxide-metal thin films with pillar-in-matrix configurations

In recent years, functional oxide-metal based vertically aligned nanocomposite (VAN) thin films have gained interest due to their intriguing physical properties and multifunctionalities stemming from the complex interactions between the two phases in the film and the substrate. In this work, we develop a model for studying the energetics of these thin film systems, including the effects of both lattice mismatch and capillary forces due to interface curvature. Each phase is incorporated into the model using a phase indicator function, and we introduce the capillary forces as body forces using a vector density representation of the interface. The model is implemented using the finite element method to study the deformation of the thin film which is composed of Au nanopillars embedded in a La0.7Sr0.3MnO3 (LSMO) matrix on an SrTiO3 (STO) substrate. The results suggest that the total energy is lowest for random configurations of pillars compared to ordered square and hexagonal lattice configurations, consistent with the random distribution of pillars found in experiments. Furthermore, we find that the interfacial energy dominates the total energy of each configuration, suggesting that interfacial energy in the system is an important design parameter for nanocomposite growth, along with the lattice mismatch.

cond-mat.mtrl-sci↗