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Jizhao Zang

Publications and source records attributed to Jizhao Zang.

17 recordsLinked to original sources
arXiv2026

Nanophotonic dispersion engineering in tantala-based microresonators with ultralow-loss claddings

Integrated photonics optimized to leverage low loss, nonlinear-optical processes and optoelectronic integration requires robust optical cladding materials and associated fabrication process flows. We develop low-loss silicon dioxide (SiO$_2$) claddings with tantalum pentoxide (Ta$_2$O$_5$, tantala) integrated photonics to realize robust, high intrinsic quality factor ($Q_i$) microresonators and photonic-crystal resonators (PhCRs) for soliton microcomb generation. Specifically, we introduce a full-wafer, low-temperature process compatible with two tantala-based films: pure tantala and an amorphous metal-oxide mixture of titanium dioxide (TiO$_2$, titania) and tantala. Combining tantala with titania enhances the film's resistance to damage from the SiO$_2$ cladding deposition process, offering access to high $Q_i$ above $4 \times 10^6$ in fully cladded microresonators. Our platform supports low-loss edge couplers, group-velocity dispersion engineering by waveguide geometry, access to nanophotonic structures particularly to control phase-matching, and high dimensional tolerance in devices across an entire wafer. Using the platform, we explore the generation of high-efficiency, dark-soliton microcombs with repetition frequency from 50 GHz to 500 GHz, which supports applications such as photonic artificial intelligence acceleration, electronic signaling, and optical data communication.

physics.optics↗
arXiv2026

Photonic-Crystal Microresonator Frequency Combs in the O-band

Photonic-crystal microresonators (PhCRs) are a powerful platform for generating Kerr frequency combs. Because Kerr-soliton dynamics in PhCRs are largely decoupled from the operating wavelength, the comb output can be engineered through customization of the device layer. Here, we demonstrate a tantalum pentoxide (tantala) PhCR platform that supports 1310 nm and 1550 nm band operation, and we explore high-efficiency O-band soliton microcombs with all-semiconductor laser pumps. We engineer the PhCRs with silicon dioxide cladding and normal dispersion with intrinsic quality factors exceeding $7\times10^{6}$. By pumping bandgap modes, we obtain robust and efficient soliton comb formation at a 200 GHz mode spacing. Our PhCRs enable systematic tuning from narrowband to broadband comb states within a single device geometry. The combs exhibit low relative intensity noise approaching the shot-noise limit, indicating stable phase-matching in the PhCR. Using a second resonator coupler, we amplify the comb output off-chip, demonstrating a pathway to high-power O-band sources. These results establish PhCR engineering in the tantala platform as a scalable approach to wavelength-agile, low-noise microcombs for applications in communications, sensing, and signaling.

physics.optics↗
arXiv2026

Induced Directional Switching of Platicon Microcombs in Photonic Crystal Ring Resonators

Microcombs in normal-dispersion photonic crystal ring resonators (PhCRs) are a versatile building block for next-generation integrated photonic circuits, yet they inherently suffer from a directional bias that favors backward-propagating states. This necessitates bulky, non-integrated optical circulators for comb extraction, creating a significant bottleneck for full on-chip integration. In this work, we demonstrate a deterministic method to control and reverse this directionality through Side-mode Induced Forward Forcing (SIFF). By engineering auxiliary mode splittings on resonances adjacent to the pump, we show that the nonlinear dynamics can be steered to favor stable, forward-propagating platicon states. We establish an optimal synchronization condition between the pump and side-mode coupling rates that ensures forward-comb dominance across a wide parameter range. Our findings, validated both numerically and experimentally, provide a critical pathway for circulator-free, integrated normal-dispersion microcombs, offering a scalable architecture for compact telecommunications and sensing systems.

physics.optics↗
arXiv2026

Nanophotonic control of collective many-body states in Kerr solitons

Spatially periodic systems of coupled bosons are governed by on-site interactions and tunneling between sites, opening a rich phase space of many-body behavior. Here, we explore nanophotonic control of collective many-body light states in a driven-dissipative Kerr microresonator. We demonstrate a non-equilibrium Mott insulator to superfluid transition that arises from the interplay of spatially local Kerr interactions that generate and mediate interference among discrete frequency modes. A photonic-crystal (PhC) lattice bandgap inscribed on the resonator controls linear mode coupling while preserving self-mode Kerr interactions. By increasing the PhC bandgap, we suppress nonlinear cross-mode coupling to access the Mott-insulator phase, wherein the soliton spectrum forms a flattop frequency comb with large and uniform power per mode. In contrast, reducing the PhC bandgap restores cross-mode coupling and drives a delocalized superfluid regime characterized by long-range phase coherence and a spectrum with non-uniform power distribution. Our work shows that many-body physics creates collective states in driven-dissipative systems, enabling advances in programmable photonics and quantum-optical computing.

physics.optics↗
arXiv2025

Monolithic 3D integration of tantalum pentoxide photonics on arbitrary substrates

The photonics landscape encompasses a wide scope of material platforms, each optimized for specific functionalities, yet no platform meets the demands of all current and evolving photonic applications. While combining integrated photonics materials enhances overall capability - such as unifying nonlinear optics, low-loss passive devices, and electro-optics - material and process compatibility remains a major challenge. We introduce full-wafer, monolithic 3D integration of tantalum pentoxide (Ta$_2$O$_5$, hereafter tantala) photonics onto arbitrary substrates, which we explore here with thin-film lithium niobate (LN) on silicon. Tantala's unique properties, importantly room-temperature deposition, low-temperature annealing, and low stress in thick films optimized for phase matching, make it well suited for monolithic 3D integration without compromising substrate performance or compatibility. We demonstrate low-loss, high-quality-factor microresonators and nanophotonics in tantala, robust quasi-phase-matching in poled LN waveguides, and efficient 3D interlayer routing. This enables us to demonstrate a rich palette of nonlinear frequency conversion processes, including $χ^{(3)}$ optical parametric oscillation (OPO) and soliton microcomb generation in tantala microresonators and photonic-crystal resonators, $χ^{(2)}$ second-harmonic generation (SHG) in periodically poled LN, and combinations thereof. Monolithic 3D integration with tantala opens a new paradigm for scalable, multifunctional photonic systems, enabling visible, near-IR, and nonlinear operation into existing photonic infrastructure.

physics.optics↗
arXiv2025

Next-generation soliton frequency combs in photonic-crystal and nanocomposite microresonators

Microresonator frequency combs offer tremendous opportunity to advance applications in fundamental research and technology by linking the optical and microwave frequency domains. Kerr-nonlinear microresonators further enable the generation of portable, integrated optical frequency combs, which are called microcombs. However, the dispersion engineering usually suffers from the small, geometric parameter space, and achieving soliton microcombs is challenging and usually requires complicated experimental techniques and setups. In recent years, the invention of photonic-crystal resonators (PhCRs) provides access to solitons in a convenient and stable way while its mechanism has not been fully understood. In this article, we highlight the perspectives of generating solitons for various applications in PhCRs and give a thorough understanding of the dynamics of soliton formation. We also propose a nanocomposite waveguide structure for the optimization of group velocity dispersion (GVD), lifting the limitation on geometric parameter space. We apply it to the design of the pump-harmonic microcomb, a new concept for f-2f self-referencing in microcombs. Inspired by the pulse-driven microresonator, we provide a scheme of two-microresonator network, retaining the convenience of using a continuous wave laser for microcomb generation. Our work depicts a blueprint of achieving the next generation soliton frequency combs in PhCR and nanocomposite microresonators and highlights their great prospects in optical metrology, precision measurement and optical data transmission.

physics.optics↗
arXiv2025

A Kerr soliton Ising machine for combinatorial optimization problems

The growing challenges of scaling digital computing motivate new approaches, especially through the dynamical evolution of physical systems that mimic neural networks and combinatorial optimization problems. While light is a hyper efficient information carrier, intrinsically weak light interactions make direct information processing difficult to implement. Recently, specialized nonlinear photonics have opened new controls over light fields with extraordinary bandwidth, coherence, and the emergence of strong interactions among nonlinear eigenstates like solitons. We harness an ensemble of hundreds of Kerr-nonlinear microresonator solitons and implement an analog feedback network to create an Ising machine with fully programmable all-to-all interactions. By increasing the feedback for self, on-diagonal interactions, each soliton exhibits a universal spin-like bifurcation. Using this palette of interactions amongst the entire soliton ensemble, we encode the Ising machine to solve the benchmark Boolean satisfiability problem (SAT). The combination of uniform soliton interactions and the compatibility of our Ising machine with high-speed data interconnects enables rapid and precise solutions of complex SAT problems. Indeed, the soliton properties bound the tradeoff of optical power and time use by the machine at approximately 10 mW and 1 $μ$s for a single feedback step. We performed >10,000 trials on more than 100 randomly generated SAT instances to evaluate the Ising machine, demonstrating the potential to exceed the performance of benchmark digital SAT solvers. Our work highlights the convergence of optical nonlinearity, ultralow loss photonics, and optoelectronic circuits, which can be combined for a wide range of computation-acceleration tasks.

physics.optics↗
arXiv2025

Universal electronic synthesis by microresonator-soliton photomixing

Access to electrical signals across the millimeter-wave (mmW) and terahertz (THz) bands offers breakthroughs for high-performance applications. Despite generations of revolutionary development, integrated electronics are challenging to operate beyond 100 GHz. Therefore, new technologies that generate wideband and tunable electronic signals would advance wireless communication, high-resolution imaging and scanning, spectroscopy, and network formation. Photonic approaches have been demonstrated for electronic signal generation, but at the cost of increased size and power consumption. Here, we describe a chip-scale, universal mmW frequency synthesizer, which uses integrated nonlinear photonics and high-speed photodetection to exploit the nearly limitless bandwidth of light. We use a photonic-integrated circuit to generate dual, microresonator-soliton frequency combs whose interferogram is fundamentally composed of harmonic signals spanning the mmW and THz bands. By phase coherence of the dual comb, we precisely stabilize and synthesize the interferogram to generate any output frequency from DC to >1000 GHz. Across this entire range, the synthesizer exhibits exceptional absolute fractional frequency accuracy and precision, characterized by an Allan deviation of 3*10^(-12) in 1 s measurements. We use a modified uni-traveling-carrier (MUTC) photodiode with an operating frequency range to 500 GHz to convert the interferogram to an electrical signal, generating continuously tunable tones across the entire mmW band. The synthesizer phase noise at a reference frequency of 150 GHz is -83 dBc/Hz at 100 kHz offset, which exceeds the intrinsic performance of state-of-the-art CMOS electronics. Our work harnesses the coherence, bandwidth, and integration of photonics to universally extend the frequency range of current, advanced-node CMOS microwave electronics to the mmW and THz bands.

physics.optics↗
arXiv2025

Implementing photonic-crystal resonator frequency combs in a photonics foundry

We explore an AIM Photonics silicon-nitride platform to fabricate photonic-crystal resonators for generating optical parametric oscillators (OPO) and soliton microcombs. Our approach leverages the scalability and fine feature size of silicon-nitride processing on large-scale silicon wafers to achieve low-loss, high-Q microresonators, functionalized by nano-scale photonic-crystal structures. We demonstrate intrinsic microresonator quality factor up to 1.2*10^7 with complete foundry fabrication on 300 mm silicon, a 700 nm thick silicon-nitride device layer, and inclusion of complex nanophotonics. These features enable a host of nonlinear nanophotonics sources on the platform, including OPOs, microcombs, parametric amplifiers, squeezed-light generators, and single-photon sources. By fine-tuning the photonic-crystal design parameters, we achieve broad tunability in the frequency of the OPO output, spanning a significant portion of the near-infrared. Additionally, we observe the formation of soliton frequency combs, enabled by the precise dispersion engineering of the microresonators. These results highlight the potential of widely accessible, photolithographically patterned, silicon-nitride photonics to enable wide access to and complex integration of frequency-comb sources, with applications in spectroscopy, metrology, and communications.

physics.optics↗
arXiv2024

Broadband Optoelectronic Mixer for Terahertz Frequency-Comb Measurements

We demonstrate ultra-broadband optoelectronic mixing of frequency combs that provides phase-coherent detection of a repetition frequency up to 500 GHz, using a high-speed modified uni-traveling carrier (MUTC) photodiode. Nonlinear photo-electron effects in the photodiode itself enable harmonic generation and down-mixing process of combs with widely different repetition frequency. Specifically, we generate two, 25 GHz frequency combs and use an optical filter to explore coherent down-mixing to baseband of comb spectral components across microwave, millimeter wave, and terahertz (THz) frequencies. The exceptional noise performance of the optoelectronic mixer enables the phase-coherent measurement of millimeter-wave and THz frequency combs with an Allan deviation of 10^-13/t for a measurement time of t. We further investigate the dependence of conversion loss on the reverse bias voltage and photocurrent. The experimental results indicate that we can minimize the conversion loss by operating the photodiode at an optimal voltage and maximum available photocurrent. Our work provides a solution for millimeter-wave and THz frequency comb measurements and facilitates fully stabilized frequency combs with microresonators.

physics.optics↗
arXiv2024

Foundry manufacturing of octave-spanning microcombs

Soliton microcombs provide a chip-based, octave-spanning source for self-referencing and optical metrology. We explore use of a silicon-nitride integrated photonics foundry to manufacture octave-spanning microcombs. By group-velocity dispersion engineering with the waveguide cross-section, we shape the soliton spectrum for dispersive-wave spectral enhancements at the frequencies for f-2f self-referencing. With the optimized waveguide geometry, we control the carrier-envelope offset frequency by adjusting the resonator radius. Moreover, we demonstrate the other considerations for octave microcombs, including models for soliton spectrum design, ultra-broadband resonator external coupling, low-loss edge couplers, and the nonlinear self-interactions of few-cycle solitons. This design process permits highly repeatable creation of soliton microcombs optimized for pump operation less than 100 mW, an electronically detectable offset frequency, and high comb mode power for f-2f detection. However, these design aspects must also be made compatible with the foundry fabrication tolerance of octave microcomb devices. Our experiments highlight the potential to manufacture a single-chip solution for an octave-spanning microcomb, which is the central component of a compact microsystem for optical metrology.

physics.optics↗
arXiv2024

The bandgap-detuned excitation regime in photonic-crystal resonators

Control of nonlinear interactions in microresonators enhances access to classical and quantum field states across nearly limitless bandwidth. A recent innovation has been to leverage coherent scattering of the intraresonator pump as a control of group-velocity dispersion and nonlinear frequency shifts, which are precursors for the dynamical evolution of new field states. A uniform periodicity nanostructure addresses backscattering with one resonator mode, and pumping that mode enables universal phase-matching for four-wave mixing with control by the bandgap. Yet, since nonlinear-resonator phenomena are intrinsically multimode and exhibit complex modelocking, here we demonstrate a new approach to controlling nonlinear interactions by creating bandgap modes completely separate from the pump laser. We explore this bandgap-detuned excitation regime through generation of benchmark optical parametric oscillators (OPOs) and soliton microcombs. Indeed, we show that mode-locked states are phase matched more effectively in the bandgap-detuned regime in which we directly control the modal Kerr shift with the bandgaps without perturbing the pump field. In particular, bandgap-detuned excitation enables an arbitrary control of backscattering as a versatile tool for mode-locked state engineering. Our experiments leverage nanophotonic resonators for phase matching of OPOs and solitons, leading to control over threshold power, conversion efficiency, and emission direction that enable application advances in high-capacity signaling and computing, signal generation, and quantum sensing.

physics.optics↗
arXiv2024

Laser-power consumption of soliton formation in a bidirectional Kerr resonator

Laser sources power extreme data transmission as well as computing acceleration, access to ultrahigh-speed signaling, and sensing for chemicals, distance, and pattern recognition. The ever-growing scale of these applications drives innovation in multi-wavelength lasers for massively parallel processing. We report a nanophotonic Kerr-resonator circuit that consumes the power of an input laser and generates a soliton frequency comb at approaching unit efficiency. By coupling forward and backward propagation, we realize a bidirectional Kerr resonator that supports universal phase matching but also opens excess loss by double-sided emission. Therefore, we induce reflection of the resonator's forward, external-coupling port to favor backward propagation, resulting in efficient, one-sided soliton formation. Coherent backscattering with nanophotonics provides the control to put arbitrary phase-matching and efficient laser-power consumption on equal footing in Kerr resonators. In the overcoupled-resonator regime, we measure 65% conversion efficiency of a 40 mW input pump laser, and the nonlinear circuit consumes 97% of the pump, generating the maximum possible comb power. Our work opens up high-efficiency soliton formation in integrated photonics, exploring how energy flows in nonlinear circuits and enabling laser sources for advanced transmission, computing, quantum sensing, and artificial-intelligence applications.

physics.optics↗
arXiv2023

Threshold and laser-conversion in nanostructured-resonator parametric oscillators

We explore optical parametric oscillation (OPO) in nanophotonic resonators, enabling arbitrary, nonlinear phase-matching and nearly lossless control of energy conversion. Such pristine OPO laser converters are determined by nonlinear light-matter interactions, making them both technologically flexible and broadly reconfigurable. We utilize a nanostructured inner-wall modulation in the resonator to achieve universal phase-matching for OPO-laser conversion, but coherent backscattering also induces a counterpropagating pump laser. This depletes the intra-resonator optical power in either direction, increasing the OPO threshold power and limiting laser-conversion efficiency, the ratio of optical power in target signal and idler frequencies to the pump. We develop an analytical model of this system that emphasizes an understanding of optimal laser conversion and threshold behaviors, and we use the model to guide experiments with nanostructured-resonator OPO laser-conversion circuits, fully integrated on chip and unlimited by group-velocity dispersion. Our work demonstrates the fundamental connection between OPO laser-conversion efficiency and the resonator coupling rate, subject to the relative phase and power of counterpropagating pump fields. We achieve $(40\pm4)$ mW of on-chip power, corresponding to $(41\pm4)$% conversion efficiency, and discover a path toward near-unity OPO laser conversion efficiency.

physics.optics↗
arXiv2022

Tunable lasers with optical-parametric oscillation in photonic-crystal resonators

By design access to laser wavelength, especially with integrated photonics, is critical to advance quantum sensors like optical clocks and quantum-information systems, and open opportunities in optical communication. Semiconductor-laser gain provides exemplary efficiency and integration but merely in developed wavelength bands. Alternatively, nonlinear optics requires control of phase matching, but the principle of nonlinear conversion of a pump laser to a designed wavelength is extensible. We report on laser-wavelength access by versatile customization of optical-parametric oscillation (OPO) with a photonic-crystal resonator (PhCR). By controlling the bandgap of a PhCR, we enable OPO generation across a wavelength range of 1234-2093 nm with a 1550 nm pump and 1016-1110 nm with a 1064 nm pump. Moreover, our tunable laser platform offers pump-to-sideband conversion efficiency of >10% and negligible additive optical-frequency noise across the output range. From laser design to simulation of nonlinear dynamics, we use a Lugiato-Lefever framework that predicts the system characteristics, including bi-directional OPO generation in the PhCR and conversion efficiency in agreement with our observations. Our experiments introduce tunable lasers by design with PhCR OPOs, providing critical functionalities in integrated photonics.

physics.optics↗
arXiv2021

A continuum of bright and dark pulse states in a photonic-crystal resonator

Nonlinearity is a powerful determinant of physical systems. Controlling nonlinearity leads to interesting states of matter and new applications. In optics, diverse families of continuous and discrete states arise from balance of nonlinearity and group-velocity dispersion (GVD). Moreover, the dichotomy of states with locally enhanced or diminished field intensity depends critically on the relative sign of nonlinearity and either anomalous or normal GVD. Here, we introduce a resonator with unconditionally normal GVD and a single defect mode that supports both dark, reduced-intensity states and bright, enhanced-intensity states. We access and explore this dark-to-bright pulse continuum by phase-matching for soliton generation with a photonic-crystal resonator, which mediates the competition of nonlinearity and normal GVD. These stationary temporal states are coherent frequency combs, featuring highly designable spectra and ultralow noise repetition-frequency and intensity characteristics. The dark-to-bright continuum illuminates physical roles of Kerr nonlinearity, GVD, and laser propagation in a gapped nanophotonic medium.

physics.optics↗