arXiv subjects

Rui Ning Wang

Publications and source records attributed to Rui Ning Wang.

At least 19 recordsLinked to original sources

arXiv2026

Entanglement Swapping with Integrated Narrowband Photon Sources for Quantum Repeaters

Promising implementations of first generation quantum repeaters are predicted to require atomic-based quantum memory systems interfaced with photonic sources. Integrated photonics provides a promising solution for fibre-based, field-deployed operation of quantum repeaters, however many leading quantum memory platforms require narrow-bandwidth photons that are challenging to generate with integrated photonics. Narrowband photons also present significant technical challenges when implementing entanglement-swapping, particularly with regards to systems-level stabilisation. This work addresses some of these fundamental and technical challenges, by demonstrating entanglement-swapping using state-of-the-art integrated photon sources with bandwidths compatible with multiple atomic-based quantum memory platforms. We obtained a background-subtracted (net) HOM visibility of 0.99$\,\pm\,$0.01, showing high photon indistinguishability and purity, with a net swapped state visibility of $\mathcal{V}$=0.88$\,\pm\,$0.06 demonstrating that the final entanglement would be sufficient to violate a Bell inequality. The experiment used independent pump lasers for each photon pair source, with highly different frequencies to mimic entanglement swapping between different repeater nodes or platforms. Phase and frequency stabilisation spanning 1.6 THz was achieved using all-fibre, commercially-available components. These results address important challenges in implementing field-deployed quantum repeaters, from the integrated photonic solutions for narrowband photon pairs, to systems-level stabilisation between independent quantum repeater nodes.

quant-ph↗

arXiv2025

Electrons herald non-classical light

Free electrons are a widespread and universal source of electromagnetic fields. The past decades witnessed ever-growing control over many aspects of electron-generated radiation, from the incoherent emission produced by X-ray tubes to the exceptional brilliance of free-electron lasers. Reduced to the elementary process of quantized energy exchange between individual electrons and the electromagnetic field, electron beams may facilitate future sources of tunable quantum light. However, the quantum features of such radiation are tied to the correlation of the particles, calling for the joint electronic and photonic state to be explored for further applications. Here, we demonstrate the coherent parametric generation of non-classical states of light by free electrons. We show that the quantized electron energy loss heralds the number of photons generated in a dielectric waveguide. In Hanbury-Brown-Twiss measurements, an electron-heralded single-photon state is revealed via antibunching intensity correlations, while two-quantum energy losses of individual electrons yield pronounced two-photon coincidences. The approach facilitates the tailored preparation of higher-number Fock and other optical quantum states based on controlled interactions with free-electron beams.

quant-ph↗

arXiv2025

Integrated Telecom Wavelength Heralded Single-Photon Source based on GHz gated detectors

We introduce a simple and flexible concept for a heralded -- spectrally pure -- single photon source. The scheme uses a probabilistic photon pair source pumped with a CW laser, whereby a rapid gating InGaAs/InP single photon avalanche diode provides a synchronous clock and temporally resolves, and hence spectrally filters, the heralded photons. We demonstrate the concept by combining this with a narrow-band integrated silicon nitride photon-pair source. This simple architecture is capable of heralding photons with high spectral purity in the telecom band, but could be adapted to other wavelengths and bandwidth regimes.

quant-ph↗

arXiv2025

Copper-impurity-free photonic integrated circuits enable deterministic soliton microcombs

Chip-scale optical frequency combs based on microresonators (microcombs) enable GHz-THz repetition rates, broad bandwidth, compactness, and compatibility with wafer-scale manufacturing. Silicon nitride photonic integrated circuits have become a leading platform due to their low loss, broad transparency, lithographic dispersion control, and commercial 200-mm-wafer foundry access. They have enabled system-level applications in optical communications, LiDAR, frequency synthesis, low-noise microwave generation, and convolutional processing. However, real-world deployment is hindered by the challenge of deterministic soliton microcomb generation, primarily due to thermal instabilities. Although techniques like pulsed pumping, fast scanning, and auxiliary lasers help mitigate these effects, they often add complexity or reduce soliton stability. In this work, we overcome thermal limitations and demonstrate deterministic soliton generation in silicon nitride photonic circuits. We trace the thermal effects to copper impurities within waveguides, originating from residual contaminants in CMOS-grade silicon wafers that are gettered into silicon nitride during fabrication. By developing effective copper removal techniques, we significantly reduce thermal instabilities. This enables soliton generation with arbitrary or slow laser scanning, removing a key barrier to microcomb deployment. Our approach is compatible with front-end-of-line foundry processing, paving the way for broader adoption of soliton microcomb technologies.

physics.optics↗

arXiv2024

Monolithic piezoelectrically tunable hybrid integrated laser with sub-fiber laser coherence

Ultra-low noise lasers are essential tools in a wide variety of 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 ultra-low loss silicon nitride (Si$_3$N$_4$) platform, have allowed attaining performance that exceeds conventional legacy laser systems, including the phase noise of fiber lasers. This platform can moreover be combined with monolithic integration of piezoelectrical materials, enabling frequency agile low noise lasers. However, this approach has to date not 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 Si$_3$N$_4$ 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 (AlN) micro-electro-mechanical system (MEMS) actuator, which enables a flat frequency actuation bandwidth extending up to 400 kHz. This combination of ultra-low noise and frequency agility 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.

physics.optics↗

arXiv2024

Piezoelectric actuation for integrated photonics

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.

physics.optics↗

arXiv2024

Ultrafast tunable photonic integrated Pockels extended-DBR laser

Frequency-agile lasers that can simultaneously feature low noise characteristics as well as fast mode hop-free frequency tuning are keystone components for applications ranging from frequency modulated continuous wave (FMCW) LiDAR, to coherent optical communication and gas sensing. The hybrid integration of III-V gain media with low-loss photonic integrated circuits (PICs) has recently enabled integrated lasers with faster tuning and lower phase noise than the best legacy systems, including fiber lasers. In addition, lithium niobate on insulator (LNOI) PICs have enabled to exploit the Pockels effect to demonstrate self-injection locked hybrid lasers with tuning rates reaching peta-hertz per second. However, Pockels-tunable laser archetypes relying on high-Q optical microresonators have thus far only achieved limited output powers, are difficult to operate and stabilize due to the dynamics of self-injection locking, and require many analog control parameters. Here, we overcome this challenge by leveraging an extended distributed Bragg reflector (E-DBR) architecture to demonstrate a simple and turn-key operable frequency-agile Pockels laser that can be controlled with single analog operation and modulation inputs. Our laser supports a continuous mode hop-free tuning range of over 10 GHz with good linearity and flat actuation bandwidth up to 10 MHz, while achieving over 15 mW in-fiber output power at 1545 nm and kHz-level intrinsic linewidth, a combination unmet by legacy bulk lasers. This hybrid laser design combines an inexpensive reflective semiconductor optical amplifier (RSOA) with an electro-optic DBR PIC manufactured at wafer-scale on a LNOI platform. We showcase the performance and flexibility of this laser in proof-of-concept coherent optical ranging (FMCW LiDAR) demonstration, achieving a 4 cm distance resolution and in a hydrogen cyanide spectroscopy experiment.

physics.optics↗

arXiv2024

Foundry compatible, efficient wafer-scale manufacturing of ultra-low loss, high-density Si$_3$N$_4$ photonic integrated circuits

Silicon nitride (Si$_3$N$_4$) photonic integrated circuits (PICs) have shown low linear loss, negligible nonlinear loss, and high power handling over traditional silicon photonics. To achieve high-density photonic integration and high effective nonlinearity through tight optical confinement, thick stoichiometric Si$_3$N$_4$ films are indispensable. However, when using low-pressure chemical vapor deposition (LPCVD) to achieve high optical material transparency, Si$_3$N$_4$ films exhibit large tensile stress on the order of GPa. Methods for crack prevention are therefore essential. The photonic Damascene process has addressed this issue, attaining record low loss Si$_3$N$_4$ PICs, but it lacks control of the waveguide height. Conversely, precise waveguide dimension and ultra-low loss have been achieved with subtractive processing, but this method is not compatible with mass production due to the use of electron beam lithography. To date, an outstanding challenge is to attain both lithographic precision and ultra-low loss in high confinement Si$_3$N$_4$ PICs that are compatible with large-scale foundry manufacturing. Here, we present a single-step deposited, DUV-based subtractive method for producing wafer-scale ultra-low loss Si$_3$N$_4$ PICs that harmonize these necessities. By employing deep etching of densely distributed, interconnected trenches into the substrate, we effectively mitigate the tensile stress in the Si$_3$N$_4$ layer, enabling direct deposition of thick films without cracking and substantially prolonged storage duration. Lastly, we identify ultraviolet (UV) radiation-induced damage that can be remedied through rapid thermal annealing. Collectively, we develop ultra-low loss Si$_3$N$_4$ microresonators and 0.5 m-long spiral waveguides with losses down to 1.4 dB/m at 1550 nm with high production yield.

physics.optics↗

arXiv2024

Hydrogen-free low-temperature silica for next generation integrated photonics

The advances in novel low-loss "on insulator" integrated photonics platforms beyond silicon, such as thin-film LiNbO3, LiTaO3, GaP and BaTiO3 have demonstrated major potential across a wide range of applications, due to their unique electro-optical or nonlinear optical properties. This has heralded novel devices, ranging from low-voltage and high-speed modulators to parametric amplifiers. For such photonic integrated circuits, a low-loss SiO2 cladding layer is a key element, serving as a passivation layer for the waveguides and enabling efficient fiber-to-chip coupling. However, numerous novel ferroelectric or III-V "on insulator" platforms have low tolerances for process temperature. This prohibits using high-temperature anneals to remove hydrogen, a common impurity that is inherent to ordinary chemical vapor deposited SiO2 and causes significant optical loss in the near infrared. Here, we satisfy the dichotomy of a low-loss wafer scale manufactured SiO2 cladding and low processing temperature. Inspired by the manufacturing of optical fibers, we introduce a hydrogen-free, low-loss SiO2 cladding that is deposited at low temperatures (300 degrees Celsius) by using SiCl4 and O2 as precursors in inductively coupled plasma-enhanced chemical vapor deposition (ICPCVD). By replacing hydrogenous silicon precursors (e.g. SiH4) with SiCl4, the deposited film is inherently free from residual hydrogen. The process temperature is compatible with the "on insulator" platforms and CMOS electronic integrated circuits. We demonstrate a wide low-loss window that covers all telecommunication bands from 1260 nm to 1625 nm. We achieve a < 2.5 dB/m waveguide loss at 1550 nm, comparable with 1200 degree Celsius annealed films. Our SiCl4 process provides a key future cladding for all recently emerged "on-insulator" photonics platforms, that is low cost, scalable in manufacturing, and directly foundry compatible.

physics.optics↗

arXiv2024

Large-scale photonic chip based pulse interleaver for low-noise microwave generation

Microwaves generated by optical techniques have demonstrated unprecedentedly low noise and hold significance in various applications such as communication, radar, instrumentation, and metrology. To date, the purest microwave signals are generated using optical frequency division with femtosecond mode-locked lasers. However, many femtosecond laser combs have a radio frequency (RF) repetition rate in the hundreds of megahertz range, necessitating methods to translate the generated low-noise RF signal to the microwave domain. Benchtop pulse interleavers can multiply the pulse repetition rate, avoid saturation of photodetectors, and facilitate the generation of high-power low-noise microwave signals, which have to date only been demonstrated using optical fibers or free space optics. Here, we introduce a large-scale photonic integrated circuit-based interleaver, offering size reduction and enhanced stability. The all-on-chip interleaver attains a 64-fold multiplication of the repetition rate, directly translated from 216 MHz to 14 GHz in microwave Ku-Band. By overcoming photodetector saturation, the generated microwave power was improved by 36 dB, with a phase noise floor reduced by more than 10 folds to -160 dBc/Hz on the 14 GHz carrier. The device is based on a low-loss and high-density photonic integrated circuit fabricated by the photonic Damascene process. Six cascaded stages of Mach-Zehnder interferometers with optical delay lines up to 33 centimeters long are fully integrated into a compact footprint of 8.5 mmx1.7 mm. The lithographically defined precision of the optical waveguide path length enables the scaling up of the interleaved frequency to millimeter-wave bands, which is challenging the fiber-based counterparts. This interleaver has the potential to reduce the cost and footprint of mode-locked-laser-based microwave generation, allowing for field deployment.

physics.optics↗

arXiv2024

Unifying frequency metrology across microwave, optical, and free-electron domains

Frequency metrology lies at the heart of precision measurement. Optical frequency combs provide a coherent link uniting the microwave and optical domains in the electromagnetic spectrum, with profound implications in timekeeping, sensing and spectroscopy, fundamental physics tests, exoplanet search, and light detection and ranging. Here, we extend this frequency link to free electrons by coherent modulation of the electron phase by a continuous-wave laser locked to a fully stabilized optical frequency comb. Microwave frequency standards are transferred to the optical domain via the frequency comb, and are further imprinted in the electron spectrum by optically modulating the electron phase with a photonic chip-based microresonator. As a proof-of-concept demonstration, we apply this frequency link in the calibration of an electron spectrometer, and use the electron spectrum to measure the optical frequency. Our work bridges frequency domains differed by a factor of $\sim10^{13}$ and carried by different physical objects, establishes a spectroscopic connection between electromagnetic waves and free-electron matter waves, and has direct ramifications in ultrahigh-precision electron spectroscopy.

physics.optics↗

arXiv2023

Free-electron interaction with nonlinear optical states in microresonators

The short de Broglie wavelength and strong interaction empower free electrons to probe scattering and excitations in materials and resolve the structure of biomolecules. Recent advances in using nanophotonic structures to mediate bilinear electron-photon interaction have brought novel optical manipulation schemes to electron beams, enabling high space-time-energy resolution electron microscopy, quantum-coherent optical modulation, attosecond metrology and pulse generation, transverse electron wavefront shaping, dielectric laser acceleration, and electron-photon pair generation. However, photonic nanostructures also exhibit nonlinearities, which have to date not been exploited for electron-photon interactions. Here, we report the interaction of electrons with spontaneously generated Kerr nonlinear optical states inside a continuous-wave driven photonic chip-based microresonator. Optical parametric processes give rise to spatiotemporal pattern formation, or dissipative structures, corresponding to coherent or incoherent optical frequency combs. By coupling such microcombs in situ to electron beams, we demonstrate that different dissipative structures induce distinct fingerprints in the electron spectra and Ramsey-type interference patterns. In particular, using spontaneously formed femtosecond temporal solitons, we achieve ultrafast temporal gating of the electron beam without the necessity of a pulsed laser source or a pulsed electron source. Our work elucidates the interaction of free electrons with a variety of nonlinear dissipative states, demonstrates the ability to access solitons inside an electron microscope, and extends the use of microcombs to unexplored territories, with ramifications in novel ultrafast electron microscopy, light-matter interactions driven by on-chip temporal solitons, and ultra-high spatiotemporal resolution sampling of nonlinear optical dynamics and devices.

physics.optics↗

arXiv2023

Hertz-linewidth and frequency-agile photonic integrated extended-DBR lasers

Recent advances in the development of ultra-low loss silicon nitride (Si3N4)-based photonic integrated circuits have allowed integrated lasers to achieve a coherence exceeding those of fiber lasers and enabled unprecedentedly fast (Megahertz bandwidth) tuning using monolithically integrated piezoelectrical actuators. While this marks the first time that fiber laser coherence is achieved using photonic integrated circuits, in conjunction with frequency agility that exceeds those of legacy bulk lasers, the approach is presently compounded by the high cost of manufacturing DFB, as required for self-injection locking, as well as the precise control over the laser current and temperature to sustain a low noise locked operation. Reflective semiconductor optical amplifiers (RSOA) provide a cost-effective alternative solution but have not yet achieved similar performance in coherence or frequency agility, as required for frequency modulated continuous wave (FMCW) LiDAR, laser locking in frequency metrology or wavelength modulation spectroscopy for gas sensing. Here, we overcome this challenge and demonstrate an RSOA-based and frequency agile integrated laser tuned with high speed, good linearity, high optical output power, and turn-key operability while maintaining a small footprint. This is achieved using a tunable extended distributed Bragg reflector (E-DBR) in an ultra-low loss 200 nm thin Si3N4 platform with monolithically integrated piezoelectric actuators. We co-integrate the DBR with a compact ultra-low loss spiral resonator to further reduce the intrinsic optical linewidth of the laser to the Hertz level -- on par with the noise of a fiber laser -- via self-injection locking.

physics.optics↗

arXiv2023

A fully hybrid integrated Erbium-based laser

Erbium-doped fiber lasers exhibit high coherence and low noise as required for applications in fiber optic sensing, gyroscopes, LiDAR, and optical frequency metrology. Endowing Erbium-based gain in photonic integrated circuits can provide a basis for miniaturizing low-noise fiber lasers to chip-scale form factor, and enable large-volume applications. Yet, while major progress has been made in the last decade on integrated lasers based on silicon photonics with III-V gain media, the integration of Erbium lasers on chip has been compounded by large laser linewidth. Recent advances in photonic integrated circuit-based high-power Erbium-doped amplifiers, make a new class of rare-earth-ion-based lasers possible. Here, we demonstrate a fully integrated chip-scale Erbium laser that achieves high power, narrow linewidth, frequency agility, and the integration of a III-V pump laser. The laser circuit is based on an Erbium-implanted ultralow-loss silicon nitride Si$_3$N$4$ photonic integrated circuit. This device achieves single-mode lasing with a free-running intrinsic linewidth of 50 Hz, a relative intensity noise of $<$-150 dBc/Hz at $>$10 MHz offset, and output power up to 17 mW, approaching the performance of fiber lasers and state-of-the-art semiconductor extended cavity lasers. An intra-cavity microring-based Vernier filter enables wavelength tunability of $>$ 40 nm within the C- and L-bands while attaining side mode suppression ratio (SMSR) of $>$ 70 dB, surpassing legacy fiber lasers in tuning and SMRS performance. This new class of low-noise, tuneable Erbium waveguide laser could find applications in LiDAR, microwave photonics, optical frequency synthesis, and free-space communications. Our approach is extendable to other wavelengths, and more broadly, constitutes a novel way to photonic integrated circuit-based rare-earth-ion-doped lasers.

physics.optics↗

arXiv2023

Frequency agile photonic integrated external cavity laser

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 presently are based on self-injection locking of distributed feedback (DFB) 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 (RSOA). 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 6 mW output power, 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 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.

physics.optics↗

arXiv2022

A heterogeneously integrated lithium niobate-on-silicon nitride photonic platform

The availability of thin-film lithium niobate on insulator (LNOI) and advances in processing have led to the emergence of fully integrated LiNbO3 electro-optic devices, including low-voltage, high-speed modulators, electro-optic frequency combs, and microwave-optical transducers. Yet to date, LiNbO3 photonic integrated circuits (PICs) have mostly been fabricated using non-standard etching techniques that lack the reproducibility routinely achieved in silicon photonics. Widespread future application of thin-film LiNbO3 requires a reliable and scalable solution using standard processing and precise lithographic control. Here we demonstrate a heterogeneously integrated LiNbO3 photonic platform that overcomes the abovementioned challenges by employing wafer-scale bonding of thin-film LiNbO3 to planarized low-loss silicon nitride (Si3N4) photonic integrated circuits, a mature foundry-grade integrated photonic platform. The resulting devices combine the substantial Pockels effect of LiNbO3 with the scalability, high-yield, and complexity of the underlying Si3N4 PICs. Importantly, the platform maintains the low propagation loss (<0.1 dB/cm) and efficient fiber-to-chip coupling (<2.5 dB per facet) of the Si3N4 waveguides. We find that ten transitions between a mode confined in the Si3N4 PIC and the hybrid LiNbO$_3$ mode produce less than 0.8 dB additional loss, corresponding to a loss per transition not exceeding 0.1 dB. These nearly lossless adiabatic transitions thus link the low-loss passive Si3N4 photonic structures with electro-optic components. We demonstrate high-Q microresonators, optical splitters, electrically tunable photonic dimers, electro-optic frequency combs, and carrier-envelope phase detection of a femtosecond laser on the same platform, thus providing a reliable and foundry-ready solution to low-loss and complex LiNbO3 integrated photonic circuits.

physics.optics↗

arXiv2022

Protected generation of dissipative Kerr solitons in supermodes of coupled optical microresonators

The driven-dissipative photonic dimer comprised of two evanescently coupled high-Q microresonators is a fundamental element of multimode soliton lattices. It has demonstrated a variety of emergent nonlinear phenomena including supermode soliton generation, symmetry breaking, and soliton hopping. In this article, we present another aspect of dissipative soliton generation in coupled resonators, revealing the advantages of this system over conventional single resonator platforms. Namely, we show that the accessibility of solitons drastically varies for symmetric and antisymmetric supermode families of the dimer. Linear measurements reveal that the coupling between transverse modes, which gives rise to avoided mode crossings, can be almost completely suppressed. We explain the origin of this phenomenon and show its crucial influence on the dissipative Kerr soliton formation process in lattices of coupled high-Q resonators of any type. Choosing a particular example of the topological Su-Schrieffer-Heeger model, we demonstrate how the edge state can be protected from the interaction with higher-order modes, allowing for the formation of topological Kerr solitons.

physics.optics↗

arXiv2022

Ultrafast tunable lasers using lithium niobate integrated photonics

Recent advances in the processing of thin-film LNOI have enabled low-loss photonic integrated circuits, modulators with improved half-wave voltage, electro-optic frequency combs and novel on-chip electro-optic devices, with applications ranging from 5G telecommunication and microwave photonics to microwave-to-optical quantum interfaces. Lithium niobate integrated photonic circuits could equally be the basis of integrated narrow-linewidth frequency-agile lasers. Pioneering work on polished lithium niobate crystal resonators has led to the development of electrically tunable narrow-linewidth lasers. Here we report low-noise frequency-agile lasers based on lithium niobate integrated photonics and demonstrate their use for coherent laser ranging. This is achieved through heterogeneous integration of ultra-low-loss silicon nitride photonic circuits with thin-film lithium niobate via direct wafer bonding. This platform features low propagation loss of 8.5 dB/m enabling narrow-linewidth lasing (intrinsic linewidth of 3 kHz) by self-injection locking to a III-V semiconductor laser diode. The hybrid mode of the resonator allows electro-optical laser frequency tuning at a speed of 12 PHz/s with high linearity, low hysteresis and while retaining narrow linewidth. Using this hybrid integrated laser, we perform a proof-of-concept FMCW LiDAR ranging experiment, with a resolution of 15 cm. By fully leveraging the high electro-optic coefficient of lithium niobate, with further improvements in photonic integrated circuits design, these devices can operate with CMOS-compatible voltages, or achieve mm-scale distance resolution. Endowing low loss silicon nitride integrated photonics with lithium niobate, gives a platform with wide transparency window, that can be used to realize ultrafast tunable lasers from the visible to the mid-infrared, with applications from OCT and LiDAR to environmental sensing.

physics.optics↗