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Erbium-doped fibre lasers exhibit high coherence and low noise as required for fibre-optic sensing, gyroscopes, LiDAR and optical frequency metrology. Endowing erbium-based gain in photonic integrated circuits can provide a basis for miniaturizing low-noise fibre lasers to the chip-scale form factor and enable large-volume applications. Although major progress has been made on integrated lasers based on silicon photonics with III–V gain media, realizing low-noise integrated erbium-based lasers has, however, remained unachievable. 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 erbium laser that achieves 50 Hz intrinsic linewidth, high output power up to 17 mW, low intensity noise and integration of a III–V pump laser, approaching the performance of fibre lasers and state-of-the-art semiconductor extended-cavity lasers. The laser circuit is based on an erbium-ion-implanted ultralow-loss silicon nitride photonic integrated circuit, with an intracavity microring-based Vernier filter that enables >40 nm wavelength tunability within the optical C and L bands and attains a 70 dB side-mode suppression ratio. This new class of low-noise, tunable integrated laser could find applications in LiDAR, microwave photonics, optical frequency synthesis and free-space communications, with wavelength extendibility using different rare-earth ion species.

Early works1and recent advances in thin-film lithium niobate (LiNbO3) on insulator have enabled low-loss photonic integrated circuits2,3, modulators with improved half-wave voltage4,5, electro-optic frequency combs6and on-chip electro-optic devices, with applications ranging from microwave photonics to microwave-to-optical quantum interfaces7. Although recent advances have demonstrated tunable integrated lasers based on LiNbO3(refs. 8,9), the full potential of this platform to demonstrate frequency-agile, narrow-linewidth integrated lasers has not been achieved. Here we report such a laser with a fast tuning rate based on a hybrid silicon nitride (Si3N4)–LiNbO3photonic platform and demonstrate its use for coherent laser ranging. Our platform is based on heterogeneous integration of ultralow-loss Si3N4photonic integrated circuits with thin-film LiNbO3through direct bonding at the wafer level, in contrast to previously demonstrated chiplet-level integration10, featuring low propagation loss of 8.5 decibels per metre, enabling narrow-linewidth lasing (intrinsic linewidth of 3 kilohertz) by self-injection locking to a laser diode. The hybrid mode of the resonator allows electro-optic laser frequency tuning at a speed of 12 × 1015hertz per second with high linearity and low hysteresis while retaining the narrow linewidth. Using a hybrid integrated laser, we perform a proof-of-concept coherent optical ranging (FMCW LiDAR) experiment. Endowing Si3N4photonic integrated circuits with LiNbO3creates a platform that combines the individual advantages of thin-film LiNbO3with those of Si3N4, which show precise lithographic control, mature manufacturing and ultralow loss11,12.

The ability to amplify optical signals is of pivotal importance across science and technology typically using rare-earth-doped fibres or gain media based on III–V semiconductors. A different physical process to amplify optical signals is to use the Kerr nonlinearity of optical fibres through parametric interactions1,2. Pioneering work demonstrated continuous-wave net-gain travelling-wave parametric amplification in fibres3, enabling, for example, phase-sensitive (that is, noiseless) amplification4, link span increase5, signal regeneration and nonlinear phase noise mitigation6. Despite great progress7–15, all photonic integrated circuit-based demonstrations of net parametric gain have necessitated pulsed lasers, limiting their practical use. Until now, only bulk micromachined periodically poled lithium niobate (PPLN) waveguide chips have achieved continuous-wave gain16,17, yet their integration with silicon-wafer-based photonic circuits has not been shown. Here we demonstrate a photonic-integrated-circuit-based travelling-wave optical parametric amplifier with net signal gain in the continuous-wave regime. Using ultralow-loss, dispersion-engineered, metre-long, Si3N4photonic integrated circuits18on a silicon chip of dimensions 5 × 5 mm2, we achieve a continuous parametric gain of 12 dB that exceeds both the on-chip optical propagation loss and fibre–chip–fibre coupling losses in the telecommunication C band. Our work demonstrates the potential of photonic-integrated-circuit-based parametric amplifiers that have lithographically controlled gain spectrum, compact footprint, resilience to optical feedback and quantum-limited performance, and can operate in the wavelength ranges from visible to mid-infrared and outside conventional rare-earth amplification bands.

Metal halide perovskite ferroelectrics possess various physical characteristics such as piezoelectric and pyroelectric effects, which could broaden the application of perovskite ferroelectrics and enhance the optoelectronic performance. Therefore, it is promising to combine multiple effects to optimize the performance of the self-powered PDs. Herein, patterned 2D ferroelectric perovskite (PMA)2PbCl4microbelt arrays were demonstrated through a PDMS template-assisted antisolvent crystallization method. The perovskite arrays based flexible photodetectors exhibited fine self-powered photodetection performance under 320 nm illumination and much enhanced reproducibility compared with the randomly distributed single-crystal microbelts-based PDs. Furthermore, by introducing the piezo-phototronic effect, the performance of the flexible PD was greatly enhanced. Under an external tensile strain of 0.71%, the responsivity was enhanced by 185% from 84 to 155.5 mA/W. Our findings offer the advancement of comprehensively utilizing various physical characteristics of the ferroelectrics for novel ferroelectric optoelectronics.

Integrated photonics facilitates extensive control over fundamental light–matter interactions in manifold quantum systems including atoms1, trapped ions2,3, quantum dots4and defect centres5. Ultrafast electron microscopy has recently made free-electron beams the subject of laser-based quantum manipulation and characterization6–11, enabling the observation of free-electron quantum walks12–14, attosecond electron pulses10,15–17and holographic electromagnetic imaging18. Chip-based photonics19,20promises unique applications in nanoscale quantum control and sensing but remains to be realized in electron microscopy. Here we merge integrated photonics with electron microscopy, demonstrating coherent phase modulation of a continuous electron beam using a silicon nitride microresonator. The high-finesse (Q0≈ 106) cavity enhancement and a waveguide designed for phase matching lead to efficient electron–light scattering at extremely low, continuous-wave optical powers. Specifically, we fully deplete the initial electron state at a cavity-coupled power of only 5.35 microwatts and generate >500 electron energy sidebands for several milliwatts. Moreover, we probe unidirectional intracavity fields with microelectronvolt resolution in electron-energy-gain spectroscopy21. The fibre-coupled photonic structures feature single-optical-mode electron–light interaction with full control over the input and output light. This approach establishes a versatile and highly efficient framework for enhanced electron beam control in the context of laser phase plates22, beam modulators and continuous-wave attosecond pulse trains23, resonantly enhanced spectroscopy24–26and dielectric laser acceleration19,20,27. Our work introduces a universal platform for exploring free-electron quantum optics28–31, with potential future developments in strong coupling, local quantum probing and electron–photon entanglement.

Integrated photonics enables signal synthesis, modulation and conversion using photonic integrated circuits (PICs). Many materials have been developed, among which silicon nitride (Si3N4) has emerged as a leading platform particularly for nonlinear photonics. Low-loss Si3N4PICs have been widely used for frequency comb generation, narrow-linewidth lasers, microwave photonics and photonic computing networks. Yet, among all demonstrated functionalities for Si3N4integrated photonics, optical non-reciprocal devices such as isolators and circulators have not been achieved. Conventionally, they are realized based on the Faraday effect of magneto-optic materials under an external magnetic field; however, it has been challenging to integrate magneto-optic materials that are not compatible with complementary metal–oxide–semiconductors and that require bulky external magnet. Here we demonstrate a magnetic-free optical isolator based on aluminium nitride (AlN) piezoelectric modulators monolithically integrated on low-loss Si3N4PICs. The transmission reciprocity is broken by spatio-temporal modulation of a Si3N4microring resonator with three AlN bulk acoustic wave resonators that are driven with a rotational phase. This design creates an effective rotating acoustic wave that allows indirect interband transition in only one direction among a pair of strongly coupled optical modes. A maximum of 10 dB isolation is achieved under 300 mW total radiofrequency power applied to three actuators, with minimum insertion loss of 0.1 dB. An isolation bandwidth of 700 MHz is obtained, determined by the optical resonance linewidth. The isolation remains constant over nearly 30 dB dynamic range of optical input power, showing excellent optical linearity. Our integrated, linear, magnetic-free, electrically driven optical isolator could be a key building block for integrated lasers and optical interfaces for superconducting circuits.

Similar to surfaces of three-dimensional (3D) bulk materials, edges are inevitable in 2D materials and have been studied a lot (e.g., for MoS2). In the current work, taking the ambient-stable MoSi2N4as an example, nonpolar and polar edges as well as polar-edge reconstructions are studied based on first-principles calculations. We demonstrate that a combination of the “local” electron counting model (ECM) at edges and “nonlocal” charge polarity analysis (CPA) across the ribbon is essential for a unified understanding of the “local” edge properties and edge reconstructions in the following aspects. For pristine edges, the semiconducting (metallic) property of nonpolar armchair (polar zigzag) edges is related to CPA, and the spin-paired (spin-polarized) electronic structure of nonpolar (polar) edges is related to the ECM. For polar-edge reconstructions: (1) the polar edges become semiconducting when the reversed dipole from edge-reconstruction partially cancels the accumulated electric dipole within the ribbon; (2) the polar edges can further be spin-paired when edge-reconstruction fulfills the ECM for both the double cation (Mo, Si)-edge and the anion N-edge; and (3) ECM and CPA give the same conclusion for edge-reconstruction. Our analysis of combining ECM and CPA not only gives the general guidance for obtaining spin-paired and semiconducting polar edges but also potentially helps deepen the understanding of edges of other 2D layered materials.

Microwave photonic technologies, which upshift the carrier into the optical domain, have facilitated the generation and processing of ultra-wideband electronic signals at vastly reduced fractional bandwidths. For microwave photonic applications such as radars, optical communications and low-noise microwave generation, optical frequency combs are useful building blocks. By virtue of soliton microcombs, frequency combs can now be built using CMOS-compatible photonic integrated circuits. Yet, currently developed integrated soliton microcombs all operate with repetition rates significantly beyond those that conventional electronics can detect, preventing their use in microwave photonics. Access to this regime is challenging due to the required ultra-low waveguide loss and large dimensions of the nanophotonic resonators. Here, we demonstrate soliton microcombs operating in two widely employed microwave bands, the X-band (~10 GHz, for radar) and the K-band (~20 GHz, for 5G). Driven by a low-noise fibre laser, these devices produce more than 300 frequency lines within the 3 dB bandwidth, and generate microwave signals featuring phase noise levels comparable to modern electronic microwave oscillators. Our results establish integrated microcombs as viable low-noise microwave generators. Furthermore, the low soliton repetition rates are critical for future dense wavelength-division multiplexing channel generation schemes and could significantly reduce the system complexity of soliton-based integrated frequency synthesizers and atomic clocks.

High-speed actuation of laser frequency1is critical in applications using lasers and frequency combs2,3, and is a prerequisite for phase locking, frequency stabilization and stability transfer among optical carriers. For example, high-bandwidth feedback control of frequency combs is used in optical-frequency synthesis4, frequency division5and optical clocks6. Soliton microcombs7,8have emerged as chip-scale frequency comb sources, and have been used in system-level demonstrations9,10. Yet integrated microcombs using thermal heaters have limited actuation bandwidths11,12of up to 10 kilohertz. Consequently, megahertz-bandwidth actuation and locking of microcombs have only been achieved with off-chip bulk component modulators. Here we demonstrate high-speed soliton microcomb actuation using integrated piezoelectric components13. By monolithically integrating AlN actuators14on ultralow-loss Si3N4photonic circuits15, we demonstrate voltage-controlled soliton initiation, tuning and stabilization with megahertz bandwidth. The AlN actuators use 300 nanowatts of power and feature bidirectional tuning, high linearity and low hysteresis. They exhibit a flat actuation response up to 1 megahertz—substantially exceeding bulk piezo tuning bandwidth—that is extendable to higher frequencies by overcoming coupling to acoustic contour modes of the chip. Via synchronous tuning of the laser and the microresonator, we exploit this ability to frequency-shift the optical comb spectrum (that is, to change the comb’s carrier-envelope offset frequency) and make excursions beyond the soliton existence range. This enables a massively parallel frequency-modulated engine16,17for lidar (light detection and ranging), with increased frequency excursion, lower power and elimination of channel distortions resulting from the soliton Raman self-frequency shift. Moreover, by modulating at a rate matching the frequency of high-overtone bulk acoustic resonances18, resonant build-up of bulk acoustic energy allows a 14-fold reduction of the required driving voltage, making it compatible with CMOS (complementary metal–oxide–semiconductor) electronics. Our approach endows soliton microcombs with integrated, ultralow-power and fast actuation, expanding the repertoire of technological applications of microcombs.

Optical frequency combs have a wide range of applications in science and technology1. An important development for miniature and integrated comb systems is the formation of dissipative Kerr solitons in coherently pumped high-quality-factor optical microresonators2–9. Such soliton microcombs10have been applied to spectroscopy11–13, the search for exoplanets14,15, optical frequency synthesis16, time keeping17and other areas10. In addition, the recent integration of microresonators with lasers has revealed the viability of fully chip-based soliton microcombs18,19. However, the operation of microcombs requires complex startup and feedback protocols that necessitate difficult-to-integrate optical and electrical components, and microcombs operating at rates that are compatible with electronic circuits—as is required in nearly all comb systems—have not yet been integrated with pump lasers because of their high power requirements. Here we experimentally demonstrate and theoretically describe a turnkey operation regime for soliton microcombs co-integrated with a pump laser. We show the appearance of an operating point at which solitons are immediately generated by turning the pump laser on, thereby eliminating the need for photonic and electronic control circuitry. These features are combined with high-quality-factor Si3N4resonators to provide microcombs with repetition frequencies as low as 15 gigahertz that are fully integrated into an industry standard (butterfly) package, thereby offering compelling advantages for high-volume production.

Thermal degradation of the composite constituted by high density polyethylene (HDPE) and microencapsulated red phosphorus (MRP) were studied using thermogravimetric (TG) data obtained at different heating rates. The kinetic models and parameters of the thermal degradation of MRP/HDPE composite were evaluated by FWO, KAS and IKP method. It indicates that the activation energy E of 4 % MRP/HDPE composite is higher than HDPE for three methods. MRP could improve the thermal stability and slow down the thermal degradation of HDPE. With adding MRP, the degradation mechanism of HDPE is changed and the degradation rate decreases.

Density functional calculations have been performed to analyze atomic corrugations, Young’s modulus, Poisson’s ratio, and the electronic structure of monolayer graphyne ribbons under uniaxial strains within generalized gradient approximations. Within particular asymmetrical critical compressive (εcrc) and tensile (εcrt) strains, graphyne ribbons will undergo a reversible deformation, which is interpreted within a framework of linear elastic stress–strain response. From the energy-displacement relations, the two-dimensional Young’s modulus is obtained, and it increases along with the width increasing. When the compressive strain is beyond εcrc, unidirectional corrugations perpendicular to the strain direction are formed in narrower ribbons, and transverse and longitudinal corrugations are formed in wider ribbons. When the tensile strains exceed εcrt, all ribbons undergo longitudinal corrugations before fracture. The corrugation wavelength is practically not dependent on the applied strain but on the ribbon width. All these ribbons are semiconductor with controllable band gaps of 0.14–1.22 eV, depending on the width and the applied strain. Furthermore, the band gaps of graphyne ribbons are sensitive to the tensile strain and can be continuously modulated regardless of the critical strain because the bands near the Fermi level are split off 2pzstates and mainly composed of π orbitals of benzenes in the graphyne sheet.

Monolayer transition-metal dichalcogenides with direct bandgaps are emerging candidates for optoelectronic devices, such as photodetectors, light-emitting diodes, and electro-optic modulators. Here we report a low-loss integrated platform incorporating molybdenum ditelluride monolayers with silicon nitride photonic microresonators. We achieve microresonator quality factors >3 × 106in the telecommunication O- to E-bands. This paves the way for low-loss, hybrid photonic integrated circuits with layered semiconductors, not requiring heterogeneous wafer bonding.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.