Abstract As 6G communications, high‐resolution imaging, and precision sensing push the boundaries of the electromagnetic spectrum, the “terahertz (THz) gap” has transformed from a scientific curiosity into a critical industry bottleneck. Traditional electronic and photonic sources struggle to simultaneously deliver ultra‐wide bandwidth, room‐temperature efficiency, and chip‐scale footprint, trapping system designs in an inevitable compromise. To shatter this bottleneck, integrated microwave photonics offer a compelling route, with thin‐film lithium niobate (TFLN) emerging as the definitive gamechanger. Harnessing its formidable Pockels effect, high nonlinearity, and sub‐wavelength optical confinement, TFLN provides an unprecedented platform for high‐performance millimeter‐wave (mmWave) and THz generation. This article systematically reviews the physical mechanisms and engineering milestones of TFLN‐based sources. We map the technological landscape across three core domains: second‐order nonlinear effects (optical rectification, difference‐frequency generation, optical parametric oscillation); Pockels effect (direct modulation, optoelectronic oscillators, electro‐optic frequency combs); and third‐order nonlinearities effect (four‐wave mixing, stimulated Brillouin/Raman scattering). Beyond generation, we highlight how on‐chip integration translates these physical phenomena into system‐level triumphs, enabling ultra‐wideband wireless links, high‐precision photonic radar, and on‐chip spectroscopic sensing. Finally, we critically assess the remaining hurdles—such as conversion efficiency and packaging—and chart a roadmap toward heterogeneous integration, metasurface coupling, and fully functional THz systems‐on‐chip.

We present a physical computing paradigm that harnesses the intrinsic nonlinear dynamics of rare earth doped core shell nanoparticles as a computational substrate. By directly exploiting cross relaxation and energy transfer upconversion processes, the system realizes a state dependent transfer function whose effective decay rate evolves with the instantaneous Er3+ population, which mathematically analogous to gating and attention mechanisms in recurrent neural networks. The three spectrally resolved emission channels inherently span disparate timescales, endowing the reservoir with native multitimescale feature extraction without auxiliary engineering. Under the reservoir computing framework, the coupled three channel system achieves a total memory capacity exceeding fourfold that of a single ion reservoir; capacity decomposition further reveals that the nonzero cross memory capacity is a direct signature of many body Tm3+@Er3+ coupling. On the Mackey Glass and Santa Fe chaotic benchmarks, the system attains normalized mean squared errors of 1.2x10-3 and 2.1x10-2, respectively, with only 125 virtual nodes. These results establish rare earth nanoparticles as a compelling platform for compact and hardware integrable neuromorphic computing, and introduce "inward evolution", the deliberate exploitation of intra material quantum dynamics, as a generalizable design principle for next generation physical computing systems.

All optical wavelength converters (AOWCs) that can effectively and flexibly switch optical signals between different wavelength channels are essential elements in future optical fiber communications and quantum information systems. A promising strategy for achieving high-performance AOWCs is to leverage strong three-wave mixing processes in second-order nonlinear nanophotonic devices, specifically thin-film periodically poled lithium niobate (TF-PPLN) waveguides. By exploiting the advantages of sub-wavelength light confinement and dispersion engineering compared with their bulk counterparts, TF-PPLN waveguides provide a viable route for realizing highly efficient and broadband wavelength conversion. Nevertheless, most existing approaches rely on a single TF-PPLN device to perform both frequency doubling of the telecom pump and the wavelength conversion process, resulting in significant crosstalk between adjacent signal channels. Here, we address this challenge by demonstrating a two-stage TF-PPLN nonlinear photonic circuit that integrates a second-harmonic generation module, a signal wavelength conversion module, and multiple adiabatic directional coupler-based pump filters on a single chip. By decoupling the two nonlinear processes and leveraging the high pump-filtering extinction ratio, we achieve low-crosstalk AOWC with a side-channel suppression ratio exceeding 25 dB, substantially surpassing the performance of single-stage devices. Furthermore, our device exhibits an ultra-broad conversion bandwidth of 110 nm and a relatively high conversion efficiency of −15.6 dB, making it an attractive solution for future photonic systems. The two-stage AOWC design shows promise for low-noise phase-sensitive amplification and quantum frequency conversion in future classical and quantum photonic systems.

Periodically poled thin-film lithium niobate (TFLN) waveguides, which enable efficient quadratic nonlinear processes, serve as crucial foundation for classical and quantum signal processing. To expand their application scope, the first investigation of nonlinear conversion processes in periodically poled TFLN waveguides at cryogenic conditions (7 K) is provided. Through systematic experimental characterization, it is found that the periodically poled TFLN waveguide retains its high conversion efficiency at both cryogenic and room temperatures for both classical second-harmonic generation and quantum photon-pair generation processes. Particularly, the photon-pair source at cryogenic conditions shows high brightness (approximate to 8 MHz mu W-1) and broad bandwidth (>100 THz). These results demonstrate the significant potential of TFLN wavelength conversion devices for cryogenic applications and foster future scalable quantum photonic systems.

2D transition metal dichalcogenides (TMDs) have attracted intensive interests for its unique electronic, optical, and thermal properties. Doping is necessary to expand the application. However, the stability of doped materials has been overlooked. This study focuses on the stability of monolayer‐doped MoS2 with different vanadium (V) concentrations. It provides a quantitative assessment of the etching results. Findings indicate that the stability of MoS2 under different etching atmospheres follows the series of lightly doped MoS2, pristine MoS2, moderately doped MoS2, and highly doped MoS2. This research indicates that the stability of the material is linked to the bonding energy of cations and anions, as well as the amount of lattice distortion, which competes with one another. Low levels of V doping do not lead to significant lattice distortion, and the binding energy between sulfur (S) and V surpasses that of molybdenum (Mo), which is the primary factor. Excessive doping results in lattice distortion, which leads to a multitude of defects and a reduction in durability. This work is important for guiding the assessment of the reliability, the protection of degradation, and application scenarios of TMDs.

Thin-film periodically poled lithium niobate(TF-PPLN)devices have recently gained prominence for efficient wavelength conversion processes in both classical and quantum applications.However,the patterning and poling of TF-PPLN devices today are mostly performed at chip scales,presenting a significant bottleneck for future large-scale nonlinear photonic systems that require the integration of multiple nonlinear components with consistent performance and low cost.Here,we take a pivotal step towards this goal by developing a wafer-scale TF-PPLN nonlinear photonic platform,leveraging ultraviolet stepper lithography and an automated poling process.To address the inhomogeneous broadening of the quasi-phase matching(QPM)spectrum induced by film thickness variations across the wafer,we propose and demonstrate segmented thermal optic tuning modules that can pre-cisely adjust and align the QPM peak wavelengths in each section.Using the segmented micro-heaters,we show the successful realignment of inhomogeneously broadened multi-peak QPM spectra with up to 57%enhance-ment of conversion efficiency.We achieve a high normalized conversion efficiency of 3802%W-1 cm-2 in a 6 mm long PPLN waveguide,recovering 84%of the theoretically predicted efficiency in this device.The advanced fab-rication techniques and segmented tuning architectures presented herein pave the way for wafer-scale integration of complex functional nonlinear photonic circuits with applications in quantum information processing,preci-sion sensing and metrology,and low-noise-figure optical signal amplification.

Doping in transition metal dichalcogenide (TMD) has received extensive attention for its prospect in the application of photoelectric devices. Currently researchers focus on the doping ability and doping distribution in monolayer TMD and have obtained a series of achievements. Bilayer TMD has more excellent properties compared with monolayer TMD. Moreover, bilayer TMD with different stacking structures presents varying performance due to the difference in interlayer coupling. Herein, this work focuses on doping ability of dopants in different bilayer stacking structures that has not been studied yet. Results of this work show that the doping ability of V atoms in bilayer AA' and AB stacked WS2 is different, and the doping concentration of V atoms in AB stacked WS2 is higher than in AA' stacked WS2. Moreover, dopants from top and bottom layer can be distinguished by scanning transmission electron microscopy (STEM) image. Density functional theory (DFT) calculation further confirms the doping rule. This study reveals the mechanism of the different doping ability caused by stacking structures in bilayer TMD and lays a foundation for further preparation of controllable-doping bilayer TMD materials.

We realize arbitrary engineering of resonant frequencies by mode splitting in both isotropic z-cut LN and anisotropic x-cut LN photonic crystal ring resonators. Spectral engineering in x-cut LN is realized by a gradient design that precisely compensates for variations in both refractive index and perturbation strength.

•Single-crystal Cu(111) is prepared on the basis of direct bonding copper method.•Specific crystal orientation relationship exists between Cu(111) and sapphire.•Cu(111) by direct bonding copper benefits the growth of single-crystal graphene.

On-chip optical microresonators are essential building blocks in integrated optics. The ability to arbitrarily engineer their resonant frequencies is crucial for exploring novel physics in synthetic frequency dimensions and practical applications like nonlinear optical parametric processes and dispersion-engineered frequency comb generation. Photonic crystal ring (PhCR) resonators are a versatile tool for such arbitrary frequency engineering, by controllably creating mode splitting at selected resonances. To date, these PhCRs have mostly been demonstrated in isotropic photonic materials, while such engineering can be significantly more complicated in anisotropic platforms that often offer more fruitful optical properties. Here, the spectral engineering of chip-scale optical microresonators is realized in the anisotropic lithium niobate (LN) crystal by a gradient design that precisely compensates for variations in both refractive index and perturbation strength. Controllable frequency splitting is experimentally demonstrated at single and multiple selected resonances in LN PhCR resonators with different sizes, while maintaining high quality-factors up to 1 × 106. Moreover, a sharp boundary is experimentally constructed in the synthetic frequency dimension based on an actively modulated x-cut LN gradient-PhCR, opening up new paths toward the arbitrary control of electro-optic comb spectral shapes and exploration of novel physics in the frequency degree of freedom.

Two-dimensional transition metal dichalcogenides (TMDs) with piezoelectric effects are ideal materials for future wearable devices. While enhancing the piezoelectric performance by forming vertical heterojunctions, shortcomings such as contamination at the heterojunction interface and limited built-in electric field width have been noticed. In this work, a lateral heterojunction of monolayer WSe2-MoSe2 with type-II band alignment was employed to amplify the electromechanical optoelectronic efficiency. The considerable built-in field width (BFW) in the lateral heterojunction facilitates rapid separation of carriers. The lattice mismatch induced a flexoelectric effect during the lateral heterojunction growth. The flexoelectric and piezoelectric effects under external strain can regulate the photodetector performance of the device. Under the compressive strain of -0.93%, the photocurrent increased 9.1 times compared to the tensile strain of 0.47%. Flexoelectric effect can reduce the dark current under no external strain. This work reveals the roles of flexoelectric and piezoelectric effects in enhancing photoelectric conversion, suggesting lateral heterojunction devices may be applied in the field of flexible low-light detection.

Optical vector analysis (OVA) is an enabling technology for comprehensively characterizing both amplitude and phase responses of optical devices or systems. Conventional OVA technologies are mostly based on discrete optoelectronic components, leading to unsatisfactory system sizes, complexity, and stability. They also encounter challenges in revealing the on-chip characteristics of integrated photonic devices, which are often overwhelmed by the substantial coupling loss and extra spectral response at chip facets. In this work, we demonstrate a miniaturized OVA system for integrated photonics devices based on broadband single sideband (SSB) modulators on a thin-film lithium niobate (LN) platform. The OVA could provide a direct probe of both amplitude and phase responses of photonic devices with kHz-level resolution and tens of terahertz measurement bandwidth. We perform in-situ characterizations of single and coupled microring resonators fabricated on the same chip as the OVA, unfolding their intrinsic loss and coupling states unambiguously. Furthermore, we achieve the direct measurement of collective phase dynamics and density of states of the Bloch modes in a synthetic frequency crystal, by in-situ OVA of a dynamically modulated microring resonator. Our in-situ OVA system provides a compact, high-precision, and broadband solution for characterizing future integrated photonic devices and circuits, with potential applications ranging from optical communications, biosensing, neuromorphic computing, to quantum information processing.

Optical vector analysis(OVA)is an enabling technology for comprehensively characterizing both amplitude and phase responses of optical devices or systems.Conventional OVA technologies are mostly based on discrete optoelectronic components,leading to unsatisfactory system sizes,complexity,and sta-bility.They also encounter challenges in revealing the on-chip characteristics of integrated photonic devices,which are often overwhelmed by the substantial coupling loss and extra spectral response at chip facets.In this work,we demonstrate a miniaturized OVA system based on broadband single-sideband(SSB)modulators on a thin-film lithium niobate(LN)platform.The OVA could provide a direct probe of both amplitude and phase responses of photonic devices with kilohertz-level resolution and tens of terahertz of measurement bandwidth.We perform in situ characterizations of single and coupled microring resonators fabricated on the same chip as the OVA,unfolding their intrinsic loss and coupling states unambiguously.Furthermore,we achieve the direct measurement of collective phase dynamics and density of states of the Bloch modes in a synthetic frequency crystal by in situ OVA of a dynamically modulated microring resonator.Our OVA system provides a compact,high-precision,and broadband solution for characterizing future integrated photonic devices and circuits,with potential applications ranging from optical communications,biosensing,and neuromorphic computing,to quantum information processing.

Integrated microwave photonics (MWP) is an intriguing technology for the generation, transmission and manipulation of microwave signals in chip-scale optical systems1,2. In particular, ultrafast processing of analogue signals in the optical domain with high fidelity and low latency could enable a variety of applications such as MWP filters3-5, microwave signal processing6-9 and image recognition10,11. An ideal integrated MWP processing platform should have both an efficient and high-speed electro-optic modulation block to faithfully perform microwave-optic conversion at low power and also a low-loss functional photonic network to implement various signal-processing tasks. Moreover, large-scale, low-cost manufacturability is required to monolithically integrate the two building blocks on the same chip. Here we demonstrate such an integrated MWP processing engine based on a 4 inch wafer-scale thin-film lithium niobate platform. It can perform multipurpose tasks with processing bandwidths of up to 67 GHz at complementary metal-oxide-semiconductor (CMOS)-compatible voltages. We achieve ultrafast analogue computation, namely temporal integration and differentiation, at sampling rates of up to 256 giga samples per second, and deploy these functions to showcase three proof-of-concept applications: solving ordinary differential equations, generating ultra-wideband signals and detecting edges in images. We further leverage the image edge detector to realize a photonic-assisted image segmentation model that can effectively outline the boundaries of melanoma lesion in medical diagnostic images. Our ultrafast lithium niobate MWP engine could provide compact, low-latency and cost-effective solutions for future wireless communications, high-resolution radar and photonic artificial intelligence.

Considering the significant advantages of single-crystal Cu(1 1 1) in the synthesis of 2D materials and many other fields, its controllable preparation has attracted widespread attention. However, the formation of a single-crystal Cu foil has always been hindered by competition among grains with different orientations. Herein, single-crystal Cu(1 1 1) was prepared on the basis of the traditional direct bonding copper method. Cu foil and c-plane sapphire substrate were bonded through Cu2O at high temperature. After the reduction of Cu2O by H2, the surface crystal structure of sapphire will guide Cu to form single-crystal Cu(1 11). The single-crystallinity of Cu(1 1 1) and the specific orientation relationship between Cu(1 1 1) and sapphire were confirmed by LEED and XRD. Furthermore, the growth of high-quality single-crystal graphene was performed on single-crystal Cu(1 11). This work not only facilitates the mass production of 2D materials such as single-crystal graphene, but also provides greater application potential to the direct bonding copper technology and single-crystal Cu.

Compared with binary transition-metal dichalcoge-nides (TMDCs), ternary alloys or heterojunctions have more abundant properties. The spin-coating method has been widely used in the synthesis of TMDCs. However, there is still a lack of research on the effect of acidity and alkalinity of precursor solutions on the epitaxial growth of TMDCs. It is found that the MoxW1-xS2 ternary alloy is formed when an acidic solution of (NH4)2MoO4 and (NH4)2WO4 is used for spin-coating, while the MoS2/WS2 lateral heterojunction with a sharp boundary is formed when an alkaline solution of Na2MoO4, Na2WO4, and NaOH is used. According to the calculation, under alkaline conditions, sulfur atoms preferentially bind to MoO42- due to lower energy and finally form a lateral heterojunction. However, under acidic and neutral conditions, MoO42- and WO42- in the precursor solution will undergo a complex reaction, respectively. Because there is no significant difference in the binding energy of the reaction between the sulfur atom and two complexes, a ternary alloy will be formed. The controllable synthesis of different types of TMDCs can be achieved by regulating acidity and alkalinity.

Waveguide crossings are elementary passive components for signal routing in photonic integrated circuits. Here, we design and characterize two multimode interferometer (MMI)-based waveguide crossings to serve the various routing directions in the anisotropic x-cut thin-film lithium niobate (TFLN) platform. To address the large measurement uncertainties in traditional cut-back characterization methods, we propose and demonstrate a resonator-assisted approach that dramatically reduces the uncertainty of insertion loss measurement (< 0.021 dB) and the lower bound of crosstalk measurement (-60 dB) using only two devices. Based on this approach, we demonstrate and verify TFLN waveguide crossings with insertion losses of < 0.070 dB and crosstalk of < -50 dB along all three routing directions at 1550 nm. The low-loss and low-crosstalk waveguide crossings in this work, together with the simple and efficient characterization strategy, could provide important layout design flexibility for future large-scale classical and quantum TFLN photonic circuits.

We realize an EO comb generator with 15× reduction in electrical power consumption using a multi-loop mode-multiplexing design, generating 47 comb lines using a moderate RF driving power of 28 dBm at 25 GHz.

Doping is widely used in semiconductor devices as an effective means to improve TMD properties. At present, the doping of monolayer TMD has made a lot of progress. However, monolayer TMD has low carrier mobility which hinders the improvement of device performance. Compared with monolayer TMD, bilayer TMD has higher carrier mobility and state density. However, there are few researches on synthesis of doped bilayer TMD. Here, V doped bilayer WS2 films were grown by liquid precursor assisted chemical vapour deposition (LACVD). STEM characterization confirmed the effective doping of V atom in bilayer WS2. The doping of bilayer TMD structure is helpful to improve the practical application of bilayer TMD in the field of optoelectronic devices.

We report thin-film lithium niobate waveguide crossings along three crystal-routing directions, which are precisely characterized by a novel resonator-based method, showing insertion loss of 0.070 dB and crosstalk of -50 dB at 1550 nm.