LiNbO3 Research Articles

Error correction based artificial neural network in multi-modes CV-QKD with simultaneous type-I and type-II parametric-down conversion entangled photon source

We model simultaneous type-I and type-II phase matching in a single non-linear crystal (NLC), based on a double periodically poled lithium niobate crystal. We also discuss entanglement based continuous variable quantum key distribution (CV-QKD), and the security of such scheme is analyzed considering an eavesdropper being capable of individual attacks. We further demonstrate efficiency of the artificial neural network (ANN) algorithm during post-processing or errors correction in such CV-QKD protocols. Results show that employing simultaneous type-I and type-II SPDC process in single NLC is a potential source to generate high dimensional (or hyper-entangled) states, strongly required for quantum information processing tasks, an example of CV-QKD. Security analysis of such a CV-QKD protocol shows a strong advantage of employing the above entangled photon state source, given that it provides a higher secure key rate and thus a secure communication within a larger distance. In addition, the suggested error correction algorithm is less time consuming and highly efficient, since full synchronization is achieved just after a few number of updates of trusted parties’ tree-parity-machines. Our results sufficiently demonstrate that the suggested CV-QKD is able to distribute secure keys in nearby inter-city areas, and therefore allows lower-cost secure communication networks.

Lithium tantalate photonic integrated circuits for volume manufacturing

Electro-optical photonic integrated circuits (PICs) based on lithium niobate (LiNbO3) have demonstrated the vast capabilities of materials with a high Pockels coefficient1,2. They enable linear and high-speed modulators operating at complementary metal–oxide–semiconductor voltage levels3 to be used in applications including data-centre communications4, high-performance computing and photonic accelerators for AI5. However, industrial use of this technology is hindered by the high cost per wafer and the limited wafer size. The high cost results from the lack of existing high-volume applications in other domains of the sort that accelerated the adoption of silicon-on-insulator (SOI) photonics, which was driven by vast investment in microelectronics. Here we report low-loss PICs made of lithium tantalate (LiTaO3), a material that has already been adopted commercially for 5G radiofrequency filters6 and therefore enables scalable manufacturing at low cost, and it has equal, and in some cases superior, properties to LiNbO3. We show that LiTaO3 can be etched to create low-loss (5.6 dB m−1) PICs using a deep ultraviolet (DUV) stepper-based manufacturing process7. We demonstrate a LiTaO3 Mach–Zehnder modulator (MZM) with a half-wave voltage–length product of 1.9 V cm and an electro-optic bandwidth of up to 40 GHz. In comparison with LiNbO3, LiTaO3 exhibits a much lower birefringence, enabling high-density circuits and broadband operation over all telecommunication bands. Moreover, the platform supports the generation of soliton microcombs. Our work paves the way for the scalable manufacture of low-cost and large-volume next-generation electro-optical PICs.

Single‐Pulse‐Driven Frame Printing of Chromatic Pixels in Lithium Niobate Crystal

AbstractHighly efficient and programmable writing of multidimensional optical data is of great value for next‐generation high‐throughput information technologies but has been rarely achieved. Here, a one‐step frame printing of chromatic pixels in lithium niobate crystal by using a single ultrafast laser pulse is reported. In this strategy, a phase superposition‐based spatial light modulation strategy is applied to split a single ultrafast laser pulse into multiple son pulses with designated optical properties and spatial distribution patterns. It is demonstrated that these son pulses allow for massively creating micro‐amorphous phase transition zones with on‐demand structural features that can modulate the intrinsic birefringence of the crystal matrix and generate wavelength‐selective interference in the visible band to form pixel‐level chromatic patterns, namely, single‐pulse‐driven frame color printing. The created chromatic pixels can be encoded into computer‐recognizable data arrays to play a role in high‐efficiency multidimensional information recording. The presented approach enables fast and programmable information batch writing in 3D space and can serve as a versatile tool boosting next‐generation information optics.

Asymmetrical Lamb wave mode resonant infrared detector based on lithium niobate thin film

This work explores the infrared (IR) detection capabilities of 750 nm thick Z-cut lithium niobate (LN) thin film resonator at asymmetric modes of various orders: the first, third, fifth, and seventh order asymmetric (A1, A3, A5, and A7), with resonant frequencies of 2.35, 6.68, 11.09, and 15.49 GHz. Under the infrared radiation of 0.575 mW, the responses about admittance minima and frequency drift corresponding to these modes have been experimentally validated. Notably, the A1 mode exhibits the most significant admittance dip response with 2.62 dB, while the A7 mode demonstrates a maximum frequency drift response of 670 kHz. The optimal parameter for noise equivalent power reaches 15.41 pW/Hz1/2, and the optimal detectivity achieves 7.40 × 106 m Hz1/2/W. These findings indicate the immense potential of LN thin-film resonators for infrared sensing applications.

High-Entropy Lithium Niobate Nanocubes for Photocatalytic Water Splitting under Visible Light.

The vast compositional space available in high-entropy oxide semiconductors offers unique opportunities for electronic band structure engineering in an unprecedented large room. In this work, with wide band gap semiconductor lithium niobate (LiNbO3) as a model system, we show that the substitutional addition of high-entropy metal cation mixtures within the Nb sublattice can lead to the formation of a single-phase solid solution featuring a substantially narrowed band gap and intense broadband visible light absorption. The resulting high-entropy LiNbO3 [denoted as Li(HE)O3] crystallizes as well-faceted nanocubes; atomic-resolution imaging and elemental mapping via transmission electron microscopy unveil a distinct local chemical complexity and lattice distortion, characteristics of high-entropy stabilized solid solution phases. Because of the presence of high-entropy stabilized Co2+ dopants that serve as active catalytic sites, Li(HE)O3 nanocubes can accomplish the visible light-driven photocatalytic water splitting in an aqueous solution containing methanol as a sacrificial electron donor without the need of any additional co-catalysts.

Giant electron-mediated phononic nonlinearity in semiconductor-piezoelectric heterostructures.

Efficient and deterministic nonlinear phononic interactions could revolutionize classical and quantum information processing at radio frequencies in much the same way that nonlinear photonic interactions have at optical frequencies. Here we show that in the important class of phononic materials that are piezoelectric, deterministic nonlinear phononic interactions can be enhanced by orders of magnitude via the heterogeneous integration of high-mobility semiconductor materials. To this end, a lithium niobate and indium gallium arsenide heterostructure is utilized to produce the most efficient three- and four-wave phononic mixing to date, to the best of our knowledge. We then show that the conversion efficiency can be further enhanced by applying semiconductor bias fields that amplify the phonons. We present a theoretical model that accurately predicts the three-wave mixing efficiencies in this work and extrapolate that these nonlinearities can be enhanced far beyond what is demonstrated here by confining phonons to smaller dimensions in waveguides and optimizing the semiconductor material properties.

Unified predictive modeling of supercontinuum spectra: Using multi-material data with Closed-Form Continuous Time Neural Networks

This paper explores the application of the Closed-Form Continuous-Time Neural Networks (CfC) model in predicting supercontinuum spectra in a unified dataset of various core materials in a planar waveguide. Through numerical simulations and dataset generation, the study constructs a robust model capable of accurately predicting spectral behavior under different conditions and material variation. Initially, the unified dataset comprises spectral data for three materials: Silicon Nitride (Si3N4), Lithium Niobate (LiNbO3), and Silicon Carbide (SiC). The CfC model demonstrates remarkable accuracy in capturing spectral nuances and exhibits a minimal Mean Squared Error (MSE) loss value of 7.2537×10−4. Subsequently, the dataset is expanded to include Tantalum Pentoxide (Ta2O5), introducing a fourth material for evaluation. The inclusion of Ta2O5 data further validates the model’s scalability and generalization capabilities with Mean Squared Error (MSE) loss value of 6.7894×10−4. The advantage of the CfC model in precisely predicting supercontinuum spectra while retaining computational efficiency is demonstrated by comparisons with conventional methods. The CfC model is a viable tool for enhancing predictive modeling in photonics research because of its scalability and generalization characteristics. This will pave the way for future developments in deep learning techniques for optical device optimization.

MEMS Oscillators-Network-Based Ising Machine with Grouping Method.

Combinatorial optimization (CO) has a broad range of applications in various fields, including operations research, computer science, and artificial intelligence. However, many of these problems are classified as nondeterministic polynomial-time (NP)-complete or NP-hard problems, which are known for their computational complexity and cannot be solved in polynomial time on traditional digital computers. To address this challenge, continuous-time Ising machine solvers have been developed, utilizing different physical principles to map CO problems to ground state finding. However, most Ising machine prototypes operate at speeds comparable to digital hardware and rely on binarizing node states, resulting in increased system complexity and further limiting operating speed. To tackle these issues, a novel device-algorithm co-design method is proposed for fast sub-optimal solution finding with low hardware complexity. On the device side, a piezoelectric lithium niobate (LiNbO3) microelectromechanical system (MEMS) oscillator network-based Ising machine without second-harmonic injection locking (SHIL) is devised to solve Max-cut and graph coloring problems. The LiNbO3 oscillator operates at speeds greater than 9 GHz, making it one of the fastest oscillatory Ising machines. System-wise, an innovative grouping method is used that achieves a performance guarantee of 0.878 for Max-cut and 0.658 for graph coloring problems, which is comparable to Ising machines that utilize binarization.

Controlled Second Harmonic Generation with Optically Trapped Lithium Niobate Nanoparticles.

We report the second harmonic generation (SHG) response from a single 34 nm diameter lithium niobate nanoparticle. The experimental setup involves a first beam devoted to the optical trapping of single nanoparticles, whereas a second arm involves a femtosecond laser source leading to the SHG emission from the trapped nanoparticles. SHG operation where one to three nanoparticles are present in the optical trap is first demonstrated, highlighting the transition between coherent and incoherent SHG, the latter known as hyper-Rayleigh scattering (HRS). With a spatial light modulator moving the optical trap in and out of the focus of the femtosecond beam, the SHG intensity is switched back and forth between a low and a high level. This controlled operation opens new avenues for nanoparticle characterization and applications in sensing or communication and information technologies and constitutes the first step in the design of active substrateless metasurfaces.

Polarization-insensitive and high-efficiency edge coupler for thin-film lithium niobate.

In this Letter, we propose and demonstrate a fiber-to-chip edge coupler (EC) on an x-cut thin film lithium niobate (TFLN) for polarization-insensitive (PI) coupling. The EC consists of three width-tapered full-etched waveguides with silica cladding and matches well with a single-mode fiber (SMF). The measured results show that the minimum coupling losses for TE0/TM0 modes remain to be 0.9 dB/1.1 dB per facet, and the polarization dependent loss (PDL) is <0.5 dB over the wavelength range from 1260 to 1340 nm. Moreover, the EC features large misalignment tolerance of ±2 µm in the Z direction and ±1.5 µm in the X direction for both polarizations for a 1 dB penalty. To the best of our knowledge, this is the first realized O-band edge coupler on TFLN with SMF. The proposed device shows promising potential for integration into TFLN polarization diversity devices.

Resistive switching properties in polycrystalline LiNbO3 thin films

LiNbO3 (LNO) is currently intensively studied as an important ferroelectric material. In this work, polycrystalline LNO films were prepared through a sputtering technique, and their ferroelectricity-related resistive switching property was investigated using a device structure of PtSi/SiO2/LNO/Pt. The device exhibits a volatile resistance switching property at lower positive sweeping voltages and a stable bipolar nonvolatile switching property at higher sweeping voltages. The resistive switching mechanism of the device is discussed based on the domain wall conductivity characteristics of the polycrystalline LNO thin films. The PtSi/SiO2/LNO/Pt memristor device has potential applications in memory and artificial neural synapses.

High-velocity and large-coupling surface wave mode using acoustic Bragg reflector stack with matched excitation condition

High-velocity, large-coupling acoustic mode is the eternal pursuit of microacoustic research. Surface mode on piezoelectric films supported by an acoustic Bragg reflector (ABR) stack is one possible solution for realizing such a goal. However, some acoustic modes exhibit lower couplings in experiments than theoretically predicted, especially when metal layers are used as high-impedance layers in the ABR. The mechanism of this performance deterioration is still unclear. In this work, the electric field distribution in a piezoelectric plate mounted to an ABR stack is analyzed by considering the inductive current effect in conductive ABR layers. The field distribution required by one mode is found to be distorted by the effect, which results in a reduction in the excitation efficiency for the mode. We propose the use of another acoustic mode with a concentrated electric field in the top layers. As analyzed in comparison, the impact of the inductive effect on the mode is negligible. On an optimized crystal cut of lithium niobate, the selected mode exhibits 22.64% coupling and an acoustic velocity of 6006 m/s.

Photon-pair generation using inverse-designed thin-film lithium niobate mode converters

Spontaneous parametric down-conversion (SPDC) has become a key method for generating entangled photon pairs. Periodically poled thin-film lithium niobate (TFLN) waveguides induce strong SPDC but require complex fabrication processes. In this work, we experimentally demonstrate efficient SPDC and second harmonic generation using modal phase matching methods. This is achieved with inverse-designed optical mode converters and low-loss optical waveguides in a single nanofabrication process. Inverse design methods provide enhanced functionalities and compact footprints for the converter. Despite the extensive achievements in inverse-designed photonic integrated circuits, the potential of inverse-designed TFLN quantum photonic devices has been seldom explored. The device shows an on-chip conversion efficiency of 3.95% W−1 cm−2 in second harmonic generation measurements and a coincidence count rate up to 21.2 kHz in SPDC experiments. This work highlights the potential of the inverse-designed TFLN photonic devices and paves the way for their applications in on-chip nonlinear or quantum optics.

Intrinsic polarization conversion and avoided-mode crossing in X-cut lithium niobate microrings

Compared with well-developed free space polarization converters, polarization conversion between TE and TM modes in the waveguide is generally considered to be caused by shape birefringence, like curvature, morphology of waveguide cross section and scattering. Here, we study the polarization conversion mechanism in 1-THz-FSR X-cut lithium niobate microrings with multiple-resonance condition, that is the conversion can be implemented by birefringence of waveguides, which will also introduce an avoided-mode crossing. In the experiment, we find that this mode crossing results in severe suppression of one sideband in local nondegenerate four-wave mixing and disrupts the cascaded four-wave mixing on this side. Simultaneously, we propose one two-dimensional method to simulate the eigenmodes (TE and TM) in X-cut microrings, and the mode crossing point. This work will provide one approach to the design of polarization converters and simulation for monolithic photonics integrated circuits, and may be helpful to the studies of missed temporal dissipative soliton formation in X-cut lithium niobate rings.

Monolithic deformable mirror based on lithium niobate single crystal for high-resolution X-ray adaptive microscopy

X-ray microscopy is very promising not only for nondestructive and high-spatial-resolution observation of the internal structure of a sample but also for elemental distribution and chemical state analysis. However, the spatial resolution of microscopes remains unsatisfactory owing to the fabrication error in the objective lens. To realize an ultra-high-resolution, we propose and develop a monolithic deformable mirror based on a lithium niobite single crystal and a novel adaptive imaging system based on it. An X-ray interferometer confirmed that shape modification is possible with an accuracy of 0.67 nm in peak to valley under high stability (0.17 nm over 7 h) and hysteresis-free deformation control. Introducing this adaptive mirror into an X-ray microscope based on advanced Kirkpatrick-Baez mirror optics and correcting the wavefront aberration demonstrated that the X-ray image quality could be significantly improved.

Broadband frequency comb generation through cascaded quadratic nonlinearity in thin-film lithium niobate microresonators.

Broadband frequency comb generation through cascaded quadratic nonlinearity remains experimentally untapped in free-space cavities with bulk χ(2) materials mainly due to the high threshold power and restricted ability of dispersion engineering. Thin-film lithium niobate (LN) is a good platform for nonlinear optics due to the tight mode confinement in a nano-dimensional waveguide, the ease of dispersion engineering, large quadratic nonlinearities, and flexible phase matching via periodic poling. Here we demonstrate broadband frequency comb generation through dispersion engineering in a thin-film LN microresonator. Bandwidths of 150 nm (80 nm) and 25 nm (12 nm) for center wavelengths at 1560 and 780 nm are achieved, respectively, in a cavity-enhanced second-harmonic generation (doubly resonant optical parametric oscillator). Our demonstration paves the way for pure quadratic soliton generation, which is a great complement to dissipative Kerr soliton frequency combs for extended interesting nonlinear applications.

Electro-Mechanical Characterization and Modeling of a Broadband Piezoelectric Microgenerator Based on Lithium Niobate.

Vibration energy harvesting based on piezoelectric transducers is an attractive choice to replace single-use batteries in powering Wireless Sensor Nodes (WSNs). As of today, their widespread application is hindered due to low operational bandwidth and the conventional use of lead-based materials. The Restriction of Hazardous Substances legislation (RoHS) implemented in the European Union restricts the use of lead-based piezoelectric materials in future electronic devices. This paper investigates lithium niobate (LiNbO3) as a lead-free material for a high-performance broadband Piezoelectric Energy Harvester (PEH). A single-clamped, cantilever beam-based piezoelectric microgenerator with a mechanical footprint of 1 cm2, working at a low resonant frequency of 200 Hz, with a high piezoelectric coupling coefficient and broad bandwidth, was designed and microfabricated, and its performance was evaluated. The PEH device, with an acceleration of 1 g delivers a maximum output RMS power of nearly 35 μW/cm2 and a peak voltage of 6 V for an optimal load resistance at resonance. Thanks to a high squared piezoelectric electro-mechanical coupling coefficient (k2), the device offers a broadband operating frequency range above 10% of the central frequency. The Mason electro-mechanical equivalent circuit was derived, and a SPICE model of the device was compared with experimental results. Finally, the output voltage of the harvester was rectified to provide a DC output stored on a capacitor, and it was regulated and used to power an IoT node at an acceleration of as low as 0.5 g.

Influence of working parameters on multi-shot femtosecond laser surface ablation of lithium niobate

This paper presents an experimental investigation on the ultrashort pulsed laser ablation of 128° Y-cut Lithium Niobate (LiNbO3) using multi-shot fs-laser pulses at different pulse repetition frequencies (1, 10 and 100kHz). The ablation threshold fluence was observed to rapidly decrease as the number N of incident laser pulses increased, regardless of the repetition frequency. This behavior, compatible with the incubation effect, was accurately modeled by a power law. The calculated single pulse ablation threshold Fth,1=1.98±0.15J/cm2 is consistent with values reported in existing literature. The incubation coefficient S∗ appears to be independent of the repetition frequencies. In contrast, the asymptotic ablation threshold Fth,∞ decreased as the repetition frequency was increased. The study delves deeper into the impact of laser operational variables, including pulse energy, repetition frequency, total pulse count, and scanning speed, on the surface roughness and milled depth of fs-laser micromilled zones on LiNbO3 substrates. A discernible trade-off between achieving control over the obtained depth and the surface finish of the process was identified, providing valuable insights for achieving precise control over fs-laser processing of LiNbO3 surfaces.

Analysis of propagation and resonance properties of longitudinal leaky surface acoustic wave on LiNbO3/SiC bonded structure

Abstract The propagation and resonance properties of longitudinal leaky surface acoustic waves (LLSAW) on a bonded structure comprising an X-cut LiNbO3 (LN) thin plate and a 4H-SiC support substrate are theoretically investigated. The strong LLSAW responses with high Q factors were obtained at the LN thin-plate thickness h where the LLSAW phase velocity was slower than the bulk shear wave of 4H-SiC of 7126 m/s, and a fractional bandwidth (FBW) of 9–10% was obtained for the normalized Al film thickness by wavelength h Al/λ = 0.06–0.07 and h/λ = 0.30–0.40. Moreover, even at h/λ with a faster phase velocity than the bulk shear wave of 4H-SiC, the strong LLSAW responses without spurious response owing to the LLSAW higher-order mode were obtained. Finally, h Al/λ = 0.031 and h/λ = 0.19 were extracted to obtain a phase velocity of 7800 m/s, high Q factors, and FBW of 7.6%.

Features of Obtaining Lead-Free Ferro-Piezoceramics Based on Sodium Niobate

The composition of the filling used in the manufacture of ferro-piezoceramic materials based on sodium niobate of the form (Na,K,Cd0.5)NbO3 and (Na,Li)NbO3 by hot pressing has been developed. It is shown that the developed filling of Al2O3+MnO + MnCO3 composition leads to a decrease in sintering temperature and improvement in the mechanical properties of the studied objects while maintaining their electrophysical parameters. An explanation is given for the observed positive effect of adding MnO + MnCO3 to Al2O3 filling. Niobate materials, made by hot pressing with the developed filling, can be used in electronic devices that experience critical external influences (thermal, field, baric).