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This article presents lithium niobate (LiNbO3) based on shear horizontal (SH0) resonators, utilizing a suspended structure, for radio frequency (RF) applications. It demonstrates the design, analysis, and fabrication of SH0 resonators based on a 36Y-cut LiNbO3 thin film. The spurious-free SH0 resonator achieves an electromechanical coupling coefficient ( k t 2 ) of 42.67% and a quality factor (Qr) of 254 at the wave-propagating orientation of 0° in the 36Y-cut plane. [ABSTRACT FROM AUTHOR]

The high‐voltage spinel lithium nickel manganese oxide (LNMO) with an operating voltage of 4.8 V is a promising cathode material for next‐generation lithium‐ion batteries (LIBs). However, LNMO/graphite (LNMO/Gr) full cells suffer capacity fading, which limits their practical applications. In this study, lithium metaborate (LBO) is applied on the LNMO surface to improve the full cell performance via a dry mixing method. The LBO‐coated LNMO delivers much better cycling stability than the uncoated LNMO in full cells with a practical 3 mAh cm−2 areal capacity. Different characterizations are performed to understand the coating effect to track the boron and its impact on the cathode, electrolyte, and anode. The LBO‐coated LNMO owns a 5 nm cathode electrolyte interphase (CEI) with mitigated phase change after long‐term cycling. The uncoated LNMO has negligible CEI with obvious phase change. However, no boron can be detected on the surface of the coated sample. Electrolyte and anode analyses indicate that the coating acts as an additive reservoir, gradually dissolves into the electrolyte, and generates BF4− species. As a result, Nickel/Manganese (Ni/Mn) dissolution from LNMO and the extensive generation of solid electrolyte interphase (SEI) on the anode side is mitigated, thus improving the full‐cell cycling stability to a great extent. [ABSTRACT FROM AUTHOR]

The high‐voltage spinel lithium nickel manganese oxide (LNMO) with an operating voltage of 4.8 V is a promising cathode material for next‐generation lithium‐ion batteries (LIBs). However, LNMO/graphite (LNMO/Gr) full cells suffer capacity fading, which limits their practical applications. In this study, lithium metaborate (LBO) is applied on the LNMO surface to improve the full cell performance via a dry mixing method. The LBO‐coated LNMO delivers much better cycling stability than the uncoated LNMO in full cells with a practical 3 mAh cm−2 areal capacity. Different characterizations are performed to understand the coating effect to track the boron and its impact on the cathode, electrolyte, and anode. The LBO‐coated LNMO owns a 5 nm cathode electrolyte interphase (CEI) with mitigated phase change after long‐term cycling. The uncoated LNMO has negligible CEI with obvious phase change. However, no boron can be detected on the surface of the coated sample. Electrolyte and anode analyses indicate that the coating acts as an additive reservoir, gradually dissolves into the electrolyte, and generates BF4− species. As a result, Nickel/Manganese (Ni/Mn) dissolution from LNMO and the extensive generation of solid electrolyte interphase (SEI) on the anode side is mitigated, thus improving the full‐cell cycling stability to a great extent. [ABSTRACT FROM AUTHOR]

Poling and structuring of ferroelectric domains form the basis for developing prospective applications using materials from the lithium‐niobate (LN) family. Applications range from second harmonic generation to electro‐optic modulators or surface acoustic wave devices. In the work presented here, hysteresis measurements are used as a standard method to quantitatively determine the poling properties of these ferroelectrics, including their spontaneous polarization Ps as well as their forward and reverse coercive fields Ec,+ and Ec,−. Systematic measurements that depend on parameters such as the ramp rate R of the applied poling voltage and the waiting time twait between domain inversions are investigated and compared between the congruent variants of LN, lithium tantalate (LT), their magnesium‐doped analogues, and stoichiometric LN. For bulk magnesium‐doped LN, for example, it is found that the resulting coercive field strongly depends on the speed of the voltage ramp, with Ec$E_{\text{c}}$ values ranging from 11 to 21 kV mm−1. These investigations are used as fundamental input for poling ferroelectric lithium niobate‐tantalate solids (LNT), a system that offers a high potential for tuning the material parameters beyond what is possible for LN or LT. [ABSTRACT FROM AUTHOR]

The correlation between photoluminescence in the near‐IR region and point defect centers in the LiNbO3 crystals co‐doped with Zn and Mg both by homogeneous and direct methods has been studied. X‐ray diffraction (XRD) analysis shows that the LiNbO3:Zn:Mg (4.68:0.9 mol%) crystal obtained by homogeneous doping has the least number of intrinsic defects compared to the others. It has been established that ZnLi defects stimulate photoluminescence (PL) in the near‐IR region of the luminescence spectrum in the LiNbO3:Zn:Mg crystals obtained by homogeneous doping. The LiNbO3:Zn:Mg (4.68:0.90 mol%) crystal has the maximum PL intensity and the LiNbO3:Zn:Mg (3.83:0.97 mol%) crystal has the minimum. Both crystals are doped homogeneously. Such defects as niobium vacancies (VNb) and niobium in the empty octahedron (Nboct) are suggested as luminescence quenchers in the co‐doped crystals. [ABSTRACT FROM AUTHOR]

We numerically demonstrate three-octave supercontinuum generation using the z-cut lithium niobate waveguide by dispersion engineering. The photonic waveguide structure is designed to exhibit anomalous dispersion when pumped at 1.55 $ \rmu {\rm m} $ μ m wavelength. By altering the waveguide width, tunable zero-dispersion wave generation has been achieved up to 6 $ \rmu {\rm m} $ μ m wavelength. Our findings show the broadest supercontinuum spanning in the mid-IR region using a lithium niobate platform, making it a promising candidate for various applications in optical communication, sensing, and imaging. [ABSTRACT FROM AUTHOR]

The linear optical response of lithium niobate under compressive as well as tensile stress is calculated from first principles. For this purpose, the elastic constants are computed with different exchange‐correlation functionals and compared with available experimental values. A good agreement with the measured quantities is obtained. A full set of the piezo‐optic and photoelastic coefficients is determined from the dependence of the dielectric permeability in the linear regime on the considered stress. The calculated coefficients agree with the experimental values as well. In contrast to the numerous experimental investigations, the coefficients are not only given for a single excitation wavelength but also within the technically relevant optical range. From the dispersion of the piezo‐optic and photoelastic coefficients, conclusions can be drawn about the refractive indices and the birefringence under strain for different excitation energies. It can be concluded that the birefringence in the long wavelength range increases under stress in the z direction. For uniaxial stress in x and y directions, the lattice symmetry is broken and the crystal becomes biaxial in the x and y directions as well. [ABSTRACT FROM AUTHOR]

A semiorganic lithium para-nitrophenolate dihydrate (LiPNP·2H2O) nonlinear optical crystal with a dimension of 18 × 11 × 4 mm 3 has been grown by slow evaporation method in a rapid growth period of 20 days by using ethanol as solvent. Powder X-ray diffraction studies revealed the crystal belong to monoclinic crystal system with space group of P21. The optical transmission study revealed a wider transparency with the lower cut-off wavelength of 457 nm and an optical bandgap of 2.91 eV. The emission properties, functional groups, and mechanical stability of the obtained crystal were determined by Photoluminescence, FTIR spectral analysis, and Vickers's microhardness measurements. The electrical conductivity and thermal stability were examined through electrochemical impedance (EIS) and TG-DTA analysis. The Second harmonic generation efficiency (SHG) of the crystal was found to be 2.6 times greater than that of the standard KDP. Therefore, LiPNP·2H2O crystal with high SHG efficiency could be a suitable candidate for nonlinear optical and optoelectronic device applications due to its optical, thermal, and mechanical properties. [ABSTRACT FROM AUTHOR]

Thin-film lithium niobate on insulator (LNOI) has recently emerged as an exciting platform for nonlinear integrated photonic devices, drawing parallels with the impact of silicon on insulator (SOI) in the electronic device realm. While the influence of interfacial states of SOI on electronic device performance, particularly their contribution to parasitic radio frequency (RF) losses, is well-documented, this aspect remains relatively unexplored in LNOI, despite their shared silicon/oxide interface structure. Here, we investigate the RF loss arising from mobile charges at the silicon/oxide interface of the LNOI platform. We show that this parasitic conduction can be exacerbated, especially during plasma etching, and leads to substantial RF losses. Through strategic incorporation of a trap-rich poly-silicon layer at this interface, we effectively eliminate this parasitic conduction, resulting in the suppression of RF losses. This work establishes crucial guidelines for harnessing LNOI in applications such as high-frequency electro-mechanical devices, high-speed electro-optic modulators, and high-efficiency microwave-to-optics converters. [ABSTRACT FROM AUTHOR]

The physical properties of near stoichiometric lithium niobate crystals (NSLN) can be improved by adding magnesium. For example, the light damage threshold of NSLN crystals mixed with a small amount of magnesium ions is higher than that of congruent lithium niobate (CLN) crystals mixed with high magnesium [1]. However, the current difficulties also lie in the deviation of SLN crystals from the congruent point, difficulty in growth, size limitation and uneven doping. SLN crystals are still not commercially available, and the size of the crystals is limited to two inches. We use the partial liquid phase method to synthesize polycrystalline materials of co-doped SLN crystals, and successfully solve the problem of uneven doping. The adjustment of process parameters and the use of continuous feeding technology greatly improved the success rate of SLN crystal growth. Then we characterized the grown NSLN crystal on optical and thermal properties. [ABSTRACT FROM AUTHOR]

Ultrafast laser‐excitation of lithium niobate (LiNbO3) crystal has triggered numerous photonic applications through the structural transitions in LiNbO3. However, the explanations for ultrafast laser‐induced modification of LiNbO3 have remained phenomenological, lacking a convincing in‐depth understanding of the fundamental laser‐lattice interaction process. Based on ab initio simulations, it is demonstrated that photoexcited anharmonic phonons play a significant role in influencing the lattice structure of LiNbO3. Harnessing the real‐time time‐dependent density functional theory, it is revealed that the excitation of TO4 phonons via electric‐phonon coupling triggers displacement‐induced lattice oscillations during multiphoton ionization. These oscillations give rise to multistage structural strains, resulting in alterations of the refractive index. Significantly, these modifications exhibit sensitivity to the incident laser energy. Experimentally, using the waveguide technique and micro‐Raman spectroscopy, the correlation between local refractive index, lattice volume density, and phonon vibrational modes has been established, exhibiting good consistency with theoretical predictions. This work provides an effective means to understand the ultrafast excitation of phonons and relaxation processes of the lattice in dielectric crystals. [ABSTRACT FROM AUTHOR]

A simple microwave photonic, reconfigurable, instantaneous frequency measurement system based on low-voltage thin-film lithium niobate on an insulator phase modulator is put forward and experimentally demonstrated. Changing the wavelength of the optical carrier can realize the flexibility of the frequency measurement range and accuracy, showing that during the ranges of 0–10 GHz, 3–15 GHz, and 12–18 GHz, the average measurement errors are 26.9 MHz, 44.57 MHz, and 13.6 MHz, respectively, thanks to the stacked integrated learning models. Moreover, this system is still able to respond to microwave signals of as low as −30 dBm with the frequency measurement error of 62.06 MHz, as that low half-wave voltage for the phase modulator effectively improves the sensitivity of the system. The general-purpose, miniaturized, reconfigurable, instantaneous frequency measurement modules have unlimited potential in areas such as radar detection and early warning reception. [ABSTRACT FROM AUTHOR]

Resonator-enhanced electro-optical (EO) combs could generate a series of comb lines with high coherence and stability. Recently, EO comb based on thin-film lithium niobate (TFLN) has begun to show great potential thanks to the high second-order nonlinearity coefficient of lithium niobate crystal. Here we demonstrate that EO comb envelope engineering based on mode crossing induced a quality factor reduction in the TFLN racetrack microcavity both in the numerical simulation and experiment. Our method paves the way for the generation of EO combs with an arbitrary envelope. [ABSTRACT FROM AUTHOR]

Raman microlasers form on-chip versatile light sources by optical pumping, enabling numerical applications ranging from telecommunications to biological detection. Stimulated Raman scattering (SRS) lasing has been demonstrated in optical microresonators, leveraging high Q factors and small mode volume to generate downconverted photons based on the interaction of light with the Stokes vibrational mode. Unlike redshifted SRS, stimulated anti-Stokes Raman scattering (SARS) further involves the interplay between the pump photon and the SRS photon to generate an upconverted photon, depending on a highly efficient SRS signal as an essential prerequisite. Therefore, achieving SARS in microresonators is challenging due to the low lasing efficiencies of integrated Raman lasers caused by intrinsically low Raman gain. In this work, high-Q whispering gallery microresonators were fabricated by femtosecond laser photolithography assisted chemo-mechanical etching on thin-film lithium niobate (TFLN), which is a strong Raman-gain photonic platform. The high Q factor reached 4.42 × 106, which dramatically increased the circulating light intensity within a small volume. And a strong Stokes vibrational frequency of 264 cm−1 of lithium niobate was selectively excited, leading to a highly efficient SRS lasing signal with a conversion efficiency of 40.6%. And the threshold for SRS was only 0.33 mW, which is about half the best record previously reported on a TFLN platform. The combination of high Q factors, a small cavity size of 120 μm, and the excitation of a strong Raman mode allowed the formation of SARS lasing with only a 0.46 mW pump threshold. [ABSTRACT FROM AUTHOR]

Four Zr: Dy: LiNbO3 crystals doped with different concentrations of Zr4+ (0, 1, 2, 4, mol%) have been grown by Czochraski technique. The effect of doping concentration of Zr4+ ions on the actual concentration of Zr4+ and Dy3+ ions in doped crystal was studied by the inductively coupled plasma-atomic emission spectrometry (ICP-AES). The results of X-ray diffraction and ultraviolet absorption spectroscopy showed that the Zr: Dy: LiNbO3 crystal still maintained the original lattice structure of the pure lithium niobate crystal, and the doped ions entered the crystal by preferential substitution of $ \hbox{Nb}^{4+}_{\rm Li} $ Nb Li 4 + , and doped ions entered the crystal When $ \hbox{Nb}^{4+}_{\rm Li} $ Nb Li 4 + is completely replaced, ions are doped to replace the normal Nb and Li positions into the crystal. The lattice constant with the increase of Zr content shows a trend of first becoming larger and then smaller. Finally, the optical uniformity of Zr4+ doped concentration on Zr: Dy: LiNbO3 crystals was studied by birefringence gradient method. The results showed that with the increase of Zr4+ ion doping concentration, the crystal optical uniformity of Zr: Dy: LiNbO3 gradually increased, and the optical uniformity reached the highest when doped at a concentration of 4 mol%. Based on the Li-site vacancy model, the experimental results are discussed in detail. [ABSTRACT FROM AUTHOR]

This work elucidates the impact of strain on the optical and electronic properties of Fe-doped lithium niobate using density functional theory. The Fe-doped lithium niobate is applied with the tensile and compressive strain (10% and 20%) and optical properties are analyzed. Lithium niobate, a large bandgap material (bandgap 3.56 eV), has absorption limited to the UV region of the optical spectrum only. For the Fe-doped lithium niobate, the bandgap is 1.38 eV, with low absorption in the visible region. The computed results show that the tensile and compressive strains have significantly narrowed down the bandgap of Fe-doped lithium niobate in compression to the unstrained structures. The decrease in the bandgap is largest for the tensile strain of 20% among all the applied strains. Further, visible light absorption is also improved due to the application of strain. The improvement in visible light absorption is highest for the tensile strain of 20% with absorption completely shifted in the desired visible region. The improved visible absorption due to the applied strain makes Fe-doped lithium niobate a potential candidate for optoelectronics and solar applications. [ABSTRACT FROM AUTHOR]

Birefringence, quantified as the maximum effective index difference of two orthogonally polarized modes, is one of the key characteristics of Lithium Niobate on Insulator (LNOI) waveguide devices. As LNOI optical properties strongly depend on the polarization of the propagating light beam, achieving the zero‐birefringence condition (ZBC) is highly desired. In this work, a rib LNOI waveguide is designed, and the influence of geometrical dimensions on the birefringence is characterized. From the result, the slab's height is found to be the dominant geometrical factor that significantly contributes to the birefringence, with an optimum slab's height found at 50 nm. For this optimized value, the influence of width and wavelength on birefringence are characterized. The analysis is extended to investigate the properties of group indices that can result in the temporal walk‐off phenomenon. This phenomenon can significantly impact the performance of single‐photon devices, as it can cause a polarization mismatch between the incident photon and the polarization properties of the medium, resulting in reduced efficiency of devices such as single‐photon detectors. In the analysis, the zero birefringence and walk‐off are achieved at narrow waveguide width, 푤 of 250 nm and wavelength, λ${\mathrm{\lambda }}$ = 1500 nm, which is within the telecommunication region band. [ABSTRACT FROM AUTHOR]

Lithium niobate (LiNbO3, LN) is a kind of multi-functional uniaxial ferroelectric material, and is widely used in optical modulators, optical frequency combs, optical waveguides, and so on. The emergence of conductive domain wall (DW), serving as a nanoscale conductive path embedded in the insulating materials and showing important application prospects in non-volatile memristor, logic gate, and transistor, etc., promoted the application of LN in the field of nano-optoelectronics. The realization of DW p-n junction in LN on an insulator (LNOI) is expected to push forward the development of opto-electronics integrated chips based on LN. This paper provides a concise review on the study of DWs in LN, including the fabrication techniques, the conduction mechanism and types of DWs as well as the development of applications based on DWs, especially the achievement of DW p-n junction. Furthermore, combined with the hot potential applications, the key issues, challenges and opportunities in the development DW-based opto-electronic devices based on LN were summarized. [ABSTRACT FROM AUTHOR]

Lithium niobate film on insulator (LNOI) is increasingly applied in the field of key devices in the new generation of information technology. With the development of the techniques of lithium niobate single crystal thin film and photonic integrated circuits, low cost, high integration is the eternal development direction. Therefore, it is urgently needed the largescale lithium niobate crystal. In this paper, the variation of natural convection of melt in large-sized crucible as the liquid level decrease was discussed, and the growth characteristics of Z- and X-axis lithium niobate crystal were discussed. The 8-inch Zand X-axis lithium niobate crystals with the size of larger than ϕ210 mm × 50 mm were obtained. The transmission of the spectral range of 380 ~ 3 300 nm is more than 70% for 1 mm thick X-axis lithium niobate wafers. The chip moire pattern images show the presence of refractive index ripple defects in the crystal, indicating that the quality of the crystal still needs improvement. [ABSTRACT FROM AUTHOR]

A method of surfactant-mediated photovoltaic transportation is proposed in this paper, the surfactant (span 80) layers self-assembled at the water-oil and oil-LN interfaces are employed to isolate photovoltaic charges in this method. The reduced electrostatic attenuation, remarkable hydrophobicity, and strong electrical breakdown suppression of the surfactant layers enable the stable and swift transportation of fL-scale aqueous microdroplets using μW-level laser in an oil medium. Three kinds of microdroplet responses to the laser illumination (unresponsive, repulsive and attractive cases) was found. With the increase of surfactant concentration, the driving mechanism can transit from the coulomb repulsion to the dielectrophoretic attraction that facilitates the photovoltaic transportation. Besides, the minimal laser power required for the attractive response was found correlated with the NaCl concentration inside the microdroplet. [ABSTRACT FROM AUTHOR]

In theory, quasi phase match (QPM) can make full use of nonlinear optical coefficient of the crystal, and has no deviation effect, which has great advantages in optical frequency conversion. Lithium niobate crystal (LiNbO3, LN) has high nonlinear optical coefficient, wide optical range and low growth cost, causing the periodically poled lithium niobate crystal (PPLN) based on the design of ferroelectric domain structure is an ideal choice for QPM. At present, the most commonly used method for fabricating PPLN crystal is applied electric field method. In the fabrication process, the parameters of electrode structure are important for the poling process. Based on the electric field poling process under real-time monitoring and finite element analysis, this paper analyzed the spatial electric field distribution of different electrode structures. It is found that the electric field maximum appears at the edge of the electrode, the electric field distribution inside the electrode is relatively uniform. Based on this phenomenon, a design scheme of multi-channel electrode structure is proposed to achieve uniform distribution of electric field in poled area. By characterizing the duty cycle ratio of each channel, it is found that the duty cycle ratio of the inner eight channels are uniform and within 50% ±5%. Through the SHG experiment of crystals, it is found that the nonlinear conversion efficiency of the inner channel relative to the edge channel in the sample of ten-channel periodic poling is significantly improved and uniformly distributed. It is proved that the middle channels have a uniform poling structure with controllable duty cycle, which provides an effective design for generating uniform poling electric fields. [ABSTRACT FROM AUTHOR]

Lithium niobate is an artificial crystal which integrates electro-optic, acousto-optic, piezoelectric and nonlinear properties, and has been known as "optical silicon" or "photonic silicon". In recent years, with the rapid development of integrated photonics based on thin film lithium niobate, lithium niobate crystals have received more and more attention. However, lithium niobate is a typical non-stoichiometric crystal, it contains a large number of intrinsic defects, which seriously affects its characteristics. The lithium niobate lattice has good solid-solution to many impurity ions, moreover, its properties vary significantly with the types and concentrations of dopants. As with defect engineering of semiconductors such as silicon, defects have and will continue to have an important effect on crystal performance and integrated photonics based on thin film lithium niobate. This paper briefly reviews the defect structure of lithium niobate crystals, especially the recent progress on thin film lithium niobate crystals, including the intrinsic defect structure, extrinsic defect structure, characterization of defect structure, theoretical calculation of defect structure, and structure-activity relationship between defect structure and crystal properties. We hope it helpful to the current research of lithium niobate integrated photonics. [ABSTRACT FROM AUTHOR]

Lithium niobate crystal has many advantages such as large electro-optical, piezoelectric and non-linear optical coefficients, wide optical transparency range, compatibility with speed matching, phase matching and dispersion engineering, long-term stability and low-cost preparation of optical-grade wafers. As an important platform for constructing optoelectronic devices such as electro-optic modulators, optical frequency combs and optical waveguides, lithium niobate holds grant promise in the fields of light generation, light transmission and light modulation in the field of information and communication. Lithium niobate is also well known as the "silicon of photonics" and has huge integration potential in both academia and industry. However, due to the insulator and weak optical absorption properties of lithium niobate, integrated application fields based on lithium niobate platforms also face the problems of low photo-to-electric conversion efficiency and thus arouse difficult in photodetection. Light demodulation and light extraction in all-optical communications require high-performance detectors, therefore, the development of photodetectors based on lithium niobate has great scientific significance and application value. Starting from the basic structural characteristics of lithium niobate, this article introduces in detail the excellent physical properties and photo-to-electric conversion mechanism of lithium niobate, reviews some recent research results of domestic and foreign scholars, and focuses on the optical waveguide integrated photodetectors and the heterogeneous type photodetectors based on lithium niobate crystals, the advantages and development potential of different routes are discussed and compared, and prospects for this field are proposed. [ABSTRACT FROM AUTHOR]

A single-frequency narrow linewidth green laser at 510 nm is a vital component for the study of Cesium Rydberg atoms. Here, we demonstrate a 510 nm laser based on single-pass second-harmonic generation (SHG) and sum-frequency generation (SFG) via waveguide Periodically Poled Lithium Niobate (PPLN) seeded with a common C-band laser (1530 nm). The final linewidth measured using the delayed self-heterodyne method reaches a narrow linewidth of 4.8 kHz. And, the optical-to-optical conversion efficiency is up to 13.1% and reaches an output power up to 200 mW. [ABSTRACT FROM AUTHOR]

Quantum transducers are key components for hybrid quantum networks, enabling the transfer of quantum states between microwave and optical photons. In the quantum community, many efforts have focused on creating and verifying the entanglement between microwave and optical fields in systems that typically operate at temperatures in the millikelvin range. Our goal is to develop an integrated microwave optical entanglement device based on a lithium niobate whispering gallery mode resonator (WGMR). To investigate the feasibility of developing such an integrated device, first, a passive photonic integrated circuit (PIC) was designed, fabricated, and characterized. The PIC was developed on a thin-film lithium niobate (TFLN) on an insulator platform, and it includes eight ring resonators and four asymmetric Mach–Zehnder interferometers. This paper presents the design and operational principles of the integrated device for microwave–optical entanglement, as well as the results of the characterization of the passive PIC. [ABSTRACT FROM AUTHOR]

As ferroelectric materials, lithium tantalate and lithium niobate share similar material characteristics, such as a high Pockels effect and nonlinear optical coefficients. When compared to lithium niobate, lithium tantalate offers a higher optical damage threshold, a broader transparent window, and lower birefringence, making it a promising candidate for high-performance electro-optical photonic integrated devices. In this study, we design and successfully fabricate micro-ring resonators on an acoustic-grade lithium-tantalate-on-insulator wafer, demonstrating their tunability and dynamic modulation capabilities. Experimental results indicate that the achieved thin-film lithium tantalate based micro-ring resonator exhibits an intrinsic Q-factor of 8.4 × 105, corresponding to a waveguide propagation loss of 0.47 dB/cm and a tuning efficiency of 1.94 pm/V. More importantly, as compared to those based on thin-film lithium niobate, a much weaker photorefractive effect and drift phenomenon around the 1550 nm wavelength under a direct-current drive are observed in the present fabricated thin-film lithium tantalate micro-rings with a silicon oxide over-cladding and a tuning electrode on top. [ABSTRACT FROM AUTHOR]

In this study, one-dimensional grating coupler on single-crystal lithium niobate thin film (lithium niobate on insulator, LNOI) that also served as a polarization splitter was designed. The coupler could separate both orthogonal polarization states into two opposite directions while coupled light from a standard single-mode fiber to a waveguide on LNOI at the same time. Using segmented and apodized designing, the peak coupling efficiencies (CEs) around telecommunication wavelength 1550 nm for fundamental TE and TM modes of −2.82 dB and −2.83 dB, respectively, were achieved. The CEs could be optimized to −1.97 dB and −1.8 dB when a metal layer was added below the silicon dioxide layer. [ABSTRACT FROM AUTHOR]

Structural changes of Er- or Yb-ion doped LiNbO3 (LN) nanocrystals were studied in relation to the high-energy ball milling process. The evolution of the size of the particles and the formation of different phases were followed by dynamic light scattering and X-ray diffraction measurements, while the electronic transitions of rare-earth (RE) ions were investigated by absorption spectroscopy in the infrared spectral range. During the milling process, RE ions left the crystal lattice and an RE2O3 phase appeared to an increasing extent next to the LN. The change in the absorption spectra and the phases formed during the grinding process were found to be very similar for both investigated RE ions and were independent of their original concentration in the starting crystal samples. The extent of the RE loss was found to be 90% after 100 min of wet grinding. [ABSTRACT FROM AUTHOR]

The design, fabrication, and validation of a thin-film lithium niobate on insulator (LNOI) electro-optic (EO) time-domain terahertz (THz) wave detector is reported. LNOI offers unprecedented properties for the EO detection of freely propagating THz wave radiation pulses and transient electric fields because of the large EO coefficient of the material, engineering of the velocity matching of the THz wave and optical wave, and much reduced detector size. The proof-of-concept device is realized using thin-film lithium niobate optical waveguides forming a Mach–Zehnder interferometer with interferometer arms electrically poled in opposite directions. THz waves are coupled effectively to the fully dielectric device from free space without using antennas or plasmonics. The detection of THz waves with frequencies up to 800 GHz is successfully demonstrated. The detector allows for the detection of THz frequency electric fields up to 4.6 MV/m. The observed frequency response of the device agrees well with theoretical predictions. [ABSTRACT FROM AUTHOR]

Efficient fiber-to-chip couplers for multi-port access to photonic integrated circuits are paramount for a broad class of applications, ranging, e.g., from telecommunication to photonic computing and quantum technologies. Grating-based approaches are often desirable for providing out-of-plane access to the photonic circuits. However, on photonic platforms characterized by a refractive index ≃ 2 at telecom wavelength, such as silicon nitride or thin-film lithium niobate, the limited scattering strength has thus far hindered the achievement of coupling efficiencies comparable to the ones attainable in silicon photonics. Here we present a flexible strategy for the realization of highly efficient grating couplers on such low-index photonic platforms. To simultaneously reach a high scattering efficiency and a near-unitary modal overlap with optical fibers, we make use of self-imaging gratings designed with a negative diffraction angle. To ensure high directionality of the diffracted light, we take advantage of a metal back-reflector patterned underneath the grating structure by cryogenic deep reactive ion etching of the silicon handle. Using silicon nitride as a testbed material, we experimentally demonstrate coupling efficiency up to − 0.55 dB in the telecom C-band with high chip-scale device yield. [ABSTRACT FROM AUTHOR]

Photocatalysts for oxidation reactions are crucial for a wide variety of industrial activities. Here, we describe a framework consisting of silver nanomaterials atop Mg-doped lithium niobate. This substrate under white light irradiation is demonstrated to support the oxidation of compounds, such as p-aminothiophenol, through the activation of charge transfer processes. This study highlights the use of doped lithium niobate materials as semiconductor platforms for plasmonic photocatalysis. [ABSTRACT FROM AUTHOR]

The complete matrix parameters of the elastic, dielectric, and piezoelectric constants of high-quality Fe-doped KTa 1-x Nb x O 3 (KTN) single crystals poled along [001] PC were successfully confirmed. The piezoelectric coefficients d 33 and k 33 , which are of interest for various applications, are 137 pC/N and 50.4 %, respectively. The orientation dependence of these properties for the single-domain Fe:KTN samples was calculated, and it was found that the [001] PC direction is the optimal orientation for the highest performance with a single-domain state, at which the sample exhibits good transparency. Further, the single-domain sample exhibits a large effective electro-optical coefficient (γ c = 126.6 p.m./V), and the combined piezoelectric and electro-optical effects provide a 0.4 % electro-optical coefficient. This is beneficial for applying high-response speed modulators with an effective electro-optical working mode and a low contribution of the inverse piezoelectric effect, owing to slower frequency response characteristics. [ABSTRACT FROM AUTHOR]

Lithium niobate is a lead-free material which has attracted considerable attention due to its excellent optical, piezoelectric, and ferroelectric properties. This research is devoted to the synthesis through an innovative sol–gel/spin-coating approach of polycrystalline LiNbO3 films on Si substrates. A novel single-source hetero-bimetallic precursor containing lithium and niobium was synthesized and applied to the sol–gel synthesis. The structural, compositional, and thermal characteristics of the precursor have been tested through attenuated total reflection, X-ray photoelectron spectroscopy, thermogravimetric analysis, and differential scanning calorimetry. The LiNbO3 films have been characterized from a structural point of view with combined X-ray diffraction and Raman spectroscopy. Field-emission scanning electron microscopy, energy dispersive X-ray analysis, and X-ray photoelectron spectroscopy have been used to study the morphological and compositional properties of the deposited films. [ABSTRACT FROM AUTHOR]

The current and future energy demands require high‐performance batteries with stable long‐term cycling, high capacities, and fast‐charging capabilities. In recent years, niobate compounds have gained significant research interests due to their attractive properties suited for battery applications. In this work, cobalt niobate, CoNb2O6, was synthesized via a simple and scalable solid‐state mechanochemical method through high‐energy ball milling, mechanical treatment (pellet formation), and calcination at 900 °C. The resulting product is a pure, columbite‐type (orthorhombic) cobalt niobate based on XRD findings. Electrochemical testing in a half‐cell against Li/Li+ of the as‐prepared free‐standing cobalt niobate anode material revealed a highly reversible process of lithiation (discharge) and delithiation (charge), with increasing pseudocapacitive behavior at higher scan rates. At 0.1 A g−1, the observed initial discharge capacity was about 900 mAh g−1. The synthesized CoNb anode material displayed an impressive rate performance, which involved increased stability at elevated current densities. During prolonged cycling tests, the anode material displayed extremely stable cycling vs Li/Li+, even at 2 A g−1, delivering a specific capacity of 700 mAh g−1 in the initial cycle, followed by a relatively constant capacity of 150 mAh g−1 throughout the majority of 5000 cycles completed. Post‐mortem analysis illustrated the reversibility of the cobalt niobate anode material and confirmed the growth and partial breakdown of the SEI film. With the results obtained from this work, cobalt niobate is full of potential as an anode material for Li‐ion battery applications. [ABSTRACT FROM AUTHOR]

Discerning weak electric fields has important implications for cosmology, quantum technology, and identifying power system failures. Photonic integration of electric field sensors is highly desired for practical considerations and offers opportunities to improve performance by enhancing microwave and lightwave interactions. Here, we demonstrate a high-Q microcavity electric field sensor (MEFS) by leveraging the silicon chip-based thin film lithium niobate photonic integrated circuits. Using the Pound-Drever-Hall detection scheme, our MEFS achieves a detection sensitivity of 5.2 μV/(m Hz ), which surpasses previous lithium niobate electro-optical electric field sensors by nearly two orders of magnitude, and is comparable to atom-based quantum sensing approaches. Furthermore, our MEFS has a bandwidth that can be up to three orders of magnitude broader than quantum sensing approaches and measures fast electric field amplitude and phase variations in real-time. The ultra-sensitive MEFSs represent a significant step towards building electric field sensing networks and broaden the application spectrum of integrated microcavities. Here the authors develop a chip-scale thin-film lithium niobate microcavity electric field sensor enabling real-time amplitude and phase measurements of various electric field waveforms. [ABSTRACT FROM AUTHOR]

Photodetectors (PDs) based on 2D materials are promising for photonics integration, offering fast response times, high responsivities, and low‐noise detection across a wide range of wavelengths. Here, a novel PD structure consisting of a 35‐nm‐thick SnSe2 layer covering a proton‐exchanged thin‐film lithium niobate (TFLN) waveguide is presented. This device displays ultrasensitive bidirectional photoresponse characteristics at various wavelengths and can detect photon energies below the SnSe2 bandgap. Under irradiation at 850 and 450 nm, the device exhibits a positive photoresponse driven by the photoconductive effect, achieving high responsivity of 761.78 A W−1 (0.95 nW) and 694.91 A W−1 (2.125 nW), respectively. Conversely, under irradiation at 1550 and 1310 nm, the device exhibits a negative photoresponse driven by the bolometric effect. The responsivity and response/recovery times under 1550 nm irradiation are measured to be 3.13 A W−1 (578 nW) and 21.3/20.4 ms, respectively. The PD exhibits one of the highest responsivities reported for 2D material‐integrated waveguide PDs. This high‐performance SnSe2/TFLN waveguide PD has broad potential for application in optical communication and multifunctional photonic circuits in the visible to near‐infrared (NIR) band. [ABSTRACT FROM AUTHOR]

Micromechanical resonators operating above 100 GHz are favorable candidates for quantum physics studies due to their stronger ability to withstand thermal fluctuations, allowing them to remain in the quantum ground state even at kelvin temperatures. Furthermore, electromechanical resonators at sub-terahertz frequencies enable high-speed data transfer in modern communication technologies, making them attractive for communication industries. Recently, sub-terahertz electromechanics has been demonstrated on z-cut thin-film lithium niobate. Yet, the x-cut thin-film lithium niobate is more advantageous for scaling above 100 GHz due to its faster acoustic velocity. Here, we report sub-terahertz electromechanics on x-cut thin-film lithium niobate utilizing the thickness-longitudinal mode. In addition, we study the orientation dependence of these mechanical resonators due to the anisotropy of lithium niobate. We find that devices with a cross section close to the xy plane can be more efficiently excited, in contrast to those near the xz plane. This difference stems from the orientation-dependent nature of the e12 piezoelectric coupling element of the x-cut lithium niobate film. This investigation could assist in optimizing resonator designs by choosing the crystallographic direction that offers the best performance for specific functionalities. [ABSTRACT FROM AUTHOR]

Optical microcavity has proven its potential for unlabeled sensing. Here, we propose and demonstrate in a lithium niobate on insulator microcavity an enhanced sensing approach enabled by the nonlinear mode oscillation generated by the competition between thermal-optic and photorefractive effect, which breaks the intrinsic limitation in wavelength resolution set by the cavity's optical quality factor. It allows us to perform precise measurements of the mode shifting introduced by a nanoscale scatterer with a signal to noise ratio of 13.1 dB and paves a distinctive way to improve resonance shift resolution in widely studied microcavity sensors with a platform of great integration capability. [ABSTRACT FROM AUTHOR]

Doping uniformity has a significant impact on crystal growth process, crystal quality and performance, so it is very important to propose and improve the preparation process of polycrystalline materials to achieve uniformly doped lithium niobate crystal growth. The synthesis of crystal polycrystalline material is one of the preparatory works before crystal growth, and also the most important step before crystal growth. The quality of crystal polycrystalline material is directly related to the quality of single crystal. Partial liquid phase method combines the advantages of solid phase method and liquid phase method, which is a superior synthesis method of polycrystalline materials. In this paper, we synthesized lithium niobate polycrystalline powder by partial liquid phase method and characterized the powder to guarantee the quality. [ABSTRACT FROM AUTHOR]

A congruent lithium niobate crystal doped with MgO particles was grown and processed. By scanning electron microscope (SEM), it can be seen that magnesium oxide exists in the form of inclusion in the crystal matrix. The mapping function of the electron probe can detect the element composition of the inclusions. The samples required for transmission electron microscope(TEM) were prepared by ion thinning method. The magnesium oxide particles were found by TEM, and the lattice phase at the interface between magnesium oxide and lithium niobate was obtained. The lattice phase analysis confirms that magnesium oxide can enter the lattice of lithium niobate in the form of ions. Finally, the sample was observed by piezoresponse force microscopy. [ABSTRACT FROM AUTHOR]

The results of experimental studies, theoretical analysis and numerical simulations of the features of the volume transmission holograms' formation by the interference pattern of laser beams with high contrast in the X-cut LiNbO3:Cu, fabricated by diffusion from a metal film, are presented. Analytic formulas that take the inhomogeneities of the distribution of copper ions and the absorption index of recording beams over the thickness of the sample into account are derived to describe the time evolution of the amplitude of the first spatial harmonic of the field. The material parameters of the LiNbO3:Cu structure are estimated. A comparative analysis of the spatial distribution of the amplitude of the first harmonic of the photorefractive hologram's field in two types of LiNbO3:Cu structures is performed. We concluded that it is necessary to use X‑cut LiNbO3:Cu diffusion structures characterized by similar distributions of impurity centers, which maximums are localized near the boundary used to capture micro- and nanoparticles, for the implementation of photovoltaic tweezers. [ABSTRACT FROM AUTHOR]

With the development of miniaturization and integration, multifunctional optical devices are necessary. However, its practical realization is a critical challenge due to the lack of simple structures with multiple functionalities. Here, a multimode metasurface is proposed by simply placing polymer nanocubes on the lithium niobate (LN) thin film. The intriguing properties of the integrated structure include high‐quality (Q) factors and different spectral characteristics, associated with quasi‐guide modes (GM) and Mie modes, respectively. The experiment demonstration reveals that Q factors of four modes are larger than 1000 and a second harmonic generation (SHG) enhancement factor of 25.4 is obtained, featuring strong light‐matter interaction. Importantly, the abundant spectral characteristics greatly boost three degrees of freedom, i.e., polarization, incident angle, and slot, to realize multifunctional designs. The results provide a sophisticated platform for developing high‐performance LN metasurfaces with the advantages of simplified fabrication processes and multifunctionality. The strategy can also be extended to other material systems, enabling the flexibility of metasurface‐inspired subwavelength engineering. [ABSTRACT FROM AUTHOR]

Terahertz (THz) phonon polaritons, fundamental quasi‐particles that couple lattice vibrations with electromagnetic fields at THz frequencies, are found in a variety of materials that offer the potential for a wide range of THz optoelectronic devices and on‐chip integrated systems. However, these compact devices and on‐chip systems are hampered by the absence of on‐chip powerful THz phonon polariton sources. In this study, the efficient generation and amplification of THz phonon polaritons are proposed and directly visualized on a lithium niobate (LN) chip via a tilted pulsefront phase matching technique. By combining lateral pumping and phase matching schemes, two orders of magnitude are successfully attained in the interaction distance between the pump light and the LN chip, accompanied by a substantial amplification of generated THz phonon polariton. The results of this study may lead to abundant potential applications in chip scale THz photonic devices and systems based on LN materials and its integrated heterostructures. [ABSTRACT FROM AUTHOR]

Generated in high‐Q optical microresonators, dissipative Kerr soliton microcombs constitute broadband optical frequency combs with chip sizes and repetition rates in the microwave to millimeter‐wave range. For frequency metrology applications such as spectroscopy, optical atomic clocks, and frequency synthesizers, octave‐spanning soliton microcombs generated in dispersion‐optimized microresonators are required, which allow self‐referencing for full frequency stabilization. In addition, field‐deployable applications require the generation of such soliton microcombs to be simple, deterministic, and reproducible. Here, a novel scheme to generate self‐emerging solitons in integrated lithium‐niobate microresonators is demonstrated. The single soliton features a broadband spectral bandwidth with dual dispersive waves, allowing 2f–3f self‐referencing. Via harnessing the photorefractive effect of lithium niobate to significantly extend the soliton existence range, a spontaneous yet deterministic single‐soliton formation is observed. The soliton is immune to external perturbation and can operate continuously for over 13 h without active feedback control. Finally, via integration with a pre‐programmed distributed feedback (DFB) laser, turnkey soliton generation is demonstrated. With further improvement of microresonator Q and hybrid integration with chip‐scale laser chips, compact soliton microcomb devices with electronic actuation can be created, which can become central elements for future LiDAR, microwave photonics, and optical telecommunications. [ABSTRACT FROM AUTHOR]

Herein, an on‐chip 8‐channel thin‐film lithium niobate (TFLN) arrayed waveguide grating (AWG) is designed and the device is fabricated using photolithography‐assisted chemo‐mechanical etching technique. The transmission of the fabricated TFLN AWG near the central wavelength of 1550 nm is experimentally measured. An on‐chip loss as low as 3.32 dB, a single‐channel bandwidth of 1.6 nm, and a total‐channel bandwidth of 12.8 nm are obtained. The cross talk between adjacent channels is measured to be below −3.83 dB within the wavelength range from 1543 to 1558 nm, and the cross talk between nonadjacent channels is below −15 dB. [ABSTRACT FROM AUTHOR]

Fiber-chip edge couplers can minimize mode mismatch in integrated lithium niobate (LiNbO3) photonics via facilitating broad optical bandwidth coupling between optical fibers and waveguide circuits. We designed a high-efficiency multi-tip edge coupler utilizing the lithium niobate on insulator (LNOI) platform for achieving superior fiber-to-chip coupling. The device comprises a bilayer LN inversely tapered waveguide, three 3D inversely tapered waveguides, and a silicon oxynitride (SiON) cladding waveguide (CLDWG). Finite difference method (FDM) and eigenmode expansion (EME) simulations were utilized to simulate and optimize the edge coupler structure specifically within the 1550 nm band. This coupler demonstrates a low fiber-chip coupling loss of 0.0682/0.0958 dB/facet for TE/TM mode at 1550 nm when interfaced with a commercially cleaved single-mode fiber (SMF) with a mode field diameter (MFD) of approximately 8.2 μm. Moreover, the 1 dB bandwidth of the coupler is 270 nm for the TE mode and 288 nm for the TM mode. Notably, the coupler exhibits a relatively large tolerance for optical misalignment owing to its large mode spot size of up to 4 μm. Given its ultra-low loss, high-efficiency ultra-broadband capabilities, and substantial tolerance features, this proposed device provides a paradigm for fiber-to-chip edge coupling within lithium niobate photonics. [ABSTRACT FROM AUTHOR]

The work presents the design, a 2D and 3D finite element method (FEM) simulation, analysis, and optimization of a surface acoustic wave (SAW) based gas sensor. The simulation of SAW gas sensors with and without the presence of nanorods is performed. Gas adsorption on a surface causes a change in the mass, modulus, and conductivity of the sensing layer, which can be accurately, detected using SAW-based gas sensors. The device is constructed using a YZ-cut lithium niobate as a substrate, which is covered by a 0.2 µm thick intermediate layer upon which ZnO nanorods are present operating at 4 µm wavelength. Simulations in COMSOL Multiphysics are performed using eigen frequency, time-dependent, and frequency domain analysis. The materials of the intermediate layer as well as interdigitated transducers (IDTs) and the height of the nanorods are varied for the optimization of the device. The frequency shift and total displacement were seen to be significantly improved for the nanorod-based SAW gas sensor device. [ABSTRACT FROM AUTHOR]

Silicon, renowned for its applications in electronic circuits, also offers significant advantages in the realm of integrated optics. While silicon does have inherent limitations in fabricating active devices, these challenges can be overcome through heterogeneous integration with other materials. Ferroelectric materials like lithium niobate (LN) and barium titanate (BTO) exhibit exceptional electrical and nonlinear optical properties, making them ideal candidates for integrated silicon photonics. Over the past few decades, the LN platform has made substantial progress, surmounting obstacles such as manufacturing difficulties, high waveguide losses, and low modulation bandwidth caused by wide electrode spacing. Consequently, LN-based devices have found widespread application in various fields. With the advent of high-quality, large-size LN on insulator wafers, LN photonics has become a burgeoning research area. At the same time, the ferroelectric material BTO, with its tremendous electro-optic response, shows promise for the next generation of integrated photonics. Recent studies have highlighted the remarkable performance of BTO-based modulators, which offer smaller device sizes compared to LN by achieving lower half-wave voltages. This comprehensive review presents various fabrication methods for integrating LN and BTO thin films on silicon, focusing on recent advancements. We discuss their electro-optic responses and provide an overview of the diverse applications enabled by these platforms. Finally, we summarize the current state of integrated LN and BTO photonics research and offer insights into future directions. [ABSTRACT FROM AUTHOR]

The piezoelectric thin film composed of single-crystal lithium niobate (LiNbO3) exhibits a remarkably high electromechanical coupling coefficient and minimal intrinsic losses, making it an optimal material for fabricating bulk acoustic wave resonators. However, contemporary first-order antisymmetric (A1) Lamb mode resonators based on LiNbO3 thin films face specific challenges, such as inadequate mechanical stability, limited power capacity, and the presence of multiple spurious modes, which restrict their applicability in a broader context. In this paper, we present an innovative design for A1 Lamb mode resonators that incorporates a support-pillar structure. Integration of support pillars enables the dissipation of spurious wave energy to the substrate, effectively mitigating unwanted spurious modes. Additionally, this novel approach involves anchoring the piezoelectric thin film to a supportive framework, consequently enhancing mechanical stability while simultaneously improving the heat dissipation capabilities of the core. [ABSTRACT FROM AUTHOR]