Nonlinear Optical Devices Research Articles

All-optical switching of an epsilon-near-zero plasmon resonance in indium tin oxide

Nonlinear optical devices and their implementation into modern nanophotonic architectures are constrained by their usually moderate nonlinear response. Recently, epsilon-near-zero (ENZ) materials have been found to have a strong optical nonlinearity, which can be enhanced through the use of cavities or nano-structuring. Here, we study the pump dependent properties of the plasmon resonance in the ENZ region in a thin layer of indium tin oxide (ITO). Exciting this mode using the Kretschmann-Raether configuration, we study reflection switching properties of a 60 nm layer close to the resonant plasmon frequency. We demonstrate a thermal switching mechanism, which results in a shift in the plasmon resonance frequency of 20 THz for a TM pump intensity of 70 GW cm−2. For degenerate pump and probe frequencies, we highlight an additional two-beam coupling contribution, not previously isolated in ENZ nonlinear optics studies, which leads to an overall pump induced change in reflection from 1% to 45%.

From Fano to Quasi-BIC Resonances in Individual Dielectric Nanoantennas.

Sharp optical resonances in high-index dielectric nanostructures have recently attracted significant attention for their promising applications in nanophotonics. Fano resonances, as well as resonances associated with bound states in the continuum (BIC), have independently shown a great potential for applications in nanoscale lasers, sensors, and nonlinear optical devices. Here, we demonstrate experimentally a close connection between Fano and quasi-BIC resonances excited in individual dielectric nanoantennas. We analyze systematically the resonant response of AlGaAs nanoantennas pumped with a structured light in the near-infrared range. We trace a variation of the scattering spectrum that fully agrees with an analytical expression governed by a Fano parameter and observe directly a transition to a quasi-BIC resonance. Our results suggest a unified approach toward the analysis of sharp resonances in subwavelength nanostructures originating from strong coupling of optical modes that can provide high energy localization for enhanced light-matter interactions.

Investigation on the optical, spectral, electrical, mechanical, and laser damage threshold studies of bis (4-acetylanilinium) tetrachloridozincate (B4ATCZ) crystal

An efficient semi-organic nonlinear optical bis (4-acetylanilinium) tetrachloridozincate [(C8H10NO)2 ZnCl4] (B4ATCZ) single crystal was synthesized and successfully grown by the slow evaporation method. The single-crystal X-ray diffraction data confirm that B4ATCZ crystallized into an orthorhombic crystal system (Cmca). The UV–Vis–NIR transmittance spectrum was taken to assess the optical transmission, cut-off wavelength, and bandgap energy. The TG–DSC investigation ensures that the B4ATCZ is stable up to 235 °C. The mechanical behavior of the B4ATCZ compound was determined by Vickers Microhardness analysis. The surface laser-induced damage threshold value of the grown B4ATCZ crystal was endowed to be 19.78 GW/cm2 on testing with 1064 nm Nd: YAG laser radiation. The positive photoconductive properties and charge transport mechanism of B4ATCZ crystal were analyzed through photoconductivity and dielectric studies. The electron excitation and lifetime measurements of the molecules in the B4ATCZ crystal were studied by fluorescence spectral analysis. The HOMO–LUMO analysis evidently interprets the occurrence of N–H⋯O and N–H⋯Cl intermolecular hydrogen bonds influencing the charge transfer in the system. The electrostatic potential surface reveals the possible sites for hydrogen bonding electrophilic and nucleophilic interactions. Third-order nonlinear optical activity evaluated by the Z-scan measurements indicates the self-focusing and reverse saturable absorption in the crystal. The aforesaid results affirm that the metal-organic B4ATCZ is a potential material for optoelectronic and nonlinear optical device applications.

Experimental and Theoretical Studies on Effects of Structural Modification of Tin Nanoclusters for Third-Order Nonlinear Optical Properties

Tin oxide based materials have attracted much attention as new sources for nonlinear optical (NLO) devices, while the electronic mechanism behind the structure and nonlinearity is still unclear. In this work, by precisely controlling different functionalization ligands, here a series of binuclear [(nBuSn)2(TEOA)2L2] (L = monocarboxylic acid ligand) complexes have been synthesized and characterized; we also adopted a new method to make the metal clusters and PMMA blend together for NLO testing. Importantly, the electronic structure, static third-order NLO properties, sum over states (SOS) have been studied by both experimental and density function theory (DFT) analysis. The effects for general NLO polarizability under various conditions, including different substitutions ligands and replacement of the metal cores, have been further investigated. The results indicate the static second hyperpolarizabilities (γ) is inversely proportional to the band gap decreases. Notably, the theory predicts that the third-order nonlinear coefficient will double through the synergistic effects of pull-push groups. The hole-electron analysis of the main excited states indicates the simultaneous introduction of pull-push electron groups into the system cause the excitation of the valence layer from LE to LLCT, which also leads to significant increase in the γ value of complex 13. This work demonstrates that an efficient adjustment for the intensity of NLO polarizability can be achieved by regulating the substitutions and the material structures, providing a new potential for the application of tin-oxo clusters in the field of nonlinear optics.

Continuous variable tripartite entanglement and steering using a third-order nonlinear optical interaction

Nonlinear optical devices are very useful for generating entanglement. One proposal for the generation of genuine tripartite entanglement [Phys. Rev. Lett. 120, 043601 (2018)PRLTAO0031-900710.1103/PhysRevLett.120.043601] is to use a third-order nonlinear optical interaction. Here, we investigate a generalization of this, where we consider the quantum nature of all modes; moreover, we also investigate quantum steering, which is a stronger and asymmetric non-local correlation. We show that the final state presents not only tripartite continuous variable entanglement but also tripartite steering.

Efficient red photoluminescence from Al3+ and Cu+ co-doped CdS QDs embedded silicate glasses

Embedding CdS QDs into glasses can improve the thermal and chemical stability of QDs, which facilitates their wide and endurable applications such as nonlinear optical devices, optical filters, LED color converter and other optical emitters. Unlike colloid CdS QDs, it is difficult to modify surface states of CdS QDs in glasses by constructing ZnS or Cd1-xZnxS shell. In this work, Cu+ ions doped CdS QDs were precipitated in silicate glasses. It was found that Al3+ ions were simultaneously incorporated into CdS QDs along with Cu+ ions. Incorporation of Al3+ ions into CdS QDs not only lead to well dispersion of Cu+ ions, but also created sulfur vacancies and formed one electron trapping level below the conduction band of CdS QDs, leading to the donor–acceptor photoluminescence with improved photoluminescence quantum yields and thermal stability. Results reported provides an effective method to alleviate the surface defects and improve the photoluminescence quantum yields, promoting their potential applications as color-converting materials for light-emitting diodes.

The exploration of the crystal nucleation parameters and physico-chemical analysis of a single crystal: 2-amino-4,6-dimethoxypyrimidinium hydrogen (2R,3R)-tartrate 2-amino-4,6-dimethoxypyrimidine.

This paper discusses the structural orientations and the physico-chemical properties of a single crystal of 2-amino-4,6-dimethoxypyrimidinium hydrogen (2R,3R)-tartrate 2-amino-4,6-dimethoxypyrimidine (2ADT). The experimental investigation of the properties of the compound improves the potential for the utilization of the crystalline compound in the fabrication of optical limiting and nonlinear optical devices. For the growth process, an organic nonlinear optical crystal of 2ADT is synthesized conventionally at varying molar concentrations to achieve an excellent yield. The structural orientations and refinements of the compound are identified and discussed with reference to a single crystal X-ray diffraction study and its supporting computations. The results of the experimental analysis via UV-vis-NIR spectrometry and a z-scan setup with a laser beam source are used in an in-depth discussion on the linear and nonlinear optical properties of the crystal together with its damage threshold induced by a Nd:YAG laser beam at 1064 nm. With optical transparency of 55% in the entire visible region, a lower cut-off wavelength at 228 nm, and a bandgap at 5.2 eV, the crystal was demonstrated to be suitable for use in optical device fabrication. The thermogravimetrically assessed thermal stability of 2ADT was examined up to 147 °C. In addition, the thermodynamic parameters responsible for activation reactions are also discussed because these give information about the material's thermal behavior. An optical limiting study revealed that the transmitted output power increases linearly with the input power at about 1.89 mW cm−2.

A Facile Strategy for Controllable Synthesis of High-Quality Two-Dimensional Tellurium by Chemical Vapor Transport

Recently, as an elementary material, tellurium (Te) has received widespread attention for its high carrier mobility, intriguing topological properties and excellent environmental stability. However, it is difficult to obtain two-dimensional (2D) Te with high crystalline quality due to its intrinsic helical chain structure. Herein, a facile strategy for controllable synthesis of high quality 2D Te nanoflakes through chemical vapor transport (CVT) in one step is reported. With carefully tuning the growth kinetics determined mainly by temperature, tellurium nanoflakes in lateral size of up to ~40 μm with high crystallinity can be achieved. We also investigated the second harmonic generation (SHG) of Te nanoflakes, which demonstrates that it can be used as frequency doubling crystals and has potential applications in nonlinear optical devices. In addition, field effect transistor (FET) devices based on the as-grown 2D Te nanoflakes were fabricated and exhibited excellent electrical properties with high mobility of 379 cm2 V-1s-1.

Optical Band Gap, Oxidation Polarizability, Optical Basicity and Electronegativity Measurements of Silicate Glasses Using Ellipsometer and Abbe Refractometer

The values of refractive index (n) for silicate glasses (silica, soda lime and borosilicate 7059) are decreased from 1.5119 to 1.5111, 1.5086 to 1.5065 and 1.5296 to 1.5281, respectively; and the optical band gap (Eg) is increased from 9.8 to 9.81 eV, 9.845 to 9.88 eV and 9.56 to 9.58 eV, respectively over the temperature range 295 - 473 K using ellipsometer at wavelength 632.8 nm. While n is decreased from 1.5276 to 1.5274, 1.5074 to 1.5070 and from 1.5283 to 1.5281, respectively; and Eg is increased from 9.59 to 9.592 eV, 9.862 to 9.870 eV, and 9.574 to 9.58 eV, respectively over the temperature range 297 - 322 K using Abbe refractometer at wavelength 589.3 nm. The values of oxide ion polarizability [αo2- (n) and αo2-(Eg)] regarding silica, soda lime and borosilicate 7059 glasses are decreased from 1.3427 to 1.3408, 1.6014 to 1.5941, 1.4329 to 1.4193, respectively over the temperature range 295 - 473 K using ellipsometer; and are decreased from 1.3786 to 1.3764, 1.5991 to 1.5969, 1.4297 to 1.4191, respectively over the temperature range 297 - 322 K using Abbe refractometer. Similarly, the values of optical basicity [A (n) and A (Eg)] of silica, soda lime, and borosilicate 7059 glasses are decreased from 0.4272 to 0.4245, 0.6271 to 0.6224, 0.5045 to 0.4933, respectively over the temperature range 295 - 473 K using ellipsometer; and are decreased from 0.4586 to 0.4567, 0.6256 to 0.6242, 0.5018 to 0.4930, respectively over the temperature range 297 - 322 K using Abbe refractometer. Further, we have found that for silica, soda lime and borosilicate 7059, the values of electronegativity (ξ1av) QUOTE ζ1av) using Zahidnumerical model [based on αO2- (n) and A (n)] are increased from 5.1035 to 5.5504, 4.0393 to 4.830, 4.8143 to 5.0111, respectively over the temperature range 295 - 473 K using ellipsometer; while these values are increased from 5.0657 to 5.2149, 5.0657 to 5.2149, 4.8357 to 5.0111, respectively over the temperature range 297 - 322 K using Abbe refractometer. It is very clear from this research report that both refractive index and optical band gap-based-oxide ion polarizability and optical basicity have the same decreasing trend as the temperature is increased, and this trend indicates that the reported glasses have a very small amount of electronic polarizability. Moreover, this decreasing trend occurs due to the decreasing amount of non-bridging oxygen (NBO) which in turn caused a decrease in refractive index within the silicate glass system at higher temperature. Since the calculated values of electronegativity are found to be in the range 4.0393 - 5.5504 for the reported silicate glasses, so all these glasses have an ionic character. Moreover, low values of optical basicity and of oxide ion polarizability suggest that the silicate glasses are not novel glasses (optical functional glasses) for non-linear optical (NLO) devices or for three dimensional displays.

The tailored saturated-unsaturateddefect modes obtained by nonlinear threshold light in graphene-based hyperbolicmetamaterial

The tailored saturated-unsaturated defect modes are realized in the proposed graphene-based hyperbolic metamaterials (HMs) in the mid-infrared and near-infrared bands by using the threshold light. In the case of saturated absorption, graphene is identified as a transparent and lossless medium. The effects of the incident angle, the number of periods, and the chemical potential of graphene are also taken into consideration. The computed results show that the greater saturated defect mode (SDM) can be observed at a smaller incident angle and a larger period. The unsaturated defect mode (USDM) cannot be affected by the incident angle while it can be controlled by the chemical potential. In addition, two novel threshold lights (0.2 MW/cm2 and 60 MW/cm2) producing bistable graphene absorption are analyzed by adopting nonlinear Kerr (NLK) materials. These results can be applied to nonlinear optical switches and logic devices.

Robust modal phase matching in subwavelength x-cut and z-cut lithium niobate thin-film waveguides

We use the nonlinear coupled-mode theory to theoretically investigate second-harmonic generation (SHG) in subwavelength x-cut and z-cut lithium niobate (LN) thin-film waveguides and derive the analytical formula to calculate SHG efficiency in x-cut and z-cut LN thin-film waveguides explicitly. Under the scheme of optimal modal phase matching (MPM), two types of LN thin films can achieve highly efficient frequency doubling of a 1064 nm laser with a comparable conversion efficiency due to very consistent modal field distribution of the fundamental wave and second-harmonic wave with efficient overlap between them. Such a robust MPM for high-efficiency SHG in both the subwavelength x-cut and z-cut LN thin-film waveguides is further confirmed in a broad wavelength range, which might facilitate design and application of micro–nano nonlinear optical devices based on the subwavelength LN thin film.

Inversion symmetry broken in 2H phase vanadium-doped molybdenum disulfide.

Two-dimensional (2D) layered transition metal dichalcogenides (TMDs) have received much attention in nonlinear optical applications due to their unique crystal structures and second harmonic generation (SHG) efficiency. However, SHG signals in TMDs show a layer-dependent behavior, consistent with the presence (absence) of inversion symmetry in even-layer (odd-layer) of TMDs. Herein, we synthesized monolayer and bilayer 2H and 3R phase vanadium (V)-doped MoS2 crystal. Raman spectroscopy, XPS, and STEM were used to identify the chemical composition and crystalline structure of as-grown nanoflakes. SHG measurement was used to research the symmetry of V-doped MoS2 crystals with different stacking orders. Significantly, the SHG efficiency in bilayer 2H phase V-doped MoS2 is equivalent to the 3R phase, indicating an inversion symmetry broken lattice structure caused by the in situ V substitute for Mo sites. This study will be conducive to promote the development of promising nonlinear optical devices based on 2D material.

Prediction of unexpected B n P n structures: promising materials for non-linear optical devices and photocatalytic activities.

In the present work, a modern method of crystal structure prediction, namely USPEX conjugated with density functional theory (DFT) calculations, was used to predict the new stable structures of BnPn (n = 12, 24) clusters. Since B12N12 and B24N24 fullerenes have been synthesized experimentally, it motivated us to explore the structural prediction of B12P12 and B24P24 clusters. All new structures were predicted to be energetically favorable with negative binding energy in the range from −4.7 to −4.8 eV per atom, suggesting good experimental feasibility for the synthesis of these structures. Our search for the most stable structure of BnPn clusters led us to classify the predicted structures into two completely distinct structures such as α-BnPn and β-BnPn phases. In α-BnPn, each phosphorus atom is doped into a boron atom, whereas B atoms form a Bn unit. On the other hand, each boron atom in the β-phase was bonded to a phosphorus atom to make a fullerene-like cage structure. Besides, theoretical simulations determined that α-BnPn structures, especially α-B24P24, show superior oxidation resistance and also, both α-BnPn and β-BnPn exhibit better thermal stability; the upper limit temperature that structures can tolerance is 900 K. The electronic properties of new compounds illustrate a higher degree of absorption in the UV and visible-region with the absorption coefficient larger than 105 cm−1, which suggests a wide range of opportunities for advanced optoelectronic applications. The β-BnPn phase has suitable band alignments in the visible-light excitation region, which will produce enhanced photocatalytic activities. On the other hand, α-BnPn structures with modest band gap exhibit large second hyperpolarizability, which are anticipated to have excellent potential as second-order non-linear optical (NLO) materials.

Effect of dimension variation for second-harmonic generation in lithium niobate on insulator waveguide [Invited

We study the effect of dimension variation for second-harmonic generation (SHG) in lithium niobate on insulator (LNOI) waveguides. Non-trivial SHG profiles in both type-0 and type-I quasi-phase matching are observed during the wavelength tuning of the fundamental light. Theoretical modeling shows that the SHG profile and efficiency can be greatly affected by the waveguide cross-section dimension variations, especially the thickness variations. In particular, our analysis shows that a thickness variation of tens of nanometers is in good agreement with the experimental results. Such investigations could be used to evaluate fabrication performance of LNOI-based nonlinear optical devices.

Enhancing third-harmonic generation by quasi bound states in continuum in silicon nanoparticle arrays

Subwavelength artificial structures of high refractive index dielectrics provide an effective way to control and manipulate light on a nanoscale by enhancing electric and magnetic fields. This kind of structure usually has low absorption loss, but its performance is also limited by radiation loss, which will reduce the efficiency of its nonlinear response. This problem can be solved by using bound states in the continuum (BICs). The BICs are a kind of unconventional state which is in continuous domain but remains localized. They exist within a light cone and have an infinite quality factor. By combining BICs with nonlinear optics, high-<i>Q</i> resonances from quasi-BICs are used to excite and enhance the nonlinear response. The simulation shows that when the symmetry of the unit cell of the silicon nanoparticle arrays is broken, the BIC become the quasi-BIC, and the transmission spectrum will produce a high-<i>Q</i> narrow resonance valley. The resonance has polarization dependence of electric field. With the change of pump wavelength, the third-harmonic generation (THG) intensity first increases and then decreases gradually. The pump wavelength changed by several nanometers can change THG intensity by at least one order of magnitude. When the pump wavelength is adjusted to the resonance wavelength, the nonlinearity is significantly enhanced as a result of the strong field localization. The THG intensity is highly sensitive to the variation of asymmetric parameters. Only a change of 75 nm will result in a decrease of THG intensity by at least one order of magnitude. There is a third-order relationship between pump power and THG power. For the proposed structure, the factors affecting the conversion efficiency of THG include pump power, pump wavelength, polarization angle of pump light, and asymmetry parameter. When the polarization direction of electric field is along the short axis of the structure and the pump light at resonance wavelength is vertically incident to the structure with an asymmetric parameter of 0.125, the conversion efficiency of THG can be increased to ～2.6 × 10<sup>–6</sup> and the intensity of THG is increased by six orders of magnitude. The results are expected to be applied to designing the silicon-based optical nonlinear devices.

Nonlinear optical responses of α-Fe2O3 nanosheets and application as a saturable absorber in the wide near-infrared region

In the present work, we report a strategy to synthesize α-Fe2O3 nanoflakes as a nonlinear optical (NLO) material for the optical pulse generation in the near-infrared (NIR) band. With the excitation wavelength of 1 µm, the effective nonlinear absorption coefficients βeff was −0.501 cm/GW and the nonlinear refractive index n2 was 9.33 × 10-4 cm2/GW. While at 1.34 µm, βeff was −0.713 cm/GW and n2 was 5.01 × 10-4 cm2/GW. The two-photon absorption cross sections at 1 and 1.34 µm were as high as 9.6 × 105 and 5.7 × 105 GM, respectively, indicating that the hematite nanosheets could be used as the nonlinear optical devices. The third-order NLO susceptibilities were 6.3 × 10-11 and 3.75 × 10-11 esu at 1 and 1.3 µm, respectively. Using the ultrafast spectroscopy, the excited state lifetime was ~2.62 ps, suitable for the (ultra)short pulse generation. Based on the marvelous nonlinear absorption properties of the α-Fe2O3 nanoflakes saturable absorber, passively Q-switched Nd:GdVO4 lasers at 4F3/2 → 2I11/2 and 4F3/2 → 2I13/2 lasing transitions were demonstrated, producing the shortest pulse duration of 135 ns. The experimental results confirmed that α-Fe2O3 nanoflakes were an excellent candidate for the short NIR pulse generation in a broad band.

Investigating the Nonlinear Optical Response of Pepper Oil under Low Power Irradiation with Continuous Wave Visible Laser Beam

The nonlinear optical properties of pepper oil are studied by diffraction ring patterns and Z-scan techniques with continuous wave beam from solid state laser at 473 nm wavelength. The nonlinear refractive index of the sample is calculated by both techniques. The sample show high nonlinear refractive index. Based on Fresnel-Kirchhoff diffraction integral, the far-field intensity distributions of ring patterns have been calculated. It is found that the experimental results are in good agreement with the theoretical results. Also the optical limiting property of pepper oil is reported. The results obtained in this study prove that the pepper oil has applications in nonlinear optical devices.

Model of thermo-optic nonlinear dynamics of photonic crystal cavities

The wavelength scale confinement of light offered by photonic crystal (PhC) cavities is one of the fundamental features on which many important on-chip photonic components are based, opening silicon photonics to a wide range of applications from telecommunications to sensing. This trapping of light in a small space also greatly enhances optical nonlinearities and many potential applications build on these enhanced light-matter interactions. In order to use PhCs effectively for this purpose it is necessary to fully understand the nonlinear dynamics underlying PhC resonators. In this work, we derive a first principles thermal model outlining the nonlinear dynamics of optically pumped silicon two-dimensional (2D) PhC cavities by calculating the temperature distribution in the system in both time and space. We demonstrate that our model matches experimental results well and use it to describe the behavior of different types of PhC cavity designs. Thus, we demonstrate the model's capability to predict thermal nonlinearities of arbitrary 2D PhC microcavities in any material, only by substituting the appropriate physical constants. This renders the model critical for the development of nonlinear optical devices prior to fabrication and characterization.

Nonlinear optical properties of halide perovskites and their applications

Nonlinear optics has undergone dramatic developments in the past 60 years, which has revolutionized the photonic and optoelectronic fields with many essential applications such as electro-optic switching, frequency mixing, optical parametric oscillation, optical phase conjugation, and so forth. As one of the new and promising candidates for both next-generation photovoltaic and optoelectronic devices, halide perovskite semiconductors have attracted extensive research attention because of their excellent electrical and optical properties demonstrated in the linear optical regime. In the past five years, halide perovskites have become a new research frontier of nonlinear optical materials because their highly tunable chemical components and multiple structures provide a variety of outstanding nonlinear optical properties, which support a broad scope of nonlinear optical applications. In this review, we have summarized the nonlinear optical properties of halide perovskites categorized according to the second-, third-, and high-order processes. Aside from the more conventional nonlinear effects, such as sum and difference frequency generation, this review also pays attention to the lesser known but important nonlinear phenomena, such as linear and circular photogalvanic effects, the high-order shift current effect, and the multi-photon pumped photoluminescence. We have also reviewed and summarized the nonlinear applications of halide perovskites, including multi-photon pumped photoluminescence imaging, multi-photon pumped amplified spontaneous emission and lasing, sub-bandgap and self-powered photodetection, all-optical and electro-optic modulation, saturable absorption, optical limiting, and so on. It is our belief that halide perovskites have proven to be excellent candidates for promoting the upgrading and updating of nonlinear optical devices with greatly improved performance and novel functionalities.

A comparative study on optical properties of BiOI, Bi7O9I3 and Bi5O7I materials

Abstract This investigation clarifies the optical properties of successive ionic layer adsorption and reaction (SILAR)-prepared BiOI, Bi7O9I3, and Bi5O7I thin films. In our study, after the annealing treatment, BiOI material transforms into Bi7O9I3 and Bi5O7I crystal phase. The crystal structure, morphology and elemental analysis have been confirmed by X-Ray Diffraction (XRD), field emission scanning electron microscope (FESEM), energy dispersive X-ray spectrometer (EDS) analysis. Moreover, we have checked and validified phase transformation and weight loss by thermo-gravimetric (TG) analysis. Here, the comparative optical characterization and assessment of the BiOI and derivatives films have been done by transmittance and reflectance. Meanwhile, with the single-oscillator Wemple-Di Domenico model, the refractive index's dispersion has been presented for BiOI, Bi7O9I3, and Bi5O7I. Interestingly, comparative analysis shows that nonlinear optical behavior becomes lower after phase transformation, confirmed via the second-order reflective index and nonlinear susceptibility estimation. This investigation will open a new window for BiOI based materials to consider it for the nonlinear optical device.