Nonlinear Optical Devices Research Articles

Tunable optical bistability based on Bloch surface waves in one-dimensional photonic crystal with graphene

Graphene possesses large nonlinear conductivity in terahertz region, which makes it a very promising material for nonlinear bistable devices. In this paper, we theoretically study the optical bistability (OB) of reflected beam in a multilayer structure with graphene embedded between the truncated layer and the substrate. The Bloch surface wave excited by the one-dimensional photonic crystal (1D PC) coupling structure significantly enhances the local electric field near the nonlinear graphene, which provides a positive condition for the realization of low-threshold OB. Through parameter optimization, we obtain a threshold electric field with an incident electric field of 105 V/m levels. Furthermore, the influences of graphene’s Fermi energy and relaxation time, as well as those of the incidence angle, on the hysteretic behavior and the threshold of OB are clarified. This approach may provide a feasible scheme for the nonlinear optical bistable devices.

Tip-induced domain growth on the non-polar cut of lithium niobate with various stoichiometry deviations

Appearance of wedge-like domains during local switching by a biased tip of a scanning probe microscope (SPM) was studied in non-polar cut plates of lithium niobate (LN) with the spatial distribution of the deviation of Li concentration from stoichiometry composition (ΔcLi) created by vapor transport equilibration. The voltage dependences of the domain sizes were measured in the areas of LN plates with various values of ΔcLi. It was shown that the domain length increased linearly with the voltage, while the domain base width demonstrated a square root voltage dependence. The obtained dependence of the base width was attributed to the spatial distribution of the polar component of the external field produced by a biased SPM tip. The obtained results were considered in terms of the kinetic approach to domain growth. The growth of wedge-like domains was attributed to step generation and kink motion. The velocities of the base growth and kink motion were defined by the excess of the local value of superposition of the polar components of an external field produced by a biased tip, depolarization field, and screening fields over the threshold values. The average length of the elementary steps at the domain walls revealed from the domain length to width ratio demonstrated the square root voltage dependence. It was revealed that the domain length and the width of the base inversely depended on ΔcLi. The obtained dependences of the domain growth parameters on the composition allow for improving the periodical poling technique used for the fabrication of the nonlinear optical devices.

Femtosecond Z-scan measurement of third-order nonlinear optical response of fluorine-doped tin oxide

The excitation wavelength dependent nonlinear optical response of fluorine-doped tin oxide (FTO) is systematically studied by the Z-scan technique. The broadband third-order nonlinear optical properties of FTO are verified and a value of nonlinear refractive index coefficient n 2 to be 2.52 × 10−16 m2 W−1 is obtained at epsilon-near-zero region. Meanwhile, a large modulation depth and nonlinear absorption coefficient β are estimated about 9.61% and −1.96 × 10−9 m W−1, respectively. The experimental results indicate that FTO is a promising nonlinear optical material and has great application potential in the field of nonlinear optical devices.

Dramatically Enhanced Second Harmonic Generation in Janus Group‐III Chalcogenide Monolayers

Abstract2D materials are excellent platforms for nonlinear optical (NLO) response, especially second harmonic generation (SHG), due to its large surface to volume ratio and sub‐nanometer thickness. The SHG susceptibility strongly relies on the symmetry of materials. Constructing Janus structures can break the out‐of‐plane mirror symmetry, bringing about asymmetric charge distribution and leading to a built‐in electric field. Consequently, SHG response along the out‐of‐plane direction can be improved. In the current work, combining first‐principles calculations with independent particle approximation, the SHG response of nine Janus group‐III chalcogenide monolayers (M2XX', MM'X2) are systematically evaluated. Both extraordinary in‐plane and out‐of‐plane SHG response are revealed in all the Janus structures. Besides, cation MM'X2 Janus structures exhibit systemically higher SHG response than that of anion M2XX’ due to stronger dipole. Among them, GaInTe2 possesses extremely high out‐of‐plane SHG response with d31 up to 10490.4 pm V−1 at photon energy (PE) of 4.7 eV, enabling promising applications in ultraviolet NLO devices. The SHG intensity polar plots from Janus structures display unusual rotational symmetry at different PEs allowed by the out‐of‐plane SHG components. This work provides theoretical guidelines for further experimental explorations in 2D group‐III monochalcogenide Janus structures and paves the way for their utilization in NLO devices.

The effect of intramolecular and intermolecular charge transfers on the third order nonlinear optical properties of the self−assemble chromophores

Self-assembled chromophores were widely used in nonlinear optical devices due to their unique charge transfer properties. The structures, intermolecular interactions, absorption spectra, charge transfer (CT) and third order nonlinear optical (NLO) responses (γ) of monomers, dimers and trimers based on N,N′-butyl-3,4,9,10-perylenediimide (PDIB) have been studied using density functional theory. It is found that with the addition of phenyl substituents, the Egap values between HOMO and LUMO of monomers as well as dimers and trimers decreases gradually, their main absorption peaks of the absorption spectra were redshifted, and intramolecular CT was more pronounced, thus their γ values increased gradually. Moreover, the intermolecular interaction energies (Eint) of dimers increases with the addition of phenyl substituents, indicating that the enhancement of Eint values increases the degree of intermolecular electron coupling and enhances intermolecular CT. On the other hand, in order to explore the effect of increasing number of layers on the optical properties of dimers and trimers, we divide the γ values by the number of layers (n = 1, 2 and 3). It is found that the average γ/n values decreases as n increases, which was due to that the CT in homomolecular self-assembly was non-directional, even isotropic and cancelling. We hope that this work will lead to the careful design of self-assembled NLO materials.

Progress on Emerging Ferroelectric Materials for Energy Harvesting, Storage and Conversion

AbstractSince the discovery of Rochelle salt a century ago, ferroelectric materials have been investigated extensively due to their robust responses to electric, mechanical, thermal, magnetic, and optical fields. These features give rise to a series of ferroelectric‐based modern device applications such as piezoelectric transducers, memories, infrared detectors, nonlinear optical devices, etc. On the way to broaden the material systems, for example, from three to two dimensions, new phenomena of topological polarity, improper ferroelectricity, magnetoelectric effects, and domain wall nanoelectronics bear the hope for next‐generation electronic devices. In the meantime, ferroelectric research has been aggressively extended to more diverse applications such as solar cells, water splitting, and CO2 reduction. In this review, the most recent research progress on newly emerging ferroelectric states and phenomena in insulators, ionic conductors, and metals are summarized, which have been used for energy storage, energy harvesting, and electrochemical energy conversion. Along with the intricate coupling between polarization, coordination, defect, and spin state, the exploration of transient ferroelectric behavior, ionic migration, polarization switching dynamics, and topological ferroelectricity, sets up the physical foundation ferroelectric energy research. Accordingly, the progress in understanding of ferroelectric physics is expected to provide insightful guidance on the design of advanced energy materials.

Plasmon-enhanced third-order optical nonlinearity of monolayer MoS2

Transition metal dichalcogenides (TMDs) have attracted broad interest in photonics owing to their unique electric band structures, which triggers various applications for functional devices. However, the optical absorbance of TMDs is relatively low because of the atomic-scale thickness, limiting further development of TMDs-based nonlinear optical devices. Here, we propose an effective method to enhance the nonlinear optical properties of TMDs using plasmons, which are from embedded silver (Ag) nanoparticles (NPs) inside the fused silica substrate. In such a configuration, the third-order nonlinear absorption coefficient of MoS2 with non-contact Ag NPs is one order of magnitude higher than that of pure monolayer MoS2 under excitation of 515 nm light, and at 1030 nm, the reverse saturable absorption switches to the saturable absorption due to the plasmonic implication. In addition, the mechanism of plasmon-enhanced nonlinear optical properties is confirmed by results of both transient absorption spectroscopy and near-field electromagnetic field simulation. This study on plasmon-enhanced third-order nonlinearity of MoS2 expands the boundaries of TMDs-based optical nonlinearity engineering.

Thermo-optical reshaping of second-harmonic emission from dimer all-dielectric nanoresonators.

All-dielectric nanophotonics offers a wide range of possibilities for thermally induced light manipulation at the nanoscale. High quality resonances allow for efficient light-to-heat conversion supported by various temperature detection approaches based on thermally sensitive intrinsic optical responses. In this work, we study theoretically a phenomenon of the photothermal reshaping of the radiation pattern of second-harmonic generation (SHG) that occurs in resonant all-dielectric systems. In the suggested geometry, a near-IR pulsed laser is used for SHG while a continuous wave visible laser simultaneously heats the structure. The thermo-optical switching of the resonant optical states in the nanostructures governs the reconfiguration of the emission pattern, without significant loss in the magnitude of the SHG. We believe, that our findings will pave the way for subwavelength-size near-IR thermally switchable nonlinear optical devices.

The ferroelectric nematic phase: an optimum liquid crystal candidate for nonlinear optics

ABSTRACT Materials that exhibit high nonlinear optical (NLO) susceptibilities are considered as promising candidates for a wide range of photonic and electronic applications. Here, we argue that the ferroelectric nematic (NF) materials have sufficient potentialities to become materials for the next-generation of NLO devices. We have carried out a study of the efficiency of optical second-harmonic generation in a prototype NF material, finding a nonlinear susceptibility of 5.6 pm.V−1 in the transparent regime, one of the highest ever reported in ferroelectric liquid crystals. Given the fact that the studied molecule was not specifically designed for NLO applications, we conclude there is still margin to obtain NF materials with enhanced properties that should allow their practical use.

Tunable optical nonlinearities of MWCNTs with core-satellite ZnS-Au structure

In order to modulate the nonlinear optical (NLO) properties of multi walled carbon nanotubes (MWCNTs) and make them applicable to ultrafast nonlinear optical devices, we fabricated a core satellite ZnS-Au nanostructure on the surface of MWCNTs via the solvothermal method. The structure and morphology of the MWCNTs-Au-ZnS product were characterized by means of the XRD, SEM and XPS, which showed that the ZnS-Au nanoassemblies were combined along with the MWCNTs through C S covalent bond and partial ionic bond. The optical nonlinearities of the MWCNTs-Au-ZnS system were investigated using the Z-scan technique under the excitation of 532 nm ps laser pulses and kinetically analyzed using the pump-probe transient absorption spectroscopy. The results showed that the saturation absorption (SA) coefficient and the third-order nonlinear susceptibility of the MWCNTs-Au-ZnS system were adjustable with the variation of the core-satellite structure. The intensity of the saturation absorption was tuned downward below that of the pure MWCNTs, while the susceptibility of the system was tuned upward above that of the pure MWCNTs, which were attributed to the combined action of two-photon absorption of ZnS, charge transfer in the system, trap states provided by Au and charge delocalization varying with the size. These tunable nonlinearities will expand the applications of the MWCNTs-Au-ZnS system in photonic devices. • Core-satellite structure of ZnS-Au is fabricated on the surface of MWCNTs via a solvothermal method. • The core-satellite structure is connected with MWCNTs via covalent bond and partial ionic bond. • The nonlinear absorption and refraction of the MWCNTs-Au-ZnS are tuned by changing the core-satellite structures.

Tunable second harmonic generation by an all-dielectric diffractive metasurface embedded in liquid crystals

We experimentally demonstrate the possibility to modulate the second harmonic (SH) power emitted by nonlinear AlGaAs metasurfaces embedded in a liquid crystal (LC) matrix. This result is obtained by changing the relative in-plane orientation between the LC director and the linear polarization of the light at the excitation wavelength. According to numerical simulations, second-harmonic is efficiently radiated by the metasurfaces thanks to the sizeable second-order susceptibility of the material and the resonant excitation of either electric or magnetic dipole field distributions inside each meta-atom at the illuminating fundamental wavelength. This resonant behavior strongly depends on the geometric parameters, the crystallographic orientation, and the anisotropy of the metasurface, which can be optimized to modulate the emitted SH power by about one order of magnitude. The devised hybrid platforms are therefore appealing in view of enabling the electrical control of flat nonlinear optical devices.

Amorphous Ge-Sb-Se-Te chalcogenide films fabrication for potential environmental sensing and nonlinear photonics

Quaternary Ge-Sb-Se-Te chalcogenide thin films were fabricated by rf magnetron sputtering from Ge19Sb17Se64−xTex (x = 5, 10, 15, 20) sputtering targets in order to select appropriate compositions for infrared sensor and optical nonlinear applications. An influence of chemical composition and deposition parameters on the optical properties, structure and wettability was thus studied. The amorphous thin films seem to be constituted by selenide entities that can include tellurium atoms in variable proportion such as [GeSe4−xTex] and [SbSe3−xTex] (x = 0, 1, 2) and Ge(Sb)-Ge(Sb) bonds according to Raman spectroscopy. Contact angle measurements of the thin films showed values of 68–71° for water and their surface energies in the range of ∼36–39 mJ·m−2 seem suitable for surface functionalization required for photonic sensor development. Furthermore, the maximum nonlinearity at the telecom wavelength with respect to the highest figure of merit value was found for the thin film with composition Ge19Sb17Se56Te8 having nonlinear refractive index of 28 × 10−18 m2·W−1. Due to their low optical bandgap energies, they may find their full interest for nonlinear optics in the mid-infrared range. Wide IR transparency in combination with high (non)linear refractive indices make these materials attractive in the field of mid-IR sensing and optical nonlinear devices.

Optical characterization and polaron radius of Bi2O3 doped silica borotellurite glasses

A system of silica borotellurite glasses containing bismuth oxide (Bi2O3) with empirical chemical relation [{(TeO2)0.7(B2O3)0.3}0.8(SiO2)0.2]1−x(Bi2O3)x (where x = 0.01–0.05 M fraction in step of 0.01) were synthesized via melt-quenching procedure. Density and molar volume, XRD, FTIR and UV–Vis spectroscopies were employed to examine some parameters related to physical, structural and optical properties of the glasses. The density, polaron radius, molar volume, oxygen packing density (OPD), oxygen molar volume and number of bonds per unit volume of the glasses were computed and discussed. The XRD and FTIR characterization results were presented and discussed accordingly. Via the obtained optical absorption and density/molar volume data, the band gap energy, Urbach energy, index of refraction, coefficient of optical transmission, metallization criterion (MC) and reflection loss were studied. The index of refraction, metallization criterion, coefficient of optical transmission and reflection loss range from 3.013 to 2.622, 0.271–0.338, 0.598–0.667 and 0.252–0.201 respectively. The values of Polaron radius range from 3.949 to 4.300 g cm−3, 73.009–72.297 g atm l−1 and 6.943–4.092 Å respectively. The obtained values of the polaron radius are termed small polarons because they are within the lattice constants of each of the constituent oxides in the BSBT glasses. The MC values of the glasses are consistent with MC of non-metallic glasses as well as new nonlinear optical materials. High values of density, index of refraction and the value range of the metallization criterion suggest that the TeO2–B2O3–SiO2–Bi2O3 glasses are suitable for optoelectronic, nonlinear optical devices and radiation attenuation windows.

Disordered ensembles of strongly coupled single-molecule plasmonic picocavities as nonlinear optical metamaterials.

We propose to use molecular picocavity ensembles as macroscopic coherent nonlinear optical devices enabled by nanoscale strong coupling. For a generic picocavity model that includes molecular and photonic disorder, we derive theoretical performance bounds for coherent cross-phase modulation signals using weak classical fields of different frequencies. We show that strong coupling of the picocavity vacua with a specific vibronic sideband in the molecular emission spectrum results in a significant variation of the effective refractive index of the metamaterial relative to a molecule-free scenario due to a vacuum-induced Autler-Townes effect. For a realistic molecular disorder model, we demonstrate that cross-phase modulation of optical fields as weak as 10 kW/cm2 is feasible using dilute ensembles of molecular picocavities at room temperature, provided that the confined vacuum is not resonantly driven by the external probe field. Our work paves the way for the development of plasmonic metamaterials that exploit strong coupling for optical state preparation and quantum control.

Synthesis, characterization, and investigation of nonlinear property of fly ash-red mud-Ag: A low-cost sustainable nanocomposite

The silver-coated fly ash-red mud nanocomposite (FARM-Ag) is synthesized through the environment-friendly facile chemical method. Scanning electron microscopy (SEM), Energy dispersive x-ray analysis (EDAX), X-ray diffraction (XRD), and UV–Visible absorption spectroscopy techniques are used to characterize the nanocomposite. A sensitive single-beam Z-scan technique is used to study its nonlinear properties under continuous-wave (CW) laser excitation as a function of sample concentration and laser power. It is observed that FARM-Ag exhibits negative refractive and positive absorptive nonlinearity due to the self-defocusing and reverse saturable absorption (RSA) effect, respectively. Here, the origin of the nonlinearity is attributed to the thermal lensing effect and the larger magnitude of the nonlinear refractive index (n2), nonlinear absorption coefficient (β), third-order nonlinear susceptibility (|χ(3)|), and thermo-optical coefficient (dn/dT) are obtained as – 2.978 × 10−12 m2W−1, 1.424 × 10−5 mW−1, 3.477 × 10−14 m2V−2, and - 3.903 × 10−5 K−1, respectively. The results suggest that this newly synthesized nanocomposite from industrial waste might have a possible use for nonlinear optical devices.

Modulating the temporal dynamics of nonlinear ultrafast plasmon resonances

Surface plasmon-induced nonlinear optical resonances have shown immense potential in advanced optical imaging and nonlinear photonic devices. However, the ultrashort lifetime of these intense nonlinear fields inhibits their effective use in the vast applications of quantum plasmonics. Here, we propose enhancement in the lifetime of fast decaying second harmonic (SH) plasmon mode through a weak and pure resonant interaction with a two-level quantum emitter (QE). We compute the time evolution of SH response under a two-coupled oscillator model, in which we examine the interaction of short-lived SH mode supported by Au nanoparticle (AuNP) with long-lived dark mode (DM) or QE systems. To analyze the effect of spectral and temporal properties of DM and QE on the SH field, we evaluate the lifetime enhancement factor as a function of coupling strength and tuned resonant frequencies. The results show that tiny object like QE with sharp spectral bandwidth, small decay rate, and large oscillating strength is more efficient to control and probe the temporal dynamics of the SH field, as compared to DM which have a wide spectral bandwidth. Also, we control the lifetime of the SH mode after the natural decay time of the fundamental mode (FM), which distinguishes SH mode irrespective of its spatial convolution with elementary modes. Our proposed AuNP-QE coupled plasmonic system supporting nonlinear signal with enhanced temporal character paves its way for designing efficient on-chip nonlinear optical devices and can be a powerful tool in ultrahigh resolution nonlinear optical imaging.

Photonic schemes of distribution and reconstruction of an entangled state from hybrid entanglement between polarization and time-bin via quantum dot

We propose photonic schemes for the distribution and reconstruction of a two-qubit entangled state using a hybrid entangled state under a noisy quantum channel. First, to generate a hybrid entangled state correlated with polarizations and time-bins, we employ a quantum dot (QD)-cavity system (nonlinear optical gate) and linear optical devices to implement controlled operation. These schemes can achieve the distribution and reconstruction of a two-qubit entangled state from hybrid entanglement by utilizing only linear optical devices without a QD-cavity system (i.e., a nonlinear optical device) for users who want to share an entangled state under a noisy quantum channel. For a feasible realization of the proposed schemes, we analyze the interaction between the photons and QD-cavity system and demonstrate the experimental conditions under which the reliable performance of the QD-cavity system is achieved.

Crystal growth and physico-chemical characterization of methyl ammonium chloride doping on the characteristics of potassium dihydrogen phosphate crystal for nonlinear optical applications

• The KDP and MACKDP single crystals were grown by the slow evaporation method. • The UV–Vis-NIR spectrums reveal that the title compounds can be used as nonlinear optical materials. • KDP and MACKDP crystal belong to the soft material category. • Third-order nonlinear optical susceptibility (χ 3 ) was found to be 5.391 × 10 −8 esu and 5.412 × 10 −8 esu for KDP and MACKDP, respectively. Potassium dihydrogen phosphate (KDP) and Methyl ammonium chloride doped KDP (MACKDP) were made into nonlinear optical single crystals using the ambient temperature slow evaporation method. An examination of powder X-ray diffraction reveals that the reflection lines of the doped KDP crystal are almost identical to those of the pure parent chemical KDP, with just a little difference in peak intensity. The space group and lattice parameters of the crystal structure were determined using XRD measurements on a single crystal. FTIR spectrum studies indicated the existence of numerous functional groups due to the shifting of peak positions. According to the results of UV–Vis-NIR testing, the UV cutoff wavelength for pure KDP is 381 nm and for methyl ammonium chloride doped potassium dihydrogen phosphate crystal is 383 nm. Growing crystals have reduced permittivity and dielectric loss tangent at increasing frequencies and temperatures. There were 1.12 times more correlated second harmonic (SHG) powers in the doped crystal than there were in pure KDP, according to the Kurtz and Perry approach. Thermogravimetric and differential thermal analysis were used to evaluate the thermal properties of an KDP doped MACKDP crystals. Vickers microhardness experiments have examined the impact of methyl ammonium chloride mixing on the hardness parameters of KDP crystal. The encouraging third-order nonlinear properties were examined employing a Z-scan technique using an Nd: YAG laser at 532 nm. To be considered a viable choice for nonlinear optical devices, the title material must exhibit a wide range of noteworthy physicochemical and optical nonlinear features.

Enhancement in non-linear optical properties of carbon nitride (C2N) by doping superalkali (Li3O): A DFT study

A systematized analysis of the electronic as well as the nonlinear optical properties of carbon nitride (C2N) doped with superalkali (Li3O) has been investigated through density functional theory (DFT) methods of B3LYP, LC-BLYP, and CAM-B3LYP at 6-31G (d,p) basis set. The FMOs value by the B3LYP method of DFT has been proved more promising to the experimental value of carbon nitride. So, it is employed as a more reliable method for computations. Doped molecules (M2 and M3) have a high interaction energy (-6.68 eV) and vertical ionization energy (3.46 eV), reduced energy gap in comparison with pure C2N indicating that designed complexes are more stable than pure C2N surface. The up-turn of UV absorption, dipole moment, and first hyperpolarizability have improved the electronic properties and interaction energies between the superalkali and carbon nitride after doping. The first hyperpolarizability and dipole moment of Li3O doped with pure surface has been increased up to 321,498 au and 5.31 D respectively. All results proved that Li3O doped with carbon nitride is a potential approach to synthesize the material by doping super alkali on carbon nitride for nonlinear optical devices.

Optical dichroism in ZnGeP2 crystals at deep levels

Undoped single crystals Z n G e P 2 have been studied by optical absorption spectroscopy in the range of 0.65–3.0 µm, where the unwanted absorption by intrinsic point defects plays a decisive role in highly efficient nonlinear optical devices. An increased optical dichroism up to 70% is achieved due to rearrangement of deep levels after low-temperature annealing (LTA). Zinc vacancies among other defects (phosphorus vacancies, cationic antisites) make the main contribution to the local structure transformation. A surprising fact is that the amplitude of optical dichroism at the deep acceptor V Z n exceeds the maximum photopleochroism ∼ 55 % for direct optical transitions in Z n G e P 2 . Structural improvement based on the distorted tetrahedron model is discussed.