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Thin-film lithium niobate (TFLN), also known as lithium niobate on insulator, is an important integrated optical platform due to its broad transparency window (from ultraviolet to mid-infrared) and exceptional nonlinear optical (NLO) properties. TFLN is a revolutionary technology that revitalizes micro/nano photonics based on LN, which holds prime importance in on-chip frequency conversion owing to its remarkable NLO properties. This review focuses on the optical nonlinearity of thin film lithium niobate and its applications in integrated optics. We commence with a brief overview of the TFLN platform. Followed by an introduction to the common device structures. We then present the recent advancements of TFLN in NLO frequency conversion, including χ (2) based optical frequency generation processes (second harmonic generation, sum frequency generation, and difference frequency generation, etc), frequency comb generation, and supercontinuum generation, etc. Finally, we propose future prospects for nonlinear photonic integrated circuits based on the TFLN platform. [ABSTRACT FROM AUTHOR]

The transformation of elliptical polarization in a layer of azobenzene-containing amorphous polymer is calculated. The dependences of the Stokes parameters for the propagation of a light wave deep into the layer are obtained. It is shown that the light-induced change in absorption leads to a decrease in the ellipticity of the light wave, which, in turn, slows down the rotation of the polarization ellipse. The obtained results are important for optical writing of phase structures in polymers. [ABSTRACT FROM AUTHOR]

Spherical quantum wells (SQWs) have proven to be excellent materials for suppressing Auger recombination due to their expanded confinement volume. However, research on the factors and mechanisms of their high-intensity optical properties, such as multiexciton properties and third-order optical nonlinearities, remains incomplete, limiting further optimization of these properties. Here, a series of CdS/CdSe (xML)/CdS SQWs with varying CdSe layer thicknesses were prepared. The modulation effects of CdSe shell variations on the PL properties, defect distribution, biexciton binding energy, and third-order optical nonlinearities of the SQWs were investigated, and their impact on the material's multiexciton properties was further analyzed. Results showed that the typical CdS/CdSe(3ML)/CdS sample exhibited a large volume-normalized two-photon absorption cross-section (18.17 × 102 GM/nm3) and favorable biexciton characteristics. Optical amplification was observed at 12.4 μJ/cm2 and 1.02 mJ/cm2 under one-photon (400 nm) and two-photon (800 nm) excitation, respectively. Furthermore, different amplified spontaneous emission spectra were observed for the first time under one/two-photon excitation. This phenomenon was attributed to thermal effects overcoming the biexciton binding energy. This study provides valuable insights for further optimizing multiexciton gain characteristics in SQWs and developing optical gain applications. [ABSTRACT FROM AUTHOR]

Objectives. Determining the patterns of dispersion properties of waveguide modes of the optical range in layered media with distributed optical properties is a both a pressing and significant matter for study. It has fundamental and applied importance in nonlinear optics and optoelectronics. The combination of a nonlinear response and gradedindex distributions of the optical properties of adjacent layers of a layered structure enables the desired values of the output characteristics using a wide range of control parameters to be selected easily. This renders such waveguides the most promising from the point of view of possible technical applications. The aim of this paper is to develop the theory of three-layer planar waveguide structures with a graded-index core and nonlinear optical liners with arbitrary profiles. By doing so it may be possible to find exact analytical solutions to nonlinear stationary wave equations describing explicitly the transverse electric field distribution of waveguide modes.Methods. The analytical methods of mathematical physics and the theory of special functions applied to nonlinear and waveguide optics are used herein.Results. The study provides a theoretical description of transverse stationary waves propagating along a symmetrical three-layer planar waveguide structure consisting of the inner graded-index layer sandwiched between nonlinear optical plates. It assumes an arbitrary spatial profile of the interlayer dielectric constant and the nature of the nonlinear response of the liner medium. The mathematical model of this waveguide structure formulated herein is based on nonlinear equations with distributed coefficients. The solutions obtained describe in general terms the transverse distribution of the amplitude of the electric field envelope. The transverse symmetry of the three-layer waveguide structure enables even and odd stationary modes corresponding to symmetric and antisymmetric transverse field profiles to be excited in it. A method was developed for constructing even (symmetric) and odd (antisymmetric) solutions which exist at certain discrete values of the effective refractive index/propagation constant. These discrete spectra were obtained in layers with graded-index linear, parabolic, and exponential profiles. The symmetrical threelayer waveguide structure with inner graded-index layer characterized by parabolic spatial profile and outer liners as Kerr nonlinear optical media is analyzed in detail, as an example of the application of the formulated theory. Analysis of the resulting exact analytical solution indicates that the electric field strength for the fundamental and first-order modes increases with increasing parabolic profile parameter, characterizing the relative change of the dielectric constant in the interlayer, while decreasing for higher order modes.Conclusions. The theory developed in this paper supports the unambiguous description of the transverse distributions of the stationary electric field in planar symmetrical three-layer waveguides in an explicit analytical form. The results extend the understanding of the physical properties of nonlinear waves and the localization patterns of light beams in distributed media, and may be useful in the design of various optical waveguide devices.

Abstract Graphene Quantum Dots (GQDs) are crucial in biomedicine for sensitive biosensing and high-resolution bioimaging and in photonics for their nonlinear optical properties. Integrating GQDs with photonic structures enhances optical properties by optimizing light-matter interactions and enabling precise control over their emission wavelengths. In this work, we explore a facile synthesis method for GQDs by pulsed laser irradiation in chlorobenzene and highlight the transformative potential of Tamm Plasmon Cavity (TPC) structures for tuning and amplifying the photoluminescence and nonlinear optical properties of GQDs. The characterization of GQDs revealed their exceptional properties, including efficient optical limiting and stable photoluminescence. The study demonstrated that the TPC structure significantly amplifies nonlinear optical effects due to the high light-matter interaction, indicating the potential for advanced optical systems, including optical limiters and nonlinear optical devices. Furthermore, introducing GQDs into the TPC structure leads to a significant enhancement and tuning of fluorescence emission. The Purcell effect, in combination with the confined electromagnetic fields within the TPC, increases the spontaneous emission rate of GQDs and subsequently enhances the fluorescence intensity. This enhanced and tunable fluorescence has exciting implications for high-sensitivity applications such as biosensing and single-molecule detection.

In the recent past the molecular engineering of coordination metal complexes has attracted new interest in the field of nonlinear optics (NLO), which find their applications in optoelectronics and optical data storage technology it is the transition metal along with the organic moieties that induce the control over the optical nonlinearity these properties of the materials not only enhance the intensity but also have a drastic effect on the polarization of incident laser light. This is an important criterion for all-optical switching applications. Coordination metal complexes are a very good target to aim at because of their robustness, physical and chemical stability, and other variable degrees that lead to an increment in NLO responses, most importantly all these properties can be either manipulated or tailored or tunable according to the requirement. Apart from the metal center, these molecules acting as legend must be chromophoric with donor-acceptor nature. In these molecules, the NLO response is intrinsically based on the 'push-pull' mechanism of the electrons. Obviously to these molecules, when a metal is in contact, the electronic push-pull mechanism alters rendering the molecule non-symmetric. This review article mainly concentrates on small mononuclear metal complexes for NLO application. [ABSTRACT FROM AUTHOR]

This paper simulates the relative performance of various artificial intelligence (AI) techniques when applied to nonlinear distortion compensation in wavelength division multiplexing (WDM) optical communication systems. These procedures are less complex than state-of-the-art compensation methods and do not necessitate prior knowledge about the properties of data in neighboring WDM channels, which can be practically challenging. In this study, Neural Networks (NNs) were integrated into both the transmitter and receiver sections of 3- and 5-channel WDM systems, and the resulting enhancement in performance (Q-factor) was assessed across varying levels of fiber nonlinearities. While the NN stage enhances the system performance, the improvement decreases as expected with the channel number and γ . Next, two-stage architectures that employ a transmitter side NN together with a classifier at the receiver side were modeled. For the systems examined in this paper simple decision tree structures, boosting, forests, extra trees, and multi-layer perceptron (MLP) classifiers all yielded enhanced system performance compared to simple chromatic dispersion compensation (CDC) with the only exception being Ada boosting which decreased the Q-factor for γ = 14 W - 1 k m - 1 . The outcomes of these investigations show that the most effective performance in highly nonlinear WDM systems is attained by employing two-stage systems, with the incorporation of random forest or extra tree AI methods at the receiver side yielding the highest results. [ABSTRACT FROM AUTHOR]

An electrically tunable nonlinear optical device working at near‐infrared wavelength is theoretically and experimentally demonstrated. Ultrahigh optical second‐order nonlinearity from titanium‐nitride‐based coupled metallic quantum wells can be electrically tuned by external electric field. Tunability of second‐order susceptibility χ(2) reaches a 63% modulation depth with an average tunability of 10.5% per volt. In addition, electro‐optic modulation of second‐harmonic signal is presented by continuous tuning of χ(2) over a long period of time with high stability. These results provide a new material platform with actively controllable strong nonlinearity for future nonlinear photonic systems, such as ultra‐compact opto‐electronic modulation devices and reconfigurable nonlinear metamaterials and metasurfaces. [ABSTRACT FROM AUTHOR]

This work presents the analysis of experimental research on the optical and nonlinear optical properties of two different representatives of metal alkanoate-based liquid crystals. Namely, ionic lyotropic liquid crystals of potassium caprylate doped with electrochromic viologen additives, and anisotropic glasses of ionic thermotropic liquid crystals of cobalt alkanoates of the homologous series (n = 7, 9, 11) and their multicomponent mixtures. Prior to the nonlinear optical experiment, the optical absorption spectra of all samples were investigated. For proposed absorbing media, laser-induced dynamic grating recording under the action of nanosecond laser pulses has been realised, observed and analysed. The studied materials were found to exhibit cubic optical nonlinearity, with cubic nonlinear susceptibility Χ(3) and hyperpolarizability γ values comparable to the best organic dyes. The possible mechanism of nonlinear response in the systems studied was considered on the basis of the data obtained. The nonlinear response mechanism is related to the non-linear polarisation of the π-electrons in the field of the laser radiation. [ABSTRACT FROM AUTHOR]

In this work, the photothermal nonlinearity within a layered bismuth telluride (Bi2Te3) is studied in detail. The dynamics of the optical nonlinearity with increasing photothermal effect are investigated via pump-probe spectroscopy. The difference between the thermally-induced and photon-induced nonlinearities was clarified and the entire photothermal nonlinearity was therefore sketched. Furthermore, by removing the thermally-induced background signal, the n2 without accumulated heat can then be estimated. For example, the n2 value is 2.80 × 10−8 cm2/W at a peak intensity of 12.81 MW/cm2. The results are compared with those obtained from another measurement to validate the reliability of the estimation. The working range of the n2 value is also discussed. To provide further validation of the feasibility of the proposed method, the photothermal nonlinearity within monolayer graphene is provided and discussed. This work provides an alternative method to deal with optical nonlinearity measurements that are subject to the photothermal effect, paving the way toward further related research.

Objectives. Theoretical studies of the waveguide properties of interfaces between nonlinear optical and graded-index media are important for application in optoelectronics. Waveguides combining layers with different optical properties seem to be the most promising, since they can be matched to optimal characteristics using a wide range of control parameters. The paper aims to develop a theory of composite optically nonlinear gradedindex waveguides with an arbitrary profile, within which it is possible to obtain exact analytical expressions for surface waves and waveguide modes in an explicit form. The main feature of the theory proposed in this paper is its applicability for describing surface waves and waveguide modes, in which the field is concentrated inside the gradient layer and does not exceed its boundary, avoiding contact with the nonlinear layer.Methods. Analytical methods of the theory of optical waveguides and nonlinear optics are used.Results. A theoretical description of the waveguide properties of the interface between two media having significantly different optical characteristics is carried out. The formulated model of a plane waveguide is applicable to media having an arbitrary spatial permittivity profile. An analytical expression describing a surface wave propagating along the interface between a medium having stepwise nonlinearity and a gradient layer with an arbitrary permittivity profile is obtained. Additionally, analytical expressions for surface waves propagating along the interface between a medium with Kerr nonlinearity (both self-focusing and defocusing), as well as graded-index media characterized by exponential and linear permittivity profiles, are obtained.Conclusions. The proposed theory supports a visual description in an explicit analytical form of a narrowly localized light beam within such waveguides. It is shown that by combining different semiconductor crystals in a composite waveguide, it is possible to obtain a nonlinear optical layer on one side of the waveguide interface and a layer with a graded-index dielectric permittivity profile on the other.

In this paper, we theoretically and experimentally demonstrated photothermal nonlinearities of both forward and backward scattering intensities from quasi-perfect absorbing silicon-based metasurface with only λ/7 thickness. The metasurface is efficiently heated up by photothermal effect under laser irradiation, which in turn modulates the scattering spectra via thermo-optical effect. Under a few milliwatt continuous-wave excitation at the resonance wavelength of the metasurface, backward scattering cross-section doubles, and forward scattering cross-section reduces to half. Our study opens up the all-optical dynamical control of the scattering directionality, which would be applicable to silicon photonic devices.

We present a comprehensive review of the optical response of graphene, in both the linear and nonlinear regime. This will serve as a reference for both beginners and more experienced researchers in the field. We introduce, derive, and extensively discuss the Dirac–Bloch equations framework, central to describing electron–photon interaction in nonperturbative, gapless materials. We use this model to re-derive several known results in the linear regime, such as the universal absorption law, and to describe the nonlinear interaction of ultrashort pulses with graphene. We compare the validity of the Dirac–Bloch equations model with the traditional Semiconductor-Bloch equations and point out advantages and shortcomings of the two models. Lastly, we present a cutting-edge model for describing the nonlinear optical response of graphene when bending becomes important, a situation that deeply affects the output spectra, and can provide insight to a novel, effective way to manipulate light in two-dimensional media. [ABSTRACT FROM AUTHOR]

In this manuscript, a pyridyl containing porphyrin, C46H36N8O4 (denoted as Tris@NTPP) and its derived polyoxometalate-porphyrin hybrid, [C4H9)4N]3[C41H26N7NHCO(NH)C(OCH2)3MnMo6 O18(OCH2)3C(NH)CONHN7 H26C41] (denoted as NTPP@POM) in which two pyridyl containing porphyrin moieties hanged onto one Anderson polyoxometalate, have been successfully synthesized and thoroughly characterized. Fluorescence quenching was observed in NTPP@POM as compared with its precursor Tris@NTPP inferring the transfer of electron/energy from porphyrin moiety to POM moiety. NTPP@POM showed notably enhanced nonlinear absorption (β = 2.32 × 10–5 esu) than Tris@NTPP (β = 0.73 × 10–5 esu). These NLO responses were associated with fluorescence decay mechanism which oriented the singlet excited(*S) states and triplet excited(*T) states of Tris@NTPP and NTPP@POM. Life time decay studies revealed that NTPP@POM (τ2 = 5.32 ns) were stayed for shorter time in excited triplet state than Tris@NTPP (τ2 = 10 ns), implying shorter life time led towards higher NLO responses. [ABSTRACT FROM AUTHOR]

Parametric infrared (IR) upconversion is a process in which low‐frequency IR photons are upconverted into high‐frequency ultraviolet/visible photons through a nonlinear optical process. It is of paramount importance for a wide range of security, material science, and healthcare applications. However, in general, the efficiencies of upconversion processes are typically extremely low for nanometer‐scale materials due to the short penetration depth of the excitation fields. Here, parametric IR upconversion processes, including frequency doubling and sum‐frequency generation, are studied in layered van der Waals NbOCl2. An upconversion efficiency of up to 0.004% is attained for the NbOCl2 nanosheets, orders of magnitude higher than previously reported values for nonlinear layered materials. The upconverted signal is sensitive to layer numbers, crystal orientation, excitation wavelength, and temperature, and it can be utilized as an optical cross‐correlator for ultrashort pulse characterization. [ABSTRACT FROM AUTHOR]

The coronavirus disease 2019 (COVID-19) has spread worldwide in unprecedented speed, and diverse negative impacts have seriously endangered human society. Accurately forecasting the number of COVID-19 cases can help governments and public health organizations develop the right prevention strategies in advance to contain outbreaks. In this work, a long-term 6-month COVID-19 pandemic forecast in second half of 2021 and a short-term 30-day daily ahead COVID-19 forecast in December 2021 are successfully implemented via a novel nanophotonic reservoir computing based on silicon optomechanical oscillators with photonic crystal cavities, benefitting from its simpler learning algorithm, abundant nonlinear characteristics, and some unique advantages such as CMOS compatibility, fabrication cost, and monolithic integration. In essence, the nonlinear time series related to COVID-19 are mapped to the high-dimensional nonlinear space by the optical nonlinear properties of nanophotonic reservoir computing. The testing-dataset forecast results of new cases, new deaths, cumulative cases, and cumulative deaths for six countries demonstrate that the forecasted blue curves are awfully close to the real red curves with exceedingly small forecast errors. Moreover, the forecast results commendably reflect the variations of the actual case data, revealing the different epidemic transmission laws in developed and developing countries. More importantly, the daily ahead forecast results during December 2021 of four kinds of cases for six countries illustrate that the daily forecasted values are highly coincident with the real values, while the relevant forecast errors are tiny enough to verify the good forecasting competence of COVID-19 pandemic dominated by Omicron strain. Therefore, the implemented nanophotonic reservoir computing can provide some foreknowledge on prevention strategy and healthcare management for COVID-19 pandemic. [ABSTRACT FROM AUTHOR]

The propagation of light in the epsilon-near-zero (ENZ) region of materials exhibits intriguing linear and nonlinear optical phenomenon that have been extensively exploited for a plethora of applications. Here, we show that the optical properties as well as the ENZ wavelength of magnetron-sputtered indium tin oxide (ITO) thin films could be judiciously engineered. The measurement of nonlinear optical properties reveals that the control of deposition conditions allows for the tuning of absorptive optical nonlinearity between saturable absorption and reverse saturable absorption. The ENZ wavelength for the ITO film is deduced as around 1553 nm. We obtain the highest third-order nonlinear absorption coefficient and imaginary part of third-order nonlinear susceptibility for the ITO thin film through Z-scan method as −50.56 cm/GW and ∼38 × 10−14 e.s.u. at 1050 nm, and −64.50 cm/GW and ∼45 × 10−14 e.s.u. at 1550 nm, respectively. We demonstrate further that the strong saturable absorption of the ITO thin film enables Q-switched pulse laser generation in ∼1050 and ∼1550 nm regions with tunable repetition rates and pulse energies. The present results suggest the great application potential of the ITO thin film in the field of nonlinear optical devices.

Osmotic conditions play an important role in the cell properties of human red blood cells (RBCs), which are crucial for the pathological analysis of some blood diseases such as malaria. Over the past decades, numerous efforts have mainly focused on the study of the RBC biomechanical properties that arise from the unique deformability of erythrocytes. Here, we demonstrate nonlinear optical effects from human RBCs suspended in different osmotic solutions. Specifically, we observe self-trapping and scattering-resistant nonlinear propagation of a laser beam through RBC suspensions under all three osmotic conditions, where the strength of the optical nonlinearity increases with osmotic pressure on the cells. This tunable nonlinearity is attributed to optical forces, particularly the forward-scattering and gradient forces. Interestingly, in aged blood samples (with lysed cells), a notably different nonlinear behavior is observed due to the presence of free hemoglobin. We use a theoretical model with an optical force-mediated nonlocal nonlinearity to explain the experimental observations. Our work on light self-guiding through scattering bio-soft-matter may introduce new photonic tools for noninvasive biomedical imaging and medical diagnosis.

Babinet complementary patterns of a spectrally tunable metamaterial incorporating a nematic liquid crystal is normally assumed to exhibit the same tuning range. Here we show that for a hybrid, liquid crystal-loaded metamaterial, the sensitivity of its terahertz resonances to the variations of the refractive index differs substantially for the two complementary patterns. This is due to a mismatch between the alignment of the liquid crystal and the direction of the local electric field induced in the metamaterial patterns. Furthermore, and more intriguingly, our experimental data indicate that it is possible to shift the resonance of the positive metamaterial pattern beyond the limit imposed by the alignment mismatch. Our analysis suggests that the observed anomalous frequency shift results from the orientational optical nonlinearity of a nematic liquid crystal.

Franckeite, a natural van der Waals heterostructure with excellent physicochemical characteristics, has shown great potential for high-performance optoelectronic device. Here, the few-layer franckeite nanosheets have been prepared by liquid phase-exfoliation method successfully, and the nonlinear optical absorption and carrier dynamics behaviors of the nanosheets have been studied experimentally. The franckeite nanosheets show wavelength- and intensity-dependent nonlinear absorption characteristics, and exhibit ultrafast carrier dynamic process. The ultrafast optical nonlinearity in franckeite nanosheets has been further validated via an Er3+-doped fiber laser to deliver stable femtosecond pulse. The experimental results reveal that franckeite heterostructure nanosheets can be an ideal candidate in the design and manufacture of ultrafast nonlinear optoelectronic devices.

In the current work, the borate-based glass specimens bearing composition (mol %) 5Na 2 O–10ZnO–10Bi 2 O 3 ‒(75‒ x)B 2 O 3 – x RE (where RE = Er 2 O 3 and Pr 6 O 11 , and x ranges from 0 to 5 mol %) were synthesized by conventional melt-quench method. The effect of rare earth ions concentration on photonic nonlinearities has been explored by the Z-scan method under the pumping of 532 nm in a nanosecond pulse regime. The Z-signatures revealed the occurrence of nonlinear absorption and refraction in the studied glass specimens. The nonlinear optical features were improved with respect to the rare earth concentration. The nonlinear optical features were superior for Er3+ doped glasses compared to Pr3+ doped glasses. This greatness of nonlinear optical features in Er3+ doped glasses was attributed to the existence of a large number of electrons (11 electrons) in the 4 f outer shell compared to those existing in the 4 f outer shell of Pr3+ (2 electrons). The enhancement of nonlinear gap features was also attributed to the creation of non-bridging oxygens in the host network when rare earths are loaded into the composition. The nonlinear photonic outcomes endorse that heavily Er3+ loaded glasses are superior over Pr3+ doped glasses for nonlinear optical device fabrications to work in the visible region. [ABSTRACT FROM AUTHOR]

Observation of strong inelastic light-matter interaction and large thermal conductivity of novel twodimensional graphene has invigorated the present research. Herein, the thermo-optic coefficient of graphene multilayers is obtained from their nonlinear refraction coefficients calculated from Z-scan experiment in closed aperture geometry. The refractive optical nonlinearity was obtained employing a continuous wave He-Ne laser and occurs due to thermal lensing effect. The graphene multilayers behave as the diverging (concave) lens giving rise to self-defocusing effect leading to negative sign of refractive nonlinearity. Accordingly, a large negative thermo-optic coefficient (-2.43×10-3 K-1) inferred for the graphene multilayers suggests its utility for thermo-optic device applications. [ABSTRACT FROM AUTHOR]

In this paper, we theoretically and experimentally demonstrated photothermal nonlinearities of both forward and backward scattering intensities from quasi-perfect absorbing silicon-based metasurface with only λ/7 thickness. The metasurface is efficiently heated up by photothermal effect under laser irradiation, which in turn modulates the scattering spectra via thermo-optical effect. Under a few milliwatt continuous-wave excitation at the resonance wavelength of the metasurface, backward scattering cross-section doubles, and forward scattering cross-section reduces to half. Our study opens up the all-optical dynamical control of the scattering directionality, which would be applicable to silicon photonic devices. [ABSTRACT FROM AUTHOR]

We consider the propagation of stationary dark and light spatial solitons and various pairs of incoherently coupled solitons in a planar waveguide based on a thin left-handed film of a Kerr substrate. It is shown that such solitons can be formed by guided modes with positive as well as negative group velocities. The conditions in which the propagation of light and dark spatial solitons in the same waveguide is possible irrespective of the sign of the nonlinear optical coefficients of the substrate. [ABSTRACT FROM AUTHOR]

This paper extends previous studies work on the application of Machine Learning (ML) to distortion compensation in optical communication systems with optical fibers nonlinear coefficients (γ) that exceed current industry standards e.g. γ > 1.4 W - 1 k m - 1 . To quantify the improvement afforded by ML methods under different transmission conditions the procedures are applied to a model of a typical single-frequency optical communication system with, a 3200 km fiber length, double polarization, and a 16-QAM modulation format. The performance of both transmitters and receivers that incorporate Neural Networks (NNs) are then examined over a wide range of γ values. In all cases considered, the system Q-factor is improved although the degree of enhancement is dependent on the signal to noise ratio. The ML structures that were investigated include Siamese neural networks (SNN) implemented at the receiver end as well as two-stage architectures that employ NNs at the transmitter together with a classifier at the receiver side. Classifiers ranging from simple decision tree structures to boosting, forests, extra trees, and Multi-layer perceptron (MLP) were further examined and found to provide significant enhancement for γ > 4 W - 1 k m - 1 . The optimal performance for highly nonlinear systems was achieved for two-stage systems with random forest or extra tree classifiers. Finally, empirical equations for each ML technique were derived that relate the Q-factor enhancement and the value of γ , and the number of triplet terms that are input into the neural network. These results could potentially be employed to relax manufacturing constraints and accordingly reduce system costs. [ABSTRACT FROM AUTHOR]

This paper studies the problem of data access at the receiver with large bit error rate and low quality factor. Due to this issue the information got inaccurately at the receiver side, the data should have high quality factor and low bit error rate to be simple of identification at the receiver when using the gates. The nonlinear properties of the semiconductor optical amplifier are utilized to accomplish the Boolean variable based math work, in which AND, NAND, and OR gates potentially used to endorse the Boolean function. Through blend this gates together any Boolean function can be accomplished and utilized to perform optical signal processing. The quality factor and BER are measured by utilizing the eye diagram analyzer, the state of the output bit and also shaped by the oscilloscope visualizer in optiwave simulation program. These models can be used for wavelength converter, header recognition, parity checking, binary addition, packet-header modification, encoding and encryption with pattern matching, and data encryption with high speed and high quality factor. [ABSTRACT FROM AUTHOR]

Graphitic carbon nitride (g-C3N4) featuring a stable heptazine ring structure and high polymerization degree, was indexed as a high thermochemical stability material, attracting rising research enthusiasm for diverse applications. However, the poor near-infrared (NIR) optical absorption and resulting limited NIR applications were pronounced for g-C3N4 due to its large bandgap of 2.7 eV. In the present work, sulfur-doping was manifested by first-principles calculations to introduce impurity level and result in anisotropic spin splitting in g-C3N4 for enhancing broadband nonlinear optical characteristics in NIR regime. The modified sulfur-doped g-C3N4 (S-C3N4) exhibited the maximum effective nonlinear absorption coefficient to be −0.82 cm/GW. Pulse duration within hundred nanoseconds was realized with high modulation stability employing S-C3N4 as saturable absorber in Q-switching operations. Moreover, broadband ultrafast photonics properties were successfully demonstrated in constructed ytterbium-doped and erbium-doped fiber lasers, generating highly stable dissipative soliton and traditional soliton mode-locking pulses. The presented S-C3N4 nanomaterial with remarkable nonlinear optical performances might explicitly boost the development and application of g-C3N4 materials in advanced optoelectronic and ultrafast photonic devices.

The present work measured the sign and the amount of nonlinear optical absorption coefficient and nonlinear refractive index of gold nanoparticles by Z-scan method. The Ti: sapphire laser is used in two modes: continuous wave and pulsed with 60 fs duration and a repetition rate of 80 MHz at the wavelength of 800 nm, with an average power of 28 mW. Gold nanoparticles were obtained by the laser ablation method with 20 ns pulses and a repetition rate of 10 Hz in SDS solution. Due to using femtosecond laser pulses with a high repetition rate, thermal and electronic nonlinear effects appeared. The results were compared with a continuous wave Z-scan at the same wavelength and exposure power to eliminate the cumulative thermal effect and separate the electronic and thermal nonlinear coefficients. The electronic and thermal nonlinear absorption coefficients were obtained 15×10-5 and 125×10-5cm.W-1, respectively. Kerr de-focusing effect occurred in both electronic and thermal nonlinearity, and the nonlinear electronic and the thermal refractions were calculated -41×10-9 and -34×10-9cm2W-1, respectively. The experiments show that the nonlinear coefficients of the sample prepared in this research are larger than the values obtained for the samples made by the chemical method.

A multiphoton spectroscopic approach is implemented to study the photoluminescence (PL) emission from excitonic traps and optical nonlinear properties of wide-bandgap semiconductor cadmium iodide single crystals. As a multiphoton approach, we use two-photon and three-photon schemes to excite the crystals for PL spectroscopic diagnosis. The PL spectra are observed and studied. The results show that PL emissions are from the defect-induced self-trapped excitons in the visible region. It is found that due to much longer absorption depth, the three-photon excitation enhances the PL yield and that the order of nonlinearity depends on the kind of the photon excitation scheme. The PL is also found to depend on the thickness of the crystals. Power-dependent activation energy of the excitonic traps is determined for both the bi-photonic and tri-photonic excitation schemes. The values range from 2.62 to 2.43 meV (2.64 to 2.45 meV) for three-photon (two-photon) excitation with pump energy within 5–40 MW/cm2. This power dependence might be related to the excitation depth. [ABSTRACT FROM AUTHOR]

Transparent conductive oxides exhibit attractive optical nonlinearity with ultrafast response and giant refractive index change near the epsilon-near-zero (ENZ) wavelength, originating from the intraband dynamics of conduction electrons. The optical nonlinearity of ENZ materials has been explained by using the overall-effective-mass and the overall-scattering-time of electrons in the extended Drude model. However, their response to optical excitation is yet the last building block to complete the theory. In this paper, the concept of thermal energy is theoretically proposed to account for the total energy of conduction electrons exceeding their thermal equilibrium value. The time-varying thermal energy is adopted to describe the transient optical response of indium-tin-oxide (ITO), a typical ENZ material. A spectrally-resolved femtosecond pump-probe experiment was conducted to verify our theory. By correlating the thermal energy with the pumping density, both the giant change and the transient response of the permittivity of ITO can be predicted. The results in this work provide a new methodology to describe the transient permittivities of ENZ materials, which will benefit the design of ENZ-based nonlinear photonic devices. [ABSTRACT FROM AUTHOR]

The realization of high-Q resonances in a silicon metasurface with various broken-symmetry blocks is reported. Theoretical analysis reveals that the sharp resonances in the metasurfaces originate from symmetry-protected bound in the continuum (BIC) and the magnetic dipole dominates these peculiar states. A smaller size of the defect in the broken-symmetry block gives rise to the resonance with a larger Q factor. Importantly, this relationship can be tuned by changing the structural parameter, resulting from the modulation of the topological configuration of BICs. Consequently, a Q factor of more than 3,000 can be easily achieved by optimizing dimensions of the nanostructure. At this sharp resonance, the intensity of the third harmonic generation signal in the patterned structure can be 368 times larger than that of the flat silicon film. The proposed strategy and underlying theory can open up new avenues to realize ultrasharp resonances, which may promote the development of the potential meta-devices for nonlinearity, lasing action, and sensing.

Despite various optical realizations of convolutional neural networks (CNNs), optical implementation of nonlinear activation functions and pooling operations are still challenging problems. In this regard, this paper proposes an optical saturable absorption nonlinearity and its atomic-level model, as well as two various optical pooling operations, namely optical average pooling and optical motion pooling, by means of 4f optical correlators. Proposing these optical building blocks not only speed up the neural networks due to negligible optical processing latency, but also facilitate the concatenation of optical convolutional layers with no optoelectrical conversions in-between, as the significant bottlenecks of implementing photonic CNNs. Furthermore, the proposed optical motion pooling layer increases the translation invariance property of CNNs, avoiding the inclusion of all corresponding translated images for the training procedure, and hence, increases the training speed of the neural network. The classification accuracy of the proposed optical convolutional layer is evaluated as the first layer of a customized version of AlexNet architecture, named as OP-AlexNet, for classification of Kaggle Cats and Dog challenge, CIFAR-10, and MNIST datasets, as 83.76%, 72.82%, and 99.25%, respectively, by using optical average pooling.

Non-linear bistable energy harvesters (BEH) can generate higher velocity responses compared with linear systems, leading to large-amplitude output voltages by stabilizing high-energy orbital oscillations of a tip magnet. Considering the centrifugal effects due to rotations shows that BEH can further maintain higher performances with wider bandwidths. However, BEH is sensitive to the centrifugal distance and can only perform well over a narrow range. Considering the need to set the centrifugal distance for the tip magnet in experiments and simulations, it is necessary to calculate an optimal centrifugal distance under different parameters. In theory, the relationship of non-linear frequency-matching between the jump-down frequency of the monostable state and the rotating frequency of the external circumstances can be utilized to solve for the optimal centrifugal distance under different parameters. The BEH performance and bandwidth are sensitive to variations in the centrifugal distance, and responses under an optimal distance are improved significantly. The non-linear system has advantages in terms of its effective operational bandwidth and capacity, especially considering the centrifugal effect. The different centrifugal distances of the installation position affect the stabilization of high-energy orbital oscillations, and the optimal installation of the centrifuge depends on a variety of corresponding physical characteristics. The simulation results for the velocity responses verify the optimal centrifugal distance to effectively broaden its frequency range. [ABSTRACT FROM AUTHOR]

Doping alkali metal atoms, especially lithium (Li), in nanocarbon materials has always been considered to be one of the most effective methods to improve the optical properties of the system. In this theoretical work, we doped a Li atom to the recently observed all-carboatomic molecule, cyclo[18]carbon (C 18), and finally obtained two stable configurations with Li inside and outside the ring. The calculation results show that the energy barrier of transition between the two Li@C 18 configurations is low, so the conversion is easy to occur at ambient temperature. Further study reveals that the state of Li@C 18 complex, namely its dominant configuration, can be switched by applying a proper external electric field (EEF). The electronic structure, absorption spectrum, and optical nonlinearity of the two configurations are found to be significantly different, which indicates that the optical properties of the Li@C 18 complex can be effectively regulated by switching the location of doped Li atom between inside and outside the carbon ring. With the help of various wavefunction analysis methods, the nature of the discrepancies in the properties of Li@C 18 complex with different configurations was deeply revealed. The relevant results are expected to provide theoretical guidance for development of cyclocarbon-based optical molecular switches. [Display omitted] [ABSTRACT FROM AUTHOR]

Graphitic carbon nitride (g-C3N4) featuring a stable heptazine ring structure and high polymerization degree, was indexed as a high thermochemical stability material, attracting rising research enthusiasm for diverse applications. However, the poor near-infrared (NIR) optical absorption and resulting limited NIR applications were pronounced for g-C3N4 due to its large bandgap of 2.7 eV. In the present work, sulfur-doping was manifested by first-principles calculations to introduce impurity level and result in anisotropic spin splitting in g-C3N4 for enhancing broadband nonlinear optical characteristics in NIR regime. The modified sulfur-doped g-C3N4 (S-C3N4) exhibited the maximum effective nonlinear absorption coefficient to be −0.82 cm/GW. Pulse duration within hundred nanoseconds was realized with high modulation stability employing S-C3N4 as saturable absorber in Q-switching operations. Moreover, broadband ultrafast photonics properties were successfully demonstrated in constructed ytterbium-doped and erbium-doped fiber lasers, generating highly stable dissipative soliton and traditional soliton mode-locking pulses. The presented S-C3N4 nanomaterial with remarkable nonlinear optical performances might explicitly boost the development and application of g-C3N4 materials in advanced optoelectronic and ultrafast photonic devices. [ABSTRACT FROM AUTHOR]

This paper focuses on the use of Cyclea peltata leaf extract for green synthesis of silver nanoparticles (CPL-AgNPs) post-optimization by one variable at a time (OVAT) approach for nonlinear optics application. The leaf extract of Cyclea peltata (10% w/v) and AgNO3 (1 mM) was used for the synthesis of silver nanoparticles (CPL-AgNPs). Reactions conditions like CPL extract concentration, salt concentration, temperature, pH, RPM, and time for synthesis were optimized by using OVAT approach. A UV-visible spectroscopic investigation confirmed the biosynthesis of CPL-AgNPs at 420 nm. Field emission scanning electron microscope (FESEM) confirmed the spherical monodispersed nanoparticles in the range of 30–50 nm and EDAX confirmed the purity of the sample. FTIR confirmed the capping of nanoparticles by plant phytochemicals. The synthesized CPL-AgNPs were evaluated for nonlinear optical properties using the Z-scan technique at 532 nm with a CW laser. Strong nonlinear absorption by the nanoparticles in the range of 2.85 × 10−2 cm/W was observed. Moreover, CPL-AgNPs display superior optical limitations. [ABSTRACT FROM AUTHOR]

Optics has already established as a very successful information carrier for computation and communication both in analog and digital domain for its several salient advantages. In last few decades, there were found several approaches where optics was suitably used to get different coded data. Here, in this paper, the authors propose a complete all-optical system for getting the intensity varied Manchester-encoded data. [ABSTRACT FROM AUTHOR]

Gold nanoparticles are excellent light absorbers at the surface plasmon resonance wavelength. This absorption process generates highly energetic electrons near the surface that enhances the local electric field on the gold nanoparticles surface, and results in modification of the refractive index. The present work focuses on interaction of the laser, both near and far from the resonance wavelength, with colloidal solution of plasmonic nanoparticles. For the laser beam interaction, we first prepared the gold nanoparticles by sol gel method and characterized the absorption spectrum in terms of particle size and morphology. The absorption peak in visible range confirmed to the formation of Au nanoparticles. Therefore, a laser at 532 nm was selected to study light matter interaction with Au nanoparticles in solution. The interaction produced diffraction rings, which changed shape over time due to convection of colloidal nanoparticles. In another experiment, a 405 nm laser with the same power produced only a laser spot on the screen. Thus, the 532 nm is closer to the surface plasmon excitation and is responsible for producing a pattern of diffraction rings in the far-field region. The produced diffraction rings provide a very simple and sensitive technique to find out induced nonlinear refractive index for the plasmonic nanoparticles. Finding plasmonic resonances holds importance for variety of applications in plasmonic sensing and these rings could be used to characterize the resonances.

Optical limiters are nonlinear devices that feature decreasing transmittance with increasing incident optical intensity, and thus can protect sensitive components from high‐intensity illumination. The ideal optical limiter reflects rather than absorbs light in its active ("limiting") state, minimizing risk of damage to the limiter itself. Previous efforts to realize reflective (rather than absorbing) limiters were based on embedding nonlinear layers into relatively thick multilayer photonic structures, resulting in substantial fabrication complexity, reduced speed and, in some instances, limited working bandwidth. In this paper, these tradeoffs are overcome by using the insulator‐to‐metal transition (IMT) in vanadium dioxide (VO2) to achieve intensity‐dependent modulation of resonant transmission through aperture antennas. Due to the large change of optical properties across the IMT, low‐quality‐factor resonators are sufficient to achieve high on–off ratios in the transmittance of the limiter. As a result, our ultrathin reflective limiter (thickness ≈1/100 of the free‐space wavelength) is broadband in terms of operating wavelength (>2 µm at 10 µm) and angle of incidence (up to ≈50° away from the normal). Our analysis of the experimental results via opto‐thermal simulations provides insight into limiter performance and is a useful guidance for further engineering efforts. [ABSTRACT FROM AUTHOR]

The thermal relaxation of second order optical nonlinearity in subsurface layer of a poled soda-lime silicate glass was studied. It is shown that the glass annealing below glass transition temperature leads to full relaxation of the nonlinearity. At the same time, the measurements of thermostimulated depolarization current demonstrate that spatial electric charge formed in the course of the glass polarization relaxes above glass transition temperature. This allows concluding that the second order optical nonlinearity in poled glasses is not induced by the spatial electric charge.

In the past two decades, extensive research and studies have been performed on graphene because of its exceptional physical properties. Owing to its ultrahigh carrier mobility, quantum Hall effect and unique optical transmittance, graphene is considered to be a multi-functional component for realizing next-generation optoelectronic and photonic devices. Significant efforts have been made towards efficient synthesis, transfer, and integration of graphene for use in device scale. However, the critical hurdles lie in developing 3D and conformal graphene, which are ideal for integrated hybrid photonic systems. Here, we review different methods of synthesizing graphene, specifically recent advances in the synthesis of direct, conformal, 3D graphene. In addition, we comprehensively summarize the latest progress made towards directly grown, 3D, conformal graphene-based photonic and optoelectronic applications. Finally, several important challenges for large-sale implementation of directly grown graphene-based optoelectronic and photonic devices are discussed. [ABSTRACT FROM AUTHOR]

The rare earth Pr3+ and Yb3+ doped phosphate glass were prepared by quenching method using electrical muful furnace. The optical band gap of rare earth Pr3+ and Yb3+ doped phosphate glass were studied. The dielectric permittivity, dielectric loss and electrical conductivity of the prepared samples have been studied using LCR meter with different frequencies at room temperature. The Vickers hardness number, brittle index, yield strength, fracture toughness of the rare earth Pr3+ and Yb3+ doped phosphate glasses were also calculated. The nonlinear optical parameters such as third order nonlinear coefficient and nonlinear refractive index were estimated using Z-scan method. The magnetic property of the Pr3+ and Yb3+ doped phosphate glass was studied using VSM analysis. The electro chemical properties of Pr3+ and Yb3+ doped phosphate glass electrodes in 5 M KOH electrolyte were studied using cyclic voltammetry, Galvanostatic charge–discharge and electrochemical impedance spectroscopy. The specific capacitance, energy density and capacity retention of Pr3+ and Yb3+ doped phosphate glasses were calculated. [ABSTRACT FROM AUTHOR]

The photo-responsive liquid crystals (LCs) close to the isotropic condition shows very large optical nonlinearity lasting for tens/hundreds of milliseconds after a pulse light illumination due to the flow-induced reorientation of liquid crystals. By optimizing the temperature and the pump light intensity, we succeeded to demonstrate various refractive index patterns due to this optical nonlinearity with a pattern illumination under a microscope. We demonstrated a rewritable hologram by using a computer generated hologram pattern on a photo-responsive LC. [ABSTRACT FROM AUTHOR]

A metamaterial film composed of gold nanoparticles wrapped in thin thermoresponsive polymer shells is described. The nanoparticle shells are kept partially hydrated so that the film acts as a "liquid mirror" and shows subtle interactions due to its composite metamaterial nature. Optically heating the film collapses the polymer, increasing the gold fill fraction and raising the reflectivity. This in turn decreases the optothermal absorption, making both the reflectivity and optothermal absorption nonlinear. When the polymer collapses, the film buckles due to thermophoretic flows competing against surface tension. These interactions generate a remarkable array of dynamic behaviors. Exposing the films to light causes an insulator‐to‐metal transition. Defects can be healed by returning the film to the liquid phase. Laser illumination of micrometer‐scale regions generates local dimples at low power and sinters microscale tracks at high power. When microbeads are combined into these films, optical switching results in quenching of their photoluminescence as well as the ability to manipulate their spatial position in real time. [ABSTRACT FROM AUTHOR]

Intersubband transitions (ISBTs) in conduction‐band quantum wells (QWs) have attracted tremendous attention for their high technological potential, ranging from quantum cascade lasers, quantum well infrared photodetectors, to various nonlinear optical elements. One of the main characteristics of using the ISBTs is their polarization selection rule, which forbids a normal‐incidence geometry. Here, it is shown that the ISBT selection rule is not strict on optical nonlinearities in metallic QWs (MQWs). The nonlinear process of second harmonic generation nearly follows the selection rule, while the optical Kerr nonlinear process severely deviates from it. The anomalous optical selection rules result from the non‐negligible ultrafast electron–electron scattering in these plasmonic systems, and a coupled mode theory is provided to get a physical grasp of the problem. The flexible selection rule in MQWs could bring drastic improvements in efficiency and diversity of ISBT‐based devices. [ABSTRACT FROM AUTHOR]

Abstract—The properties of the aberrational pattern resulting from the self-action of the light radiation mode TEM01 in liquid-crystal systems are studied. It is found that the interference of light rays corresponding to two peaks of intensity and nonlinear phase shift leads to the formation of a system of fringes in the Fraunhofer region; their angular period is controlled by the distance between peaks. These fringes fill the entire aberrational pattern (concentric ring pattern) or only its part, depending on the type of the profile of the light-induced phase shift. The possibilities of using the properties of the aberrational pattern in the TEM01 mode for studying the light-induced reorientation of the nematic liquid crystal director are shown. [ABSTRACT FROM AUTHOR]