Nonlinear Optical Devices Research Articles

Enhanced Electrochemical Properties of KTiOPO4–rGO Negative Electrode for Sodium and Potassium Ion Batteries

Potassium titanyl phosphate (KTiOPO4) is a well-known material for nonlinear optical device applications, but its electrochemical properties are not yet well understood. This study investigates sodium and potassium storage properties of KTiOPO4 using alkali metal fluorosulfonyl amide based nonaqueous electrolytes and a higher stiffness sodium alginate binder. The prepared KTiOPO4-reduced graphene oxide (rGO) composite electrode delivers stable desodiation and depotassiation capacities of 97 and 123 mAh g–1, respectively, at 0.075 C (10 mA g–1) over 70 cycles. The potassium cells demonstrate excellent cycle stability and high rate capability performances. Operando and ex situ XRD measurements confirm the multiple structural changes by potassiation/depotassiation and the high reversibility of the phase evolution.

Study of nonlinear optical phenomena in silicone films encapsulated with SiO2 and Si/SiO2 spherical particles

Infrared converters to visible range are in demand for creation of optoelectronic devices, infrared visualizers and other non-linear optical devices. In this work we study nonlinear optical properties of monodisperse SiO2 and Si/SiO2 spheres encapsulated into silicone films. The fabricated silicone films containing SiO2 spheres demonstrated a bright third harmonic generation signal, and films with Si/SiO2 spheres demonstrated a significant second harmonic generation signal in the whole visible range. The developed materials and methods provide a platform for future infrared to visible converters based on silicon.

Synthesis, Crystal Structure, Biological Evaluation, DFT Calculations and Third Order Nonlinear Optical Studies of Pyrazolines

• Synthesis of a novel series of pyrazolines. • Chemical structures were confirmed by crystal study and spectral techniques. • In-silico and anticancer properties of compounds were tested against MCF-7 and HCT116 cell lines. • DFT computational studies were carried out to understand structural, absorption, and first static hyperpolarizability properties. • NLO properties were studied using open/closed aperture z-scan techniques. Novel pyrazoline derivatives were synthesized and characterized by FTIR, NMR, UV-visible, and mass spectral studies. All the synthesized compounds 6a-f were screened for anticancer activity against MCF-7 and HCT 116 cell lines via SRB assay. Among the synthesized pyrazolines 6b and 6f showed appreciable anticancer activity. The molecular docking study was done with two proteins (PDB No: 1M17 and 5ZTO) to study the binding interactions of the compounds with proteins. ADME study showed that the compounds exhibited drug-likeness properties, following Lipinski's rule of five. The molecular structure of compound 6b was studied using the single-crystal X-ray diffraction method. The structural, absorption and first static hyperpolarizability properties of the compound 6b were studied using density functional theory (DFT) calculations. The experimental data and calculated FTIR and UV-visible spectral data are in good agreement. The third order nonlinear optical properties were studied using open and closed aperture z-scan techniques. The compound 6b showed nonlinear absorption ( β ) of 1.94 × 10 − 11 m/W at intensity ( I 0 ) is 4.49 GW / c m 2 . Third order nonlinear susceptibility is of the order of 10 −12 esu and this indicates the molecule has the potential to be used in nonlinear optical device applications.

Exploitation of electric field assisted optical signal amplification in ferroelectric photorefractive K0.50Na0.50NbO3 thin film

The exploitation of non-linear optical property of potassium sodium niobate [K x Na 1-x NbO 3 (x = 0.50 or KNN-50)] thin film using the two-wave mixing technique in the presence of an external electric field has been performed for the first time. The results show that the presence of external electric field enhances the non-linear optical activity in the KNN-50 medium. For this study, the KNN-50 thin film was prepared on fused quartz substrate by pulsed laser deposition (PLD) technique. XRD study confirms the formation of perovskite phase, and the FESEM image supports the growth of densely packed micro-structured KNN-50 thin film. The band gap of 800 nm thick KNN-50 thin film was found to be 4.1 eV. The electric field assisted nonlinear optical studies are promising, and opens large opportunity of incorporation of these KNN-50 thin films in the development of non-linear optical devices. • The exploitation of non-linear optical property of potassium sodium niobate [K x Na 1-x NbO 3 (x = 0.50 or KNN-50)] thin film using the two-wave mixing technique in the presence of an external electric field has been performed for the first time. • K 0.50 Na 0.50 NbO 3 films were deposited on fused quartz substrate using PLD technique. • XRD study confirms the formation of perovskite phase, and the FESEM image supports the growth of densely packed micro-structured KNN-50 thin film. • Strong non-linear optical property was observed in photorefractive KNN thin films using Two wave mixing technique via the pump-probe set-up. • The obtained results in the present work for KNN thin film are of great significance for its prospective applications in the field of photorefractive devices, electro-optic devices and light modulators .

Ultrafast third-order nonlinear optical properties of self-assembled PCPDTPhSO3Na/C70-(EDA)8 periodically overlapping film

A set of ultrathin multilayer films with alternated layers containing Poly[4,4-bis(4-sulfobutyl)-4H-cyclopenta[2,1-b:3,4-b′]dithiophene-2,6-diyl]-1,4-phenylene sodium sa (PCPDTPhSO3Na) as donor and amine group modified fullerene derivative C70-(ethylenediamine)8 (C70-(EDA)8) as acceptor were prepared using layer-by-layer assembly technique on a quartz substrate. Driven by the electrostatic force, C70-(EDA)8 and PCPDTPhSO3Na were alternately adsorbed on the substrate to form donor–acceptor periodically overlapping structure. The growth of the film was monitored by UV-Vis absorption spectra, showing regularly consecutive deposition process. The ultrafast third-order nonlinear optical properties of the films were investigated via a 4f coherent imaging system with phase object (NIT-PO) with 190 fs laser pulses at 400 nm. Experimental results demonstrate that the ultrathin films exhibit excellent self-focusing effect (n2∼4.02 × 10−16 m2/W) and reverse saturable absorption properties (β∼7.75 × 10−10 m/W). Our studies indicate that the PCPDTPhSO3Na/C70-(EDA)8 film has significant potential for applications in future nonlinear optical devices.

Azimuthal and radial modulation of double-four-wave mixing in a coherently driven graphene ensemble.

We investigate in detail the azimuthal and radial modulation (i.e., the azimuthal order lj and radial order pj with j = 1, 2) of double-four-wave mixing (double-FWM) by use of two higher-order Laguerre-Gaussian (LG) beams in a Landau quantized graphene ensemble. A pair of weak probe pulses in the graphene ensemble interacts with two LG beams and thus two vortex FWM fields with the opposite vorticity are subsequently generated. In combination with numerical simulations, we reveal that (i) there appear l1 + l2 periods of phase jumps in the phase profiles under any conditions; (ii) p + 1 concentric rings emerge in the intensity profile and the strength is mainly concentrated on the inner ring when the two LG beams have the same radial orders (i.e., p1 = p2 = p); (iii) there are p raised narrow rings occurring in the phase profile in the case of p1 = p2 = p and l1 ≠ l2, and the raised narrow rings would disappear when p1 = p2 and l1 = l2; (iv) pmax + 1 concentric rings appear in the intensity profile, meanwhile, |p1 - p2| convex discs and pmin raised narrow rings emerge in the phase diagram in the case of p1 ≠ p2, here pmax = max(p1, p2) and pmin = min(p1, p2). Moreover, the two generated FWM fields have the same results, and the difference is that the phase jumps are completely opposite. These findings may have potential application in graphene-based nonlinear optical device by using LG beams with adjustable mode orders.

Synthesis and Third-Order Nonlinear Synergistic Effect of ZrO2/RGO Composites.

Tuning the third-order nonlinear properties of graphene by hybrid method is of great significance in nonlinear optics research. ZrO2/reduced graphene oxide (RGO) composites with different ZrO2 concentrations were prepared by a simple hydrothermal method. The morphology and structure show that ZrO2 nanoparticles were uniformly dispersed on the surface of graphene nanosheets. The nonlinear optical (NLO) characteristics of composites with different ZrO2 concentrations were studied by the Z-scan technique of 532 nm picosecond pulsed laser. The results showed that ZrO2/RGO composites had saturated absorption and positive nonlinear refraction characteristics. Meanwhile, the third-order nonlinear susceptibility of the ZrO2/RGO composite with a 4:1 mass ratio of ZrO2 to graphene oxide could reach 23.23 × 10−12 esu, which increased tenfold compared to RGO, and the nonlinear modulation depth reached 11.22%. Therefore, the NLO characteristics could be effectively adjusted by controlling the concentration of ZrO2, which lays a foundation for further research on the application of ZrO2/RGO composites in NLO devices.

Asymmetric all-dielectric active metasurface for efficient dual reflection modulation

Active metasurface provides an efficient way to achieve optical response in the subwavelength range, dielectric metasurface has attracted much attention due to its low-loss mode and excitable electric/magnetic resonance mode, resulting in a far wider range of applications. However, the resonance spectrum is relatively broad due to the strong radiative loss of the symmetric dielectric metasurface, which limits its application in large modulation extinction ratio. Hence, an active metasurface integrated with the phase change material Ge2Sb2Te5 (GST) is proposed. The active metasurface can support the symmetry-protected quasi bound states in the continuum (QBIC) and excite resonance modes with extremely high quality-factors. As an active medium, the GST layer undergoes a transition from the amorphous state to the crystalline state when the temperature increases, leading to a change in the amplitude/phase of the reflection spectrum. It is demonstrated that dual reflection modulation and the figure-of-merit (FoM) can reach up to 92.0% at the wavelength of 1.45 μm and 92.5% at the wavelength of 1.52 μm as the GST layer is in the middle of nanodisks. An extremely high FoM of 98.5% is also realized when the surface of silicon nanodisks is coated with the GST layer. In addition, the modulation mechanism of the optical response of the active metasurface has been investigated, which is of great significance to the design of the active metasurface. The proposed active all-dielectric asymmetric metasurface has a huge potential in tunable nonlinear optical devices.

Giant Third-Harmonic Optical Generation from Topological Insulator Heterostructures

The downscaling of nonlinear optical devices is significantly hindered by the inherently weak nonlinearity in regular materials. Here, we report a giant third-harmonic generation discovered in epitaxial thin films of V-VI chalcogenide topological insulators. Using a tailored substrate and capping layer, a single reflection from a 13 nm film can produce a nonlinear conversion efficiency of nearly 0.01%, a performance that rivals micron-scale waveguides made from conventional materials or metasurfaces with far more complex structures. Such strong nonlinear optical emission, absent from the topologically trivial member in the same compound family, is found to be generated by the same bulk band characteristics that are responsible for producing the band inversion and the nontrivial topological ordering. This finding reveals the possibility of obtaining superior optical nonlinearity by examining the large pool of newly discovered topological materials with similar band characteristics.

Investigation on synthesis, growth, optical, mechanical, dielectric and third order non linear optical properties of cadmium chloride monohydrate doped sulphamic acid crystals for nonlinear optical device fabrications

Sulphamic acid is a potential material that exhibits excellent optical properties. Good qualities of cadmium chloride monohydrate doped sulphamic acid crystals were grown successfully by slow evaporation method at room temperature. The grown CCMSA crystals were characterized by single crystal X-ray diffraction and conforms the unit cell parameters as, a = 8.10 Å, b = 8.15 Å, c = 9.28 Å, α = β= γ = 90̊ and volume V = 612 Å3. The grown crystal belongs to the orthorhombic crystal system. The well defined sharp peaks in the powder XRD pattern reveal the good crystalline nature of the grown crystal. The transmittance ability of the grown crystal was confirmed by UV Visible spectral analysis. The functional groups of the crystal were confirmed by FTIR spectrum. The dielectric response of the crystal was analyzed in the frequency range between 10 – 90 kHz for two different temperatures at 35 °C and 55 °C. Micro hardness study is carried out to investigate the mechanical properties such as fracture toughness, brittleness index, and elastic stiffness coefficient. The nonlinear refractive index, absorption coefficient and third order susceptibility were estimated by Z - scan technique. All the results were compared and discussed in detail to get an insight into the effect of doping concentration on sulphamic acid crystal.

Investigation of Spontaneous Raman Scattering in Few-Mode Fibers: Dependence on Polarization and Spatial Modes

We study Raman gain in few-mode fibers (FMFs) by measuring spontaneous Raman scattering in polarization-maintaining FMF, mode-maintaining FMF and common FMF. The results show that the intensities of spontaneous Raman scattering in different polarization and spatial modes are affected by vector mode coupling of the degenerate modes in FMFs, which weakens the polarization- and spatial-mode dependence of Raman gain. Our investigation can be used for developing the FMF-based nonlinear-optical devices and sub-systems.

Nonlinear nanophotonics based on surface plasmon polaritons

Surface plasmon polaritons (SPPs), elementary excitation of the hybrid states between collective motion of electrons and photons, are associated with strong local field enhancement and deep subwavelength mode confinement. The use of SPPs in nonlinear optics can amplify intrinsically weak nonlinear processes and shrink down the size of nonlinear optic devices to a nanometer scale. In this Perspective, we review the nonlinear optic processes using SPPs in the plasmonic waveguides and foresee their potential in developing compact nonlinear integrated circuits. We discuss the key factors to enhance the conversion efficiency from the plasmonic waveguide, including the spatial overlap between the interacting modes and the nonlinear materials, and the momentum conservation that allows the coherent constructive superposition. Strategies toward this goal include shrinking the effective mode area through adjusting the geometry of the plasmonic waveguide, proper incorporation of the nonlinear susceptibilities to the plasmonic near field, and the use of counter-propagating configurations or phase compensation techniques. We also forecast the future developments of nonlinear plasmonics based on propagating SPPs in active nonlinear devices.

Suspended AlGaAs waveguide for integrated nonlinear photonics

AlxGa1-xAs compound is one of the promising platforms to realize high performance nonlinear optical devices, which provide ultra-high third order nonlinearity and negligible two-photon absorption in the range of telecom wavelength. To achieve highly efficient optical confinement, the conventional AlGaAs waveguide cladding layer is achieved by using SiO2 via the wafer bonding process or AlGaAs with higher Al concentration, which requires a complex fabrication process. In this work, we demonstrate a suspended Al0.5Ga0.5As waveguide structure directly grown on the GaAs substrate by using the molecular beam epitaxy system. Both self-phase modulation and four-wave-mixing experiments are performed. By solving the nonlinear Schrödinger equations and the degenerated parametric amplification process, the n2 value is calculated to be 1.6 × 10−17 m2/W, and the nonlinear parameter is determined to be 155 W−1 m−1. As the AlGaAs thin film can be directly grown on the Si based substrate, this suspended waveguide platform could potentially be developed on a large scale silicon wafer for integrated nonlinear photonic devices.

Investigation of structure, morphology, photoluminescence, linear and third-order nonlinear optical properties of Sn1−xLaxO2 thin films for optical limiting applications

Transparent nano-crystalline thin films of Sn1−xLaxO2 (x = 0–0.1) were deposited on glass substrates using the cost-effective chemical spray pyrolysis method. The influence of La3+ concentration on the structural, morphological, linear and third-order nonlinear optical properties of the films were analysed. All the films possessed tetragonal crystalline structure, having a preferred (1 1 0) plane orientation irrespective of the doping content. Till a doping of 3 at%, the crystallite size showed a decreasing tendency. The fibrous morphology exhibited by the pure film got transformed into dense spherical microstructures at lower La doping levels. The films with lower doping content showed above 60% of transmittance in the visible wavelength region. The modification in the energy band gaps of the films were observed due to variations in the La concentration. The presence of various defects identified in the deposits by photoluminescence (PL) spectra analysis in the ultraviolet and visible region. Near white light emission was noticed in the films due to these defects. All the films exhibited third-order optical nonlinearity with an observed switching between reverse saturable absorption (RSA) and saturable absorption (SA). The films exhibited self-focussing and defocussing nature due to variation in the doping level. Sn0.94La0.06O2 film was identified as suitable for optical limiting application due to its least limiting threshold value. Hence, these spray pyrolyzed La doped films can be used in optical and nonlinear optical devices.

Multistate Tuning of Third Harmonic Generation in Fano‐Resonant Hybrid Dielectric Metasurfaces

AbstractHybrid dielectric metasurfaces have emerged as a promising approach to enhancing near field confinement and thus high optical nonlinearity by utilizing low loss dielectric rather than relatively high loss metallic resonators. A wider range of applications can be realized if more design dimensions can be provided from material and fabrication perspectives to allow dynamic control of light. Here, tunable third harmonic generation (THG) via hybrid metasurfaces with phase change material Ge2Sb2Te5 (GST) deposited on top of amorphous silicon metasurfaces is demonstrated. Fano resonance is excited to confine the incident light inside the hybrid metasurfaces, and an experimental quality factor (Q‐factor ≈ 125) is achieved at the fundamental pump wavelength around 1210 nm. Not only the switching between a turn‐on state of Fano resonance in the amorphous state of GST and a turn‐off state in its crystalline state are demonstrated, but also gradual multistate tuning of THG emission at its intermediate states. A high THG conversion efficiency of η = 2.9 × 10−6% is achieved, which is 32 times more than that of a GST‐based Fabry–Pèrot cavity under a similar pump laser power. Experimental results show the potential of exploring GST‐based hybrid dielectric metasurfaces for tunable nonlinear optical devices.

All-optical polarization and amplitude modulation of second-harmonic generation in atomically thin semiconductors

Second-harmonic generation is of paramount importance in several fields of science and technology, including frequency conversion, self-referencing of frequency combs, nonlinear spectroscopy and pulse characterization. Advanced functionalities are enabled by modulation of the harmonic generation efficiency, which can be achieved with electrical or all-optical triggers. Electrical control of the harmonic generation efficiency offers large modulation depth at the cost of low switching speed, by contrast to all-optical nonlinear devices, which provide high speed and low modulation depth. Here we demonstrate all-optical modulation of second-harmonic generation in MoS2 with a modulation depth of close to 100% and speed limited only by the fundamental pulse duration. This result arises from a combination of D3h crystal symmetry and the deep subwavelength thickness of the sample, it can therefore be extended to the whole family of transition metal dichalcogenides to provide great flexibility in the design of advanced nonlinear optical devices such as high-speed integrated frequency converters, broadband autocorrelators for ultrashort pulse characterization, and tunable nanoscale holograms.

Enhancing Si3N4 Waveguide Nonlinearity with Heterogeneous Integration of Few-Layer WS2.

The heterogeneous integration of low-dimensional materials with photonic waveguides has spurred wide research interest. Here, we report on the experimental investigation and the numerical modeling of enhanced nonlinear pulse broadening in silicon nitride waveguides with the heterogeneous integration of few-layer WS2. After transferring a few-layer WS2 flake of ∼14.8 μm length, the pulse spectral broadening in a dispersion-engineered silicon nitride waveguide has been enhanced by ∼48.8% in bandwidth. Through numerical modeling, an effective nonlinear coefficient higher than 600 m–1 W-1 has been retrieved for the heterogeneous waveguide indicating an enhancement factor of larger than 300 with respect to the pristine waveguide at a wavelength of 800 nm. With further advances in two-dimensional material fabrication and integration techniques, on-chip heterostructures will offer another degree of freedom for waveguide engineering, enabling high-performance nonlinear optical devices, such as frequency combs and quantum light sources.

Temperature-dependent optical properties of AgGaS2 in the terahertz range

The temperature-dependent optical properties of the AgGaS2 crystal were characterized in the 0.2–2 THz range by terahertz time-domain spectroscopy (TDS). The refractive indices and the absorption coefficients along and orthogonal to the optical axis (c axis) were measured, and the temperature-dependent Sellmeier equations were fitted for various applications of linear and nonlinear optical devices. An E mode vibrating orthogonal to the c axis centering at 1.03 THz (34 cm−1) and a B2 mode along the c axis centering at 1.86 THz (62 cm−1), were observed for the first time. The phonon softening during the temperature rise was discussed and analyzed with the help of Raman spectroscopy. According to the measured absorption spectrum of AgGaS2, we also fitted the parameters of the low-frequency phonon modes at room temperature with the Lorentz dispersion model, which is helpful in predicting the lattice dynamics and optical behaviors of the crystal.

DFT study of new organic materials based on PEDOT and 4-[2-(2-N, N-dihydroxy amino thiophene) vinyl] benzenamine.

In the present study, we theoretically determine the optoelectronic, electronic, nonlinear optical (NLO) and thermodynamic properties of new materials from the conjugated organic polymer poly (3,4-ethylenedioxythiophene) (PEDOT) doped with halogens (fluorine and chlorine), combined with the organic semiconductor 4-[2-(2-N, N-dihydroxy amino thiophene) vinyl] benzenamine (DATVB). The molecular geometry of the ground state, the optoelectronics and electronic parameters have been calculated by combining the 6-311++G (d, p) basis set with various functionals of the density functional theory (DFT). The functionals B3LYP and CAM-B3LYP have been used for NLO parameters. The energy gaps obtained for all the compounds are less than 3.0 eV. These results clearly show that PEDOT and its derivatives can be considered as good semiconductors. They can be tested for use in the manufacture of organic solar cells (OSC) and organic light-emitting diodes (OLED). The first order hyperpolarizabilities of these PEDOT hybrid compounds are much higher than those of the reference compound for NLO applications, namely para-nitroaniline (p-NA), which opens up a new field of application for PEDOT in NLO devices. The thermodynamic parameters such as the zero-point vibrational energy (ZPVE), the enthalpy (H), the heat capacity at constant volume (cv), the entropy (S) and the free energy (G) have been calculated and are reported herein.

Dynamical manipulation of a dual-polarization plasmon-induced transparency employing an anisotropic graphene-black phosphorus heterostructure.

Dynamical tunable plasmon-induced transparency (PIT) possesses the unique characteristics of controlling light propagation states, which promises numerous potential applications in efficient optical signal processing chips and nonlinear optical devices. However, previously reported configurations are sensitive to polarization and can merely operate under specific single polarization. In this work we propose an anisotropic PIT metamaterial device based on a graphene-black phosphorus (G-BP) heterostructure to realize a dual-polarization tunable PIT effect. The destructive interference coupling between the bright mode and dark modes under the orthogonal polarization state pronounced anisotropic PIT phenomenon. The coupling strength of the PIT system can be modulated by dynamically manipulating the Fermi energy of the graphene via the external electric field voltage. Moreover, the three-level plasmonic system and the coupled oscillator model are employed to explain the underlying mechanism of the PIT effect, and the analytical results show good consistency with the numerical calculations. Compared to the single-polarization PIT devices, the proposed device offers additional degrees of freedom in realizing universal tunable functionalities, which could significantly promote the development of next-generation integrated optical processing chips, optical modulation and slow light devices.