Spatial Self-phase Modulation Research Articles

Recent Advances of Spatial Self-Phase Modulation in 2D Materials and Passive Photonic Device Applications.

Optical nonlinearity in 2D materials excited by spatial Gaussian laser beam is a novel and peculiar optical phenomenon, which exhibits many novel and interesting applications in optical nonlinear devices. Passive photonic devices, such as optical switches, optical logical gates, photonic diodes, and optical modulators, are the key compositions in the future all-optical signal-processing technologies. Passive photonic devices using 2D materials to achieve the device functionality have attracted widespread concern in the past decade. In this Review, an overview of the spatial self-phase modulation (SSPM) in 2D materials is summarized, including the operating mechanism, optical parameter measurement, and tuning for 2D materials, and applications in photonic devices. Moreover, some current challenges are also proposed to solve, and some possible applications of SSPM method are predicted for the future. Therefore, it is anticipated that this summary can contribute to the application of 2D material-based spatial effect in all-optical signal-processing technologies.

Spatial phase modulation and all-optical switching of tris(2`,2-bipyridyl)iron(II) tetrafluoroborate

The spatial self-phase modulation technique was applied to investigate the nonlinear optical properties of Tris(2`, 2-bipyridyl)iron(II) tetrafluoroborate solution. The obtained results show a strong pump laser beam (λ = 532 nm) that could modulate a weak probe laser (λ = 635 nm), indicating for new applications in nonlinear optical modulation. The temporal evolutions of diffraction rings were recorded, at the same time, the collapse effect was observed. Furthermore, our results led to evaluate many nonlinear parameters: the nonlinear refractive index (n2), Δn and thermo-optic coefficient (dn/dT). Our sample is candidate for all-optical switching devices.

Diffraction ring patterns and nonlinear measurements of the Tris(2′,2-bipyridyl)iron(II) tetrafluoroborate

The nonlinear optical properties of the Tris(2,2′-bipyridyl)iron(II) tetrafluoroborate in aqueous solution was investigated by the spatial self-phase modulation (SSPM) technique using CW laser at λ = 532 nm. The experimental results show large nonlinear refractive index (n2) and the thermo-optic coefficient (dn/dT) equal to −3.17 × 10−6 cm2/W and the 3.17 × 10−3 k−1, respectively. The effect of input power of excitation laser and the temporal evolution on the shape of the diffraction patterns were studied. Consequently, the collapse effect of the diffraction ring patterns was explained.

Observation of spatial self-phase modulation induced via two competing mechanisms.

Two spatial self-phase modulation (SSPM) patterns were observed in suspensions of Bi2TeSe2 nanosheets. Two mechanisms were found to produce SSPM with different occurrence times and power dependence. The Type I (narrow) rings are attributed to the coherent third-order nonlinear optical Kerr effect, which induces self-diffraction in 2D materials, and the Type II (wide) rings are assigned to the contribution of a thermal effect. The nonlinear refractive index of Bi2TeSe2 is found to be 2.30×10-5cm2W-1 at 700 nm. The findings described here provide an explanation for the formation of rings in 2D systems due to SSPM.

Nonlinear Optical Response of Chinese Teas Probed by Spatial Self-Phase Modulation

Chinese tea is the most highly consumed beverage globally. Its different types exhibit a strong nonlinear optical response as probed previously by Z-scan technique at various time scales. In this work, infusions of commercially available black, green, and white Chinese teas, prepared by running one cycle of a Soxhlet extraction, were studied by spatial self-phase modulation of a CW laser; each sample was found to have a different nonlinear refractive index n2, which can be used to distinguish these teas.

Liquid phase exfoliated boron nanosheets for all-optical modulation and logic gates

Boron nanosheets possess unique photoelectric properties, including photosensitivity, photoresponse, and optical nonlinearity. In this article, we show the interaction between light and boron nanosheets in which concentric rings formed in the far field, which attributed to the strong Kerr nonlinearity of boron nanosheets. Furthermore, the distortion, regulation and relationship between the Kerr nonlinearity and effective mass or carrier mobility of the diffraction rings of boron nanosheets have been investigated. Our work shows that the spatial self-phase modulation effect of boron nanosheets is indeed caused by nonlocal electronic coherence. In addition, we have implemented all-light modulation and all-light logic gates based on the prepared boron nanosheets. We believe that our results will provide a powerful demonstration of nonlinear photonic devices based on boron nanosheets and a reference for photonic devices based on two-dimensional materials.

Spatial self-phase modulation in WS2 and MoS2 atomic layers

Laser field-induced spatial self-phase modulation (SSPM) in WS2 and MoS2 atomic layer liquid suspensions displayed the diffraction profile of concentric rings at the far-field due to the coherent superposition of transverse wave vectors with characteristic spatial nonlinear phases. The evolution of the number of rings indicated the spatial alignment of anisotropic atomic layers in the liquid base solution. The intensity-dependent number of symmetric rings revealed the nonlinear refraction coefficients of MoS2 and WS2 atomic layers which were estimated to be ∼ −1.96 × 10−16 m2/W and ∼ −1.11 × 10−16 m2/W, respectively. The central interference profile and the diffraction pattern identified the negative polarity of nonlinear refraction. The vertically asymmetric diffraction ring indicates the phase distortion of optical field due to the heat convection.

Broadband spatial self-phase modulation and ultrafast response of MXene Ti3C2Tx (T=O, OH or F)

Abstract Two-dimensional layered materials (2DLM) have become the subject of intensive research in various applications such as electronics, photonics and optoelectronics due to their unique physical properties. As a new class of 2DLM, MXenes have attracted great interest due to their superior performance in a wide variety of applications such as batteries, supercapacitors, catalysts, electronics and optics. Here, we have investigated the broadband spatial self-phase modulation (SSPM) and ultrafast response of the MXene Ti3C2Tx (T=O, OH or F) experimentally. The MXene Ti3C2Tx exhibited the broadband nonlinear optical response via SSPM from 400 nm to ~1 μm under the ultrafast laser excitation, and ultrafast carrier characteristics with an ultrafast recovery time with femtosecond transient absorption spectroscopy. The experimental results have shown that the MXenes have the broadband nonlinear optical response, which can lay a foundation for the application prospect for the MXene-based ultrafast optoelectronic devices.

Low-cost nonlinear optics experiment for undergraduate instructional laboratory and lecture demonstration: A second experiment

This communication presents a second simple and affordable experiment on nonlinear optics which is suitable for an undergraduate educational laboratory and is useful as a tabletop demonstration in a lecture on nonlinear optics. The experiment is based on the spatial self-phase modulation of a laser beam that generates in the far-field a typical pattern of interference rings. Such a nonlinear optical effect is due to thermally induced changes on the phase of a Gaussian laser beam that impinges on an optically absorbing medium. As the absorber, we propose to use a commercial soy sauce or grape juice, both of which are sold in supermarkets and exhibit strong optical absorption. The activities proposed for the experiment allow us to obtain the nonlinear refractive index of the sample.

Optical and Thermal Properties of Laser-Ablated Platinum Nanoparticles Graphene Oxide Composite.

Platinum nanoparticles were synthesized in graphene oxide aqueous solution using a laser ablation technique to investigate the effect of optical linear, nonlinear and thermal properties of platinum-graphene oxide nanocomposite solution. The samples were prepared with different ablation times. The platinum nanoparticles that formed a spherical shape on the surface of graphene oxide solution were authenticated using UV-visible spectrum and transmission electron microscopy patterns. The particle size decreased with increasing ablation time, and the concentration and volume fraction of samples were increased. To obtain the optical linear, nonlinear and thermal properties of platinum-graphene oxide nanocomposite solution, UV-visible spectroscopy, Z-scan, thermal lens and photoacoustic techniques were used. Consequently, the linear and nonlinear refractive indices increased with an increase in the volume fraction of platinum nanoparticles. It was observed from the spatial self-phase modulation patterns that, the optical nonlinear property of the graphene oxide was enhanced in the presence of platinum nanoparticles, and the nonlinearity increased with an increase in the volume fraction of platinum nanoparticles inside the graphene oxide solution. The thermal diffusivity and thermal effusivity of platinum nanoparticles graphene oxide were measured using a thermal lens and photoacoustic methods, respectively. The thermal diffusivity and thermal effusivity of samples were in the range of 0.0341 × 10−5 m2/s to 0.1223 × 10−5 m2/s and 0.163 W s1/2 cm−2 K−1 to 0.3192 W s1/2 cm−2 K−1, respectively. Consequently, the platinum enhanced the optical and thermal properties of graphene oxide.

Two-dimensional Bi2S3-based all-optical photonic devices with strong nonlinearity due to spatial self-phase modulation

Abstract Bismuth sulfide (Bi2S3) is a binary chalcogenide semiconductor compound that has received much attention in optoelectronic devices because of its stratified structure. In this work we showed that the two-dimensional (2D) Bi2S3 shows strong nonlinearity using spatial self-phase modulation and that the all-optical photonic devices, e.g. the all-optical switches and all-optical diodes, have been demonstrated experimentally by observing the nonlinear behavior of the diffraction rings. In addition, an all-optical diode is designed in this work using combined structure with 2D Bi2S3/SnS2 nanosheet by taking advantage of the reverse saturated absorption of 2D SnS2 and saturated absorption of 2D Bi2S3. Nonreciprocal light propagation has been achieved with different incident wavelength and a variety of incident intensities. Those characteristics make 2D Bi2S3 a potential candidate for the next generation nonreciprocal all-optical device.

Transverse effect of superradiation due to nonlinear effect in Rb atomic medium.

We report on the investigation on the transverse effect of superradiation (SR) in Rb atomic medium by analyzing and comparing the diffraction patterns in the far-field under the circumstances that Gaussian and Bessel beam are taken as the excitation respectively. It is found that Gaussian SR shows a ring-pattern and its beam profile is closely dependent on the incident power and position of the sample cell. The experimental results are in good agreement with the simulations using semi-classical theory of SR together with spatial self-phase modulation (SPM), indicating that the transverse effect of SR is mainly attributed to its propagation in the nonlinear medium. By contrast, the beam profile of Bessel SR is hardly influenced by the input power thanks to its non-diffraction property. The comparison further confirms that the transverse effect of the SR is the result of the nonlinear effect for SR. This work provides useful information in understanding the physics behind the transverse effect of SR, which would be of significance in the applications of SR, such as enhancement on the beam quality and efficiency of the SR sources.

Nonlinear optical response spatial self-phase modulation in MoTe2: correlations between χ(3) and mobility or effective mass.

We report on an unambiguous observation of the third-order nonlinear optical effect, spatial self-phase modulation (SSPM), in a MoTe2 dispersion. The values of the third-order nonlinear optical coefficients effectively for one-layer MoTe2, χone-layer(3), are obtained through the SSPM method at excitation wavelengths 473, 532, 750, and 801nm, respectively. The wind-chime model is used to explain the ring formation time. The wavelength dependence of χone-layer(3) compares well with the photo-absorption spectra. Significantly, we find a correlation between χ(3) and the carrier mobility μ or effective mass m*, which again further supports the laser-induced ac electron coherence in 2D materials.

Anisotropic nonlinear refractive index measurement of a photorefractive crystal via spatial self-phase modulation.

We show that the refractive index modification photoinduced in a biased nonlinear photorefractive crystal can be accurately measured and controlled by means of a background incoherent illumination and an external electric field. The proposed easy-to-implement method is based on the far-field measurement of the diffraction patterns of a laser beam propagating through a self-defocusing medium undergoing spatial self-phase modulation. For various experimental conditions, both saturation intensity and maximum refractive index modification have been measured. We also clearly evidence and characterise the anisotropic nonlinear response of the crystal in the stationary regime.

Synthesis of bilayer graphene nanosheets by pulsed laser ablation in liquid and observation of its tunable nonlinearity

Bilayer graphene nanosheets (B-GNSs) have been synthesized from dry-cell graphite electrode by using facile laser ablation in liquid technique in ambient condition. The plasma plume generated on incidence of ns pulsed Nd: YAG laser fundamental radiation of 1064 nm has facilitated the transformation of bulk graphite (BG) into B-GNSs via liquid carbon phase within 30 min of laser irradiation, and the layer number is are found to be increased with further increase in laser ablation time. The thickness dependent coherent nonlinear optical (NLO) response of the synthesized materials in aqueous dispersion has been determined by spatial self-phase modulation technique. The oxygen-containing surface defects in multilayer GNSs (M-GNSs) have led to scarcity in amount of e-h pairs in compared to that in B-GNSs. Therefore, a better NLO polarization has been observed in B-GNSs in compared to that of M-GNSs. Moreover, the thickness dependent thermal conductivity and hydrodynamic performance of GNSs-water dispersion has led to the observation of tunable NLO response with change in temperature as well as with the intensity of pump laser. The experimental findings obtained in this work may be considered as a key step towards fabrication of graphene from graphitic waste materials for development of future nonlinear photonics devices.

A review on spatial self-phase modulation of two-dimensional materials

Self-diffraction appears when the strong laser goes through two-dimensional material suspension, and this spatial self-phase modulation (SPPM) phenomenon can be used to measure nonlinear optical parameters and achieve optical switch. At present, the mechanism of SPPM is still ambiguous. The debate mainly focuses on whether the phenomenon is caused by the nonlinear refractive index of the two-dimensional material or the thermal effect of the laser. The lack of theory limits the dimension of the phase modulation to the radius of the diffraction ring and the vertical imbalance. Therefore, it is urgent to establish a unified and universal SSPM theoretical system of two-dimensional material.

Enhanced nonlinear optical properties of solution dispersed carbon dots decorated graphene oxide with varying viscosity

Nonlinear optical response of solution dispersed Carbon Dots decorated Graphene Oxide (CDs-GO) with viscosity has been investigated. Spatial self-phase modulation and Z-scan technique were utilized to study the nonlinearity of the composite which was synthesized by microwave assisted route. The strong self-diffraction effect was observed on excitation with 403,450 and 532 nm wavelengths from a DPSS laser. The estimated value of χ(3) is 3.2 × 10−4 esu in water obtained using SSPM technique. The nonlinearity of the sample is due to the reorientation of the graphene oxide sheet with the strong electromagnetic field of lasers and two photon absorption. Enhanced nonlinearity observed with increase in input pump power and viscosity of the solvents endows them new potentials in nonlinear optical applications.

All-optical applications for passive photonic devices of TaS2 nanosheets with strong Kerr nonlinearity

2D Tantalum disulphide (TaS2) has been widely studied as a typical transition metal dichalcogenides (TMDCs) with excellent optical, chemical and electrochemical properties. However, there is little research on the comprehensively characterizing the interaction between light and the 2D TaS2 material. In this work, we studied the nonlinear optical response of the high quality few-layer TaS2 nanosheets and its all-optical applications. Our research shows that 2D TaS2 nanosheet has a broadband characteristic and exhibits a strong Kerr nonlinear optical response based on the spatial self-phase modulation (SSPM). More importantly, by taking advantage of the highly nonlinear optical response of the2D TaS2, typical all-optical phenomena, such as all-optical switching and nonreciprocal light propagation, have been demonstrated experimentally. This work can be viewed as an important demonstration of a TMDCs-based application prototype in nonlinear photonics, which could potentially indicate an essential step toward miscellaneous TMDCs-based passive photonic devices (all-optical diodes, all-optical switches, etc.)

Kerr Nonlinearity in germanium selenide nanoflakes measured by Z-scan and spatial self-phase modulation techniques and its applications in all-optical information conversion.

Germanium selenide (GeSe) has attracted considerable research interest due to its unique photoelectric characteristics: high abundance occurrence, low toxicity, high stability, and environmentally sustainable. To the best of our knowledge, less literature is available on the nonlinear optical (NLO) properties of GeSe and on its significance of the electronic structure. In this work, the GeSe nanoflake ethanol suspensions have been studied by using liquid phase exfoliation method and then characterized by Raman, transmission electron microscopy (TEM), transmittance and atomic force microscopy (AFM). The NLO properties of GeSe suspensions with different concentration are investigated by Z-scan and spatial self-phase modulation (SSPM) methods with continuous wave laser, which are coherent with the parameter nonlinear refractive index n2 and the third order nonlinear polarizabilities χ(3). The nonlinear refractive index n2 of GeSe dispersions basically occur in the order of 10-9 cm2/W for Z-scan methods and 10-6 cm2/W for SSPM technique, whereas the third-order nonlinear polarizabilities χ(3) total are within the range of 10-6 esu for SSPM method. On the basis of these substantial characteristics of the NLO response and high stability of the 2D GeSe, we have experimentally studied the applications of the GeSe suspensions on all-optical information conversion technique.

Preparation and optoelectronic studies of the organic compound [2-(2,3-dimethyl phenylamino)-N-Phenyl benzamide doped(PMMA)

The optical characteristics of organic compound, 2- (2,3-dimethyl phenylamino)-N-Phenyl benzamide, for two configurations, compound solution and compound doped PMMA as a film have been investigated. The compound was characterized by elemental analysis, FTIR, 1HMR, 13CNMR and theoretical study by using AM1-semi-empirical method. The optical properties were studied by using microscopic image surface, Fourier Transform Infrared (FT-IR), Atomic Force Microscopy images and an Ultraviolet–visible spectrometer. The thermal optical nonlinearity of organic compound has been studied by using Diode laser with the wavelength 473 nm. The samples were prepared by the microwave irradiation under solvent free condition within short time and appreciable yields. The Morphological structure dependence of the optoelectronic properties was also studied. The values of optical energy gaps to the direct ( $$E_{g}^{d}$$ ) and indirect ( $$E_{g}^{in}$$ ) for the compound doped film estimated to be 2.99 eV, 2.75 eV respectively. Optically smooth and homogeneous 2-(2,3-dimethyl phenylamino)-N-Phenyl benzamide doped Poly methyl methacrylate (PMMA) film was experimentally investigated for the surface distribution by scan with 2θ. Also, the spatial self-phase modulation (SSPM) is characterized. The observed induced patterns have been simulated numerically by using Fresnel-Kirchhoff’s theory. The value of nonlinear refractive index n2 in the case of compound solution is confirmed to have less value than in a compound doped film.