Third-order Nonlinear Materials Research Articles

Click on the Chemically Modified New Third-Order Nonlinear Organic Materials

Click on the Chemically Modified New Third-Order Nonlinear Organic Materials

Third-order nonlinearity with subradiance dark-state in ultra-strong excitons and surface plasmon coupling using self-antiaggregation organic dye

A strong coupling regime with dressed states is formed when a propagating surface plasmon (PSP) mode coherently exchanges energy with an ensemble of excitons at a rate faster than the system’s losses. These states are superpositions of superradiance excitons and PSP modes, accompanied by remaining subradiance or ‘dark’ exciton states. Dark-states are ubiquitous, especially in disordered systems, and they rise in number as the number of excitons increases. Here, the ultra-strong coupling regime was experimentally observed with the coupling strength to bare energy as high as g/∼ 0.23 using a self-antiaggregation organic dye, BOBzBT2 in an Otto-SPR configuration. We show that the hybrid system of excitons in a nonlinear organic dye layer and a PSP mode can be described by employing dark-state in a theory of nonlinear third-order sum-frequency generation (TSFG). Close agreement between the theory and the experiment has been demonstrated. The study opens up a new perspective for establishing a relationship between the optical properties of a third-order nonlinear material and the extent of strong coupling.

Phenothiazine-based donor–acceptor covalent–organic frameworks with keto–enol irreversible tautomerism as a promising third-order nonlinear optics material

Keto–enol tautomerization endowed TFP-TZ with more D–A interaction strengths and an electron-withdrawing CO group in the keto form facilitated charge transfer.

A FETD scheme and analysis for photonic crystal waveguides comprising third-order nonlinear and linear materials

In this paper, we design a time-domain finite element (FETD) algorithm for solving Maxwell’s equations in third-order nonlinear media. The Cardano’s method is used to solve the nonlinear constitutive equation. At the same time, we also establish the continuous stability of the third-order nonlinear model and the numerical stability of the FETD scheme. In order to reduce the wave reflection from the truncated domain boundary, the anisotropic perfectly matched layer model is developed and solved. Extensive numerical simulations are carried out and they demonstrate that bistable transmission switches depending on the incident wave’s intensity can be obtained if a number of rods made of Kerr-type nonlinear materials are inserted around the bend of the linear bent photonic crystal waveguides.

Efficient Quadrature Squeezing from Biexcitonic Parametric Gain in Atomically Thin Semiconductors.

Modification of electromagnetic quantum fluctuations in the form of quadrature squeezing is a central quantum resource, which can be generated from nonlinear optical processes. Such a process is facilitated by coherent two-photon excitation of the strongly bound biexciton in atomically thin semiconductors. We show theoretically that interfacing an atomically thin semiconductor with an optical cavity makes it possible to harness this two-photon resonance and use the biexcitonic parametric gain to generate squeezed light with input power an order of magnitude below current state-of-the-art devices with conventional third-order nonlinear materials that rely on far off-resonant nonlinearities. Furthermore, the squeezing bandwidth is found to be in the range of several meV. These results identify atomically thin semiconductors as a promising candidate for on-chip squeezed-light sources.

Optical Properties of New Third-Order Nonlinear Materials Modified by Click Chemistry.

A high-yielding click reaction was used to synthesize a series of highly conjugated, symmetrical, as well as asymmetrical compounds with a benzene core. Cyclic voltammetry and ultraviolet/visible absorption spectroscopy were carried out, and proved that the side groups of the benzene derivatives played an important role in the energy gaps, and affected the third-order non-linear optical response. The maximum absorption wavelength of the series of benzene derivatives showed an obvious red-shift. Moreover, the addition of resilient electron-withdrawing groups significantly narrowed the energy levels as compared with precursors. The third-order nonlinear properties of this benzene derivative were tested by the Z-scan technique. The expected properties of this series of molecules were obtained, and it was found that the series of molecules undergoes a transition from reverse saturable absorption to saturable absorption, which has certain reference significance for a nonlinear optical field.

Synthesis of pyrene-based materials with third-order nonlinearity optical property by click chemistry modification

PurposeCurrently, conjugated nonlinear optical (NLO) materials suffer from the drawbacks of complex manufacturing process and high cost. To further study the NLO materials with cost-effective, it is necessary to prepare new NLO materials with satisfactory performance.Design/methodology/approachPyrene derivatives with good third-order NLO properties were synthesized by combining pyrene compounds with TCNE, TCNQ, F4-TCNQ and other molecular systems by clicking chemical method.FindingsThe pyrene derivatives were characterized by ultraviolet spectrum and Z-scan. The charge-transfer of the D-p-A structures plays a key role in the absorption peak shifts. And the third-order nonlinear absorption of the products revealed good third-order NLO susceptibilities.Research limitations/implicationsThe synthesis technology of pyrene derivatives is not mature enough and is in the preliminary exploration stage. So, the authors produced a relatively small number of samples and did not conduct a very comprehensive test.Practical implicationsThis novel pyrene derivative is suggestive and can promote the exploration and development of the third-order nonlinear materials.Originality/valueFour new pyrene derivatives were synthesized by selecting new molecular systems. Because of its good chemical properties and stable properties, it can be a reference for the development of third-order nonlinear materials in the future.

Generation of sum- and difference-squeezing by the beam splitter having third-order nonlinear material

We study the possibilities of generation of bimodal version of the higher-order squeezing, sum- and difference-squeezing by using the ‘beam splitter of materials having third-order nonlinearity (BSTN)’. We find that these higher-order squeezing can be generated by using this BSTN under different conditions. As a simplest case, we inject light with coherent state at one input port and the vacuum at another input port and our analysis shows the generation of sum- and difference-squeezing at the output port of BSTN. In this way, this BSTN acts as a novel quantum device to generate the radiation exhibiting sum- and difference-squeezing.

Modelling spontaneous four-wave mixing in periodically tapered waveguides.

A periodically tapered waveguides technique is an emerging potential route to establish quasi-phase-matching schemes in third-order nonlinear materials for efficient on-demand parametric interactions. In this paper, I investigate this method in enhancing spontaneous photon-pair emission in microstructured fibres and planar waveguides with sinusoidally varying cross sections. To study this process for continuous and pulsed-pump excitations, I have developed a general robust quantum model that takes into account self- and cross-phase modulations. The model shows a great enhancement in photon-pair generation in waveguides with a small number of tapering periods that are feasible via the current fabrication technologies. I envisage that this work will open a new area of research to investigate how the tapering patterns can be fully optimised to tailor the spectral properties of the output photons in nonlinear guided structures.

Backward Third-Harmonic Pulse Generation in a One-Dimensional PIM/NIM Structure

In this work, a set of couple-mode equations for describing a backward third harmonic generation (BTHG) in a one-dimensional periodic structure of positive-index material (PIM) layers and third-order nonlinear negative-index material (NIM) layers was analysed using multiple-scale method. Due to the negative-index phase matching and band-edge field enhancement the intensities of backward third-harmonic pulsed generated from the PIM/NIM periodic structure is increased for 100 time of those generated from a single NIM medium.

Insight on the growth, mechanical, optical and thermal studies of pyrrolidinium 2-carboxy 6-nitrophthalate (PY3N) single crystal-An effective third-order nonlinear optical material for optical limiting applications

A new interesting third-order nonlinear (NLO) organic material Pyrrolidinium 3-nitrophthalate (PY3N) is synthesized by water solvent in an equimolar ratio by room temperature solution growth technique. The crystal system (monoclinic), space group (P21/c and lattice constants (a = 13.245 (9) Å, b = 11.775 (7) Å, c = 8.612 (5) Å, β = 99.265 (2)°) were obtained from single crystal XRD. The vibrational and NMR spectral analyses confirmed the different functional groups and chemical environment of molecules present in the crystal lattice. The UV–vis study showed the crystal has good transparency with band gap and the index of refraction displays the normal dispersion behavior. The crystal demonstrates moderate surface tolerance to laser power (4.887 GW cm−2). The non-linear parameters were estimated by Z-scan technique. We have investigated the second order hyperpolarizability ‘γ’ of PY3N crystal with electric field and frequency by using HF method with 6-311++g(d, p) level. The theoretical third order susceptibility χ(3) value is 0.196 × 10−6 esu. The experimental χ(3)value is 3.131 × 10–6 esu. The effective optical limiting action is directed by PY3N crystal. The crystal is identified as a soft material from hardness measurement. The PY3N crystal has thermal stability (189 °C) which is identified using thermal analysis. The thermal activation energy (77.286 kJ mol−1) is determined from TGA data. The good quality of the crystal is confirmed from the intense photoluminescence peak. The etching study revealed the elongated square pattern on the developed crystal surface.

Quasi-phase-matched χ(3) -parametric interactions in sinusoidally tapered waveguides

In this article, I show how periodically tapered waveguides can be employed as efficient quasi-phase-matching schemes for four-wave mixing parametric processes in third-order nonlinear materials. As an example, a thorough study of enhancing third-harmonic generation in sinusoidally tapered fibers has been conducted. The quasi-phase-matching condition has been obtained for nonlinear parametric interactions in these structures using Fourier-series analysis. The dependencies of the conversion efficiency of the third harmonic on the modulation amplitude, tapering period, longitudinal-propagation direction, and pump wavelength have been studied. In comparison to uniform waveguides, the conversion efficiency has been enhanced by orders of magnitudes. I envisage that this work will have a great impact in the field of guided nonlinear optics using centrosymmetric materials.

Observation of Third-order Nonlinearities in Graphene Oxide Film at Telecommunication Wavelengths

All-optical switches have been considered as a promising solution to overcome the fundamental speed limit of the current electronic switches. However, the lack of a suitable third-order nonlinear material greatly hinders the development of this technology. Here we report the observation of ultrahigh third-order nonlinearity about 0.45 cm2/GW in graphene oxide thin films at the telecommunication wavelength region, which is four orders of magnitude higher than that of single crystalline silicon. Besides, graphene oxide is water soluble and thus easy to process due to the existence of oxygen containing groups. These unique properties can potentially significantly advance the performance of all-optical switches.

Nonlinear optimization of slot Si waveguides: TPA minimization with FOM(TPA) up to 4.25.

The χ(3) nonlinear properties of slotted crystalline silicon photonic waveguides filled with third-order nonlinear materials (NM) are studied by calculating the effective nonlinear susceptibilities associated to the silicon and cladding material, respectively. The adopted approach circumvents the assumptions that the introduced NM dominates the nonlinear behavior of the slotted waveguide and that strong light confinement in the slot allows neglecting the two-photon absorption (TPA) process in the silicon rails. Optimization of the geometry of silicon-slotted waveguides is performed on the basis of the nonlinear figure of merit (FOM(TPA)) of the guided mode, which is related to the balance between the Kerr and the TPA effects, allowing to reach a FOM(TPA)=4.25. The obtained results reveal the importance of properly choosing the waveguide width of the silicon rails in order to minimize the TPA effect even by tolerating a reduced overall nonlinearity.

Optical multiple bistability in metal-insulator-metal plasmonic waveguides side-coupled with twin racetrack resonators

We investigate the resonant transmissions surface plasmons that propagate in a metal-insulator-metal (MIM) waveguide side-coupled to two MIM racetrack resonators in which optical third-order nonlinear material is filled, by the coupling mode analyses and finite-difference time-domain simulations. We find the multiple bistabilities and the hysteresis phenomena in the transmission coefficient as the input intensity varies. Furthermore, the mode conversion between the bistable states can be controlled by varying the input-gate intensity with a short switching time of about 333 fs, indicating that the MIM waveguide system may have applications in multiple switches, logic operations, and electromagnetically induced transparency.

An Exponential Time Differencing Algorithm for the FDTD-PML Analysis of Nonlinear Photonic Bandgap Structures

An exponential time differencing (ETD) algorithm is presented for the analysis of photonic crystal structures comprising the third-order nonlinear materials. Compared with the well known Z-transform method and auxiliary differential equation method for incorporating the nonlinearity, the proposed ETD algorithm has the least memory requirement and shows the same accuracy. The stretched coordinates perfectly matched layer (PML) with the complex frequency shifted variable implemented using the ETD algorithm is applied to terminate nonlinear photonic bandgap structures. Compared with the conventional PML and the convolutional PML, the proposed implementation can improve the absorbing performance significantly with similar memory requirement.

Third-order nonlinear plasmonic materials: Enhancement and limitations

We develop a rigorous and physically transparent theory of enhancement of third-order nonlinear optical processes achievable in plasmonic structures. The results show that the effective nonlinear index can be enhanced by many orders of magnitude, but, due to high metal losses the most relevant figure of merit, the amount of phase shift per one absorption length, remains very low. This makes nonlinear plasmonic materials a poor match for applications requiring high efficiency, such as all-optical switching and wavelength conversion, but does not preclude the applications where overall high efficiency is not required, such as sensing.

Tensorial split-field finite-difference time-domain approach for second- and third-order nonlinear materials

The split-field finite-difference time-domain (SF-FDTD) method for one-dimensionally periodic structures is extended to include the coefficient-tensor description of second- and third-order nonlinear-optical media. A set of nonlinear equations related to the split-field values of the electric field is established. An iterative fixed-point approach for solving the coupled nonlinear system of equations needed to update the electric field components in the SF-FDTD is then developed. The third-order nonlinear susceptibility dispersion is also considered by means of the Raman effect and its implementation in the SF-FDTD scheme. Different scenarios are considered in order to verify the reliability of the method for simulating second- and third-order nonlinear-optical media. First, second-harmonic generation and its efficiency are investigated in a homogeneous layer with and without the quasi-phase-matching technique. Second, the nonlinear dispersion is analyzed by means of the generation of solitons in Kerr media due to the Raman effect. Last, a set of binary phase gratings with nonlinear pillars is considered under oblique incidence. Here the nonlinear refractive index is generated by different physical mechanisms modeled with the nonscalar third-order susceptibility.

Phase filtering in nonlinear-imaging technique with a phase object

Using the nonlinear-imaging technique with a phase object (NIT-PO), we have studied third-order nonlinearities of various samples. In this work, we develop, for pure nonlinear refractive materials, an approximate method to calculate the nonlinear refractive coefficient analytically. By decomposing the object field passing through the phase object into two top-hat beams of different phases and beam radius, we acquire the approximate phase contrast, from which we extract the nonlinear refractive coefficient. This approximation is valid when the on-axis nonlinear phase shift by the sample is less than π. In addition, this approximation serves to estimate the sensitivity and monotonic interval for nonlinearity measurements more easily and thus helps us to maximize both the sensitivity and monotonic interval of measurements. We test this method with CS(2), a well-characterized third-order nonlinear refractive material using 21 ps laser pulses at 532 nm. We expect this method can be applied to high-order nonlinear refraction cases.

Quadratic Electro-Optic Kerr Effect: Applications to Photonic Devices

We propose novel applications of the quadratic electro-optic Kerr effect to photonic devices. Specifically in this work, two new illustrative examples are described, namely an electrically controlled multistable switch (ECMS), and an electrically tunable Bragg grating (ETBG). Their functionality is based on the third-order nonlinearity in an isotropic medium. On one hand, we note that the first key feature is the all-optical as well as electro-optical control/tunability. This can be achieved only in the third-order nonlinear material as opposed to a more frequently used linear electro-optic effect exploited in optical crystals. On the other hand, the second important key feature is the availability of integrated and compatible materials that show third order nonlinearity. In the first application proposed here, ECMS, the interplay between the quadratic electro-optic and all-optical Kerr effects is crucial for its tunable operation and leads to an interesting feature of storing an electrical information optically. In the second example, ETBG, employing the quadratic electro-optic effect makes it attractive thanks to the existence of the third-order nonlinearity in many interesting isotropic materials that are suitable for device integration. Devices such as modulators, switches, mixers, variable attenuators or optical limiters can be designed.