Journal of Nonlinear Optical Physics & Materials

In this work, based on nonlocal heat effect and Fresnel diffraction theory, the characteristics of closed Z-scan in materials with a large nonlinear phase shift have been studied and a formula for Z-scan transmittance is derived. Numerical computations show that the shapes of Z-scan curves are greatly affected by the values of thermal nonlinear phase shift. The Z-scan behavior is compared to the conventional thermal Z-scan theories, including the thermal thin lens and aberrant thermal lens model. We have used the Z-scan models to determine the nonlinear refraction of gold nanoparticle (AuNP) dispersed in cyclohexanone under irradiation of a low power CW laser at 532 nm. The Z-scan theory based on the conventional models does not fit the experimental data well. It is found that peak-to-valley features of the AuNPs colloid Z-scan curve behave the same as the derived Z-scan theory for large thermal nonlinear phase shift. This allows us to measure nonlinear refractive index up to -1.0 × 10^-6 cm²/W in the tested samples. The optical limiting performance of the colloidal AuNPs is also investigated for device application. The results show that the optical limiting threshold of the AuNPs can be improved by making an appropriate choice of design geometry and increasing the AuNPs concentration of the colloids.

We study p-polarized nonlinear surface polaritons (NLSP) propagating along the interface of an epsilon-near-zero metamaterial with saturable nonlinearity, very small negative linear permittivity and an optically linear medium. On the basis of the exact solution of Maxwell's equations, we investigate the relationship between the NLSP propagation constant and the NLSP energy flux for self-focusing and self-defocusing cases. In both cases, for the chosen value of propagation constant, calculations due to Kerr model lead to the lowest NLSP energy flux compared with the energy flux for metamaterial with saturable permittivity.

This paper reports on the preparation of high purity ZnS nanoparticles by a facile single step solvent-free route via thermal decomposition of zinc acetate dihydrate and thiourea in air atmosphere. The third-order optical nonlinearity of the prepared ZnS nanoparticles were measured by Z-scan technique using continuous wave 532-nm diode pumped Nd:YAG laser. From nonlinear optical (NLO) measurements, the prepared ZnS nanoparticles possess negative nonlinearity i.e., self-defocusing. Open aperture Z-scan measurement shows saturable absorption within the medium. These results show that the prepared ZnS nanoparticles are promising candidate for various potential applications in the field of nonlinear optics.

This paper obtains soliton solutions in optical couplers. The governing equation is solved by the aid of G′/G-expansion scheme. There are four types of nonlinear media that are taken into consideration. These are Kerr law, power law, parabolic law, and dual-power law. There are two kinds optical couplers studied in this paper. They are twin-core couplers and multiple-core couplers, where coupling with nearest neighbors as well as coupling with all neighbors are considered. Dark and singular soliton solutions are retrieved. These soliton solutions come with constraint conditions that must hold for the solitons to exist.

Quasi-1D quantum structures with spectra scaling faster than the square of the eigenmode number (superscaling) can generate intrinsic, off-resonant optical nonlinearities near the fundamental physical limits, independent of the details of the potential energy along the structure. The scaling of spectra is determined by the topology of the structure, while the magnitudes of the transition moments are set by the geometry of the structure. This paper presents a comprehensive study of the geometrical optimization of superscaling quasi-1D structures and provides heuristics for designing molecules to maximize intrinsic response. A main result is that designers of conjugated structures should attach short side groups at least a third of the way along the bridge, not near its end as is conventionally done. A second result is that once a side group is properly placed, additional side groups do not further enhance the response.

Ultrafast all-optical XOR and XNOR logic gates have been analyzed based on photonic crystal fiber (PCF) nonlinear optical loop mirror (NOLM). The performance of the logic operation is evaluated numerically using the coupled nonlinear Schrödinger equation and split step Fourier method. The wavelength allocation, peak power and the pulse width of signal with respect to the group velocity dispersion (GVD) and the nonlinearity of PCF affect the performance of logic gate. A highly nonlinear PCF with flattened dispersion is proposed to obtain 1 Tb/s operation.

Nanostructured zinc sulfide (ZnS) thin films were synthesized in polyvinyl alcohol matrix by chemical bath deposition and self-assembly techniques. ZnS nanostructured thin films show second harmonic generation (SHG) under irradiation with a pico-second Nd:YAG laser system and the second harmonic intensity is higher for self-assembled nanotree like structured ZnS thin film in comparison with that from chemical bath deposited thin film. Under nanosecond laser pulses, thin films possess good saturable absorption behavior. The optical bandgap and visible luminescence also get enhanced.

In the Schrödinger picture, we find explicit solutions for two models of degenerate parametric oscillators in the case of multi-parameter squeezed input photons. The corresponding photon statistics and Wigner's function are also derived in coordinate representation. Their time evolution is investigated in detail. The unitary transformation and an extension of the squeeze/evolution operator are briefly discussed.

We demonstrate an optical diode by building a domain wall with one-dimensional waveguide array. The domain wall can be described by dividing the one-dimensional waveguide array into two equal parts, which have different refractive index, so that the waveguide array exists local potential. A Gaussian beam is kicked moving toward the domain wall and interacts with it. Transmission and reflection during the interaction between the Gaussian beam and the domain wall are found by changing related parameters. The detailed behavior of the Gaussian beam dynamics is analyzed numerically. Transmission of the Gaussian beam in one direction is much bigger than the opposite under certain circumstances and optical nonreciprocity is found in such a model, high transmission ratio of such model up to 300 is obtained. Thus the system can serve as an optical diode.

A study of the effects of relaxation times on the Four-Wave Mixing (FWM) signal response in frequency space for a two-level system is presented where the collisional effects of the solvent and the presence of the electromagnetic field are considered. The model is a generalization of the conventional two-level approach in that it includes a simplified description of the molecular structure associated with the non-zero permanent dipole moments. Significant changes in both the FWM-intensity and nonlinear optical properties are observed, due mainly to changes in the ratio between the longitudinal and transversal relaxation times.

We report the existence and stability of multi-peak gap solitons in PT-symmetric optical lattice with the real part of the refractive index in the form of superlattice and the imaginary part having two different profiles; one with odd periodic lattice and the second with odd superlattice supported by a defocusing nonlinearity. Linear-stability spectra analysis and simulation results show that they can be stable in the scope of the first gap. The profile of the multi-peak solitons and the power-flow vector is found to be different from those of one cycle lattice.

We derive a rigorous quantum formula called topological trajectory to describe orbital angular momentum (OAM) index based on linear momentum density of Laguerre–Gauss (L–G) light beam. By considering the correspondence between optics and quantum theory, we construct a coherent state from two L–G modes light beam. The light beams with fractional OAM are described by the coherent state. By making use of topological trajectory, we present the conditions that OAM index is fractional.