Journal of Nonlinear Optical Physics & Materials

We study the fundamental nonlinear modes in a dual-cylinder waveguide shell, which features a self-focusing Kerr effect, coupled by a double-well connection. This double-well connection is twisted by a pitch rate and creates a spatial dependent linear mixing, which plays the role of an effective rotating double-well potential. Symmetry transition between the waveform and the power distribution of the fundamental nonlinear modes in this system can be induced both by the total power and by the rotation speed of the connection. Four types of modes — wave symmetry and power symmetry (WSPS), wave symmetry and power asymmetry (WSPA), wave asymmetry and power symmetry (WAPS) and wave asymmetry and power asymmetry (WAPA) — are found from the system. The dependence of these modes on the total power of the light field, the rotation speed and the coupling strength of the connection are systematically studied through the paper. The finding of this paper may offer potential applications in fabrication of new types of nonlinear all-optical devices.

Nonlinear plasmonic metasurfaces have recently attracted considerable interest, due to their potential for enabling nanoscale nonlinear optics. Here, we review the current progress in this topic while paying special attention to existing challenges. In order to limit our scope, we concentrate on nonlinear metasurfaces utilizing inter-particle and lattice effects and focus on metasurfaces operating close to visible and near-infrared frequencies. We will also critically discuss the short and longer term prospects of nonlinear metasurfaces to start rivaling traditional nonlinear materials in applications.

In this paper, wavelength conversion based on optofluidic infiltration of photonic crystal fibers (PCFs) is investigated to achieve the suitable wavelength over wide tunable range. For this purpose, two designs of PCFs (the so-called PCF1 and PCF2) with appropriate dispersion properties are simulated, and wavelength conversion via four-wave mixing process for pump wavelengths in both normal and anomalous dispersion regimes is studied. By changing the refractive index $n_F$ of the optical fluid infiltrated into the PCF air-holes and then varying the fiber dispersion properties, the converted wavelength region can be tuned. The results show that for the pump wavelength in the normal dispersion regime, the PCF1 infiltrated with $n_F=1.32$ and PCF2 infiltrated with $n_F=1.34$ exhibit the maximum wavelength shift. Moreover, the wavelength shift is much higher than that obtained in the anomalous dispersion regime and it can be further increased by increasing the input pump power.

A series of branched styryl derivatives based on 1,3,5-triazine were studied by nonlinear optical property measurement, degenerated pump-probe, and time-resolved fluorescence anisotropy methods to elucidate the two-photon absorption (TPA) properties and intramolecular interactions between branches. Significant enhancement of the TPA cross-section was observed in multi-branched derivatives. The anisotropy of multi-branched compounds shows faster decay and small residual values, indicating strong intramolecular interactions between branches, which further confirmed the TPA enhancement mechanism.

We present a theoretical analysis of a single $n$-photon absorption process. We found an approximate analytical but closed-form expression of the normalized transmittance for a thin nonlinear material under an elliptic Gaussian incident beam. The obtained expression can be used to fit the experimental $Z$-scan traces, allowing the determination of material’s multiphoton absorption coefficient and Rayleigh lengths of the input elliptic Gaussian beam.

In this work, Silicon oxide (SiO₂) nanoparticles, graphene oxide nanosheet (GO) and GO–SiO₂ nanohybrid composites have been synthesized. The role of GO concentration in the starting solution was investigated and correlated to the morphological, structural and optical properties of the studied samples. The structural studies for nanohybrid composites showed that by increasing GO:weight ratio from 0.5 to 2.0, not only does the SiO₂ crystalline phase change from cubic to orthorhombic, but the structure of GO also transformed to RGO. The related FESEM images indicate that GO sheets are well-covered by SiO₂ nanoparticles with very small grain size and that the accumulation of nanoparticles on each sheet has a high density. Linear Optical measurements showed two optical band gaps of $\sim 3.2$eV and 5.3eV for SiO₂ nanoparticles, and band gap value of 4.15eV for GO nanosheets, which it reduces to 3.3eV after formation of the nanohybrid composite with GO: SiO₂ weight ratio of 2.0. The nonlinear optical properties of GO–SiO₂ with different weight ratio are measured using Z-scan technique. The results showed that the nonlinear refractive index of SiO₂ and GO nanoparticles and nanohybrid composite (0.5:1,1:1,2:1) ($\mathrm{\text{GO}}$–${\mathrm{\text{SiO}}}_2$) changed and has a negative sign. It was observed that the nonlinear refractive index changes in different ratios of compounds. Experimental results show that after the formation of the composite, the nonlinear refractive index shows a significant increase in the presence and effectiveness of the GO.

We study the thermodynamic properties of coherent photons in self-focusing nonlinear waveguides. The equation of the superfluid state of photons has been derived. There is a transition temperature $T_c$, above which the photon gas is in the coherent state, but below which the photon gas is in the superfluid state. At $T_c$, the photon system undergoes a first-order phase transition from the coherent to the superfluid state. To determine the fugacity $z$ and the transition temperature $T_c$ of the photon gas, we numerically solve the equation of the superfluid state of photons. The fugacity $z$ is a monotonically decreasing function of temperature $T$ and light intensity $I$. The transition temperature $T_c$ is a monotonically decreasing function of light intensity $I$.

Dual-band unidirectional reflectionlessness is investigated in a system consisting of three stub resonators side-coupled to a metal-insulator-metal plasmonic waveguide based on near-field coupling in terahertz domain. Reflectivities of $\sim 0(\sim 0.65)$ and $\sim 0(\sim 0.97)$, respectively, at two exceptional points 4.11THz and 4.695THz are obtained for forward (backward) direction. More than that multi-band unidirectional reflectionlessness is demonstrated based on multi-stub resonators side-coupled to an MIM plasmonic waveguide.

The paper focuses on a problem that describes propagation of transverse-electric (TE) waves in a plane dielectric waveguide filled with nonlinear medium. The nonlinearity is characterized by the power term $\alpha |E{|}^{2q}$, where $\alpha$, $q>0$ are constants and $E$ is the electric term of the guided electromagnetic field. The layer is located between two half-spaces filled with linear media having constant permittivities. It is proved that the nonlinear problem has infinitely many propagation constants (PCs), whereas the corresponding linear problem has only a finite number of them. The nonlinearity leads to the occurrence of infinitely many nonperturbative solutions of the nonlinear problem. Results of the paper show that the power nonlinearity (for any $q>0$) and Kerr nonlinearity (for $q=1$) produce qualitatively similar outcomes. In addition, the found results allow one to study very important cases of quintic, septimal, etc. nonlinear permittivities in the focusing regime.