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A one-dimensional photonic crystal structure with a nonlinear metal-dielectric nanocomposite defect layer is proposed to control the optical bistability (OB) of the transmitted wave by tuning the externally applied dc electric field. Using the transfer matrix method for dielectric layers and solving the Helmholtz nonlinear equation in the nonlinear composite layer, the linear transmittance spectrum and the nonlinear transmission curve are illustrated graphically for different applied fields. A field-dependent defect mode is observed in the linear transmittance spectrum. Consequently, the OB switch-up and -down thresholds can be manipulated via the applied field intensity. Due to the field dependence of composite layer refractive index, the physical response of the observation is the dynamical shifting of the defect mode. Moreover, it is shown that the volume fraction, shape, and type of the embedded nanoparticles as well as the kind of the dielectric host have large influences on the OB threshold. The proposed structure has significant potential applications in optical integrated devices. [ABSTRACT FROM AUTHOR]

In this paper, the nonlinear responses and optical properties modification in SK3 glass sample are investigated. The nonlinear responses measurements were performed by using of nonlinear transmission monitoring of 200 fs at 800 nm laser pulses. The optical power limiting threshold of the sample is measured to be about 40 mJ/cm2. The decrease of transmitted intensity is about 63% compared to the theoretical linear transmission at 270 mJ/cm2 incident pulse energy. For prediction of the experimental nonlinear behavior results, a theoretical model based on three-photon absorption and absorption of free carriers is presented. By fitting of experimental data with theoretical model, three-photon absorption coefficient and free-carrier absorption cross-section are reported. The photo-induced optical properties modification of the SK3 sample is investigated also. The modifications that appear as darkening are observed below breakdown threshold intensity. To analyses of modified region sizes, the laser pulse energy accumulation model is applied. [ABSTRACT FROM AUTHOR]

This paper investigates the optical properties of the two plasma photonic crystal structures. The first structure contains periodic thin layers of plasma with heterogeneous densities, and in the second one, the heterogeneous plasma layer has been applied as the defect layer of a one-dimensional photonic crystal. Herein, the plasma density distribution function is considered a continuous function of plasma critical density as follows: n = n cr f ( r →), where n cr = m e ε 0 ω 2 / e 2 represents the critical density of the plasma and f ( r →) indicates the plasma density distribution function. The heterogeneous plasma layer is assumed to be composed of several homogeneous sublayers with constant density. The transfer-matrix method is applied in calculations, and the total transfer matrix is obtained by multiplying the transfer matrices of each sublayer. Properties and behavior of the photonic bandgap and the defect mode for five different plasma density distribution functions and applied external constant magnetic field are comparatively investigated. Results show that, in the first structure, increasing the incident angle from 0° to 30° causes a bandgap shift to higher frequencies. So, the incident angle is a parameter that can control the bandgap. In the defective structure, the intensity of the defect modes is almost the same in all five distributions, but their locations in the spectrum are different. The effect of the lateral position of the maximum density and external constant magnetic field on the defect mode position is also investigated. The capability of controlling the photonic bandgaps and defect modes of the plasma photonic crystals creates wide applications in promising tunable optical devices, such as optical filters.

Background: Carbon dots (C-dots) are photoluminescent nanoparticles with less than 10 nm in size. Today, many studies are performed to exploit the photoluminescence (PL) property of carbon dots, and our focus in this study is to estimate the dipole moment of carbon dots. For reaching our aims, C-dots were synthesized and dissolved in the different solvents., Results: Carbon dots with intense photoluminescence properties have been synthesized by a one-step hydrothermal method from a carbon bio-source. In this research, we report on the effect of aprotic solvents on absorption and fluorescence spectra and dipole moments of C-dots dispersed in a range of many aprotic solvents with various polarity and dielectric constant at room temperature. The change in the value of dipole moment was estimated by using the Stokes shifts. The difference between the dipole moment of the excited state and the ground state was shown using an extended form of Lippert equations by Kawski and co-workers., Conclusions: The values found for μ g  = 1.077 D, and μ e  = 3.157 D, as well as the change in the dipole moments. The results showed that the dipole moment of the excited state is more than the ground state, indicating a high density and redistribution of electrons in the excited state. Finally, the quantum yield of C-dots in the eclectic aprotic solvents was communicated and discussed., (© 2021. The Author(s).)

All-optical-diode tunability with externally applied voltage in a one-dimensional photonic crystal structure of arrangement (BA) 5 /AgLiNbO 3 Ag/(AB) 5 (AABB) 5 was investigated. It is an asymmetric hybrid Fabry-Perot resonator which is composed of distributed Bragg reflector segments (AB 5 ) containing the linear (B layers) and nonlinear (A layers) optical materials. The LiNbO 3 , (LNO) sandwiched with two pairs Ag layers, is employed as a defect. The electro-optical (EO) effect and optical nonlinear response (Kerr effect) of LNO is considered. The linear transmittance (LT) spectrum, nonlinear transmission (NT) curves and field distribution, for left to right (L-R) and right to left (R-L) incidents at different applied voltages are graphically illustrated. Results show that with an increase in the applied voltage, L-R and R-L NT curves deflect, amplify, and compress in comparison to zero applied voltage. At negative voltages, due to accumulation of the EO and Kerr effects, variations are more sensitive. The EO effect in LNO causes tunability of the LT spectrum, and the Kerr effect in nonlinear layers dynamically tunes the optical bistability threshold. The results of this study can be useful in designing externally tunable basic elements for optoelectronic devices.

In this study, the effects of incident angle and state of wave polarization on electrically-tunable defect mode in a one-dimensional photonic crystal (1DPC) structure with an anisotropic defect layer is theoretically investigated. A 4×4 transfer matrix method is employed to calculate the transmittance spectrum of the structure with biased defect layer at different incident angles for TE and TM polarizations. The results indicate that at both polarizations, the peak wavelength of the defect mode shifts toward blue as the angle of incidence increases. Also, blue and red shifts can be observed in the defect mode for positive and negative biases, respectively. In addition, the defect mode compresses at TE (TM) polarization at negative (positive) biases and broadens for positive (negative) biases. A tunability defect mode may have potential application in the design of controllable optical filters in all optoelectronic devices.

The dependence of the optical responses of microcavity-type one-dimensional (1D) photonic crystals and 1D magnetophotonic crystals (1D-MPCs) on the arrangement order ratio (AOR), which is the ratio of the first and second layers' refractive indexes of Bragg reflectors, is studied. It is demonstrated that the optical properties of two microcavity structures resulting from exchanging the order of Bragg reflector layers so that they have the same optical contrast ratios and different AORs would be different. This difference will be more noticeable in the case of microcavity type 1D-MPCs. Regarding the arrangement-dependent magneto-optical properties of the structures, we can propose the efficient Bragg reflectors with high transmittance enhanced Faraday rotation.