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In this study, 8-(4-methoxyphenyl)-6-oxo-3-p-tolyl-6H-pyrido[1,2-b][1,2,4]triazine-7,9-dicarbonitrile (A) was prepared and then the nonlinear optical properties of this compound, including nonlinear refractive index (n2) and nonlinear absorption coefficient (β) were measured using Z-scan technique by continuous wave laser diode at wavelengths of 405 and 532 nm. At wavelength of 532 nm, by increasing the incident intensity a switch over from saturable absorption (SA) to reverse saturable absorption (RSA) was observed. The results showed that the nonlinear optical properties of this compound depend on the wavelength. It was also observed that with decreasing incident intensity, the thermal nonlinear refractive coefficient increased accordingly, while its thermo-optic coefficient decreased. In addition, the third-order susceptibility of this compound in wavelength of 532 nm was obtained higher than 405 nm.

In this paper, firstly we have synthesized ZnO nanowires using zinc acetate, ethanol and ammonium hydroxide by a thermo-chemical method and then ZnO nanorods (NRs) have been prepared by microwave irradiation (MI) of an initial solution containing ZnO nanowires. X-ray diffraction (XRD) analysis showed the rare zinc-blende phase which grows on the surface of NRs and its crystallite size increases with the increase of microwave power. The average length and width of rods were observed several hundreds of nanometer and 80[Formula: see text]nm, respectively, from scanning electron microscope (SEM) analysis. Ultraviolet-visible (UV-vis) absorption spectroscopy indicates that a band tail forms due to MI, which has roughly 2[Formula: see text]eV energy gap. Photoluminescence (PL) spectroscopy indicated a blue emission and a white emission for ZnO nanowires and NRs, respectively. MI quenches the UV emission from ZnO NRs and enhances the surface defects’ emission. The resultant visible PL of the samples increases with the increase of microwave power that shows the growth of zinc-blende phase which has crucial effect on the defect density of NRs.

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Microring tower resonators, which are a chain of microring resonators stacked on top of each other, are of great interest for nonlinear optics due to their unique features such as very high compactness, coupling efficiency and quality factor. In this research, we investigate the optical bistability in microring tower (MRT) with Kerr nonlinearity by using the coupled mode theory, and demonstrate how a proper defect into the structure can lead to low threshold bistability. In particular, we observed optical bistability in nonlinear defect modes with switching power as low as 165 μW through numerical calculations in a structure with a overall loss on the order of 0.01 mm. In addition, we also develop an analytical model that excellently gives the position of defect modes in linear regime.