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The development of single-mode lasers with a high side-mode suppression ratio (SMSR) is challenging but highly desirable for integrated photonics devices and long-distance communications due to their high spectral purity and stability. Here, we demonstrate a single-mode laser with a high side-mode suppression ratio based on size-mismatched triple-coupled microrings. With the exact engineering of several key parameters of the structure like air gap and radii of microrings for controlling the free spectral range (FSR), a predominant mode is selected to lase in amplified spontaneous emission (ASE) of the gain material and all side and high order modes are suppressed by Vernier effect. In this work, we show that a single-mode operation is efficiently generated with an improved side-mode suppression ratio of over 20 dB in a three-ring-coupled microcavity laser. The single-frequency output persists for a wide power range. The theoretical calculations and numerical simulations' results confirm the validity of the experimental results. Our structural engineering creates new opportunities in a variety of frontier applications in single-mode lasers and high-quality sensors. [ABSTRACT FROM AUTHOR]

The paper presents the synthesis of a series of polyesters containing nitro-substituted phenyl azothiazole, azobenzothiazole and azobenzene chromophores and their characterization by 1H NMR, FTIR and UV-Vis spectroscopy. Also the solubility, glass transition temperatures, thermal stability of the synthesized polyesters as well as the surface morphology of thin films of the polyesters were studied. [ABSTRACT FROM AUTHOR]

In this paper, the growths of ZnO nano- and microstructures by VLS mechanism have been studied. A piece of silica fiber (SMF-28 optical fiber) was used as a substrate. By controlling the experimental conditions, nano- and microstructures of ZnO with different shapes and sizes were grown around the optical fiber, which can be used as an optical fiber sensor. A star-shaped ZnO microstructure was obtained in this research. Pyramidal structures were grown on each side of vertical hexagonal microrods which formed the seven-pointed star-shaped microstructures. This growth process was carried out in a special quartz container in a tube furnace at temperatures around 400-550 °C without any additional catalyst. XRD, SEM and PL spectroscopy were used for the characterization of the produced nanostructures. The influence of temperature, reactant and carrier gases flow rate on the morphology of ZnO nanostructure was investigated. [ABSTRACT FROM AUTHOR]

High refractive index (RI) thin films are capable of pulling waveguide mode profiles towards themselves. In this study, it is shown that by applying high RI coatings with specific thicknesses on the side of optical waveguides, significantly different mode profiles for orthogonal polarizations can be achieved. This phenomenon, that we call it polarization-selective mode shaping, can be extensively used in the enhancement of polarization-dependent integrated optical devices. As an illustrating application, a tri-layer structure consisting of poly(methyl methacrylate)/graphene/chalcogenide on a side-polished fiber is designed to realize an extremely high extinction ratio polarizer. This structure changes the mode profiles in a way that the attenuation of TE mode is maximized, while the power carried by the TM mode remains relatively constant. Simulations and experimental characterizations confirm that polarization-selective mode shaping coordinates four loss mechanisms to maximize the extinction ratio and minimize the insertion loss of the polarizer. The fabricated polarizer is examined in the O, C, and L telecommunication frequency bands. This configuration achieves the high extinction ratio of 51.3 dB and its maximum insertion loss in the tested wavelengths is 1.79 dB. The proposed polarizer has been compared with other state-of-the-art polarizers in the conclusion section which shows its superiority. [ABSTRACT FROM AUTHOR]