Graphene-induced unique polarization tuning properties of excessively tilted fiber grating

By exploiting the polarization-sensitive coupling effect of graphene with the optical mode, we investigate the polarization modulation properties of a hybrid waveguide of graphene-integrated excessively tilted fiber grating (Ex-TFG). The theoretical analysis and experimental results demonstrate that the real and imaginary parts of complex refractive index of fewlayer graphene exhibit different effects on transverse electric (TE) and transverse magnetic (TM) cladding modes of the Ex-TFG, enabling stronger absorption in the TE mode and more wavelength shift in the TM mode. Furthermore, the surrounding refractive index can modulate the complex optical constant of graphene and then the polarization properties of the hybrid waveguide, such as resonant wavelength and peak intensity. Therefore, the unique polarization tuning property induced by the integration of the graphene layer with Ex-TFG may endow potential applications in all-in-one fiber modulators, fiber lasers, and biochemical sensors

Theoretical and experimental analysis of excessively tilted fiber gratings

We have theoretically and experimentally investigated the dual-peak feature of tilted fiber gratings with excessively tilted structure (named as Ex-TFGs). We have explained the dual-peak feature by solving eigenvalue equations for TM0m and TE0m of a circular waveguide, in which the TE (transverse electric) and TM (transverse magnetic) core modes are coupled into TE and TM cladding modes, respectively. Meanwhile, in the experiment, we have verified that one of the dual peaks at the shorter wavelength is due to the TM mode coupling whereas the other one at the longer wavelength arises from TE mode coupling when a linearly polarized light launched into the Ex-TFG. We have also investigated the peak separation of TE and TM cladding mode for different surrounding medium refractive indexes (SRI), revealed that the dual peaks separation is decreasing as increasing of SRI, which agrees very well with the theoretical analysis results

Ion-Imprinted Chitosan-Based Localized Surface Plasmon Resonance Sensor for Ni²⁺ Detection

Heavy metals are important sources of environmental pollution and cause disease in organisms throughout the food chain. A localized surface plasmon resonance sensor was proposed and demonstrated to realize Ni2+ detection by using ion-imprinted chitosan. Au nanoparticles were coated on the multimode fiber to excite the local surface plasmon resonance, and Ni2+-imprinted chitosan was then functionalized by using the dip coating technique. Ethylene diamine tetra-acetic acid was used to release the Ni2+ ions and hence form countless voids. Ni2+ was refilled into the voids to increase the refractive index of the sensing material, thus realizing the measurement of Ni2+ by monitoring the wavelength shift in the localized surface plasmon resonant peak. The coating thickness of the Ni2+–chitosan gel was optimized to obtain greater sensitivity. Experimental results show that the proposed Ni2+ sensor has a sensitivity of 185 pm/μM, and the limit of detection is 0.512 μM. The comparison experiments indicated that the ion-imprinted chitosan has better selectivity than pure chitosan

Influence of fading on characteristics of thermal analysis curve of compacted graphite iron

In general, during the production of compacted graphite iron (CGI), the active residual magnesium reduces and the effect of inoculation fades after magnesium treatment. In this paper, characteristics of the thermal analysis curve of CGI are compared with those of ductile iron and grey cast iron. The fading effect on the compacted graphite percentage and thermal analysis curve were also studied. Results indicate that the undercooling of CGI is as low as that of ductile iron, but CGI shows evident recalescence. In fading process, the magnesium element acts with oxygen. For a decrease in magnesium content, both the compacted graphite percentage and the austenitic liquidus temperature increase. The temperature of eutectic undercooling (TEU) decreases before the flake graphite appears. After that, TEU increases quickly, up to as high as 20℃, and then gradually decreases. The evolution of recalescence degree is opposite to that of TEU

Microstructure and Properties of Cold Sprayed NiCrAl Coating on AZ91D Magnesium Alloy

Herein, a NiCrAl coating was prepared on the AZ91D magnesium alloy by cold spraying technology. The microstructure, wear resistance, and corrosion resistance of the cold sprayed NiCrAl coating were studied and compared with two NiCrAl coatings prepared by plasma spraying. The results showed that the porosity of the two-plasma sprayed NiCrAl coatings was 3.21% and 2.66%, respectively, while that of the cold sprayed NiCrAl coating was only 0.68%. The hardness of the cold sprayed NiCrAl coating (650 HV0.1) was higher than those of the two-plasma sprayed NiCrAl coatings (300 HV0.1, 400 HV0.1). In the abrasion resistance test, the cold sprayed NiCrAl coating showed a lower friction coefficient (0.346), less wear volume (3.026 mm3), and superior wear resistance accordingly compared with the two-plasma sprayed NiCrAl coatings. Moreover, the scanning electron microscopy (SEM) morphology at the bottom of the wear trace of the cold sprayed NiCrAl coating showed a compact mechanically mixed layers (MML) structure, and its wear mechanism was mainly abrasive wear, with some fatigue wear. In the electrochemical test, the corrosion current density of the cold sprayed NiCrAl coating (4.404 × 10−2 A·cm−2) was much lower than those of two plasma sprayed coatings (25.96 A·cm−2, 26.98 A·cm−2), indicating that the cold sprayed NiCrAl coating had superior corrosion resistance. Therefore, preparing a cold sprayed NiCrAl coating is a feasible method to comprehensively improve the wear resistance and corrosion resistance of the AZ91D magnesium alloy