Search

Used tea leaves, or tea waste (TW), were crushed into powder and mixed with graphene oxide (GO) in water, followed by adjusting the pH value of the resulting suspension with ammonia to 11, adding FeCl2·4H2O under magnetic stirring, filtration and drying to prepare a rGO/Fe3O4/TW (with mass ratios of 1:2:1) hybrid material. The structure and crystalline phases of the material were characterized by FTIR and XRD. Isotherms for uranium adsorption were obtained and its kinetics were measured in a conical bottle that was placed in a shaker. The effects of the pH value of the uranium solution, adsorption time and initial concentration on the uranium adsorption were investigated. Results indicate that the hybrid has a much faster adsorption rate than TW with a uranium removal rate up to nearly 100% in 20 min for an initial uranium concentration of 10 mg L−1. The maximum adsorption capacity of the hybrid is 103.84 mg g−1 while that of TW is 97.70 mg g−1. The hybrid with adsorbed uranium can be easily separated from the solution by applying a magnetic field. The isotherms and kinetics of uranium adsorption on the hybrid are best fitted by the Langmuir isotherm model and the pseudo-second-order model, respectively. The hybrid has good reusability with an uranium removal rate of about 85% after 5 cycles.

In this work, a simple method was developed to fabricate micron scale three-dimensional (3D) conductive objects on a flexible PDMS substrate. 3D microstructures were fabricated by the two photon polymerization (TPP) technique and metalized by a subsequent electroless plating step. The PDMS substrate was pre-treated with plasma to develop temporary compatible wettability of the photopolymerizable resin Ormocomp monomer. After the TPP fabrication, hydrophilic 3D microstructures were printed and adhered well to the PDMS surfaces, which recovered hydrophobicity after the TPP process. The printed 3D microstructures were then activated and immersed in an electroless copper plating bath. Due to the hydrophilicity differences, conformal conductive coatings were selectively and uniformly deposited on the 3D microstructures. Several 3D metallic microstructures with complex shapes were demonstrated to show the potential aspects of applying this technology for flexible 3D conductive objects.

A simple method is introduced to measure the refractive index (RI) of a liquid with an experimental device composed of a graduated cylinder and a beaker which are coaxial. A magnified image of the graduated cylinder is formed as the liquid is poured into the beaker. Optical path analysis indicates that the RI of the liquid is equal to the product of the image's diameter magnification and the RI of air, irrelevant to the beaker. Theoretically, the RI measurement range is unlimited and the liquid dosage could be small as well. The device is used to carry out experiments by means of both the photographic method and telescope method to measure RIs of three kinds of liquids. The results show that the measured RIs all fit their published values well.

The barrier for low-level radioactive wastes repositories calls for the use of concrete. In a underground situation, the repository may be subject to intrusion of various elements from the external environment and may cause concrete deterioration and reduces its durability. This study focuses on the effect of leaching of concrete as simulated in the laboratory to assess the durability in long term use of concrete materials. The basic mixture of cement, mortar and concrete were used to produce test specimens that were exposed to different conditions such as pure water and substitute ocean water to simulate calcium loss under different circumstances. The possible mechanism of calcium loss and potential influence on concrete durability were then carefully examined. The results of the extensive laboratory experiments show that : (1) concrete materials has better resistance against calcium leaching as compared to mortar and cement paste based on the SEM-EDS measurements on the Ca/Si ratio; (2) the increase in duration of exposure of cement mortars resulted in increases in the porosity of the specimen as exhibited by the decreases of bulk density; (3) microstructural observation showed that mortar samples in ammonium nitrate solution experience accelerated leaching, resulting in the severe deterioration of the region near the exposed surface.

We report the first experimental breakthrough of a net gain of optical signals in a broadband chromium-doped fiber amplifier (CDFA) for next-generation optical communication systems. Current fiber amplifiers, including commercial erbium-doped fiber amplifier, cover only a relatively small portion of the entire transmission bandwidths (1300-1600 nm) of the low-loss windows of silica fibers. The newly developed CDFAs have opened up the possibility of utilizing the 300-nm entire spectrum of the low-loss fibers to further increase the transmission capacity. In this paper, we present the experimental demonstration of a net gain of 1.2 dB employing gain enhancement technique. With the help of an optical-fiber system examination for the CDFA, a 40-Gb/s error-floor free data transmission was successfully demonstrated by realizing the high-speed transmission of signal with gain through the chromium-doped fibers (CDFs). Further gain improvement in the CDFAs employing few-mode or single-mode CDFs will be presented and discussed.

A new scheme of a double-variable-curvature microlens (DVCM) employing a single-step grinding technique with fully automated fabrication for efficient coupling between high-power 980-nm laser diodes and single-mode fibers is proposed and demonstrated. The grinded fiber endface exhibited a double-variable curvature in the major axis, and was clearly observed for both major and minor axes after slight fusion polish. The perfect aspherical shape of the DVCM results in less grinding offset of 0.2 μm and better curvature radii control that leads to high average coupling efficiency of 83%. This clearly indicates that the performance of the DVCM can achieve high average coupling efficiency better than any other grinding techniques to form asymmetric microlenses. The versatility in double-variable-curvature design, fully automated fabrication, and the excellent performance of aspherical microlens makes the proposed DVCM extremely attractive for use in many lightwave interconnection applications.

The crystalline structure and morphology of the PLA crystallized isothermally from the glassy state on highly oriented PE substrates at 130°C were investigated by means of optical microscopy, AFM and X-ray diffraction. The results indicate that the PE substrate influences the crystallization behavior of PLA remarkably, which leads to the growth of PLA crystals on PE substrate always in edge-on form rather than the twisted lamellar crystals from edge-on to flat-on when crystallizing the PLA on glass surface under the same condition. The edge-on PLA lamellae on the PE substrate are preferentially arranged with their long axes in the chain direction of the PE substrate crystals. It is further demonstrated that except for the different crystal orientation, the PE does not influence the crystalline modification and crystallinity of the PLA.

This study performs experimental investigation into the application of abrasive jet polishing (AJP) to the surface finishing of electrical-discharge-machined SKD61 mold steel workpieces. The results indicate that the AJP processing conditions which optimize the surface quality of the SKD61 workpiece when polishing using #2000SiC abrasives are as follows: an abrasive material to additive ratio of 1:2, an impact angle of 30°, a gas pressure of 4 kg/cm2 (0.4 MPa), a nozzle-to-workpiece height of 10 mm, a platform rotational velocity of 200 rpm, and a platform travel speed of 150 mm/s. Under these processing conditions, a polishing time of 20 min is sufficient to reduce the surface roughness from an initial value of Ra = 1.7 μm to a final value of Ra = 0.27 μm, corresponding to an improvement of 84.12%. The experimental results demonstrate that the maximum attainable improvement in the surface quality of the polished workpiece is limited by a surface-hardening effect caused by the ball-impact phenomenon and the embedment of #2000SiC fragments in the workpiece surface.

High-power light-emitting diode (LED) modules encapsulated with different lens shapes after a thermal-aging test were studied experimentally and numerically. Samples from different manufacturers were aged at 80degC, 100degC, and 120degC under a constant driving voltage of 3.2 V. The results showed that the LED modules encapsulated with a hemispherical-shaped plastic lens exhibited a better lifetime due to better thermal dissipation than those with cylindrical-or elliptical-shaped plastic lenses. Results also showed that the optical power of the LED modules increased after removing the plastic lens because degradation of the lens material decreased the amount of light. The key module package-related failure modes under thermal-aging were identified as the degradation of the plastic lens and lens material. A finite-element method (FEM) simulation showed that thermal and major principle stress distributions of the high-power LED modules were dependent on aging temperature. Both experimental and FEM simulated results clearly indicated that a uniformly thermal dissipation to minimize the thermal effect along the thermal path from the LED chip to the plastic lens is essential to extend the operating life of high-power LED modules.

This paper proposes a new scheme for the lensed fiber employing a quadrangular-pyramid-shaped fiber endface (QPSFE) for coupling between the high-power 980-nm laser diodes and the single-mode fibers (SMFs). The QPSFE was fabricated by grinding and polishing techniques and then heating in a fusing splicer to form an elliptical microlens endface. A coupling efficiency of 83% has been demonstrated. Based on the far-field profile measurements, the higher coupling efficiency of the QPSFE lensed fiber was attributed to the better matching of both the elliptical Gaussian field distribution and the aspect ratio between the laser source and the fiber lens, The advantage of the QPSFE structure was to be able to control two axial curvatures, and, therefore, this novel QPSFE can form any different aspect ratios of elliptical microlenses to match the far field of the high-power diode lasers as well as the commercial diode lasers used in lightwave communications.

The fabrication of broadband single-mode Cr-doped silica fibers (SMCDSFs) using the fiber drawing-tower method with the modified rod-in-tube technique is demonstrated for the first time. A single-mode characteristic of SMCDSF was observed when the propagation wavelengths were longer than 1310 nm. The transmission loss was about 8 dB/m at 1550 nm. The successful fabrication of SMCDSFs may facilitate the possibility for utilizing the SMCDSFs as a new generation broadband fiber amplifier to cover the bandwidths in the whole 1300- to 1600-nm range of low-loss windows of silica fibers.

We propose and demonstrate a new scheme of aspherical microlens (ASM) employing a single-step grinding technique with fully automated process for efficient coupling between the high-power 980-nm laser diodes and single mode fibers. The grinded fiber endface exhibited a double-variable curvature in the major axis, and was clearly observed for both major and minor axes after slight fusion polish. The perfect aspherical shape of the ASM resulted in less grinding offset of 0.2 µm and better curvature radii control that led to high average coupling efficiency of 83 %. The result clearly demonstrated that the performance of the ASM exhibited high average coupling efficiency better than any other grinding techniques to form asymmetric microlenses.

A new scheme of a double-variable curvature microlens (DVCM) grinding technique for efficient coupling between the high-power 980-nm laser diodes and single mode fibers (SMFs) is proposed. The DVCMs has high average coupling efficiency of 54%. In comparison with the previous works of microlens fabricated by grinding and polishing technique, the advantages of DVCMs are a single-step without fused process, reproducible fabrication, less process time, and high yield. Furthermore, the proposed technique enables to offer variety designed microlenses for efficient coupling between laser diodes and SMFs used in interconnections.

The as-grown ferroelectric domain of the BiPbFeO 3 film is characterized by the vertical and lateral piezoresponse force microscope. A stripe domain with cross structure resulted by the spontaneous polarization along the [111] directions of BiPbFeO 3 film is observed. The vertical piezoresponse signal, polarization versus voltage curve, is obtained. Based on the amplitude hysteresis curve, the d 33 coefficient of the 300nm-thick BiPbFeO 3 film is obtained with a value of around 30.47 pm/V.

Publisher Summary This chapter investigates the physicochemical properties of raw and 3-aminopropyl-triethoxysilane (APTS)-modified carbon nanotubes (CNTs) and their CO2 adsorption properties. Effects of temperature and moisture on the CO2 adsorption in modified CNTs are also given. Carbon nanotubes are unique and one-dimensional macromolecules that have outstanding thermal and chemical stability. These nanomaterials have been proven to possess good potential as superior adsorbents for removing many kinds of organic and inorganic pollutants in air streams or in aqueous environments. The large adsorption capacity of pollutants by CNTs is mainly attributable to their pore structure and the existence of a wide spectrum of surface functional groups, which can be achieved by chemical modification or thermal treatment to make CNTs that possess optimum performance for particular purposes. The raw and APTS-modified CNTs were selected as adsorbents to study their characterizations and adsorption properties of CO2 from air streams. The physicochemical properties of CNTs were improved after modification, including the increase in defective structure and surface functional groups, which made CNTs, adsorb more CO2. With the 50% CO2 inlet, the amount of adsorbed CO2 on raw and modified CNTs was 69.2 and 96.3 mg/g, respectively. The CO2 adsorption performance of modified CNTs decreased with an increase in temperature but increased with an increase in relative humidity. The modified CNTs possess higher CO2 adsorption capacity than many types of APTS-modified silica adsorbents reported in the literature, suggesting that the APTS-modified CNTs are promising adsorbents for the capture of CO2 from air streams.

The fabrication of ultra-broadband singlemode Cr-doped fibers (SMCDFs) using fiber drawing-tower method is demonstrated for the first time. The success in fabrication of SMCDFs may open the possibility for utilizing SMCDFs as ultra-broadband fiber amplifiers.

A new scheme of asymmetric elliptic-cone-shaped microlens (AECSM) employing a single-step fabrication technique for efficient coupling between the high-power 980-nm laser diodes and the single-mode fibers is proposed. The AECSMs are fabricated by asymmetrically shaping the fiber during the single-step grinding process and elliptically lensing the fiber tip during the fusing process. A maximum coupling efficiency of 85% and a high-average coupling efficiency of 71% have been demonstrated for a 980-nm laser diode with a high aspect ratio of 5. In comparison with the previous works on asymmetric fiber microlenses fabricated by the multi-step processes with complicated fabrication, the advantages of the AECSM structure for achieving high coupling are a single-step fabrication, a reproducible process, and a high-yield output. Therefore, this AECSM can form different aspect ratios of asymmetric elliptical microlenses to match the far field of the high-power diode lasers that is suitable for use in commercial high-power pump laser modules.

We report on the first fabrication of a Cr-doped fiber using a drawing-tower method with Cr:YAG as the core of the preform. Both Cr3+ and Cr4+ ions coexist in the Cr-doped fiber, and the amplified spontaneous emission (ASE) spectrum shows a broadband emission of 1.2 to 1.55 mum which can not be realized by using currently available fiber amplifiers. This indicates that the new Cr-doped fibers have the potential for being used as a broadband fiber amplifier to cover the bandwidth of the entire 1.3-1.6 mum range which exhibit 300 nm usable spectral bands.

High-power laser module with multi-mode passive fiber is proposed and fabricated. The measured maximum coupling of the module was up to 91.9% by using an optimized 30deg angle of the wedge-shaped fiber.

Wavefront measurements with large dynamic range on high-power diode lasers are demonstrated. The wavefront sensor exhibited a large dynamic range of pi/2 to -pi/2 and high accuracy of the wavefront slope angle of 0.05 degree. The result of this study may provide an accuracy method for measuring the wavefront distributions of the diode lasers and the light sources with large divergence angles, such as a 980-nm high-power diode laser.

We demonstrate the fabrication of a broadband Cr-doped fiber using a drawing-tower method with a negative pressure control. In comparison with the fiber drawing without a negative pressure control, this new process significantly improve the quality and performance of the fabricated Cr-doped fibers. The Cr-doped fibers exhibited better core circularity, good continuity of drawing process, and excellent interface between core and cladding. The ASE spectrum showed a 300-nm broadband emission with the output power density of a few nW/nm. The results indicate that this new Cr-doped fiber may be used as a broadband fiber amplifier to cover the bandwidths in the whole 1.3-1.6 μm.

We report on the first fabrication of a Cr-doped fiber using a drawing-tower method with Cr:YAG as the core of the preform. The Cr-doped fibers have potential for use as fiber amplifier to cover the bandwidths in the whole 1.3-1.6 /spl mu/m range.

We propose a novel quasi-ellipsoidal microlens employing a quadrangular-pyramid-shaped fiber endface (QPSFE) for the coupling between high-power 980 nm laser diodes and single mode fibers. The QPSFE was fabricated by using a grinding and polishing technique and then heating in a fusing splicer to form a quasi-ellipsoidal microlens endface. A coupling efficiency of 60% has been demonstrated. Based on the Gaussian beam approximation, a simple theoretical calculation of the effect ellipsoidal-axis and working distance on coupling efficiency is presented.

A method of direct measurement of near-field phase and intensity distribution of laser diodes employing a single-mode fiber interferometer is proposed and demonstrated. The phase and intensity of the output beam of the laser in the vicinity of the output facet are measured directly via interferometry. Using a 980 nm laser diode as an example, we obtained a beam width of 0.9 and 3.6 μm at the output facet in the vertical and horizontal axes, respectively. In addition, the phase information of the output beam was also obtained by using interferometry. This technique is particularly useful for laser diodes whose near-field phases are difficult to measure directly. The measured vertical and horizontal wavefront radius of curvatures of a laser diode are in good agreement with the calculation from Gaussian beam theory. Detailed understanding and measurement of the near-field phase and intensity distributions of light sources and optical components are essential for micro-optic designs with better mode matching to minimize the insertion loss.

A new scheme of optical fibers with different types of end-faces by applying different types of periodical variable torques to control the polishing pressure is proposed and fabricated. Two types of mechanisms, mechanical torque and electrical torque controls, are developed to generate different types of periodical variable torques. The mechanical torque control type is mainly designed for fabricating an elliptical-cone-shaped fiber end-face that can be used in efficient coupling between a laser diode and fiber with a coupling efficiency up to 83% (Lu et al 2007 Opt. Express 15 1434). The electrical torque control type is even more versatile for fabricating optical fibers or micro-probes with polygon pyramid end-faces that may have other potential applications, such as various kinds of micro-indenters. Both types of fiber end-faces can deliver satisfactory results with single-step fabrication, a high fabrication yield and sufficient optical coupling efficiency.