We report high-power efficient green light generation by frequency doubling from a periodically poled MgO doped LiNbO(3) ridge waveguide. The ridge waveguide is fabricated by the annealed proton-exchanging and precise diamond blade dicing techniques. The ridge structure exhibits a surface roughness of only 3.7 nm, and near-90° vertical sidewall. The total insertion loss of an 8.5 µm wide and 1.4 cm long uncoated waveguide is 3.0 dB under direct fiber coupling. 466 mW of continuous-wave green light with an optical-to-optical conversion efficiency of 69.7% is obtained. To the best of our knowledge, this is the highest green light output power reached to date using a ridge-type LiNbO(3) waveguide device. Phase-matching temperature shift, tuning curve distortion, and waveguide loss increase are observed under high power operation. Our analysis shows that the photorefractive effect and the green induced infrared absorption are responsible for the observed phenomena, which becomes prominent under several megawatt per square centimeter power density.
The optical characteristics of one-dimensional metallodielectric photonic crystals (MDPC), constructed by inserting metal aluminum layers of certain thickness into the Si/SiO2 system, were studied theoretically with the transfer matrix method. The results show that the reflection efficiency can be enhanced considerably after the introduction of metallic layers, e. g. the rejection level of each period increased from 7.2 dB([Si(46 nm)/SiO2 (120 nm)]5) to 20 dB ([Si(46 nm)/SiO2 (60 nm)/Al (10 nm)/SiO2 (60 nm)]5). In addition, high omnidirectional reflection band with broader width can be obtained, e. g. bandwidth of 550 nm can be offered with [Si(46 nm)/SiO2 (60 nm)/Al (30 nm)/SiO2 (60 nm)]5. Rules of how the absorption, thickness and position of the metal layers affect the optical characteristics of the MDPC are also discussed. These MDPC structures may be used as compact-size, low-loss and broad-band optical reflectors.
The stress distribution, failure depth, and shape and range of overlying strata of the stope are important bases for the prevention of roof water hazards and determination of reasonable locations of roof roadways. Based on the hydrogeological data of the E9103 workface, FLAC numerical simulation software was used to establish a numerical calculation model of the overlying strata of the E9103 inclined coal seam, and the stress distribution and failure characteristics of the overlying strata were analyzed. The development height of the caving and water-flowing fractured zones in the overlying strata of the workface was determined. Results showed that the stress reduction area appeared above the goaf in the form of an “arched” distribution, and tensile stress occurred in the local area of the overburden. The overburden relief arch of the workface was symmetrically distributed along the advanced direction and asymmetrically distributed along the inclined direction, with the arch crown deflecting above the workface. The horizontal and vertical displacements of the overlying strata of the stope increased with the advancing distance of the workface. The horizontal displacement in the -direction presented two obvious regions, and the critical points of the two regions moved forward with the advancement of the workface and showed a certain degree of symmetry. The horizontal displacement in the -direction presented an “inverted bowl” distribution and increased with the advancement of the workface. The main failure forms of the overlying strata of the workface were a tensile and shear failure, and shear failure was dominant in the upper direction. The height of the overburden caving zone in the workface had little relationship with the advancing distance of the workface and increased slowly as the advancing distance of the workface increased. The development height of the caving zone is 7.2–18.13 m. The development height of the water conduction fissure zone increased rapidly with the increase in the advancing distance of the workface. When the advancing distance was equal to the length of the workface, the development height of the water conduction fissure zone was flat and basically maintained at a stable value. The development height of the water conduction fissure zone is 30.8–62.2 m. These research findings have important engineering importance for ensuring safe and efficient mining of E9103 workface.
Rib spalling of loose thick coal wall seriously restricts the high yield, high efficiency of coal mine, affecting the safety production of coal mine. Based on the engineering background of water injection to control rib spalling of loose thick coal seam in the Luling Coal Mine of the Huaibei Mining Group, the mineral composition and microscopic morphology of III811 loose thick coal seam in Luling Coal Mine were analyzed by X-ray diffraction and scanning electron microscope. Through uniaxial compressive strength tests of coal samples with different moisture content, the relationship between uniaxial compressive strength, peak strain and moisture content, and their failure characteristics was studied. The results showed that the natural moisture content of III811 coal seam in Luling coal mine is low, and it contains a large amount of kaolinite (75.2%) belonging to clay mineral which is easy to absorb water and then expand, fully bond loose coal body and fill cracks to improve the integrity of coal body. These two factors provide feasibility for injecting water in workface to prevent rib spalling. The compressive strength of coal samples decreased slowly with the raise of moisture content, while the peak strain increased first and then decreased. The peak strain was the largest when the water content was 6.0%. The failure degree of coal samples intensifies with the increase of water content, and the failure form changes from tensile failure at low water content to shear failure at high water content. Considering the relationship between compressive strength, peak strain, and moisture content of coal samples, the optimal moisture content of III811 workface in loose thick coal seam is determined to be 4.5% ~6%.
The mechanical course is very practical and the content is abstract, and is a machine and institutions as the main research object of the course. To meet the needs of the complex machinery of the applied talents training, in this paper, the virtual reality technology is applied to the teaching of the theory and practice. The use of virtual simulation technology in teaching will help to design a vivid and guide students into the state of autonomous learning, which can help improve the ability of student to analyze and solve problems and innovation. It can improve the teaching effect and improve the teaching effect and quality.
Efficient cw 532 nm green-light generation is demonstrated using a periodically poled MgO:LiNbO3 ridge waveguide prepared by a process that combines annealed proton exchange and precise dicing. Performance of waveguides with different widths has been investigated. The 6-μm-wide, 1.6-cm-long uncoated ridge waveguide has achieved a green output power of 127 mW under a coupled fundamental light power of 250 mW. The highest conversion efficiency achieved is 53%.
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