We report the dark blue nonlinear Cerenkov radiation by the second harmonic generation （SHG） in a two-layer-stacked hexagonal periodically-poled-MgO： LiNbO3s （PPMgOLNs）. Based on the direct wafer bonding of two target PPMgOLNs rotating around the axis perpendicular to the plane wi twelve bright spots as twice of those in a single PPMgOLN are shown at each second-h ring. The experimental results agree with the theoretical ones and present a promising application in the fabrication of three-dimensional （3D） PPMgOLNs.
We propose a polarization-insensitive and broadband subwavelength grating reflector based on a multilayer structure.The reflector has an overlapped high reflectivity（〉99.5%） bandwidth of 248 nm between the TE and the TM polarizations,which is much higher than the previously reported results.We believe this subwavelength grating reflector can be applied to unpolarized devices.
采用直接反应烧结法制备了(Ba1-x Ca x)(Ti0.85Zr0.15)O3无铅压电陶瓷,分析了不同的Ca含量时陶瓷的晶相结构、微观结构、密度及电性能。结果表明,采用直接反应烧结法制备的(Ba1-x Ca x)(Ti0.85Zr0.15)O3无铅压电陶瓷具有纯的钙钛矿相结构;微观结构致密,晶粒大小比较均匀,陶瓷样品出现较大的直径收缩率(25%左右);随着Ca含量的增加陶瓷的居里温度略微降低,室温介电常数出现较大增加,压电常数变大,其中x=0.15时压电性能最好,d33为208 pC/N。
We report rigorous coupled-wave analysis(RCWA) method to non-destructively characterize the domain structure of periodically poled lithium niobate(PPLN) crystal. The strong light diffraction effect is achieved by applying a proper external voltage. We can observe reversed domain pattern and employ the detected diffraction intensity to optimally fit the result of RCWA based on least square method. Compared with conventional scalar diffraction theory, more accurate domain structure parameters with accuracies of 0.05 μm and 0.005 for the period and duty cycle are obtained respectively. It is proved that accurate, real-time and nondestructive characterization can be realized via this method.
