A strip/slot hybrid horizontal silicon nitride slot waveguide is designed to provide an ultraflat and low dispersion. By optimizing the height and width of the structure, an ultraflat and low dispersion of ∼0±7 ps/nm/km over 812 nm wavelength range (from 1137 to 1949 nm) can be achieved. The waveguide with a 20-nm conformal overlayer has chromatic dispersion within ±1 ps/nm/km over 682-nm bandwidth. So the flatness is 0.0015, which is the lowest flatness in near-infrared regime of this kind of waveguide to our knowledge. The influence of the waveguide sidewall to dispersion is also discussed.
To study the relationship between Aerosol Optical Depth (AOD) and concentration of PM2.5（Particulate Matter) basing on CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) data, 51 samples among the CALIPSO Level 2 aerosol profile data of local region from January to April 2014 are selected. After screening these 51 samples under the decided conditions, such as system stability and the type of the materials, the AODs of the samples are calculated. Then a linear regression model is constructed through Matlab software, in which AOD is independent variable and PM2.5 is dependent variable. All the data are fit by the selected five functions: linear, logarithmic, exponential, power, and quadratic. Experimental results show that the value of correlation coefficient of the quadratic equation model is the best one among the functions. So it is feasible to monitor the concentration of PM2.5 using the AOD calculated from CALIPSO Level 2 data.
Nano-particles and nano-period ripples can be used to form some micro-nano-instruments in microelectronics. In this
paper a femtosecond (fs) pulse laser (148fs, 1KHz, center wavelength=775nm) is used to irradiate on metal surface, then
nano-particles and nano-period ripples can be obtained in the focal scale, the size of which is shorter than the center
wavelength. For describing the formation time and characteristic of nano-particles and nano-period ripples, we have
increased the laser fluence from the threshold of material to a higher value and increased the laser exposure time in fixed
laser fluence on different materials. Experimental results show that nano-particles occur earlier than nano-period ripples.
And as the fs laser pulse number being increased, the periodical nano-ripples is clearer and clearer and the depth of
ripples is deeper and deeper. Finally, permanent ablation will occur in the focal scale basing on the nano-ripples. After
surface plasmon polaritons theory is used, the period of nano-ripples can be explained exactly. This work is the basic
research for micro-nano-instruments by fs laser ablation technique on metal surface.
We report a preliminary experiment result of poling in a femtosecond-laser-treated LiNbO3 (LN) crystal. Because of the precision of the femtosecond laser machine, we can control the width and depth of snicks exactly. Then the high-voltage electric field was operated on +z side of the LN crystal. The visible poling pattern was observed by a microscope and machining parameter influences the electric field distribution in the crystal. This approach does not need expensive masks and the periods of PPLN can be adjusted flexibly. Although the mechanism of core formation is not very clear yet, we believe that it would provide a novel technique of making prototype PPLN and other periodically poled crystals.