Study Of Nd³⁺ Doped Silica Microsphere Cavity Laser

Whispering gallery mode in microsphere cavity has a smaller volume and higher quality factor Q(1010)than other micro resonators that have found,which means the threshold pump power is smaller and it has a higher utilization efficiency for the pump power,so now study of microsphere cavity becomes a hot topic.To satisfy people's demand for new type of laser and the study for physical properties of microsphere cavity,we take the two topics of microsphere cavity and rare earth ions doped glass gain medium as the starting point,to study Nd3+ doped microsphere cavity laser.To explore the optical properties of the neodymium-doped microspheres cavity laser,we have carried on a detailed theoretical derivation of whispering gallery mode(WGM),double tapered fiber coupler and the coupling under ideal conditions firstly through electromagnetic theory and geometrical in this article,we also have a simplified simulation for coupling system through the software COMSOL Multiphysics.For the preparation of microsphere cavity,we select silica materials as microspheres laser matrix material,which is with good optical properties,abundant and cheap.We make microspheres through the electrode discharge fused silica fiber and its surface tension.On doping method,we used the sol-gel process.To make Nd3+doped silica microspheres,we touched colloid which containing Nd3 + ions for a few times,through high temperature treatment,thus there will be a coating for a certain thickness coated silica microsphere surface.the process for using silica as the basic structure of the microspheres satisfy doping Nd3 + ions target without introducing other impurities.In the experiments,we chose the best coupler:the double tapered fiber coupling with Nd3+ doped silica microspheres as experiment platform,using the 808 nm laser pump source.We got the output laser in 1060-1100 nm band for both single mode and multiple mode,and analysis the conversion relationship between the output laser and pump laser power.We also analysis the pattern of multiple longitudinal mode laser output properties.Compared with the same output laser in the band of 976 nm laser pumped Yb3+ doped matrix,the output frequency shift is bigger.In practical applications,it will be easier to implement signal filtering separation of light.In addition,we also observed the output laser in 1060-1100 nm band in the Nd3+ doped phosphorus silicate microspheres.when 808 nm pump laser power increases,the output laser power of the stimulated radiation near 1080 nm wavelength will increase,and because the silica is Raman active medium,we observed the Raman laser at the wavelength of 1143nm in the Nd3+ doped silica microspheres which was stimulated by the 1080nm wavelength laser.We called it self-stimulated Raman laser.In the in the Nd3+ doped silica microspheres,we not only observed the laser based on ion energy level transition of Nd3+,but also the Raman laser based on nonlinear optical effect.Thus we can see that the advantage of the Nd3+ doped silica microspheres cavity.