Research And Fabrication Of Waveguide In Sapphire With Femtosecond Laser Pulses

Due to its eximious properties,such as high melting point(2053℃),excellent mechanical strength,well-documented corrosion-resistant and transparency in near-infrared wave bands and so on,sapphire has been one of the most valuable materials to be studied and researched as a kind of insulative oxide crystal for a long period of time.However,it is really difficult to fabricate devices with such material, because of its hardness.While,femtosecond laser processing is famous for its high-precision,cold working characteristic and the processing is able to become the only option for hard materials.In this paper,we launched our research on the base of a internal preparation of a simple waveguide line in the transparent sapphire material.On one hand,we tried to seek the right power,the appropriate objective lens,and the proper move-speed of the sample to fabricate ideal waveguide lines in sapphire.We observed the capacity of the optical optical waveguide by light-guiding testing with my dual-lens coupling system. At the same time,we estimated the refractive index of sapphire waveguides as well as the waveguide loss,and analyzed the alteration of nature where exposed to IR.On the other hand,we explored the self-focusing effect which is accompanied by high-intensity laser processing.To start with the phenomenon of self-focusing in the vertical direct-writing waveguides,we made a deep exploration on the conditions and characteristics for the occurrence of self-focusing.Further,we first designed the filaments forming experiments in sapphire,and obtained series of filaments with different lengths with nature be minutely analyzed.At the last part of the paper,we made an explanation for super-white light due to the self-phase modulation theory.Specifically,the paper's main job may be divided into three parts as the following list.1.To fabricate waveguide in sapphire with laser direct-writing in vertical direction.If a high magnification and high numerical aperture objective lens was used as well as laser power seriously controlled within 5mw,a very good direct-writing waveguide would be obtained with its width about 5μm.In the experiments,two kinds of objective lens,with their NA 0.7 and 0.85 respectively,were taken use of, and the power was set at 5mw,while the sample move speed range from 300steps/s to 600steps/s(1step=2.5μm),high-quality waveguide lines would be fabricated. Incidentally,the threshold requirement by laser direct-writing in sapphire was significantly than that of quartz glass.The inevitable result of asymmetrical focusing light made sapphire waveguides showing thin section plane,which guides light at the top.2.Fabricating sapphire waveguide by laser direct-wring in the parallel direction. Since the mutual constraints between focus distance and working distance of objective lens,the prepared waveguide always got a relatively short size with a uneven width.In the paper,we chose a 10-magnification lens,with its NA equals 0.25 and working distance 7.5mm.This kind of lens may take a well balance between focus distance and working distance.A large increase in direct-writing threshold due to the lose of lens' NA.Like the expected results,when the power exceeded 40mw or even more,waveguide lines would be observed inside.Different from the above mentioned waveguides,these waveguides had a standard circular section plane.3.Study on self-focusing phenomenon introduced by laser radiation. Self-focusing was a negative impact,unexpected to occur in laser direct-writing, while the phenomenon itself was great valuable for physical researching.Through the experiments,we revealed several factors that strongly affected the self-focusing process,such as laser power,focal length of lens,depth of focus,time accumulation, and so on.It was also the first time to with the help of self-focusing to form long filaments in sapphire.According to the texture distribution caused by HF corrosion in quartz glass,we realized the direction and mode of self-focusing.Because of the instability of self-focusing,the attempt which made using of self-focusing to fabricate waveguides got to fail.At the last part of paper,we gave a brief description of super-continuum white light,and gave some reason for why this phenomenon occurred.