Simulation And Fabrication Of Sapphire Rib Waveguides Using Femtosecond Laser

Sapphire has a high hardness,stable physicochemical properties,and a wide optical window of transmission,which make it widely used in optical windows,instrumentation,semiconductor and consumer electronics.However,with high hardness and high wearability,sapphire is difficult to process,which limits the further application of sapphire.In this paper,by utilizing the excellent optical properties of sapphire,the fabrication of sapphire rib waveguides is studied through femtosecond laser micromachining.The sapphire rib waveguide was designed and simulated by RSoft software with built-in finite-difference beam propagation method.The effects of waveguide rib width and etching depth on the light-guiding performance of the waveguide were studied.By analyzing the influence of structural parameters on the normalized power and mode birefringence effects,the rib width of 200μm and the etching depth of 172μm were finally determined.The error analysis of the groove wall inclination existing in the actual machining was carried out.It was found that when the groove wall inclination angle reached about 16°,the normalized output power was reduced by about 5% compared with the case where the groove wall inclination angle was zero.The alignment-coupling between the sapphire rib waveguide and the fiber was studied.By calculating the overlap integral of the waveguide mode field and the fiber mode field,the variation of the mode field coupling efficiency when the fiber has lateral position deviation and deflection deviation was obtained.The distribution of the waveguide mode fields and the transmission of the fundamental mode light field in the waveguide were simulated.The sapphire scribing process of femtosecond laser was studied.The effects of laser power and scanning speed on the scribing process were tested respectively,and the influence on the scribing process was analyzed.The laser power of 450 mW and the scanning speed of 10mm/s is preferably on the premise of both processing accuracy and material removal rate.The influence of line spacing on the surface topography of the groove bottom was studied.The line spacing was determined to be 10μm while considering the surface roughness and groove depth.The scanning layer spacing of 5μm was determined,and the relationship between the number of scanning layers and the etching depth was investigated.According to the above analysis of the process parameters,the process parameters of the sapphire rib waveguide were determined,and the sapphire rib waveguide satisfying the size requirement was fabricated.A coupling test platform was built,and the loss of sapphire rib waveguides was measured by the cut-off method.The average power loss per unit length of the sapphire rib waveguide was.The influence of the thermal expansion of sapphire rib waveguide in a high temperature environment was analyzed by simulation software.The coupling power drop due to coupling misalignment is calculated,which shows that there is little effect of actual high temperature on sapphire rib waveguide.