The Modulation And Characterization Of Surface Refractive Index Of Lithium Niobate

The modulation and characterization of surface refractive index of lithium niobate is quite important for fabrication of the integrated optical components such as optical waveguide,optical frequency conversion,and electro-optical modulation.However,for creating a high-quality structure of the refractive index,the acquisition of the real-time information and selective modification of the refractive index are very important by direct laser writing and proton-exchange.In this paper,the real-time direct laser writing and photo-assised proton exchange technology were proposed,and careful studied of the modulation and characterization of surface refractive index of lithium niobate.Firstly,the real-time direct laser writing system is build to modulate and characterize the refractive index in the transmission and reflection configuration,and theoretical calculation ensures the reliability of the system.In the transmission configuration,we use the phase-delay probing to characterize of the refractive index of the lithium niobate.In the reflection configuration,the refractive index change is occurred of the surface of lithium niobate by focusing light field,and successfully controlled by extracting the real-time information as the feedback for tuning the exposure time or scanning speed of the focused laser.Through real-time direct laser writing technique,one is able to realize the multi-dimensional structures of the refractive index on lithium niobate with micron-size accuracy by inducing a strong photorefractive effect at the focal region.Then,photo-assisted proton exchange process is carried out on both the c-and y-surfaces of Fe-doped lithium niobate crystals by the experimental setup.The proton spatial distribution is confined by the incident laser beams.Stand-alone FT-IR microscope and Micro-Raman spectrometer are used to characterize the proton distributions of the surface of the treated samples,and an optical microscope and a scanning electron microscope are employed to observe the morphology of the treated surface.It is found that the etching morphology of the y-surface show apparent directional features along the c-axis,and the range and number of these micro-cracks can be controlled by the experimental parameters.Moreover,we characterize the sample after photo-assisted proton exchange by transmission and reflection configuration,and ensure the selective modification of the refractive index.