Study On The Fabrication Of Sapphire Optical Fiber Cladding

This paper specifies two processes:chemical vapor deposition and atomic layer deposition to deposit thin films on the surface of sapphire single crystal fibers.The purpose is to fabricate a fiber cladding with good compatibility and stability with sapphire fiber,so as to solve the problem of optical loss of light transmission inside the fiber and provide effective protection for the fiber.Sapphire single crystal fiber has excellent physical and chemical properties,and has very good application prospects in high temperature fiber sensing and near infrared sensing.However,unlike quartz fiber and polymer fiber,sapphire fiber is a non-clad single crystal fiber,that is,bare fiber,due to limitations of its own preparation process.In order to extend the life of the fiber and expand the working range of the fiber,it is necessary to carry out cladding growth on the surface of the sapphire fiber.The hBN and alumina films have excellent physical and chemical properties,meeting the requirements of the sapphire fiber for the properties of the cladding material.At present,the research on sapphire fiber cladding is very enthusiastic at home and abroad,but the research on the preparation of hBN cladding by chemical vapor deposition and the preparation of alumina by atomic layer deposition has not been reported.The chemical vapor deposition method is suitable for preparing a dense and uniform hBN film;the atomic layer deposition method can accurately control the thickness and density of the aluminum oxide film,and conveniently obtain a cladding film having a desired refractive index.This paper studies the material selection,preparation process and film properties of the sapphire fiber cladding.In the paper,two methods for preparing cladding are detailed.One is to grow hBN film on the surface of sapphire fiber by chemical vapor deposition.The result of SEM,Raman and ellipsometry of hBN film shows that sapphire is based on LPCVD.It is feasible to grow hBN film on the surface of the fiber.The hBN film grown on the sapphire fiber at 1000?is relatively dense and uniform,and has good crystallization properties.And the crystallization property of the hBN film grown on the optical fiber by the process can be consistent with the crystallization property of the growth material on the planar substrate.In addition,in this experiment,atomic layer deposition?ALD?technology was also used to deposit and grow aluminum oxide film on the surface of sapphire single crystal fiber,and the film was annealed.The results showed that the cavity and microcracks in the inner region of the film were treated by annealing process.Most of the defects are reduced.At anneal temperatures from1200°C to 1300°C,the film structure appears denser and more uniform,and the pores in the structure no longer exist.The refractive index of alumina increases first and then increases with the increase of annealing temperature.In the stable trend,when the annealing temperature is between 1200?and 1300?,the refractive index tends to be stable,and the value is about 1.726.The Al-0 crystal phase exists inside the annealed alumina film,and the crystal phase of the alumina film after annealing at1200?and 1300?is more similar to?-Al₂O₃ and?-Al₂O₃.