Design And Preparation Of Magnetooptic Monocrystalline Garnet Thick Film Materials And Its Application Research In Planar Magneto-optic Isolator

The magneto-optic devices based on Faraday effect are widely used in many fields such as the optical communication,laser,power measurement,aerospace,and medical.With the development of science and technology requiring increasingly higher performance of magneto-optic materials and devices,increasing the Faraday effect and the Verdet constant,and reducing the optical absorption loss is a powerful driving force for the development of magneto-optic materials.The magneto-optic garnet crystal represented by yttrium iron garnet(Y₃Fe₅O₁₂,YIG)has the lower light absorption coefficient and excellent magneto-optic performance at near-infrared wavelengths,and are currently the only materials applicable to the near infrared band of optical communications.Especially,the Bi-doped YIG film?Bi:YIG?which has giant Faraday effect has been widely concerned.This article focuses on improving the Faraday effect of magneto-optic films and aims to prepare magneto-optic films with high quality and excellent performance for magneto-optic isolator,and the monocrystalline?BiTm?₃?Ga Fe?₅O₁₂ films were studied systematically from theory,simulation and experiment three aspects for the first time.In this paper,the main research work and innovation are as follows:Firstly,the first-principles calculations were performed using the CASTEP module to simulate the effect of Bi doping on the electronic structure of YIG.By comparing electronic structure of Y₃Fe₅O₁₂2 and Bi₃Fe₅O₁₂,it is found that O 2p orbitals acts as an intermediary,Bi 6p orbitals first hybridize with O 2p and then hybridize with Fe 3d,which induces a change in the band width of Fe 3d and O 2p,and eventually makes Fe 3d orbitals and Bi 6p orbitals is almost completely overlapped with O 2p orbitals respectively.This orbital overlap is the basis for spin-orbit splitting and hybridization and is the basis for the enhancement of the Faraday effect.Secondly,Single-crystal?BiTm?₃?GaFe?₅O₁₂ films were designed and prepared on Germanium Garnet?GGG?substrates by a lead-free Liquid Phase Epitaxy?LPE?process.The effects of growth rate and film thickness on the structure and properties of the films were investigated.It was found that Bi³⁺content in the film not only directly affects the lattice mismatch,but also plays a decisive role in the Faraday effect.The excessive lattice mismatch can cause defects in the film surface,which will result in poor mirror reflection effect and will also affect the Faraday effect.The influence of the lattice mismatch stress on the uniaxial anisotropy is the fundamental reason for the change of the domain structure.Even if the film thickness is more than 60?m,the lattice mismatch stress still exists,and the domain width is affected not only by the film thickness,but also by the stress relaxation.The films growth rate is between 0.65-0.85?m/min with the best mirror effect,the films growth rate is 0.75?m/min with the smallest lattice mismatch.The Faraday effect is mainly influenced by the incident wavelength,the content of Bi³⁺and the optical loss caused by the defect.When the film growth rate is 0.85?m/min,the maximum Faraday angle is 0.041°/?m@1550 nm,and the maximum Verdet constant is-2.595×10^-4°/?Oe·?m?@1550 nm.The growth rate of 0.85?m/min is the optimal growth parameter.Finally,based on the single-crystal?BiTm?₃?GaFe?₅O₁₂ thick film prepared in our laboratory as the Faraday rotor,a new magneto-optic isolator is designed.When the external magnetic field is 800 Gs,the saturated Faraday angle is 53°@1550 nm,when the external magnetic field is 590 Gs,the Faraday angle is 45°@1550 nm,the optical absorption coefficient 15cm^-1@1550 nm,and the optical transmission coefficient is 85%@1550 nm,meeting the design requirements.