Study On Optimization Of Quaternary Sulfide Phase Change Thin Films And Application Of Optical Swithches

Phase change materials,a class of materials with reversible phase transitions,are also a kind of multiplexed functional materials,which are of great significance to the development of new generation photonic devices.Phase change materials generally have two phase states,crystalline and amorphous,and the two states have great differences in electrical and optical properties such as resistance and refractive index.Phase change films of sulphur compounds,which are typical phase change materials,have been widely used due to their nonvolatile.In particular,Ge-Sb-Se-Te(GSST),a quaternary chalcogenide phase change film,has low loss in the communication band and can be combined with siliconbased materials for use in various types of optical waveguide structure devices,which is more conducive to the integration of silicon-based photonics devices and makes the devices develop towards more miniaturisation and higher integration.This paper focuses on the transmission loss of sulphur compound phase change materials in the C-band of communication,and uses Magnetron Sputtering Deposition(MSD)to prepare Ge-Sb-Se-Te films,and uses Ag doping modification to optimize the quality of the film preparation.Simulation and application studies on the multiplexing of optical waveguide switches were also carried out using the phase change films prepared in the laboratory.The main contents include:(1)Phase change films consisting of four elements,Ge,Sb,Se and Te,in the atomic ratio of 2:2:4:1,were prepared using MSD.The refractive indices and extinction coefficients of the GSST films were investigated in the crystalline and amorphous states,respectively,and the effect of annealing conditions on the crystallisation of the films.The crystallisation of GSST films with a thickness of approximately 50 nm at 5 min of deposition resulted in a refractive index of 5.13+0.35i and 2.86+0.2×10-2i in the amorphous and crystalline state,respectively.The figure of merit(FOM)of GSST was as high as 6.4.In addition,after crystallization of the 250 nm thick film deposited for 25 min,the refractive index was 4.58+0.51i,and the refractive index in the amorphous state was 2.85+0.01i,with a phase transition figure of 3.65.To improve the quality of the 250 nm thick film,Ag doping was performed,and when the Ag doping concentration was 2.53%,the refractive index of the crystallized film was 5.13+0.37i,and the refractive index in the amorphous state was 3.02+7.4×10-4i,with a phase transition figure of 5.7.The complex refractive index in the amorphous state was 3.02+7.4×10-4i,with a phase transition figure of 5.7,which is a huge improvement compared to the undoped phase transition figure.(2)The optical parameters of GSST thin films obtained experimentally in two phase states are used to carry out an applied simulation study of optical switch multiplexing.A three-dimensional time-domain finite-difference method and supermode coupling theory are used to study the design of 2×2 reconfigurable mode multiplexed switch units,and the combination of these switch units is used to study the structure of 4×4,6×6 and other arraytype multiplexed switch structures to achieve multiple-input and multiple-output transmission functions.The results show that the extinction ratio of the 4×4 optical switch is greater than 13 dB and the insertion loss is less than 1.5 dB at 1550 nm,while the extinction ratio of the 6×6 optical switch is greater than 9 dB and the insertion loss is less than 2 dB.