Design Of Reconfigurable Photonic Devices Based On Phase-Change Materials

With the rapid development of modern communication technology,there is an increasing demand for miniaturization of photonic devices.Reconfigurable photonic devices can realize dynamic switching of different device functions in the same structure,thus facilitating device miniaturization.In this paper,based on the phase-change material Ge₂Sb₂Te₅（GST）,two reconfigurable photonic devices are investigated and designed,which can be applied to the study of high-density integrated micro and nano optics and have applications in the design of new generation optical communication systems.The main research of this paper is as follows:（1）The switching between different optical types of singular points at the optical communication wavelength of 1.55μm is achieved by using phase-change materials for a non-parity-time（PT）symmetric multilayer structure.The transmission matrix method is used to analyze the formation conditions of various types of optical singular points in the multilayer structure,and the FDFD method is applied to perform numerical simulation and optimize the structure parameters by combining with genetic algorithm.Firstly,absorbing singularities can be switched to exceptional points（EPs）in a two-layer structure consisting of a phase-change material layer and a lossy layer by switching the phase-change material GST from its crystalline to its amorphous phase.Next,a three-layer structure consisting of GST,lossless medium and gain material is designed,spectral singularities（SSs）can be switched to EPs in this structure is realized by switching the phase-change material GST from its crystalline to its amorphous phase.Then,a three-layer structure consisting of absorber material,GST and gain material is designed by combining the genetic algorithm,self-dual SSs can be switched to unidirectional spectral singularities by switching the phase-change material GST from its amorphous to its crystalline phase.A new active device with a large modulation depth is also designed based on unidirectional spectral singularities.The sensitivity of the left side reflectivity of the device to the imaginary part of the absorbing material is as high as 3250.the results of this study contribute to the development of a new generation of reconfigurable optical devices based on optical singular point.（2）Analogous to the AAH model,we consider a periodic plasmonic structure consisting of metal-dielectric-metal（MDM）stub resonators side-coupled to an MDM waveguide.AAH systems are the one-dimensional momentum-space projection of two-dimensional integer quantum Hall systems and exhibit nontrivial topological properties.The optical properties of the structure are analyzed by the transport matrix method and the mode coupling method,and numerical simulations are performed by FDFD.By filling the side-coupled MDM resonant cavity with GST phase-change material,the dynamic switching between the left and right topological edge states at the same frequency and in the same structure can be realized when GST is switched between its amorphous and crystalline phases.