Research On Non-volatile And All-optical Modulation Of Silicon Microring Based On Phase Change Materials

Due to its compact size and excellent optical characteristics,microring resonators have become one of the essential components in the field of silicon photonics.Tunable silicon microrings based on thermo-optic effect and plasma dispersion effect have been widely used in optical switches,optical modulators,optical signal processing and other fields;The use of new materials such as graphene and black phosphorus to achieve microring tuning has also aroused extensive research interests.Recently,phase change materials have gradually emerged in the field of integrated optics.In different phase states,phase change materials have significant differences in complex refractive index;Different phase states can be switched rapidly,reversible and repeatable under the trigger of electric signal or optical signal;Meanwhile,its phase transition is"non-volatile",i.e.,it does not need continuous energy input to maintain the change in refractive index.This thesis proposes to hybridly integrate Ge₂Sb₂Te₅（GST）,a typical phase change material,onto a silicon-based microring to realize a non-volatile and all-optical modulation structure.The phase state of GST is switched by optical pulses,which indirectly leads to the resonance tuning of the microring.The main contents are as follows:（1）The development of silicon photonics and silicon-based microring resonators,especially the research status and important applications of active tuning microrings are introduced.The application history of phase change materials in integrated optics is reviewed.The latest research results of on-chip modulation assisted by phase change materials are introduced in detail.（2）The working principle of microring and the material properties of GST are discussed and summarized.The feasibility of integrating GST film onto silicon-based microring to realize non-volatile and all-optical modulation is analyzed.Based on the simulation results,the size parameters of Si-GST microring are designed and optimized on the 220nm SOI platform.（3）The device is fabricated through a series of CMOS compatible steps.The effects of different protective layer materials such as indium tin oxide and silicon dioxide on the film forming of GST are compared;The problem of difficulty in lift-off after material deposition was solved through process optimization.Finally,the GST film with precise size and low roughness is deposited on the specific area of the microring.（4）Bidirectional pump-probe experimental setup is designed to observe and verify the static spectral-domain response and dynamic time-domain response of the non-volatile and all-optical modulation process.Based on the Si-GST microring structure,a modulation depth of 14d B is achieved and 8 independent modulation levels are obtained in the"quasi-continuous"tuning process.The response time of the device is below 14μs.Furthermore,the effect of effective width of GST on modulation depth and modulation levels is discussed.The natural non-volatile nature of GST allows Si-GST microring to significantly reduce energy consumption in applications such as optical switches and on-chip optical storage.The on-chip optical pumping method avoids the use of large-size electrodes or off-chip bulky focusing systems,potentially improving device integration.