Principles And Realization Of Fast Response Optical Modulation Based On Phase Transformation Of Vanadium Oxide

Optical modulators are an important devices in all-optical interconnection and integrated optics.In recent years,they have become a research hotspot in the field of micro-nano optics.The optical modulators based on planar integration technology have the advantages of low cost,compact structure and high integration.However,there are still many problems to be solved,such as power consumption,modulation speed,extinction ratio and so on.Phase change materials（PCM）can produce significant changes in electromagnetic properties under specific conditions,which can be used in the design of light modulators.Among them,phase change VO₂is a particularly attractive candidate for light modulator.The semiconductor-metal reversible transition occurs near 67°C,accompanied by a structural change from monoclinic to tetragonal structure.The resistivity and refractive index parameters of VO₂change significantly.Importantly,phase transitions in VO₂can be triggered by multiple excitation methods in addition to thermal excitations,including strain,electric field,or optical excitations.The optical response of the devices can be effectively adjusted without changing the physical structure.The work of this thesis mainly includes the following aspects:（1）Using VO₂nanowire to achieve low power consumption and fast response on-chip light modulator.The VO₂nanowires are transferred to the bottom of the straight waveguide.The VO₂nanowires are connected to electrodes on both sides.Voltage is applied to heat the VO₂to change the dielectric environment of the straight waveguide and regulate the coupling between the straight waveguide and the resonator,so as to realize the modulation of the transmission spectrum of the coupled system.Due to the small size of VO₂nanowires,low power consumption required for phase transformation and fast heating,low power consumption and fast response of on-chip light modulator can be realized.（2）Low power consumption ultra-fast optical modulation is realized by using plasmonic thermal electron injection to accelerate VO₂phase transition.A hybrid structure of VO₂thin film,Au gratings and Si O₂substrate was designed,and the grating period was appropriately selected to excite local surface plasmon resonance（LSPR）on Au gratings.When VO₂is in the semiconductor phase,LSPR can also be formed between Au grating and VO₂film.When the excitation light is at this resonant wavelength,plasmonic thermal electrons on Au surface can be transferred to the conduction band of VO₂,which changes the electron density of VO₂and induces the phase transition of VO₂.The mechanism can be applied to the on-chip all-optical VO₂modulator because of the high speed and low threshold of the VO₂phase transition induced by thermo-electron ion implantation.