Study On Simultaneous Anomalous Dispersion And Topological Propagation For Both Acoustic Waves And Light In Phoxonic Crystals

Artificial microstructural materials have attracted significant attention due to their unique physical structures and extraordinary acousto-opto-thermo-electrical properties,showing broad application prospects in various scientific and engineering technology fields.Artificial microstructural materials possess precise geometric structures and dimensions comparable to the operating wavelengths,allowing them to exhibit acousto-optic response characteristics that conventional materials lack.Artificial microstructural materials are commonly used for controlling the transmission of electromagnetic and elastic waves,including various types such as phononic crystals,photonic crystals,and phoxonic crystals.In recent years,simultaneous manipulation of light and sound at the micro-nano scale has become a hot topic,aiming to achieve integrated opto-acoustic control and enhance opto-acoustic(mechanical)coupling.Traditional approaches have focused on forming a dual bandgap for both sound and light within the same phoxonic crystal,while the special band structure can provide unconventional and efficient control of opto-acoustic phenomena through anomalous dispersion.Meanwhile,backscattering and losses induced by fabrication errors are significant challenges that affect the practical application of phoxonic crystals,and topology can solve these inherent issues in physical principle.In this thesis,the finite element numerical simulation method is employed to establish appropriate couplings among optical properties,structural parameters,and acoustic properties.On one hand,this thesis investigates the realization of simultaneous control of light and sound through anomalous dispersion.On the other hand,the topological concept is introduced into phoxonic crystals,providing new ideas and methods for constructing compact,low-loss,and multifunctional acoustic-optic integrated systems and enhancing acoustic-optic coupling.The main research contents and results include:(i)A proper coupling of optical equal-frequency contours,structural parameters and acoustic equal-frequency contours is constructed by achieving a suitable phononic and phononic band in a two-dimensional triangular photonic crystal.Then the simultaneous self-collimation and negative refraction effects of sound and light are achieved in the two-dimensional phoxonic crystal.Starting from the phoxonic bands,the band structures of the triangular lattice phoxonic crystal are calculated.The phononic and photonic dispersion surfaces and equal-frequency contours are analyzed.By investigating the relationship between the equal-frequency contours and the group velocity,the physical mechanism of simultaneous self-collimation and negative refraction of sound and light with anomalous dispersion is explored.The field distribution of transverse electric mode,transverse magnetic mode and sound wave with simultaneous self-collimation and negative refraction is simulated.The corresponding relationships between the incident angle and the refracted angle of phoxonic negative refraction are studied.Furthermore,the relationship between the maximum angle of phoxonic negative refraction and the equal-frequency contours is discussed.The characteristics of simultaneous large-angle negative refraction of sound and light are analyzed.The simultaneous transmission of sound and light with negative refraction and subwavelength imaging characteristics in the same microstructure are achieved.(ii)Based on a two-dimensional valley phoxonic crystal with a trifoil unit cell,an appropriate coupling between optical topology,structural parameters,and acoustic topology is established.By breaking the mirror symmetry through rotating trifoil-shaped scatterers while maintaining time-reversal symmetry,the synchronous opening and closing of phononic and photonic Dirac points at the K point of the Brillouin zone are achieved.This leads to band inversion and valley-Hall phase transition for both phononic and photonic modes.The phoxonic topological edge states formed by assembling phoxonic crystals with different topological properties demonstrate low losses even at sharp bends,strong immunity to backscattering,and robustness against various defects when both sound and light are guided in the valley phoxonic crystal waveguide.To address the issue of limited width in the valley phoxonic waveguide,trivial phoxonic crystals and nontrivial phoxonic crystals are placed on the outer sides,with a certain thickness of phoxonic crystal containing Dirac points is inserted in the middle.This results in a tunable-width valley phoxonic crystal waveguide with topological properties.Based on this,the function and robustness of topological phoxonic beam expansion are verified by design and simulation.(iii)Based on a two-dimensional phoxonic crystal with a trident-shaped unit cell,a topological waveguide-cavity coupling system in the valley phoxonic crystal is designed and studied.The robustness of the valley phoxonic crystal waveguide is verified and the coupling characteristics between the waveguide modes and defect states in the valley phoxonic waveguide are explored,and the system achieves simultaneous resonant absorption of sound and light.The moving interface effect and photoelastic effect during the coupling of sound and light in the waveguide-cavity coupling system are computed and analyzed.It is found that the moving interface effect dominates the acousto-optical interaction,while the photoelastic effect leads to a weaker acousto-optical coupling.The importance of single-phonon exchange and double-phonon exchange processes play an important role in the acousto-optical interaction.The corresponding optical frequency modulation is calculated and analyzed.