Research On Simultaneous Topological Pseudospin-dependent Transmissions Of Light And Acoustic Based On Dielectric Phoxonic Crystals

With the development of fabrication technology extending to the nanoscale and the realization of more precise microstructures,much attention has been paid to the simultaneous manipulation of light and sound in the same microstructure.Periodic microstructures combining photonic and phononic band gaps can achieve this manipulation,which is also known as phoxonic crystals.Since light and sound can be manipulated simultaneously at the wavelength or subwavelength scale,phoxonic crystals can integrate the control of light and sound at the micro-nano scale.At the same time,the wide application of topology in condensed matter physics has led to some interesting topological effects,such as the quantum Hall effect,the quantum spin Hall effect,and the quantum valley Hall effect.One of the most impressive features is the domain wall between two materials with different topological indices supporting edge states that show robustness to the backscattering.Due to this unique characteristics,topology has attracted widespread attention and is soon expanded to other classical fields from the quantum field,providing a new degree of freedom to control light and sound in respective artificial structures.However,the study in topological transport of sound and light is independently of each other.Recently,more and more attention has been paid to the acousto-optic synchronous topological transmission.Introducing the concept of topology into phoxonic crystals and realizing the acousto-optic synchronization topological transmission can provide a strong guarantee for the construction of compact,low-loss and multi-functional acousto-optic integration.By using an external magnetic field to break the time-reversal symmetry,the acousto-optic dual topological states can be achieved,however,the harsh external conditions limit the practical application.Based on the quantum spin Hall effect,this thesis,for the first time,proposed dual topologically protected edge states and waveguide states to achieve acousto-optic synchronization topological transmission in two-dimensional phoxonic crystals without external conditions.The main research contents of this thesis are:(1)Topological pseudospin-dependent edge states are designed to realize acousti-optic synchronization topological transmission in two-dimensional honeycomb lattice phoxonic crystals.The phoxonic crystal consists of regular triangular silicon pillars arranged in the air to form a honeycomb lattice unit cell.By shrinking and expanding honeycomb unit cells and changing the rotation angle of the triangle,the mechanism of the band inversion in the photon and the phonon modes are respectively explored.And the supercell formed by two different topological phases is established to calculate the projection bands,and the topological phoxonic pseudospin-dependent edge states can be clearly seen in the bulk bandgap.Then,we construct a waveguide structure to verify the unidirectional transmission characteristics of the acousto-optic pseudospin states and the robustness of the topological waveguide to defects,disorder and Z-shaped bends.The light and sound of transmission spectra corresponding to straight waveguides,defects,disorder,and Z-shaped bends are calculated near the corresponding frequency range of the topological pseudospin states,showing the high transmittance and the robustness of the acousto-optic pseudospin-dependent states.Finally,a cross-waveguide beam splitter is designed,and pseudospin-dependent edge states with different spin directions have different propagation behaviors in the cross-waveguide.The transmission spectrum of each port under the cross-waveguide beam splitter is calculated,and the unidirectional transmission characteristics of the acousto-optic topological pseudospin-dependent edge states are further verified.(2)Topological pseudospin-dependent waveguide states are realized based on the same dielectric photonic crystal showed above.We construct acousto-optic topological pseudospin-dependent waveguides by inserting a phoxonic crystal with double Dirac cones into the original interface formed by the topologically trivial and topologically non-trivial phoxonic crystals.To verify the existence of pseudospin-dependent waveguide states,projected band structure is calculated.Acousto-optic synchronization transmission is performed at different layers,and a topological waveguide beam splitter is further designed to verify the unidirectional transmission properties and robustness to defects.Finally,a topological concentrator is designed,showing the ability to achieve the acousto-optic synchronous convergence or aggregation,on the basis of topological pseudospin-dependent waveguide.