Acousto-optical Localization And Coupling In Phoxonic Crystal

Phoxonic crystal is a periodic artificial material that can manipulate optical and acoustic waves in the same time and spatial domains.Its important feature is the ability to have both phononic and photonic band gaps.It has broad application prospect in optical communication,optical mechanics sensor,quantum computations,phoxonic crystal integrated devices and so on.Two-dimensional phoxonic crystal structures are widely used in research and can be involved in the design of various devices,such as waveguides,sensors,and so on.Therefore,the research of two-dimensional phoxonic crystals has important experimental and application value.In this paper,we have studied the phonon and photon double band gaps of two-dimensional phoxonic crystals,the bulk and surface wave modes of phonons and photons,the design of heterostructure resonators with air-slot,the acousto-optical coupling in resonators,and two-dimensional phoxonic crystal sensors.This paper starts with an introduction to the theoretical basis and introduces the basic theory of the interaction between sound and light in phoxonic crystals.Then,the electromagnetic and elastic wave equations are introduced,as well as the specific methods for calculating the energy bands of sound and light.In the relevant calculations,we adopted relevant software based on finite element method(FEM)for research.In this paper,we adopt a silicon-based two-dimensional square lattice structure,which can exhibit wide band gap of phonons and photons simultaneously.Then a periodic rectangular structure was introduced on the surface,and the effects of the width and height of the rectangle on the optical and acoustic surface wave modes were analyzed.Based on the mode gap effect,a surface heterostructure composed of rectangles with different heights and widths is constructed.Then,two identical surface heterostructures are placed face to face with an air slot in the middle,and connected with silicon substrate on both sides,which form an air slot heterostructure cavity.Multiple phonon cavity modes and photon cavity modes are obtained,the coupling rates between acoustic and optical modes in the structure are calculated.The results show that the acousto-optical coupling ratio between acoustic cavity mode and optical cavity mode with the same symmetry and maximum overlap is the largest.Finally,we designed a phoxonic crystal liquid sensor based on the previously studied two-dimensional phoxonic crystal structure.Different liquids are added to the air slots and holes of the heterostructure resonator to calculate the sound velocity and refractive index of the liquid,such as sodium chloride solution,glucose solution,and 1-propanol mixture solution.The results indicate that in solutions of different concentrations,the wavelength(frequency)of the optical(acoustic)cavity mode also linearly increases with the increase of the liquid refractive index(velocity).Because the velocity of sound and refractive index in a solution are related to the concentration of the solution,this structure can be used to make phoxonic crystal liquid sensors.From the simulated data,both the optical cavity sensitivity(up to 1047.5 nm/RIU)and the acoustic cavity sensitivity(up to 3370.69 k Hz/m)have very high values.