Research On Simultaneous Self-Collimation Effect Of Light And Acoustic Waves In Phoxonic Crystals

It has become a new research hotspot to control simultaneously optical and acoustic waves at the micro and nano scale,realizing the integrated control of optical and acoustic waves as well as enhancing the acousto-optic coupling.The current methods mainly focus on constructing the coexistence of photonic and phononic band gaps in a same micro or nano structure.From another point of view,a special band structure can form abnormal dispersion,thereby realizing another kind of efficient modification way for simultaneously controlling optical and acoustic waves,which is different to the methods based on phoxonic bandgaps.Self-collimation effect is an anomalous dispersion phenomenon in the passband,which is characterized by the fact that electromagnetic(EM)wave or acoustic wave(elastic wave)can propagate straightly in a certain direction without diffraction.As an anomalous dispersion phenomenon,self-collimation originating from flat equal-frequency contours(EFCs)has been intensively investigated,which enable EM or acoustic waves propagate along a certain direction without diffraction in defect-free structures.Therefore,narrow lateral confinement for propagating fields can be formed via self-collimation-based waveguides(SCWs)requiring neither bandgaps nor line defects.Furthermore,the defect-free waveguide does not require precise alignment to couple an incident wave into the narrow waveguides.Hence,SCWs offers much advantages over BGW.Although researchers focused on investigating the SCWs for EM waves in photonic crystals(PtCs)and acoustic waves in phononic crystals(PnCs),respectively,few studies have focused on dual photonic and phononic waveguides based on selfcollimation effect.Obviously,the exploration of this integrated phoxonic manipulation method can not only overcome the inherent defects of bandgap-based application,but also greatly expand the application range of phoxonic crystals(PXCs),which is an indispensable part of the research and application of phoxonic crystals.Therefore,it is very necessary and beneficial.In this paper,we firstly propose the concept of phoxonic self-collimating effect,which means the EM waves and acoustic waves(elastic waves)can be simultaneously manipulated using the self-collimation effect in PXCs.And the finite element method is employed.The main contents include:Firstly,we have realized the simultaneous phoxonic virtual waveguides in the twodimensional defect-free PXCs by using self-collimation effect.The study shows that dual photonic and phononic waveguides based on self-collimation effect can be realizing in special PXCs.Besides,the phenomenon still can be achieved even if under the condition such as low refractive index ratio and low filling ratio.The tolerance of incident angles with a range is practicable,which helps to efficiently and simultaneously guide EM and acoustic waves in PXCs.By designing special constructure,the propagation path of EM and acoustic waves can be simultaneously bended,thus the propagation path can be easily manipulated.Secondly,we verify the phoxonic self-collimation effect in the PXCs slab.The research shows that dual photonic and phononic self-collimation waveguides can also be realized in the PXCs slab.Thirdly,we have verified the self-collimation effect of the out-of-plane elastic transverse wave(SH wave)in two-dimensional phononic crystals.By designing special constructure,the propagation path of EM and acoustic waves can also be manipulated.The results of this paper not only provide a new idea for simultaneously manipulate sound and light,but also overcome the inherent defect of that based on bandgaps.It provides a new platform for the design of integrated acousto-optic devices,acousto-optic modulation and highly controllable acousto-optic interaction.