| Metasurface devices can control the polarization,phase,amplitude and intensity of light,so they have wide applications,such as: 100% absorption of light,phase adjustment of scattered light,polarization direction control,light focusing,holographic imaging and so on.In the field of surface enhanced infrared absorption,because the infrared absorption is proportional to the square of electric field,it is necessary to use metasurface to achieve strong field enhancement.In the field of refractive index sensors,it is necessary to design a sensor with high quality factor,which requires that the half-width of the absorption peak is minimal,so it is necessary to use metasurface to produce devices with smaller half-width and using plasmon.In the past,the structure of the grating is always fixed.If we want to change the direction of light transmission,we need to manually or rotate the grating.However,the combination of metasurface and graphene can adjust the direction of light transmission.So in this article,it mainly involves three aspects:(1)The development of surface-enhanced infrared absorption is limited in two aspects.One is the field enhancement factor.One is that the bandwidth of the resonance wavelength of the metal resonator is small.In view of this,a new structure combining crescent resonator with graphene is proposed.The structure of the crescent resonator is similar to that of the open-loop resonator,but it has a high field enhancement factor.The effect of graphene on the field enhancement of the crescent resonator is systematically studied.Furthermore,the interaction between the crescent resonator and the propagating plasmons in graphene has been found.The interference of plasmon waves leads to a larger field enhancement factor in the crescent gap,and it is found that there is field enhancement on the whole surface of graphene,which is different from the properties of metal plasmons in the past.(2)The plasmon gap mode of metal-insulator-metal(MIM)structure is promising for realizing refractive index sensors.This is mainly because it has nearly 100% absorption.However,the sensing performance of gap mode is limited by its wide resonance bandwidth,which corresponds to a larger energy loss.In view of this,a square array based on MIM structure is proposed to excite surface plasmon and Rayleigh anomaly simultaneously.Moreover,it is proved that they have excellent sensing performance.For Rayleigh anomaly,the sensitivity is 1470 nm/RIU and the FWHM is 0.23 nanometer.Its quality factor is 6400(calculated according to wavelength shift)or 58000(calculated according to intensity change).These two Wood anomalies have opposite angle-dependent characteristics.This can be explained by the opposite direction of surface wave propagation.(3)In the past decades,graphene plasmon has attracted much attention because of its low energy loss and adjustable resonance wavelength.However,the interaction between graphene and incident light is weak,which is due to the lower carrier density of graphene and the small thickness of graphene.This seriously limits the practical application of graphene plasmon.In the infrared wavelength range,graphene can be used as an adjustable material to adjust the resonance wavelength and loss of metal plasmon.This has been successfully applied to adjust the intensity and phase of light.In view of this,an adjustable grating is proposed.This grating is a square grating composed of several phase bits.Each phase bit includes a metal ring resonator and graphene and a metal reflector and electrode.By adjusting the voltage to change the phase of the reflected light,the phase difference is 0 or pi.This large phase adjustment occurs because of the interaction between graphene and metal plasmon.By changing the phase of the reflected light at different positions,the direction of light propagation can be adjusted.This is the principle of adjustable grating. |
