Research On Surface Phonon Polariton Coupling Structure For Enhancing Graphene Infrared Absorption

As collective oscillations of phonons in a polar dielectric under an external electromagnetic wave illumination,surface phonon polaritons have many advantages that surface plasmons do not have,such as low loss,subwavelength structure and adjustable spectral response range,and have great application potential in graphene infrared detection technology.In this paper,different structures of enhanced optical absorption or switchable absorption are designed for mid-infrared（8～14μm）graphene detector.These absorption structures utilize grating to excite surface phonon polaritons,and couples the energy into the graphene and to enhance the graphene absorbance.Based on the design of infrared absorption structures,their absorption characteristics and other optical properties are studied by simulating in Finite Difference Time Domain method.The main contents are as follows:1.Starting from the surface phonon polariton theory,the principle and conditions of surface phonon polariton generation are described,and a mid-infrared absorption structure that utilizes surface phonon polariton coupling to increase graphene absorbance is designed.The structure is composed of Si C/Al N/Graphene/BN/Grating stacked structure.Under the external light field illumination,the metal grating provides additional wave vectors so that the incident wave meets the wave vector matching conditions.Surface phonon polaritons are excited in the Si C/Al N layer,and surface waves propagate along the Si C/Al N interface,coupling energy into graphene to enhance the absorbance of graphene in the infrared spectrum,and the absorption peak of the graphene atλ=10.58μm is significantly enhanced（35.7%）.2.Based on this,the structure parameters of the infrared absorber are optimized,and the origin of the absorption peak is analyzed and explained.By optimizing the grating period and metal width,we found that when the grating period is p=10μm,the single-period metal width w=5.7μm,and aluminum nitride thickness d_{Al N}=20 nm,the absorption peak at a wavelength ofλ=10.6μm is the strongest.The designed device has an absorbance of 100%and the graphene layer has an absorbance of 43.6%.In addition,the article explores and analyzes the effect of changes in device structure parameters on graphene absorbance.3.A tunable mid-infrared absorber structure based on surface phonon polariton is proposed.This structure utilizes the material properties of graphene and the temperature phase transition characteristics of vanadium dioxide thin films,with reasonable grating design,realizes the coupling of surface phonon polaritons and increases graphene absorbance and the infrared absorption of the device can be controlled by adjusting the temperature.The simulation results show that at 54℃～59℃,the absorbance of the absorber reaches 100%,and the graphene absorbance decreases with the temperature from40%corresponding to 54℃to 33%corresponding to 59℃.As the temperature continues to rise,the infrared absorbance of the absorber drops to 98%and 83%at 60 and 68℃,respectively,while the infrared absorbance of graphene decreases to 25%and 3%at 60℃and 68℃,respectively.At the same time,it is also found that the red shift of the absorption peak can be achieved by increasing the temperature.When the vanadium dioxide phase transition temperature of 68℃was reached,the infrared absorbance of graphene dropped to 3%or less,which achieved the purpose of temperature-controlled graphene infrared absorption.