| Mid-infrared(MIR)contains two atmospheric transmission windows,which is also the intrinsic vibration absorption frequency band of most materials in nature.It has numerous applications in medical,military,industrial and other fields.The optical metasurface based on the MIR has the advantages of good process compatibility,high freedom of control,and simple preparation process.The metasurface is composed of artificially arranged sub-wavelength unit structures.It has excellent electromagnetic wave manipulation capabilities.Among them,the dielectric metasurface is more conducive to practical applications due to its simple structure,easy integration,and low loss.Infrared photoelectric detection based on two-dimensional materials has received great attention due to physical properties of atomic-level thickness,high carrier mobility and easy integration.However,two-dimensional materials also limit the absorption of light to a certain extent for their inherent atomic-level thin layer thickness.With the help that electromagnetic parameters of the metasurface are arbitrarily adjustable,the power flux can be concentrated to the reduced photosensitive area,which can effectively improve the absorption of photosensitive area.And it is beneficial to improve the performance of the photodetector.The main research work of this paper is as follows:1.Using the rectangular silicon waveguide structure,change the length of the silicon waveguide to control the phase,and an all-dielectric phase gradient metasurface working in the MIR is designed.Under Generalized Snell's Law,change the geometric parameters of the rectangular silicon waveguide,and the abnormal reflection of the light beam is realized at the incident wavelength of 3.6 ?m.It has been verified that this structure can achieve a good deflection effect whether the electromagnetic wave is incident perpendicularly or obliquely.In addition,by optimizing the sizes of unit structures,a metasurface which can couple vertically incident electromagnetic waves into surface waves propagating along the surface of the structure is designed.2.On the basis of the above structural design,the structure is further optimized as a three-dimensional ring structure.When x polarized light with a wavelength of 3.6?m is incident perpendicularly,due to the opposite phase gradient,the designed phase-gradient metasurface structure can generate two rows of surface waves propagating in opposite directions and achieve enhanced electric field intensity in the center of the structure.Subsequently,the influence of incident light with different polarization directions on the electric field intensity distribution is studied.The electric field intensity under different number of ring periods is also characterized and compared numerically.3.The thin layer of black phosphorus is integrated with the designed ring phase gradient supersurface.The simulation results prove that the phase gradient metasurface improves the absorption of thin layer black phosphorus with the size of 5?m×5 ?m to 3.77% at 3.6 ?m,which is about 20 times larger than that of bare thin layer black phosphorus.Finally,the effect of phase gradient metasurface on different sizes and thickness black phosphorus is also investigated.Thin-layer black phosphors of different sizes are integrated with the phase gradient super-surface,and the light absorption of black phosphors is explored.The best size under high absorption rate is found.Finally,when the black phosphorus side length is a fixed value,it is studied that the influence of the phase gradient metasurface structure on the absorption of black phosphorus with different thicknesses from 10 nm to 100 nm. |
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