Design And Performance Analysis Of Infrared Metalens

Metasurface,as a two-dimensional array of sub-wavelength structures,can be used in many applications,such as active tuning,polarization control,and wavefront shaping.It can effectively modulate the beam to achieve specific functions.Among them,the all-dielectric Metalens is a new type of optical device.Compared with other traditional devices,it has the advantages of small size,high performance,and easy processing.The periodic arrangement of nano-structure units has high optical efficiency,and can avoid the multi-order diffraction effectively,which usually appears in traditional optics.At the same time,the Metalens can be compatible with the existing CCD image sensor,which provides a new solution for the device's performance improvement,integration and lightweight development.1.Based on the application requirements of near-infrared band(780-1100nm),the Finite Difference Time Domain algorithm(FDTD)is used as the main simulation method,and the Rigorous Coupled Wave Analysis(RCWA)is used as the auxiliary algorithm to verify the accuracy of the electromagnetic response in the structural unit.The simulation design of the cylindrical structure of high contrast crystalline silicon,low contrast silicon nitride,both of which are based on silica substrate and integrated crystalline silicon were carried out respectively.Through the analysis of the structure size,the three unit structures can meet the requirements of high transmittance and achieve 2 full phase coverage when the maximum aspect ratios are 3.3:1,10.4:1 and 3.75:1.2.According to the optimized design of the structure unit and the compatibility with CCD device,this thesis presents two kinds of design schemes of Metalens,that is,the frontilluminated type and the back-illuminated type.Hyperbolic phase distribution design is adopted in both Metalens.The lens size is 22?m×22?m,and the multi-ring circular arrangement is realized under the rectangular aperture,which effectively increases the utilization rate of light energy.The structural unit of the front-illuminated lens uses the optimized design of crystalline silicon and silicon nitride mentioned before.In compatible with the CCD,the equivalent fill factor in the working waveband can be increased by approximately 53.1% and 49% in the center of the 7?m×7?m photosensitive area.The design of the back-illuminated metalens uses edge-to-edge equidistant close-layout arrangement,and the nano-pillar and substrate materials are both silicon.The equivalent filling factor in the working band can be increased by an average of approximately 46%.Meanwhile,because it is directly etched on the CCD device substrate,it is easy to vaporize the antireflection coating and there is no joint surface between the devices.The light energy loss is small,which is helpful for the integrated design of the device.