Design And Machining Error Analysis Of The Mid-infrared Metasurface Imaging Lens

With the development of technology and the progress of nanotechnology,optical devices are gradually becoming miniaturized,compact,lightweight and multifunctional.It is difficult for traditional optical devices to fulfill these requirements,but metasurface can realize the flexible and effective regulation of electromagnetic wave polarization,amplitude,phase,propagation mode and other characteristics,and it is small in size,high degree of freedom and rich in functions,which brings the dawn for the development of new optical devices.However,most of the research on metasurface is focused on visible or near infrared band,while the research on mid-infrared metasurface is very few.This is mainly due to the fact that most substrates have a limited high refractive index layer in the mid-infrared band and become opaque when the wavelength exceeds 3μm.However,compared with visible metasurface,midinfrared metasurface requires lower manufacturing accuracy,and has special roles in spectral analysis,biomedicine,military and industrial fields.However,the high quality manufacturing of nanoscale devices is still a challenge.Manufacturing defects can affect the performance of nano-devices.The current manufacturing methods of metasurface more or less introduce machining errors,and it is necessary to analyze and control these errors.This paper mainly focuses on the research status of mid-infrared metasurface as follows:(1)We designed a mid-infrared full dielectric metalens based on transmission phase.The 3D electromagnetic field simulation software(CST)is used for the simulation and optimization design of a single unit,and the regulation of the optical local wavefront by a single unit is obtained.By studying the phase distribution mechanism of the transmission metalens,the polarization-insensitive and efficient whole silicon metalens working at 3.77μm is designed.Then the metalens was processed by lithography,we used multiple methods to characterize the performance of the metalens sample,and tested its optical performance by integrating it with the camera.(2)Error analysis of metalens processing methods.We conducted processing and application-oriented studies through different processing methods and present three typical errors,including random topology defects,inclined sidewall defects,CD bias defects.The typical errors are introduced into the standard metalens and simulated by the time-domain finite difference software(FDTD).We used focal efficiency,half-height and full width(FWHM),focal length,and modulated transfer function(MTF)to characterize the imaging and focusing capabilities of metalenses to qualitatively analyze the impact of these typical errors on metalens performance,while providing potential solutions to mitigate the impact of processing defects.