Simple aberration elimination on a long-wave infrared metasurface by the germanium lens

While achieving multifunctional integration of light wave phase, polarization, focusing, filtering, and more, metasurfaces often encounter challenges in ensuring optical imaging quality, including optical distortions like aberrations. This paper addresses the significant aberration challenges in far-field imaging of long-wave infrared metasurfaces by proposing the use of an infrared germanium lens point spread function (PSF) to optimize aberration phenomena in metasurface imaging. This study also demonstrated that the phase distribution of the metasurface unit cells achieved a complete coverage of 0-2<i>π</i>, thereby validating the precise phase modulation capability of the designed metasurface. We demonstrated that the modulation transfer function curves obtained via the point light source method and the blade edge method were highly consistent, confirming the reliability and accuracy of our PSF far-field measurement technique. Additionally, we showed that introducing the prior noise factor during the deconvolution process yields improved results, highlighting its necessity in computational methods. By comparing the threshold filtering method and Richardson-Lucy iterative method with the aberration elimination method, our method showed its superior performance. Specifically, by our proposed aberration correction method, structural similarity index (SSIM) increased by 0.07, peak signal-to-noise ratio (PSNR) decreased by 0.96 dB, root mean square error (RMSE) decreased by 0.05, and edge-preserving index (EPI) reached 0.8943. Moreover, the main reason for the decline of PSNR is that the aberration of long-wave infrared metasurface imaging is also included in the PSNR calculation. Furthermore, we also proved the feasibility of the aberration elimination method in this paper at the wavelength of 8-12 µm by experiments; the PSNR increased by 4.61 dB, the SSIM increased by 0.7549, the RMSE decreased by 0.1644, and the EPI remained at 0.8178 after aberration correction. This paper presents a breakthrough in metasurface imaging by using the PSF of a germanium lens to correct aberrations, enhancing imaging quality and versatility. It also simplifies the optical structure, making it more compact and lightweight, thus improving its practical applicability in real-world systems.