High-NA and high-efficiency polarization-based metalenses with pitch size control utilizing silicon-rich nitride

This study investigates the use of silicon-rich nitride (SRN) for designing high numerical aperture (NA) metalenses, by optimizing pitch size to improve focusing efficiency. Utilizing the tunable refractive index of SRN, we designed and simulated a geometric phase metalens (MK1) with an NA of 0.99 and focusing efficiency of 26.4%, and a propagation phase metalens (MK2) with an NA of 0.93 and efficiency of 37.5%. The full width at half maximum (FWHM) were 0.56λ for MK1 and 0.74λ for MK2 and an aspect ratio of 4:1 (height vs tooth) for both phase types. Our results demonstrate the effectiveness of pitch size optimization in enhancing metalens performance, highlighting SRN's potential for high-efficiency applications at a 685 nm wavelength.