Polarization-based Metalenses with High Numerical Aperture and Focusing Efficiency Utilizing Silicon-rich Nitride

We explore the cutting-edge application of silicon-rich nitride (SRN) in the realm of high numerical aperture (NA) metalens design, focusing on the crucial role of pitch size optimization in amplifying lens efficiency through advanced simulations. Our investigation unveils how the exceptional tunable high refractive index of SRN can be harnessed to achieve significant advancements in metalens performance. By meticulously designing and simulating two innovative SRN-based metalenses - Mk1, with an NA of 0.9, reaching an impressive 75% focusing efficiency with full width at half maximum (FWHM) of 0.53{\lambda}, and Mk2, with an NA of 0.99, achieving a 42% efficiency while maintaining an FWHM of 0.48{\lambda}. We demonstrate the critical influence of reduced pitch size on enhancing efficiency. This study not only highlights the unparalleled potential of SRN in optimizing metalens efficiency but also represents a significant leap forward in the field of nanophotonics, offering new pathways for the development of highly efficient flat photonic devices.