Researchers have developed subwavelength-thick, polarization-insensitive micro-lenses with high numerical apertures and large focusing efficiencies using high contrast transmitarrays (HCTAs). These lenses operate at telecom wavelengths and achieve focal spots as small as 0.57 wavelengths with a focusing efficiency of up to 82%. The lenses are fabricated using silicon nano-posts on glass, enabling high-throughput photo or nanoimprint lithography for widespread adoption. HCTAs are composed of high index dielectric scatterers on a periodic sub-wavelength 2D lattice, allowing for precise control of optical phase fronts. The design enables the creation of diffractive elements with rapidly varying phase profiles, leading to high performance in imaging and on-chip optoelectronic integration. The lenses are designed to focus light from a single mode fiber to points at varying distances, with a focusing distance ranging from 50 to 500 micrometers. The performance of the lenses was evaluated using 3D finite difference time domain (FDTD) simulations, which showed that the lenses can focus light to a focal spot size of 0.57 wavelengths with a focusing efficiency of up to 82%. The lenses were fabricated using a hydrogenated amorphous silicon film on a fused silica substrate, and their performance was verified through experimental measurements. The study demonstrates the potential of HCTAs for creating flat, high NA micro-lenses with exceptional performance, enabling the development of on-chip optical systems. The results show that HCTAs can achieve the best performance among any types of flat high NA micro-lenses experimentally reported so far, with a focusing efficiency of up to 82% and a focal spot size down to 0.57 wavelengths. The structures are suitable for integration into optical systems due to their planar form factor and compatibility with wafer-scale processing.Researchers have developed subwavelength-thick, polarization-insensitive micro-lenses with high numerical apertures and large focusing efficiencies using high contrast transmitarrays (HCTAs). These lenses operate at telecom wavelengths and achieve focal spots as small as 0.57 wavelengths with a focusing efficiency of up to 82%. The lenses are fabricated using silicon nano-posts on glass, enabling high-throughput photo or nanoimprint lithography for widespread adoption. HCTAs are composed of high index dielectric scatterers on a periodic sub-wavelength 2D lattice, allowing for precise control of optical phase fronts. The design enables the creation of diffractive elements with rapidly varying phase profiles, leading to high performance in imaging and on-chip optoelectronic integration. The lenses are designed to focus light from a single mode fiber to points at varying distances, with a focusing distance ranging from 50 to 500 micrometers. The performance of the lenses was evaluated using 3D finite difference time domain (FDTD) simulations, which showed that the lenses can focus light to a focal spot size of 0.57 wavelengths with a focusing efficiency of up to 82%. The lenses were fabricated using a hydrogenated amorphous silicon film on a fused silica substrate, and their performance was verified through experimental measurements. The study demonstrates the potential of HCTAs for creating flat, high NA micro-lenses with exceptional performance, enabling the development of on-chip optical systems. The results show that HCTAs can achieve the best performance among any types of flat high NA micro-lenses experimentally reported so far, with a focusing efficiency of up to 82% and a focal spot size down to 0.57 wavelengths. The structures are suitable for integration into optical systems due to their planar form factor and compatibility with wafer-scale processing.