Construct Achromatic Polymer Microlens For High-Transmission Full-Color Imaging

Traditional microlens focuses the beam with spherical convex surface, which achieves high transmission by restraining the scattering loss yet brings spherical aberration and chromatic aberration. While recently-developed metalens, which relies on phase modulation by elaborately designing local resonators, has realized diffraction-limited focusing. Yet, the issues of scattering loss of nanoresonators and chromatic aberration remain serious. Here, the design strategies of both metalens and traditional microlens are combined by introducing accurate phase modulation for the wavefront into microlens designing; and a broadband, polarization-independent, and achromatic microlens with high efficiency is realized. With concentric-circular polymer (phenolic resin) terrace as basic building blocks, a precise thickness profile is constructed and a high-index polymer microlens is formed by electron-beam grayscale lithography. The diffraction-limited focusing possesses less than 5% change of focal length when the wavelength varies from 425 to 700 nm, showing the full-color imaging and detection with a focusing efficiency of 80% (at 700 nm wavelength). Moreover, the rotation symmetry of the microstructures of microlens makes it work for arbitrary polarization. The achromatic imaging capability of the microlens is verified by whitelight imaging. It is expected that this high-efficiency polarization-independent broadband achromatic polymer microlens may have wide applications in high-efficient imaging and sensing.