Continuous achromatic flat subwavelength grating lens over whole visible bandwidths

One of the major challenges for emerging planar subwavelength micro lens/metasurfaces is the significant chromatic behavior due to phase mismatch of subwavelength phase shifters. In this work, the continuous achromatic micro lens covering the whole visible wavelength is demonstrated for the first time based on relatively low index contrast gratings. Based on the unique chromatic phase shift behavior of polymer nano structure, we have designed and fabricated a broadband continuous subwavelength achromatic microlens that can cover 250 nm of visible bandwidths (from 435 nm to 685 nm) with focal shift less than 5%. Our works represent the first time to design, fabricate and characterize micro scale lens (7 microns in size) promising for compact integrated nanophotonic devices on chip. There are many advantages of using a polymer based micro lens such as easy fabrication on flexible substrate and potential applications including imaging, spectroscopy, lithography, laser fabrication and future integrated wearable devices.