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.
InAs nanowires directly integrated on Si platform show great promise in fabricating next generation mid-infrared optoelectronic devices. In this study we demonstrated the growth of catalyst-free, selective-area InAs nanowire arrays on electron beam patterned Si3N4/Si(111) by molecular beam epitaxy. Growth parameters were studied, and nanowire growth kinetics dependence on patterned mask opening diameter and interwire distance was investigated. Under certain growth conditions, nanowire diameter was found to be relatively independent of nanohole diameter and pitch. We also realized the growth of randomly-nucleated, self-assembled nanowires on Si(111) and investigated the temperature, flux influence on nanowire morphology.
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