High Numerical Aperture Hexagonal Stacked Ring-Based Bidirectional Flexible Polymer Microlens Array Rajib Ahmed Ali K. Yetisen Haider Butt 10.1021/acsnano.7b00211.s001 https://acs.figshare.com/articles/journal_contribution/High_Numerical_Aperture_Hexagonal_Stacked_Ring-Based_Bidirectional_Flexible_Polymer_Microlens_Array/4718917 Flexible imprinted photonic nanostructures that are able to diffract/focus narrow-band light have potential applications in optical lenses, filters, tunable lasers, displays, and biosensing. Nanophotonic structures through holography and roll-to-roll printing may reduce fabrication complexities and expenses and enable mass production. Here, 3D photonic nanostructures of a stacked ring array were imprinted on acrylate polymer (AP) over poly­(ethylene terephthalate) (PET) substrate through holography and lift-off processes to create a microlens array (MLA). The surface structure of the array consisted of circular nonostepped pyramids, and repeated patterns were in hexagonal arrangements. Stacked-ring-based MLA (SMLA) on a flexible AP–PET substrate showed efficient bidirectional light focusing and maximum numerical aperture (NA = 0.60) with a reasonable filling factor. The nanostructures produced a well-ordered hexagonally focused diffraction pattern in the far field, and power intensities were measured through angle-resolved experiments. The variation of nanostep dimensions (width and height) and the number of steps resulted in different photonic bandgaps, and the arrays produced distance-dependent narrow-band light focusing. The validation of the SMLA was demonstrated through the text, image, and hologram projection experiments. It is anticipated that imprinted bidirectional SMLA over flexible substrates may find applications in optical systems, displays, and portable sensors. 2017-03-02 19:34:51 microlens array distance-dependent narrow-band light angle-resolved experiments substrate diffraction pattern mass production holography Polymer Microlens Array well-ordered hexagonally Ring-Based Bidirectional power intensities acrylate polymer ring array nonostepped pyramids 3 D photonic nanostructures photonic bandgaps NA hologram projection experiments photonic nanostructures roll-to-roll printing bidirectional SMLA display High Numerical Aperture Hexagonal tunable lasers lift-off processes Nanophotonic structures application bidirectional light AP nanostep dimensions fabrication complexities surface structure Stacked-ring-based MLA