Fabrication of two-dimensional dimple and conical microlens arrays from a highly periodic toroidal-shaped liquid crystal defect array

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Abstract
A self-assembly fabrication method was developed for the preparation of microlens arrays (MLAs). The procedure used the focal conic structures of semi-fluorinated smectic liquid crystals (LCs), the periodic toric focal conic domains (TFCDs), which were prepared on a surface-modified substrate. This LC-based MLA system focuses light via the intrinsic molecular orientations of the TFCDs, leading to a highly efficient MLA with good optical properties. The thickness of the smectic LC film could be used to control both the microlens feature size, over the range 5–15 μm, and the microlens focal length, over the range 1–3 μm. In addition, we prepared two-dimensional hexagonally packed polymer MLAs with conical or dimple shapes by successive replica molding, using a UV-curable photopolymer (NOA63) and polydimethylsiloxane (PDMS), from a TFCD array template containing a dimple structure. The LC-based TFCD MLAs and the secondary replicated polymer MLAs, using NOA63 and PDMS molds, showed good lens performances. We anticipate that this LC self-assembly method will be applicable to the large-scale fabrication of MLAs. The method allows fabrication of dynamic MLAs that are responsive to external fields, such as electric or magnetic fields, or to thermal variations.

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