Figure - available from: Advanced Materials Technologies
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Elastomeric MWs. a) Schematic view of the replica molding process of the elastomeric MWs. A template is 3D‐printed (i) and covered with PDMS pre‐polymer (ii), which is then cured. The resulting elastomeric MW (iii) is peeled off from the substrate. b) Target image and c) corresponding image projected by the 3D‐printed MWs. d) Target image with inverted black and white areas with respect to the one shown in (b). Corresponding images projected by the e) 3D‐printed MW and f) PDMS replica, realized starting from (e). Scale bars: 1 cm.
Source publication
Refractive freeform components are becoming increasingly relevant for generating controlled patterns of light, because of their capability to spatially modulate optical signals with high efficiency and low background. However, the use of these devices is still limited by difficulties in manufacturing macroscopic elements with complex, 3D surface re...
Citations
... Controlling the spatial profile of light beams is critically important in various scientific and technological fields, including high resolution microscopy, [1] endoscopy, [2] lithography and additive manufacturing, [3] optical manipulation of micro-objects, [4] wireless communication [5] and computation. [6] Various methods have been reported to this aim, mostly based on diffractive elements and digital holography, which exploit arrays of micromirrors, [7] liquid crystal-based modulators [8] or metasurfaces. [9] While such techniques allow high spatial resolution in modulated beams as well as both static and dynamic light patterns to be generated, they typically need highly complex optical elements. ...
Refractive freeform components are becoming increasingly relevant for generating controlled patterns of light, because of their capability to spatially-modulate optical signals with high efficiency and low background. However, the use of these devices is still limited by difficulties in manufacturing macroscopic elements with complex, 3-dimensional (3D) surface reliefs. Here, 3D-printed and stretchable magic windows generating light patterns by refraction are introduced. The shape and, consequently, the light texture achieved can be changed through controlled device strain. Cryptographic magic windows are demonstrated through exemplary light patterns, including micro-QR-codes, that are correctly projected and recognized upon strain gating while remaining cryptic for as-produced devices. The light pattern of micro-QR-codes can also be projected by two coupled magic windows, with one of them acting as the decryption key. Such novel, freeform elements with 3D shape and tailored functionalities is relevant for applications in illumination design, smart labels, anti-counterfeiting systems, and cryptographic communication.
This paper presents a novel method to spatially vary the intra‐layer birefringence of Fused Filament Fabricated (FFF) parts by controlling chain alignment during extrusion along individual rasters. The role of print speed, extrusion factor and layer separation on the birefringence of single PLLA layers is explored, at thicknesses ranging from 50–125 µm and print speeds 1000–6000 mm min⁻¹. The cumulative and subtractive effect of multiple PLLA layers are explored to elicit colours corresponding to a range of retardations, achieve complete extinction, and printing a physical Michel‐Levy chart. By increasing print speed and reducing layer separation and extrusion factor, a birefringence up to Δn = 9 × 10⁻⁴ could be achieved in single layers. In multi‐layer structures, retardations of 0–800 nm are demonstrated. These results suggest that spatially varied birefringence can be used to store data, text or images, which can be resolved when parts are illuminated between polarizers. This effect is utilized to present a steganographic technique embedding information within bulk printed parts. These techniques might find application in a range of printed optics and devices, where spatial control over molecular alignment and associated influence on the propagation of light is desirable, including the ability to encode information within a print.
The ambition of this review is to provide an up-to-date synopsis of the state of 3D printing technology for optical and photonic components, to gauge technological advances, and to discuss future opportunities. While a range of approaches have been developed and some have been commercialized, no single approach can yet simultaneously achieve small detail and low roughness at large print volumes and speed using multiple materials. Instead, each approach occupies a niche where the components/structures that can be created fit within a relatively narrow range of geometries with limited material choices. For instance, the common Fused Deposition Modeling (FDM) approach is capable of large print volumes at relatively high speeds but lacks the resolution needed for small detail ( ${\gt}{{100}}\;{\rm{\unicode{x00B5}{\rm m}}}$ > 100 µ m ) with low roughness ( ${\gt}{{9}}\;{\rm{\unicode{x00B5}{\rm m}}}$ > 9 µ m ). At the other end of the spectrum, two-photon polymerization can achieve roughness ( ${\lt}{{15}}\;{\rm{nm}}$ < 15 n m ) and detail ( ${\lt}{{140}}\;{\rm{nm}}$ < 140 n m ) comparable to commercial molded and polished optics. However, the practical achievable print volume and speed are orders of magnitude smaller and slower than the FDM approach. Herein, we discuss the current state-of-the-art 3D printing approaches, noting the capability of each approach and prognosticate on future innovations that could close the gaps in performance.
