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Register a new user3D photo-responsive optical devices manufactured by advanced printing technologies
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Authors
A. Szukalski
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Photonic components responsive to external optical stimuli are attracting increasing interest, because their properties can be manipulated by light with fast switching times, high spatial definition, and potentially remote control. These aspects can be further enhanced by novel architectures, which have been recently enabled by the availability of 3D printing and additive manufacturing technologies. However, current methods are still limited to passive optical materials, whereas photo-responsive materials would require the development of 3D printing techniques able to preserve the optical properties of photoactive compounds and to achieve high spatial resolution to precisely control the propagation of light. Also, optical losses in 3D printed materials are an issue to be addressed. Here we report on advanced additive manufacturing technologies, specifically designed to embed photo-responsive compounds in 3D optical devices. The properties of 3D printed devices can be controlled by external UV and visible light beams, with characteristic switching times in the range 1-10 s.
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3D printing technologies are currently enabling the fabrication of objects with complex architectures and tailored properties. In such framework, the production of 3D optical structures, which are typically based on optical transparent matrices, optionally doped with active molecular compounds and nanoparticles, is still limited by the poor uniformity of the printed structures. Both bulk inhomogeneities and surface roughness of the printed structures can negatively affect the propagation of light in 3D printed optical components. Here we investigate photopolymerization-based printing processes by laser confocal microscopy. The experimental method we developed allows the printing process to be investigated in-situ, with microscale spatial resolution, and in real-time. The modelling of the photo-polymerization kinetics allows the different polymerization regimes to be investigated and the influence of process variables to be rationalized. In addition, the origin of the factors limiting light propagation in printed materials are rationalized, with the aim of envisaging effective experimental strategies to improve optical properties of printed materials.
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Two-photon photopolymerization delivers prints without support structures and minimizes layering artifacts in a broad range of materials. This volumetric printing approach scans a focused light source throughout the entire volume of a resin vat and takes advantage of the quadratic power dependence of two photon absorption to produce photopolymerization exclusively at the focal point. While this approach has advantages, the widespread adoption of two photon photopolymerization is hindered by the need for expensive ultrafast lasers and extremely slow print speeds. Here we present an analogous quadratic process, triplet-triplet-annihilation-driven 3D printing, that enables volumetric printing at a focal point driven by <4 milliwatt-power continuous wave excitation. To induce photopolymerization deep within a vat, the key advance is the nanoencapsulation of photon upconversion solution within a silica shell decorated with solubilizing polymer ligands. This scalable self-assembly approach allows for scatter-free nanocapsule dispersal in a variety of organic media without leaking the capsule contents. We further introduce an excitonic strategy to systematically control the upconversion threshold to support either monovoxel or parallelized printing schemes, printing at power densities multiple orders of magnitude lower than power densities required for two-photon-based 3D printing. The application of upconversion nanocapsules to volumetric 3D printing provides access to the benefits of volumetric printing without the current cost, power, and speed drawbacks. The materials demonstrated here open opportunities for other triplet fusion upconversion-controlled applications.
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