Multi-material additive manufacturing based on µ-dispenser technology for tailored polymer micro-optics

Abstract

Integrated optics are an innovation driver for a multitude of industrial applications like autonomous driving or point-of-care diagnostics. With the increasing demand for miniaturized, low-cost optical systems, new methods for fabricating tailored graded index micro-optics are required. Additive manufacturing is a promising technology for this not only due to its high design freedom, but also because of the potential for function integration via multi-material printing or the integration into digitized process chains. In fact, additive manufacturing of optical elements has not matured yet due to the requirement to fabricate 3D objects with optical quality. In this contribution, µ-dispenser direct ink writing based on transparent photopolymers is presented that enables the production of multi-material micro-optical elements. It will be shown that the achievable printing resolution for 0D-and 1D-structures is mainly depending on the needle diameter. Mono-material spherical and cylindrical lenses with a geometric dimension in the range of a few micrometers have been successfully fabricated and characterized. The geometric shape fidelity of printed 2D-layers, which suffers from surface tension effects due to the material's molecular cohesive forces, is optimized by proper printing strategies. In an outlook, the route towards the production of micro-optic, function-integrated 3D GRIN elements is given, by using a mixer module to realize combined and gradable extrusion of two photopolymers.

Exploring the unique chromatic properties of multi-material gradient-index optics

“…Instead, one simply needs to measure or calculate the optical power. For a radial GRIN, typically defined as 𝑛 "#$% (𝑅) = 𝑁 88 + 𝑁 /8 𝑅 1 + 𝑁 18 𝑅 @ + ⋯ (9) where 𝑅 is the un-normalized radial coordinate, Marchand [38] analytically derived the power to be 𝛷 "#$% = −2𝑁 /8 𝑡 (10) where Φ "#$% is the power of the GRIN, 𝑡 is the GRIN lens thickness, and 𝑁 /8 is the coefficient for the 𝑅 1 term describing the GRIN. By analytically calculating the power of a multi-material GRIN according to Eq.…”

“…In recent years, and arguably for the first time in its history, the potential of a new GRIN fabrication technique has far outpaced the knowledge of its design capabilities. The latest advancements in optical additive manufacturing have allowed for the manufacture of arbitrary refractive index distributions, both in polymers [6][7][8][9] and in glass [10]. Until quite recently, no design tools or techniques existed which took full advantage of the new fabrication method.…”