GOALI: Additive Manufacturing of Glass Based Gradient Index Optics

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Optical lens systems are ubiquitous in industry, consumer products, and scientific instruments. Conventional optical lenses control the path of light by bending it at the interfaces. This limits the degree-of-freedom available for designing a lens. The traditional solution of combining multiple lenses adds expense, size, and weight to the system. Gradient index lenses use non-homogenous materials to create a varying refractive index and continuously bend the light throughout the lens. This Grant Opportunity for Academic Liaison with Indusry (GOALI) award supports fundamental research to provide knowledge needed to create a new additive manufacturing process for producing gradient index lenses using optical-quality inorganic (glass-based) materials. The new additive manufacturing process can fabricate gradient index lenses with performance that could not previously be realized. Beyond gradient index lenses, the ability to use additive manufacturing to deposit high quality glass will benefit integrated photonics and electronics packaging. The new additive manufacturing process utilizes a novel filament-fed, laser-heated process to deposit transparent glass. Multiple filaments, fed at different rates into the molten region, will produce spatially varying properties by changing the composition of the deposited glass. The first research objective is to test the hypothesis that bubble generation in printed glass is a result of phase separation during laser heating. Glass specimens, deposited under conditions to preclude bubble entrapment, will be sectioned to determine the onset of bubble nucleation and measure subsequent evolution. In-situ spectroscopy of the molten region will identify chemical changes during processing. These results will be compared to the temperature profile determined from modeling and pyrometery. Bubble formation will then be corroborated with thermodynamic models for gas saturation in glass. The second research objective is to test the hypothesis that mechanical agitation of the molten region during deposition will enhance mixing and lead to a smooth index profile. The feed-rate of colored filaments will be dithered at different frequencies and amplitudes. The mixing will be quantified by microscopic observation of the color distribution in printed specimens. The third research objective is to determine the effects of the thermal profile on the diffusion coefficient between layers. Prisms will be printed using different layers of optical quality glass. The local index of the printed prisms will be measured as a function of position before and after prolonged annealing in a furnace and compared to the nominal profile.