GOALI: Additive Manufacturing of Glass Based Gradient Index Optics

光学透镜系统在工业、消费品和科学仪器中无处不在。传统的光学透镜通过在界面处弯曲光来控制光的路径。这限制了设计镜头的自由度。结合多个镜头的传统解决方案增加了系统的成本、尺寸和重量。梯度折射率透镜使用非均匀材料来产生不同的折射率，并在整个透镜中连续弯曲光线。这项“与行业学术联络资助机会”（GOALI）奖项支持基础研究，为使用光学质量无机（玻璃基）材料生产梯度折射率透镜创造新的增材制造工艺所需的知识。新的增材制造工艺可以制造具有以前无法实现的性能的梯度折射率透镜。除了梯度折射率透镜，使用增材制造沉积高质量玻璃的能力将有利于集成光电子和电子封装。新的增材制造工艺采用了一种新颖的长丝馈送、激光加热工艺来沉积透明玻璃。多个细丝以不同的速率进入熔融区域，通过改变沉积玻璃的成分，将产生空间上不同的性能。第一个研究目标是验证激光加热过程中相分离在印刷玻璃中产生气泡的假设。在防止气泡夹持的条件下沉积的玻璃样品将被切片以确定气泡成核的开始并测量随后的演变。熔融区域的原位光谱将识别加工过程中的化学变化。这些结果将与由模拟和测热法确定的温度分布进行比较。然后用玻璃中气体饱和度的热力学模型来证实气泡的形成。第二个研究目标是验证在沉积过程中熔融区域的机械搅拌将增强混合并导致平滑指数剖面的假设。有色细丝的进给速率在不同的频率和幅度下会发生抖动。混合将通过显微镜观察印刷标本的颜色分布来量化。第三个研究目标是确定热剖面对层间扩散系数的影响。棱镜将使用不同层的光学质量玻璃印刷。印刷棱镜的局部折射率将作为在炉中长时间退火前后位置的函数进行测量，并与标称轮廓进行比较。

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.