Dissertation Defense: Zhihan Hong, "Additive Manufacturing of Freeform Optics"

    Friday, August 5, 2022 - 10:00am

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    Computer-controlled additive manufacturing (AM) processes, also known as three-dimensional (3D) printing, create 3D objects by the successive adding of a material or materials. There have been tremendous developments in AM; however, the 3D printing optics lag due to the limits in materials and tight requirements for optical applications, such as the highly controlled surface accuracy and surface roughness.

    Currently, most commercial printing system relays on ultra-violet (UV) curing methods. On the contrary, the yellowish problem significantly limits the transmission performance of a short wavelength. Therefore, we pioneered a precision additive freeform optics manufacturing (AFOM) method using a pulsed infrared (IR) laser. Compared to ultraviolet (UV) curable materials, thermally curable optical silicones have several advantages, such as solid UV stability, non-yellowing, and high transmission, making them particularly suitable for optical applications. Pulsed IR laser radiation offers a distinct advantage in processing optical silicones, as the high peak intensity achieved in the focal region allows for curing the material quickly. At the same time, the brief duration of the laser-material interaction creates a negligible heat-affected zone.

    Furthermore, as 3D printing optics has gained increasing attention in the optical industry, we have started to print inorganic glass instead of polymer. Based on that, we developed a new liquid silica resin (LSR) with higher curing speed, lower sintering temperature, reduced shrinkage, and, ultimately, glass with better mechanical properties. Our advanced printing method has also been demonstrated to print lenses with flat, spherical, aspherical, freeform, and discontinuous surfaces with proper surface shape and high quality for imaging applications. Furthermore, the 3D-printed optical systems with multiple optical elements broaden the potential for modern complex optical design evaluated for compact and integrated imaging applications. Most importantly, the Alvarez-lens pair can be printed and implemented in a movable zoom optical system, endowing substantial flexibility and functionality in imaging magnification. This study has paved the path for low-cost fabrication of complex glass optical systems for imaging applications.​