|Fabrication of Gradient Index Lenses
Goal: The goal of this program is to use 3D Printing to fabricate lenses which refract light due to variations of index of refraction and not due to the geometry of the lens surface. Such lenses are called Gradient Index Lenses, or GRIN lenses. GRIN lenses offer advantages in size and integration (multiple lens elements can be replaced by a single GRIN lens).
Approach: The fabrication of GRIN lenses rests on the ability of 3D Printing to locally control the composition of the lens. The powderbed is made of fine silica powder (1 micron) which is deposited using the slurry deposition method. A slurry of powder is jetted through a nozzle which is raster-scanned over the surface of the powderbed in order to meter out a precise layer of fine powder. The wet layer is dried and then binder is ink-jet printed into the layer. (Wet deposition of the layer is required when fine powder is used as fine powder cannot be easily spread in the dry condition.) For GRIN lenses, two or more binders will be printed, each carrying a different dopant. These dopants will locally modify the index of refraction of the silica. After firing, a lens with locally controlled index of refraction results.
Challenges: Challenges include firing a silica powderbed to optical quality and designing dopants which modulate the index of refraction while allowing the body to sinter uniformly.
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