March 08, 2011
Light generally travels in straight lines and, although an ordinary lens can bend light, it is often impossible to get a single lens to make all the light end up where it’s supposed to. Instead, many lenses must be used in combination, where each lens does its part to have the light end up where it is supposed to. This approach leads to large, heavy and complex optical assemblies and a higher manufacturing cost for specialized optics.
But what if these cumbersome assemblies could be reduced to one or two optics with little to no assembly? What if a laser range finder or night vision goggle could be reduced to half its size and weight? Imaging systems could benefit by using fewer optical elements to achieve better control of light with equal or better performance than conventional optics.For example, this translates to high resolution cameras for micro unmanned aerial vehicles.
Recent advances in the design and fabrication of gradient index (GRIN) optics promises to make this possible, and the implications will be far-reaching. DARPA’s Manufacturable Gradient Index Optics (M-GRIN) program seeks to leverage these advances to make custom GRIN lenses readily available within the next three years.
“In the past century, every component of an optical system has become lighter and smaller, except the optics,” said Stefanie Tompkins, DARPA program manager. “The impact of smaller, lighter optics on anything used to focus light, from contact lenses and corneal implants to lasers and solar arrays would be enormous.”
Among the recent advances in GRIN lenses is a method for fabricating them from layers of polymer, creating a lens that can control the light within the lens along arbitrary paths, so the light no longer needs to travel in straight lines. “GRIN optics can be shaped to fit a system, rather than making the system conform to the optics, resulting in reduced size, weight and assembly cost. For the first time, manufacture of just a few custom lenses can be made at any point during a high-volume run without increasing the unit cost.” said Tompkins.
The new GRIN fabrication technology lends itself naturally to flexible and inexpensive manufacturing techniques, and the program seeks to develop a manufacturing capability while advancing GRIN lens design and fabrication technology. M-GRIN will make maximum use of commercial manufacturing capabilities (both technology and business models) and lend itself to a distributed manufacturing model, where design is separate from fabrication, and the fabrication steps themselves are simple enough to be done at different locations without a loss in yield. Developers will be able to rapidly design, prototype and test new systems throughout the development process. In addition, providing the tools for manufacturable GRIN optics will expand the reach of GRIN lens design and fabrication methods beyond current optics application space.
The program kicked off the first phase in September 2010 and will conduct preliminary design reviews in the next month for two challenge problems: wide field-of-view solar concentrators and lightweight night vision goggles. The first phase of the program emphasizes technology development and seeks to expand the range of GRIN lens materials and extend commercial design tools to accommodate M-GRIN lenses. Future work will emphasize manufacturability, with a goal of reaching low-rate initial production by September 2013.
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