We already knew that future generations of Google’s Glass headset would include prescription frames and lenses in addition to rumors of the company working with trendy designers to make the frames more fashionable. Today we get a hint at some of the ideas Google is floating around for future iterations of the hardware via a patent application published today by the US Patent & Trademark Office and first spotted by UnwiredView.

As highlighted by the patent drawing above, Google’s idea is to use see-through displays in order to make Glass look more like an ordinary, traditional pair of sunglasses. Google describes the invention as “A near-to-eye optical system includes an optically transmissive substrate having a see-through display region and a repeating pattern of diffraction elements:

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A head mounted display (“HMD”) for displaying computer generated image (“CGI”) light to a user, the HMD comprising: a frame assembly to support the HMD for wearing on a head of the user; an eyepiece secured to the frame assembly and positioned to form a see-through display, the eyepiece including: an optically transmissive substrate; and a repeating pattern of diffraction elements disposed across a viewing region of the optically transmissive substrate and organized into a reflective diffraction grating that both bends and focuses the CGI light; and a light engine mounted to the frame assembly and oriented to illuminate the reflective diffraction grating with the CGI light.

You can read more in Google’s patent application, which was originally filed in October 2011, on the USPTO’s website here.