The patent is titled "A Directional Particle Filter"; it implements a light (or other particle) filter which blocks all light approaching from a specific direction. Here is a brief explanation:

1. Imagine a sheet of glass, which is spattered with a random pattern of opaque ink so that a total of half of the surface is opaque. If you look through this glass, half of the light will be blocked.
2. Now take a second sheet of glass, with an exact inverse of the first sheet's pattern, so that wherever the first sheet is opaque the second is transparent, and vice versa. This sheet, too, blocks half of the light.
3. Take the two sheets and place them in contact, with the patterns aligned. Wherever one sheet allows light to pass the other will block it, so this combination will block all of the light.
4. Now take the two sheets and slide them so they are mis-aligned. Each sheet blocks half of the light, so the combination passes 25% of the light.
5. Finally, realign the sheets and space them so there is a gap between them. To light approaching perpendicular to the sheets, the sheets will appear aligned so that all such light is blocked. To light approaching at an angle to the sheets, the sheets will appear mis-aligned so that 25% of the light passes through. This is a directional light filter.

This filter can be implemented in many other ways. The filtered direction can be at any angle to the sheets. The sheets do not have to be planar. The filtered direction can be different at different locations on the sheet, e.g. a filter could block all light from a nearby point source. Multiple directions can be blocked (with a reduction in the amount of light passed elsewhere).

You can find the patent at the US Patent and Trademark Office's database. The main page of the PTO is at http://www.uspto.gov/; the patent itself can be seen here.