We all know Sony’s solution to archive phase AF by using a semitransparent mirror. And looking at the latest Panasonic patent it looks like there are even smarter solutions! The sensor itself can reflect some of the light to the phase AF sensor (N.13 on the picture). There is a sort of reflective material between the pixels. That solution is called “Front side illuminated sensor”. There is also a second solution where some of the RGB pixels have been replaced with Phase-AF-Pixels like it works on the Fuji’s F300EXR (it is a compact camera).
Now, I doubt that Panasonic will ever introduce such a phase detection system. The current Olympus E-P3 and Panasonic GH2 have already an exceptional fast contrast autofocus. My bet is that in a few years every camera will use contrast AF only. Phase AF is only a waste of space and resources!
More about the patent at Egami (Click here to read the translation).