I know DVD readers use a laser to sense minute fluctuations on the disk to transfer them electronically into a signal. So my idea is to have multiple layers on each side of the disk. You would then have to have a reader which knew which layer it was reading and could avoid the signal from the others. You would also have to have a disk made to where the actual fluctuations on the disk could be picked up by the laser, or could be looked through so to speak to the other layers. For instance...