Data storage devices and methods

A method for storing data comprising:

• providing a substrate having oppositely disposed surfaces, at least one groove in at least one of the surfaces, and a plurality of volumes arranged along tracks between the surfaces, wherein the grooves are configured to diffract light through at least one of the oppositely disposed surfaces;
• and,
• forming a plurality of micro-holograms in the substrate;
• wherein, each of the micro-holograms is substantially contained in a corresponding one of the plurality of volumes and the presence or absence of a micro-hologram in each of the plurality of volumes is indicative of a corresponding portion of the data;
• sensing at least one diffraction pattern resulting from the at least one groove;
• and,
• determining a depth in the substrate dependently upon the sensed diffraction pattern.