Three-dimensional optical memory

A three-dimensional optical memory, comprising:

• a recording medium, including a plurality of layers in a thickness direction thereof;
• a plurality of recording surfaces respectively formed on said layers, the recording surfaces each having data recording tracks;
• and
• sample servo marks, onto which an optical beam is focused, provided respectively on said recording surfaces,
• wherein said sample servo marks each has at least two mark portions, and
• wherein the at least two mark portions are arranged in a zig-zag manner in the thickness direction of said recording medium, thereby interposing one of said data recording tracks.

A method of selecting a single layer from a multi-layer recording medium, comprising the steps of:

• (a) directing an optical beam onto said multi-layer recording medium having a plurality of recording surfaces therein, wherein servo marks and data recording tracks are placed on a corresponding recording surface;
• (b) detecting an intensity difference of said optical beam reflected from the sample servo marks, wherein the sample servo marks are shifted in a thickness direction on said multi-layer recording medium;
• and
• (c) focusing said optical beam on a layer between the servo marks, and onto the data recording tracks of one of the plurality of recording surfaces, upon detecting the intensity difference in step (b).