Patent ID: 8139462

Claim:
A method for calculation of recording depth in a holographic disk, the method comprising: applying a first external voltage to one or more actuators coupled to an objective lens to focus a tracking beam of radiation having a first wavelength on a reference layer of the disk, wherein the reference layer comprises at least one of a partially dichroic coating or a partially metallized coating; applying a second external voltage to the one or more actuators coupled to the objective lens to focus a recording beam of radiation on the reference layer of the disk, wherein the recording beam comprises a second wavelength different from the first wavelength of the tracking beam; computing a difference between the first external voltage and the second external voltage; calculating a lens-shift distance based upon the difference using a voltage-distance calibration curve, wherein the lens-shift distance comprises shift in distance of the objective lens in order to focus the tracking beam of radiation and the recording beam of radiation on the reference layer respectively; and calculating the recording depth based upon the lens shift distance.