Patent ID: 8553515

Claim:
A method for servoing when reading out a recorded holographic disk or recording in a preformatted holographic disk, the method comprising: detecting a primary signal of a reflected primary beam from a target data track of a target data layer of the holographic disk, the primary beam of radiation comprising a first wavelength, wherein said detecting a primary signal comprises detecting a power distribution from the reflected primary beam; comparing a power measurement of the primary signal with a threshold value of power; detecting a tracking signal of a reflected tracking beam from a reference layer of the holographic disk in an event that the power measurement of the primary signal is below the threshold value of power, the tracking beam of radiation comprising a second wavelength, wherein said detecting a tracking signal comprises detecting a reflected power distribution from the reflected tracking beam; generating a servo error signal based upon the primary signal or the tracking signal; and actuating an optical sub-system based upon either of the primary servo error signal or the tracking servo error signal such that the primary beam focuses on the target data layer.