Patent ID: 7859955

Claim:
An apparatus for recording/reproducing holographic data, in which a position of a recording layer in a holographic data storage medium is adjusted, the holographic data storage medium comprising a substrate, a first reflective layer from which a first light having a first wavelength is reflected, a second reflective layer from which a second light having a second wavelength is reflected, and a holographic medium layer on which holographic data is recorded, the second reflective layer being adjacent to the holographic medium layer, and the first reflective layer is disposed to be closer to or farther away from a side on which light is incident than the second reflective layer, and a reflective layer of the first and second reflective layers that is disposed to be close to the side on which light is incident is a transreflective layer through which light having one wavelength of the first and second lights having the first and second wavelengths, is transmitted and from which light having another wavelength, is reflected, the apparatus comprising: first and second light sources configured to emit the first and second lights, respectively; an objective lens configured to condense the first and second lights on the holographic data storage medium; a driving unit configured to drive the objective lens; a focus movement unit to move a focus of the second light in a direction of an optical axis; a first photodetector configured to detect the first light reflected from the holographic data storage medium and to generate a first detection signal; a second photodetector configured to detect the second light reflected from the holographic data storage medium and to generate a second detection signal; and a controller configured to control the apparatus for recording/reproducing holographic data to adjust a focal position of the second light in the holographic medium layer based on the first light, wherein: the controller is further configured to control the focus movement unit to move a focal position of the second light so that the focal position of the second light is adjusted to the position of a desired recording layer while the objective lens reciprocatingly moves in a direction of an optical axis, and the focus movement unit is further configured to move a focus of the second light in the direction of the optical axis until a time difference between the time at which the first detection signal is generated when the first light is reflected from the first reflective layer and the time at which a second detection signal is generated when the second light is reflected from the second reflective layer equates to a value corresponding to a position of a desired recording layer.