Patent attributes
An example hologram recording and reproducing apparatus includes a recording unit which records information on a holographic recording medium by recording interference fringes formed by irradiation of a reference light and an object light corresponding to recording information, a reproducing unit which generates detected information data and a focus error signal on the basis of detected light from the holographic recording medium, and a focus servo unit that carries out focus servo on the basis of the focus error signal. The focus servo unit has a servo target value setting unit which sets a target value for focus servo on the basis of the detected information data. The detected information data also includes information indicative of the position relationship between the recording medium and the reference light or the like. Accordingly, by utilizing the detected information data to set the target value for focus servo, it is possible to carry out more precise focus servo, with managing a variation in the focus servo target value caused by a change in environment such as temperature or a variation in the thickness of the recording medium.
