Patent ID: 8085642

Claim:
A servo controlling apparatus of a holographic information recording/reproducing system that changes a foci of a reference light and a signal light in a depth direction of a holographic information storage medium to record information over a plurality of information layers, the servo controlling apparatus comprising: a servo signal detecting unit that detects a servo signal; and a signal processing unit that outputs a between-movement servo control signal during the movement between the plurality of information layers using a before-movement servo signal detected by the servo signal detecting unit before the movement between the plurality of information layers; a low pass filter that averages before-movement servo control signals; and a memory unit that stores an average before-movement servo control signal obtained by the low pass filter, wherein the servo controlling apparatus changes a servo control from a normal servo operation to a between-movement servo operation while a movement between the plurality of information layers is made during a recording operation, and changes the servo control back to the normal servo operation when the movement between the plurality of information layers is completed, wherein the signal processing unit processes an average before-movement servo control signal as the between-movement servo control signal, and wherein the servo controlling apparatus, in the between-movement servo operation maintains a servo control state based on the average before-movement servo control signal.