Patent ID: 7193955
Filing Date: 2007-03-20
Classification: G11B

Abstract:
1. An optical head device, comprising: a light source; a condensing lens that collects light emitted from the light source onto an information layer as a target among a plurality of information layers included in an optical information recording medium; an optical element that collects (a) light reflected from the target information layer and (b) light reflected from adjacent information layers that are adjacent to the target information layer at positions different from each other in the direction of optical axis; a light receiving element that detects each reflected light collected by the optical element and obtains a detection signal; and arithmetic circuitry that obtains a reproduction signal using the detection signal, wherein the light receiving element comprises: a first light receiving portion that detects a first detection signal from reflected light containing the light reflected from the target information layer; a second light receiving portion that detects a second detection signal from light reflected from a first adjacent information layer located at a position more distant from the condensing lens than the target information layer among the adjacent information layers; and a third light receiving portion that detects a third detection signal from light reflected from a second adjacent information layer located on a side closer to the condensing lens than the target information layer among the adjacent information layers and the arithmetic circuitry multiplies the second detection signal by a constant K that is determined in accordance with a space between the target information layer and the first adjacent information layer and multiplies the third detection signal by a constant L that is determined in accordance with a space between the target information layer and the second adjacent information layer, and performs a differential operation to subtract the second detection signal multiplied by K and the third detection signal multiplied by L from the first detection signal.