Optical head and optical disc device

• Main Authors: KOMMA YOSHIAKI, ARAI AKIHIRO
• Format: Patent
• Language: English
• Published: 13.03.2008
• Subjects: INFORMATION STORAGE; INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORDCARRIER AND TRANSDUCER; PHYSICS

The present invention aims to provide an optical head including a diffraction element capable of improving the quality of a TE signal by a DPP method even if light amounts of two sub-spots are unbalanced for optical discs having different groove pitches. In a three-beam optical head, a diffraction element 12 is divided in a radial direction of an optical disc into a first area 31 , a second area 32 and a third area 33 , wherein the second area 32 is further divided into a fourth area 321 and a fifth area 322 . The periodic structure of the first area 31 is displaced from that of the fourth area 321 by a ¼ period, the periodic structure of the third area 32 is displaced from that of the first area 31 by a ½ period, and the periodic structure of the fifth area 322 is displaced from that of the third area 33 by a ¼ period and from that of the fourth area 321 by a ½ period.