[OPTICAL REVIEW Vol. 1, No. 1 (1994) 27-29]
Dual Focus Optical Head for 0.6 mm and 1.2 mm Disks
Yoshiaki KOMMA, Seiji NISHINO and Sadao MIZUNO
Materials and Devices Laboratory, Matsushita Electric Industrial Co., Ltd., 1006, Kadoma, Kadoma, Osaka 571, Japan
(Accepted July 22, 1994)
We propose a dual focus optical head with a holographic optical element (HOE) which corrects spherical aberrations in order to read both 0.6 mm disks and 1.2 mm disks. The thin disks are read using transmitted light and the thick disks are read using +1st order diffracted light of the blazed HOE. The good quality of the focused spots and the focusing error signals was experimentally confirmed. No influence of unnecessary diffracted light was observed.
Key words : optical disk, dual focus, optical head, 0.6 mm disk, 1.2 mm disk, holographic optical element, spherical aberration, large numerical aperture, high density optical storage