Single Objective Lens Having Numerical Aperture of 0.85 for a High Density Optical Disk System

Abstract

For the optical disk systems in the next generation, a GaN laser and a high numerical aperture lens are key components. This paper describes the first single objective lens that have the numerical aperture of 0.85. The lens form, which is the most important factor in realizing the lens, is analyzed. The measured wavefront aberration was 0.027λ which is was well below the diffraction limit of 0.07λ. The lens was installed in an optical pickup and write/read characteristics of the pickup with phase-change disks were investigated on a drive. Data-to-clock jitter of a read back signal was 9.5% of channel clock at a disk capacity of 25 Gbytes per 120-mm-diameter disk. The direct overwrite (DOW) characteristic was also measured. The jitter remained stable up to 1×105 cycles. These results confirm the performance of the objective lens.