[OPTICAL REVIEW Vol. 5, No. 6 (1998) 334-339]

Diffractive-Refractive Achromatic Lens for Optical Disk System by Glass Molding

Yasuhiro TANAKA, Michihiro YAMAGATA and Tomohiko SASANO

AVC Products Development Laboratory, Matsushita Electric Industrial Co., Ltd., 1006, Kadoma, Kadoma-shi, Osaka, 571-8501 Japan

(Received June 15, 1998; Accepted July 28, 1998)

An erasable optical disk system requires an objective lens having minimum chromatic aberration. We estimated the chromatic aberration of a conventional refractive singlet. At shorter wavelengths, the focus shift of an objective lens exceeds its depth of focus. A diffractive-refractive hybrid lens can compensate chromatic aberration perfectly. Diffraction efficiency, however, decreases with the degree of compensation. We simulated the relationship between chromatic aberration and diffraction efficiency. Fabrication of designed lenses by glass molding was achieved, and the results showed excellent agreement with the simulation.

Key words : diffractive element, grating, achromat, optical disk, lens design, objective lens, diffraction efficiency