OPTICAL DISC WRITE/READ EMPLOYING PASSIVE FOCUS MAINTENANCE

摘要

Method for maintaining a write/read light beam (B) in sharp focus on the information surface (41) of a rotating flexible optical disc (13) notwithstanding variations in the thickness of the disc's support (43) which alter the distance between such inforamtion surface and a focusing lens (9) for the light beam. Such method comprises the steps of (a) directing the write/read light beam through the disc's support, and (b) positioning the disc relative to the focusing lens so that the disc's neutral plane (NP) is spaced from the lens by a distance equal to FL-(t/n - t/2), where FL is the focal length of the lens, and t and n are the nominal thickness and refractive index of the disc support (43), respectively. By such a method, variations in the support thickness and spherical aberrations induced thereby cause the spot focus to remain in focus on the disc's information surface without any need for refocusing the lens or repositioning the lens relative to the disc.