Abstract

In a typical optical disk drive, the beam of a semiconductor laser diode is collimated, shaped, polarized, and then sent through an aberration-free, high-NA lens to be focused on the "active" surface of an optical disk. To reach this active surface, the beam must pass through the disk substrate, which is typically a plastic or glass medium of known thickness and refractive index. During recording and/ or erasure, the focused laser beam creates or annihilates certain "marks" in the active region. During readout, the same focused beam, attenuated to avoid recording and/or erasure, picks up the information as represented by marks, and returns to the objective lens. The lens recollimates the beam and sends it to the detection channel, where focus-error, track-error, and data signals are extracted from the returning beam.

© 1996 Optical Society of America