CD playback using a monolithic confocal laser coupler with a confocal knife edge (CKE) structure

Sekimoto et al. (1994) reported a monolithic optical pick-up based on confocal optics. Although the optical pick-up is very stable in principle for a lens displacement, we found some substantial problems in using the confocal optical system for the detection of the tracking-error (TE) signal. In this paper, we discuss the inherent characteristics of the TE signal using the confocal optical system and we also propose another monolithic optical pick-up which has an improved TE detection method to be applied to the optical disk with any pit depth. Using this novel optical pick-up, we demonstrate CD playback with a single-beam device for the first time. Jitter level achieved is 6.7 ns. Drastic improvement in the DC offset against lens shift in the radial direction was also achieved compared with the conventional push-pull method. The new optical pick-up is demonstrated to be a substantially stable system.