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

We previously reported a monolithic optical pick-up based on confocal optics (Narui et al. 1998). 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 detection of tracking-error (TE) signal. In this paper, we discuss the inherent characteristics of the TE signal using the confocal optical system, based on the results of numerical analysis and we also propose another monolithic optical pick-up which has an improved TE detection method. 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 DC offset against lens shift in the radial direction is also achieved compared with the conventional push-pull method. The new optical pick-up also demonstrates to be a substantially stable system.