Compact Optical Light Paths

The primary function of an optical pickup is twofold: focusing the laser light using a high-quality objective lens into a diffraction-limited spot on the information layer of the disc and detecting the changes in the reflected light due to the layer's microstructure. Two other important functions of the pickup are the generation of the focus- and tracking-error signals [I]. The light reflected from the disc is partly coupled to a detector by a beamsplitter. The reliability of the detected signals is mainly determined by the mutual positional stability of the laser, beamsplitter and detector. This stability can be improved by putting these components close together. Another critical component in an optical recorder or player concerning its positional stability is the focusing and tracking actuator. An improved stability may be achieved by integrating the whole optical pickup together with the actuator in one device. In this paper we distinguish three kinds of applications for optical pickups: read-only systems, systems for recording and/or erasing in phase-change, ablative or dye materials, and Magneto-Optical (MO) players.