Compact Disk (CD) [2]
- Introduction
- CD Drive: basic design
- Compact disk (CD): basic design
- Data encoding
- Making CDs
- Spin rates and Data transfer rates
- Interfaces
- Multi-beam technology
- White Papers on compact disk technology
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CD Drive: Basic design
A schematic of an optical three-beam pick-up of a CD drive is shown in the next figure along with the laser beam route through the system.
The laser beam from the laser diode passes through the diffraction grating to produce two secondary beams needed to maintain correct tracking of the disk. Then, the beam passes polarizing prism (beam splitter) and only the vertical polarized light passes. The light beam is then converged into a parallel beam (by the collimator) and passes through the 1/4-wave plate where the beam polarization plane is rotated by 45 degrees. The beam is then focused onto the disk surface by a lens and a servo-controlled mechanism called 2-axis device. Polarization plane of the reflected beam is rotated by another 45 degrees turning its initial vertical polarization into a horizontal. After a few more reflections, all beams reach six photo detectors: 4 main spot detectors and 2 side spot detectors enabling read-out of the pit information from the disk. To see an animated version of this schematic, go to the following page (you will need an SVG plug-in from Adobe).
