Jeroen Wals

Liquid crystal aberration compensation devices

The application of aberration compensation devices can support the trend to higher information densities in optical data storage. The information content of a disc may be increased while maintaining acceptable tolerance levels. For example, disc tilt dependence may require coma compensation, whereas double layer formats require spherical aberration compensation. Liquid crystals (LCs) can be successfully applied in such devices. The design of two practical implementations is discussed; a coma compensating LC-cell with special electrode-design for optimized tolerances w.r.t. decentering, and a lens made of photopolymerizable LC, which can be used to compensate for spherical aberration.

Fast-Access Optical Drive.

A slim-line linear motor is presented for fast access in optical drives. By applying a three-phase commuting linear motor in combination with a split-optical head, an average seek time of 11 ms is realised for a 120-mm optical disc. The rotational latency is reduced by spinning the disc at 100 Hz, resulting in a total average access time of 25 ms. Two-stage radial tracking is applied, along with a one-dimensional lens actuator to attain high mechanical bandwidths. In addition, a novel scheme for counting tracks during high-speed access is proposed.