Dynamic focus control of the Blu-ray optical pickup unit

The collimator in BD/DVD/CD compatible optical pickup unit has been designed to motivate and translate along the optical axis by the motor, for multi kinds of disc compatibilities of spherical aberration compensation incurred when reading and writing. The driving motor is huge and not easy to activate. Another technical obstacle to be handled is the alignment so that the reflective mirror should be adjusted and rotated along two axes. In this paper, this kind of optical pickup unit might be minimized, and realize dynamic focus control by micro machined deformable mirror. The optimal sensitivity should be achieved when the focusing spot size is equal to the diffraction limited diameter of the focal spot of the reflected beam.