Precise track-following control using a micro-electromechanical-system tracking mirror in high-density optical disk drives

We developed a very-precise dual-stage track-following system using a micro-electromechanical-system (MEMS) tracking mirror as a fine actuator. The MEMS mirror was mounted on a linear positioner replacing an ordinary fixed folding mirror. The mirror had good optical performances of reflectance, phase difference between s- and p-polarized lights and surface flatness. It had also a good actuator performance with a damped 1st resonance. Controllers for the positioner and mirror were arranged in parallel taking only a tracking error signal as their feedback input. Thus no extra sensor was required. Using `µ-analysis and synthesis,' we designed a controller that can coordinate the motions of two actuators. Finally we experimentally demonstrated a tracking error of less than 10 nm.