Electrostatic Torsion Mirror for Optical Heads

Abstract

A new electrostatic torsion mirror with a silicon/silicon structure has been developed for optical heads. It positions the beam spot accurately on an optical disk having a high track density. This torsion mirror is composed of a hexagonal mirror plate, twin supporting beams, and a pair of driving electrodes. The natural frequency of mirror rotation is defined by the moment of inertia of the mirror plate and the stiffness of the beams. The squeeze effect between the mirror plate and the electrodes generates the damping force. These mechanical parameters are designed to satisfy the specifications for a high-frequency positioning of the beam spot. Experimental frequency responses showed that a test model had a second modal mechanical frequency of over 50 kHz, and the characteristics were in good agreement with the designed values. This torsion mirror will make possible more accurate spot positioning than can be achieved using conventional electromagnetic actuators.