Tracking servo device for optical storage disk using optical deflector element for adjusting beam spot on the disk

A tracking servo device for changing a position on an optical storage disk at which the storage disk is irradiated by a light beam, said servo device being responsive to a tracking error signal indicative of a deviation of said position with respect to a recording track provided on a surface of said storage disk, said servo device comprising:

• an optical deflector element including a substrate having a flat surface which is substantially perpendicular to said surface of said storage disk, said optical deflector element comprising a thermo-optical element, and a waveguide formed on said flat surface of said substrate and disposed in a path of said light beam for guiding said light beam therethrough toward said surface of said optical storage disk so as to deflect said light beam during propagation thereof through said waveguide, said optical deflector element emitting the deflected light beam from an end face of said waveguide opposite to said surface of the storage disk;
• and
• deflector control means for controlling an angle of deflection of said light beam by said optical deflector element, based on said tracking error signal, said deflector control means comprising means for changing a temperature gradient in said optical waveguide.