LINEAR RULER

摘要

PURPOSE: A linear ruler is provided to achieve an enhanced resolution and accuracy while arranging a hologram module of an optical pickup device to be rotated at a predetermined angle. CONSTITUTION: A linear ruler comprising a reference ruler(100) having concave and convex portions at regular spacings, and an optical pickup device(200) for generating a pulse signal in accordance with a coherency of a beam reflected and diffracted by the concave and convex portions of the reference ruler(100), wherein the optical pickup device(200) further comprises a beam focusing member(220) for allowing incidence of beam to a lower portion of the reference ruler(100), focusing the beam reflected and diffracted by the reference ruler(100), and outputting the focused beam, and a hologram module(210) arranged as being rotated from the beam focusing member(220) so that a signal generated from ±1st light from among the light generated by the beam from the focusing member(220) has a phase difference.