| 摘要 |
PROBLEM TO BE SOLVED: To prevent the S/N ratio of a signal in recording or reproducing desired information from depending on the direction of a rotary mirror installed on the rotary axial center of a swing arm, by nearly circularly polarizing a laser beam that enters from a fixed optical system to a movable optical system having the swing arm. SOLUTION: A fixed optical system 7 makes a parallel beam, with a collimator lens 19, from a linearly polarized laser beam generated by a laser light source 20, forming a desired cross sectional shape, e.g. a circle, with a prism 18, circularly polarizing the beam with a λ/4 wavelength plate 12, and making it enter a rotary mirror 6 in a movable optical system 21 through a mirror 16. The circularly polarized laser beam is symmetrical in the polarizing characteristics around the optical axis and, when reflected by a rotary mirror 6 rotating around the optical axis, its reflectance is not dependent on the direction of the rotary mirror 6. As a result, in recording or reproducing desired information on a magneto-optical disk 8, the S/N ratio of a signal is free from dependence on the direction of the rotary mirror 6, permitting a stable operation. |
