| 摘要 |
PURPOSE:To prevent the adverse influence of birefringence even when the birefringence exists by providing an optical means to guide a beam from a light source as a linearly polarized beam so that the light source and a polarizing face can be coincident with the advanced and delayed phase axes of a transparent substrate. CONSTITUTION:A second lambda/4 plate 15 and a Faraday rotor 16 are rotated and controlled in the direction of an optical axis so that the advanced and delayed phase axes of the birefringence of a substrate 12 can be coincident with the beam polarizing face on a tape T. The beam made incident in this way is reflected on the optical tape T and returned back to an optical system 6 and at such a time, the reflected linearly polarized beam is rotated at 45 deg. on the polarizing face by the rotor 16. When the beam returns to the plate 15, the polarizing face is rotated at 90 deg. in comparison with the incident time. Therefore, this beam is transformed to a circularly polarized beam so that the rotational direction can be made opposite to the incident time, and when the beam is transmitted through a lambda/4 plate 10, it is transformed to the linearly polarized beam so that the polarizing face can be orthogonal to that of the incident time. Then, the beam is almost fully reflected by S waves in a polarized beam splitter 8 and made incident to a photoelectric converting element. Thus, the adverse influence caused by the birefringence of the substrate can be prevented. |
