| 摘要 |
PURPOSE:To eliminate the need for an optical member such as a half-mirror and to reduce the size of the optical head more by separating return light from a recording medium from an optical path extending from a semiconductor laser to the recording medium. CONSTITUTION:The P-polarized elliptic beam 15 from the semiconductor laser 2 is transmitted through a coated plate 4 and major-axis side part of the beam is photodetected by a photodetector 11 for front monitoring while reflected, diffracted, and converged by a reflection type hologram 6. The light beam which has both its major-axis side ends cut by the hologram 6 to become nearly circular and is transmitted through a dielectric multi-layered film 5. This light is transmitted through a polarization hologram 8 and passed through a 1/4-wavelength plate 9 and an objective 10 to irradiate the recording medium 3. Its reflected light is passed through the lens 10 and wavelength plate 9, diffracted by the polarization hologram 8 as the return light, and reflected totally by the multi-layered film, so that the light is made incident on and diffracted by the hologram 8 again. A photodetector 16 performs focus detection from astigmatism generated by the hologram 8 and also detects a tracking error by a push-pull method. |
