| 摘要 |
PROBLEM TO BE SOLVED: To enlarge a ratio of luminous flux made incident in an effective aperture of an objective lens in the luminous flux outgoing from a semiconductor laser by making a reflection surface of a recording medium side of a half mirror concaved. SOLUTION: The luminous flux outgoing from the semiconductor laser 1 is made incident on a curved surface half mirror 10 through a diffraction grating 2. The curved surface half mirror 10 is constituted so that its semiconductor laser side surface is concaved, and its opposite side surface is convexed, and a half-transmissive half-reflective film is formed on the concaved surface, and the transmission and the reflection are each 50%. The luminous flux from the semiconductor laser 1 is reflected by a concave half-transmissive half- reflective surface to be led to the objective lens 5. Since the reflection surface is concaved, the reflection luminous flux receives a convergent action, and much light quantity is fetched by the objective lens. An optical card 6 is irradiated by the beam converged by the objective lens 5, and a part of the beam is reflected, and returns through the same optical path, and is made incident on the concave of the curved surface half mirror 10 to be transmitted. |
