| 摘要 |
PROBLEM TO BE SOLVED: To easily control an optical beam diameter without requiring a power supply for operation by cutting off mainly an outer peripheral part of the optical beam cross section in a transmittance variation part provided in an optical path from a light source up to an optical recording medium and variable in transmittance, based on wavelength. SOLUTION: Light beams made incident on a diffraction granting 5 are separated into a primary beam and a secondary beam, which are then made incident on collimator lens 6 and are made parallel rays from diverging rays to be made incident on a splitter 7. The light beams made incident on the splitter 7 are reflected in the direction of an objective lend 9, and are made incident on the objective lend 9 through an optical element 8 to be made into converging rays, which form a spot on a recording surface of an optical recording medium. Here, for example, when light beam of 650nm wavelength is used, the optical element 8 transmits approximately 100 percent of the light beam over the entire surface. On the other hand, when light beam of 780nm wavelength is used, the optical element 8 transmits approximately 100 percent of the central part of the light beam, bur almost cuts off the peripheral part of the light beam. Therefore, a power supply is not needed for operation and the beam of light is easily controlled. |
