| 摘要 |
PURPOSE:To provide a reader which obviates generation of zero order diffracted light and aberration in an objective lens part by using a reflection type hologram lens as an objective lens for focusing a laser beam to an information track on an information recording medium. CONSTITUTION:A laser beam is made incident to a quarter-wave plate 3 and is converted to circularly polarized light. The beam is made incident as reproduced reference light to a reflected light hologram lens 4, from which the reproduced object light is focused to the information track on a recording medium 5. The reflected beam is made incident through the plate 3 and a beam splitter 2 to a photodetector 6. Focusing is accomplished by moving the entire part of the optical system or the lens 4 alone in the direction orthogonal to the surface of the medium 5 as the incident point of the incident beam on the lens 4 changes. Tracking is accomplished similarly by inclining the optical system or the lens so as to move the beam spot in a radial direction. Since the space between the interference fringes is narrow, the lens 4 does not produce zero order diffracted light. The recording object light and the reference object light are in the same direction and therefore no aberration is generated. |
