| 摘要 |
PURPOSE:To improve the productivity and to reduce the cost by forming an objective lens into a large-aperture distributed index rod lens of less aberration which has the end face, on which the light from a light source is made incident, spherically formed. CONSTITUTION:With respect to a distributed index rod lens 15 of small aberration and large numerical aperture (NA) where a diameter (D) is large >=3mm and an end face 14 on which the light from the light source is made incident is formed to a spherical face whose radius R of curvature is 0.6-0.9 times as large as the diameter D, the end face in the opposite side (in the side of a recording medium 17) is made plane, and reflection preventing films 30 are formed on both end faces by vapor-deposition or the like. This distributed index rod lens 15 is fixed in a lens holding frame 31. Thus, the number of constituting lenses is one to reduce considerably the man-hour for the polishing work of the lens and the vapor-deposition work of reflection preventing films, and adjustments such as alignment of the optical axis for assembling are made unnecessary. |
