| 摘要 |
PURPOSE:To use the same lens used for a collimator lens (a first optical means) also for an objective lens (a second optical means) to image-form a small spot by composing the first optical means and the second optical means of the same optical element and specifying the relation between the thickness of an optical member for an emitting window and the thickness of a transparent substrate on a prescribed surface. CONSTITUTION:Flux emitted from a semiconductor laser chip 11 is passed through a plane-parallel plate 12 of a flux emitting window, made into parallel flux by a collimator lens (the first optical means) 2, transmitted through a beam splitter 3, and image-formed on an information recording medium 82 of an optical card 8 by an objective lens (the second optical means) 4 as the small spot. Further, the first optical means 2 and the second optical means 4 are composed of the same optical element, and the relation between thickness T1 of the optical member 12 for the light source flux emitting window and thickness T2 of a transparent substrate 81 provided on the prescribed surface is made into the one expressed by a shown expression. Thus, the same lens can be used, and the problem of correcting an aberration can be solved. |
