| 摘要 |
PURPOSE:To eliminate the possibility of a condensing device from collision with an information storage medium even when focusing deviation occurs by providing a luminous flux state changing device that changes the state of divergence or convergence of luminous flux that passed a collimating device. CONSTITUTION:When the state of flux L of laser beam passed through a collimating lens 23 is set to parallel luminous flux, the flux L of laser beam passed the collimating lens 23 converges at a position close to an objective 25 in a case where the collimating lens 23 is placed apart from a semiconductor laser 21. When the collimating lens 23 is placed apart from the semiconductor laser 21 and an information storage medium 22 gets off from the objective 25, focused state can be maintained by bringing the collimating lens 23 close to the semiconductor laser 21. Accordingly, it is not necessary to shift a condensing device to the direction of its optic axis and there is no possibility of colliding of the condensing device against the information storage medium even when focus deviation occurs. |
