| 摘要 |
PURPOSE:To realize highly accurate tracking with a small-sized and lightweight device, by constituting the rotary shaft of an objective lens firmly fitted to a supporting plate of an optically transmissive material. CONSTITUTION:An optically transmissive rotary shaft 3 is fixed to an objective lens supporting plate 5 and light passing through an opening 1 is reflected by a reflecting surface 4 and made incident on an objective lens 7 through a prism 6. Thus the light is converged. The rectangular prism 6 is fixed to the objective lens 7 and the rotary shaft 3 is composed of a cubic body equipped with a cylindrical shaft 3a and the reflecting surface 4. Since light having track information returns the same route, accurate tracking error signals are obtained and highly accurate track follow-up can be done, and, since the diameter of the luminous flux made incident on the objective lens 7 is equal to that of the opening 1, the loss in light quantity is remarkably improved and the burden of a laser is lightened. As a result, the device becomes extremely simple. |
