| 摘要 |
PURPOSE:To prevent the efficiency of optical detection from being reduced by constituting the titled optical system so that the center line of a converged beam is vertically irradiated to an optical disk and the reflected light from the optical disk is always returned to the original direction even if the converged point of light is moved by a deflector. CONSTITUTION:A converged beam reflected by the deflector 21 and converged to the 2nd lens L2 is used as incident light. When it is defined that the focal distance of the 1st lens L1 is f1, the focal distance of the 2nd lens L2 is f2, a distance between the surface of the optical disk 1 and the 1st lens L1 is l', a distance between the 1st lens L1 and the 2nd lens L2 is 2f2+l, and a distance between the 2nd lens L2 and the deflector 2 is 2f2, the optical system is satisfied with the relation of 1/(2f2+l)+1/l'=1/f1 and l/2f2=l'/(2f2+l). Consequently, the center line of the beam is moved around the center C of the deflector 2 as shown by a dotted line, and after being passed through the 2nd lens L2, converted into a point B. Thereby, the center line of the beam is vertically irradiated to the optical disk 1 after being transmitted through the 1st lens L1. |
