| 摘要 |
<p>An optical head which reproduces information recorded on an optical disc whose disc substrate thickness is t1 (0.6 mm) or t2 (1.2 mm) by using a dual-wavelength light beam and using one object lens. A convergent device is composed of a center part whose optimum-designed substrate thickness is t1 x 0.6-t1 and an outer circumference part whose optimum-designed substrate thickness is 0.6 mm. By providing a difference in level in the convergent device, information can be recorded/reproduced onto/from both an information medium with a disc substrate thickness of t1 and an information medium with a disc substrate thickness of t2 in a state with few side lobes. Or, a difference in level is provided in an object lens and an optical distance (L2) between a 2nd light emission source and a condensation optical system is selected to be 80 - 95 % of a distance (L1) between a 1st light emission source and the condensation optical system. Or, only a light with a 1st wavelength is shielded or diffracted in a circular belt shape.</p> |
