| 摘要 |
PURPOSE:To ensure the sure automatic focus control even with a recording medium having a low frequency by dividing light into plural beams through a beam splitter and carrying out the focus control by a beam excluding those beams radiated on the recorded information. CONSTITUTION:The laser light radiated from a semiconductor laser 11 is divided into plural beams like 0th order, + or -1st order beams, etc by a beam splitter 14. The 0th order beam is projected on the recorded information bits of an optical recording card 16 via an objective lens 15, etc. While the + or -1st order is projected on the areas among those information bits. Therefore the recorded information is not affected as long as the reflected beams including a -1st order beam, etc., are received by a four-split sensor 19, etc. Then, the focus error information component can be satisfactorily extracted even with a recording medium having a low frequency. As a result, the sure focus control is attained. |
