| 摘要 |
PROBLEM TO BE SOLVED: To reduce the number of parts and to miniaturize an optical pick-up by receiving one portion of light being emitted from first and second light sources together with one photo detector. SOLUTION: A light source 2 is used for a high-density disk 18 and outputs a beam with a wavelength of 650 n. A light source 9a is used for a low-density disk 19 and outputs a beam with a wavelength of 780 nm. Holograms 34 and 35 are formed on surfaces opposite to the light sources 2 and 9, respectively, in an optical member 5. The holograms 34 and 35 are transmission-type holograms, pass a large quantity of incident light as it is, but diffract it partially toward a photodetector 36. The photodetector 36 converts the incident light to an electrical signal and outputs it to the power supply control circuit of the light sources 2 and 9a. Then, a voltage being added to the light sources 2 and 9a is changed and the quantity of light being discharged from the light sources 2 and 9a toward a storage medium is controlled. Therefore, only one photodetector for monitoring is required. |
