| 摘要 |
PURPOSE:To detect the depth of a hole double without influences of the ununiformity of the reflection factor to attain large-capacity optical recording by irradiating two or more monochromatic lights different in wavelength to the same position of an information recording medium to obtain a light quantity ratio of reflection to transmission. CONSTITUTION:Lights 2a and 2b having wavelengths lambda1 and lambda2 of semiconductors 1a and 1b are converted to parallel luminous fluxes, and the light 2a passes a dielectric mirror 4 but the light 2b is reflected on it. Lights 2a and 2b are converted to circularly polarized waves by a 1/4 wavelength plate 7 after passing a polarizing beam splitter 6 and are reflected on a mirror 8 and are condensed on a recording hole of a recording track 21 on a recording medium 20. The reflected light from the medium 20 passes the lens 9 and the mirror 8 and is converted back to linearly polarized light by the plate 7 and is reflected on the splitter 6. This reflected light is divided to lights 12 and 13 having wavelengths lambda1 and lambda2 by a mirror 15, and the quantity of light 12 is detected by a photodetector 14, and the light 13 is divided into two by a mirror 15 and is detected by a detector 17. A ratio of the sum signal of the detector 17 to the detection signal of the photodetector 14 is operated by a comparator 18, and the output is obtained as a detection signal for the depth of the hole. |
