| 摘要 |
PROBLEM TO BE SOLVED: To precisely reproduce signals of an SD and a CD of a specific thickness at a low cost without any loss of the quantity of light by meeting a specified condition among the wavelength of a light source, the numerical aperture of an objective, etc., for recording or reproducing information from an optical information recording medium excellently and optically without any aberration. SOLUTION: The optical head which records or reproduces information from the optical information recording medium optically and excellently without any aberration and has light source wavelength λ1 and an objective numerical aperture NA1 and the optical head which has a square mean square root wave front aberration Wrms, light source wavelength λ2, and an objective numerical aperture NA2 are provided, and the condition shown by an expression are met. In the expression, n1 and n2 are the refractive indexes of an information recording medium substrate corresponding to the wavelengths λ1 and λ2 and (d) is information bit depth. And, the objective 1 reproduces an SD2 using a substrate of 0.6mm in thickness with NA0.6 and a CD3 using a substrate of 1.2mm in thickness with NA0.42. |
