| 摘要 |
PURPOSE: To obtain the same reproducing signal characteristic in the case when a compact disk having a normal density produced so as to be reproduced by a pickup with a wavelength λ1 and a numerical aperture NA1 is reproduced by a pickup having a wavelength λ2 and a numerical aperture NA2 and capable of reproducing a disk having density higher than that of the normal disk, as in the case when the normal disk is reproduced by the normal pickup with the wavelength λ and numerical aperture NA1 . CONSTITUTION: This device is an optical information reproducing device reading out a disk in which information are recorded as pits by using a laser beam and is provided with the pickup having the wavelength λ2 and the numerical aperture NA2 . In the case of reproducing the disk having the normal density with this pickup, the wavelength λ2 and the numerical aperture NA2 are defined to be combinations within a range satisfying all of next conditions (1), (2) and (3). (1) (λ2 /NA2 )<(λ1 /NA1 ), (2) 0.76×λ1 <λ2 , (3)I1 ×I2 ×I3 >=1 (f=fH), I1 ×I2 ×I3 >=0.75 (fh>f>=fL) where I1 is the relative value of a reproducing signal, I2 , I3 are the amplitude values of reproducing signals, f is a recording frequency, fL is the lowest frequency and fH is the highest frequency. |
