Optical pickup device for recordable disc and dichroic mirror

Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium

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G11B 700

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active

052609278

ABSTRACT:
Laser light beams from first and second laser light sources 11 and 12 having different wavelengths are synthesized by a dichroic mirror 16 and irradiated on a magneto-optical disc 20 as a recordable disc and the reflected light is separated into the laser light of the first and second wavelengths. In respect of the laser light of the first wavelength, the phase difference between the P- and S-polarization components produced by the dichroic mirror 16 is compensated by a phase compensation plate 32 and the P-and S-polarization components are separated from each other by a polarization beam splitter 36 so as to be received by photodetector elements 37 and 38, respectively. Such dichroic mirror 16 is used in which the difference between the minimum transmittance in a working range of the laser light of the first wavelength and the maximum transmittance in a working range of the laser light of the second wavelength is 90% or higher for reducing changes in the phase difference between the P- and S-polarization components. Optimum signals may be obtained at the photodetector elements 37 and 38 while high wavelength separation characteristics are maintained.

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