| 摘要 |
PROBLEM TO BE SOLVED: To use a hologram or a photodetector as a common element by receiving the light from a polarizing hologram which diffracts the light reflected from a recording face so as to record and reproduce the information. SOLUTION: The linearly polarized light emitted from a second semiconductor laser 12 for 635 nm or 650 nm wavelength transmits a three-beam generating diffraction grating 13 and through a polarizing hologram 14 and a 1/4 wavelength film 15 to be converted into circularly polarized light. The light irradiates the disk face and is reflected to return to the 1/4 wavelength film 15. The light is converted into linearly polarized light different from that of the outgoing light and enters the polarizing hologram 14. The +1-order diffracted light 20 and the -1-order diffracted light 21 are received by a first light-accepting element 16 and a second light-accepting element 17, respectively, to detect signals. The three-beam generating diffraction grating 13 used in this method, generates diffracted light for the light at 780 nm wavelength for a CD system, and the grating hardly generates diffracted light for the light at 635 nm or 650 nm wavelength for a DVD system. |
