| 摘要 |
An optical head includes semiconductor lasers for 455 nm, 655 nm, and 785 nm bands; a polarization change element and a polarizing beam splitter for luminous flux with a wavelength of 455 nm band, a first collimation lens for converting luminous flux having passed through the polarizing beam splitter into parallel flux, a first quarter-wave plate, a BD objective for focusing the flux onto a signal recording surface of BD, a first photo-detector for receiving light reflected by BD, a composite prism for reflecting flux reflected by the splitter and transmitting most of flux from the lasers for 655 nm and 785 nm bands, a second collimation lens for converting flux emitted from the composite lens into parallel flux, a second quarter-wave plate, an objective compatible with HD DVD, DVD, and CD; and a second photo-detector for receiving light reflected by HD DVD, DVD, and CD.
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