| 摘要 |
PROBLEM TO BE SOLVED: To fully secure sensitivity and receive return light with a sufficient S/N ratio for stable access even if a return light wavelength is short by setting a photodetector to a Schottky diode type. SOLUTION: By setting a photodetector 12 of return light to a Schottky diode type, metal is used instead of the P-type semiconductor of a silicon PN junction type photodetector for creation, thus making thinner than the P-type semiconductor and increasing the quantity of arrival light to a depletion layer by that amount. Also, non-output components can be reduced by direct coupling as in light being absorbed by the P-type semiconductor part by the silicon PN junction type photodetector or the like. In the photodetector 12, sensitivity can be fully secured even if a laser beam L1 has a short wavelength, thus securing a sufficient S/N ratio by a reproduction signal RF or the like of the output of a matrix operation circuit (MA) 14 by that amount in an optical disk device 1. Therefore, the wavelength of the laser beam L1 is reduced and recording density is improved sufficiently for stable access.
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