OPTICAL ELEMENT FOR DIFFRACTION AND OPTICAL PICKUP UNIT

摘要

PROBLEM TO BE SOLVED: To propose an optical axis adjusting element which adjusts the optical axis of light of each wavelength of a two-wavelength light source type optical pickup unit and has high diffraction efficiency.

SOLUTION: The optical axis of laser light L1 of 650 nm for DVD which is emitted by a two-wavelength light source of the two-wavelength light source type optical pickup unit is aligned with the optical axis of a system, but the optical axis of the other laser light L2 of 780 nm for CD deviates from the system optical axis, so an optical axis adjusting element 10 diffracts it to adjust the optical axis. The optical axis adjusting element 10 is equipped with a binary blaze grating 11 and its diffraction efficiency is properly designed corresponding to the actual oscillated wavelength of the laser light source in operation, its step height h is (650+α)/(n-1) and the blaze height H is 5×(780+α)/(n-1), where α is 2 to 8 nm. The diffraction efficiency of the optical axis adjusting element is designed suitably for the oscillation wavelength of the laser light source in the actual use state, so the use efficiency of the light can be made higher than before.

COPYRIGHT: (C)2004,JPO