| 摘要 |
PROBLEM TO BE SOLVED: To propose an optical head device equipped with a staircase diffraction element which can efficiently guide respective lights emitted by light sources, emitting the lights differing in wavelength, to a common optical system. SOLUTION: A 2-wavelength optical head device 1 employs the staircase diffraction element 20 as a phase diffracting element which aligns the optical axes of the laser lights L1 and L2 having different wavelengths to each other; and the steps of step surfaces 23 of the staircase diffracting element 20 are so set that the light of long-wavelength side wavelength λ1 travels straight and the number of staircase gratings of the staircase diffraction element 20 is the integer closest to α found from λ1/λ2=α/(α+1) so that the diffraction efficiency of the diffracted light of (-1)th order of the light of short-wavelength side λ2 is maximum. Consequently, the lights L1 and L2 emitted by the different light sources can be guided to the common optical system Lo with small light quantity loss. |
