An optical head device, comprising:
- a blue laser light source for emitting a blue light beam;
- a red laser light source for emitting a red light beam;
- an infrared laser light source for emitting an infrared light beam;
- and
- an objective lens for receiving the light beams and focusing them into a spot on a recording surface of an optical disk;
- wherein a spherical aberration correcting element that controls a spherical aberration of the spot is provided in a light path shared by the blue light beam and the red light beam,
- wherein the blue light beam is focused on a recording surface of a first optical information medium having a transparent substrate with a thickness t1 through the transparent substrate with the thickness t1,
- wherein the red light beam is focused on a recording surface of a second optical information medium having a transparent substrate with a thickness t2 through the transparent substrate with the thickness t2,
- wherein the infrared light beam is focused on a recording surface of a third optical information medium having a transparent substrate with a thickness t3 through the transparent substrate with the thickness t3,
- wherein t3 is larger than t2 and larger than t1,
- wherein the spherical aberrations of the spot of the blue light beam and the spot of the red light beam are controlled by the spherical aberration correcting element,
- wherein both of the spherical aberration generated due to an error in thickness when the blue light beam passes through the transparent substrate with the thickness t1 and the spherical aberration generated due to an error in thickness when the red light beam passes through the transparent substrate with the thickness t2 are controlled by the spherical aberration correcting element,
- wherein the spherical aberration correcting element is a collimating lens,
- the collimating lens being configured to displace relatively to the blue laser light source and the red laser light source in a direction of an optical axis to control both of the spherical aberration when the blue light beam is focused through the transparent substrate with a thickness t1 and the spherical aberration when the red light beam is focused through the transparent substrate with a thickness t2, and
- wherein the spherical aberration correcting element is displaced closer to the red laser light source in the direction of the optical axis shared by the red laser light source and the blue laser light source so as to turn the red light beam traveling toward to the object lens into divergent light, when the red light beam is focused through the transparent substrate with the thickness t2 than when the blue light beam is focused through the transparent substrate with the thickness t1.