Optical pickup device and optical disk device

An optical pickup device, comprising:

• a light source that emits light with a wavelength λ1 and light with a wavelength λ2 that is longer than the wavelength λ1, to an optical disk from adjacent positions;
• an optical receiver that detects light reflected from the optical disk;
• and
• an astigmatism-generating element that generates light used for focus control in a condition that a focusing position on one of two perpendicular cross sections including an optical axis of the light reflected from the optical disk is located ahead of the optical receiver and a focusing position on the other cross section is located behind the optical receiver,
• wherein the astigmatism-generating element is a Fresnel mirror configured to include a plurality of reflecting mirrors;
• a level difference between the reflecting mirrors that are adjacent to each other is a value in a range from a depth of substantially (natural number/2) times the wavelength λ1 to a depth of substantially natural number/2 times the wavelength λ2 from a region where the light with the wavelength λ1 is incident toward a region where the light with the wavelength λ2 is incident and
• an overlapping region wherein the region on which the light with the wavelength λ1 is incident and the region on which the light with the wavelength λ2 is incident overlap each other exists between the region on which the light with the wavelength λ1 is incident and the region on which the light with the wavelength λ2 is incident.

An optical pickup device, comprising:

• a light source that emits light with a wavelength λ1 and light with a wavelength λ2 that is longer than the wavelength λ1, to an optical disk from adjacent positions;
• an optical receiver that detects light reflected from the optical disk;
• and
• an astigmatism-generating element that generates light used for focus control in a condition that a focusing position on one of two perpendicular cross sections including an optical axis of the light reflected from the optical disk is located ahead of the optical receiver and a focusing position on the other cross section is located behind the optical receiver,
• wherein the astigmatism-generating element is a Fresnel mirror configured to include a plurality of reflecting mirrors;
• a level difference between the reflecting mirrors that are adjacent to each other is a value in a range from a depth of substantially (natural number/2) times the wavelength λ1 to a depth of substantially natural number/2 times the wavelength λ2 from a region where the light with the wavelength λ1 is incident toward a region where the light with the wavelength λ2 is incident;
• and
• an overlapping region on which the light with the wavelength λ1 is incident and the light with the wavelength λ2 is incident overlap each other exists on the reflecting mirrors, wherein the value of the level difference between the reflecting mirrors that are adjacent to each other continuously changes within a range from the depth of substantially (natural number/2) times the wavelength λ1 to the depth of substantially (natural number/2) times the wavelength λ2 within the overlapping region.

An optical disk device comprising:

• a light source that emits light with a wavelength λ1 and light with a wavelength λ2, which is longer than the wavelength λ1, toward an optical disk from adjacent positions;
• a optical receiver that detects light reflected from the optical disk;
• an astigmatism-generating element that generates light used for focus control in a condition that a focusing position on one of two perpendicular cross sections including an optical axis of the light reflected from the optical disk is located ahead of the optical receiver and a focusing position on the other cross section is located behind the optical receiver;
• a signal processing portion for generating signals representative of parameters associated with the light generated by the astigmatism-generating element;
• and
• a servo processing portion for generating focus control signals and error control signals based upon the signals generated by the signal processing portion,
• wherein the astigmatism-generating element is a Fresnel mirror configured to include a plurality of reflecting mirrors,
• a level difference between the reflecting mirrors adjacent to each other is a value in a range from a depth of substantially (natural number/2) times the wavelength λ1 to a depth of substantially (natural number/2) times the wavelength λ2, from a region where the light with the wavelength λ1 is incident toward a region where the light with the wavelength λ2 is incident, and
• the light with the wavelength λ1 is incident on a side of the Fresnel mirror on which the reflected light is incident at a larger incident angle, and the light with the wavelength λ2 is incident on a side of the Fresnel mirror on which the reflected light is incident at a smaller incident angle.

An optical disk device comprising:

• a light source that emits light with a wavelength λ1 and light with a wavelength λ2 which is longer than the wavelength λ1, toward an optical disk from adjacent positions;
• a optical receiver that detects light reflected from the optical disk;
• an astigmatism-generating element that generates light used for focus control in a condition that a focusing position on one of two perpendicular cross sections including an optical axis of the light reflected from the optical disk is located ahead of the optical receiver and a focusing position on the other cross section is located behind the optical receiver;
• a signal processing portion for generating signals representative of parameters associated with the light generated by the astigmatism-generating element;
• and
• a servo processing portion for generating focus control signals and error control signals based upon the signals generated by the signal processing portion,
• wherein the astigmatism-generating element is a Fresnel mirror configured to include a plurality of reflecting mirrors,
• a level difference between the reflecting mirrors adjacent to each other is a value in a range from a depth of substantially (natural number/2) times the wavelength λ1 to a depth of substantially natural number/2 times the wavelength λ2 from a region where the light with the wavelength λ1 is incident toward a region where the light with the wavelength λ2 is incident, and
• an overlapping region on which the light with the wavelength λ1 is incident and the light with the wavelength λ2 is incident overlap each other exists on the reflecting mirrors, wherein the value of the level difference between the reflecting mirrors that are adjacent to each other continuously changes within a range from the depth of substantially (natural number/2) times the wavelength λ1 to the depth of substantially (natural number/2) times the wavelength λ2 within the overlapping region.