Error detecting device for optical head

An error detecting device for an optical head, comprising:

• optical means for converting a reflected light of a light irradiating a surface to be irradiated into an astigmatic pencil of rays having a first focal point and a second focal point, said optical means having a first focusing means for focusing said reflected light on said first focal point of said astigmatic pencil of rays, and a second focusing member for focusing said reflected light on said second focal point of said astigmatic pencil of rays, said first and second focusing members being made integral;
• and
• means for detecting errors of said light irradiating the surface to be irradiated, based on a detecting signal of a spot of said reflected light formed by said first focusing member, and a detecting signal of a spot of said reflected formed by said second focusing member, wherein said optical means is provided by a Fresnel lens, said lens including;
• a first, second, third and a fourth Fresnel lens member divided in four by two parting lines passing the center of said Fresnel lens,
• said first and said third Fresnel lens members opposed to each other across said center has said first focal point, and
• said second and said fourth Fresnel lens members opposed to each other across said center has said second focal point;
• and
• said detecting means having:
• a first, a second, a third and a fourth detecting section for respectively detecting a spot of said reflected light formed by said first, said second, said third and said fourth Fresnel lens members,
• a focusing error computing unit for computing a focusing error signal, based on detecting signals from said first, said second, said third and said fourth detecting sections, and
• a tracking error computing unit for computing a tracking error signal, based on detecting signals from at least said second and said fourth detecting sections.

An error detecting device for an optical head, comprising:

• optical means for converting a reflected light of a light irradiating a surface to be irradiated into an astigmatic pencil of rays having a first focal point and a second focal point, said optical means having a first focusing means for focusing said reflected light on said first focal point of said astigmatic pencil of rays, and a second focusing member for focusing said reflected light on said second focal point of said astigmatic pencil of rays, said first and second focusing members being made integral;
• and
• means for detecting errors of said light irradiating the surface to be irradiated, based on a detecting signal of a spot of said reflected light formed by said first focusing member, and a detecting signal of a spot of said reflected formed by said second focusing member, wherein said optical means is provided by a convex lens, said zone plate including;
• a first, second, third and a fourth convex lens member divided in four by two parting lines passing the center of said convex lens,
• said first and said third convex lens members opposed to each other across said center has said first focal point, and
• said second and said fourth convex lens members opposed to each other across said center has said second focal point;
• and
• said detecting means having:
• a first, a second, a third and a fourth detecting section for respectively detecting a spot of said reflected light formed by said first, said second, said third and said fourth convex lens members,
• a focusing error computing unit for computing a focusing error signal, based on detecting signals from said first, said second, said third and said fourth detecting sections, and
• a tracking error computing unit for computing a tracking error signal, based on detecting signals from at least said second and said fourth detecting sections.