Optical head apparatus

An optical head apparatus, comprising:

• a semiconductor laser light source;
• a photodetector that receives at least one part of light from said semiconductor laser light source;
• a light reflection element provided with a peripheral section that reflects peripheral light of the light from said semiconductor laser light source and condenses it into said photodetector and a central section that transmits central light of the light from said semiconductor laser light source;
• and
• a condenser lens that condenses the light that passes through said light reflection element onto an optical disc,
• wherein:
• each surface of the central section of said light reflection element has a flat shape;
• at least one surface of the peripheral section of said light reflection element has a spherical or non-spherical curved shape, the spherical or non-spherical curved shape forming a surface of rotation about the central section of the light reflecting element;
• both surfaces of the central section of said light reflection element are parallel and inclined at a predetermined angle with respect to a direction perpendicular normal to an optical axis of the light from said semiconductor laser light source;
• and
• the astigmatism produced by the inclined placement of the central section of said light reflection element compensates the astigmatic difference of said semiconductor light source.

An optical head apparatus, comprising:

• a semiconductor laser light source;
• a plurality of photodetectors placed adjacent to said semiconductor laser light source;
• a reflection type hologram element provided with a peripheral section that reflects and diffracts peripheral light of the light from said semiconductor laser light source and condenses it into one or said plurality of photodetectors and a central section that transmits central light of the light from said semiconductor laser light source;
• and
• a condenser lens that condenses the light that passes through the central section of said reflection type hologram element onto an optical disc,
• wherein:
• said photodetector that receives said reflected and diffracted light is placed closer, with respect to said semiconductor laser light source, in the direction of the major axis of an ellipse than in the direction of the minor axis of the ellipse of an elliptic far field pattern of outgoing light from said semiconductor laser light source;
• and
• the photodetector that receives signal light from said optical disc is placed closer, with respect to said semiconductor laser light source, in the direction of the minor axis of the ellipse than in the direction of the major axis of the ellipse of an elliptic far field pattern of outgoing light from said semiconductor laser light source.

An optical head apparatus, comprising:

• a semiconductor laser light source;
• a photodetector that receives at least one part of light from said semiconductor laser light source;
• a light reflection element provided with a peripheral section that reflects peripheral light of the light from said semiconductor laser light source and condenses it into said photodetector and a central section that transmits central light of the light from said semiconductor laser light source;
• and
• a condenser lens that condenses the light that passes through said light reflection element onto an optical disc,
• wherein:
• both surfaces of the central section of said light reflection element have a flat shape and are parallel;
• normals of both surfaces of the central section of said light reflection element are inclined at a predetermined angle with respect to a direction of an optical axis of the light from said semiconductor laser light source;
• and
• astigmatism produced by the inclined placement of the central section of said light reflection element compensates an astigmatism difference of said semiconductor laser light source.