Optical head and optical recording and reproducing apparatus

An optical head which performs recording and/or reproducing of a signal to an optical recording medium, comprising:

• a light source;
• an objective lens that converges light released from the light source onto the optical recording medium;
• a spherical aberration correcting device that corrects spherical aberration that occurs when the optical recording medium has a base-substrate thickness that deviates from a standard base-substrate thickness;
• a light separation device that is placed in a light path from the spherical aberration correcting device to the optical recording medium;
• a lens that converges light that has been separated by the light separation device;
• a light-source light-quantity controlling opening that aperture-controls light that has been converged by the lens;
• a first light detector that receives light that has been aperture-controlled by the light-source light-quantity controlling opening;
• and
• a second light detector that receives light that has been reflected by the optical recording medium.

An optical head which performs recording and/or reproducing of a signal to an optical recording medium, comprising:

• a light source;
• an objective lens that converges light released from the light source onto the optical recording medium;
• a spherical aberration correcting device that corrects spherical aberration that occurs when the optical recording medium has a base-substrate thickness that deviates from a standard base-substrate thickness;
• a light separation device that is placed in a light path from the light source to the spherical aberration correcting device;
• a first light detector that receives light that has been separated by the light separation device;
• and
• a second light detector that receives light that has been reflected by the optical recording medium;
• wherein the spherical aberration correcting device is an optical element comprising a phase change layer placed between a pair of substrates having transparent conductive thin films.