Polarizing optical element, diffractive optical element, optical element unit, optical pickup apparatus, and optical disk drive apparatus

A diffractive optical element used in an optical pickup apparatus, comprising:

• a first optical member;
• a second optical member;
• and
• a polarizing optical element,
• wherein a diffraction grating (hologram) is formed on said polarizing optical element and a diffraction efficiency of said diffraction grating varies depending on a polarization direction of an optical beam incident thereon,
• wherein, when a duty ratio of the diffraction grating is defined as a ratio of a width of a protrusion of the diffraction grating to a grating period, the duty ratio of the diffraction grating is within a range of 0.4-0.5, and
• wherein the polarizing optical element is sandwiched between said first optical member and said second optical member.

An optical element unit, comprising:

• a unit into which a light source and a photodetector are integrated;
• and
• a diffractive optical element using a polarizing optical element,
• wherein a diffraction grating (hologram) is formed on said polarizing optical element, and a diffraction efficiency of said diffraction grating varies depending on a polarization direction of an optical beam incident thereon,
• wherein, when a duty ratio of the diffraction grating is defined as a ratio of a width of a protrusion of the diffraction grating to a grating period, the duty ratio of the diffraction grating is within a range of 0.4-0.5, and
• wherein said unit is integrated with the diffractive optical element.

An optical pickup apparatus that converges light from a light source to a recording medium by a converging lens so as to perform recording and/or reproducing thereon, said optical pickup apparatus comprising:

• an optical system comprising:
• a diffractive optical element arranged on a light path so as to diverge a reflected light from the recording medium;
• and
• a photodetector that receives the reflected light,
• wherein said diffractive optical element includes a polarizing optical element having a diffraction grating (hologram) formed thereon, and a diffraction efficiency of said diffraction grating varies depending on a polarization direction of an optical beam incident thereon, and, when a duty ratio of the diffraction grating is defined as a ratio of a width of a protrusion of the diffraction grating to a grating period, the duty ratio of the diffraction grating is within a range of 0.4-0.5.

An optical disk drive apparatus that performs recording and/or reproducing of information with respect to a recording medium by using an optical pickup apparatus,

• said optical pickup apparatus converging light from a light source to the recording medium by a converging lens so as to perform recording and/or reproducing thereon, and said optical pickup apparatus comprising:
• an optical system comprising:
• a diffractive optical element arranged on a light path so as to diverge a reflected light from the recording medium;
• and
• a photodetector that receives the reflected light, wherein said diffractive optical element includes a polarizing optical element having a diffraction grating (hologram) formed thereon, and a diffraction efficiency of said diffraction grating varies depending on a polarization direction of an optical beam incident thereon, and, when a duty ratio of the diffraction grating is defined as a ratio of a width of a protrusion of the diffraction grating to a grating period, the duty ratio of the diffraction grating is within a range of 0.4-0.5.