Ring zonal phase correction lens and optical system and optical head device

An optical system comprising:

• a ring zonal phase correction lens for use with a laser, the lens being made of resin comprising a refraction face which is formed on at least one of a first lens face and a second lens face, the refraction face comprising three or more ring zonal shaped refraction curved surfaces which are structurally formed to be adjacent to each other through step portions structurally formed in an optical axis direction for correcting a phase of a laser beam emitted from the laser by respective ring zonal shaped refraction curved surfaces;
• wherein the step portion is structurally formed such that a lens thickness of an outer ring zonal shaped refraction curved surface becomes thicker than a lens thickness of an inner ring zonal shaped refraction curved surface and the step portion is structurally formed at a half or more outer area location of an effective radius of the refraction face;
• the laser having a characteristic such that a wavelength of emitted laser beam shifts on a longer wavelength side when temperature rises;
• wherein a following expression is satisfied:
• (T×(n−1)×K/wavelength)>1.5
• wherein:
• “K” (nm/° C.) is a variation amount of wavelength of the laser beam per temperature of 1° C.;
• “T” is an absolute value of a total of adjacent step portions in which a lens thickness of an outer ring zonal refractive curved surface is thicker than a lens thickness of an inner ring zonal refractive curved surface;
• and
• “n” is a refractive index of the ring zonal phase correction lens.

An optical head device comprising:

• an optical system comprising a ring zonal phase correction lens for use with a laser, the lens being made of resin comprising a refraction face which is formed on at least one of a first lens face and a second lens face, the refraction face comprising three or more ring zonal shaped refraction curved surfaces which are structurally formed to be adjacent to each other through step portions structurally formed in an optical axis direction for correcting a phase of a laser beam emitted from the laser by respective ring zonal shaped refraction curved surfaces;
• wherein the step portion is structurally formed such that a lens thickness of an outer ring zonal shaped refraction curved surface becomes thicker than a lens thickness of an inner ring zonal shaped refraction curved surface and the step portion is structurally formed at a half or more outer area location of an effective radius of the refraction face;
• the laser having a characteristic such that a wavelength of emitted laser beam shifts on a longer wavelength side when temperature rises;
• wherein a following expression is satisfied:
• (T×(n−1)×K/wavelength)>1.5
• wherein:
• “K” (nm/° C.) is a variation amount of wavelength of the laser beam per temperature of 1° C.;
• “T” is an absolute value of a total of adjacent step portions in which a lens thickness of an outer ring zonal refractive curved surface is thicker than a lens thickness of an inner ring zonal refractive curved surface;
• and
• “n” is a refractive index of the ring zonal phase correction lens.