Optical information recording/reproducing optical system and optical information recording/reproducing apparatus

An optical information recording/reproducing apparatus for recording information to and/or reproducing information from an optical disc by a laser beam impinging on a recording layer of the optical disc, comprising an optical information recording/reproducing optical system,

• the optical information recording/reproducing optical system including:
• a light source that emits the laser beam;
• an optical element that converts the laser beam emitted by the light source into a substantially collimated beam;
• an objective lens that converges the laser beam emerging from the optical element onto the recording layer of the optical disc;
• and
• a photoreceptor that receives light from the optical disc and performs photoelectric conversion;
• wherein:
• a wavelength λ (unit:
• nm) of the laser beam falls within a range defined by a following condition:
• 390<λ<420;
• the optical element and the objective lens comprise same or different resin materials having a glass transition temperature Tg satisfying a condition:
• Tg>115° C.;
• a first multilayer functional film, a second multilayer functional film and a third multilayer functional film are provided on an optical disc side optical surface of the objective lens, a light source side optical surface of the optical element, and an optical disc side optical surface of the optical element, respectively;
• a light source side optical surface of the objective lens opposite to the optical disc side optical surface of the objective lens is provided with a fourth multilayer functional film having four or more layers;
• the fourth multilayer functional film does not contain titanium (Ti);
• each of the first, second and third multilayer functional films includes a non-high refractive index layer comprising a composition containing one of silicon oxide, aluminum oxide, aluminum fluoride and magnesium fluoride or a mixture of at least two of silicon oxide, aluminum oxide, aluminum fluoride and magnesium fluoride;
• each of the first, second and third multilayer films does not have a layer containing a composition comprising at least one of elements titanium (Ti), tantalum (Ta), hafnium (Hf), zirconium (Zr), niobium (Nb), molybdenum (Mo) and chromium (Cr),
• a layer of the fourth multilayer functional film closest to a base material comprises the non-high refractive index layer;
• the fourth multilayer functional film is configured such that a wavelength λmax(2) at which reflectivity at vertical incidence of the fourth multilayer film has a maximum value and a wavelength λmin(2) at which reflectivity at vertical incidence of the fourth multilayer film has a minimum value respectively satisfy the following conditions:
• 350<λmax(2)<420
• 600<λmin(2)<750;
• and
• the fourth multilayer functional film is configured such that the reflectivity of the fourth multilayer functional film at vertical incidence decreases monotonously from the wavelength λmax(2) to the wavelength λmin(2).

An objective lens that converges a laser beam from an optical element onto a recording layer of an optical disc, wherein a wavelength λ (unit:

• nm) of the laser beam falls within a range 390<λ<420, the optical element and the objective lens comprise same or different resin materials having a glass transition temperature Tg, such that Tg>115° C., multilayer functional films provided on a light source side surface and on an optical disc side surface of the optical element the objective lens comprising
• a first multilayer functional film, a second multilayer functional film and a third multilayer functional film are provided on an optical disc side optical surface of the objective lens, a light source side optical surface of the optical element, and an optical disc side optical surface of the optical element, respectively;
• a light source side optical surface of the objective lens opposite to the optical disc side optical surface of the objective lens is provided with a fourth multilayer functional film having four or more layers;
• the fourth multilayer functional film does not contain titanium (Ti);
• each of the first, second and third multilayer functional films includes a non-high refractive index layer comprising a composition containing one of silicon oxide, aluminum oxide, aluminum fluoride and magnesium fluoride or a mixture of at least two of silicon oxide, aluminum oxide, aluminum fluoride and magnesium fluoride;
• each of the first, second and third multilayer films does not have a layer containing a composition comprising at least one of elements, of titanium (Ti), tantalum (Ta), hafnium (Hf), zirconium (Zr), niobium (Nb), molybdenum (Mo) and chromium (Cr),
• a layer of the fourth multilayer functional film closest to a base material comprises the non-high refractive index layer;
• the fourth multilayer functional film is configured such that a wavelength λmax(2) at which reflectivity at vertical incidence of the fourth multilayer film has a maximum value and a wavelength λmin(2) at which reflectivity at vertical incidence of the fourth multilayer film has a minimum value respectively satisfy following conditions:
• 600<λmax(2)<420
• 600<λmin(2)<750;
• and
• the fourth multilayer functional film is configured such that the reflectivity of the fourth multilayer functional film at vertical incidence decreases monotonously from the wavelength λmax(2) to the wavelength λmin(2).