Abstract: An object of the invention is to improve the quality of a servo signal and a reproduction signal. Shape-wise thicknesses tr1, tr2, . . . , and trN of a cover layer and first through (N?1)-th intermediate layers of an optical recording medium having refractive indexes nr1, nr2, . . . , and nrN are converted into thicknesses t1, t2, . . . , and tN of the respective layers having a predetermined refractive index “no” which makes a divergent amount equal to a divergent amount of a light beam resulting from the thicknesses tr1, tr2, . . . , and trN, a difference DFF between the sum of a thickness “ti” through a thickness “tj”, and the sum of a thickness “tk” through a thickness “tm” is set to 1 ?m or more (where i, j, k, and m are each any positive integer satisfying i?j<k?m?N), and the thicknesses t1, t2, . . . , and tN are calculated by products of a function f(n) expressed by the following formula (1), and the thicknesses tr1, tr2, . . . , and trN: f(n)=?1.088n3+6.1027n2?12.042n+9.

Abstract: An optical head device compatible to different types of optical discs and capable of guaranteeing a sufficiently wide dynamic range for a low density optical disc, and the like are provided. The optical head device includes a plurality of light sources switchably usable; an objective lens for converging light emitted from one of the plurality of light sources to an information recording layer of an optical disc; and a light detector for receiving the light reflected by the information recording layer and outputting an electric signal based on the amount of the received light. The plurality of light sources include a first light source for emitting light having a first wavelength and a second light source for emitting light having a second wavelength shorter than the first wavelength.

Abstract: An object of the present invention is to reduce the influence of a stray light incident on a light receiving device by reflection of an unnecessary diffraction light not contributing to write or read on a disc surface at write or read of an optical disc having a large surface reflectivity with respect to an information recording surface. A position in which a diffraction light with an n-order in an advancing path and the n-order in a returning path, reflected on the information recording surface of a first information recording medium, is focused by a condensing lens is different from a position in which a diffraction light different from the n-order diffraction light in at least one of the advancing path and the returning path, reflected on a surface of the first information recording medium, is focused by the condensing lens.

Abstract: In the present invention, at the time of pulling a focus on an information recording surface of a disc, a focus servo is first pulled in a disc surface of the disc, and with the servo in a settled state, a driving signal necessary for following surface wobble is stored, and a focus is pulled in the information recording surface of the disc based upon a signal superimposed with the driving signal and a focus search driving signal.

Abstract: A complex objective lens composed of a hologram and an objective lens, capable of realizing stable and high-precision compatible reproducing/recording of a BD with a base thickness of about 0.1 mm for a blue light beam (wavelength ?1) and a DVD with a base thickness of about 0.6 mm for a red light beam (wavelength ?2). In an inner circumferential portion of the hologram, a grating is formed, which has a cross-sectional shape including as one period a step of heights in the order of 0 time, twice, once, and three times a unit level difference that gives a difference in optical path of about one wavelength with respect to a blue light beam, from an outer peripheral side to an optical axis side. The hologram transmits a blue light beam as 0th-order diffracted light without diffracting it, and disperses a red light beam passing through an inner circumferential portion as +1st-order diffracted light and allows it to be condensed by an objective lens.

Abstract: An objective lens unit according to the present invention includes a first objective lens 41; and a first lens holder 2 for supporting the first objective lens 41. The first lens holder 2 is formed of a material which transmits ultraviolet. Preferably, the first lens holder 2 includes a through-hole, having first and second openings 2a and 2b, through which light incident on the first objective lens 41 passes, and an opening limiting section 3 provided along a circumferential direction of the through-hole and projecting toward a central axis of the through-hole. The first objective lens 41 is supported so as to block the first opening 2b. The opening limiting section 3 guides light incident thereon from the second opening 2a in a direction away from an optical axis of the first objective lens.

Abstract: An objective lens unit according to the present invention includes a first objective lens 41; and a first lens holder 2 for supporting the first objective lens 41. The first lens holder 2 is formed of a material which transmits ultraviolet. Preferably, the first lens holder 2 includes a through-hole, having first and second openings 2a and 2b, through which light incident on the first objective lens 41 passes, and an opening limiting section 3 provided along a circumferential direction of the through-hole and projecting toward a central axis of the through-hole. The first objective lens 41 is supported so as to block the first opening 2b. The opening limiting section 3 guides light incident thereon from the second opening 2a in a direction away from an optical axis of the first objective lens.

Abstract: An objective lens unit according to the present invention includes a first objective lens 41; and a first lens holder 2 for supporting the first objective lens 41. The first lens holder 2 is formed of a material which transmits ultraviolet. Preferably, the first lens holder 2 includes a through-hole, having first and second openings 2a and 2b, through which light incident on the first objective lens 41 passes, and an opening limiting section 3 provided along a circumferential direction of the through-hole and projecting toward a central axis of the through-hole. The first objective lens 41 is supported so as to block the first opening 2b. The opening limiting section 3 guides light incident thereon from the second opening 2a in a direction away from an optical axis of the first objective lens.

Abstract: A highly reliable optical pickup which is not likely to collide with an optical disk is provided. Relative positions of two objective lenses 100 and 101 (along a focus direction) on a lens holder 102 are determined so that, while the objective lens 101 having a longer working distance is focused on an optical disk 200, the objective lens 100 having a shorter working distance and a protective member 103 are at positions which are more distant from the optical disk 200 than a height h of a protrusion which is present in an inner peripheral region of the optical disk optical disk 200.

Abstract: An optical head for recording or reproducing a signal on or from an optical recording medium including a light source, an objective lens for condensing light emitted from the light source to the optical recording medium, and a light-separating device arranged between the light source and the objective lens in order to separate the light reflected from the optical recording medium from the light emitted from the light source. The light-separating device includes a first glass, a multilayer film formed on the first glass, and an adhesive layer arranged on the multilayer film in order to bond a second glass onto the multilayer film. The majority of the light emitted from the light source enters into the light-separating device through the first glass and is reflected by the multilayer film.

Abstract: An objective lens for converging light onto a recording surface of an optical information recording medium in order to perform at least one of recording, reproduction and deletion of information on the optical information recording medium. The objective lens is a bi-convex single lens having at least one aspheric surface, and satisfies the following conditions: 0.8<R1/r1<0.85 and 0.9<d/f<1.1. Here, a numerical aperture NA on the optical information recording medium side of the objective lens satisfies NA?0.85. R1 is a paraxial curvature radius [mm] on a light source side of the objective lens, r1 is an effective radius [mm] on a light source side of the objective lens, d is a thickness [mm] on the optical axis of the objective lens, and f is a focal length [mm] of the objective lens.

Abstract: A complex objective lens composed of a hologram and an objective lens, capable of realizing stable and high-precision compatible reproducing/recording of a BD with a base thickness of about 0.1 mm for a blue light beam (wavelength ?1) and a DVD with a base thickness of about 0.6 mm for a red light beam (wavelength ?2). In an inner circumferential portion of the hologram, a grating is formed. The hologram transmits a blue light beam as 0th-order diffracted light without diffracting it, and disperses a red light beam passing through an inner circumferential portion as +1st-order diffracted light and allows it to be condensed by an objective lens. Because of this, the focal length of the red light beam becomes longer than that of the blue light beam, whereby a working distance is enlarged.

Abstract: An optical recording medium having three or more information recording layers reduces crosstalk caused by multi-reflected beams and improves signal quality. In the optical recording medium having three or more information recording layers, the refractive index of a plurality of intermediate layers disposed between adjacent information recording layers is greater than the refractive index of a cover layer disposed between a light incident surface and an information recording layer being the closest from the light incident surface.

Abstract: An object of the invention is to provide an optical recording medium and an optical information device that enable to improve the quality of a servo signal and a reproduction signal.

Abstract: An object of the invention is to provide an optical recording medium and an optical information device that enable to improve the quality of a servo signal and a reproduction signal.

Abstract: An optical head includes a laser light source of emitting laser, an objective lens which focuses the laser emitted from the laser light source on an optical recording medium and an optical element placed between the light source and the optical recording medium, of which the transmittance varies depending on a voltage applied. The voltage applied to the optical element is switched so that the optical element has a lower transmittance upon reproducing a signal on the optical recording medium than upon recording a signal on the optical recording medium, at times when recording a signal on the optical recording medium and when reproducing a signal on the optical recording medium.

Abstract: A complex objective lens composed of a hologram and an objective lens, capable of realizing stable and high-precision compatible reproducing/recording of a BD with a base thickness of about 0.1 mm for a blue light beam (wavelength ?1) and a DVD with a base thickness of about 0.6 mm for a red light beam (wavelength ?2). In an inner circumferential portion of the hologram, a grating is formed, which has a cross-sectional shape including as one period a step of heights in the order of 0 time, twice, once, and three times a unit level difference that gives a difference in optical path of about one wavelength with respect to a blue light beam, from an outer peripheral side to an optical axis side. The hologram transmits a blue light beam as 0th-order diffracted light without diffracting it, and disperses a red light beam passing through an inner circumferential portion as +1st-order diffracted light and allows it to be condensed by an objective lens.

Abstract: An adhesive positions a beam shaping element in such a manner as to satisfy the following relational expressions (1) and (2): 0<L??WA/(?·?·SAS)??(1) SAS=1000(0.5 m2+1.5m?2)[m?/mm]??(2), if it is assumed that m is the beam shaping magnification of a beam shaping element, L[mm] is the distance from a light source side surface of the beam shaping element to a center position of the adhesive, ?[1/K] is the linear expansion coefficient of a light source retaining holder, ?WA[m?] is amount of astigmatic aberration caused by the beam shaping element, and ?T[K] is an environmental temperature variation amount.

Abstract: An object of the invention is to improve the quality of a servo signal and a reproduction signal. Shape-wise thicknesses tr1, tr2, . . . , and trN of a cover layer and first through (N?1)-th intermediate layers of an optical recording medium having refractive indexes nr1, nr2, . . . , and nrN are converted into thicknesses t1, t2, . . . , and tN of the respective layers having a predetermined refractive index “no” which makes a divergent amount equal to a divergent amount of a light beam resulting from the thicknesses tr1, tr2, . . . , and trN, a difference DFF between the sum of a thickness “ti” through a thickness “tj”, and the sum of a thickness “tk” through a thickness “tm” is set to 1 ?m or more (where i, j, k, and m are each any positive integer satisfying i?j<k?m?N), and the thicknesses t1, t2, . . . , and tN are calculated by products of a function f(n) expressed by the following formula (1), and the thicknesses tr1, tr2, . . . , and trN: f(n)=?1.088n3+6.1027n2?12.042n+9.

Abstract: An optical pickup device which can improve heat radiation efficiency and an optical disk apparatus including the optical pickup device are provided. The optical pickup device having a base (110), a laser unit (141), an optical system (140) which propagates a laser beam, and an adjusting member (142) includes a heat radiation part (146) which is fixed to a heat radiation surface (141b) of the laser unit and which conducts heat from the heat radiation surface to the adjusting member. Therefore, heat generated by the laser unit is transmitted to the adjusting member and then the base through the heat radiation part to make it possible to efficiently perform heat removal for the laser unit.