JP2008176916A5

JP2008176916A5 -

Info

Publication number: JP2008176916A5
Application number: JP2008010048A
Authority: JP
Filing date: 2008-01-21
Publication date: 2009-01-15
Anticipated expiration: 2021-10-02

Claims

A light source, a coupling lens for changing a divergence angle of diverging light emitted from the light source, and an objective lens for condensing a light beam through the coupling lens on an information recording surface via a transparent substrate of an optical information recording medium; An optical pickup device that records and / or reproduces information on the optical information recording medium by detecting reflected light from the recording surface,
The optical information recording medium has a structure in which a plurality of transparent substrates and information recording layers are alternately laminated on the same light incident surface side,
By changing the coupling lens in the direction of the optical axis, the variation in spherical aberration caused by the difference in the thickness of the transparent substrate from the light incident surface to each information recording layer is corrected,
The objective lens is a single lens having at least one aspheric surface,
An annular diffractive structure is formed on at least one surface of the objective lens,
The objective lens satisfies the following expression.
NA ≧ 0.7
5.0 ≦ fD / f ≦ 65.0
NA: a predetermined image-side numerical aperture necessary for recording and / or reproduction on an optical information recording medium,
fD: an optical path difference added to the transmitted wavefront by the diffractive structure formed on the i-th surface,
When expressed by an optical path difference function defined by Φ _bi = ni · (b _2i · hi ² + b _4i · hi ⁴ + b _6i · hi ⁶ +..., Where ni is diffraction order of the diffracted ray having the maximum diffracted light among diffracted light generated in the formed diffractive structure, hi is the height from the optical axis _{(mm), b 2i, b} 4i, b 6i, ··· each 2nd order, 4th order, 6th order,... Optical path difference function coefficients (also referred to as diffraction plane coefficients)),
Focal length (mm) of only the diffractive structure defined by fD = 1 / Σ (−2 · ni · b _2i )
f: Focal length (mm) of the entire objective lens system combining the refractive power and the diffraction power of the diffraction structure

The optical pickup device according to claim 1, wherein:
5.0 ≦ fD / f ≦ 40.0

The optical pickup device according to claim 1, wherein the following expression is satisfied.
0.03 ≦ λ · f · Σ (ni / (Mi · Pi ²² )) ≤ 0.70
Where ni is the order of the diffracted light having the maximum amount of diffracted light among the diffracted light generated in the diffractive structure formed on the i-th surface in the diffractive structure,
Mi: the number of annular zones of the diffractive structure formed on the i-th surface,
Pi: the minimum value (mm) of the annular interval of the diffractive structure formed on the i-th surface,
f: Focal length (mm) of the entire objective lens system,
λ: Wavelength used (mm)

A light source, a coupling lens for changing a divergence angle of diverging light emitted from the light source, and an objective lens for condensing a light beam through the coupling lens on an information recording surface via a transparent substrate of an optical information recording medium; An optical pickup device that records and / or reproduces information on the optical information recording medium by detecting reflected light from the recording surface,
The optical information recording medium has a structure in which a plurality of transparent substrates and information recording layers are alternately laminated on the same light incident surface side,
By changing the coupling lens in the direction of the optical axis, the variation in spherical aberration caused by the difference in the thickness of the transparent substrate from the light incident surface to each information recording layer is corrected,
The objective lens is a single lens having at least one aspheric surface,
An annular diffractive structure is formed on at least one surface of the objective lens,
The objective lens satisfies the following expression.
NA ≧ 0.7
0.03 ≦ λ · f · Σ (ni / (Mi · Pi ²² )) ≤ 0.70
NA: a predetermined image-side numerical aperture necessary for recording and / or reproduction on an optical information recording medium,
ni: In the diffractive structure, of the diffracted light generated by the diffractive structure formed on the i-th surface, the order of the diffracted light having the maximum diffracted light amount,
Mi: the number of annular zones of the diffractive structure formed on the i-th surface,
Pi: the minimum value (mm) of the annular interval of the diffractive structure formed on the i-th surface,
f: Focal length (mm) of the entire objective lens system,
λ: Wavelength used (mm)

The optical pickup device according to claim 4, wherein the following expression is satisfied.
0.10 ≦ λ · f · Σ (ni / (Mi · Pi ²² )) ≤ 0.65

The optical pickup device according to claim 5, wherein:
0.20 ≦ λ · f · Σ (ni / (Mi · Pi ²² )) ≤ 0.60

The optical pickup device according to claim 1, wherein the objective lens is made of an optical plastic material.

The optical pickup device according to claim 7, wherein the optical plastic material is polyolefin.

The optical pickup device according to claim 1, wherein the following expression is satisfied.
λ ≦ 500nm
Where λ is the wavelength used for recording and / or reproduction on the optical information recording medium

The optical pickup device according to claim 1, wherein the objective lens satisfies the following expression.
0.35 <(X1-X2). (N-1) / (NA.f) <0.55
However,
X1: in the optical axis direction between the plane perpendicular to the optical axis and in contact with the apex of the surface on the light source side, and the surface on the light source side in the outermost periphery of the effective diameter (the position on the surface on the light source side where the NA marginal ray is incident) The difference (mm) is positive when measured in the direction of the optical information recording medium with the tangent plane as a reference, and negative when measured in the direction of the light source.
X2: an optical information recording medium in a plane perpendicular to the optical axis and in contact with the apex of the surface on the optical information recording medium side, and in the outermost periphery of the effective diameter (position on the surface on the optical information recording medium side where the NA marginal ray is incident) The difference (mm) in the optical axis direction with respect to the side surface is positive when measured in the direction of the optical information recording medium with the tangent plane as a reference, and negative when measured in the direction of the light source.
N: Refractive index at the working wavelength of the objective lens
f: Focal length (mm) of the entire system of the objective lens

The optical pickup device according to claim 10, wherein the objective lens satisfies the following expression.
0.39 <(X1-X2). (N-1) / (NA.f) <0.52.

The optical pickup device according to claim 1, wherein chromatic aberration of the objective lens satisfies the following expression.
│ △ fB ・ NA ²² │ ≦ 0.25μm
ΔfB: change in focal position of the objective lens when the wavelength of the light source is changed by +1 nm (μm)

The optical pickup device according to claim 1, wherein the objective lens satisfies the following expression.
−200 ≦ b _4i4i ・ Hi _maxmax ^4Four / (Λ · f · NA ^4Four ) ≤ -5
However,
b _4i4i : The optical path difference added to the transmitted wavefront by the diffractive structure formed on the i-th surface,
Φ _bibi = Ni · (b _2i2i ・ Hi ²² + B _4i4i ・ Hi ^4Four + B _6i6i ・ Hi ⁶⁶ (Where ni is the diffracted light having the largest amount of diffracted light among the diffracted light generated by the diffractive structure formed on the i-th surface). Diffraction order, hi is the height from the optical axis (mm), b _2i2i , B _4i4i , B _6i6i ,... Are second-order, fourth-order, sixth-order,... Optical path difference function coefficients (also referred to as diffraction plane coefficients), respectively.
hi _maxmax : Maximum height of effective diameter of i-th surface (mm)

The optical pickup device according to claim 1, wherein the objective lens satisfies the following expression.
0.4 ≦ | (Ph / Pf) −2 | ≦ 25.0
However, Pf: diffraction zone difference (mm) at a predetermined image-side numerical aperture required for recording and / or reproduction on an optical information recording medium
Ph: diffraction zone interval (mm) at a numerical aperture which is 1/2 of a predetermined image-side numerical aperture required for recording and / or reproducing on an optical information recording medium

The following expression is satisfied, where ΔSA (μm) is a change amount of spherical aberration of the marginal ray when the wavelength of the light source changes by +10 nm. Optical pickup device.
│ △ SA│ ≦ 1.5

When the diffractive action as a diffractive lens is combined with the refractive action as a refracting lens, it has an axial chromatic aberration characteristic such that when the wavelength of the light source is shifted to the longer wavelength side, the back focus changes in a shorter direction. The optical pickup device according to claim 1, wherein the following expression is satisfied.
-1 <ΔCA / ΔSA <0
However,
ΔCA: Amount of axial chromatic aberration change with wavelength change (mm)
ΔSA: Change amount of spherical aberration of marginal ray with respect to wavelength change (mm)

The optical pickup device according to claim 1, wherein the following expression is satisfied.
t ≦ 0.6mm
However,
t: thickness of the transparent substrate protecting the information recording surface of the optical information recording medium

The nth order diffracted light amount generated in the diffractive structure is larger than any other order diffracted light amount, and the objective lens is generated in the diffractive structure for recording and / or reproducing information on the optical information recording medium. The optical pickup device according to claim 1, wherein the next diffracted light can be condensed on an information recording surface of the optical information recording medium. Here, n is an integer other than 0 and ± 1.

Among the diffractive structures, the diffractive structure formed on at least one surface has a diffracted light quantity of the nth order diffracted light out of the diffracted light generated in the diffractive structure when n is an integer other than 0 and ± 1. 19. The step amount in the optical axis direction of each diffraction ring zone is determined so as to be larger than the diffracted light amount of any other order of diffracted light. 19. Optical pickup device.

The optical pickup device according to claim 1, wherein the objective lens is made of a material having a saturated water absorption rate of 0.5% or less.

21. The optical pickup device according to claim 1, wherein the objective lens is made of a material having an internal transmittance of 85% or more at a thickness of 3 mm in a use wavelength region.

2. The spherical aberration of the objective lens satisfies the following expression when the third-order spherical aberration component is SA1, and the sum of the fifth-order, seventh-order, and ninth-order spherical aberration components is SA2. The optical pick-up apparatus of any one of -21.
| SA1 / SA2 |> 1.0
However,
SA1: Third-order spherical aberration component when the aberration function is expanded into a Zernike polynomial
SA2: Square root of the square sum of fifth-order spherical aberration component, seventh-order spherical aberration component, and ninth-order spherical aberration component when the aberration function is expanded into a Zernike polynomial

The optical pickup device according to any one of claims 1 to 22, wherein the optical pickup device has a wavelength characteristic that changes in a direction in which a back focus is shortened when the wavelength is changed to a long wavelength side.

The optical pickup device according to any one of claims 1 to 23, wherein axial chromatic aberration is corrected.

25. The coupling lens according to any one of claims 1 to 24, wherein the coupling lens has a two-group configuration in which a positive lens having a relatively large Abbe number and a negative lens having a relatively small Abbe number are cemented. The optical pickup device according to Item.

The optical pickup device according to any one of claims 1 to 25, wherein the coupling lens is a single lens having a zonal diffraction structure on at least one surface.

27. The variation in spherical aberration caused by a minute variation in the oscillation wavelength of the light source is corrected by shifting the coupling lens along the optical axis direction. 2. An optical pickup device according to claim 1.

The objective lens is made of a plastic material,
28. The light according to claim 1, wherein the coupling lens corrects a variation in spherical aberration caused by a temperature change by moving along the optical axis direction. Pickup device.

The coupling lens corrects a variation in spherical aberration caused by a minute variation in a thickness of a transparent substrate of the optical information recording medium by moving along the optical axis direction. Item 30. The optical pickup device according to any one of Items 1 to 28.

When the spherical aberration fluctuates to the over side, the coupling lens shifts along the optical axis direction so as to increase the distance between the objective lens and the spherical aberration before the spherical aberration fluctuates. Is shifted to the under side, the coupling lens shifts along the optical axis direction so as to cause an interval with the objective lens as compared to before the spherical aberration fluctuates. 30. The optical pickup device according to claim 1, wherein fluctuations are corrected.

A sound and / or image recording device and / or a sound and / or image reproducing device comprising the optical pickup device according to any one of claims 1 to 30.