US4927247A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Objective lens for optical disk system and optical head using the same
Assignee: Panasonic Holdings Corp
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Filing: 1989-04-26
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Granted: 1990-05-22
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Expires: 2009-04-26
Abstract
Abstract A lens controls the chromatic aberration of an objective lens for practical use in an optical disk system. The lens has first and second aspherical surfaces each providing a positive refractive power for focusing a light through a transparent plate and satisfies a condition: ##EQU1## where f L =focal length of the lens, d c =thickness of the transparent plate, n c =refractive index of the transparent plate, λ=center wavelength of the light, NA=numerical apperture of the lens, ν L =local dispersion of the lens, and ν c =local dispersion of the transparent plate. The local dispersion of each element is expressed by: ##EQU2## where n 80 is refractive index at a center wavelength λ nm, n.sub.λ +5 a refractive index at λ+5 nm, and n.sub.λ -5 a refractive index at λ-5 nm.
Inventors
- 👤 Yasuhiro Tanaka
- 👤 Masaaki Sunohara
- 👤 Yasuo Nakajima
- 👤 Shinichi Tanaka
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-08 16:06
CPC Classifications
G; G11; G11B; G11B7/00; G11B7/12; G11B7/135; G11B7/1372; G11B7/1374; G01; G01B; G01B13/00; G01B13/24; G02; G02B; G02B13/00; G02B13/08; G02B13/10; G02B13/24; G11B19/00; G11B19/02; G11B19/12
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
155 words
An objective lens for an optical disk system, having opposite first and second aspherical surfaces each providing a positive refractive power for focusing a light to form a light spot through a transparent plate, and satisfying substantially the following condition: ##EQU14## where, f L : focal length of the lens, d c : thickness of the transparent plate, n c : refractive index of the transparent plate, λ: center wavelength of the light, NA: numerical appertures of the lens, ν L : local dispersion of the lens, and ν c : local dispersion of the transparent plate, the local dispersion being expressed by: ##EQU15## where n.sub.λ is a refractive index at a center wavelength λ of the light, n.sub.λ+5 is a refractive index at a wavelength 5 nm longer than the center wavelength of the light, and n.sub.λ-5 is a refractive index at a wavelength 5 nm shorter than the center wavelength of the light.
Claim 2
Dependent Claim
155 words
An objective lens for an optical disk system, having opposite first and second aspherical surfaces each providing a positive refractive power for focusing a light to form a light spot through a transparent plate, and satisfying substantially the following condition: ##EQU14## where, f L : focal length of the lens, d c : thickness of the transparent plate, n c : refractive index of the transparent plate, λ: center wavelength of the light, NA: numerical appertures of the lens, ν L : local dispersion of the lens, and ν c : local dispersion of the transparent plate, the local dispersion being expressed by: ##EQU15## where n.sub.λ is a refractive index at a center wavelength λ of the light, n.sub.λ+5 is a refractive index at a wavelength 5 nm longer than the center wavelength of the light, and n.sub.λ-5 is a refractive index at a wavelength 5 nm shorter than the center wavelength of the light.
Claim 3
Dependent Claim
23 words
An objective lens as defined in claim 1, wherein a distance between the lens and the transparent plate is at least 0.7 mm.
Claim 4
Dependent Claim
20 words
An objective lens as defined in claim 1, wherein the thickness of the transparent plate is at least 0.8 mm.
Claim 5
Dependent Claim
204 words
An optical head comprising: an objective lens for focusing a light from a light source on an information recording medium; light separator means for separating a light reflected from the information recording medium and passed through the objective lens from the light from the light source; and photo-detecting means for detecting the separated reflected light, the objective lens having opposite first and second aspherical surfaces each providing a positive refraction for focusing the light through a transparent substrate of the recording medium and satisfying substantially the following condition: ##EQU16## where, f L : focal length of the lens, d c : thickness of the transparent substrate, n c : refractive index of the transparent substrate, λ: center wavelength of the light. NA: numerical of appertures of the lens, ν L : local dispersion of the lens, and ν c : local dispersion of the transparent substrate, the local dispersion being expressed by: ##EQU17## where n.sub.λ is a refractive index at a center wavelength λ of the light, n.sub.λ+5 is a refractive index at a wavelength 5 nm longer than the center wavelength of the light, and n.sub.λ-5 is a refractive index at a wavelength 5 nm shorter than the center wavelength of the light.
Claim 6
Dependent Claim
204 words
An optical head comprising: an objective lens for focusing a light from a light source on an information recording medium; light separator means for separating a light reflected from the information recording medium and passed through the objective lens from the light from the light source; and photo-detecting means for detecting the separated reflected light, the objective lens having opposite first and second aspherical surfaces each providing a positive refraction for focusing the light through a transparent substrate of the recording medium and satisfying substantially the following condition: ##EQU16## where, f L : focal length of the lens, d c : thickness of the transparent substrate, n c : refractive index of the transparent substrate, λ: center wavelength of the light. NA: numerical of appertures of the lens, ν L : local dispersion of the lens, and ν c : local dispersion of the transparent substrate, the local dispersion being expressed by: ##EQU17## where n.sub.λ is a refractive index at a center wavelength λ of the light, n.sub.λ+5 is a refractive index at a wavelength 5 nm longer than the center wavelength of the light, and n.sub.λ-5 is a refractive index at a wavelength 5 nm shorter than the center wavelength of the light.
Claim 7
Dependent Claim
24 words
An optical head as defined in claim 4, wherein a distance between the objective lens and the transparent substrate is at least 0.7 mm.
Claim 8
Dependent Claim
20 words
An optical head as defined in claim 4, wherein the thickness of the transparent substrate is at least 0.8 mm.
Claim 9
Dependent Claim
26 words
An optical head as defined in claim 4, further comprising a collimator means for arranging the light irradiated from the light source into a parallel light.
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