Object lens for optical pickup and method for designing the same
First Claim
1. An object lens for an optical pickup, said object lens being of finite conjugate type for use in an optical pickup having a unit, in which a semiconductor laser diode array including light emitting portions for respectively emitting light of different wavelengths, a photo detector and said object lens are integrated so that a relative positional relationship between said object lens and said semiconductor laser diode array is fixed, and capable of recording data in and reproducing data from a first optical recording medium and a second optical recording medium respectively having recording faces at different heights,optical paths from said light emitting portions for respectively emitting light of different wavelengths to the object lens being the same regardless of wavelength,a distance from the light outgoing face of the object lens to the surface of said first and second optical recording mediums in an optical system being changed by moving said unit entirely, andcurvatures and aspheric coefficients of said object lens being defined so that said object lens has a plurality of numerical apertures to be changed in accordance with switching between said different wavelengths, whereby allowing said laser beam to be focused on said first optical recording medium or said second optical recording medium.
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Accused Products
Abstract
An optical pickup records data in or reproduces data from optical recording media respectively having recording faces at different heights, and includes a semiconductor laser diode array having light emitting portions for respectively emitting laser beams of different wavelengths. A finite conjugate type object lens used in this optical pickup is designed so that the numerical aperture of the object lens can be controlled to be changed in accordance with switching between the different wavelengths for allowing a laser beam to be focused on each optical recording medium.
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Citations
7 Claims
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1. An object lens for an optical pickup, said object lens being of finite conjugate type for use in an optical pickup having a unit, in which a semiconductor laser diode array including light emitting portions for respectively emitting light of different wavelengths, a photo detector and said object lens are integrated so that a relative positional relationship between said object lens and said semiconductor laser diode array is fixed, and capable of recording data in and reproducing data from a first optical recording medium and a second optical recording medium respectively having recording faces at different heights,
optical paths from said light emitting portions for respectively emitting light of different wavelengths to the object lens being the same regardless of wavelength, a distance from the light outgoing face of the object lens to the surface of said first and second optical recording mediums in an optical system being changed by moving said unit entirely, and curvatures and aspheric coefficients of said object lens being defined so that said object lens has a plurality of numerical apertures to be changed in accordance with switching between said different wavelengths, whereby allowing said laser beam to be focused on said first optical recording medium or said second optical recording medium.
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5. A method for designing an object lens for an optical pickup,
said object lens being of finite conjugate type for use in an optical pickup having a unit, in which a semiconductor laser diode array including light emitting portions for respectively emitting light of different wavelengths, a photo detector and said object lens are integrated so that a relative positional relationship between said object lens and said semiconductor laser diode array is fixed, and capable of recording data in or reproducing data from a first optical recording medium and a second optical recording medium respectively having recording faces at different heights, wherein a distance from the light outgoing face of the object lens to the surface of said first and second optical recording mediums in an optical system being changed by moving said unit entirely, and in a condition where optical paths from said light emitting portions for respectively emitting light of different wavelengths to the object lens are the same regardless of wavelength, curvatures and aspheric coefficients of said object lens are defined so that said object lens has a plurality of numerical apertures to be changed in accordance with switching between said different wavelengths for allowing said laser beam to be focused on said first optical recording medium or said second optical recording medium.
Specification