 Objective lens for optical pick-up head of optical disk drive |
| It is therefore the principle object of the present invention to provide an objective lens for ... |
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| Optical head |
| For solving the problem of the prior art, an optical head of the present invention comprises, light ... |
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| Compound objective lens having two focal points |
| A first object of the present invention is to provide, with due consideration to the drawbacks of ... |
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| Polarizing plate and liquid-crystal display containing the same |
| What is claimed is: 1. A polarizing plate comprising: a protective film, 5 to 150 μm thick, ... |
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| Polarization independent wavelength tunable filter based on birefringence compensation |
| It is an object of the present invention to provide a tunable, polarization independent wavelength ... |
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| Wavelength division multiplexer and demultiplexer |
| This invention is based on the observation that many filters have the characteristic property that ... |
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| Tunable filtering device for optical communications |
| To solve the above problems, it is an objective of the present invention to provide a tunable ... |
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| Wavelength selection switches for optical application |
| This invention is based on the observation that, by making use of filters that selectively passes ... |
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Compound objective lens having two focal points
| Details |
Inventors: Komma, Yoshiaki; Mizuno, Sadao; Nishino, Seji;
Assignee: Matsushita Electric Industrial Co., Ltd. (Osaka, JP)
Primary Examiner: Lerner; Martin
Assistant Examiner:
Attorney, Agent or Firm: Lowe, Price, Leblanc & Becker
A compound objective lens is composed of a hologram lens for transmitting a part of incident light without any diffraction to form a beam of transmitted light and diffracting a remaining part of the incident light to form a beam of first-order diffracted light, and an objective lens for converging the transmitted light to form a first converging spot on a front surface of a thin type of first information medium and converging the diffracted light to form a second converging spot on a front surface of a thick type of second information medium. Because the hologram lens selectively functions as a concave lens for the diffracted light, a curvature of the transmitted light differs from that of the diffracted light. Therefore, even though the first and second information mediums have different thicknesses, the transmitted light incident on a rear surface of the first information medium is converged on the its front surface, and the diffracted light incident on a rear surface of the second information medium is converged on the its front surface. That is, the compound objective lens has two focal points. |
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DETAILED DESCRIPTION A first object of the present invention is to provide, with due consideration to the drawbacks of such a conventional objective lens having a focal point, a compound objective lens having two focal points.
A second object of the present invention is to provide an imaging optical system having the compound objective lens in which light transmitting through the compound objective lens is converged at a diffraction limit on two converging spots placed at different depths of an information medium.
A third object of the present invention is to provide an optical head apparatus having the imaging optical system in which information is recorded, reproduced or erased on or from one of the converging spots of the information medium at which light is converged by the action of the imaging optical system.
A fourth object of the present invention is to provide a high density optical disk in which a series of first recording pits is formed to record pieces of information at high density on a thin substrate.
A fifth object of the present invention is to provide an optical disk apparatus in which information is recorded or reproduced on or from the optical disk with the compound objective lens regardless of whether a series of recording pits expressing pieces of information is recorded or reproduced on or from the high density optical disk having a thin thickness or a conventional compact disk having an ordinary thickness.
A sixth object of the present invention is to provide a binary focus microscope having two focal points in which two types of images drawn at different depths are simultaneously observed.
A seventh object of the present invention is to provide an alignment apparatus in which two types of images drawn at different depths are aligned with the binary focus microscope.
An eighth object of the present invention is to provide a focusing method for focusing light on an information medium with the optical head apparatus.
A ninth embodiment of the present invention is to provide an information reproducing method for reproducing a piece of recording information recorded on a high density optical disk having a thin thickness
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Optical Systems 
