Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
2000-03-28
2003-11-18
Tran, Thang V. (Department: 2653)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C369S044230, C369S044370
Reexamination Certificate
active
06650612
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an optical head provided with a plurality of light sources including a short-wavelength laser source (for emitting a beam with a wavelength between 350 nm and 500 nm), which is used for recording and/or reproduction of an information recording medium such as an optical disk. The present invention also relates to a recording and reproduction method of recording and/or reproduction of an information recording medium using a plurality of light sources including a short-wavelength laser source.
BACKGROUND OF THE INVENTION
FIG. 13
is a structural view of a conventional optical head using a short-wavelength laser source. As a light source used for recording and reproduction of an information recording medium, a short-wavelength laser source (for emitting a beam with a wavelength of 425 nm) is used, which includes a semiconductor laser (for emitting a beam with a wavelength of 850 nm) and an SHG (Second Harmonic Generation) element for shortening the wavelength of an incident beam to half by generating second harmonics. As shown in the figure, a laser beam
103
emitted from a light source including a semiconductor laser
101
and an SHG element
102
for shortening the wavelength of the laser beam emitted from the semiconductor laser
101
to half is converted into parallel light by a collimate lens
104
, which is reflected to an information recording medium
109
side by a mirror
106
for guiding light upward and is converted into circularly polarized light by a ¼ wave plate
107
. After that, the circularly polarized light is focused on an information recording surface
110
of the information recording medium
109
by an objective lens
108
. Then, reflected light from the information recording surface
110
is converted into linearly polarized light whose polarization direction is perpendicular to a polarization direction of the laser beam
103
in an incoming path (a path from the light source to the information recording surface
110
) by the
¼ wave plate 107, which is then reflected by a polarization be am splitter 105. After that, the reflected light enters a detection lens 111 and is focused on receiving optics 112, thus detecting a signal.
In a conventional optical head for recording and reproducing a high-density information recording medium using a short-wavelength laser source for emitting a beam with a short wavelength within a range between 350 nm and 500 nm, when a beam with a wavelength of red light and a beam with an infrared wavelength enter the same optical system including an objective lens, an aberration occurs due to chromatic dispersion caused by the material of the objective lens with respect to the beams with such wavelengths. Therefore, with respect to DVDs (with an operating wavelength of about 650 nm), DVD-Rs (with an operating wavelength of about 650 nm), CDs (with an operating wavelength of about 800 nm), CD-Rs (with an operating wavelength of about 800 nm) and CD-RWs (with an operating wavelength of about 800 nm) that use such wavelengths, information cannot be recorded and/or reproduced using the same optical system as that in the above-mentioned optical head, which has been a problem.
SUMMARY OF THE INVENTION
The present invention is intended to solve the above-mentioned problem and to provide an optical head that can record and/or reproduce information using the same optical system with respect to a plurality of information recording media with different specifications employing different operating wavelengths, such as high-density disks (with an operating wavelength of about 350 nm-500 nm), DVDs, DVD-Rs, CDs, CDRs, CD-RWs, and the like. Particularly, the present invention aims to provide a small optical head that is provided with a light source for emitting light with a wavelength between 350 nm and 500 nm and at least one of light sources for emitting light with a wavelength between 600 nm and 700 nm and for emitting light with a wavelength between 700 nm and 900 nm and enables excellent property of focusing the respective lights to be obtained using a common single optical system. The present invention also is intended to provide a recording and reproduction method in which, with respect to a plural kinds of information recording media with different operating wavelengths, information can be recorded and/or reproduced using an optical head provided with a plurality of light sources for emitting lights with different wavelengths and a common single optical system.
In order to achieve the aforementioned objects, the present invention employs the following configurations.
An optical head according to a first configuration of the present invention includes: a first light source for emitting light with a first wavelength; a second light source for emitting light with a second wavelength longer than the first wavelength; and an objective lens for focusing the light with the first wavelength and the light with the second wavelength on information recording surfaces of information recording media corresponding to the lights with the respective wavelengths. The objective lens is designed so as to reduce aberration with respect to the light with the first wavelength. An optical-path length from the second light source to the objective lens is shorter than that from the first light source to the objective lens so that aberration caused by the objective lens due to chromatic dispersion caused by a material of the objective lens is reduced with respect to the light with the second wavelength.
By setting both the optical-path lengths as described above, the aberration caused by the objective lens with respect to the light with the second wavelength can be reduced, thus improving the property of focusing the light with the second wavelength. Therefore, using the same optical system, recording and/or reproduction can be carried out with respect to an information recording medium corresponding to the second wavelength in addition to an information recording medium corresponding to the first wavelength. Furthermore, since a common optical system can be used, the optical head can be simplified in configuration and can be reduced in size.
An optical head according to a second configuration of the present invention includes: a first light source for emitting light with a first wavelength; a second light source for emitting light with a second wavelength longer than the first wavelength; and an objective lens for focusing the light with the first wavelength and the light with the second wavelength on information recording surfaces of information recording media corresponding to the lights with the respective wavelengths. The objective lens is designed so as to reduce aberration with respect to the light with the second wavelength. An optical-path length from the first light source to the objective lens is longer than that from the second light source to the objective lens so that aberration caused by the objective lens due to chromatic dispersion caused by a material of the objective lens is reduced with respect to the light with the first wavelength.
By setting both the optical-path lengths as described above, the aberration caused by the objective lens with respect to the light with the first wavelength can be reduced, thus improving the property of focusing the light with the first wavelength. Therefore, using the same optical system, recording and/or reproduction can be carried out with respect to an information recording medium corresponding to the first wavelength in addition to an information recording medium corresponding to the second wavelength. Furthermore, since a common optical system can be used, the optical head can be simplified in configuration and can be reduced in size.
An optical head according to a third configuration of the present invention includes: a first light source for emitting light with a first wavelength; a second light source for emitting light with a second wavelength longer than the first wavelength; a third light source for emitting light with a third wavel
Kasazumi Ken'ichi
Matsuzaki Keiichi
Saimi Tetsuo
Shiono Teruhiro
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
Tran Thang V.
Vuong Bach
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