Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
2001-06-27
2003-11-04
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
C369S112050
Reexamination Certificate
active
06643245
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical head apparatus for reproducing or deleting information recorded on an optical medium such as an optical disk and an optical card, or recording information onto the optical medium. The present invention also relates to a light source apparatus and an optical element used in such an optical head apparatus. Furthermore, the present invention relates to an optical information processing apparatus including an optical head apparatus.
2. Description of the Related Art
In recent years, with the development of an optical disk, standards of various kinds of optical disks, such as recording/reproducing optical disks and read-only memory (ROM) optical disks, have been proposed and utilized. Various kinds of different laser beams are used often with respect to these optical disks. In such a circumstance, an optical head is proposed that has light sources with two wavelengths so that, in the same apparatus, information can be recorded onto/reproduced from different kinds of incompatible optical disks using different laser beams. Such a procedure is disclosed by Sadao Mizuno et al. “Optical head for Integrated DVD” (National Technical Report Vol. 43, No. 3, June, p. 275 (1997)). In such an optical head, it is required to dispose each light source point on a common optical axis.
As a procedure for realizing the above, optical axes of light beams from two light sources generally are aligned by a dichroic mirror. In order to simplify an optical system, a method for aligning optical axes using a diffraction element also is proposed (JP 11(1999)-110785 A, JP 10(1998)-320814 A, JP 10(1998)-326428A, and JP 10(1998)-319318 A). However, the diffraction element with the above-mentioned configuration generates not only diffracted light but also transmitted light, resulting in a light source with an unsatisfactory light utilization efficiency.
In order to solve the above-mentioned problem, a method using a polarization anisotropic hologram is proposed (JP 11(1999)-161996 A, JP 10(1998)-289468 A).
Hereinafter, a conventional light source and optical head apparatus will be described by illustrating JP 11(1999)-161996 A.
FIG. 16
shows a configuration of a conventional optical head apparatus. Two different semiconductor lasers are provided in a package
119
(described later) so as to emit light beams L
1
and L
2
with different wavelengths in an upward direction of the package
119
from different points. Furthermore, the light beams L
1
and L
2
are polarized so that their polarization directions are orthogonal to each other. The light (L
1
and L
2
) output from the package
119
is incident upon a polarization splitting hologram
120
. The polarization splitting hologram
120
diffracts light polarized in a particular direction, and transmits light polarized in a direction orthogonal to the particular direction. Herein, the polarization splitting hologram
120
is disposed so as to diffract the light beam L
2
and transmit the light beam L
1
.
The polarization splitting hologram
120
is designed so that the light beam L
2
is diffracted, and an apparent emission point of the diffracted light coincides with an emission point of the light beam L
1
. Thus, the optical axes of the light beams L
1
and L
2
are aligned. The resultant light is incident upon an objective lens
103
, and condensed onto a recording surface of an optical disk
350
by the objective lens
103
.
Next, light sources in the package
119
will be described with reference to
FIGS. 17A and 17B
.
FIG. 17A
is a plan view seen from an output direction of the package
119
, and
FIG. 17B
is a cross-sectional view in a plane of the package
119
substantially parallel to an optical axis. Semiconductor lasers
611
and
612
are provided in the package
119
, and respectively emit light beams L
1
and L
2
. The semiconductor lasers
611
and
612
are attached to the package
119
via holders
301
and
302
so that the polarization directions of emitted light beams are orthogonal to each other. Light beams emitted from the semiconductor lasers
611
and
612
are reflected in an upward direction of the package
119
by reflective mirrors
641
and
642
.
Because of the above-mentioned configuration, a high-efficiency two-wavelength optical head with optical axes aligned can be realized.
Furthermore, JP 11(1999)-161996 A discloses an optical head apparatus using, as the semiconductor lasers
611
and
612
, those which oscillate in different polarization directions and are disposed in the same direction. Even with the use of this technique, a high-efficiency two-wavelength optical head apparatus with optical axes aligned can be realized.
However, according to the method of JP 11(1999)-161996 A, it is required to mount the semiconductor lasers
611
and
612
in the package
119
in different directions so that polarization directions of two wavelengths are orthogonal to each other, which results in a complicated configuration and a high production cost.
Furthermore, according to the method using semiconductor lasers oscillating in different polarization directions and disposed in the same direction as disclosed in JP 10(1998)-289468 A, it is difficult to realize a semiconductor laser that oscillates stably in a TE mode, and the production cost thereof also is high.
SUMMARY OF THE INVENTION
Therefore, with the foregoing in mind, it is an object of the present invention to provide an inexpensive light source apparatus that generates two light beams with different wavelengths at a high efficiency. Another object of the present invention is to provide a low-cost optical element that is capable of generating two light beams with different wavelengths at a high efficiency. Still another object of the present invention is to provide an optical head apparatus and an optical information processing apparatus using such a light source apparatus. Still another object of the present invention is to provide a method for adjusting positions of emission points in such a manner that apparent positions of light sources of two light beams with different wavelengths are aligned with each other as desired.
In order to achieve the above-mentioned objects, the present invention has the following construction.
A light source apparatus according to a first construction of the present invention includes: a first light source for emitting light having a first wavelength and polarized in a first direction; a second light source for emitting light having a second wavelength different from the first wavelength and polarized in the first direction; a wavelength plate that functions substantially as a (2m+1)&lgr;/2 plate (m is an integer) with respect to light having the first wavelength, and functions substantially as a n&lgr; plate (n is an integer) with respect to light having the second wavelength; and a diffraction element that diffracts light polarized in the first direction and transmits light polarized in a second direction orthogonal to the first direction, wherein the wavelength plate converts light emitted from the first light source into light polarized in the second direction so as to transmit it, and transmits light emitted from the second light source without converting a polarization direction thereof, and the diffraction element diffracts light emitted from the second light source, passing through the wavelength plate, whereby the light emitted from the second light source, diffracted by the diffraction element, has an apparent emission point different from an emission point of the second light source. According to this construction, a light source apparatus can be provided at a low cost in a simple configuration, which is capable of emitting two light beams having different wavelengths with optical axes aligned at a high efficiency.
In the above-mentioned first light source apparatus, the apparent emission point of the light emitted from the second light source can be allowed to coincide with an emission point of the first light source. According
Hayashi Hideki
Kadowaki Shin-ichi
Yamamoto Hiroaki
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
Tran Thang V.
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