Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
2001-05-24
2004-10-26
Huber, Paul W. (Department: 2653)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C369S112110
Reexamination Certificate
active
06810001
ABSTRACT:
BACKGROUND
1. Field
This patent specification relates to an optical pickup apparatus which records/reproduces data on different kinds of optical recording media by using selectively laser light of different wavelengths.
2. Discussion of Related Art
In a pickup apparatus, a laser light from a laser diode is incident onto a signal recording surface of an optical recording medium by way of, for example, a hologram device, and light reflected from the signal recording surface is detected by a photodetection device by way of the hologram device, thereby recording/reproducing on an optical recording medium such as DVD or CD. The laser light is controlled to maintain an optimum level by monitoring an output level of the laser light in order to record/reproduce stably.
Therefore, conventionally, as illustrated in
FIG. 9
, a photodetection device for monitor
8
is arranged on an optical path in an optical pickup apparatus, and an output level of a laser light emitted from a laser diode
1
is detected by a photodetection device for monitor
8
and the control is performed on the basis of a detected value so that the laser light can be maintained at an optimum level. Numeral
3
is a hologram device and numeral
4
is a collimator lens.
However, in this method, a photodetection device for monitor
8
in addition to a photodetection device for the main signal needs to be arranged. The photodetection device for monitor
8
needs to fit in a limited space, thus complicating the design and, moreover, a detection amount of the photodetection device for monitor
8
changes greatly by inaccuracies in its positioning.
In order to deal with this problem, as illustrated in
FIG. 10
, a method for detecting the level of the laser light from the laser diode
1
is adopted such that a reflection hologram
9
is formed on the hologram device
3
, and the laser light from the laser diode
1
is reflected and diffracted by the reflection hologram
9
and is detected by a photodetection device
7
. In this method, the photodetection device for the main signal and the photodetection device for monitoring can be formed on one plate, and the number of devices is reduced and further the photodetection device is simply adjusted.
In this case, when laser light of different wavelengths (635 nm or 650 nm, and 780 nm) from the laser diode
1
and a laser diode
2
are used, the laser light of 635 nm or 650 nm from the laser diode
1
and the laser light of 780 nm from the laser diode
2
pass the hologram device
3
as illustrated in
FIG. 11A
, and a reflecting type-diffraction element
10
a
which reflects the laser light of 635 nm or 650 nm and a reflecting type-diffraction element
10
b
which reflects the laser light of 780 nm are formed.
(In this patent specification, the term “laser light” refers to a beam (or beams) of light emitted from a laser (of from lasers), reflected by an optical recording medium, and/or acted on by devices such as lenses, diffraction grantings, etc.
Each of the reflection light from the reflecting type-diffraction element
10
a
and the reflection light from the reflecting type-diffraction element
10
b
is guided to and detected on a photodetection element for monitor
7
m
formed in the photodetection device
7
, and the output levels of the laser light from the laser diodes
1
and
2
can be monitored respectively.
When the output levels of laser light of the different wavelengths described above are monitored, the laser diodes
1
and
2
are spaced apart each other and the laser light emitted from a collimator lens
4
proceeds in a slant direction, and is incident to an objective lens slantingly, and thus aberration occurs in a spot formed on the optical recording medium
Therefore, the laser diodes
1
and
2
can be very close to each other, and still the emitted patterns from the laser diodes
1
and
2
on the surface of the hologram device
3
would be as illustrated in FIG.
11
A. Thus, for example, when the laser light
1
is illuminated, the laser light of 635 nm or 650 nm is emitted, however, the laser light is incident not only onto the reflecting type-diffraction element
10
a
but also the reflecting type-diffraction element
10
b
as illustrated in FIG.
11
B. Numeral
25
a
is a diffraction light from the diffraction element
10
a
and numeral
25
b
is a diffraction light from the diffraction element
10
b.
In this case, as illustrated in
FIG. 11C
, the reflection light from the reflecting type-diffraction device
10
a
forms a small spot
26
a
and focuses, and the output level of the laser light from the laser diode
1
can be detected. On the other hand, the reflection light from the reflecting type-diffraction element
10
b
becomes a large spot
26
b
before focusing on the photodetection device
7
, and is incident onto a different photodetection element
27
and thereby a flare light occurs. As a result, the detection accuracy of the output level of the laser light from the laser diode
1
can decrease.
SUMMARY
Accordingly, an object of this patent specification is to provide an optical pickup apparatus in the number of components devices is decreased and complicated adjustment is not necessary, and further output levels of laser light of plural wavelengths can be accurately monitored by suppressing flare light.
According to a preferred embodiment, an optical pickup apparatus for reading/reproducing data on an optical recording medium, includes a plurality of laser diodes configured to emit laser light of different wavelengths respectively, a photodetection device configured to detect each laser light, a diffraction type-optical device configured to transmit each laser light from the plurality of laser diodes to the optical recording medium, and to diffract each laser light from the optical recording medium to the photodetection device; and wherein the diffraction type-optical device includes a plurality of reflecting type-diffraction elements configured to reflect and diffract each laser light of a corresponding wavelength from the plurality of light diodes, to the photodetection device so that the photodetection device can detect each laser light of the corresponding wavelength to monitor each laser light, and a suppression setting device configured to set each of the plurality of reflecting type-diffraction elements to suppress reflection of laser light other than the laser light of the corresponding wavelength to the photodetection device.
Further, the suppression setting device sets each of the plurality of reflecting type-diffraction elements at a position such that only the laser light of the corresponding wavelength is diffracted.
Further, the suppression setting device sets each of the plurality of reflecting type-diffraction elements to enhance only diffraction efficiency of the laser light of the corresponding wavelength.
Further, the suppression setting device sets each of the plurality of reflecting type-diffraction elements to diffract only the laser light of the corresponding wavelength by suitably coating each of the plurality of reflecting type-diffraction elements.
Still further, the plurality of reflecting type-diffraction elements are formed on a surface in the diffraction type-optical device facing the optical recording medium, and coating is performed so as to transmit only the laser light of the corresponding wavelength, on a surface of a side of the laser diodes in the diffraction type-optical device.
According to another preferred embodiment, an optical pickup apparatus for reading/reproducing data on an optical recording medium, includes a plurality of laser diodes configured to emit laser light of different wavelengths respectively, a photodetection device configured to detect each laser light, a diffraction type-optical device configured to transmit each laser light from the plurality of laser diodes to the optical recording medium, and to diffract each laser light from the optical recording medium to the photodetection device, and wherein the diffraction type-optical device includes a reflecting type-diffraction elemen
Cooper & Dunham LLP
Huber Paul W.
Ricoh & Company, Ltd.
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