Dynamic information storage or retrieval – Condition indicating – monitoring – or testing – Including radiation storage or retrieval
Reexamination Certificate
1999-05-11
2002-10-08
Young, W. R. (Department: 2653)
Dynamic information storage or retrieval
Condition indicating, monitoring, or testing
Including radiation storage or retrieval
C369S112060, C369S112100, C369S112180, C369S112190, C369S118000
Reexamination Certificate
active
06463023
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical head and a method for monitoring a light source output in the optical head and, more particularly, to a smaller optical head capable of efficiently monitoring a light beam output such as a laser beam output supplied by a predetermined light source means.
2. Description of the Related Art
Hitherto, as shown in
FIGS. 1 and 2
, for example, an optical head has a structure wherein a light beam emitted from a semiconductor laser
1
, which is an example of a light source means, passes through a polarization beam splitter
2
to be split into a light beam reflected toward a collimating lens
7
and a light beam transmitted toward a power monitoring means
6
at a certain ratio of light amount before they are provided for use.
Disposed in a matrix on the surface of the power monitoring means
6
are arbitrary photodetecting elements
16
divided and defined in an appropriate number. The light beams that are reflected by a reflection surface
13
of the polarization beam splitter
2
and used for recording or reproducing information are, for example, irradiated onto an appropriate recording medium
12
via the collimating lens
7
retained by an appropriate lens holder
8
, a quarter wavelength plate
9
, a riser mirror
10
, and an object lens
11
.
The light beam reflected back from the recording medium
12
passes through the reflection surface of the polarization beam splitter
2
and enters a predetermined signal detection sensor
14
via a condensing lens
15
.
In the optical head having the structure described above, a luminous flux A representing the whole amount of light emitted from the semiconductor laser
1
is not directed toward the collimating lens
7
. Instead, a part of the luminous flux A is transmitted through the polarization beam splitter
2
and supplied to the power monitoring means
6
.
Hence, in a typical optical head, the receiving of light by the power monitoring means
6
for detecting the amount of light emitted from the semiconductor laser
1
deteriorates the utilization efficiency of light beams in the optical head.
In the optical head, the required power for applying semiconductor laser beams to the recording medium
12
is restricted, while the value of this power and the light beam utilization efficiency of the optical head determine the required emitting output of the semiconductor laser
1
.
Hence, the lower the light beam utilization efficiency of an optical head is, the larger the optical output of the semiconductor laser
1
must be. This has been posing a problem of higher cost of components.
Further, increasing the output of a short wavelength semiconductor laser is limited, so that the required light output to the recording medium
12
cannot be obtained if the light beam utilization efficiency of the optical head is low. This has been presenting a problem in that the performance of an apparatus incorporating the optical head cannot be improved or a satisfactory apparatus cannot be implemented.
Japanese Unexamined Patent Publication (JP-A) No. 212910/1997 has disclosed an example wherein a light beam output from the same light source means is split into two light beams. The optical pickup described in the publication is configured so that one light beam of the split light beam is irradiated to a first recording medium having a first thickness, while the other light beam is irradiated to a second recording medium having a second thickness. The example discussed in the publication has not disclosed that the power levels of a part of the split light beam and a light beam emitted from the light source means are monitored.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide an optical head capable of improving light beam utilization efficiency by using a simple configuration.
Another object of the present invention is to provide a method for monitoring a light source output in an optical head. The method permits monitoring an output state of a light beam emitted from a light source means without deteriorating light utilization efficiency.
To this end, an optical head according to one aspect of the present invention includes a light source means for generating a light beam, a polarization beam splitter, an object lens opposed to a recording medium, and a power monitoring means for monitoring the power of the light beam emitted from the light source means. The power monitoring means is configured to monitor the power of the light beam emitted from the light source means by utilizing a portion of the light beam other than a portion thereof substantially used for reproducing or recording predetermined information from or onto the recording medium.
In a method for monitoring a light source output in an optical head according to another aspect of the present invention, the optical head has a light source means for generating a light beam, a polarization beam splitter, an object lens opposed to a recording medium, and a power monitoring means for monitoring the power of the light beam emitted from the light source means. The power monitoring means monitors the power of the light beam emitted from the light source means by making use of a portion of the light beam other than a portion thereof substantially used for reproducing or recording predetermined information from or onto the recording medium.
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McGinn & Gibb PLLC
NEC Corporation
Young W. R.
LandOfFree
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