Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
1998-11-17
2001-04-03
Hindi, Nabil (Department: 2651)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C369S112120, C369S044420
Reexamination Certificate
active
06212149
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to optical pickups. More particularly, the invention relates to an optical pickup used to read information out of an optical disc (hereinafter referred merely to as “disc”) such as CD and DVD.
2. Description of the Prior Art
There is one example of an optical pickup adapted to read information out of a disc as disclosed in Japanese Patent Publication No. H5-9851 [G11B7/09, G02B7/28, G11B7/135]. The optical pickup of this kind is required to have functions to detect focusing and tracking errors, in addition to the function to reproduce record information. Conventionally, the well-known Foucault's method, astigmatic method and the like have been utilized to detect focusing errors while the push-pull method, three-beam method and the like have been used to detect tracking errors. Where using the Foucault×s method and the three-beam method in combination, a photo-detector
1
has been used which includes light receiving elements
2
a-
2
c
for receiving a main beam and light receiving elements
3
a
and
3
b
for receiving sub-beams. Due to this, a focusing error signal is determined from a difference (S
2
a−
S
2
b
) of between output signals of the light receiving elements
2
a
and
2
b
, while a tracking error signal is determined by a difference (S
3
a
−S
3
b
) between output signals of the light receiving elements
3
a
and
3
b.
In general, the reflected light sub-beam from the disc travels through the lens in a somewhat oblique fashion. Accordingly, the two sub-beams separated by a diffraction elements
4
are not even but different in spot size. That is, the separated two beams include one beam greater in spot size (hereinafter referred to as “light-shield”) and another beam smaller in spot size (hereinafter referred to as “aperture”). Due to this, the beam portion diffracted as an aperture side and the beam portion diffracted as a light-shield side will not constitute symmetry on a light receiving surface of the photo-detector
1
. On the light receiving surface, the beam B as a light-shield side is greater in spot size than the beam A as an aperture side.
In the photo-detector
1
for a conventional optical pickup, such a phenomenon as stated above is not taken into consideration in design. That is, the light receiving elements
3
a
,
3
b
are each formed in a constant width throughout its entire length, with the result that the beam B on the light-shield side tends to go out of the light receiving elements
3
a
,
3
b
as shown in FIG.
13
. Due to this, there has been a problem that tracking error balance or jitter is greatly varied by change of temperature, resulting in instability in optical pickup characteristics.
Meanwhile, when adjusting the positional relationship between the diffraction element
4
and the light receiving element
1
in the optical pickup of this kind, focusing servo is effected by employing a servo circuit while actually rotating the disc to displace the diffraction element
4
such that jitter values observed by a jitter meter exhibit a best. Due to this, there has been a problem that operation of adjustment is troublesome and time consuming. Further, the requirement of a servo circuit leads to increase in cost. In addition, there has also been a problem that the optical pickup is unstable in characteristic because the diffraction element is displaced by using as a reference a jitter value that is liable to suffer from noises.
SUMMARY OF THE INVENTION
Therefore, it is a primary object of the present invention to provide a novel optical pickup.
It is another object of this invention to provide an optical pickup which is easy to conduct adjustment.
It is still another object to provide an optical pickup which can stabilize a defocusing characteristic.
An optical pickup according to the present invention, comprises: a laser element for emitting laser light; a lens for causing the laser light to converge on a disc; a diffraction element having first and second region each of which diffracts reflection light from the disc; a photo-detector for receiving the reflection light traveled through the diffraction element, the photo-detector includes a first light receiving element on which the reflection light diffracted by the first region converges, a second light receiving element on which the reflection light diffracted by the second region converges and a third light receiving element, the second light receiving element and the third light receiving element being separated by a divisional line extending almost in a same direction as a direction of diffraction by the second region; and a blind zone for dividing a light receiving surface of the first light receiving element into two.
An optimal jitter value can be obtained while preventing against focusing offset, if the diffraction element is displaced such that an intersection of between second and third waveforms each representative of a relationship between a lens position in a direction perpendicular to a disc surface and output values of second and third light receiving elements, i.e., a point for which focusing servo is made, is superimposed on a center point in a maximum value range of the first waveform representative of the relationship between the lens position and the output value of the first light receiving element, i.e., on a point at which the spot size becomes minimum.
In the present invention, because the blind zone is provided to divide the light receiving surface of the first light receiving element into two, the first waveform has a point (edge) decreased in the output value of the first light receiving element appearing at a center of the maximum value range. Accordingly, if the edge point is taken as a mark, it is possible to easily perform positional adjustment between the diffraction element and the photo-detector. Also, cost reduction is possible because of no necessity of separately providing a servo circuit, etc. Furthermore, the optical pickup is stabilized in characteristic because an optimal jitter value is obtained by reducing the spot size to a minimum at a point where focusing servo is effected.
In one aspect of the present invention, an optical pickup, comprises: a splitting element which splits a laser beam from a laser element into one main beam and two sub-beams; a lens for causing the main beam and the sub-beams to converge on a disc; a diffraction element divided into first and second regions to diffract reflection light from the disc; a photo-detector for receiving the reflection light traveled through the diffraction element, the photo-detector including first and second light receiving portions for respectively receiving the main beam and the sub-beams diffracted by the first region and the second region; the second light receiving portion being broader in width at a light shield side region, for receiving the sub-beam diffracted as a light shield side by the diffraction element, than a width at an aperture side region, for receiving the sub-beam diffracted as an aperture side.
On the light receiving surface of the second light receiving portion of the photo-detector, the sub-beam diffracted as the light shield side by the diffraction element is greater in width than the sub-beam diffracted as the aperture side by the diffraction element. However, because the light shield side region for receiving the light-shield-side sub-beam has a width broader than a width of the aperture side region for receiving the aperture-side sub-beam, there is no fear that the light-shield-side sub-beam will go out of the light receiving surface, thus stabilizing the characteristics of the optical pickup.
The above described objects and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 4904856 (1990-02-01), Nagaham et al.
patent: 4926036 (1990-05-01), Maeda
patent: 6014359 (2000-01
Nakata Naotaro
Yamamoto Takeshi
Hindi Nabil
Hoffmann & Baron , LLP
Rohm & Co., Ltd.
LandOfFree
Modified light-receiving element in an optical pickup for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Modified light-receiving element in an optical pickup for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Modified light-receiving element in an optical pickup for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2517394