JPH0675293B2 - Optical pickup device - Google Patents

Description

The present invention relates to an optical pickup device used in a compact disc player, an optical video disc player, or the like.

[Conventional technology]

2. Description of the Related Art In an optical pickup device used for a compact disc player or the like, a technique for reducing the number of components of an optical system by utilizing a diffraction element has been developed.

In such a conventional optical pickup device, for example, as shown in FIG. 3, a semiconductor laser 11 serving as a laser light source and a diffraction element 12
It includes a collimating lens 14, an objective lens 15, and a light receiving element 17.

The light receiving element 17 is arranged beside the semiconductor laser 11 and has a fourth
As shown in the figure, it comprises six light receiving parts 17a to 17f. Of these, the light receiving units 17a to 17d detect the reproduction signal and the focus error signal, while the light receiving units 17e and 17f detect the tracking error signal.

The laser light emitted from the semiconductor laser 11 is reflected by the diffraction element 12
Are separated by a main beam for detecting a reproduction signal and a focus error signal in the three-spot method and two sub-beams for detecting a tracking error signal. The three separated laser beams are further diffracted by the diffractive element 13, pass through the collimator lens 14, and are focused on the record carrier 16 by the objective lens 15. At this time, the main beam is focused on the pit on the record carrier 16, and the sub-beam is focused on the front and rear positions along the track direction of the pit on which the main beam is focused.

The main beam and the sub beam are condensed on the record carrier 16 and are reflected at the same time, pass through the objective lens 15 and the collimator lens 14, and are diffracted by the diffraction element 13.
Then, the rain beam is condensed on the light receiving units 17a to 17d,
The two sub beams are focused on the light receiving units 17e and 17f. The light receiving units 17e and 17f output according to the light amount of the received light, and if the output signal is Se · Sf, the tracking error signal is detected by the calculation of (Se−Sf).

When the tracking is performed correctly based on the 3-spot method, the light amounts incident on the light receiving units 17e and 17f become equal,
Since the output signals Se and Sf for both light receptions are also equal, the tracking error signal becomes zero. On the contrary, when the tracking is not performed correctly, the amount of light incident on the light receiving units 17e and 17f is different and the output signals Se and Sf are also different, so that the tracking error signal does not become zero. At this time, tracking is performed so that the tracking error signal becomes zero.

By the way, as shown in FIG. 5, the far-field pattern of the laser light emitted from the laser light source of the optical pickup device is, as shown in FIG. 5, a minor axis in a direction perpendicular to the optical axis and parallel to the PN junction surface 11b. And an elliptical shape having a major axis in a direction orthogonal to this, the laser light focused on the record carrier 16 is also an elliptical shape. At this time, the light receiving element for the semiconductor laser 11
The state of the light spot focused on the record carrier 16 varies depending on the position where the 17 is installed.

For example, the light receiving element 17 may be replaced by the PN junction surface 11b of the semiconductor laser 11.
And the angle between the light emitting point 11a and the straight line connecting the centers of the light receiving elements 17 is θ, this angle θ is 0 ° or 180 °.
If the light receiving element 17 is installed at the position where
The light spot focused on is in the shape of an ellipse that is long in the direction orthogonal to the track direction (pit row direction), and the light spot impinges on the adjacent track, which may cause the detection of an erroneous tracking error signal. In addition, the angle θ
When the light receiving element 17 is installed at a position where the angle is 90 ° or 270 °, the light spot focused on the record carrier 16 becomes an ellipse that is long in the same direction as the track direction (pit row direction), and the pit length is long. The resolution for reading the depth deteriorates. Therefore, the light receiving element 17 has an angle θ of 90 degrees in consideration of the quality of the reproduction signal.
It was installed at a position other than an integral multiple of °.

[Problems to be Solved by the Invention]

However, in the above conventional optical pickup device, a part of the light emitted from the semiconductor laser 11 is generated by the diffraction elements 12 and 13,
The so-called stray light, which is irrelevant to the reproduction of information, is reflected by a member for fixing the optical system or a holder for holding them. In particular, stray light due to the reflection of the diffraction elements 12 and 13 spreads over a wide range, so that part of it enters the light receiving element 17 and is detected as an output signal.

As shown in FIG. 4, this stray light has an elliptical distribution of the light intensity like the emitted light of the semiconductor laser 11, so that the light receiving element 17 is placed at a position where the angle θ is other than an integral multiple of 90 °. When installed, the amount of stray light incident on the light receiving units 17e and 17f differs, and an offset occurs in the tracking error signal. That is, according to the arrangement of the light receiving element 17 as shown in FIG. 4, the output signals Se and Sf of the light receiving portions 17e and 17f are (Se <Sf) even though they are correctly tracked. Since the tracking error signal (Se-Sf) does not become 0, there is a problem that tracking is performed at an incorrect position.

Further, in order to reduce the size and weight of the pickup, it is necessary to bring the light receiving element 17 closer to the semiconductor laser 11, but the light intensity of the stray light due to the diffraction elements 12 and 13 is the same as that of the emitted light of the semiconductor laser. Therefore, there is a problem that as the light receiving element is closer to the semiconductor laser, the offset amount is increased due to the influence thereof.

[Means for Solving the Problems]

In order to solve the above problems, the optical pickup device according to the present invention provides a laser light source that emits a laser beam having an elliptical beam cross section and a reflected light from a record carrier that is provided outside the optical axis of the laser beam. The light receiving element for detection and the laser light emitted from the laser light source, which is provided in the optical path from the laser light source to the record carrier, are separated into three-direction laser light in the three-spot method, and part of the laser light is not changed And a diffractive element that reflects the reflected light from the record carrier to the light receiving element while reflecting to the laser light source, and the light receiving element is provided with the minor axis of the cross section of the laser light, the optical axis of the laser light and the center of the light receiving element In an optical pickup device arranged at a position other than an integral multiple of 90 ° formed by a straight line connecting two lines, two light receiving portions for detecting tracking error are provided on both sides of the center of the light receiving element. It is characterized in that the laser light emitted from the laser light source is arranged so that the distances from the optical axis are different from each other so that the amounts of light incident at the time of locking are equal.

[Action]

According to the above configuration, the two light receiving portions for detecting the tracking error are arranged such that the distances from the optical axis of the laser light emitted from the laser light source are different from each other so that the light quantities incident on the combined track become equal. Therefore, even when stray light having a non-uniform light intensity distribution is received during correct tracking, the light receiving amounts of the two light receiving portions can be made equal. As a result, accurate tracking can be performed without causing an offset in the tracking error signal obtained from the difference in the amount of light received by the two light receiving units.

Further, when changing the position where the light receiving element is arranged, the effective light receiving area of the light receiving section may be set in consideration of the amount of stray light received at that position, so the light receiving element can be brought close to the laser light source, It is possible to reduce the size and weight of the optical pickup device.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

As shown in FIG. 1, a diffraction element 2 and 3, a collimator lens 4 and an objective lens 5 are arranged in front of the semiconductor laser 1 in the optical pickup device, and the laser light emitted from the semiconductor laser 1 is a record carrier. It is designed to lead to 6.

The diffraction element 2 separates the laser light emitted from the semiconductor laser 1 into 0th-order diffracted light and ± 1st-order diffracted light. Like the diffractive element 2, the diffractive element 3 converts the laser light into 0th-order diffracted light and
The first-order diffracted light is separated, and the reflected light from the record carrier 6 is given astigmatism to be guided to the light-receiving element 7 off the optical axis.

The beam cross section of the laser light emitted from the semiconductor laser 1 is, for example, as shown in FIG.
It has an elliptical shape having a minor axis in a direction parallel to the PN junction surface 1b and a major axis in a direction orthogonal to the minor axis. Therefore, the light receiving element 7 is located at the lateral position of the semiconductor laser 1, that is, at the second position.
As shown in the figure, the minor axis of the cross section of the laser light, that is, the PN junction surface 1b of the semiconductor laser 1, and the optical axis of the laser light, that is, the light emitting point 1a
Further, when an angle formed by a straight line connecting the centers of the light receiving elements 7 is θ, the angle θ is set at a position other than an integral multiple of 90 °.

Further, the light receiving element 7 is arranged on the side of the semiconductor laser 1 and comprises six light receiving portions 7a to 7f as shown in FIG.
Of these, the light receiving units 7a to 7d form four light receiving units in which a square light receiving unit is divided by diagonal lines, and detect a reproduction signal and a focus error signal based on the light intensity of the reflected light from the record carrier 6. The light receiving portions 7e and 7f are provided on both sides of the light receiving portions 7a to 7d, respectively, and detect the tracking error signal based on the light amount of the reflected light from the record carrier 6. The light receiving portions 7e and 7f are arranged so that the distances from the optical axis of the laser light emitted from the semiconductor laser 1 are different from each other so that the amounts of light incident on the combined tracks become equal.

In the above configuration, the laser light emitted from the semiconductor laser 1 is diffracted by the diffractive element 2 and separated into 0th-order diffracted light (hereinafter referred to as main beam) and ± 1st-order diffracted light (hereinafter referred to as sub-beam) in the three-spot method. These three separated beams are further diffracted by the diffractive element 3,
The 0th-order diffracted light of each beam passes through the collimator lens 4,
It is focused on the record carrier 6 by the objective lens 5. At this time, the rain beam is focused on the pit, and the sub-beam is focused in the track direction with a large amount with respect to the position where the main beam is focused, and with a slight shift in the radial direction.

The main beam and the sub beam are condensed on the record carrier 6 and reflected at the same time, pass through the objective lens 5 and the collimator lens 4, are diffracted by the diffraction element 3, and the first-order diffracted light of each beam is guided to the light receiving element 7. . Further, the main beam is guided to the light receiving portions 7a to 7d of the light receiving element 7 and is condensed at the intersection of the diagonal lines dividing these light receiving portions 7a to 7d, while the sub-beam is the light receiving portions 7e and 7f of the light receiving element 7. Is guided to and condensed.

The light receiving units 7a to 7d photoelectrically convert the light amount of the received light and output the light. However, when each output signal of the light receiving units 7a to 7f is Sa to Sf,
The focus signal is based on the astigmatism method [(Sa + Sc)-
(Sb + Sd)]. The tracking error signal is detected by the calculation of (Se-Sf) based on the three-spot method, and the reproduction signal is (Sa + Sb).
+ Sc + Sd) is detected.

When the tracking is performed correctly based on the three-spot method, the light amounts received by the light receiving units 7e and 7f need to be equal. However, the light receiving units 7e and 7f include diffraction elements other than the reflected light of the record carrier 6. Stray light such as reflected light from 2 and 3 is also received, and since the light intensity distribution of this reflected light is elliptical and not uniform, both output signals of the light receiving parts 7e and 7f are shown. To produce an offset in the tracking error signal. Therefore, the light amounts of the light received by the light receiving portions 7e and 7f are equalized at the position where the light receiving element 7 is arranged,
The light receiving parts 7e and 7f are arranged so that the distances from the optical axis of the laser light emitted from the semiconductor laser 1 are different from each other so that no offset occurs in the tracking error signal.

Further, when changing the position where the light receiving element 7 is arranged, the light receiving section 7e is considered in consideration of the amount of stray light received at that position.
・ It is enough to set the effective light receiving area of 7f.
Can be brought closer to the semiconductor laser 1, and the size and weight of the optical pickup device can be reduced.

Although the astigmatism method is used as the focus error detection method in the present embodiment, the present invention is not limited to this, and other focus error detection methods may be used.

〔The invention's effect〕

As described above, the optical pickup device according to the present invention includes a laser light source that emits laser light having an elliptical beam cross section, and a light receiving element that is provided outside the optical axis of the laser light and that detects reflected light from a record carrier. And separating the laser light emitted from the laser light source provided in the optical path from the laser light source to the record carrier into laser light in three directions in the three-spot method,
While reflecting a part of it to the laser light source without changing the beam cross-sectional shape, and a diffraction element for guiding the reflected light from the record carrier to the light-receiving element, the light-receiving element, the minor axis of the cross section of the laser beam, In an optical pickup device arranged at a position other than an integral multiple of 90 ° formed by a straight line connecting the optical axis of laser light and the center of the light receiving element, a tracking error is detected on both sides of the center of the light receiving element. Two light receiving parts
The laser light emitted from the laser light source is arranged so that the distances from the optical axis are different from each other so that the amounts of light incident on the combined tracks become equal.

As a result, the amounts of stray light received by the two light-receiving units that detect the tracking error become equal, so that no offset occurs in the tracking error signal. Therefore, it is possible to obtain a good tracking error signal and easily improve the reliability of the three-spot method.

[Brief description of drawings]

1 and 2 show an embodiment of the present invention. FIG. 1 is an explanatory view showing the structure of an optical pickup device, and FIG. 2 is a structure of a light receiving element and a light receiving element and a laser light source. It is explanatory drawing which shows the positional relationship. FIGS. 3 to 5 show a conventional example.
FIG. 4 is an explanatory diagram showing the configuration of the optical pickup device, FIG. 4 is an explanatory diagram showing the configuration of the light receiving element and the positional relationship between the light receiving element and the laser light source, and FIG. 5 is a far-field image of the light emitted from the laser light source. FIG. 1 is a semiconductor laser, 2 and 3 are diffraction elements, 6 is a record carrier,
Reference numeral 7 is a light receiving element, and 7a to 7f are light receiving portions.

Claims (1)

[Claims] 1. A laser light source that emits laser light having an elliptical beam cross section, a light-receiving element that is provided outside the optical axis of the laser light and that detects reflected light from a record carrier, and a laser light source to a record carrier. The laser light emitted from the laser light source provided in the optical path is separated into the three-direction laser light in the three-spot method, and a part of the laser light is reflected by the laser light source without changing the beam cross-sectional shape and reflected from the record carrier. A diffractive element that guides light to the light receiving element is provided, and the light receiving element is an integral multiple of 90 ° formed by the minor axis of the cross section of the laser light and the straight line connecting the optical axis of the laser light and the center of the light receiving element. In an optical pickup device disposed at a position other than the above, two light receiving portions for detecting a tracking error are provided on both sides of the center of the light receiving element so that the amounts of light incident on the combined track become equal. That they are disposed at different each other a distance from the optical axis of the laser beam emitted from the optical pickup apparatus according to claim.