JPH025232A - Optical pickup device - Google Patents

Abstract

PURPOSE:To obtain a satisfactory tracking error signal by setting two photodetecting parts with different distances secured from a laser light source and therefore securing the same photodetecting value of the stray light between both photodetecting parts which detect the tracking errors. CONSTITUTION:The same quantity of light must be received by the photodetecting parts 7e and 7f as long as a correct tracking action is carried out based on a 3-spot method. In this case, however, both parts 7e and 7f receive the reflected light from diffraction elements 2 and 3 in addition to the reflected light of a recording carrier 6. The luminous intensity distribution of said reflected light is oval and not uniform and therefore a difference is produced between the output signals of both parts 7e and 7f. Thus the tracking error signal has an offset. In this respect, both parts 7e and 7f are set with different distances secured from a semiconductor laser 1 so that the same quantity of light is received by both parts 7e and 7f at the position of a photodetecting element 7. Thus the tracking error signal has no offset.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical pickup device used in compact disc players, optical video disc players, and the like.

[Conventional technology]

2. Description of the Related Art In optical pickup devices used in compact disc players and the like, techniques have been developed to reduce the number of parts in an optical system by using a diffraction element.

For example, as shown in FIG. 3, such a conventional optical pickup device includes a semiconductor laser 11 serving as a laser light source, diffraction elements 12 and 13, and a collimating lens 14 in order to reproduce information using a record carrier 16. and objective lens 1
5 and a light receiving element 17.

The light receiving element 17 is arranged on the side of the semiconductor laser 11,
As shown in FIG. 4, it consists of six light receiving sections 17a to 17f. Of these, the light receiving sections 17a to 17d detect reproduction signals and focus error signals, while the light receiving sections 17e and 17d detect playback signals and focus error signals.
17f detects a tracking error signal.

The laser beam emitted from the semiconductor laser 11 is diffracted by the diffraction element 12, and is divided into 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. separated. The three separated laser beams are further diffracted by the diffraction element 13, pass through the collimator lens 14, and are focused onto the record carrier 16 by the objective lens 15. At this time, the main beam is focused on the bit on the record carrier 16, and the sub-beam is focused on the front and rear positions along the track direction of the bit on which the main beam is focused.

The main beam and sub-beams are focused onto the record carrier 16 and simultaneously reflected, pass through the objective lens 15 and the collimating lens 14, and are diffracted by the diffraction element 13. The main beam is transmitted through the light receiving sections 17a to 17.
The two sub-beams are focused on the light receiving section 17e, 1
The light is focused on 7f. The light receiving sections 17e and 17f output signals according to the amount of light received, and the output signals are 5s-S.
f, the trunking error signal is (Se-3f)
It is detected by the calculation.

When 1-racking is performed correctly based on the three-spot method, the amounts of light incident on the light receiving sections 17e to 17f are equal, and the output signals Se and Sf for both light receptions are also equal, so the tracking error signal becomes O. Conversely, when tracking is not performed correctly, the light receiving section 17e.1
Since the amount of light incident on 7f is different and the output signals 5e-3f are also different, the tracking error signal does not become O. At this time, tracking is performed so that the tracking error signal becomes O.

By the way, as shown in FIG. 5, the far-field image of the laser light emitted from the laser light source of the optical pickup device is centered on the optical axis and has a short axis in a direction perpendicular to the optical axis and parallel to the PN junction surface 11b. Since it is an ellipse having a major axis in a direction perpendicular to this, the laser beam focused on the record carrier 16 also has an elliptical shape.

At this time, the state of the light spot focused on the record carrier 16 differs depending on the position where the light receiving element 17 is installed with respect to the semiconductor laser 11.

For example, if the angle between the PN junction surface 11b of the semiconductor laser 11 and the straight line connecting the light emitting point 11a and the center of the light receiving element 17 is θ, the light receiving element 17 receives light at a position where the angle θ is Oo or 180''. When the element 17 is installed, the light spot focused on the record carrier 16 becomes an elongated ellipse in the direction perpendicular to the trunk direction (bit string direction), and the light spot falls on the adjacent track, resulting in an erroneous There is a risk of detecting a tracking error signal. Furthermore, if the light receiving element 17 is installed at a position where the angle θ is 90" or 270", the light spot focused on the record carrier 16 will be in the track direction (focus row). The light-receiving element 17 is placed at a position where the angle θ is not an integral multiple of 90°, taking into consideration the quality of the reproduced signal. It was installed.

[Problem to be solved by the invention]

However, in the conventional optical pickup device described above, a part of the light emitted from the semiconductor laser 11 is transmitted through the diffraction element 12.
13. The light is reflected by the member that fixes the optical system, the holder for holding them, etc., and becomes so-called stray light that is unrelated to information reproduction, etc. In particular, the diffraction element 12.
Since the stray light reflected by 13 spreads over a wide range, a part of it enters the light receiving element 17 and is detected as an output signal.

As shown in FIG. 4, the light intensity of this stray light is distributed in an ellipse like the light emitted from the semiconductor laser 11, so the light receiving element 17 is placed at a position where the angle θ is not an integral multiple of 90''. When installed, the amount of stray light incident on the light receiving sections 17e and 17f differs, causing an offset in the tracking/knocking error signal.In other words, according to the arrangement of the light receiving elements 17 as shown in FIG. Nevertheless, the output signals 5e-3f of the light receiving sections 17e and 17f satisfy (Se<S
f) and the tracking error signal (Se-s r
) does not become 0, so there is a problem in that tracking is performed at an incorrect position.

Furthermore, in order to make the pickup smaller and lighter, it is necessary to bring the light receiving element 17 closer to the semiconductor laser 11, but the light intensity of the stray light from the diffraction elements 12 and 13 has a Gaussian distribution similar to the light emitted from the semiconductor laser. Because I am doing
The problem has been that the closer the light receiving element is to the semiconductor laser, the larger the amount of offset becomes due to its influence.

[Means to solve the problem]

In order to solve the above problems, an optical pickup device according to the present invention includes a laser light source that emits laser light, a lens system that focuses the light emitted from the laser light source on a record carrier, and a record carrier. and a diffraction element that is provided in the optical path from the laser light source to the record carrier and separates the laser light emitted from the laser light source into laser light in three directions in the three-spot method. In the optical pink-up device, the light-receiving element has two light-receiving parts for detecting tracking errors, and the two light-receiving parts are arranged at different distances from the laser light source. .

[For production]

With the above configuration, the two light receiving sections that detect tracking errors can
Even if stray light with a non-uniform light intensity distribution is received, the amount of received light is equalized by being placed at different distances from the semiconductor laser, so there is no offset in the tracking error signal and accurate tracking can be achieved. Tracking can be done. Furthermore, when changing the position of the light receiving element, the effective light receiving area of the light receiving section can be set by considering the amount of stray light received at that position, so the light receiving element can be brought closer to the laser light source. The optical pickup device can be made smaller and lighter.

〔Example〕

An embodiment of the present invention will be described below based on FIGS. 1 and 2.

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

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

The light receiving element 7 is arranged on the side of the semiconductor laser 1, and the second
As shown in the figure, it consists of six light receiving sections 7a to 7f. Among these, the light receiving sections 7a to 7d form four light receiving sections each having a square shape 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. Further, the light receiving sections 7e and 7f are provided on both sides of the light receiving sections 7a to 7d, respectively, and detect a tracking error signal based on the amount of reflected light from the record carrier 6. The light receiving sections 7e and 7f are arranged at different distances from the semiconductor laser 1 so that the amount of light incident thereon at the time of track alignment is equal.

In the above configuration, the laser beam emitted from the semiconductor laser 1 is diffracted by the diffraction element 2 and separated into O-order diffraction light (hereinafter referred to as main beam) and ±1st-order diffraction light (hereinafter referred to as sub-beam) in the three-spot method. These three separated beams are further diffracted by the diffraction element 3,
The O-order diffracted light of each beam passes through the collimating lens 4,
The light is focused onto a record carrier 6 by an objective lens 5. At this time, the main beam is focused on the pit, and the sub-beam is focused in the trunk direction (and slightly shifted in the radial direction) from the position where the main beam is focused.

The main beam and sub-beams are focused on the record carrier 6 and simultaneously reflected, pass through the objective lens 5 and the collimating 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 parts 7a to 7d of the light receiving element 7,
The light is focused at the intersection of the diagonal lines that divide these light receiving parts 7a to 7d', while the sub beams are focused on the light receiving part 7 of the light receiving element 7.
The light is guided and focused by e.7f.

The light receiving units 7a to 7d photoelectrically convert the amount of light they receive and output them.
If r, the focus signal is based on the astigmatism method (
It is detected by the calculation (Sa+5c)-(Sb+5d)). Further, the tracking error signal is detected by the calculation of (Se-3f) based on the three-spot method, and the reproduced signal is further detected by the calculation of (3a+3b+3c+3d).

When tracking is performed correctly based on the three-spot method, the amount of light received by the light receiving sections 7e and 7f needs to be equal; The reflected light from 2 and 3 is also received, and as shown in Figure 2, the light intensity distribution of this reflected light is elliptical and not uniform, so there is a difference in the re-output signals of the light receiving sections 7e and 7f. This causes an offset in the tracking error signal. For this reason, the light receiving sections 7e and 7r are arranged at different distances from the semiconductor laser 1 so that the amounts of light received by the light receiving sections 7e and 7f are equal at the position where the light receiving element 7 is arranged, and the tracking error signal is This ensures that no offset occurs.

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

〔Effect of the invention〕

As described above, the optical pickup device according to the present invention includes a laser light source that emits laser light, a lens system that focuses the light emitted from the laser light source onto a record carrier, and a lens system that collects light reflected from the record carrier. An optical pink-up device that is equipped with a light receiving element that detects the light, and a diffraction element that is provided in the optical path from the laser light source to the record carrier and that separates the laser light emitted from the laser light source into laser light in three directions in the three-spot method. In the apparatus, the light receiving element has two light receiving sections for detecting tracking errors, and the two light receiving sections are arranged at different distances from the laser light source.

As a result, the amounts of stray light received by the two light receiving sections 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 the reliability of the three-spot method can be easily improved.

[Brief explanation of the drawing]

1 and 2 show an embodiment of the present invention, in which FIG. 1 is an explanatory diagram showing the configuration of an optical pickup device, and FIG. 2 is an explanatory diagram showing the configuration of a light receiving element and the relationship between the light receiving element and a laser light source. It is an explanatory view showing the positional relationship of. Figures 3 to 5 show conventional examples.
The figure is an explanatory diagram showing the configuration of the optical pickup device, Figure 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 Figure 5 is a far field image of the emitted light from the laser light source. It is an explanatory diagram. 1 is a semiconductor laser, 2 and 3 are diffraction elements, 4 is a collimating lens, 5 is an objective lens, 7 is a light receiving element, ? a to 7f are light receiving sections.

Claims (1)

[Claims] 1. A laser light source that emits laser light, a lens system that focuses the light emitted from the laser light source onto a record carrier, and a light receiving element that detects reflected light from the record carrier;
The laser beam provided in the optical path from the laser light source to the record carrier and emitted from the laser light source is
In an optical pickup device equipped with a diffraction element that separates laser beams into directional laser beams, the light receiving element has two light receiving sections that detect tracking errors, and these two light receiving sections are configured to adjust the distance from the laser light source to each other. An optical pickup device characterized by being arranged differently.