JPH025231A - Optical pickup device - Google Patents

Abstract

PURPOSE:To obtain a satisfactory tracking error signal by setting the effective photodetecting areas of two photodetecting parts at different values and therefore securing the same photodetecting value of the stray light between both photodetecting parts which detect the tracking error. CONSTITUTION:The same photodetecting value 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 pats 7e and 7f receive the reflected light from the 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 the difference is produced between the output signals of both parts 7e and 7f and the tracking error signal has an offset. In this respect, the effective photodetecting areas of both parts 7e and 7f are set different from each other 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 pink amplifier device includes a semiconductor laser 11 serving as a laser light source, diffraction elements 12 and 13, and a collimating lens in order to reproduce information using a record carrier 16. 14 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. Among these, the light receiving sections 17a to 17d detect reproduction signals and focus error signals, and the light receiving sections 17e and 17d detect playback signals and focus error signals.
7f 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 a pit on the record carrier 16, and the sub-beam is focused on the front and rear positions along the track direction of the focal point where the main beam is focused.

The main beam and the sub-beams are reflected onto the record carrier 6 at the same time, 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 units 17e and 17f output signals according to the amount of light received, and the output signals are
When f is the tracking error signal, the tracking error signal is detected by the calculation of (Se-3f).

When tracking is performed correctly based on the three-spot method, the amounts of light incident on the light receiving sections L7e and 17f are equal, and the output signals Se and Sf for both light receptions are also equal, so the tracking error signal becomes 0. Conversely, when tracking is not performed correctly, the light receiving sections 17e and 17f
The tracking error signal does not become O because the amount of light incident on the two is different and the output signals 5e-5f are also different. 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. , and the major axis in a direction perpendicular to these, 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 semiconductor laser 110PN junction surface 11b 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 is located at a position where this angle θ is 00 or 180 @. 17 is installed, the light spot focused on the record carrier 16 becomes an ellipse long in the direction perpendicular to the track direction (pit row direction), and the light spot covers the adjacent trunk.
There is a risk that an incorrect tracking error signal will be detected.

In addition, when the light receiving element 17 is installed at a position where the above angle θ is 90' or 270°, the 411u body 1
The light spot focused on the lens 6 has an elliptical shape that is elongated in the same direction as the track direction (focus row direction), and the resolution for reading the focus length deteriorates. For this reason, the light receiving element 17 has been installed at a position where the angle θ is not an integral multiple of 90°, taking into account the quality of the reproduced signal.

[Problem to be solved by the invention]

However, in the conventional optical big amplifier 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 moved to a position where the angle θ is other than an integral multiple of 90'. , the amount of stray light incident on the light receiving sections 17e and 17f will be different, causing an offset in the tracking error signal. That is, according to the arrangement of the light receiving element 17 as shown in FIG.
f) and the tracking error signal (Se-3f) does not become 0, resulting in the problem 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 greater the amount of offset will be affected by the light receiving element.

[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 onto 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 sections for detecting tracking errors, and the two light-receiving sections have different effective light-receiving areas.

[For production]

With the above configuration, the two light receiving sections that detect tracking errors receive effective light so that even if they receive stray light with an uneven light intensity distribution when tracking is performed correctly, the amount of received light is equal. Since the areas are different from each other, accurate tracking can be performed without causing an offset in the tracking error signal. 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 O-order diffraction light and ±1st-order diffraction light.

Similar to the diffraction element 2, the diffraction element 3 separates the laser beam into O-order diffraction light and ±1st-order diffraction light, imparts astigmatism to the reflected light from the record carrier 6, and sends the light receiving element off the optical axis. It is designed to lead to 7.

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 73 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 have different effective light receiving areas so that the amount of light incident thereon at the time of matching track is equal.

In the above configuration, the laser light emitted from the semiconductor laser 1 is diffracted by the diffraction 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-beams) 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 largely in the track direction and slightly shifted in the radial direction with respect to 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. . The main beam is guided to the light receiving parts 7a to 7d of the light receiving element 7 and is focused at the intersection of the diagonal lines dividing these light receiving parts 7a to 7d, while the sub beams are guided to the light receiving parts 7e and 7f of the light receiving element 7.
The light is guided and focused.

The light receiving sections 7a to 7d photoelectrically convert the amount of light received and output the same, and each output signal of the light receiving sections 7a to 7f is converted to a signal 5a to 3.
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-3r) based on the three-spot method, and the reproduced signal is further detected by the calculation of (Sa+Sb+Sc+Sd).

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 the light intensity distribution of this reflected light is as shown in Figure 2.
Since it has an elliptical shape and is not uniform, a difference occurs in the re-output signals of the light receiving sections 7e and 7f, causing an offset in the tracking error signal. For this reason, the effective light-receiving areas of the light-receiving parts 7e and 7f are made different from each other so that the amount of light received by the light-receiving parts 7e and 7f is equal at the position where the light-receiving element 7 is arranged, and an offset occurs in the tracking error signal. I try not to.

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 pink-up 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 focuses the light emitted from the laser light source on a record carrier. Optical pink that includes a light receiving element that detects light 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 close-up device, the light-receiving element has two light-receiving sections for detecting tracking errors, and the two light-receiving sections have different effective light-receiving areas.

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 pick amplifier 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 light emitted 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, and 7a to 7f are light receiving sections. Fig. Fig. Fig. Fig. Fig. Fig. Fig.

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 including a diffraction element that separates laser beams into directional laser beams, the light receiving element has two light receiving sections for detecting tracking errors, and the effective light receiving areas of the two light receiving sections are different from each other. An optical pickup device characterized in that: