JP3127974B2 - Optical pickup device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device for recording / reproducing information on / from an information recording medium by using an elliptical beam emitted from a semiconductor laser.

[0002]

2. Description of the Related Art Conventionally, in various optical recording / reproducing apparatuses, an optical pickup apparatus using a semiconductor laser as a light source has been widely used. In this optical pickup device,
The beam emitted from the semiconductor laser is narrowed down by optical means such as an objective lens, and is radiated in a spot shape on an information track formed on an information recording medium,
The reflected light from the information recording medium is received as a detection beam on each light receiving surface of a plurality of light receiving elements, and information is written / read based on the detection signal output from each of the light receiving elements.
A control operation at the time of reading is performed.

For example, in the case of a so-called three-beam system in which an objective lens performs a tracking operation, first, a main beam for recording / reproducing information is spot-shaped on an information track formed on an information recording medium. , And two sub-beams are radiated in spots on both sides of the main beam in the track direction. And each reflected light of these main beam and sub beam,
The light is received by the light receiving elements 1, 2, 3 as shown in FIG.

Reference numeral 1 in FIG. 2 indicates a main four-piece light receiving element for receiving a main detection beam 4 which is a reflected light of the main beam, and is arranged so as to sandwich the main four-piece light receiving element 1. The two sub-light receiving elements 2 and 3 receive the sub-detection beams 5 and 6 as reflected light of the two sub-beams, respectively. Then, a predetermined output difference is obtained between the two sub-light receiving elements 2 and 3 based on the difference in the amount of received light between the two sub-detection beams 5 and 6, and the output difference is used as a tracking error signal to perform tracking control on the objective lens. The operation is performed.

[0005]

However, each of the detection beams 4, 4 received by each of the light receiving elements 1, 2, 3 described above.
5, 6 are diffracted light beams 4a, 5a, 6 due to astigmatism from the periphery of the original beam given by geometrical optics.
a extends, for example, so as to trail in all directions. Therefore, as shown by the broken line in FIG. 2, when the detection beams 4, 5, and 6 move with the above-described tracking control operation, for example, a part 5 ′ of the sub-detection beam 5 becomes
There is a case where the light goes out of the light receiving surface area of the sub light receiving element 2 and a so-called “light receiving spill” occurs. Such "light reception spill" tends to occur particularly when the tracking control operation of the objective lens becomes large, causing an imbalance in the amount of light received by the light receiving element. , The tracking control operation may be executed at a position deviated from the original position.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical pickup device capable of satisfactorily eliminating a tracking offset phenomenon and stably performing a tracking control operation.

[0007]

According to a first aspect of the present invention, an elliptical beam emitted from a semiconductor laser is narrowed by an objective lens, and an elliptical spot is irradiated on an information track formed on an information recording medium. An optical pickup configured to receive the reflected light as a detection beam on each light receiving surface of a plurality of light receiving elements and obtain a tracking error signal for causing the objective lens to perform a tracking control operation from the light receiving elements. In the apparatus, the light intensity distribution of the elliptical beam is set to a distribution state that complements an imbalance in the amount of received light due to spillage of light received on a light receiving surface of a light receiving element caused by movement of a detection beam during a tracking control operation. Beam long axis tilt direction θ
Is set as a predetermined inclination angle direction between the direction parallel to the information track and the direction perpendicular to the direction in which the information track extends.

[0008]

[0009]

According to a second aspect of the present invention, an elliptical beam emitted from a semiconductor laser is narrowed down by an objective lens, an elliptical spot is radiated on an information track formed on an information recording medium, and the reflected light is reflected by a plurality of light receiving elements. In the optical pickup device configured to receive a detection beam on each of the light receiving surfaces and to cause the objective lens to perform a tracking control operation, the light intensity distribution of the elliptical beam is used for moving the detection beam during the tracking control operation. The oblique direction θ of the major axis of the elliptical beam is perpendicular to the direction in which the information track extends so as to make the distribution state complementary to the variation in the amount of received light corresponding to the received light spill on the light receiving surface of the light receiving element. The optical design conditions are set so as to set a predetermined tilt angle direction between them.

On the other hand, according to a third aspect of the present invention, an elliptical beam emitted from a semiconductor laser is narrowed by an objective lens, an elliptical spot is irradiated on an information track formed on an information recording medium, and the reflected light is reflected by a plurality of light receiving elements. Received as a detection beam on each light receiving surface, from the light receiving element, in the optical pickup device configured to obtain a tracking error signal for causing the objective lens to perform a tracking control operation, the light intensity distribution of the elliptical beam, The tracking output fluctuation caused by the spill of light on the light receiving surface of the light receiving element caused by the movement of the detection beam during the tracking control operation
Complementarily , the inclination direction θ of the major axis of the elliptical beam is set to be parallel and perpendicular to the extending direction of the information track so that a light intensity distribution state in which a normal tracking error signal is always obtained from the light receiving element. In this case, the optical design conditions for a predetermined tilt angle direction are set.

[0012]

In each of the means of the present invention having such a configuration, the detection beam moves on the light receiving element in accordance with the tracking control operation, and "detection spillover" occurs on the light receiving surface of the light receiving element. Even in this case, the imbalance of the amount of received light due to the “spillover of received light” may be caused by the inclined arrangement of the light intensity distribution of the elliptical beam on the objective lens entrance surface.
Complementary , a normal tracking error signal is always obtained from the light receiving element, and a good tracking control operation is maintained.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. First, as shown in FIG. 6, a semiconductor laser 11 as a light source is mounted at a predetermined position on a fixed frame 10 of an optical pickup device. As will be described later, the semiconductor laser 11 is adjusted so that the mounting angle in the rotation direction is a predetermined angle direction. The light emitted from the semiconductor laser 11 is split into beams in three directions through a diffraction grating 12. These three beams are reflected by a half mirror 13, then reflected by a total reflection mirror 14, and focused by an objective lens 15. Thus, the light is focused and radiated on an information track formed on the information recording disk 16 in a spot shape.

These three beams are three elliptical beams 21, 22, 23 as shown in FIG. 1 on the XX 'plane in FIG. 6 of the objective lens 15. This is because the emission shape of the light emitted from the semiconductor laser 11 is not isotropic but has an elliptical shape, and the emission intensity distribution is also distributed along the major axis and the minor axis of the ellipse. Only part of the light passing through the objective lens surface indicated by the circle in FIG. 1 is condensed and spotted on the disk.

Each of these elliptical beams 21, 22, 23
Are arranged in parallel in the direction in which the information tracks extend, the central elliptical beam 21 is a main beam for writing and reading information, and the elliptical beams 22 and 23 on both sides of the elliptical beam 21 are This is a sub-beam for obtaining a tracking error signal. At this time, each of the elliptical beams 2
A line segment (not shown) connecting the centers of 1, 2, and 23 is set to make about 1 ° with respect to the track extending direction on the disk.
The adjustment is made by rotating the attachment angle of the diffraction grating 12 (see FIG. 6).

When the mounting angle is set to a predetermined angle in the rotation direction of the semiconductor laser 11, each of the elliptical beams 21, 22, 23 is moved with respect to the information track extending direction (vertical direction in the figure). It is arranged in an inclined state. That is, each of the above elliptical beams 21, 22,
23, the major axis direction of each ellipse is arranged in a predetermined inclination angle direction between a direction parallel to and perpendicular to the track extending direction. Here, when the objective lens 15 is driven by tracking and moves from 15 to 15 ′ in FIG. 1, the amount of light incident on the objective lens 15 increases or decreases by a small amount on the sub-beam 22 side. Sub beam 2
3, the amount of incident light is greatly reduced. That is, when the elliptical beam of the semiconductor laser 11 has an inclination angle with respect to the track extending direction, the tracking operation of the objective lens 15 causes a light amount imbalance. This will be described later.

Referring back to FIG. 6, the reflected light from the information recording disk 16 passes through the objective lens 15, is reflected by the total reflection mirror 14, passes through the half mirror 13, passes through the sensor lens 17, and receives the light. The element 18 is configured to be received as a detection beam.

The light receiving element 18 is the same as that shown in FIG.
The main detection beam 4 which is the reflected light of the main beam irradiated on the information recording disk 16 is received on the light receiving surface of the main quadrant light receiving element 1. On the light receiving surfaces of the two sub light receiving elements 2 and 3 arranged on both sides of the main four-divided light receiving element 1, sub detection beams 5 and 6, which are reflected lights of the sub beams irradiated onto the information recording disk 16, are provided. Has been received. The output difference is obtained between the two sub-light receiving elements 2 and 3 based on the difference in the amount of received light between the two sub-detection beams 5 and 6, and the output difference is used as a tracking error signal. A tracking control operation is performed.

On the other hand, as shown in FIG. 1, the elliptical shape of each elliptical beam 21, 22, 23 on the objective lens is
As described above, the emission shape of the light emitted from the semiconductor laser 11 is not isotropic but has an elliptical shape, and the emission intensity is also distributed along the major axis and the minor axis of the elliptical shape. . In this embodiment, the major axis direction of each of the elliptical beams 21, 22, and 23 is a predetermined inclination angle direction between parallel and perpendicular to the extending direction (vertical direction in the drawing) of the information track. Specifically, it is set to a predetermined inclination direction of 5 ° to 25 °.

As described above, the inclined arrangement direction of each of the elliptical beams 21, 22, 23 is set by rotating and adjusting the mounting angle of the semiconductor laser 11, but in setting the specific angle. Is set in accordance with the fact that the sub-detection beams 5 and 6 on the sub-light receiving elements 2 and 3 move on the light receiving elements along with the tracking control operation. That is, at the time of the tracking control operation, as the objective lens 15 is controlled to move in the direction perpendicular to the information track, the sub detection beams 5 and 6 on the light receiving surfaces of the sub light receiving elements 2 and 3 are also indicated by broken lines in FIG. And the detection beams 5 and 6 move, for example, a part 5 ′ of the sub-detection beam 5 may come off the edge of the sub-light receiving element 2, resulting in a so-called “light leakage”. Therefore, in the present invention, the elliptical beams 22, 23
Are arranged obliquely, and the light intensity distributions of the elliptical beams 22 and 23 are changed to “light spills” on the light receiving surfaces of the sub light receiving elements 2 and 3.
Is configured to compensate for and cancel the imbalance in the amount of received light due to “light leakage” as described above. Hereinafter, this point will be described in detail.

First, as an optical design value considered as an optical pickup device, as shown in FIG. 3, the beam pitch P on the light receiving surface of the sub light receiving element 2 with respect to the design center A, the light receiving surface of the sub light receiving element 2 Detection beam diameters D ₁ and D
_2, the pattern pitch A ₁ sub light receiving element 2, A _2, there is.

Here, the beam diameter D ₁ in the above item is a beam diameter obtained by geometrical optics, and the beam diameter D ₂ in the same item is a beam diameter including diffracted light due to the effect of astigmatism. Thus, these two beam diameters D ₁ and D ₂ have a relationship of D ₂ = D ₁ × k. Here, the constant k in the above equation is a constant for adding a linear spread of light due to astigmatism (diffraction effect).

Next, the sub detection beams 5 and 6 on the light receiving surfaces of the sub light receiving elements 2 and 3 accompanying the movement of the objective lens 15 are shown.
Is shown in FIG. As shown, the deviation d from the sub-beam displacement [Delta] x, the imaging point of the light receiving surface caused by the movement amount x _OL astigmatism of the objective lens 15 O on the light receiving surface, the imaging distance L in the light-receiving-side region, and to Then, from these, Δx = x _OL × d / L.

The change in the mounting angle of the semiconductor laser 11 is represented by θ (0 ° when the bonding surface of the semiconductor laser 11 is perpendicular to the track extending direction), and the change in the mounting angle θ of the semiconductor laser 11 accompanies the change. Consider the following relationship based on the change in light intensity. That is, the tracking error offset change TEO, the “light spill” f ₁ (P, D, A, ΔX) of the sub detection beams 5 and 6 on the light receiving surfaces of the sub light receiving elements 2 and 3, the light receiving surface of the sub light receiving elements 2 and 3 Since the tracking error offset is considered to be mainly caused by the above, TEO = f ₁ (P, D, A, ΔX) when the light intensity difference f ₂ (θ) between the sub detection beams 5 and 6 at + F ₂ (θ).

Here, "spillover of received light" of the sub detection beam 5 is performed.
In FIG. 5, f ₁ = g × [{A ₁ − (P ₂ −ΔX)} / (D ₂ −D ₁ )] / 2 f ₂ = h × θ.

Here, g in the above equation is a variable for converting the influence of the light intensity caused by astigmatism in the light intensity distribution of the sub-detection beam 5 into a tracking error offset amount. When θ is 0 °, It is obtained by actually measuring the tracking error offset amount. According to experiments confirmed by the inventors of the present application, it was confirmed that g = 5 to 20 in general specifications such as the amount of astigmatism of a semiconductor laser used for an optical disk.

Experimentally, the coefficient h in the above equation indicates the beam divergence angle (approximately 10 ° × 30 °) of a semiconductor laser for an optical disk generally used, a collimating lens or a finite objective lens (NA of 0.1). (Before and after), it was confirmed that h = about 0.1 to 0.2.

Therefore, tracking error offset change
If TEO = 0 is set as a condition that does not cause TEO, the mounting angle θ of the semiconductor laser is θ = g × [{A ₁ − (P−D ₂ −ΔX)} / (D ₂ −D ₁ )] / 2h ... Formula 1 is obtained.

In an optical system used for a general optical disk, the following specific numerical values are used. Since the astigmatic difference is several 100 μm, 1.2 <k <
2.5, since the imaging distance is 15 to 30 mm, 0 <ΔX <
50 μm, sub-beam pitch P is 150 to 230 μm, beam diameter D ₁ is 40 to 120 μm, and pattern pitch A ₁ of sub-light receiving elements is 90 to 120 μm
m, Then, when these are applied to the above equation 1, 5 ° <θ <25 ° is determined.

As described above, in this embodiment, even when the sub-detection beams 5 and 6 move on the sub-light-receiving elements 2 and 3 due to the tracking control operation and "light-receiving spillage" occurs, the " The unbalance of the amount of received light due to “spillover of received light” is caused by the tilted elliptical beam 2 on the objective lens.
The light intensity distributions are complemented and canceled by the light intensity distributions 2 and 23, and the imbalance in the amount of received light is eliminated. Therefore, a normal tracking error signal is always obtained from the sub light receiving elements 2 and 3, and a good tracking control operation is stably maintained.

Japanese Patent Publication No. 2-39022 discloses a technique in which the major axis direction of an elliptical beam emitted from a semiconductor laser is arranged in a direction perpendicular to the track direction of information recording. However, the proposed device merely sets the spread direction of the elliptical beam only from the imaging conditions on the disk, and cannot eliminate the imbalance in the amount of light received by the light receiving element.

Although the invention made by the inventor has been specifically described based on the embodiments, the present invention is not limited to the above-described embodiments, and can be variously modified without departing from the gist thereof. Needless to say.

[0033]

As described above, according to the present invention, even when the detection beam moves on the light receiving element due to the tracking control operation and the "light receiving spillage" occurs, the "light receiving" on the light receiving surface of the light receiving element is performed. The imbalance in the amount of received light due to "spillover" is complemented by the light intensity distribution of the inclined irradiated elliptical spot on the objective lens so that the amount of received light is balanced and a normal tracking error signal is always obtained from the light receiving element. , The inclination direction θ of the major axis of the elliptical beam,
Since it is configured in the direction of a predetermined inclination angle between parallel and perpendicular to the direction in which the information track extends, it is possible to satisfactorily eliminate the tracking offset phenomenon and stably perform the tracking control operation. Thus, the reliability of the optical pickup device can be improved.

[Brief description of the drawings]

FIG. 1 is a principle explanatory view showing an arrangement shape of an elliptical beam on an objective lens according to an embodiment of the present invention.

FIG. 2 is an explanatory front view showing an arrangement relationship of light receiving elements and a detection beam received on the light receiving elements.

FIG. 3 is an explanatory partial front view showing optical design values around a light receiving element.

FIG. 4 is an explanatory side view showing a change in the position of a detection beam on a light receiving element due to movement of an objective lens.

FIG. 5 is a partial front view illustrating a state in which a detection beam is spilled on a detection beam;

FIG. 6 is an explanatory diagram of an optical mechanism showing a schematic configuration of an optical pickup device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Main light receiving element 2, 3 Sub light receiving element 4 Main detection beam 5, 6 Sub detection beam 11 Semiconductor laser 15 Objective lens 16 Information recording medium 21, 22, 23 Elliptical beam

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-61-190731 (JP, A) JP-A-2-195532 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 7/09-7/135

Claims (3)

(57) [Claims] An elliptical beam emitted from a semiconductor laser is narrowed down by an objective lens, an elliptical spot is radiated on an information track formed on an information recording medium, and reflected light is reflected on each light receiving surface of a plurality of light receiving elements. An optical pickup device configured to receive the detection beam as the detection beam and to cause the objective lens to perform the tracking control operation, wherein the light intensity distribution of the elliptical beam is adjusted by a light receiving element generated by the movement of the detection beam during the tracking control operation. complement the imbalance in the amount of light received by the light receiving spilled on the light-receiving surface
Optical design conditions are set such that the inclination direction θ of the major axis of the elliptical beam is a predetermined inclination angle direction between a direction parallel to and perpendicular to the direction in which the information track extends so that a distribution state is obtained. An optical pickup device characterized by the above-mentioned. 2. An elliptical beam emitted from a semiconductor laser is narrowed down by an objective lens, an elliptical spot is irradiated on an information track formed on an information recording medium, and reflected light is reflected on each light receiving surface of a plurality of light receiving elements. An optical pickup device configured to receive the detection beam as a detection beam and to cause the objective lens to perform a tracking control operation, wherein a light intensity distribution of the elliptical beam is generated by a light-receiving element generated by movement of the detection beam during the tracking control operation. The oblique direction θ of the major axis of the elliptical beam is perpendicular to the direction parallel to the information track so that the distribution state complements the received light amount fluctuation corresponding to the received light spill on the light receiving surface. An optical design condition in which a predetermined tilt angle direction is set between the optical design conditions. 3. An elliptical beam emitted from a semiconductor laser is narrowed down by an objective lens, an elliptical spot is radiated on an information track formed on an information recording medium, and reflected light is reflected on each light receiving surface of a plurality of light receiving elements. An optical pickup device configured to receive a tracking error signal for causing the objective lens to perform a tracking control operation from the light receiving element, and obtain a light intensity distribution of the elliptical beam during the tracking control operation. To compensate for tracking output fluctuations caused by spills on the light receiving surface of the light receiving element caused by the movement of the detection beam
Te, As the light intensity distribution obtained at all times normal tracking error signal from the light receiving element, the inclination direction θ of the long axis of the elliptical beam, between the parallel and perpendicular to the extending direction of the information track Optical design conditions for the specified tilt angle direction