JP2003173550A - Optical pickup - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup in which a focusing condition is easily controlled without causing a defocusing. <P>SOLUTION: The optical pickup 11 is so composed that the optical pickup is provided with a means 15 with which information is recorded on or reproduced from a recording medium 10 and the recording medium 10 is irradiated with a light beam, an optical path separation means 18 which separates a returning light beam reflected on the recording medium 10 into a plurality of light beams, and a light receiving element PD which receives the separated light beams, respective light beams form a spot at respective different positions on the light receiving element PD, the optical path separation means 18 has diffraction patterns 16 and 17 which generate astigmatism on spots formed on the light receiving element PD, the light receiving element PD is arranged at a height so that the spots become minimum circle of confusion, and the diameter of at least a spot among respective light beam spots formed on the light receiving element PD has a diameter different from the diameters of other spots. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup for reproducing and recording information on a recording medium.

[0002]

2. Description of the Related Art FIG. 1 shows a schematic configuration diagram of an integrated optical pickup. FIG. 1A shows a schematic diagram of an optical system of the optical pickup, and FIG. 1B shows a perspective view of a main part of the optical pickup. This integrated optical pickup 11 is a laser LD
And a light receiving element PD integrated with each other, a holographic element 13, a collimator lens 14 and an objective lens 15.

The holographic element 13 is a laser LD.
The optical beam emitted from the optical disc and the optical beam of the return light reflected by the signal recording surface of the optical disc 10 which is the recording medium are branched to guide the return light to the light receiving element PD. One surface of the holographic element 13, that is, FIG.
In B, the hologram 18 (16,
17) has been formed.

The hologram 18 is formed with a hologram pattern so that spots of return light are formed at different positions of the light receiving element PD by the semicircular portions 16 and 17 which are divided into two. Then, each of the semicircular portions 16 and 17 causes astigmatism in the return light, and the optical axis is bent by diffraction to irradiate the light receiving element PD. As shown in FIG. 1B, the light receiving element PD is vertically or horizontally divided into four, that is, divided into four.

The integrated optical pickup 11 normally detects various signals as follows. As shown in FIG. 2, the light receiving element PD is divided into four parts A, B, C, and D. Then, the return light that has passed through one portion 16 of the hologram 18 is irradiated to the two left portions A and B of the light receiving element PD, and becomes a spot S1. Hologram 1
The return light that has passed through the other portion 17 of
The two portions C and D on the right side of are illuminated and become spots S2.

These two spots S1 and S2 have a semicircular shape in which the return light is diffracted by the hologram pattern of the hologram 18 so that the semicircular portions 16 and 17 are rotated clockwise by 90 degrees.

The position signal (position signal) is obtained by calculating the signals detected by the respective parts A, B, C and D of the light receiving element PD as follows. X direction position signal XP = (A + B)-(C + D) Y direction position signal YP = (A + D)-(B + C)

Similarly, the focus error signal FE, the tracking error signal TE, and the main information signal (so-called RF signal) M are obtained by calculating as follows. Focus error signal FE = (A + C)-(B + D) Tracking error signal TE = {phase comparison} [(A +
C)-(B + D)] Main information signal M = A + B + C + D The above-mentioned arithmetic expression of the tracking error signal TE is an arithmetic expression when tracking servo is performed using a so-called DPD (Differential Phase Detection) method or the like.

This method has an advantage that the focus error signal FE and the tracking error signal TE can be obtained with a simple structure of a beam divided into two and a PD divided into four.

Incidentally, FIG. 2 shows the state of just focus (focus), and the focus error signal FE = 0.

In the structure shown in FIG. 2, the spots S1 and S on the light receiving element PD due to the change of the focus state.
The shape of No. 2 and the change of the focus error signal FE are shown in FIG. In FIG. 3, the hologram 18 and the light receiving element PD
A change indicated by an arrow from the upper left figure to the upper right figure due to a change in the distance between the two and the focus state. In this case, the spots S1,
It can be seen that the shape of S2 changes while rotating clockwise. FE = (A + C)-(B
+ D) <0. FE =
(A + C)-(B + D) = 0, that is, the state of just focus is shown. Similar to FIG. 2, the spots S1 and S2 are both semicircular. FE =
The state of (A + C)-(B + D)> 0 is shown.

As shown in the central views of FIGS. 2 and 3, each of the semicircular portions 16 and 17 of the hologram 18 is composed of 9 parts.
By setting the just focus state when the spots S1 and S2 have a semicircular shape rotated clockwise by 0 degrees, the so-called S of the focus error signal FE or the like is obtained.
The character signal becomes a signal that facilitates focus control.

[0013]

However, when the focus state is controlled by the astigmatism method using the hologram 18 composed of the semicircular portions 16 and 17 described above, the holographic element 13 is Defocus occurs unless accurate control is performed in the three directions of the X direction, Y direction, and θ direction (see FIG. 4).

Particularly in the direction corresponding to the Y direction, there is no means for accurately determining the position in the actual manufacturing process, and therefore it is difficult to control so that defocusing does not occur.

In order to solve the above-mentioned problems, the present invention provides an optical pickup which can easily control the focus state without causing defocus.

[0016]

An optical pickup of the present invention is for recording or reproducing information on a recording medium, and means for irradiating the recording medium with a light beam and a light beam for the recording medium. An optical path separating means for separating the reflected light reflected into a plurality of light beams, and a light receiving element for receiving the plurality of light beams separated by the optical path separating means,
The plurality of light beams separated by the optical path separating means form spots at different positions on the light receiving element, and the optical path separating means generates a diffraction pattern on the spot formed on the light receiving element. And the light receiving element is arranged at a height such that the spot becomes a circle of least confusion,
Of the spots of each light beam formed on the light receiving element,
The diameter of at least one spot has a value different from the diameters of other spots.

According to the above-mentioned configuration of the optical pickup of the present invention, the optical path separating means has a diffraction pattern for producing astigmatism in the spot formed on the light receiving element,
Of the spots of each light beam formed on the light receiving element,
Since the diameter of at least one spot has a value different from the diameters of the other spots, the difference in diameter between the spot having a value different from the diameters of the other spots and the other spots causes the optical path separation means to be horizontal. Since it is possible to equalize the change in the focus error signal due to the deviation in the direction and the change in the focus error signal due to the change in the spot diameter, it is possible to cancel these changes by acting in the opposite directions. Become. This makes it possible to prevent defocusing when manufacturing the optical pickup without adjusting, for example, the above-described horizontal position of the optical path separating unit.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is an optical pickup for recording or reproducing information on or from a recording medium, wherein the means for irradiating the recording medium with the light beam and the recording medium reflect the light beam. The optical path separation means for separating the return light into a plurality of light beams and the light receiving element for receiving the plurality of light beams separated by the optical path separation means are provided. The light beam forms spots at different positions on the light receiving element, and the optical path separating means has a diffraction pattern that produces astigmatism on the spot formed on the light receiving element, and the spot becomes the circle of least confusion. A light receiving element is arranged at a height, and at least one of the spots of each light beam formed on the light receiving element has a diameter that is different from the diameters of other spots. It is.

According to the present invention, in the above optical pickup, the spot diameter of each light beam formed on the light receiving element is set to d1, d2 ... dn, and the plurality of light beams are separated by the optical path separating means. Let L1, L2 ... Ln be the distances from the optical axis of the spot to the spots of the respective light beams formed on the light receiving element, and L1 <L2 <...
Assuming that the relationship of n holds, d1 <d2 <d3 ...
-The configuration has a relationship of <dn.

The outline of the optical pickup of the present invention will be described. Hereinafter, the present invention is applied to the integrated optical pickup 11 shown in FIG.
A description will be given of a configuration in which astigmatism is applied by the semicircular portions 16 and 17 to form return light spots S1 and S2 on the light receiving element PD.

The integrated optical pickup 11 shown in FIG.
Is for recording or reproducing information on or from the optical disc 10 as a recording medium, and has an objective lens 15 or the like as a means for irradiating the optical beam onto the optical disc, and returns light returned from the optical beam reflected by the optical disc. A holographic element 13 having a hologram 18 (16, 17) is provided as an optical path separating means for separating the two light beams, and the two light beams separated by the hologram 18 are used as a light receiving element PD.
The two light beams that are received by and are separated by the hologram 18 are used as spots S1 and S2 formed at different positions on the light receiving element PD. The integrated optical pickup 11 shown in FIG.
For example, the optical pickup is suitable for a read-only DVD (digital video disc).

When manufacturing the integrated optical pickup 11 having this structure, in order to obtain a correct control signal (tracking error signal, focus error signal, etc.) and main information signal (RF signal), a laser LD is used in an intermediate step. It is necessary to determine the positional relationship between the holographic element 13 and the package 12 in which the light receiving element PD is integrated.

In general, the positional relationship in the holographic element 13 having the shape shown in FIG. 1 is determined as follows. As shown in FIG. 4, the hologram 18
The direction perpendicular to the dividing line is taken as the X direction, and the direction parallel to the dividing line is taken as the Y direction. The return light is incident on the hologram 18 at a spot S0 having a substantially circular shape, and the spot S0 is located substantially at the center of the hologram 18 in FIG. The positional relationship between the package 12 and the holographic element 13 can be set by adjusting the positions of the hologram 18 in the X direction, the Y direction, and the rotation direction (θ direction). still,
The right side of FIG. 4 shows two spots S1 and S2 on the light receiving element PD in the state shown in FIG. 2, which is shown for comparison with FIG.

Next, the position adjustment of the hologram 18 will be described with reference to FIG. 5A and 5B show the hologram 18
It is a figure explaining the position adjustment of the X direction of. As shown in FIG. 5A, when the hologram 18 shifts to the upper side in the figure, the return light spot S0 shifts to the lower semicircular portion 16. At this time, the spot S1 formed by the lower semi-circular portion 16 becomes larger than the other spot S2, so that the X-direction position signal XP = (A + B)-(C + D)>
It becomes 0. On the other hand, as shown in FIG.
Shifts to the lower side in the figure, the spot S0 of the return light shifts to the upper semicircular portion 17, so the spot S2 becomes larger than the spot S1, and the X-direction position signal XP = (A
+ B)-(C + D) <0. In either case, if the position of the hologram 18 is adjusted so that the X direction position signal XP = (A + B) − (C + D) = 0, the hologram 1
The position of 8 in the vertical direction, that is, the X direction can be adjusted.

FIGS. 5C and 5D show the θ of the hologram 18.
It is a figure explaining position adjustment of a direction. As shown in FIG. 5C, when the hologram 18 is shifted counterclockwise in the drawing, the two spots S1 and S2 are biased to the portions A and D of the light receiving element PD in the drawing, so that the Y-direction position signal YP =
(A + D)-(B + C)> 0. On the other hand, as shown in FIG. 5D, when the hologram 18 is shifted clockwise in the drawing, the two spots S1 and S2 are biased to the lower portions B and C of the light receiving element PD in the drawing, so that the Y-direction position signal YP =
(A + D)-(B + C) <0. In either case,
If the position of the hologram 18 is adjusted so that the Y direction position signal YP = (A + D) − (B + C) = 0, the rotation direction of the hologram, that is, the position in the θ direction can be adjusted.

As described above, the position of the hologram 18, that is, the positional relationship between the holographic element 13 and the package 12, is determined by using the X direction position signal (X position signal) XP in the X direction and the Y direction position signal (Y position). Signal) Y
The position in the θ direction can be adjusted and determined using P.

However, as described above, the position in the Y direction cannot be adjusted by such a method. The reason for this will be described with reference to FIGS. 6 and 7. Figure 6A
As shown in, when the hologram 18 shifts to the right side in the figure,
The return light spot S0 shifts to the left. At this time, since the two spots S1 and S2 are biased to the portions A and D in the figure of the light receiving element PD, the Y direction position signal YP = (A + D)
-(B + C)> 0. On the other hand, as shown in FIG. 6B,
When the hologram 18 shifts to the left side in the figure, the return light spot S0 shifts to the right side. Since the two spots S1 and S2 are biased to the lower portions B and C of the light receiving element PD in the figure, the Y direction position signal YP = (A + D) − (B + C) <0.
That is, when the hologram 18 shifts in the Y direction, the spots S1 and S2 on the light receiving element PD move in the vertical direction, that is, the Y position direction in FIG. 6 due to the effect of astigmatism.

Next, as shown in FIG. 7A, consider adjusting the position of the hologram 18 in the state shown in FIG. 6A. At this time, two spots S before and after
Since the amount of astigmatism with respect to S1 and S2 is the same, the amount of movement of the two front and rear spots S1 and S2 is the same, and the spots are parallel.

Here, as shown in FIG. 7B, when the correction is performed by adjusting the position of the hologram 18 in the rotation direction, that is, the θ direction, the return light spot S0 does not coincide with the rotation center of the hologram 18, so that the correction is correctly performed. Can not do it. Specifically, since the two spots S1 and S2 on the light receiving element PD are substantially point-symmetrical with respect to the center of the light receiving element PD, the X-direction position signal XP = (A + B) − (C +
D) = 0, Y direction position signal YP = (A + D)-(B +
C) = 0, but the focus error signal FE = (A + C) − (B + D)> 0 due to the bias toward A and C, resulting in defocusing. Therefore, it becomes impossible to correctly control the focus state using the focus error signal FE.

Here, from FIG. 4 to FIG.
When the spots S1 and S2 are formed on the light receiving element PD by the astigmatism method in the semicircular portions 16 and 17 of X,
It can be seen that the direction position signal XP depends on the accuracy of the hologram 18 in the X direction, but the Y direction position signal YP depends on the accuracy of the hologram 18 in the Y direction and the θ direction. In this way, the Y direction position signal YP becomes
Since it depends on the accuracy of the direction, there are innumerable solutions in the combination of the Y direction and the θ direction. Therefore, even if the Y-direction position signal YP changes, the Y-direction position signal YP is set to 0 when the behavior of the hologram 18 in the Y-direction is different from that in the θ-direction. Depending on the solutions of the movement amount of the hologram 18 in the Y direction and the movement amount in the θ direction, defocus occurs as shown in FIG.

Therefore, in order to prevent defocusing even if the position in the Y direction is displaced, it is necessary to use another method. Therefore, in the present invention, there is provided a method for adjusting the X direction position signal XP and the Y direction position signal YP without defocusing even when the hologram is displaced in the Y direction, that is, in the direction parallel to the hologram dividing line. provide.

When the hologram is displaced in the Y direction, there is a problem that defocusing occurs even if correction is made by adjusting the rotation direction of the hologram as shown in FIG. Further, since the return light is made incident on the hologram 18 in a converged state, when the hologram 18 is displaced in the Y direction, the position where the return light passes is actually displaced, so that the incident angle to the hologram 18 is increased. Since it deviates from the predetermined angle, the diffraction state by the portions 16 and 17 of the hologram 18 also changes. Therefore, the focus state changes and defocus occurs. As a result, the shapes of the spots S1 and S2 on the light receiving element PD change from the semicircular shape (shape at the time of just focus) shown in FIGS. 6 and 7. That is, spots S1, S on the light receiving element PD due to astigmatism
In addition to defocus in which the focus error signal FE cannot be adjusted to 0 due to the movement of the position of 2, defocus due to a change in the focus state occurs. Therefore, it is necessary to make a correction in consideration of this point as well.

FIG. 8 shows changes in the positions and shapes of the spots S1 and S2 on the light receiving element PD when the hologram moves in the Y direction. Here, the defocus component caused by the movement of the positions of the spots S1 and S2 due to the above-mentioned astigmatism is the first defocus component DF1, and the defocus component caused by other changes in the focus state is the second defocus component. DF2. These defocus components D
It is assumed that F1 and DF2 are in a strengthening direction and a canceling direction with respect to each other. The defocus in each case is as follows: in the strengthening direction: defocus = DF1 + DF2 In the canceling direction: defocus = DF1-DF2.

First, as shown in FIG. 8A, the hologram 1
Consider a case where 8 is displaced to the right in the figure and the spot S0 of the returning light is displaced to the left. Two defocus components DF
When the actions of 1 and DF2 are in the direction of mutually enhancing (defocus = DF1 + DF2), the spots S1 and S2 move to the upper side by the action of the first defocus component DF1, as shown in the center diagram. Therefore, the Y direction position signal YP = (A + D)-(B + C)> 0. In addition, due to the action of the second defocus component DF2, the spot S
The directions of 1 and S2 are shifted clockwise.

On the other hand, each portion 16 and 17 of the hologram 18
When the direction of the astigmatism given by is opposite to the direction described above (the directions of the spots S1 and S2 change by 180 degrees at this time), the two defocus components DF
The actions of 1 and DF2 tend to cancel each other. In this case (defocus = DF1-DF2), as shown in the right figure, since the direction of the astigmatism is opposite, the spots S1 and S2 move downward due to the action of the first defocus component DF1, and Y Directional position signal YP = (A + D)-(B + C) <
It becomes 0. Further, due to the action of the second defocus component DF2, the directions of the spots S1 and S2 deviate from the semicircle in the counterclockwise direction.

Similarly, as shown in FIG. 8B, consider a case where the hologram 18 is displaced to the left in the figure and the spot S0 of the returning light is displaced to the right. Two defocus components DF
When the actions of 1 and DF2 are in the direction of mutually enhancing (defocus = DF1 + DF2), the spots S1 and S2 move downward due to the action of the first defocus component DF1, as shown in the center diagram. Therefore, the Y direction position signal YP = (A + D) − (B + C) <0. In addition, due to the action of the second defocus component DF2, the spot S
The directions of 1 and S2 are shifted counterclockwise.

On the other hand, the two defocus components DF1 and D
When the actions of F2 cancel each other (defocus = DF1-DF2), as shown in the diagram on the right side,
The spots S1 and S2 move upward due to the action of the first defocus component DF1, and thus the Y-direction position signal YP
= (A + D)-(B + C)> 0. Further, due to the action of the second defocus component DF2, the spots S1, S
The direction of 2 shifts clockwise from the semicircle.

Next, FIG. 9 shows a method of correcting when the hologram 18 shown in FIG. 8A is shifted to the right. Figure 9
A shows the same state as FIG. 8A. When the hologram 18 is rotated clockwise from this state, the state shown in FIG. 9B is obtained.

Two defocus components D shown in the central figure
When the actions of F1 and DF2 are in a direction in which the effects of F1 and DF2 are mutually enhanced (defocus = DF1 + DF2), the Y-direction position signal YP = (A +
D)-(B + C) = 0. At this time, the spots S1 and S2 are still A and C of the light receiving element PD.
The focus error signal FE = (A +
C)-(B + D)> 0. When the actions of the two defocus components DF1 and DF2 shown in the figure on the right are in directions canceling each other (defocus = DF1-DF2)
In order to rotate the hologram 18, the hologram 18 is rotated counterclockwise, which is opposite to the direction on the left. By this rotation, the Y direction position signal Y
It can be set to P = (A + D)-(B + C) = 0. At this time, due to the magnitude relationship between the first defocus component DF1 and the second defocus component DF2, the focus error signal FE = (A + C) − (B + D) is FE> 0.
Or FE <0. That is, when DF1> DF2, FE
When <0 and DF1 <DF2, FE> 0.

As described above, in the state of FIG. 9B, since the focus error signal FE = 0 has not been reached yet, defocus remains. Therefore, the defocus is corrected by changing the size ratio of the spots S1 and S2 before and after the light receiving element PD. Specifically, the size ratio of the spots S1 and S2 is changed by changing the ratio of the amount of astigmatism given by each portion 16 and 17 of the hologram 18. FIG. 9C shows a state in which the size ratio of the spots S1 and S2 is changed from the state of FIG. 9B.

Two defocus components D shown in the central figure
When the actions of F1 and DF2 are in the direction of mutually enhancing (defocus = DF1 + DF2), the hologram 1
By making the spot S1 on the left side of the light receiving element PD by the lower part 16 of 8 and the spot S2 on the right side of the light receiving element PD by the upper part 17 of the hologram 18 large, the focus error signal FE = ( A + C)-
It can be set to (B + D) = 0. When the actions of the two defocus components DF1 and DF2 shown in the diagram on the right are in directions canceling each other (defocus = DF1-DF
In 2), the focus error signal FE = (A + C) is obtained by changing the size ratio of the two spots S1 and S2 in accordance with the magnitude relationship between the first defocus component DF1 and the second defocus component DF2. )-(B + D) = 0
Can be adjusted to For example, when DF1> DF2, the left spot S1 is enlarged and the right spot S1 is increased.
Decrease 2. For example, when DF1 <DF2, the left spot S1 is made smaller and the right spot S2 is made larger. When DF1 = DF2, the correction can be performed without changing the astigmatism amount.

In the present invention, as shown in FIG. 9C, the defocus is corrected by changing the size ratio of the spots S1 and S2 on the light receiving element PD. To that end, for example, as described above, each part 1 of the hologram 18
Change the ratio of astigmatism given by 6,17.

To provide astigmatism, in the semicircular portions 16 and 17 of the hologram 18, specifically, for example, the distance between the diffraction gratings in the upper right and lower left directions is narrow, and the distance between the diffraction gratings in the upper left and lower right directions is small. Make it wider. Then, different astigmatisms can be given to the lower semi-circular portion 16 and the upper semi-circular portion 17 by varying the degree of widening the spacing of the diffraction grating.

In other words, this defocusing correction method uses the spot S1 on the light receiving element PD as the third defocusing component DF3 in order to cancel the first defocusing component DF1 and the second defocusing component DF2. ，
The defocus component is generated according to the size ratio of S2, and the third defocus component DF3 is optimized.

That is, for the first defocus component DF1 and the second defocus component DF2, when these are in the direction of increasing, DF1 + DF2 = DF3 When they are in the direction of canceling, DF1-DF2 = DF3 To satisfy the third defocus component DF
If the amount of 3 or the size ratio of the spots S1 and S2 is determined,
Defocus can be suppressed.

Here, as a special case, when the second defocus component DF2 has almost no effect or when the second defocus component DF2 is sufficiently smaller than the first defocus component DF1. The amount of change in the size ratio of the spots S1 and S2 on the light receiving element PD can be easily obtained. This case will be described below.

When the first defocus component DF1 mainly acts, the defocus can be reduced by correcting the movement of the spots S1 and S2 due to the displacement of the hologram 18. In this case, in order to reduce the defocus by correction, it is necessary to uniquely determine the movement amount of the hologram 18 in the Y direction and the movement amount in the θ direction. That is, in the hologram 18, X direction, Y direction, θ
Accuracy is required in three directions.

However, if the behaviors of the spots S1 and S2 are almost equal when the hologram 18 is moved in the Y direction and when it is moved in the θ direction, the problem of defocusing after the correction is solved. In this way spots S1, S2
If the behavior of the
Since the movements of the spots S1 and S2 when moving in the Y direction and the movements of the spots S1 and S2 when moving the hologram 18 in the θ direction are indistinguishable, in principle, a myriad of numbers are determined by the combination of the Y direction and the θ direction. No defocus should occur anywhere in the solution. Therefore, there is one degree of freedom in the two directions of the Y direction and the θ direction, that is, the X direction and the Y direction.
It becomes possible to adjust with two degrees of freedom in the direction or in the X direction and the θ direction.

Specifically, specifically, the hologram 18
Of the spot S1 on the light receiving element PD due to the movement in the θ direction of
The movement of S2 is as shown in FIGS. 5C and 5D, and the movement equivalent to this is performed by the spots S1 and S2 on the light receiving element PD.
With respect to the movement of the hologram 18 in the Y direction, the correction can be performed by moving or rotating the hologram 18 in the θ direction as in the conventional case. As the hologram 18 moves in the Y direction, the spots S1 and S2 on the light receiving element PD move in a direction perpendicular to the Y direction as shown in FIG.
The reason for this is the effect due to the astigmatism generated in the portions 16 and 17 of the hologram 18, and the spots S1 and S2.
The amount of movement of is almost proportional to the amount of astigmatism. Therefore, in each of the portions 16 and 17 of the hologram 18, if an astigmatism amount proportional to the distance from the origin (center of the optical axis of the outward path) to the light receiving element PD is given, the case of moving in the Y direction and the case of θ rotation It becomes possible to equalize the behavior of the spots S1 and S2.

Further, the spots S1, S on the light receiving element PD
The diameter d of 2 is also substantially proportional to the amount of astigmatism provided by the portions 16 and 17 of the hologram 18. Therefore, when the distance between the left spot S1 and the origin is L1, the shape of the left spot S1 is d1, the distance between the right spot S2 and the origin is L2, and the diameter of the right spot S2 is d2, the following relation When the expression L1 = kL2 (k is a constant), the hologram pattern of each portion of the hologram 18 is formed so that the spots S1 and S2 satisfying d1 = kd2 are formed.
This makes it possible to equalize the relationship between the movement of the hologram 18 in the Y direction and the movement in the θ direction.

Then, after setting the hologram 18 under these conditions, the hologram 18 is rotated for adjustment. This specific adjusting method will be described with reference to FIGS.
Consider a case where the hologram 18 is shifted to the right as shown in FIG. From the above relational expression, d1: d2 = L1: L2
It has become. Since L1 <L2, d1 <d2, that is, the right spot S2 is larger than the left spot S1. At this time, the moving amount Δ1 of the left spot S1 and the moving amount Δ2 of the right spot S2 are also Δ
The relationship of 1: Δ2 = L1: L2 is satisfied.

Here, as shown in FIG. 11A, when the hologram 18 is rotated clockwise, the X-direction position signal XP is generated.
= (A + B)-(C + D) = 0, Y direction position signal YP =
(A + D)-(B + C) = 0, focus error signal F
It can be seen that E = (A + C)-(B + D) = 0 and defocus is lost.

At this time, regarding the rotation, as shown in FIG. 11B, at the rotation angle θ1 of the spot S1 and the rotation angle θ2 of the spot S2, θ1 = Δ1 / L1 = Δ2 / L2 =
Since θ2 is established, it is understood that the defocus can be corrected by rotating at the rotation angle θ = θ1 = θ2.

Next, how to configure the integrated optical pickup 11 in response to the changes in the spots S1 and S2 and the method for adjusting the hologram 18 of the holographic element 13 will be described.

For example, with the distances L1 and L2 set to the designed values, the hologram 18 is moved in the Y direction and the spot S is moved.
By investigating the change of 1 and S2, the optimum spot S
The size ratio d1: d2 of 1 and S2 is obtained. Then, the hologram pattern of each of the portions 16 and 17 of the hologram 18 is formed so that the spots S1 and S2 satisfying this size ratio are formed. Especially the first defocus component D
When F1 is the main, the size ratio d1: d2 of the spots S1 and S2 can be easily calculated from the values of the distances L1 and L2.

If the hologram pattern of the hologram 18 is formed in advance in this way, when the optical pickup 11 is manufactured, only adjustment of the hologram 18 in the X direction and adjustment of the rotation direction (θ direction) will finally be performed. The optical pickup 11 can be manufactured so that it can be adjusted so that defocus does not occur, and the accuracy is good in the three directions of the X direction, the Y direction, and the θ direction. This makes it possible to easily manufacture the optical pickup 11 that does not cause defocus with a high yield.

Since the behavior of the spot on the light receiving element PD with respect to the change of the hologram 18 in the Y direction and the behavior of the spot on the light receiving element PD with respect to the change of the hologram 18 in the θ direction are equivalent, If adjustment is performed, adjustment in the Y direction can be omitted. This eliminates the need for a configuration for adjusting the Y direction, and simplifies the configuration of the optical pickup 11 or the configuration of the manufacturing apparatus (adjustment apparatus) for the optical pickup 11.

In the embodiment shown in FIG. 1 used in the above description, the light beam of the returning light is branched into two light beams by the hologram 18, but in the present invention, three or more returning lights are used. It is also possible to adopt a configuration in which the light beam is split into two.

At this time, the spot diameters of the light beams branched into n are defined as d1, d2 ... dn, respectively.
Then, in order to correct the defocus by changing the spot size ratio, at least one of d1 to dn
It suffices that one spot diameter has a value different from other spot diameters. For example, in three divisions, d1, d2,
The above-mentioned conditions are satisfied except that all d3 have the same value. For example, in the case of four divisions, the above-mentioned condition is satisfied, except that d1, d2, d3, and d4 all have the same value and twos each have the same value.

In particular, when the action of the defocus component (the above-mentioned second defocus component DF2) due to the change of the focus state is sufficiently small, further from the branch element such as the hologram to the spot of each light beam on the light receiving element. L1 <L2 <... <L, where the distances are L1, L2 ... Ln
When n, d1 <d2 <... <dn may be satisfied.

The present invention is not limited to the embodiment of the integrated optical pickup 11 shown in FIG. 1, and can be applied to various other configurations without departing from the scope of the present invention.

[0062]

According to the above-described optical pickup of the present invention, adjustment in the Y direction can be omitted out of adjustments in the three directions of the X direction, the Y direction, and the θ direction. The configuration for performing can be omitted. By adjusting the remaining two directions, for example, the X direction and the θ direction, it is possible to manufacture an optical pickup that can easily control the focus state without causing defocus with a high yield. Therefore,
It is possible to simplify the configuration of the optical pickup or the optical pickup manufacturing apparatus (adjustment apparatus).

[Brief description of drawings]

1A and 1B are schematic configuration diagrams of an integrated optical pickup to which the present invention is applied.

FIG. 2 is a diagram for explaining signal detection in the integrated optical pickup of FIG.

FIG. 3 is a diagram for explaining signal detection in the integrated optical pickup of FIG.

FIG. 4 is a diagram illustrating a position adjusting method in the holographic element of FIG.

5 is a diagram illustrating a position adjusting method in the holographic element of FIG. It is a figure explaining the position adjustment of the A and B hologram in the X direction. It is a figure explaining the position adjustment of the C and D hologram in the (theta) direction.

FIG. 6 is a diagram showing movement of spots when A and B holograms are displaced in the Y direction.

7A is a diagram showing a state of FIG. 6A. FIG. B FIG. 7B is a diagram showing a state when the hologram is rotated clockwise from the state of FIG. 7A.

FIG. 8 is a diagram showing movement of spots when A and B holograms are displaced in the Y direction.

9A is a diagram showing a state of FIG. 8A. FIG. B FIG. 9B is a diagram showing a state when the hologram is rotated clockwise from the state of FIG. 9A. FIG. 9C is a diagram showing a state in which the ratio of the amount of astigmatism generated by the hologram is changed from the state of FIG. 9B.

FIG. 10 is a diagram showing movement of a spot when a hologram is displaced in the Y direction.

11A is a diagram showing a state when the hologram is rotated clockwise from the state of FIG. FIG. 9 is a diagram showing the relationship among the rotation angle of the B hologram, the amount of movement of the spot, and the distance from the origin to the spot.

[Explanation of symbols]

10 optical disc, 11 (integrated type) optical pickup, 12 package, 13 holographic element,
14 collimator lens, 15 objective lens, 18 hologram, LD laser, PD light receiving element, S1, S2
spot

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 5D118 AA06 AA13 BA01 CA11 CA23                       CC02 CC03 CC15 CD02 CF05                       DA08 DA20 DA21 DB12 DB17                 5D119 AA28 AA38 BA01 EA03 JA09                       JA14 JA15 KA19 LB13                 5D789 AA28 AA38 BA01 EA03 JA09                       JA14 JA15 KA19 LB13

Claims (2)

[Claims] 1. An optical pickup for recording or reproducing information on or from a recording medium, comprising means for irradiating the recording medium with a light beam and return light reflected by the recording medium. An optical path separating means for separating the plurality of light beams, and a light receiving element for receiving the plurality of light beams separated by the optical path separating means, and the plurality of light beams separated by the optical path separating means are Each light beam forms a spot at a different place on the light receiving element, and the optical path separating means has a diffraction pattern for generating astigmatism on the spot formed on the light receiving element. The light-receiving element is arranged at a height at which the circle is the circle of least confusion, and at least one of the spots of the light beams formed on the light-receiving element has a diameter of another spot. Tsu optical pickup and having a value different from the diameter of the bets. 2. With respect to the plurality of light beams, the diameter of the spot of each light beam formed on the light receiving element is d1,
d2 ... dn, and the distance from the optical axis of the portion separated by the optical path separating means to the spot of each light beam formed on the light receiving element is L1, L2 ... Ln,
The optical pickup according to claim 1, wherein the relationship of d1 <d2 <d3 ... <dn is established when the relationship of L1 <L2 <...