JP2001160223A - Optical pickup - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical pickup which quadrisects a light spot by two axes of a tack direction and a radial direction and does not affect an astigmatism error signal. SOLUTION: This optical pickup condenses a laser beam L1 to a spot form, irradiates the information surface of an optical disk with this laser beam, focuses the reflected light from the information surface by this irradiation to a spot, irradiates the surface of a quadrisecting optical sensor 14 with this spot and detects the deformation of the spot on the quadrisecting optical sensor by an astigmatism method. A luminous flux splitting member 22 which splits the luminous flux of the reflected light from a beam splitter side to four split luminous fluxes and emits this luminous fluxes, respectively, is inserted between a beam splitter 6 and a detecting lens 10 or between the detecting lens and a cylindrical lens 12. The four split luminous fluxes from the luminous flux splitting member create dead zones near the diving lines of the sensor by having four inclined exit surface S1 to S4 which respectively emit the four split luminous fluxes to be condensed and cast to the inside of the respective photodetecting regions exclusive of the dead zones 30 disposed in the four photodetecting regions constituting the quadrisecting optical sensor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an optical pickup for reading and writing information on an optical disk or the like.

[0002]

2. Description of the Related Art Recently, a DVD (Digital Ver.)
In order to reproduce a two-layer disc having two recording layers, a pickup for a side disc (side disc) selectively focuses a spot on each of the 0 and 1 surfaces, and when reproducing information, it reflects from a non-reproducing surface. The reflected stray light may return to the light detection sensor and cause crosstalk to the focus signal, thereby disturbing the focus signal. In order to reduce the interference with the focus signal, the upper limit is defined by the size of the pattern of the light detection sensor projected onto the disk surface. As a result, the size of the light detection sensor is reduced.

Further, since the transfer rate of the read signal is increased by performing higher-speed reproduction than the normal-speed reproduction of DVD, the photoelectric conversion system (IV-AMP and light detection sensor) has a high frequency characteristic band. Therefore, the shape and dimensions of the light detection sensor are reduced in order to reduce the stray capacitance in the light detection sensor pattern. For example, one side is approximately 1.
It is a light detection sensor of about 00 μm. The spot here is about 50 μm, which is half of that.

Here, a conventional optical pickup using the astigmatism method for focus detection will be described. FIG. 8 is a configuration diagram showing a conventional optical pickup. In the figure, reference numeral 2 denotes a semiconductor laser element for outputting a laser beam L1 for reading and writing, 4 denotes a collimator lens for converting the laser beam L1 into parallel light, 6 denotes a beam splitter, and 8 condenses the laser beam L1 on an optical disk D. An objective lens 10, a detection lens 10 for condensing the reflected light from the optical disc D passing through the beam splitter 6, a cylindrical lens 12 having a lens function in only one direction, and a beam 14 passing through the cylindrical lens 12 This is a four-division optical sensor that detects light. The four-division optical sensor 14 is divided into four parts by orthogonal division lines as shown in FIG.
It has four photodetection areas indicated by C and D, takes the sum signals of the diagonal photodetection areas, A + C and B + D, and inputs these sum signals to the differential amplifier 16 to
The focus signal FE is obtained.

[0005] The laser beam L 1 emitted from the semiconductor laser element is collimated by the collimator lens 4. A light beam is incident by an objective lens 8 through a beam splitter 6 for separating the light in the forward path and the return path. The laser light L focused by the objective lens 8 having a numerical aperture of about 0.6
Reference numeral 1 is applied to the information surface of the DVD optical disk D and reflected. The reflected light passes through the return optical system, is reflected by the beam splitter 6, passes through the detection lens 10 composed of a convex lens and the cylindrical lens 12, and a pattern is formed on the sensor 14. Here, the same direction as the track direction of the optical disc D is referred to as a Tan direction (hereinafter referred to as a tangential direction), and a direction perpendicular to the track is referred to as a Rad direction (hereinafter referred to as a radial direction). In FIG. 8, the direction perpendicular to the paper surface is the radial direction, and the direction parallel to the paper surface is the tangential direction. The cross section of the optical path after passing through the beam splitter 6 is also shown in FIG. 8, where the X axis is the radial direction and the Y axis is the tangential direction. The cylindrical lens 12 is inserted so that the direction of 45 degrees is the generatrix in the optical path cross section in order to cancel the modulation of the reflected light by the track crossing.

When the light spot formed on the information surface of the optical disk D is shifted from the position of the spot having the smallest diameter in the direction of the optical axis, the reflected light is diffused or converged. This is deformed by the astigmatism optical system, and on the four-division optical sensor 14, as shown in FIG.
It changes to an elliptical shape. When the difference between the diagonal sum signals is formed by the arithmetic circuit shown in FIG.
E is formed.

[0007]

Here, it is very important to accurately adjust the positional relationship between the beam splitter 6 and the four-divided optical sensor 14. For example, the beam splitter 6 is fixed to a housing surface (not shown) with an adhesive. Here, foreign matter enters between two contact surfaces between the housing surface on which the beam splitter 6 is mounted and the bonding surface on the beam splitter 6 side, Deformation due to corrosion causes a very slight change in angle in the vertical direction. Further, in the case where the adhesive is fixed only by the adhesive, when the adhesive is solidified, if there is unevenness in the stress, the adhesive is pulled and the angle slightly changes in the left-right direction.

The change in the angle is as follows. The spot diameter on the four-divided optical sensor 14 is about 50 μm as described above, and the permissible dimension of the spot is several μm, so that the focal length of the detection lens 10 is 20 mm. In this case, the angle variation is tan ^-1 (0.003 / 20) = 8.5 × 10 ^-3 degrees. This is the case of a 5 mm square beam splitter 6,
Underneath, dust of 0.75 μm is sandwiched, which becomes 0 μm with the passage of time. This is a very fine angle that can occur even when the bonding surface changes due to rust or the like. For this reason, unless the countermeasures against the fluctuation of the reflection surface are taken with very high precision, the optical pickup cannot be realized.

The accuracy of the focus adjustment of the focus signal (adjustment at which the RF signal becomes the best at the 0V point of the S-order characteristic) is also limited to the jig accuracy and time of the adjustment process, and the ideal zero value is obtained. Cannot be adjusted. For example, at the time of this adjustment, the alignment of the four-division optical sensor 14 is performed by mechanical alignment using eccentric pins so as to balance the output signals of the four-division optical sensor 14 in the X direction and the Y direction. Since the only variation accuracy that can be accepted is OK.
An error occurs between the center of the pattern on the four-division optical sensor and the midpoint of the division line. Such cause (small angle change in the return path system, pattern position accuracy on the 4-split optical sensor)
As a result, the optical axis was moved, and as a result, the spot on the four-divided optical sensor was moved, causing a deviation between the dividing line and the center of the pattern.

As a result, it is known that an offset of the push-pull error signal and a track crossing signal are mixed into the focus error signal. When the pattern moves on the 4-split optical sensor, when reproducing the recorded area of the disk, the recorded RF signal mixed with the wobble signal recorded by the undulation of the groove becomes unbalanced and differential. The C / N of the wobble signal is degraded because it is not canceled by the calculation. FIG. 11 shows a state where a positional shift of Δt occurs between the optical axis and the pattern on the four-divided optical sensor as described above. As a related application of the present invention, Japanese Patent Application Laid-Open No. 7-176061 is disclosed, which discloses an improvement of a fluctuation of a focus signal due to track crossing. In this improvement, a light beam is split by a transparent roof prism, astigmatism is given to the light beam, and one of the light beams is received to detect focus, but this is a measure for crossing tracks. However, since this does not reduce the dimensional accuracy between the sensor and the pattern intended in the present invention, the relationship differs from the present invention.

The present invention focuses on the above problems,
The purpose of the present invention is to effectively solve this problem. The purpose is to divide a light spot on a four-division optical sensor into four parts by two axes in a tangential direction and a radial direction, and to divide a sensor dividing line and a spot. An optical pickup configured so that a dead zone is formed between the end line and an astigmatism error signal is prevented from being caused by an angle change of a reflection surface of a reflected light beam or an adjustment error between a quadrant light sensor and a spot. To provide.

[0012]

According to the first aspect of the present invention, a laser beam emitted from a light source is supplied to a collimator lens,
Through the beam splitter and the objective lens in order,
The light is condensed in the form of a spot on the information surface of the optical disc and irradiated, and the reflected light is irradiated from the information surface by the irradiation of the objective lens, the beam splitter, the detection lens, and the cylindrical lens in this order through the cylindrical lens. The spot is condensed and radiated on the quadrant optical sensor located on the exit side of the optical disc, and the spot is radiated on the information surface of the optical disc by an astigmatism method for detecting the deformation of the spot on the quadrant optical sensor. An optical pickup having a configuration for detecting a focus error of a spot light, wherein the beam splitter side is provided between the beam splitter and the detection lens, or between the detection lens and the cylindrical lens. A light beam splitting member that emits the light beam of the reflected light emitted from the light beam as four split light beams is inserted. The light beam splitting member emits light from the light beam splitting member when the respective optical axes of the beam splitter, the light beam splitting member, the detection lens, the cylindrical lens, and the quadrant light sensor are matched. The four divided light fluxes for condensing and irradiating each of the four divided light sensors in each light detection area, excluding a dead zone provided near each boundary of the four light detection areas constituting the four divided light sensor. This is provided with four inclined emission surfaces for emitting one divided light beam.

Thus, by the action of the light beam splitting element,
Since the light beam is divided into four and the light beams in the respective divided regions are given different angles with respect to the optical axis, a dead zone is generated between the division line of the four-division optical sensor and the division end line of the spot. Even if there is a slight change in the angle of the reflection surface of the reflected light beam or an adjustment error between the spots of the quadrant light sensor, this does not adversely affect the astigmatism error signal.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the optical pickup according to the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a configuration diagram showing an optical pickup of the present invention, FIG. 2 is a diagram showing a light beam splitting element, and FIG. 3 is a diagram showing details of each part of the light beam splitting element. The optical pickup 20 of the present invention differs from the optical pickup shown in FIG. 8 except that a light beam splitting element 22 as a light beam splitting member, which is a feature of the present invention, is inserted between the beam splitter 6 and the detection lens 10. The configuration is exactly the same. In the following description, the light beam splitting element 2
2 is inserted between the beam splitter 6 and the detection lens 10, but the invention is not limited to this, and the light beam splitting element 22 is connected to the detection lens 10 and the cylindrical lens 12.
The same effect can be obtained by interposing between them.

In FIG. 1, reference numeral 2 denotes a semiconductor laser element for outputting a read / write laser beam L1, 4 denotes a collimator lens for converting the laser beam L1 into parallel light, 6 denotes a beam splitter, 8
Is an objective lens for condensing the laser beam L1 on the optical disc D, 10 is a detection lens for condensing the reflected light from the optical disc D passing through the beam splitter 6, and 12 is a cylindrical lens which exhibits a lens function only in one direction. , 1
Reference numeral 4 denotes a four-division optical sensor that detects light passing through the cylindrical lens 12. In the figure, reference numeral 14a denotes a sensor surface of the four-split optical sensor 14, and 22a denotes a light beam splitting element surface of the light beam splitting element 22. As shown in FIG. 9, the four-division optical sensor 14 is divided into four parts by orthogonal division lines d1 and d2 (partition lines 26 and 28 to be described later), and A, B,
It has four photodetection areas indicated by C and D, takes the sum signals of the diagonal photodetection areas, A + C and B + D, and inputs these sum signals to the differential amplifier 16 to
The focus signal FE is obtained. In FIG. 1, the cross section of the optical path after being reflected by the beam splitter 6 is also shown.

As described above, in the middle of the optical path between the beam splitter 6 and the detection lens 10, the light beam is divided into four by two axes in the tangential direction and the radial direction, and the light beam is A light beam splitting element 22 having inclined exit surfaces S1 to S4 for giving different angles to the axis 24 is interposed. Specifically, the light beam splitting element 22 is formed as shown in FIG. FIG. 2 (A)
2 is a perspective view of the light beam splitting element, FIG. 2B is a side view as viewed from the direction of arrow A1 in FIG. 2A, and FIG.
2A is a side view as seen from the direction of arrow A2, and FIG. 2D is a side view as seen from the direction of arrow A3 in FIG. 2A. The optical axis 24 and the exit surface of the light beam splitting element 22 (the light beam splitting element surface 2
2a) Intersection with the center on the side (detection lens 10 side)
And the seat axes of the plane passing through the center O and orthogonal to the optical axis 24 are the X-(-X) axis and the Y-(-Y) axis.
The entire light beam splitting element 22 is, for example, transparent glass,
Alternatively, it is made of a molded element made of plastic, and its incident surface (on the side of the beam splitter 6) is a single plane. On the exit surface side, there are four inclined exit surfaces S1, S composed of inclined surfaces formed in a triangular shape with the center O as the center.
2, S3 and S4 are formed. Slant exit surfaces S1 and S
2 and S3 and S4 are arranged so as to face the center O, respectively.

One of the opposed inclined emission surfaces S1, S2 is
The angle formed by the plane passing through the center O and perpendicular to the optical axis 24 is shown in FIG.
When the angles are defined as shown in FIG. 2, the angles are −θ and + θ, respectively, and the angle formed by the other opposed inclined emission surfaces S3 and S4 with the surface passing through the center O and orthogonal to the optical axis 24 is as shown in FIG. Are defined as + θ and −θ, respectively. Here, each boundary line S1b, S1c, S2b, S2c, S3b, S of each inclined emission surface S1, S2, S3, S4.
The directions of 3c, S4b, and S4c match the directions of the dividing lines 26 and 28 of the four-divided optical sensor 14, and the generatrix direction 12 of the cylindrical lens 12 is along the 45-degree direction of the XY coordinates. FIG. 3 shows the inclined emission surfaces S1 and S3 as representatives.
4 and FIG. 5 are views showing the change of the light beam by the light beam splitting element 22. FIG. FIG. 4 shows the inclined exit surface S1 as a representative, and FIG. 5 shows the inclined exit surface S4 as a representative.

FIGS. 4A and 5A are perspective views and FIG.
(B) and FIG. 5 (B) are side views, FIG. 4 (C) and FIG.
(C) shows top views, respectively, with and without insertion of the light beam splitting element 22 (without splitting element,
(Indicated as present) is shown together with the change in the traveling direction of the light beam. In FIG. 4, it is assumed that the inclination angle −θ of the inclined exit surface S1 is set to about +0.1 degrees (see FIGS. 2 and 3). 4 and 5 are diagrams showing patterns on the sensor surface. Here, the coordinate axes on the sensor surface are once condensed by the detection lens 10 and the cylindrical lens 12, and then the corresponding X axis is reversed in the + and-directions. On the other hand, the Y axis corresponding to the sensor surface without being inverted is left as it is. In addition, the tangential axis and the radial axis are rotated by 90 °, and are thus rotated. The coordinate axes on the assumption that the coordinate axes described by the light beam splitting element 22 are projected are shown. Here, FIG.
As shown in the figure, the side S1a of the inclined exit surface S1 is X-
Since it is not inclined with respect to the (-X) axis, the parallel light beam passes through as it is. Further, since the generatrix direction 12b of the cylindrical lens 12 is set to the Y-(-Y) axis direction, the parallel luminous flux viewed from the upper surface (FIG. 4C) is a combined focal position (condensing point) of the detection lens 10 and the cylindrical lens 12. Is converged to. On the other hand, the inclined exit surface S1 is inclined by -θ degrees with respect to the Y-(-Y) axis.
After exiting the inclined exit surface S1, the light beam is refracted away from the optical axis 24. As a result, the light beam converging at the focal point of the detection lens 10 passes through the cylindrical lens 12 without any effect, and the focal length f × Tan of the detection lens 10
The convergent spot moves away from the optical axis 24 by an angle of + θ. As a result, as shown in FIG. 3, the area designated by TOR, that is, the spot pattern SS1 of the light beam passing through the inclined exit surface S1 moves upward (Y direction) as also shown on the right side in FIG. As a result, from the dividing lines 26 and 28 of the four-divided optical sensor 14, the end SS
1a and SS1b are separated. Similarly, the area designated by -TO-R, that is, the spot pattern SS2 of the light beam that has passed through the inclined exit surface S2 moves below the four-split optical sensor 14 (in the -Y direction). Sensor 14
End SS2a of the pattern SS2 from the dividing lines 26 and 28 of
SS2b leaves.

On the other hand, FIG. 5 shows a region designated by -ROT in FIG. 3, that is, a light beam passing through the inclined exit surface S4. In FIG. 3, for convenience, the region designated by RO-T, that is, the inclined exit surface S3 is divided and described, but the surface facing this surface S3 is the inclined exit surface S4. Since the side S4a of the inclined exit surface S4 is not inclined with respect to the Y axis, the parallel light beam passes through as it is. On the other hand, when viewed from above, the inclined exit surface S4 is inclined at an angle −θ, for example, about −0.1 degrees with respect to the X-axis, so that the light flux is combined with the detection lens 10 and the cylindrical lens 12 at the combined focal position (condensing position). (Point), a position shift due to the angle −θ occurs. That is, the movement is a movement of the combined focal length fg × tan-θ. As a result, the spot pattern SS4 of the luminous flux that has passed through the -ROT region, that is, the light exit surface S4, moves in the X direction (left direction) on the four-divided optical sensor 14 (FIG. 5).
(See also the figure on the right, which is also included inside.) As a result, the ends SS4a and SS4b of the pattern SS4 are separated from the division lines 26 and 28 of the four-division optical sensor 14. Similarly, the spot pattern SS3 of the luminous flux that has passed through the RO-T area, that is, the inclined exit surface S3, moves in the -X direction (rightward) of the four-division optical sensor 14. As a result, the ends SS3a and SS3 of the pattern SS3 are obtained from the dividing lines 26 and 28 of the four-divided optical sensor 14.
b leaves.

These are divided into four regions TOR, -TO-R,
RO-T, -ROT, that is, when acting on the inclined exit surfaces S1 to S4, the patterns SS1 to SS4 on the sensor surface are cut open in the direction along the dividing lines 26 and 28, as shown in FIG. And dividing line 2 on the sensor surface
The dead zone 30 (that is, SS1b-S)
Between S3b, SS4a-SS2a, SS1a-SS4b
(Between SS2b and SS3a). In FIG.
At the time of defocus, at the time of focusing, and at the time of + defocus, respectively. As shown in FIG. 9, the width of the dead zone 30 does not change even if the spot on the sensor moves due to the fluctuation of the reflection surface or the deviation of the adjustment of the sensor 14, as shown in FIG. Even if the diagonal sum is calculated, no offset occurs in the focus signal. Also,
(A + D)-(B +) for forming a push-pull signal
Even if the calculation of C) is performed, no offset is generated. Also, since there is no mismatch between the dividing lines 26 and 28 and the center of the pattern on the sensor in the tangential direction, the error of the detection signal and the focus noise signal generated when the sensor pattern crosses the track due to the displacement in the tangential direction. Does not occur.

Here, the angle θ is a value determined by the combined focal length f of the astigmatism system and the width of the dead zone 30 formed on the sensor 14. If the width of the dead zone 30 is 2 W, θ =
tan ^-1 (W / f). FIG. 7 shows the noise included in the focus signal of the conventional optical pickup and the focus signal of the optical pickup of the present invention. When the dead band width is set to 20 μm, the noise of the focus signal due to the displacement of the sensor in the X direction by the astigmatism method. Generation is caused by the formation of the dead zone 30 ±
It was found that the margin was widened without generation up to 10 μm.

[0022]

As described above, according to the optical pickup of the present invention, the following excellent functions and effects can be exhibited. Since the detection of the focus signal by the astigmatism method is performed by an optical system provided with a light beam splitting element in the middle of the optical path, a split pattern is formed on the sensor at a distance from the split line, and the DVD When a small size photodetection sensor is used for dual layer disc reproduction and high speed reproduction, the strict dimensional accuracy required so far is relaxed, and a margin in assembly is obtained. ,
After assembling, the movement of the pattern on the sensor due to the fluctuation of the reflection surface can be prevented from being affected at all within the dead zone, and the margin for long-term stability can be expanded. As a result, when playing back an optical disc such as a DVD-RAM which has an L / G format and in which noise across the groove is likely to occur, the track crosses the track groove which is generated due to insufficient adjustment accuracy in the sensor section. Thus, it is possible to avoid a problem that an unnecessary error component is generated and a difference in an optimum focus point between a land and a groove is thereby generated. Even with respect to the tilt of the optical disk, it does not affect the detection signal at all within the dead zone.
It is possible to avoid the occurrence of a state in which a focus servo is deviated by generating a track cross interference signal at the time of access.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an optical pickup of the present invention.

FIG. 2 is a diagram showing a light beam splitting element.

FIG. 3 is a diagram showing details of each part of a light beam splitting element.

FIG. 4 is a diagram showing a change of a light beam by a light beam splitting element.

FIG. 5 is a diagram showing a change of a light beam by a light beam splitting element.

FIG. 6 is a diagram showing a state in which a dead zone is formed across a dividing line on the sensor surface.

FIG. 7 is a diagram illustrating noise included in focus signals of a conventional optical pickup and the optical pickup of the present invention.

FIG. 8 is a configuration diagram showing a conventional optical pickup.

FIG. 9 is a diagram illustrating a photodetection region divided into four by a division line.

FIG. 10 is a diagram showing a state where a spot changes on a four-division optical sensor.

FIG. 11 is a diagram illustrating a state in which a position shift of Δt occurs between the optical axis and the pattern on the four-divided optical sensor.

[Description of References] 2 ... Semiconductor laser element, 4 ... Collimator lens, 6 ... Beam splitter, 8 ... Objective lens, 10 ... Detection lens,
12 ... cylindrical lens, 14 ... quadrant optical sensor,
Reference numeral 20 denotes an optical pickup, 22 denotes a light beam splitting element, 24 denotes an optical axis, 26 and 28 denotes a dividing line, 30 denotes a dead zone, D denotes an optical disk, L1 denotes a laser beam, and S1 to S4 denotes an inclined exit surface.

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) JA24 JA43 JA70 KA19 KA24 KA26 LB05

Claims (1)

[Claims] 1. A laser beam emitted from a light source is condensed in a spot shape on an information surface of an optical disk through a collimator lens, a beam splitter, and an objective lens in order, and is irradiated on the information surface. The reflected light is condensed on a four-division optical sensor located on the emission side of the cylindrical lens through the objective lens, the beam splitter, the detection lens, and the cylindrical lens in this order, and irradiated. By the astigmatism method to detect the deformation of the spot on the split optical sensor,
An optical pickup having a configuration for detecting a focus error of a spot light irradiated on the information surface of the optical disc, between the beam splitter and the detection lens, or
Between the detection lens and the cylindrical lens,
The reflected light beam emitted from the beam splitter side
A light beam splitting member that emits each of the two split light beams is interposed. The light beam splitting member is configured to set the optical axis of each of the beam splitter, the light beam splitting member, the detection lens, the cylindrical lens, and the quadrant light sensor. When the four divided light beams emitted from the light beam dividing member are coincident with each other, each of the four divided light beams excluding a dead zone provided near each boundary of the four light detection regions constituting the four divided light sensor is included in each light detection region. An optical pickup, comprising: four inclined emission surfaces for emitting the four divided light beams, respectively, for condensing and irradiating the divided light beams.