JPH0750030A - Optical pickup device - Google Patents

Abstract

PURPOSE:To stably remove the crosstalk component in a reproduced signal without depending on the movement of a received light pattern with focus servo and the change in distribution of the intensity of light. CONSTITUTION:A polarization separating type hologram 3 and a 1/4-wavelength plate 4 are arranged on the opposite side of a semiconductor laser 1 in the proximity of an objective lens 2. These parts are driven as a unitary body. The incident light on the objective lens 2 is split and diffracted in a space by the use of a hologram. The diffracted light is received with a plurality of photodetectors provided on the same plane as the semiconductor laser 1. Thus, the crosstalk component is removed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording / reproducing apparatus or an optical information reproducing apparatus.

[0002]

2. Description of the Related Art In recent years, the density of optical information recording / reproducing devices has been increasing. In particular, the wavelength of the light source is shortened by using a light source using a red semiconductor laser or a second harmonic generation element (hereinafter abbreviated as SHG light source) as a light source, and the numerical aperture of the objective lens (hereinafter Research and development to raise the NA (abbreviated as NA) is underway. With these, the signal track pitch and the pit length can be reduced in proportion to the light source wavelength and in inverse proportion to the NA of the objective lens. For example, regarding the track width, a current compact disc reproducing device (hereinafter abbreviated as CD) uses a light source with a wavelength of 780 nm and an objective lens with an NA of 0.45 to read a signal with a track pitch of 1.6 μm. If a red semiconductor laser is used and an objective lens of NA 0.65 is used, it is possible to read a signal having a track pitch of 0.97 μm. However, when the track width is made narrower than that, the crosstalk noise component from the adjacent track is mixed in the signal, which hinders the signal reproduction. In order to overcome this, it is necessary to introduce a new recording / reproducing optical system and a new signal processing system.

A crosstalk canceller has been proposed as a method of narrowing the track width without degrading the signal.

As one method of crosstalk canceller,
There is a method (one-beam crosstalk canceller) in which reflected light from an optical disc is received by a photodetector divided into three areas in the track direction, and the amount of received light in each area is weighted and added (eg, Ito et al., Japanese Patent Application No. 03-336503
No. 60-138748). The operating principle will be described below.

FIG. 16 shows an example of the configuration of an optical pickup which realizes a one-beam crosstalk canceller. Part of the reflected light from the optical disk 5 passes through the half mirror 10 and irradiates the three-division photodetector 9. Here, the light intensity distribution on the objective lens 2 is projected on the three-divided photodetector 9 in a one-to-one manner. FIG. 17 illustrates the light intensity distribution of the reflected light from the optical disc on the objective lens surface.

When considering the light intensity distribution of FIG. 17, the reflected light from the optical disk is treated as a set of some diffracted light. An enlarged view of the pit row 5a is shown in FIG. That is, the pit string pattern of the optical disc 5 is modeled as a two-dimensional diffraction grating in which the unit cells 18 are two-dimensionally distributed with an infinite size as shown in FIG. At this time, the intensity distribution of the light reflected from the disk 5 is represented by the product of the intensity distribution of the light spot 17 (approximate Gaussian distribution) and the complex reflectance of the two-dimensional diffraction grating. Further, since the light intensity distribution on the objective lens can be obtained by Fourier transforming the light intensity distribution of the reflected light, the reflected light returning to the lens is the diffraction pattern on the two-dimensional diffraction grating and the light spot 1.
Given in convolution with the far field pattern of 7. The diffracted light from the two-dimensional diffraction grating has a two-dimensional lattice shape, and the far field pattern of the light spot 17 on the disk surface has a Gaussian distribution like the spot. From the above, the light intensity distribution on the objective lens surface is shown in FIG.
7, a circular Gaussian distribution pattern is two-dimensionally arranged in a grid pattern. Of this reflected light, the light returned to the portion surrounded by the circle of 25 is captured by the objective lens 2 and guided to the three-division photodetector 9. Therefore, for the output signal of the photodetector, the total power of the light within the 25 circles may be calculated.

Here, the diffraction order of the diffracted light having the diffraction order m in the radial direction and the diffraction order n in the tangential direction is represented by the (m, n) order. At this time, (m, 0)
Since the next diffracted light does not include a signal component, and the diffracted light of the second or higher order does not enter the diameter of the objective lens, it does not affect the signal output. As described above, the crosstalk components included in the signal are the (1,1) th order diffracted light 21, the (0,1) th order diffracted light 24, the (-1,1) th order diffracted light 27, the (1, -1) th order diffracted light 23, ( Six diffracted lights of 0, -1) diffracted light 26 and (-1, -1) diffracted light 29 and (0, 0) diffracted light 25
It can be seen that it is caused by the interference with. That is, the crosstalk component is generated when the objective lens diameter 16 in FIG.
Among the inner regions, the regions 41 to 43 are the shaded portions.

The light intensity distribution in this area is modulated by crosstalk. It should be noted here that the (1,1) order diffracted light 21, the (1, -1) order diffracted light 27, the (-1,1) order diffracted light 23, and the (-1, -1) order diffracted light 29 (in FIG. 13). (Represented by a solid line circle) and (0,1) -order diffracted light 22, (0,-
1) A phase relationship between the diffracted light 28 (represented by a broken line circle in FIG. 13). Since the phases of the two are inverted, the diffracted light interferes with the (0,0) th-order diffracted light in regions 44 and 46 (hatching part in the upper right direction in FIG. 13) and region 45 (in the upper left direction in FIG. 13). In the hatched part),
Crosstalk signal components whose phases are opposite to each other are generated.

FIG. 19 shows the (1,1) th order diffracted light 21 and
An example of the phase relationship between the (0,1) -th order diffracted light 22 and the (0,0) -th order diffracted light is illustrated. FIG. 19 shows the (0,0) th order diffracted light 25.
FIG. 6 is a diagram when the phases of the (0, 1) th order diffracted light 22 are inverted by 180 °. Phase 53 of (1, 1) th order diffracted light 21
Is the opposite phase to the phase 52 of the (0,1) th order diffracted light 22,
It is in phase with the phase 51 of the (0,0) th order diffracted light.
As a result, the diffracted lights 25 and 21 strengthen each other, and the diffracted lights 25 and 22
On the contrary, they interfere so as to weaken each other.

In FIG. 17, this state corresponds to the interference that strengthens each other in the area 41 and weakens each other in the area 42. Eventually, signals of opposite phases exist outside and inside the area dividing line 19. I understand.

The light receiving pattern on the lens surface in FIG.
Since the light is projected on the photodetector in a pair 1, if the photodetector is divided at the position corresponding to the area dividing line 19, signals in which the crosstalk components of the signals are mixed in opposite phases to each other can be obtained. The crosstalk components can be removed by weighted addition of the outputs from the respective regions of the photodetector so that the antiphase crosstalk components are balanced. That is, the central portion P ₂ of the split photodetector 'output signal from the S _C and both side portions P _1', the output signal S _S from P ₂ ', with no crosstalk signal S S = k _It is sufficient to define ₁ * S _C + k ₂ * S _S and optimize k ₁ and k ₂ .

[0012]

One of the drawbacks of the above-described method of removing crosstalk is that the objective lens does not operate stably when moved by the tracking servo, and the other is the installation of a photodetector. The position accuracy is extremely strict. The instability due to the tracking servo will be described with reference to FIG.

As shown in FIG. 20, in this system, the photodetector is installed at a position 16 apart from the semiconductor laser position 11, and the light intensity distribution on the surface of the objective lens 2 is projected on the photodetector in a one-to-one manner. It At this time, when the optical disc 5 is rotated, the track position viewed from the optical pickup changes due to the eccentricity of the disc (T1 → T2). At this time, the position of the light receiving pattern on the surface of the photodetector 6 also moves from P1 to P2. When the distance between the photodetector and the semiconductor laser is LPD-LD and the distance between the objective lens and the semiconductor laser is LLENS-LD, the movement amount P1P2 of the light receiving pattern on the photodetector surface corresponding to the movement amount T1T2 of the tracking position. Is expressed by P1P2 = T1T2 * LPD-LD / (LLENS-LD + LF). Here, LF is the disc-side focal length of the objective lens. For example, LF = 2.6 mm, LPD-LD = 1
mm, LLENS-LD = 27.4 mm, T1T2 = 500 μm
Then, the amount of movement of the light receiving pattern P1P2 = 17 μm, and assuming that the lens diameter is 3 mm, the size of the photodetector is 1.
This is 00 μm, and the amount of movement of the light-receiving pattern becomes a size that cannot be ignored with respect to the size of the photodetector.

The installation position accuracy of the photodetector at this time is calculated. First, with reference to FIG. 17, the light receiving pattern on the photodetector is projected on the objective lens and considered. Dividing line 19 of FIG.
The position of is determined from the diffraction angles of the first-order diffracted lights 24 and 26. When the NA of the lens is 0.5, the focal length is 2.6 mm, the lens diameter is 3 mm, the track pitch is TP = 0.7 μm, and the light source wavelength is λ = 0.68 μm, the diffraction angle θ of the first-order diffracted light is θ = sin−1 (λ / TP) = 29 °. At this time, the position P1st of the 1st-order diffracted light with respect to the 0th-order diffracted light on the lens surface is P1st = LF × tan θ = 1.44 mm, and from FIG. 17, the position of the dividing line is P1st / 2 = 0.
It becomes 72 mm. That is, the area division of the photodetector is 0.72 mm, 1.56 mm, 0.7 on the objective lens surface.
It corresponds to an area of 2 mm. When this is projected on the photodetector, it corresponds to 24 μm, 52 μm, and 24 μm. If the installation accuracy of the photodetector is 1/10 of the divided area width, 2.
It is 4 μm, which means that extremely precise manufacturing accuracy is required.

When the lens position is changed by the tracking servo, the light amount distribution on the lens surface is changed in addition to the movement of the light receiving pattern described above. The emitted light from the semiconductor laser does not have a uniform distribution but has a Gaussian distribution approximately. FIG. 21 is a conceptual sectional view of the intensity distribution of the 0th, + 1st, and −1st order diffracted light of the reflected light from the disc when the pit row pattern of the disc is regarded as a virtual two-dimensional diffraction grating. FIG. 21A shows a state in which the objective lens is not displaced, and FIGS. 21B and 21C show a state in which the objective lens is displaced by the tracking servo operation.

In FIG. 21, crosstalk signals are generated in the 0th, 1st, and -1st-order overlapping portions (hatched portions in the drawing), but (b), (c), and (a) are compared. Then, the magnitude of the signal in the hatched part has changed,
An error occurs in the detection of the crosstalk component.

Further, the detection error of the crosstalk component is promoted by the area dividing line of the photodetector. FIG. 22 shows
17 shows the detection sensitivity distribution of the photodetector 9 used in the optical pickup optical system shown in FIG. In FIG. 22, the sensitivity near the area dividing line 95 of the photodetector 9 is tentatively represented by a straight line (broken line portion), but it is actually difficult to control the photodetection sensitivity in this area in the photodetector manufacturing process. Therefore, the sensitivity varies from chip to chip. This area is exactly where the crosstalk component is mixed, and the variation in the photodetection sensitivity is reflected as the variation in the mixing rate of the crosstalk component, resulting in a large error in crosstalk detection.

In summary, the crosstalk signal is not stably observed due to the movement of the light receiving pattern on the photodetector due to the movement of the objective lens and the change of the light intensity spatial distribution of the light receiving pattern, and the area of the photodetector. It is a problem to be solved that the instability of the above-mentioned crosstalk detection is promoted because the photodetection sensitivity in the vicinity of the dividing line is uncertain and that the installation position accuracy of the photodetector is severe.

[0019]

In the optical pickup according to the present invention, a hologram is installed close to the objective lens,
Servo drive is integrated with the objective lens. Diffracted light from each region of the hologram divided into three regions is received by a separate photodetector, and the output signals of the respective regions are weighted and added to remove the crosstalk component.

[0020]

In the conventional optical pickup having the crosstalk removing function, the light beam is emitted from one area-divided photodetector, whereas in the optical pickup of the present invention, the light beam is spatially divided by the hologram. The different light beams illuminate different, separate photodetectors. For this reason,
The size of the photodetector can be made larger than the photodetection pattern on the photodetector, and even when the photodetection pattern moves on the photodetector due to the tracking servo operation, the light amount of each divided light beam is It is possible to stably detect, and it is possible to stably detect and remove the crosstalk component in the signal.

[0021]

In the present invention, the hologram installed in the vicinity of the objective lens is not limited to the polarization separation type, but it is possible to easily explain as the following examples. A pick-up device will be taken as an example for further explanation.

FIG. 1 shows an embodiment of the optical pickup according to the present invention. The light emitted from the semiconductor laser 1 first passes through the polarization split hologram 3. Polarization split hologram 3
Has the effect of diffracting polarized light in a certain direction, but straightening it without diffracting polarized light orthogonal to it. This polarization-separated hologram can be easily prepared by proton-exchanging and etching a lithium niobate substrate in a lattice shape, as described in detail in, for example, Yamamoto et al., Japanese Patent Application No. 05-77839. In the present invention, the polarization axis direction of the polarization split hologram is set so as to match the direction in which the light emitted from the laser is not diffracted. The laser light that has passed through the polarization split hologram 3 is
The light passes through the quarter-wave plate 4 and is focused on the optical disk 5 by the objective lens 2, and again reaches the polarization separation hologram 3 through the objective lens 2 and the quarter-wave plate 4. At this time, since the polarization direction is rotated 90 ° by passing through the quarter-wave plate 4 twice, when passing through the polarization separation hologram 3 in the return path, it is spatially divided according to the pattern on the hologram. The light is diffracted to illuminate the photodetectors 6 (P1 to P6).

FIG. 2 shows how the detector 6 is illuminated at this time.
Will be explained. The lower diagram of FIG. 2 is a plan view of an example of the polarization split hologram 3. The polarization separation hologram 3 is divided into three regions on the center and on both sides, and the lattice spacing in each region is the region 32 in the center and the regions 3 on both sides.
A grid having a large grid spacing is formed in the order of 3 and 31. The diffraction angle of the light passing through the central region 32 is small, and the light passing through the region P3 and P4 of the photodetector shown in FIG.
The light passing through illuminates P2 and P5, respectively.

As described in the conventional example, of the reflected light from the disk 5, the amount of light passing through the regions 31 and 33 on both sides of the lens and the amount of light passing through the central region 32 of the lens are weighted and added to cross the signal. The talk component can be removed. In the present invention, in FIG. 2, assuming that the output signal of each photodetector is SPn, the reproduction signal S of the optical disc is S = k1 * (SP1 + SP2 + SP5 + SP6) + k2 * (SP3
+ SP5), and the crosstalk component of the signal can be removed by appropriately selecting the constants k1 and k2.

The features of the present invention are as follows.
FIG. 3 shows a sectional configuration diagram of an example of the optical pickup according to the present invention. When the optical disc or the motor shaft for rotating the optical disc has an eccentricity, the optical disc 5 moves laterally, so that the integral component of the objective lens 2-polarization separation hologram 3/4 wavelength plate 4 also becomes As indicated by an arrow 100 in FIG. 3, the optical disc moves in the radial direction of the disc, and the light receiving pattern 10 on the photodetector 6 also slightly moves in the radial direction of the disc. Position where the photodetector 6 is conjugate with the spot 17 on the optical disk 5 (light emitting surface of semiconductor laser)
When it is placed on the photodetector 6, since the entire optical system becomes a confocal system, the light receiving pattern on the photodetector 6 becomes a minute light spot,
And even if the objective lens 2 moves, the light spot is detected by the photodetector 6
Do not move on. However, in order to remove the crosstalk component by the one-beam method, it is necessary to observe the light intensity distribution within the beam of the reflected light from the disk, so the photodetector 6 is installed away from the light emitting surface of the semiconductor laser 1. It is necessary to move the light receiving pattern on the photodetector.

Here, the essential difference from the conventional optical pickup is that the reflected light beam is split on the photodetector in the conventional optical pickup of FIG. In the optical pickup, the reflected light beam is spatially divided by the hologram 3 integrated with the objective lens 2. Therefore, even if the objective lens 2 moves, the reflected light beam can always be split at a fixed position with respect to the reflected light beam and can be guided to the respective photodetectors. At this time, since the size of the photodetector 6 is larger than the light receiving pattern 10, even if the light receiving pattern 10 on the photodetector moves, the output signal of each photodetector 6 does not change, and the crosstalk component is not generated. It has a remarkable effect that the removed signal can be stably detected. Further, when the wavelength variation of the semiconductor laser 1 occurs other than the movement of the objective lens 2,
The light receiving pattern 10 moves in the radial direction of the optical disc due to the change of the diffraction angle in the polarization separation hologram 3, but the signal can be detected without any effect.

Further, when the objective lens 2 moves, not only the movement of the light receiving pattern 10 but also the spatial distribution of the light intensity of the light receiving pattern 10 changes. FIG. 21 shows the light intensity distribution of the reflected light from the disk 5 on the objective lens 2 at that time. As shown in FIG. 18, the optical disc 5 is regarded as a two-dimensional diffraction grating composed of repeating unit cells 18. The cross sections of the light intensity distribution of the diffracted light from the diffraction grating are represented by 61, 62, and 63 in FIG. 21, which show the intensity distributions of the 0th-order, the -1st-order, and the 1st-order diffracted light, respectively. In FIG. 21, the size of the objective lens 3 is 0th order diffracted light 61.
Since it has the same width as, the light intensity distribution in the range of the spread of the 0th-order diffracted light 61 determines the output signal.

The emitted light of the semiconductor laser has a Gaussian distribution approximately, and a part of the light passes through the objective lens. Therefore, when the center axis of the objective lens 5 is at the center of the optical axis of the semiconductor laser emission light, the light receiving pattern has a symmetrical intensity distribution as shown in FIG. 21B, the light intensity distribution of the diffracted light becomes asymmetrical as shown in FIGS. 21B and 21C. Here, since the crosstalk component in the signal is generated by the interference in the portion where the 0th-order diffracted light and the 1st-order diffracted light overlap, the crosstalk component is included in the shaded portion in FIG. As is clear from the figure, when the lens moves, the intensity of the crosstalk component contained in the left and right regions changes, and the detection accuracy of the crosstalk signal deteriorates.However, the outputs of the left and right photodetectors are weighted. It is possible to correct by adding.

After all, the reproduction signal S of the disc is S = k ₁ * (S _P1 + S _P6 ) + k ₁ ′ * (S _P2 + S _P5 ) + k ₂ *
It will be represented by (S _P3 + S _P4 ). In this equation, k ₁ and k ₁ 'are uniquely determined by the amount of displacement of the objective lens 2. It is necessary to dynamically change the optimum values of k ₁ and k ₁ 'according to the moving amount of the objective lens 2 during signal reproduction, but as is clear from FIG. Since the intensities of the 0th-order diffracted light detected by the detector differ between the left and right, the amount of movement of the objective lens 3, and thus k ₁ and k ₁ ′, can be determined from the DC components of the photodetector outputs on both sides. For example,
As shown in FIG. 21B, when the DC component from the photodetector on the right side of the three-division photodetector increases, it can be seen that the lens has moved to the left side, and the amount of movement of the lens can be known from the amount of change. Alternatively, k ₁ and k ₁ 'may be determined from the actuator drive signal of the tracking servo circuit.

The crosstalk correction method described here is
This is effective when the pickup optical system is composed of a finite system, but a remarkable effect is obtained especially when the pickup optical system is composed of an infinite system. The case where the optical system is a finite system and the case where the optical system is an infinite system are compared with each other in FIGS.

FIG. 4 shows a sectional configuration diagram of an optical pickup constituted by a finite system and a distribution of reflected light from the disk 5 on the hologram 3. The positions of the objective lens 2 and the hologram 3 are shown by a solid line when a positional deviation occurs in the tracking servo operation, and by a broken line when there is no positional deviation. When the objective lens 2 is displaced in the finite optical pickup shown in FIG. 4, the central axis of the objective lens 2 and the optical axis of the light passing through the objective lens 2 are not parallel to each other, so that reflection from the disc Part of the light returns to a position outside the aperture of the objective lens. As a result, the distribution 90 of reflected light from the disk irradiates only a part of the hologram 3 as shown in the figure, and the hologram 3
There is a difference in the amount of light that passes through the areas 31 and 33. On the other hand, in the optical pickup having the infinite system shown in FIG. 5, the center axis of the objective lens 2 and the optical axis are always kept parallel to each other even if the objective lens 2 is displaced, so The reflected light always illuminates the entire hologram 3 and does not cause a crosstalk component detection error. However, as is clear from the figure, the aperture of the collimator lens 91 needs to be larger than the aperture of the objective lens 2 by the amount of movement of the objective lens or more.

Next, the focus error detection function of the optical pickup according to the present invention will be described.

Since the optical system described above uses the hologram, it is possible to easily combine the focus error detection function called the CSD method.

The state of focus error detection by the CSD method will be described with reference to FIG. Of the diffracted light from the polarization separation hologram, the first-order diffracted light is shown by a solid line and the -1st-order diffracted light is shown by a broken line. Since each region of the polarization separation hologram 3 has a shape of a part of a Fresnel lens and has a slight power, the focal positions of the 1st-order diffracted light and the -1st-order diffracted light move forward and backward, respectively. The optical paths are set so that the light is condensed on the front side and the rear side of the light emitting surface, respectively. When the photodetector is placed on the same surface as the semiconductor laser 1, the light receiving patterns of the 1st-order and -1st-order diffracted light on the photodetector 6 are beams having substantially the same size. FIG. 6 shows an optical path when the optical disc 5 approaches the objective lens 2 side. The condensing point of the -1st order diffracted light approaches the photodetector surface, and the condensing point of the 1st order light moves further away from the photodetector surface. The light receiving pattern on the photodetector 6 at this time is as shown in the lower part of FIG. In order to detect the displacement amount of the optical disk 5 by the size of both diffracted light beams, the output SP _nL of each photodetector 6
For SP _nC and SP _nR , SF = (SP _1L + SP _1R -SP _1C ) + (SP _2L + SP _2R -SP _2C ) + (S
P _3L + SP _3R -SP _3C )-(SP _4L + SP _4R -SP _4C )-(SP _5L + SP
_{5R -SP 5C) - (SP 6L} + SP 6R -SP 6C) made it retrieve the signal represented by the formula.

The drawback of the optical pickup having the structure shown in FIG. 6 is that since the photodetector 6 is divided into a large number, the number of wirings thereof is also large, the photodetector chip becomes large, and the number of wiring man-hours increases. It is to raise the cost. FIG. 7 shows the configuration of an optical pickup in which the number of divisions of the photodetector is reduced in order to eliminate this adverse effect, and FIG. 8 shows a conceptual plan view of a hologram used in the optical pickup having the configuration of FIG. As shown in FIG. 7, the diffraction grating formed in the central area 32 of the hologram 3 has power, and the light diffracted in the area 32 is irradiated on the photodetectors P3 and P4 divided into three to focus error by the CSD method. Give rise to a signal. On the other hand, a linear diffraction grating is formed in the regions 31 and 33 on both sides of the hologram,
The 1st-order and -1st-order diffracted lights diffracted by 33 are respectively focused on one point on the photodetectors P1, P2, P5, and P6. If the focus error signal is detected from the outputs of the photodetectors P3 and P4 and the crosstalk signal component is detected from the output signals of the photodetectors P1 to P6, signal detection similar to that of the optical pickup having the configuration of FIG. 1 can be performed.

Further, in FIG. 1, a semiconductor laser 1 and a photodetector 6 use a light emitting / receiving unit on the same plane, but as shown in FIG. There is also a method of separately providing the polarization beam splitter 82 to separate the light on the forward path and the light on the return path. This is a configuration useful for a recording / reproducing optical system in which the light utilization efficiency is desired to be high, and the beam shaping optical system 81 can be inserted after the semiconductor laser 1. This system has the same performance as that of the optical pickup having the configuration of FIG. 1 such that the utilization efficiency of light does not decrease and stray light does not occur.
However, since the polarization beam splitter 82 is not available at a low cost and the semiconductor laser 1, the photodetector 6, the polarization beam splitter 82 and the like need to be precisely aligned, the productivity is deteriorated.

In the structure using the beam splitter as shown in FIG. 9, it is not always necessary that the diffraction grating pattern exists in all three regions on the hologram. In this case, the number of photodetectors can be further reduced as compared with the optical pickup having the configuration of FIG. FIG. 11 shows a configuration example thereof, and FIG. 11 shows a hologram in the example of FIG. In the structure in which the regions 31 and 33 are flat plates without a hologram as shown in FIG. 11, the light passing through the regions 31 and 33 passes through P2 of the photodetector,
The light passing through the region 32 is diffracted and illuminates P1 and P3 of the photodetectors. Here, by setting the disc reproduction signal S to be S = k ₁ · (S _P1 + S _P3 ) + k ₂ · S _P2 , the crosstalk component can be stably removed from the signal. However, at this time, since the influence of the light intensity distribution of the light receiving pattern as shown in FIG. 21 cannot be removed, the crosstalk removing operation may be slightly unstable.

Up to this point, only the case of having the focus error detection function by the CSD method has been described, but the optical pickup according to the present invention detects the focus error signal by the CSD method.
It is not limited to the law. FIG. 12 shows a conceptual diagram of an example of an optical pickup having a focus error detection function by the astigmatism method as another example.

In FIG. 1, the polarization separation hologram 4 has the shape of a Fresnel lens, whereas the optical pickup having the configuration of FIG. 12 is a simple one-dimensional diffraction grating as shown in FIG. At this time, since the polarization hologram has no power, the photodetector 6 and the optical disc 5 have a conjugate positional relationship with each other, and the movement of the light receiving pattern due to the movement of the objective lens is eliminated.

In the optical pickup having this structure, the focus error is detected by the photodetector divided into four parts, which is designated by P3, among the photodetectors 6. In FIG. 12, the optical disk 5
The reflected light beam from has astigmatism when passing through the polarization beam splitter 82. At this time, the light spot on the photodetector 6 has a shape as shown in FIG. That is, when the optical disc is on the lens side of the objective lens focus, it becomes an ellipse shown by a solid line, and when it is far from the lens, it becomes an ellipse shown by a broken line. Utilizing this, the focus error signal SF is detected by the photodetectors P3A, P3B, P3C,
Output signals from P3D, SP3A, SP3B, SP3C,
It can be detected by finding SF = SP3A + SP3B- (SP3C-SP3D) from SP3D.

In the above description, the structure in which the polarization separation hologram and the quarter wavelength plate are integrated with the lens has been described. However, the hologram is a normal hologram having no polarization separation function, and the quarter hologram is used. The same effect can be obtained with a structure in which the wave plate is omitted. At this time, unlike the optical pickup having the configuration of FIG. 1, diffracted light is generated even when the emitted light of the semiconductor laser passes through the hologram in the outward path (the optical path from the semiconductor laser to the optical disk). This situation is shown in Figure 1.
4 shows. In FIG. 14, a large number of light spots are generated on the optical disk 5 by the unnecessary diffracted light 72 generated in the outward path, but the reflected light enters the photodetector 6 and becomes noise. For example, of the outward first-order diffracted light, the light diffracted in the return path (the optical path from the optical disk to the photodetector) in the 0th direction is the light of the outward 0th-order diffracted light that is diffracted in the first order in the return path (signal Light) reach the same photodetector.

In order to reduce the influence of these stray lights, the hologram is blazed as shown in FIG. 15 to reduce the minus order diffracted light, and the photodetector 6 detects the minus order diffracted light. It is necessary to take measures such as removing the vessels. FIG. 15 shows an example of a structure using a blazed hologram. As shown in FIG. 15, the blazed hologram is a hologram in which the cross-sectional shape of each grating is inclined, and the ratio of high-order diffracted light or negative-order diffracted light is controlled by changing the depth and cross-sectional shape of the grating. You can

In the present invention, since the 0th-order light on the outward path and the 1st-order light on the return path are used as the signal light, the diffracted light of the negative order and the
A shape that reduces the number of higher-order diffracted light beams higher than the second order is selected. At this time, in addition to the signal light of the 0th order light of the forward path and the 1st order light of the return path, (the 0th order light of the backward path by the −1st order diffracted light of the forward path),
(Outgoing first-order diffracted light and returning second-order diffracted light)
(3rd-order diffracted light in the return path by the 2nd-order diffracted light), etc., all light whose return-order diffraction order is one greater than the outward path is condensed on the photodetector to become stray light, and the photodetector output signal Cause noise. Since the design is made so that the ratio of the 0th-order light and the 1st-order diffracted light in the diffracted light is large, the problem of the above stray light is that (the 1st-order diffracted light in the forward path and the 2nd-order diffracted light in the return path) and (the forward path -1st-order diffracted light and 0-order return light). That is, it may be designed so that the −1st order and the 2nd order diffracted light are reduced. If the diffraction efficiency of the n-th order diffracted light is ηn, in order to reduce the proportion of stray light, the cross section of the hologram grating should be such that (η ₋₁ · η ₀ + η ₁ · η ₂ ) / η ₀ · η ₁ becomes the smallest. You will have to choose the shape.

There are technical difficulties in producing a hologram grating having an arbitrary cross-sectional shape. In order to easily manufacture this using a conventional semiconductor process, a hologram grating having an arbitrary cross-sectional shape may be approximated by a stepwise cross-section. For example, when a four-step staircase hologram is used, it can be manufactured by exposing and etching the wafer twice. According to the simulation, if the cross-sectional shape is optimized with a four-step staircase hologram, (η ₋₁ · η ₀ + η ₁ · η ₂ ) / η ₀
-It is known that a value of η ₁ = 0.21 can be realized (Kanema et al., Japanese Patent Application No. 03-046630).

However, when a hologram that does not depend on polarization is used, unnecessary diffracted light is generated in both the forward and backward paths, and the light utilization efficiency is reduced. Further, of the light reflected by the optical disk, the return light to the semiconductor laser increases, so that the laser noise may increase.

[0046]

Since the size of the photodetector is larger than the light receiving pattern, the crosstalk component of the signal is stably removed even if the light receiving pattern is moved by the servo operation.

Furthermore, since the photodetector and the semiconductor laser are on the same substrate, the positioning of the two becomes easy and the productivity of the optical pickup is improved.

[Brief description of drawings]

FIG. 1 is a structural conceptual diagram of an example of an optical pickup according to the present invention.

2A is a plan configuration diagram of the photodetector in FIG. 1B. FIG. 2B is a conceptual plan view of a polarization separation hologram of the optical pickup in FIG.

3 (a) is a conceptual diagram showing how the return light from the disc is diffracted by a polarization hologram in the optical pickup of FIG. 1 (b) shows the light receiving pattern on the photodetector in the optical pickup of FIG. Figure

4A is a conceptual cross-sectional view of an optical pickup according to the present invention, which is composed of a finite optical system. FIG. 4B is a plan view of intensity distribution on a hologram of reflected light from an optical disc.

FIG. 5 (a) is a conceptual sectional view of an optical pickup according to the present invention, which is composed of an infinite optical system. (B) is a plan view of the intensity distribution on the hologram of the reflected light from the optical disc.

6A is a conceptual sectional view of the optical pickup shown in FIG.
Conceptual diagram showing the state of diffracted light when the optical disc is slightly displaced from the focus position to the pickup side. (B) Diagram showing the light-receiving pattern on the photodetector

FIG. 7 is a conceptual configuration diagram of an optical pickup according to the present invention in which regions on both sides of a hologram are configured by linear gratings to reduce the number of photodetectors.

8A is a plan view of a hologram of the optical pickup shown in FIG. 7B is a diagram showing a light receiving pattern on a photodetector.

FIG. 9 is a conceptual configuration diagram of an example of an optical pickup according to the present invention using a polarization beam splitter.

FIG. 10 is a diagram showing an example of a configuration in which an optical pickup according to the present invention has a diffraction grating only in a central portion of three regions of a polarization hologram.

11A is a plan view of a photodetector, and FIG. 11B is a conceptual plan view of a polarization hologram used in the optical pickup shown in FIG.

FIG. 12 is a conceptual diagram of a configuration having a focus error signal detection function in the optical pickup according to the present invention.

13 (a) is a conceptual plan view of a photodetector of the optical pickup shown in FIG. 12 (b) is a conceptual plan view of a polarization hologram used in the optical pickup shown in FIG.

FIG. 14 is a conceptual diagram illustrating a state of diffracted light in a hologram in an example using a polarization-independent hologram that is not blazed in the optical pickup according to the present invention.

FIG. 15 is a conceptual diagram illustrating a state of diffracted light in a hologram in an example using a blazed polarization independent hologram in the optical pickup according to the present invention.

16A is a diagram showing a configuration example of a conventional optical pickup having a crosstalk component removing function by the one-beam method. FIG. 16B is a plan conceptual diagram of a photodetector of the optical pickup.

FIG. 17 is a conceptual diagram illustrating the intensity distribution of reflected light from a disc when the disc is regarded as a two-dimensional grating in which unit cells are virtually repeated infinitely.

FIG. 18 is a conceptual diagram of an optical disc that is regarded as repeating virtual unit cells.

FIG. 19 is a diagram showing an example of a phase relationship of diffracted light from an optical disc, which includes a crosstalk component.

FIG. 20 is a view for explaining the movement of the light receiving pattern on the photodetector due to the movement of the objective lens, which is a cross-sectional conceptual diagram of the optical pickup

FIG. 21 (a) is a diagram for explaining a change in intensity distribution of a light receiving pattern on the photodetector when the objective lens is not displaced. (B) On the photodetector when the objective lens is displaced. FIG. 6 is a diagram for explaining a change in intensity distribution of the light receiving pattern. (C) A diagram for explaining a change in intensity distribution of the light receiving pattern on the photodetector when the objective lens is displaced.

22A is a plan view showing the photodetector of the optical pickup having the configuration of FIG. 16B. FIG. 22B is a diagram showing the distribution of the photodetection sensitivity by the area dividing line of the photodetector in the optical pickup of the configuration of FIG.

[Explanation of symbols]

1 Semiconductor Laser 2 Objective Lens 3 Polarization Separation-type Hologram 4 Quarter Wave Plate 5 Optical Disc 6 Photodetector 7 Polarizing Beam Splitter 8 Actuator 9 3 Division Photodetector 10 Light-Receiving Pattern on Photodetector 11 Semiconductor Laser Position 12 3 3 Divided light detector position 13 Optical disc information surface 14 Light spot position 15 Light spot position when the lens is moved 16 Objective lens diameter 17 Light spot 18 Unit cell 19 Dividing line 21 (1,1) -order diffracted light 22 (1,0) Diffraction light 23 (1, -1) Diffraction light 24 (0,1) Diffraction light 25 (0,0) Diffraction light 26 (0, -1) Diffraction light 27 (-1,1) Diffraction light 28 (-1, 0) Diffraction light 29 29 (-1, -1) Diffraction light 31 Region of polarization separation hologram 32 Region of polarization separation hologram 33 Polarization separation hologram Area 41 Interference area 42 Interference area 43 Interference area 44 Light intensity distribution of diffracted light from optical disc 45 Light intensity distribution of diffracted light from optical disc 46 Light intensity distribution of diffracted light from optical disc 47 Light of diffracted light from optical disc Intensity distribution 48 Light intensity distribution of diffracted light from optical disc 49 Light intensity distribution of diffracted light from optical disc 51 Phase of (0,0) order diffracted light 52 Phase of (0,1) order diffracted light 53 (1,0) order diffracted light Phase 61 0 light intensity distribution of 0th order diffracted light 62 1 light intensity distribution of 1st order diffracted light 63 light intensity distribution of 1st order diffracted light 71 blazed hologram 72 unwanted diffracted light from hologram 81 beam shaping optical system 82 polarization beam splitter 90 from optical disk Intensity distribution of the reflected light on the hologram 91 Collimating lens 95 Area dividing line of photodetector 100 Direction of movement of objective lens

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Seiji Nishino 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Noboru Ito, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. 72) Inventor Sadao Mizuno 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Akimasa Sano 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. 1006 Kadoma, Kadoma-shi, Matsushita Electric Industrial Co., Ltd. (72) Hidehiko Wada, 1006 Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (4)

[Claims] 1. An optical pickup device comprising a light source for emitting a coherent beam and a focusing optical system for focusing a beam emitted from the light source into a minute spot on an optical information carrier. A hologram is installed integrally with the system, and the hologram has a region divided into at least three or more in a direction perpendicular to the signal information sequence direction of the optical information carrier, and from the three or more regions of the hologram. At least two or more separate photodetectors that individually generate diffracted light and independently receive the diffracted light, or a photodetector divided into two or more regions, and at least three separate photodetectors Alternatively, the optical pickup device is provided with a circuit for individually weighting and adding the output signals of the photodetector divided into at least three regions. 2. The optical pickup device according to claim 1, wherein at least three or more photodetector output signals or 3
An optical pickup device characterized by further comprising a second signal processing circuit for changing the weight of the weighted addition in response to the change of the output signal from each area of the photodetector divided into the above areas. . 3. The optical pickup device according to claim 1, wherein the hologram is a polarization separation type hologram, and a quarter wavelength plate is provided between the focusing optical system and the hologram. Pickup device. 4. The optical pickup device according to claim 2, wherein the hologram is a polarization separation type hologram, and a quarter wavelength plate is provided between the focusing optical system and the hologram. Pickup device.