JPH0362327A - Optical pickup device - Google Patents

Abstract

PURPOSE:To reduce the number of components by forming a focus of a diffracted light from a prescribed area of a diffraction element to this side of a photodetector and a remote side at the focusing state of an optical system so as to detect focus/tracking error. CONSTITUTION:A luminous flux radiating from a semiconductor laser 12, reflected in an optical disk 16 and diffracted at areas 13a, 13c of a diffraction element 13 is converged to a focus f1 to form light spots P1, P3 to photodetection sections 17a, 17c of a photodetector 17. On the other hand, the luminous flux diffracted at areas 13b, 13d is converged to a focus f2 to form light spots P2, P4 on photodetectors 17b, 17d. Then the size of the spots P1-P4 is equal at the focus state but reduced/magnified at the defocus state. Thus, a focus error is detected from a difference between sums of output signals of photodetector element on diagonal lines and a tracking error is detected from the phase difference between the difference of the sums and the sum of the output signals of all the photodetector elements by using one photodetector. Thus, the number of components of the photodetector.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical pickup device used for recording and reproducing information on various types of optical discs, such as read-only type and write-once type.

[Conventional technology]

As shown in FIG. 14, in the conventional optical pickup device, the emitted light from the semiconductor laser 1 is converted into 0th-order diffracted light (hereinafter referred to as the main beam) by the first diffraction element 2, and The main beam is divided into ±1st-order diffracted lights (hereinafter referred to as a pair of sub-beams) separated by a predetermined angle, and guided to the second diffraction element 3.

Here, each of the three beams is further diffracted, and each O-order index light passes through a collimator lens 4 and is focused onto an optical disk 6 by an objective lens 5.

At this time, for example, if the optical disc 6 is a compact disc, the main beam is focused on the pits on the optical disc 6 in order to read the recorded information recorded as pits, and the recorded information is reproduced based on the reflection intensity. It will be done. Also, a focus error signal is obtained based on the main beam, as described later.

On the other hand, the pair of sub-beams are relatively far apart from the main beam in opposite directions in the track direction of the optical disk 6, and are slightly shifted in opposite directions from the main beam in the radial direction of the optical disk 6. The light is focused on the position. A tracking error signal is then obtained from the reflection intensity of the pair of sub-beams.

The main beam and sub beam reflected from the optical disk 6 pass through the objective lens 5 and the collimating lens 4,
The light is diffracted by the second diffraction element 3, and each first-order diffracted light is guided to the photodetector 7.

As shown in FIG. 15(a), the second diffraction element 3 is separated by a dividing line 3c extending in the diffraction direction of the second diffraction element 3.
It is divided into two areas 3a and 3b. Each area 3a/3
In b, lattices 3d, 3d..., 3e, 3e,
... are formed in a direction perpendicular to the dividing line 3C at mutually different pitches.

On the other hand, as shown in FIG. 15(b), the photodetector 7 is divided into six photodetectors 7a to 7f, each extending in the direction of diffraction in the second diffraction element 3. In a focused state with no focus error, the main beam diffracted by the region 3a of the second diffraction element 3 is focused on the dividing line 7g to form a light beam (p+'), and is diffracted by the region 3b. The main beam is focused on the dividing line 7h to form a light spot P2. Further, the pair of sub-beams diffracted by the second diffraction grating 3 are respectively focused on photodetectors 7e and 7f.

Output signals 5 obtained from each of the photodetectors 7a to 7f
Based on a-3f, the focus error signal FES is F
Obtained by calculating ES= (Sa+5d)-(Sb+Sc), the tracking error signal RES is RES=Se-3
The pit signal (recorded information) RF is obtained by calculating f.
It is obtained by calculating =Sa+Sb+Sc+Sd.

Note that the gratings 3d, 3d... in the second diffraction element 3
In addition to the conventionally used rectangular cross section shown in FIG. 16(a), the cross-sectional shape of 3e, 3C...
A sawtooth-shaped blaze shape with high light utilization efficiency, as shown in FIG. 6(b), is also being considered.

[Problem to be solved by the invention]

However, in the above configuration, in FIG. 15(b),
In order to detect focus errors, the photodetectors 7a and 70 and 7b and 7d are arranged side by side in the longitudinal direction, and the two light spots PI' and P2 are focused at a considerable distance in the diffraction direction of the second diffraction element 3. Therefore, the photodetecting sections 7a to 7f are considerably elongated when viewed in the direction of diffraction by the second diffraction element 3. Moreover, since the photodetectors 7e and 7f for detecting tracking errors are provided separately from the photodetectors 7a to 7d for detecting focus errors and recorded information, the number of photodetectors 7a to 7f increases. the result,
As the area occupied by the photodetectors 7a to 7f becomes larger,
There is a problem that manufacturing costs also increase.

Moreover, the gratings 3d, 3d..., 3 in the second diffraction element 3
When adopting the blaze shape shown in FIG. 16(b) as the cross-sectional shape of gratings 3d and 3e, the difference in diffraction angles between the two regions 3a and 3b of the second diffraction element 30 is quite large. . . . and the pitches of the gratings 3e, 3e, . . . need to be significantly different.

Therefore, it is difficult to process the regions 3a and 3b into a blaze shape with the same cross section.
Not only does the machining work for e/3e... become complicated, but
Grits 3d, 3d..., 3e are formed between the two regions 3a and 3b.
The difference in the cross-sectional shape of 3e causes a difference in light utilization efficiency, causing a problem that focus error cannot be detected accurately. Note that in order to reduce the difference in light utilization efficiency between regions 3a and 3b, it is necessary to change the blaze shape in both regions 3a and 3b to a shape different from the optimal shape. It becomes impossible to obtain high light utilization efficiency.

Furthermore, since the above-mentioned optical pickup device employs the so-called three-beam method, it requires a first diffraction element 2 that splits the emitted light from the semiconductor laser I into three beams, which leads to the problem of an increase in the number of parts. It had

[Means to solve the problem]

In order to solve the above problems, an optical pickup device according to the present invention includes a light generating means, a light emitted from the light generating means is focused on an optical disk, and a reflected light from the optical disk is guided to a diffraction element. In the optical pickup device, the optical pickup device includes an optical system, a diffraction element that diffracts reflected light from the optical disk toward a photodetector, and a photodetector that receives the diffracted light from the diffraction element and converts it into an electrical signal. The diffraction element is divided into four regions with dividing lines extending approximately in the track direction of the optical disk and dividing lines extending approximately in the radial direction of the optical disk as boundaries, and the focal position of the diffracted light in each of the two diagonal areas. The distances to the two areas are set to be almost the same, and the focal position of the diffracted light in the two areas on one diagonal line is located in front of the photodetector when no focus error occurs,
The focal position of the diffracted light in the other two diagonal areas is located further away from the photodetector, and the photodetector is positioned approximately midway between the two focal positions. is provided with at least four photodetectors including at least one photodetector corresponding to each region of the diffraction element, and the sum of the output signals of all the photodetectors of the photodetector is A focus error is detected based on the difference between the sums of the output signals of the recorded information detection means that detects the information recorded on the optical disc based on the information recorded on the optical disk, and the photodetection section corresponding to each of the two diagonal areas of the diffraction element. and the difference between the sums of the output signals of the photodetectors corresponding to each of the two diagonal areas of the diffraction element, and the phase of the sum of the output signals of all the photodetectors. and tracking error detection means for detecting a tracking error by comparing.

[For production]

According to the above configuration, when the optical system is focused, the diffracted light from the two areas at one diagonal position of the diffraction element forms a focal point in front of the photodetector, and from the two areas at the other diagonal position. Since the diffracted light forms a focal point on the side far from the photodetector, a light spot having a predetermined area is formed on the photodetector when the optical system is focused. When a focus error occurs, the light spot due to the diffracted light from the two areas at one diagonal position expands or contracts, and the light spot due to the diffracted light from the two area pairs at the other diagonal position conversely shrinks or contracts. Since the amount of light received by each photodetector of the photodetector changes due to the enlargement, focus error is detected based on this.

Furthermore, when no tracking error occurs, the light and dark pattern of the reflected light from the optical disc, which is generated on the diffraction element by recorded information such as pits on the optical disc, is symmetrical with respect to the dividing line extending in the track direction of the optical disc as a boundary. , the sums of the output signals of the photodetectors corresponding to each of the two diagonal areas are equal, and the difference therebetween is "OII".

On the other hand, if a tracking error occurs and the light spot on the optical disc deviates from the center of the track in either direction, the light and dark pattern of the reflected light from the optical disc on the diffraction element will change with the dividing line in the track direction of the optical disc as the boundary. The left and right sides become asymmetrical.

Therefore, the sums of the output signals of the photodetectors corresponding to each of the two diagonal areas are different, and the difference has a positive or negative value. In that case, the light and dark pattern on the diffraction element is reversed depending on the direction in which the light spot on the optical disk deviates from the track center, so the output signal of the photodetector corresponding to each of the two diagonal areas of the diffraction element is The polarity of the difference between the sums of is reversed depending on the direction in which the light spot on the optical disc deviates from the track center.

Note that when a tracking error occurs, the light and dark pattern on the diffraction grating changes as the light spot on the optical disc moves along recorded information such as pits,
Accordingly, the difference between the sums of the output signals of the photodetecting sections corresponding to each of the two diagonal areas of the diffraction element depicts a substantially sinusoidal wave. The phase of this sine wave changes depending on the direction in which the optical spot on the optical disk deviates from the track center. On the other hand, the sum of the output signals of all the photodetectors also forms a sine wave as the optical spot on the optical disc moves along the recorded information such as pits, but the phase of this sine wave causes a tracking error. It remains almost constant regardless of whether Therefore, the difference between the sums of the output signals of the photodetectors corresponding to each of the two diagonal areas of the diffraction element is drawn (a sine wave and a sine wave drawn by the sum of the output signals of all the photodetectors). Tracking errors can be detected by comparing the phases of .

In the above configuration, the light detection parts of the photodetector that receives the diffracted light from the light detection parts of the diffraction element can be provided relatively close to each other, and the focus error and recorded information can be Since the number of photodetectors can be reduced by performing detection and tracking error detection using a common photodetector, it is possible to reduce the area occupied by the photodetector and the manufacturing cost.

Furthermore, since the respective photodetecting parts of the photodetector are provided at relatively close positions, the difference in diffraction angles in each region of the diffraction element can be made sufficiently small. As a result, when the cross-sectional shape of the grating in each region of the diffraction grating is made into a blaze shape, the blaze shape in each region can be made almost equal, making it easier to manufacture the grating, and also making it easier to manufacture the grating in each region. The efficiency of light use is sufficiently high, and
The difference in utilization efficiency can be made sufficiently small.

Furthermore, in the above configuration, since the focus error and tracking error are detected without dividing the emitted light from the light generating means into the main beam and the sub beam, the emitted light is divided into the main beam and the sub beam. A diffraction element becomes unnecessary, and the number of parts can be reduced.

[Embodiment 1] An embodiment of the present invention will be described below based on FIGS. 1 to 8.

The optical pickup device 11 according to this embodiment is used as a playback device for playback-only optical discs such as compact discs and video discs. As shown in FIG. 2, the emitted light from the semiconductor laser 12 as a light generating means reaches the collimating lens 14 via the diffraction element 13, and after being converted into parallel light by the collimating lens 14, it is passed through the objective lens 1.
Reach 5. The collimating lens 14 and objective lens 15 described above constitute an optical system.

The light beam transmitted through the objective lens 15 is used to read recorded information recorded in advance as pits on the optical disc 16.
The light is focused on pits on the optical disc 16.

The light beam reflected from the optical disk 16 is transmitted through the objective lens 15.
The first-order diffracted light that passes through the collimating lens 14 and is diffracted in the X direction by the diffraction element 13 is guided to the photodetector 17.

As shown in FIG. 1(b), the photodetector 17 includes a dividing line 17 extending in the Y direction, which is the track direction of the optical disc 16.
h and a dividing line 17g extending in the X direction, which is the radial direction of the optical disc 16, each of which has a rectangular shape is divided into four photodetecting sections 17a to 17d. The photodetectors 17a-17d correspond to the later-described regions 13a-13d of the diffraction element 13, respectively, and are adapted to receive diffracted light from the regions 13a-13d.

As shown in FIG. 3, the diffraction element 13
The dividing line 13i extending in the track direction of the optical disc 1
The area is divided into four areas 13a to 13d by a dividing line 13j extending in the radial direction of 6.

In each region 13a to 13d of the diffraction element 13, gratings 13e, 13e, . Two areas 13 at one diagonal position centered on the optical axis Ll connecting the semiconductor laser 12 and the optical disk 16
A・13c grid 13e-L3e... 13g-13
g- is the same point f in front of the photodetector 17, where the light beam reflected from the optical disk 16 and diffracted by the regions 13a-13C occurs when the optical system is focused without a focus error.

The direction and pitch are determined so that the zero points are connected.

On the other hand, the other diagonal position 2 centered on the optical axis
Grids 13f, 13f, in two regions 13b-13d.
... 13h, 13h, etc. are directed and directed so that the light beams reflected from the optical disk 16 and diffracted at the regions 13b and 13d at the time of the above focusing are focused at the same point f2 which is far from the photodetector 17. The pitch is determined. The focal positions fI and fz are both the intersection of the optical axis and the diffraction element 13, and the dividing line 17g.1 on the photodetector 17.
Located on the optical axis L2 of the diffracted light connecting the intersection of 7h,
And, at the time of the above focusing, the photodetector 17 is at the focal position f, -
It is set to exist at approximately the middle position of f2.

As mentioned above, the two areas 13a and 13a at one diagonal position
For example, in order to make the distance to the focal position f1 of the diffracted light from the region 13c different from the distance to the focal position f2 of the diffracted light from the other two diagonal regions 13b and 13d, for example, the region 13a and 13C are Convergence function (convex lens function)
The regions 13b and 13d are provided with a light diverging function (concave lens function).

Note that the lattice 13e13e of each region 13a to 13d
...~13h, 13h... are created by the well-known two-beam interferometry method, or by determining the shape of the interference fringes using an electronic computer and drawing the interference fringes directly on a dry plate using an electron beam exposure device. can do. In that case, grid 1
The cross-sectional shape of 3e, 13e... to 13h, 13h... is the rectangular shape shown in FIG. 16(a), or the cross-sectional shape of FIG.
) can be made into a blaze shape as shown in FIG.

Detection of recorded information, focus error signal, and tracking error signal will be described below.

The light beam emitted from the semiconductor laser 12, reflected by the optical disk 16, and diffracted by the region 13a of the diffraction element 13 is once converged at the focal point f1, and then reversed to form a sector-shaped light beam in the light detection section 17a of the photodetector 17. light spot P
form 1. Further, the light beam reflected from the optical disk 16 and diffracted at the area 13c on the same diagonal as the area 13a is once converged at the same focal position Rf1 as above, and then reversed to the photodetecting section 17c of the photodetector 17. A fan-shaped light spot P3 is formed.

On the other hand, the light beam reflected from the optical disk 16 and diffracted by the region 13b of the diffraction element 13 does not converge in front of the photodetector 17, but forms a fan-shaped light spot P2 on the photodetector 17b. Further, the light beam reflected from the optical disk 16 and diffracted in a region 13d on the same diagonal as the region 13b in the diffraction element 13 does not converge in front of the photodetector 17, but forms a fan-shaped light spot on the photodetector 17d. Form P4.

In a focused state where the distance between the objective lens 15 and the optical disc 16 is appropriate, the photodetector 17 is at two focal positions f,
・Since it is located almost in the middle of f2, Fig. 1 (b
As shown in ), the sizes of each optical block (PI-P4) are equal. Therefore, the output signals 5a-3d of the respective photodetectors 17a-17d are equal.

On the other hand, when the optical disk 16 comes too close to the objective lens 15 and a focus error state occurs, the focal position f approaches the photodetector 17, while the focal position "2" moves away from the photodetector 17. As shown in figure (a), the light spots P, ・P, shrink, and conversely, the light spots P2 ・P
4 expands.

In that case, the light quantity itself of each light spot P, ~P4 does not change depending on the size, but in reality, as shown in Fig. 4, the dividing lines 17g and 17h have a predetermined width (for example, about 5 μm)
and the fan-shaped chord part of each optical spot P, ~P4 is located on the center line of the dividing lines 17g and 17h, and the sensitivity to the optical signal is eliminated on the dividing lines 17g and 17h, or It is attenuated. In the states shown in FIGS. 1(a) and 4, the optical spora l-P,
P3 has a better light spot P2 and dividing line 17 compared to P4
Since the proportion (area ratio) protruding above g·17h is large, the output signals 5a-3c of the photodetectors 17a, 17c are smaller than the output signals 5b-3d of the photodetectors 17b, 17d.

Conversely, if the optical disc 16 is too far away from the objective lens 15 and a focus error occurs, the optical spots P and -P3 expand, while the optical spot P
2. Since P4 is reduced, the output signals 5a-3c of the photodetectors 17a and 17c become larger than the output signals 5b-3d of the photodetectors 17b and 17d.

Therefore, the focus error signal FES is
The sum of the output signals 5a-3c of the photodetectors 17a and 17c corresponding to the two regions 13a and 13c at one diagonal position, and the two regions 13 at the other diagonal position of the diffraction element 13.
It is determined by the difference between the sum of the output signals 5b-3d of the photodetectors 17b and 17d corresponding to the signals b and 13d (hereinafter referred to as a diagonal difference signal). That is, the focus error signal FES is determined by the calculation of FES=(Sa+5c)-(Sb+Sd) by a focus error detection means (not shown), and the objective lens 15 is adjusted by a focus servo system (not shown) so that this FES becomes "0". Driven. On the other hand, the recorded information RF recorded as pits is detected by all the optical detection units 17a by recorded information detection means (not shown).
The sum of the output signals S a - S d of ~17d (hereinafter referred to as a sum signal) is obtained by calculating RF=Sa+Sb+Sc+Sd.

As will be described later, the brightness pattern of the luminous flux E (see FIGS. 7(a) to (C)) of the reflected light from the optical disc 16 on the diffraction element 13 is determined by the optical spora 1-D (
6(a) to (C)) changes depending on the position on the pit C when passing over the pit C in the direction of arrow A, and as a result, the output signal S a % of each photodetector 17a to 17d
The value of S d also changes as the optical spora) D moves over the pit C. Therefore, when generating the focus error signal FES, the values of the output signals S a - S d of the respective photodetectors 17 a - 17 d are, for example, average values during the time when the light spot D passes through the pins l-C. good.

Next, the tracking error signal RES is obtained by a so-called heterodyne method.

That is, as shown in FIG. 6(b), the optical disc 16
If the light spot D is irradiated at the center of the track where the upper pits C are aligned and no tracking error occurs, the light spot D will begin to pass over the pit C when it approaches the pit C. At this point in time, the light and dark pattern of the luminous flux E of the reflected light from the optical disc 16 on the diffraction element 13 is as shown in FIG. 7(b), bright in the upper and lower parts of the figure, and dark in the central part. In this case, since the light and dark pattern of the luminous flux E is symmetrical, the above diagonal difference signal is “°
0”.

As shown in FIG. 6(a), an optical spora l-
If D deviates from the center of the track to the left in the figure, causing a tracking error, the light and dark pattern of the light beam E on the diffraction element 13 at the time when the light spot D approaches the pit C will be as shown in FIG. 7(a). As shown, the light becomes brighter in the upper left and lower right of the figure, and darkens in the center. At this time, the amount of light received by the photodetectors 17a and 17c on the photodetector 17 becomes relatively large,
On the other hand, since the amount of light received by the photodetectors 17b and 17d is relatively small, the above diagonal difference signal (Sa+5c)-(Sb
+Sd) is a positive value.

Furthermore, the light and dark pattern of the luminous flux E on the diffraction element 13 at the time when the optical spot D finishes passing through the pin node C with the optical spora L-D shifted to the left from the center of the track is shown in Fig. 7(c). ), it is bright in the upper right and lower left of the figure, and dark in the center. At this time, the amount of light received by the photodetectors 17a and 17c becomes relatively small, and the amount of light received by the photodetectors 17b and 17d becomes relatively large, so the diagonal difference signal (Sa
+5c)-(Sb+Sd) is a negative value.

Therefore, when the optical spot D on the optical disc 16 is shifted to the left with respect to the pit C, the diagonal difference signal (Sa
+5c) - (Sb+Sd), as the light spot D on the optical disc 16 moves on the pit C in the six directions of the arrows, curves approximately like a sine wave as shown in FIG. 8(b).

On the other hand, as shown in FIG. 6(C), if the optical spot D on the optical disc 16 shifts from the track center to the right side in the figure and causes a tracking error, the diffraction element at the time when the optical spot D approaches the focus C The light and dark pattern of the luminous flux E on the light beam 13 is as shown in FIG. 7(C). At this time, the amount of light received by the photodetectors 17a and 17C becomes relatively small, and the amount of light received by the photodetectors 17b and 17d becomes relatively large.
The above diagonal difference signal has a negative value.

In addition, the light and dark pattern of the light beam E on the diffraction element 13 at the time when the light spot D finishes passing through the pit C with the light spora l-D shifted to the right from the center of the track is shown in FIG.
It will be like a). At this time, the amount of light received by the photodetectors 17a and ltc becomes relatively large, and the photodetectors 17b to 17d
Since the amount of received light becomes relatively small, the above-mentioned diagonal difference signal takes a positive value.

Therefore, the optical spot D on the optical disc 16 is located at the pitch I-C.
If it is shifted to the right side, the diagonal difference signal (S
a+5c)-(Sb+Sd) is photospora) D is pip)
As you move on C in the six directions of the arrow
), it draws an almost sinusoidal curve. However, the phase of the sine wave in this case is 180° different from that in the case where the rice spot D is shifted to the left with respect to the pit C.

On the other hand, the above sum signal Sa+Sb+Sc+Sd draws a sinusoidal curve as shown in FIG. 8(a) as the optical spot D passes through the pit C on the optical disc 16. The phase of this sine wave is almost constant regardless of whether or not a focus error occurs. When the optical spora) D is shifted to the left on the optical disk 16, the sine wave drawn by the diagonal difference signal ((b) in FIG. 8) is the sine wave of the sum signal ((a) in FIG. 8). On the other hand, when the optical spot D is shifted to the right on the optical disk 16, the diagonal difference signal becomes a grooved sine wave ((C
)) has a phase lead of 90° with respect to the sine wave of the sum signal.

Therefore, by comparing the phases of the diagonal difference signal and the sum signal using tracking error detection means (not shown), it is possible to detect to which side the optical spot D has shifted.

The above phase comparison can be performed, for example, by a hetero gain detection circuit. On the other hand, when no tracking error occurs, the diagonal difference signal becomes "0" as described above.

Note that the bright and dark pattern in FIG. 7 is for a case where the depth of the pit C is 1/4 of the wavelength of the laser beam used.

Here, due to a change in the wavelength of the laser beam emitted from the semiconductor laser 11, the wavelength of the laser beam changes to the diffraction element 13.
When the light beam diffracted at the point f and f2 become shorter than the reference wavelength set to converge at the point f2, the area 13a13c
The diffracted light from is at point f.

It converges at a position closer to the photodetector 17 than the area 13b.
Since the diffracted light from 13d converges at a position closer to the photodetector 17 than the point f2, each of the optical spots P1 to P4 on the photodetector 17 becomes smaller than at the above-mentioned reference wavelength.

Therefore, the wavelength fluctuation of the semiconductor laser 11 does not affect the focus error signal FES. Similarly, if the wavelength of the laser beam is longer than the reference wavelength, each of the optical spots P+ to P4 will be larger than at the reference wavelength, so no error will occur in the focus error signal FES.

Furthermore, if frequency fluctuation occurs in the laser beam, the result shown in Fig. 5 (a)
) and (b), the optical spots P1 to P4 move on the photodetector 17 in the X direction, that is, in the diffraction direction in the diffraction element 13. However, in this case, the photodetector 1
The increase/decrease in the output signal Sa of the photodetector 17a and the increase/decrease in the output signal Sc of the photodetector 17c cancel each other out, and the increase/decrease in the output signal sb of the photodetector 17b and the increase/decrease in the output signal Sd of the photodetector 17d cancel each other out. Since the amounts cancel each other out, no error occurs in the focus error signal FES as a whole.

Note that in this embodiment, each photodetector 17a of the photodetector 17
~17d are formed close to each other, and
Detection of focus errors and detection of tracking errors are performed by the common light detection sections 17a to 17d, and the light detection section 17a
Since the number of photodetectors 17a to 17d is reduced, the area occupied by the photodetectors 17a to 17d can be reduced, and manufacturing costs can be reduced.

Furthermore, since the photodetecting parts 17a to 17d are close to each other, the diffraction angles in each region 13a to 13d of the diffraction element 13 become approximately equal, and therefore, the gratings 13e, 13e, . . .
・～13h・13h... Figure 16(b) shows the cross-sectional shape of ・～13h・13h...
In the case of the blaze shape shown in , the gratings 13e, 13e,
Since the pitches of ~13h, 13h, etc. can be made almost equal, the processing of the diffraction element 13 can be carried out smoothly, and there is no difference in light utilization efficiency, making it an optimal method to obtain a sufficiently high utilization efficiency. Can be formed into a blaze shape.

Note that since the diffracted light from the diffraction element 13 condensively has the property of astigmatism, the focus control method may be a method using a known astigmatism method.

[Example 2] Next, a second example will be described based on FIGS. 9 and 10.

As shown in FIG. 9, in the second embodiment, the photodetector 17 is
As in the first embodiment, the optical disc 16 is divided into four photodetectors 17a to 17d by dividing lines 17h and 17g extending in the track direction and radial direction, respectively.

However, the width of each photodetector 17a=17d in the X direction is expanded compared to the first embodiment. And the photodetector 17a
~17d, light spot P1 ・P2 and light spot P,・
The diffraction element 13 is configured such that it is separated from P4 by an interval in the X direction.

That is, as in the first embodiment, the diffraction element 13 is divided into four regions 13 by dividing lines 13i and 13j extending in the track direction and radial direction of the optical disc 16, as shown in FIG.
It is divided into a-13d. As shown in FIG. 10, the light beam diffracted by the region 13a of the diffraction element 13 is focused at the focal point flb on the front side of the photodetecting sections 17a and 17b in the photodetector 17, and then reversed. Photodetector 17
region 13a so as to form a photospora l-P on a.
lattice 13e, 13e... are designed.

Further, the light beam diffracted by the region 13c of the diffraction element 13 is focused at the focal point f1m on the front side of the photodetection section 17c17d of the photodetector 17, and then reversed to form a light spot P3 on the photodetection section 17c. It is designed to form a

Further, in the area 13b of the diffraction element I3, the focal position of the light beam diffracted in this area 13b is located at the photodetecting section 1 of the photodetector 17.
It is formed to be a point fib behind 7a and 17b,
Thereby, the diffracted light from the region 13b is not reversed and forms a light spot P2 on the photodetector 17b. Further, the region 13d of the diffraction element 13 is formed such that the focal position of the diffracted light from the region 13d is a point f on the rear side of the photodetecting parts 17c and 17d of the photodetector 17, and the focal position of the diffracted light from the region 13d is A light spot P4 is formed on the light detection portion 17d of the photodetector 7 without the diffracted light being reversed.

In this second embodiment, the focus error signal FES is
As in the embodiment, assuming that the output signals of the respective photodetectors 17a to 17d are 5a to 3d, the diagonal difference signal (Sa+5c)=(
Sb+Sd).

Also, as in the first embodiment, the tracking error signal RES is based on the phase of the diagonal difference signal and the sum signal Sa+sb+sc.
The reproduction signal RF of recorded information recorded as bits is obtained by comparing the phase of +sd with the above sum signal.

In the second embodiment, since the optical spots P, -P2 and the optical spots P3 and P4 are separated by an interval in the X direction, the optical spots P, -P4 are caused by frequency fluctuation of the laser beam from the semiconductor laser 11 Even if the light spots Pl to P4 move in the X direction as shown in the imaginary line, the light detection unit 1 corresponding to each light spot Pl to P4
The light is focused within 7a to 17d. In the second embodiment, the diffraction angles in the regions 13a and 13b of the diffraction element 13 and the diffraction angles in the regions 13c and 13d are slightly different, but the difference in the diffraction angles is considerably reduced compared to the conventional one. .

[Example 3] Next, a third embodiment will be described based on FIG. 11.

In the third embodiment, the photodetector 20 is connected to a dividing line 20i extending in the X direction, which is the radial direction of the optical disc 16,
Three dividing lines 20j to 20 extend in the Y direction, which is the track direction of the optical disc 16.
42 in the X direction, and eight photodetecting sections 20a.
~20h is provided.

On the other hand, similarly to the first embodiment, the diffraction element 13 is divided into four parts as shown in FIG. By inverting, a light spot P is formed on the photodetecting portions 2oh and 20g on the photodetector 20.

Moreover, the diffracted light diffracted by the region 13c of the diffraction element 13 is
Once focused at focal position f, the light is reversed to form a light spot P3 on the light detection sections 20a and 20b on the photodetector 20.

On the other hand, the focal position of the diffracted light diffracted by the regions 13b and 13d of the diffraction element 13 is set to f2. Therefore,
The diffracted light diffracted by the region 13b forms a light spot P2 on the light detection parts 20c and 20d without being reversed, and the diffracted light diffracted by the light detection part 20d forms a light spot P2 on the light detection parts 20c and 20d without being reversed. A light spot P4 is formed on 20e and 20f.

Now, the output signals of the photodetectors 20a to 20h are
When a −S h, the focus error signal FES is generated by the photodetectors 20b, 20c, 2Of, and 20g located inside of the two photodetectors corresponding to each region 13a to 13d of the diffraction element 13. FES= (Sc+5f)-(Sbf
Sg), and the bit signal RF is determined by the sum signal as RF=Sa+Sb+Sc+5dfSe+Sf+
It is obtained by calculating Sg + Sh.

Next, the tracking error signal RES is transmitted to the photodetecting sections 20b and 2 located inside of the two photodetecting sections corresponding to each region 13a to 13d of the diffraction element 13, respectively.
It is obtained by comparing the phase of the diagonal difference signal (Sc+Sf) - (Sb+3g) resulting from the output signal of 0c.20f 20g with the phase of the sum signal. In this case as well, the light spot P1 is changed due to the frequency fluctuation of the laser beam.
~ Even if P4 moves in the X direction, the focus error signal F
No error occurs in ES.

[Example 4] Next, a fourth embodiment will be described based on FIG. 12.

The photodetector 21 of the fourth embodiment has a circular shape as a whole. This photodetector 21 has two dividing lines 21j and 2 extending in the track direction and the radial direction of the optical disc 16.
1i and a circular dividing line 21k, eight photodetectors 21 are formed.
It is divided into a to 21h.

On the other hand, like the first embodiment, the diffraction element 13 has the four-division configuration shown in FIG. P
, the diffracted light from the region 13c is reversed to form a light spot Pz on the photodetecting sections 21a and 21b.

Further, the diffracted light from the region 13b of the diffraction element 13 is not reversed and forms a light spot P2 on the light detection parts 21C and 21d of the photodetector 21, and the diffracted light from the region 13d is not reversed and is Light spot P on detection parts 21e and 21f
4.

When the output signals of the respective photodetectors 21a to 21h are Sa to sh, the focus error signal FES is generated by the photodetector 21 corresponding to each region 13a to 13d of the diffraction element 13.
Of each of the two photodetectors, the photodetector 2 located inside
As diagonal difference signals of 1b, 21c, 21f, and 21g,
It is obtained by calculating FES=(Sc+5f)-(Sb+3g).

Also, when focusing the optical system, Sa+Sd+Se+5h=sb
By adjusting the diameters of the optical spots P and -P on the photodetector 21 so that +sc+sf+sg, FES-(S
d-3c)+ (Se-3f)+ (Sg-3h)+
(Sb-3a)=(Sd+Se+Sg+Sb)=(
The focus error signal FES can also be obtained by calculating Sc+Sf+Sh+Sa). In this case as well, even if the optical spots P, -P4 move in the X direction due to frequency fluctuations of the laser beam, no error occurs in the focus error signal FES.

On the other hand, the reproduction signal RF of recorded information recorded as pits
is a sum signal, RF=Sa+Sb+Sc+sd+se
It is determined by the calculation +sf+sg+sh.

Next, the tracking error signal RES is obtained by comparing the phase of the diagonal difference signal (Sc+Sf)-(Sb+3g) with the phase of the sum signal.

[Example 5] Next, a fifth embodiment will be described based on FIG. 13.

In the fifth embodiment, the photodetector 22 is separated by five dividing lines 22g to 22k extending in the track direction of the optical disc 16.
It is divided into two photodetecting sections 22a to 22f.

On the other hand, the diffraction element 13 has four regions 13a to 13a as shown in FIG.
It is divided into 13d. The diffracted light in the area 13a is once focused at the focal position on the front side of the photodetectors 22a to 22c of the photodetector 22, and after being reversed,
to form a light spot P1 on 2b and 22c,
A lattice 13e13e of the region 13a is designed. Further, the diffracted light in the region 13c of the diffraction element 13 is once focused at the same focal position as above, and then reversed and sent to the photodetector 22.
A light spot P is formed on the light detecting sections 22a and 22b of the light detecting section 22a and 22b.

On the other hand, the focal position of the diffracted light diffracted by the areas 13b and 13d of the 01 diffraction element 13 is at the photodetecting section 22d of the photodetector 22.
~22°f, and therefore the area 13b
The diffracted light at
Light spots P2 and P4 are formed on 2d to 22f.

In this embodiment, the output signals of the photodetectors 22a to 22f are set to 5a to 3f, respectively, and the focus error signal FES is FES=Sb−3e or FES=(Sb+
It is obtained by calculating Sd+5f)-(Sa+Sc+Se). On the other hand, the reproduction signal RF of recorded information recorded as pits is expressed as a sum signal RF=Sa+Sb+Sc+Sd+
It is determined by the calculation Se+Sr.

Next, the tracking error signal RES is transmitted to, for example, the photodetectors 22a, 22c, 22d, and 22, which are the photodetectors corresponding to the regions 13a to 13d of the diffraction element 13, respectively.
Diagonal difference signal of the output signal of f (Sa+5c)−(Sd+
Sf) and the phase of the sum signal.

In this embodiment, the optical spots P, P and the optical spot P2 are
・Since the light spots P4 and P4 are separated by an interval in the X direction, even if the light spots P, ~P4 move in the
~22c, and the light spots P2 and P4 are received by the photodetectors 22d~22f.

In embodying the present invention, the diffraction element 13 and the photodetectors 17, 20, 21, and 22 may be divided by a method other than that exemplified in each of the above embodiments.

Further, in each of the above embodiments, an optical pickup device for a read-only type optical disk has been described, but the present invention can also be applied to an optical pickup device for a so-called write-once type optical disk.

〔Effect of the invention〕

As described above, the optical pickup device according to the present invention includes a light generating means, an optical system that focuses the light emitted from the light generating means onto an optical disk, and guides reflected light from the optical disk to a diffraction element. In an optical pickup device that includes a diffraction element that diffracts reflected light from an optical disk toward a photodetector, and a photodetector that receives the diffracted light from the diffraction element and converts it into an electrical signal, the diffraction element is approximately The optical disc is divided into four regions with the dividing line extending in the track direction of the optical disc and the dividing line extending approximately in the radial direction of the optical disc as boundaries, and the distance to the focal position of the diffracted light in each of the two diagonal regions is They are set so that they almost match each other, and when no focus error occurs, the focal position of the diffracted light in the two areas at one diagonal position is located on the near side of the photodetector, and the focal position of the diffracted light in the two areas at the other diagonal position is located in front of the photodetector. The focal position of the diffracted light in one area is located further away from the photodetector, and the photodetector is positioned approximately midway between the two point positions, and the photodetector is provided with the diffraction element. At least four photodetectors including at least one photodetector corresponding to each area are provided, and recording is performed on the optical disc based on the sum of output signals of all the photodetectors of the photodetector. recorded information detection means for detecting the information recorded in the diffraction element; and focus error detection for detecting a focus error based on the difference between the sums of the output signals of the photodetection sections corresponding to each of the two diagonal positions of the diffraction element. tracking by comparing the difference between the sums of the output signals of the photodetectors corresponding to each of the two diagonal areas of the diffraction element and the phase of the sum of the output signals of all the photodetectors. This configuration includes tracking error detection means for detecting errors.

As a result, when the optical system is focused, the diffracted light from the two areas on one diagonal line of the diffraction element forms a focal point in front of the photodetector, and the diffracted light from the two areas on the other diagonal line forms a focus. Since the focal point is formed on the side farther away from the photodetector, a light spot having a predetermined area is formed on the photodetector when the optical system is focused. When a focus error occurs, the light spot due to the diffracted light from the two areas at one diagonal position expands or contracts, and the light spot due to the diffracted light from the two area pairs at the other diagonal position conversely shrinks or contracts. Since the amount of light received by each photodetector of the photodetector changes due to the enlargement, focus error is detected based on this.

Furthermore, when no tracking error occurs, the light and dark pattern of the reflected light from the optical disc, which is generated on the diffraction element by recorded information such as pits on the optical disc, is symmetrical with respect to the dividing line extending in the track direction of the optical disc as a boundary. , the sums of the output signals of the photodetectors corresponding to each of the two diagonal areas are equal, and the difference therebetween is 0.

On the other hand, if a tracking error occurs and the light spot on the optical disc deviates from the center of the track in either direction, the light and dark pattern of the reflected light from the optical disc on the diffraction element will change with the dividing line in the track direction of the optical disc as the boundary. The left and right sides become asymmetrical.

Therefore, the sums of the output signals of the photodetectors corresponding to each of the two diagonal areas are different, and the difference has a positive or negative value. In that case, the light and dark pattern on the diffraction element is reversed depending on the direction in which the light spot on the optical disk deviates from the track center, so the output signal of the photodetector corresponding to each of the two diagonal areas of the diffraction element is The polarity of the difference between the sums of is reversed depending on the direction in which the light spot on the optical disc deviates from the track center.

Note that when a tracking error occurs, the light and dark pattern on the diffraction grating changes as the light spot on the optical disk moves along recorded information such as bits,
Accordingly, the difference between the sums of the output signals of the photodetecting sections corresponding to each of the two diagonal areas of the diffraction element depicts a substantially sinusoidal wave. The phase of this sine wave changes depending on the direction in which the optical spot on the optical disk deviates from the track center. On the other hand, the sum of the output signals of all the photodetectors also draws a sine wave as the optical spot on the optical disc moves along the recorded information such as pits, but the phase of this sine wave may be affected by tracking error. It remains almost constant regardless of whether it is true or not. Therefore, the sine wave drawn by the difference between the sums of the output signals of the photodetectors corresponding to each of the two diagonal areas of the diffraction element, and the sine wave drawn by the sum of the output signals of all the photodetectors. Tracking errors can be detected by comparing the phases.

In the above configuration, the light detection parts of the photodetector that receives the diffracted light from the light detection parts of the diffraction element can be provided relatively close to each other, and the focus error and recorded information can be Since the number of photodetectors can be reduced by performing detection and tracking error detection using a common photodetector, it is possible to reduce the area occupied by the photodetector and the manufacturing cost.

Furthermore, since the respective photodetecting parts of the photodetector are provided at relatively close positions, the difference in diffraction angles in each region of the diffraction element can be made sufficiently small. As a result, when the cross-sectional shape of the grating in each region of the diffraction grating is made into a blaze shape, the blaze shape in each region can be made almost equal, making it easier to manufacture the grating, and also making it easier to manufacture the grating in each region. The efficiency of light use is sufficiently high, and
The difference in utilization efficiency can be made sufficiently small.

Furthermore, in the above configuration, since the focus error and tracking error are detected without dividing the emitted light from the light generating means into the main beam and the sub beam, the emitted light is divided into the main beam and the sub beam. A diffraction element becomes unnecessary, and the number of parts can be reduced.

[Brief explanation of drawings]

1 to 8 show one embodiment of the present invention. FIGS. 1A to 1C are schematic diagrams showing changes in the light spot on the photodetector when the objective lens is moved in the optical axis direction. FIG. 2 is a schematic front view of the optical pickup device. FIG. 3 is a schematic plan view of the diffraction element. FIG. 4 is a partially enlarged explanatory diagram showing the main part of FIG. 1(a) in an enlarged manner. FIGS. 5(a) and 5(b) are schematic explanatory diagrams showing a case where frequency fluctuation occurs in the laser light of a semiconductor laser. FIGS. 6(a) to 6(C) are explanatory diagrams showing the positional relationship between a light spot and a pit on an optical disc. FIGS. 7(a) to 7(c) are explanatory diagrams showing brightness and darkness patterns of light spots on the diffraction element. FIG. 8 is a graph showing the transition of the reproduced signal etc. when the light spot moves over the pit. FIGS. 9 and 10 show a second embodiment. FIG. 9 is a schematic explanatory diagram showing a photodetector. FIG. 10 is a partial front view of the optical pickup device. FIGS. 11 to 13 are schematic explanatory diagrams showing photodetectors in third to fifth embodiments, respectively. 14 to 16 show conventional examples. FIG. 14 is a schematic front view of the optical pickup device. FIG. 15(a) is a schematic plan view of the second diffraction element. FIG. 15(b) is a schematic explanatory diagram of a photodetector. FIGS. 16(a) and 16(b) are partial vertical cross-sectional views showing the cross-sectional shape of the grating of the second diffraction element, respectively. 12 is a semiconductor laser (light generation means), 13 is a diffraction element,
13a to 13d are areas, 13!13j are dividing lines, 14 is a collimating lens (optical system), 15 is an objective lens (optical system), 16 is an optical disk 17, 20, 21, and 22 is a photodetector, 17a to 17d20a ~ 20h21a ~21
h22a to 22f are photodetectors.

Claims (1)

[Claims] 1. A light generating means, an optical system that focuses the light emitted from the light generating means onto an optical disk and guides the reflected light from the optical disk to a diffraction element, and a light generating means that collects the light emitted from the optical disk. In an optical pickup device including a diffraction element that diffracts light toward a photodetector side and a photodetector that receives diffracted light from the diffraction element and converts it into an electrical signal, the diffraction element extends substantially in the track direction of the optical disk. It is divided into four regions with the dividing line and a dividing line extending approximately in the radial direction of the optical disk as boundaries, and the distances to the focal position of the diffracted light in each of the two diagonal regions are approximately the same. 2 of one diagonal position when no focus error occurs.
The focal position of the diffracted light in one area is located in front of the photodetector, and the focal position of the diffracted light in the other two diagonal areas is located further away from the photodetector. A photodetector is set to be located at an intermediate position, and the photodetector is provided with at least four photodetectors including at least one photodetector corresponding to each region of the diffraction element. and recorded information detecting means for detecting information recorded on the optical disk based on the sum of output signals of all the photodetecting parts of the photodetector, and two areas each at a diagonal position of the diffraction element. focus error detection means for detecting a focus error based on the difference between the sums of the output signals of the photodetectors respectively corresponding to the output signals of the photodetectors corresponding to each of the two diagonal position areas of the diffraction element; What is claimed is: 1. An optical pickup device comprising tracking error detection means for detecting a tracking error by comparing the difference between the sums of and the phase of the sum of the output signals of all the photodetectors.