JPH0344831A - Optical pickup device - Google Patents

Abstract

PURPOSE:To securely perform a focus error adjustment by comparing a sum of output signals of 1st and 3rd photodetectors with a sum of output signals of 2nd and 4th photodetectors. CONSTITUTION:A diffraction element 13 is divided into 1st and 2nd areas 13a and 13b, forming a spot on the 3rd photodetector 20c out of focus error detecting light diffracted by the 1st area 13a at the time of generating no focus errors and focused in front of a photodetector 20 and then inverted. On the other hand, detecting light diffracted by the 2nd area 13b is set to form a spot in approximately the same size as the spot of the 3rd photodetector 20c on the 2nd photodetector 20b without inversion in front of the photodetector 20. Then, a focus error is detected by comparing the sum of the output signals of the 1st and 3rd photodetectors 20a and 20c with the sum of the output signals of the 2nd and 4th photodetectors 20b and 20d. By this method, the focus error adjustment securely is performed, and the manufacturing cost is reduced by decreasing the occupied area 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 on or reproducing various types of optical disks, such as read-only type, write-once type, and rewritable type.

[Conventional technology]

As shown in FIG. 7, a conventional optical pickup device includes, for example, a semiconductor laser 11, a first diffraction element 12 that splits the light emitted from the semiconductor laser 11 into a main beam and a pair of sub beams, and an optical disk 16. A second diffraction element 13' that diffracts the reflected light toward the photodetector 17', a collimating lens 14, an objective lens 15, and a second diffraction element 13' receive the diffracted light from the second diffraction element 13' and record it on the optical disc I6. Some devices are known that include a photodetector 17' for reproducing information, detecting focus errors, and the like.

As shown in FIG. 8(a), the second diffraction element 13' is divided into first and second regions 13a' and 13b' by a dividing line 130' extending in the direction of diffraction in the second diffraction element 13'. It is divided. Each region 13a'13b' has grids 13d'-13d'... 13e' and 13e.
'... are formed at mutually different pitches in a direction perpendicular to the dividing line 13c'.

On the other hand, as shown in FIG. 8(b), the photodetector 17'
Six photodetecting portions 17a' to 17f' are provided, each extending in the diffraction direction of the second diffraction element 13'. When the focus is just focused without a focus error, the main beam diffracted by the first region 13a' of the second diffraction element 13' is focused on the dividing line 17g' to form a spot PI'. The main beam diffracted by the two regions 13b' is focused on the dividing line 17h' to form a sub-nod Pz'. Further, the i pairs of sub-beams are respectively focused on the photodetecting sections 17e' and 17f'.

Note that the gratings 13d' and 13 in the second diffraction element 13'
d'...13e', 13e'... In addition to the conventionally used rectangular cross section shown in FIG. 9(a), the cross-sectional shape of 13e', 13e'... Sawtooth-shaped blazes, which are highly efficient in using light, are also being considered.

However, in the above configuration, in FIG. 8(b), the photodetectors 17a' and 170' and 17b' and 17d'
are arranged side by side in the longitudinal direction, and the pair of beam substrates P+' and P2' are condensed at a fairly large interval in the radial direction of the optical disc 16. 17f' is considerably elongated vertically when viewed in the direction of diffraction at the second diffraction element 13'. As a result, the area occupied by the photodetectors 17a' to 17r' increases, and manufacturing costs also increase.

Also, the grating 13d'13d' in the second diffraction element 13'
... 13e', 13e'... When adopting the blaze shape shown in FIG. 9(b) as the cross-sectional shape, the first region 13a' and the second region 13b' of the second diffraction element 3
Since the difference in diffraction angle between the grating 13d'
It is necessary to make the pitches of the gratings 13d'- and 13e' and the gratings 13e' and 13e' significantly different. Therefore, it is difficult to process the first region 13a' and the second region 13b' into a blaze shape with the same cross section, so the grating 13d'.1
3d'..., 13e', 130'... not only becomes complicated, but also the first and second areas 13a'.
・Grid 13d' between 13b'・13d' -13e
The difference in the cross-sectional shape of ' . Note that in order to reduce the difference in light utilization efficiency between the first and second regions 13a' and 13b', the blaze shapes in both regions 13a' and 13b' are changed to shapes different from the optimal shapes. However, in that case, a problem arises in that a sufficiently high light utilization efficiency cannot be obtained.

In order to eliminate the above-mentioned problems, it is conceivable to configure the optical pickup device as shown in FIGS. 2 and 3.

That is, in this optical pickup device, the structures of the second diffraction element 13 and the photodetector 17 are changed from those described above. Note that parts having the same configuration as those of the optical pickup device shown in FIGS. 7 to 9 are given the same reference numerals, and redundant explanation will be omitted.

As shown in FIG. 10, the photodetectors 17 each have a second
Four rectangular photodetectors 17a to 17d extending in the diffraction direction of the diffraction element 13 are provided, each of the photodetectors 17a to 1
7d are juxtaposed only in the direction perpendicular to the diffraction direction in the second diffraction element 13. Two central photodetectors 17a
-17b is for reproducing recorded information and generating a focus error signal, and is separated from each other by a dividing line 17e extending in the direction of diffraction by the second diffraction element 13. or,
The two photodetectors 17c and 17d at both ends are for obtaining a tracking error signal based on a pair of sub-beams.

As shown in FIG. 3, the second diffraction element 13 has a first and a second semi-circular shape, each having a substantially semicircular shape, by a dividing line 13c extending in the Y direction, that is, in a direction perpendicular to the diffraction direction in the second diffraction element 13. It is divided into regions 13a and 13b. In the first region 13a, the main beam diffracted in the first w4 region 13a is located at a position f on the near side of the photodetector 17 during just focus without a focus error.
.

The direction and pitch are changed so that the spot P1 converges once and forms a semicircular spot Pl- on the photodetecting portion 17b of the photodetector 17, with the left and right direction reversed from that of the semicircular shape of the first area 13a. Determined grids 13d, 13d, . . . are formed.

Further, in the second region 13b, the focal position f2 of the main beam diffracted in the second region 13b is on the far side from the photodetector 17 during the above-mentioned just focusing, and therefore,
The main beam diffracted by the second region 13b is detected by the photodetector 1.
The gratings 13e, 13e, 13e, which have a determined direction and pitch so as to form a semicircular spot P2 in the same direction as the spot P1 on the photodetector 17a of the photodetector 17 without converging on the near side of the photodetector 17. ... is formed. The focal positions r and f2 are set so that the photodetector 17 is located approximately at the center thereof when in just focus.

According to the above configuration, each photodetector 17a of the photodetector 17
~17d is Y perpendicular to the diffraction direction in the second diffraction element 13
Since they are juxtaposed only in the direction, the length of the photodetector 17 seen in the direction of diffraction by the second diffraction element 13 can be shortened, thereby reducing the area occupied by the photodetector 17 and the manufacturing cost. It is possible to reduce the

Further, in the above configuration, the first region 13 of the second diffraction element 13
A spot P on the photodetector 17 of the main beam diffracted by a and a spot P2 on the photodetector 17 of the main beam diffracted in the second region 13b are the second diffraction element 1.
3, the first region 13a and the second region 13b
The difference in diffraction angles can be made sufficiently small.

Accordingly, the first and second? Grids 13d, 13d... 13e, 13e... in IN region 13a-L3b
When the cross-sectional shape of is a blaze shape, the lattice 13d.1
3d... Since the cross-sectional shapes of 13e, 13e... can be made almost equal, the lattice 13d, 13d...
13e, 13e... can be easily manufactured, and the light usage efficiency in the first and second regions 13a, 13b can be made sufficiently high and the difference in usage efficiency can be made sufficiently small. become.

By the way, in the optical pickup devices shown in FIGS. 2, 3, and 10, the sizes of the spots P and P2 are equal at the time of just focus, as described above.

Therefore, Spora) P+ fits within the photodetector 17b,
Since the spot P2 falls within the photodetector 17a, the output signal Sa of the photodetector 17a and the output signal sb of the photodetector 17b become equal.

On the other hand, if a focus error occurs and the optical disc 16 approaches the objective lens 15 too closely or leaves the objective lens 15 too far, one of the spots P1 and P2 will expand and protrude from the photodetector 17a or 17b, but the other will contract. Since the two output signals Sa and Sb are different from each other, a focus error can be detected based on the difference between the two output signals Sa and Sb.

That is, the focus error signal FES is FES=Sa
-3b, and the objective lens 15 is driven so that this FES becomes "0". On the other hand, the reproduction signal R3 of the recorded information is obtained by the calculation of R3=Sa-1-Sb.

However, as described above, simply providing two photodetectors 17a and 17b for detecting focus errors does not make it possible to sufficiently increase the dynamic range in detecting focus errors.

That is, the horizontal axis in FIG. 11 indicates the amount of displacement from the just focus position of the objective lens 15, and
The side) is the side where the objective lens 15 is excessively far away from the optical disc 16, and the NEAR side (- example) is the side where the objective lens 15 is transiently close to the optical disc 16.

In FIG. 11, the curve ■ represents the transition of the output signal Sa of the photodetector 17a, and the curve ■ represents the transition of the output signal sb of the photodetector 17b. Moreover, the song vAV represents the transition of the focus error signal FES'. As is clear from the figure, the dynamic range DRI for focus error detection
is in a relatively narrow range of -4 μm to 4 μm. In addition,
The data shown in Fig. 11 was obtained by computer simulation.
The distance between each point in the figure, the optical characteristics of the collimating lens 14 and the objective lens 15, etc. were set as shown in Table 1.

Moreover, Y of the photodetecting parts 17a-17b in the photodetector 17
The width d in the direction was 25 μm, the width of the dividing line 17e in the Y direction was 5 μm, and the diameter of the spots P, P2 at the time of just focus was 20 μm.

In order to solve the above problem and increase the dynamic range in the focus error detection table, the fifth
As shown in the figure, it is conceivable that the photodetector 18 is divided into six parts, and the four central photodetectors 18a to 18d detect focus errors and recording information.

In that case, the output signal of each photodetector 18a to 18f is
-3f, the focus error signal FES is FE
It is obtained by calculating S=(Sb+5d)-(Sa+SC).

FIG. 11 shows simulation results of the focus error signal FES when a six-divided photodetector 18 is used. In the figure, curve I represents the transition of the output signal Sa of the photodetector 18a, curve ■ represents the transition of the output signal sb of the photodetector 18b, curve ■ represents the transition of the output signal Sc of the photodetector 18c, and curve ■ represents the transition of the output signal Sd of the photodetector 18d. The focus error signal FES changes as shown by the curve (2). In this case, the dynamic range DR2 for focus error detection is -6 μm to 5 μm, which is improved compared to the four-divided photodetector 17. In addition, in the above simulation, the distance between each point of the optical pickup device, the optical characteristics of each lens 14, 15, etc. are 4.
As in the case of using the divided photodetector 17, the values are as shown in Table 1. In addition, each photodetector 18a of the photodetector 18
The width d2 in the Y direction of 18d is 25 μm2 Each dividing line 18g ~
The width of the photodetector 18i in the Y direction is 5 μm, and spots P and P2 each having a diameter of 20 μm are formed in the photodetecting portions 18b and 18c at the time of just focus.

[Problems to be Solved by the Invention] By the way, focus error adjustment is performed by moving the objective lens 15 closer to the optical disk 16 if the focus error signal FES is a positive value, and by moving the objective lens 15 closer to the optical disc 16 if the focus error signal FES is a negative value. This is done in such a way as to separate it from the optical disc 16. Therefore, in order to properly perform focus servo, it is necessary that FES always take a positive value in the F A R region of FIG. 11, and that FES always take a negative value in the N E A R region.

However, in reality, D I-D in the F A R91 area
Since FES takes a negative value in the interval t and positive value in the interval D3 to D4 in the NEAR region,
There is a possibility that focus error adjustment may not be performed properly. Although it is normally not possible for the objective lens 15 to approach the optical disc 16 to the point D3 on the NEAR side, when the optical disc 16 is installed in the device, the objective lens 15 should be separated from the optical disc 16 by a large distance towards the FAR side. After mounting, move the objective lens 15 to the just focus position.
Therefore, when the optical disc 16 is mounted, the objective lens 15 may move toward the FAR side up to the section D1 to D2. In that case, if the objective lens 15 moves within the section D1 to D2 and the focus error signal FES takes a negative value, it becomes impossible to guide the objective lens 15 to the just focus position after mounting the optical disc 16. Therefore, at least F A
In the Riff region, it is necessary to set the polarity of the FES so that it will not be reversed.

The inventor of the present invention searched for the reason why the polarity of the FES is reversed at intervals such as -D2, and found that it is based on the following phenomenon.

That is, FIG. 12 shows spots P, P2 on the photodetector 18 when the objective lens 15 gradually moves toward the FAR side.
This shows the change in In the figure, (a) shows spots P and P at the just focus position. As the objective lens 15 moves toward the FAR side, (b) (
As shown in C), spot P gradually expands, and spot P
2 shrinks.

When the objective lens 15 further moves toward the FAR side, the focal value Wrz of the main beam diffracted by the second region 13°b of the second diffraction element 13 moves toward the front side of the photodetector 18, so that As shown in (d), the direction of the subbutton 1-P2 is reversed. Then, when the objective lens 15 continues to move toward the FAR side, a part of the spot P comes to protrude from the light detection section 18d, as shown in (e) in the figure. in this way,
When the spot P protrudes from the photodetection section 18d, the output signal Sd of the photodetection section 18d becomes smaller, which causes the polarity of the focus error signal FES to be reversed.

Note that even when the objective lens moves significantly toward the NEAR side, due to the same phenomenon described above, the focus error signal FE
The polarity of S will be reversed.

[Means for Solving the Problems] In order to solve the above-mentioned problems, an optical pickup device according to a first aspect of the present invention includes a light generation means and an objective lens, and the optical pickup device according to the first aspect of the present invention includes a light generation means and an objective lens. An optical system that focuses light onto an optical disk and guides the reflected light from the optical disk to a diffraction element, a diffraction element that diffracts the reflected light from the optical disk toward a photodetector, and detects the light diffracted by the diffraction element. In the optical pickup device, the photodetector includes at least first to first photodetectors arranged in parallel in a direction substantially orthogonal to the direction of diffraction in the diffraction element.
A fourth photodetector is provided, and the width of the fourth photodetector located at at least one end in a direction substantially orthogonal to the diffraction direction is set to be larger than the width of the other photodetectors in a direction substantially orthogonal to the diffraction direction. The diffraction element is divided into a first and second region, and the light for focus error detection that is diffracted in the first region when no focus error occurs is focused on the front side of the photodetector. Tie and invert,
While a spot is formed on the third photodetector of the photodetector, the focus error detection light diffracted in the second region is not reversed on the near side of the photodetector and is transferred to the third photodetector. It is set to form a spot of approximately the same size as the spot of the photodetector, and the sum of the output signals of the first and third photodetectors in the photodetector and the output signals of the second and fourth photodetectors are The present invention is characterized in that a focus error detection means is provided for detecting a focus error by comparing the output signal with the sum of the output signals.

Further, the optical pickup device according to the second aspect of the present invention includes:
an optical system comprising a light generating means and an objective lens, condensing the light emitted from the light generating means onto an optical disk and guiding reflected light from the optical disk to a diffraction element; and a photodetector for detecting the reflected light from the optical disk. In an optical pickup device including a diffraction element that diffracts the light toward the side, and a photodetector that detects the light diffracted by the diffraction element, the photodetector sequentially at least rotates the light in a direction substantially perpendicular to the direction of diffraction in the diffraction element. The diffraction element is provided with first to fourth light detection sections arranged in parallel, and the above-mentioned diffraction element is divided into a first and second region, and a focus error detection section that is diffracted in the first region when no focus error occurs. The light is focused on the front side of the photodetector and reversed to form a spot on the third photodetection part of the photodetector, while the light for focus error detection that is diffracted in the second area is photodetected. It is set so that a spot of approximately the same size as the spot of the third photodetector is formed in the second photodetector without being reversed on the front side of the device, and the first and third spots in the photodetector are A focus error detection means detects a focus error by comparing the sum of the output signals of the light detection section and the sum of the output signals of the second and fourth light detection sections; The fourth photodetector is characterized in that it is provided with a sensitivity adjusting means that lowers the sensitivity of the fourth photodetector or increases the sensitivity of the fourth photodetector compared to the other photodetectors.

[For production]

According to the first aspect of the present invention described above, since the first to fourth photodetecting parts in the photodetector are arranged in parallel only in a direction substantially perpendicular to the direction of diffraction in the diffraction element, the diffraction in the second diffraction element The length of the photodetector viewed in the direction can be shortened, and as a result, the area occupied by the photodetector can be reduced and manufacturing costs can be reduced.

In that case, at the just focus position, as above,
The size of the spot on the photodetector of the light for focus error detection diffracted by the first region of the diffraction element and the size of the spot of the light for focus error detection diffracted in the second region on the photodetector The sizes are almost equal. On the other hand, when a focus error occurs, the intermediate position between the respective focal points of the light diffracted in the first and second regions shifts from the light receiving surface of the photodetector, so the size of each spot on the photodetector increases. It expands and contracts in a direction substantially perpendicular to the direction of diffraction in the diffraction element. Therefore, a focus error can be detected by comparing the sum of the output signals of the first and third photodetectors with the sum of the output signals of the second and fourth photodetectors.

Further, in the first aspect of the present invention, the spot of the diffracted light in the first region of the diffraction element on the photodetector and the spot of the diffracted light in the second region on the photodetector are different from each other. Since it is arranged to be shifted in a direction substantially perpendicular to the direction of diffraction in the diffraction element, the difference in diffraction angles between the first region and the second region can be made sufficiently small. As a result, when the cross-sectional shape of the grating in the first and second regions is made into a blaze shape, the blaze shapes in the first and second regions can be made almost equal, so that the grating can be easily manufactured. , the light usage efficiency in the first and second regions can be made sufficiently high, and the difference in usage efficiency can be made sufficiently small.

Furthermore, according to the first aspect, at least the width in the direction substantially orthogonal to the diffraction direction in the diffraction element of the fourth photodetecting section is
Since the width is set larger than the width in the same direction of other photodetecting parts, even when the objective lens moves significantly toward the FAR side or the NEAR side, the focus diffracted by the first and second regions of the diffraction element is The spot of the error detection light on the photodetector will no longer protrude from the fourth photodetector, and therefore the polarity of the focus error signal will not be reversed at least on the FAR side. As a result, focus error adjustment can be performed reliably.

Further, according to the second aspect of the present invention, as in the first aspect, the area occupied by the photodetector is reduced, the manufacturing cost is reduced, and the cross-sectional shape of the grating of the diffraction element is made into a blaze shape. It is possible to facilitate the manufacture of the lattice, improve the light usage efficiency in the first and second regions, and reduce the difference in the usage efficiency.

Furthermore, in the second aspect, the sensitivity of the 4th photodetector in the photodetector is made lower than the other photodetectors, or the sensitivity of the 4th photodetector is made higher than the other photodetectors. However, this prevents the polarity of the focus error signal from being reversed at least on the FAR side. Therefore, even if the objective lens is moved significantly toward the FAR side when the optical disc is mounted, focus errors can be adjusted appropriately after mounting. Note that in the first and second aspects described above, the polarity of the focus error signal may be reversed on the NEAR side, but on the NRAR side, it is actually impossible for the objective lens to move to a section where the polarity is reversed. Therefore, no problem will occur.

[Example 1] First aspect of the present invention (Claim 1 in the claims column)
An example of the embodiment (corresponding to section 1) will be described below based on FIGS. 1 to 4.

The present optical pickup device is used, for example, as a playback device for a read-only optical disc such as a so-called compact disc, or a recording/playback device for a write-once or rewritable optical disc.

As shown in FIG. 2, the emitted light from the semiconductor laser 11 as a light generating means is converted into an O-order diffracted light (hereinafter referred to as a main beam) by a first diffraction element 12 and the main beam in a plane substantially perpendicular to the plane of the paper. The diffraction light is divided into ±1st-order diffraction light (hereinafter referred to as a pair of sub-beams) that are separated by a predetermined angle, and guided to a second diffraction element 13 as a diffraction element in the claims section. Here, each of the three beams is further diffracted, and each O-order diffracted light passes through the collimator lens 14 and is focused onto the optical disk 16 by the objective lens 15. The first diffraction element 12, the collimating lens 14, and the objective lens 15 constitute an optical system.

The main beam that has passed through the objective lens 15 is used to record information on the optical disc 16 or to read recorded information.
The light is focused on the center of the trunk of the optical disc 16. on the other hand,
The pair of sub-beams are relatively thick (separated from each other in the trunk direction of the optical disk 16 (Y direction in FIG. 2) in opposite directions, and are separated from the main beam in the radial direction of the optical disk 16 (Y direction in FIG. 2). (X direction), the lights are focused at slightly shifted positions in opposite directions.

The main beam and the pair of sub beams reflected from the optical disk 16 are passed through the objective lens 15 and the collimating lens 1.
4 and is diffracted in the X direction by the second diffraction element 13,
Each first-order diffracted light beam is guided to a photodetector 20.

As shown in FIG. 4(b), the photodetector 20 includes first to sixth photodetectors 20a to 2Of each having a rectangular shape and extending in the X direction, which is the direction of diffraction by the second diffraction element 13. . First to fourth photodetectors 20a located in the center
20d is divided from adjacent ones by dividing lines 20g to 20i extending in the X direction. Specifically, the width d4 of the first and fourth photodetectors 20a and 20d in the Y direction is considerably larger than the width d3 of the second and third photodetectors 20b and 20c in the Y direction. For example, it is set to about 4 times.

In addition, the fifth and sixth photodetectors 20e-2Of located at both ends
are formed on both sides of the first to fourth photodetectors 2oa to 2od at intervals in the Y direction perpendicular to the diffraction direction in the second diffraction element 13. As described above, the first to sixth photodetectors 20a to 20f are arranged in parallel only in the Y direction orthogonal to the diffraction direction of the second diffraction element 13, and in the X direction which is the diffraction direction of the second diffraction element 13. Two or more photodetectors 20a to 20r are not arranged in parallel.

As shown in FIG. 3, the second diffraction element 13 has first and second regions 13a, each having a substantially semicircular shape, defined by a dividing line 13c extending in the Y direction perpendicular to the diffraction direction of the second diffraction element 13. It is divided into 13b. 1st area 1
3a, this first area 13 at the time of just focus
The main beam, which is the focus error detection light diffracted by a, once converges at a position r1 on the near side of the photodetector 17, and the first
? Gratings 13d, 13d, . . . with a defined direction and pitch are formed so as to form a semicircular spot P1 whose left and right directions are reversed from the semicircular shape of the il region 13a.

On the other hand, in the second region 13b, the focus value TZ r z of the main beam diffracted in the second region i3b during the above-mentioned just focus is on the far side from the photodetector 20, and therefore, the main beam is diffracted in the second region 13b. The direction and pitch are set so that the main beam does not converge in front of the photodetector 20 and forms a semicircular spot P2 in the same direction as the spot P1 on the second photodetection section 2Ob of the photodetector 20. lattices 13e, 13e, . . . are formed.

The focus positions fl'fz are set so that the photodetector 20 is located approximately at the center of the focus positions during just focus. In this way, the first and second regions 13a and
In order to vary the distance to the focal point of the diffracted light from 13b, the first region 13a is provided with a light convergence function (convex lens function), and the second region 13b is provided with a light divergence function (concave lens function). Granted.

Note that the lattice 13d1 of the first and second regions 13a and 13b
3d.=13e.13e-... is the well-known 2
It can be created by a beam interferometry method, or by determining the shape of interference fringes using an electronic computer and directly drawing the interference fringes on a dry plate using an electron beam exposure device. In that case, the cross-sectional shape of the gratings 13d, 13d, . . . , 13e, 13e, .
It can be made into the blaze shape shown in .

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

As mentioned above, when the distance between the objective lens 15 and the optical disc 16 is just focused, as shown in FIG. 4(b).
As shown in the figure, the spots P1 and P2 have the same size, and the spot PI falls within the third light detection section 20C, while the spot Pz falls within the second light detection section 2Ob.

On the other hand, when the objective lens 15 moves to the NEAR side, that is, to the side that approaches the optical disk 16 excessively, resulting in a focus error state, the focal position r approaches the photodetector 20, and the focal position f2 approaches the photodetector. 20, as shown in FIG. 4(a), the spot P1 shrinks while the spot P2 expands and protrudes outside the second light detection section 2Ob, and enters the first and third light detection sections 20a and 20c. It also comes to extend.

Conversely, if the objective lens 15 moves to the FAR side, that is, to the side where it is excessively separated from the optical disc 16, resulting in a focus error state, the spot P1 expands and becomes the second and second spot, as shown in FIG. 4(C). While it extends to the four light detection sections 20b and 20d, the spot P2 is reduced. Therefore, the focus error detection means (not shown) detects the first to fourth light detection sections 20a to 20a.
A focus error signal FES is obtained by comparing the output signals of 20d.

That is, the output signal of each photodetector 20a to 20f is
-3f, the focus error signal FES is FES
= (Sb+5d)-(Sa+Sc), and the objective lens 15 is driven so that this FES becomes O''.

Here, the width d4 in the Y direction of the first and fourth photodetectors 20a and 20d is 100 μm, and the second and third photodetectors 20b-20
The results obtained by simulating the transition of the focus error FES when the width d of c is 25 μm, the width of the dividing lines 20g to 20i in the Y direction is 5 μm, and the diameter of the spot Pl'Pt during just focus is 20 μm. Shown in Figure 1. However, the distance between each point of the optical pickup device, the optical characteristics of the collimating lens 14 and the objective lens 15, etc. were set as shown in Table 1 above.

In FIG. 1, curves l to {circle around (2)} show the transition of the output signals 5a-3d of the first to fourth photodetectors 20a to 20d, respectively, and curve {circle over (2)} shows the transition of the focus error signal FES1. As is clear from the figure, in this embodiment, by expanding the width in the Y direction of the first and fourth light detection sections 20a and 20d located on both end sides of the focus error detection section, the FAR side and NEAR side Inversion of the polarity of the focus error signal FES1 is prevented. Therefore, even if the objective lens 5 is moved significantly toward the FAR side when the optical disc 16 is mounted, no problem will occur in the subsequent focus servo. Note that the dynamic range DR3 for focus error detection in this example is -6 μm.
~6 μm, which is 4 μm, which is one of the dynamic range DRI of the focus error signal FES' when using the conventional photodetector 17 (see FIG. 1) shown by the curve ■ in FIG.
It is extended from m to 4 μm.

Further, in this embodiment, the reproduction signal R3 of the recorded information is R3
It is obtained by calculating =S a +S b.

The sub-beams reflected by the optical disk I6 and diffracted by the second diffraction element 13 are focused on the fifth and sixth photodetectors 20e and 2Of. The tracking error signal RES is
=Se-3r, and tracking adjustment is performed so that this RES becomes "0 par."

In this embodiment, each photodetector 20a to 2O of the photodetector 20
f are arranged in parallel only in the direction orthogonal to the diffraction direction of the second diffraction element 13, and a plurality of light detection parts are not arranged in parallel in the diffraction direction of the second diffraction element 13, so that the light detection part 20a
It becomes possible to reduce the occupied area of ~20 f and also to reduce the manufacturing cost.

Moreover, the first and second regions 13a and 13 of the second diffraction element 13
The gratings 13d, 13d, etc. of the second diffraction element 13 are arranged so that the spot P+/P2 on the photodetection 2S17 by the main beam diffracted by b is shifted in the direction orthogonal to the diffraction direction in the second diffraction element 13. 13e-13e
... was formed, the first and second regions 13a and 13
The diffraction angles at 'b' become almost equal. Therefore, grid 1
When the cross-sectional shapes of 3d-13d... and 13e, 13e... are made into the blaze shape shown in FIG. 9(b), the pitches of the gratings 13d-13d... and 13e, 13e... are approximately equal. Therefore, the second diffraction element 13 can be processed smoothly, and it can be formed into an optimal blaze shape with no difference in light utilization efficiency and a sufficiently high utilization efficiency.

Note that in the above embodiment, the first and fourth photodetectors 20a
・The width d4 of 20d in the Y direction is
The width in the Y direction of c is larger than d3, but instead of this,
Only the width d4 of the fourth photodetector 20d in the Y direction may be made larger than the widths of the other photodetectors 20a to 20c in the Y direction. In this case, at least, the polarity of the focus error signal FES on the FAR side can be prevented from being reversed, so the focus error can be adjusted accurately.

[Example 2] An example of the second aspect of the present invention (corresponding to claim 2 of the claims) will be described as follows based on FIGS. 5 and 6. be.

As shown in FIG. 5, in the second embodiment, the photodetector 1
8 is provided with rectangular first to sixth photodetectors 183 to 18f each extending in the X direction, which is the diffraction direction of the second diffraction element 130. As in the first embodiment, the center first to
The focus error signal and recorded information are detected using the fourth photodetectors 18a to 18d, and the tracking error signal is detected using the fifth and sixth photodetectors 18e and 18f at both ends. ing. However, in this embodiment, the width d in the Y direction of the first to fourth photodetecting parts L8a to L8d
2 are set equal. Further, the parts of the optical pickup device other than the photodetector 18 are constructed in the same manner as in the first embodiment.

In the second embodiment, the sensitivity of the first photodetecting section 18a in the photodetector 18 is adjusted to a second level by a sensitivity adjusting means (not shown).
- The sensitivity is set lower than the sensitivity of the fourth photodetectors 18b to 18d. Specifically, the first to fourth photodetectors 18a to 18
The output signals of d are each amplified, but the first photodetector 1
The amplification factor of the output signal of 8a is determined by the second to fourth photodetectors 18b-
It is set lower than the amplification factor of the output signal of 18d.

The configuration of the optical pickup device is as shown in Table 1, and
The width d2 in the Y direction of the first to fourth photodetectors 18a to 18d is 25 // m, the width in the Y direction of the dividing lines 18g to 18i is 5 μm, and the spora 1 to P1 during just focus.
The diameter of P2 is 20 μm, and the first photodetector 18a
The amplification factor of the output signal of the second to fourth photodetectors 18b to 18
FIG. 6 shows the transition of the focus error signal FES2 when the amplification factor of the output signal d is set to 0.7 times.

In this case, if the output signals of the first to fourth photodetectors 18a to 18d after being amplified at a constant amplification factor are Sa to Sd,
Focus error signal FES2 is detected by focus error detection means (not shown) as FBS2=(Sb+Sd)
It is obtained by the calculation of (SaXo, 7+Sc). Curve I in Figure 6 represents the transition of 5aX0.7, and curves
It shows the transition of b-3d. Further, the curve V shows the transition of the focus error signal FES2 according to this embodiment, and the curve 2 shows the transition of the focus error signal FES' when the conventional photodetector 17 (FIG. 10) is used. Note that the dynamic range DR4 of the focus error signal FES2 is -6 μm to 5 μm.

As is clear from the curve (2) in the figure, the focus error signal FES2 does not take a negative value on the FAR side. As a result, even if the objective lens 15 is moved significantly toward the FAR side when the optical disc 16 is mounted, there will be no problem with the focus servo thereafter. On the other hand, NEAR
On the side, the polarity of the focus error signal FES2 is reversed after the 0 point, but in reality, the objective lens 15 is
R(!II does not move to point D, so there is no problem.

Note that in the above, the sensitivity of the first photodetector 18a is lowered, but instead, the sensitivity of the fourth photodetector 18d is increased than the sensitivity of the first to third photodetectors 18a to 18c. By doing so, the same effect as described above can be obtained.

〔Effect of the invention〕

As described above, the optical pickup device according to the first aspect of the present invention includes a light generating means and an objective lens, and focuses the light emitted from the light generating means onto an optical disk, and also reflects light from the optical disk. An optical pickup device including an optical system that guides light to a diffraction element, a diffraction element that diffracts reflected light from an optical disk toward a photodetector, and a photodetector that detects the light diffracted by the diffraction element, The photodetector includes at least first to fourth photodetectors arranged in sequence in a direction substantially orthogonal to the diffraction direction in the diffraction element, and substantially parallel to the diffraction direction of the fourth photodetector located at at least one end. The width in the orthogonal direction is set to be larger than the width of the other photodetecting sections in the direction substantially perpendicular to the diffraction direction, and the diffraction element is divided into first and second regions, and also prevents focus errors from occurring. When the focus error detection light is diffracted in the first region, it is focused on the front side of the photodetector and reversed,
While a spot is formed on the photodetector, the focus error detection light diffracted in the second region is not reversed on the near side of the photodetector and is formed on the second photodetector with the spot of the third photodetector. It is set to form a spot of approximately the same size, and the sum of the output signals of the first and third photodetectors and the sum of the output signals of the second and fourth photodetectors in the photodetector is This configuration is provided with focus error detection means that detects focus errors by comparison.

As a result, the first to fourth photodetectors in the photodetector are arranged in parallel only in the direction substantially perpendicular to the diffraction direction in the diffraction element, so that the length of the photodetector seen in the diffraction direction in the second diffraction element is As a result, the area occupied by the photodetector can be reduced and manufacturing costs can be reduced.

In that case, at the just focus position, as above,
The size of the spot on the photodetector of the light for focus error detection that is diffracted in the first region of the diffraction element and the second region of the diffraction element.
The size of the spot on the photodetector of the light for focus error detection that is diffracted in the area is approximately equal to the size of the spot on the photodetector. on the other hand,
When a focus error occurs, the intermediate position of each focal point of the light diffracted in the first and second regions shifts from the light receiving surface of the photodetector, so the size of each spot on the photodetector changes, It expands and contracts in a direction substantially perpendicular to the direction of diffraction in the diffraction element. Therefore, a focus error can be detected by comparing the sum of the output signals of the first and third photodetectors with the sum of the output signals of the second and fourth photodetectors.

Further, in the first aspect of the present invention, the spot of the diffracted light on the photodetector in the first region of the diffraction element and the spot on the photodetector of the diffracted light in the second region are the same. Since the positions are shifted in a direction substantially orthogonal to the diffraction direction in the two diffraction elements, the first region and the second w! The difference in diffraction angles in the region can be made sufficiently small. As a result, when the cross-sectional shape of the grating in the first and second regions is made into a blaze shape, the blaze shapes in the first and second regions can be made almost equal, so that the grating can be easily manufactured. , the light usage efficiency in the first and second a regions can be made sufficiently high, and the difference in usage efficiency can be made sufficiently small.

Furthermore, according to the first aspect, the width of at least the fourth light detection section in a direction substantially orthogonal to the diffraction direction in the diffraction element is set to be larger than the width of the other light detection sections in the same direction. Therefore, even if the objective lens moves significantly toward the FAR side, the spot on the photodetector of the light for focus error detection that is diffracted by the first and second regions of the diffraction element will be transferred to the fourth photodetector. Therefore, at least on the FAR side, the polarity of the focus error signal will not be reversed. As a result, focus error adjustment can be performed reliably.

Further, the optical pickup device according to the second aspect of the present invention includes:
an optical system comprising a light generating means and an objective lens, condensing the light emitted from the light generating means onto an optical disk and guiding reflected light from the optical disk to a diffraction element; and a photodetector for detecting the reflected light from the optical disk. In an optical pickup device including a diffraction element that diffracts the light toward the side, and a photodetector that detects the light diffracted by the diffraction element, the photodetector sequentially at least rotates the light in a direction substantially perpendicular to the direction of diffraction in the diffraction element. The diffraction element is divided into first and second regions, and detects a focus error diffracted in the first region when no focus error occurs. The focus error light is focused on the front side of the photodetector and is inverted to form a spot on the third photodetection part of the photodetector, while the focus error detection light diffracted in the second area is It is set so as to form a spot on the second photodetector that is approximately the same size as the spot on the third photodetector without being reversed on the near side of the detector, and A focus error detection means detects a focus error by comparing the sum of the output signals of the three photodetectors and the sum of the output signals of the second and fourth photodetectors; The fourth photodetector is configured to include a sensitivity adjustment unit that lowers the sensitivity of the fourth photodetector or increases the sensitivity of the fourth photodetector compared to the other photodetectors.

As in the first aspect, this reduces the area occupied by the photodetector, reduces manufacturing costs, and facilitates manufacturing of the grating when the cross-sectional shape of the grating of the diffraction element is blazed. - It is possible to improve the light usage efficiency and reduce the difference in usage efficiency in the second region.

Furthermore, in the second aspect, the sensitivity of the first photodetector in the photodetector is lowered than that of other photodetectors, or the sensitivity of the fourth photodetector is made higher than that of other photodetectors. However, this prevents the polarity of the focus error signal from being reversed at least on the FAR side. Therefore, even if the objective lens is moved significantly toward the FAR side when the optical disc is mounted, focus errors can be adjusted appropriately after mounting. Note that although the polarity of the focus error signal may be reversed on the NEAR side, no problem occurs on the NRAR side because it is practically impossible for the objective lens to move to an area where the polarity is reversed.

[Brief explanation of drawings]

1 to 4 show one embodiment of the present invention. FIG. 1 is a graph showing the transition of the focus error signal as the objective lens moves. FIG. 2 is a schematic front view of the optical pickup device. FIG. 3 is a schematic plan view of the second diffraction element. FIGS. 4(a) to 4(C) are schematic explanatory diagrams showing changes in the spot on the photodetector as the objective lens moves. FIGS. 5 and 6 show other embodiments. FIG. 5 is a schematic explanatory diagram of a photodetector. FIG. 6 is a graph showing the transition of the focus error signal as the objective lens moves. 7 to 12 show conventional examples. FIG. 7 is a schematic front view of the optical pickup device. FIG. 8(a) is a schematic plan view of the second diffraction element. FIG. 8(b) is a schematic explanatory diagram of a photodetector. FIGS. 9(a) and 9(b) are partial cross-sectional views showing the cross-sectional shape of the grating of the second diffraction element. FIG. 10 is a schematic explanatory diagram of a photodetector. FIG. 11 is a graph showing the transition of the focus error signal as the objective lens moves. FIG. 12 is an explanatory diagram showing changes in the spot on the photodetector when the objective lens moves toward the FAR side. 11 is a semiconductor laser (light generating means), 12 is a first diffraction element (optical system), 13 is a second diffraction element (diffraction element), 13
a is a first region, 13b is a second region, 14 is a collimating lens (optical system), 15 is an objective lens, 16 is an optical disk, 18.2o is a photodetector, 18a to 18d, 20a
-20d are first to fourth photodetectors.

Claims (1)

[Scope of Claims] 1. An optical system comprising a light generating means and an objective lens, condensing the light emitted from the light generating means onto an optical disk and guiding reflected light from the optical disk to a diffraction element, and an optical disk. In an optical pickup device, the optical pickup device includes a diffraction element that diffracts light reflected from The first to fourth photodetectors are arranged in sequence in a direction substantially orthogonal to the direction, and the fourth photodetector is located at at least one end.
The width of the photodetecting section in a direction substantially perpendicular to the diffraction direction is set larger than the width of the other photodetecting sections in the direction substantially orthogonal to the diffraction direction, and the diffraction element is divided into first and second regions. Along with being
The focus error detection light that is diffracted in the first region when no focus error occurs is focused on the front side of the photodetector and reversed, forming a spot on the third photodetection section of the photodetector. On the other hand, the focus error detection light diffracted in the second region is not reversed in front of the photodetector, and forms a spot on the second photodetector that is approximately the same size as the spot on the third photodetector. It is set as follows.
and a focus error detection means for detecting a focus error by comparing the sum of the output signals of the first and third photodetectors and the sum of the output signals of the second and fourth photodetectors in the photodetector. An optical pickup device comprising: 2. An optical system comprising a light generating means and an objective lens, condensing the light emitted from the light generating means onto the optical disk and guiding the reflected light from the optical disk to a diffraction element, In an optical pickup device including a diffraction element that diffracts light toward a detector side and a photodetector that detects light diffracted by the diffraction element, the photodetector is arranged at least in a direction substantially perpendicular to the direction of diffraction in the diffraction element. The diffraction element is divided into a first region and a second region, and the diffraction element is divided into a first region and a second region.
The focus error detection light that is diffracted in the first region when no focus error occurs is focused on the front side of the photodetector and reversed, forming a spot on the third photodetection section of the photodetector. On the other hand, the focus error detection light diffracted in the second region is not reversed in front of the photodetector, and forms a spot on the second photodetector that is approximately the same size as the spot on the third photodetector. It is set as follows.
and a focus error detection means for detecting a focus error by comparing the sum of the output signals of the first and third photodetectors and the sum of the output signals of the second and fourth photodetectors in the photodetector; , a sensitivity adjusting means for lowering the sensitivity of the first light detecting section relative to the other light detecting sections or increasing the sensitivity of the fourth light detecting section relative to the other light detecting sections. pickup device.