JPH0770084B2 - Optical pickup device - Google Patents

Description

The present invention relates to an optical pickup device used for recording and reproducing information on various optical disks such as a read-only type and a write-once type.

[Conventional technology]

As shown in FIG. 14, in the conventional optical pickup device, the emitted light of the semiconductor laser 1 is 0 by the first diffraction element 2.
Second-order diffracted light (hereinafter referred to as main beam) and ± first-order diffracted light (hereinafter referred to as a pair of sub-beams) that form a predetermined angle with respect to the main beam in a plane substantially orthogonal to the paper surface and are separated from each other. It is divided and guided to the second diffraction element 3. Here, each of the three beams is further diffracted, and each 0th-order diffracted light passes through the collimator lens 4 and is condensed on the optical disc 6 by the objective lens 5.

At that time, if the optical disc 6 is a compact disc, the main beam is focused on the pits on the optical disc 6 to read the recorded information recorded as pits, and the recorded information is reproduced based on the reflection intensity thereof. Done. In addition, a focus error signal can be obtained based on the main beam as described later.

On the other hand, the pair of sub-beams are relatively far apart from each other in the track direction of the optical disc 6 with respect to the main beam, and are slightly deviated from the main beam in the radial direction of the optical disc 6 in the opposite directions. It is focused on the position. Then, a tracking error signal is obtained from the reflection intensities of the pair of sub-beams.

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

As shown in FIG. 15 (a), the second diffraction element 3 is divided into two regions 3a and 3b by a division line 3c extending in the diffraction direction of the second diffraction element 3. In each of the regions 3a and 3b, gratings 3d, 3d ..., 3e, 3e ... Are formed at different pitches in a direction perpendicular to the dividing line 3c.

On the other hand, as shown in FIG. 15 (b), the photodetector 7 is divided into six photodetector portions 7a to 7f each extending in the diffraction direction of the second diffraction element 3. Then, in the focused state where there is no focus error, the main beam diffracted in the region 3a of the second diffractive element 3 is condensed on the dividing line 7g to form a light spot P ₁ ′ and diffracted in the region 3b. The main beam is focused on the dividing line 7h to form a light spot P ₂ ′.
The pair of sub-beams diffracted by the second diffraction grating 3 are focused on the photodetectors 7e and 7f, respectively.

Then, the output signals Sa to Sf obtained from the respective photodetectors 7a to 7f
Based on, the focus error signal FES is FES = (Sa + S
d)-(Sb + Sc), the tracking error signal RES is obtained by RES = Se-Sf, and the pit signal (recording information) RF is obtained by RF = Sa + Sb + Sc + Sd.

The gratings 3d, 3d ..., 3e, 3e ... in the second diffraction element 3
In addition to the rectangular cross section shown in FIG. 16 (a) which has been conventionally used, a saw-blaze shape with high light utilization efficiency is also examined as shown in FIG. 16 (b). ing.

[Problems to be Solved by the Invention]

However, in the above configuration, in FIG. 15 (b), the photodetectors 7a and 7c and 7b are provided for detecting the focus error.
7d are arranged side by side in the longitudinal direction, and the two light spots P ₁ ′ and P ₂ ′ are arranged so as to be considerably separated in the diffraction direction of the second diffraction element 3, so that the light detection portions 7a to 7a
7f is considerably long when viewed in the diffraction direction of the second diffraction element 3. Moreover, the photodetection units 7e and 7f for tracking error detection
The photodetector 7a for detecting focus error and recorded information
7 to 7d are separately provided, the number of photodetectors 7a to 7f is increased. As a result, there is a problem that the occupation area of the photodetectors 7a to 7f becomes large and the manufacturing cost also increases.

Further, when the blazed shape shown in FIG. 16 (b) is adopted as the cross-sectional shape of the gratings 3d, 3d ..., 3e, 3e ... in the second diffractive element 3, the two regions 3a, 3b of the second diffractive element 3 are Since the difference in the diffraction angles of the gratings is quite large, the gratings 3d and 3d ... and the gratings 3e and 3e
It is necessary to make the pitches of ... differ greatly. for that reason,
Since it is difficult to form the blazed shape having the same cross section in the regions 3a and 3b, not only the machining work of the lattices 3d, 3d ..., 3e, 3e ... becomes complicated, but also the lattice between the two regions 3a and 3b is formed. 3d / 3d
.., 3e, 3e .. .., 3e .. 3e. In order to reduce the difference in light utilization efficiency between the regions 3a and 3b, it is necessary to change the blaze shape in both the regions 3a and 3b to a shape different from the optimum shape, but in that case, it is sufficient. It is not possible to obtain high light utilization efficiency.

Furthermore, since the above-mentioned optical pickup device employs the so-called three-beam method, the first diffraction element 2 for splitting the emitted light of the semiconductor laser 1 into three beams is required, which causes an increase in the number of parts. Had.

[Means for Solving the Problems]

In order to solve the above-mentioned problems, an optical pickup device according to the present invention condenses a light generation unit and light emitted from the light generation unit onto an optical disc and guides reflected light from the optical disc to a diffraction element. An optical pickup device comprising: an optical system; a diffractive element that diffracts reflected light from an optical disc toward a photodetector; and a photodetector that receives diffracted light from the diffractive element and converts the diffracted light into an electric signal. The diffractive element is divided into four regions with a dividing line extending substantially in the track direction of the optical disc and a dividing line extending substantially in the radial direction of the optical disc as boundaries, and the focal position of the diffracted light in each of the two diagonal positions. Are set so that the distances up to are almost equal to each other, and the focus of the diffracted light in the two areas at one diagonal position is obtained when no focus error occurs. Position is located in front of the photodetector,
The focal position of the diffracted light in the other two diagonal positions is located farther from the photodetector, and the photodetector is set to be located approximately at an intermediate position between the two focal positions. Is provided with at least four photodetector sections including at least one photodetector section corresponding to each region of the diffraction element, and the sum of output signals of all photodetector sections of the photodetector is Based on the difference between the sum of the output signals of the recording information detecting means for detecting the information recorded on the optical disc based on the recording information detecting means and the two areas of the diagonal position of the diffraction element, the focus error is detected. And a difference between the sum of the output signals of the photodetector corresponding to each of the two regions of the diagonal position in the diffraction element and the sum of the output signals of all the photodetectors. It and a tracking error detecting means for detecting a tracking error by comparing is characterized in.

[Action]

According to the above configuration, when the optical system is focused, the diffracted light from the two regions at one diagonal position in the diffractive element forms a focus on the front side of the photodetector, and from the two regions at the other diagonal position. Since the diffracted light of (1) forms a focal point on the far side from the photodetector, it forms a light spot having a predetermined area on the photodetector when the optical system is in focus. Then, when a focus error occurs, the light spots due to the diffracted light from the two regions at one diagonal position expand or contract, and the light spots due to the diffracted light from the two region pairs at the other diagonal position contract or conversely. Since the amount of received light at each photodetector of the photodetector changes due to the enlargement, the focus error is detected based on that.

Further, when no tracking error occurs, the light-dark pattern of the reflected light from the optical disc generated on the diffraction element by the recording information such as the pits on the optical disc becomes symmetrical with the dividing line extending in the track direction of the optical disc as a boundary. , The sums of the output signals of the photodetector corresponding to the two diagonal positions are equal, and the difference between them is “0”.

On the other hand, when a tracking error occurs and the light spot on the optical disc deviates in either direction from the track center, the light-dark pattern on the diffractive element of the reflected light from the optical disc has a dividing line in the track direction of the optical disc as a boundary. It becomes asymmetrical. Therefore, the sums of the output signals of the photodetector corresponding to each of the two diagonal positions are different, and the difference has a positive or negative value. In that case, the light-dark pattern on the diffractive element is inverted depending on the direction in which the light spot on the optical disc deviates from the center of the track.
The polarity of the difference between the sums of the output signals of the photodetector corresponding to each of the two diagonal positions of the diffractive element is reversed depending on the direction in which the light spot on the optical disc deviates from the track center.

When a tracking error occurs, the bright-dark pattern on the diffraction grating changes as the light spot on the optical disc moves along with recorded information such as pits,
Along with that, the difference between the sums of the output signals of the photodetector corresponding to the respective two regions of the diagonal position of the diffraction element draws a sine wave. The phase of this sine wave changes according to the direction in which the light spot on the optical disc deviates from the center of the track. On the other hand, the sum of the output signals of all the photodetectors also draws a sine wave as the light spot on the optical disc moves along the recorded information such as pits. Does the phase of this sine wave cause a tracking error? It is almost constant regardless of whether or not. Therefore, the sine wave drawn by the difference between the sums of the output signals of the photodetector and the sine wave drawn by the sum of the output signals of all the photodetectors corresponding to the two diagonal regions of the diffraction element. Tracking error can be detected by comparing the phases.

Further, in the above configuration, each photodetector of the photodetector that receives the diffracted light from each photodetector of the diffraction element can be provided at a position relatively close to each other, and the focus error and the recorded information Since the detection of the tracking error and the detection of the tracking error are performed by the common photodetector, the number of photodetectors can be reduced, so that the area occupied by the photodetector and the manufacturing cost can be reduced.

Further, since the photodetectors of the photodetector are provided at relatively close positions, it is possible to sufficiently reduce the difference in diffraction angle between the regions of the diffraction element. Thereby, when the cross-sectional shape of the grating in each region of the diffraction grating is a blazed shape, the blazed shapes of the respective regions can be made substantially equal to each other, so that the grating can be easily manufactured and the grating can be easily manufactured in each region. Light utilization efficiency is high enough, and
The difference in utilization efficiency can be made sufficiently small.

Further, in the above configuration, the focus error and the tracking error are detected without splitting the outgoing light of the light generating means into the main beam and the sub beam, so that the outgoing light is split into the main beam and the sub beam. Since the diffraction element is unnecessary, the number of parts can be reduced.

[Embodiment 1] The following will describe one embodiment of the present invention with reference to FIGS. 1 to 8.

The optical pickup device 11 according to the present embodiment is used as a reproducing device for a reproduction-only optical disc such as a compact disc or a video disc. As shown in FIG. 2, the emitted light of the semiconductor laser 12 as the light generating means reaches the collimator lens 14 through the diffraction element 13, is collimated by the collimator lens 14, and then reaches the objective lens 15. . The collimator lens 14 and the objective lens 15 described above constitute an optical system.

The light flux that has passed through the objective lens 15 is focused on the pits on the optical disc 16 in order to read the recording information recorded as pits on the optical disc 16 in advance.

The light flux reflected from the optical disk 16 passes through the objective lens 15 and the collimator lens 14, and the first-order diffracted light 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 is an optical disc.
Dividing line 17h extending in the Y direction, which is the track direction of 16,
The four photodetection units 1 each having a rectangular shape by the dividing line 17g extending in the X direction which is the radial direction of the optical disc 16.
It is divided into 7a to 17d. The photodetectors 17a to 17d correspond to respective regions 13a to 13d of the diffraction element 13, which will be described later, and receive diffracted light from the respective regions 13a to 13d.

As shown in FIG. 3, the diffractive element 13 has four regions 13a to 13a by a dividing line 13i extending in the track direction of the optical disc 16 and a dividing line 13j extending in the radial direction of the optical disc 16.
It is divided into d.

The regions 13a to 13d of the diffractive element 13 have gratings 13e-1 for diffracting the reflected light from the optical disk 16 in the X direction.
3e ... ~ 13h and 13h are formed. Lattices 13e, 13e ..., 13g, 13g ... of two regions 13a, 13c at one diagonal line centered on the optical axis L ₁ connecting the semiconductor laser 12 and the optical disc 16
Is a direction in which the light flux reflected from the optical disk 16 and diffracted by the areas 13a and 13c is focused at the same point f ₁ in front of the photodetector 17 when the optical system without a focus error is focused. And the pitch is defined.

On the other hand, the gratings 13f, 13f ..., 13h, 13h ... in the two regions 13b, 13d at the other diagonal position with the optical axis L ₁ as the center.
Is reflected from the optical disc 16 at the time of focusing and the area 13
The direction and pitch are determined so that the light beam diffracted by b · 13d is focused at the same point f ₂ far from the photodetector 17. The focal points f ₁ and f ₂ are both the intersection of the optical axis L ₁ and the diffractive element 13 and the dividing lines 17g and 17h on the photodetector 17.
It is located on the optical axis L _{2 of the} diffracted light that connects the intersections of the _two , and
At the time of focusing, the photodetector 17 is set so as to be located at a substantially intermediate position between the focus positions f ₁ and f ₂ .

As mentioned above, the two areas 13a and 13c at one diagonal position
In order to make the distance to the focal point position f ₁ of the diffracted light from and the distance to the focal point position f ₂ of the diffracted light from the two areas 13b and 13d at the other diagonal position different, for example, in the areas 13a and 13c Is provided with a light converging function (convex lens function), and the area 13b
・ 13d has a light diverging function (concave lens function).

It should be noted that the lattices 13e, 13e, ..., 13h, 13h, ... Of the regions 13a to 13d ...
Can be created by a well-known two-beam interference method, or can be created by obtaining the shape of interference fringes by an electronic computer and drawing the interference fringes directly on the dry plate by an electron beam exposure device. In that case, the cross-sectional shape of the lattices 13e, 13e ... ~ 13h, 13h ... Is the rectangular shape shown in Fig. 16 (a), or Fig. 16 (b).
The blaze shape shown in FIG.

The detection of the recording information, the focus error signal and the 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 diffractive element 13 has a focal position f.
_By once converging at ₁ and reversing, a fan-shaped light spot P ₁ is formed at the photodetector 17a in the photodetector 17.
Further, the light beam reflected from the optical disc 16 and diffracted by the region 13c on the same diagonal line as the region 13a once converges at the same focal point position f _{1 as} described above and is inverted, whereby the photodetection unit of the photodetector 17 is detected. A fan-shaped light spot P ₃ is formed on 17c.

On the other hand, the area 13 of the diffraction element 13 is reflected by the optical disk 16.
The light beam diffracted by b does not converge on the front side of the photodetector 17 and forms a fan-shaped light spot P ₂ on the photodetection unit 17b. Further, the light beam reflected from the optical disc 16 and diffracted by the region 13d on the same diagonal line as the region 13b in the diffraction element 13 does not converge on the front side of the photodetector 17, and the photodetector section does not converge.
A fan-shaped light spot P ₄ is formed on 17d.

Then, in the focused state where the distance between the objective lens 15 and the optical disk 16 is proper, the photodetector 17 is located at an almost intermediate position between the _two focal positions f ₁ and f ₂ , so that FIG. As shown in, the light spots P _{1 to} P _{4 have} the same size. Therefore, the output signals Sa to Sd of the photodetectors 17a to 17d become equal.

On the other hand, when the optical disc 16 approaches the objective lens 15 too much and enters a focus error state, the focus position f ₁ approaches the photodetector 17, while the focus position f ₂ moves away from the photodetector 17, so As shown in FIG. 7A, the light spots P ₁ and P ₃ are reduced, and conversely, the light spots P ₂ and P ₄ are enlarged. In that case, the light amount of each of the light spots P _{1 to} P ₄ does not change depending on the size, but in reality, as shown in FIG.
7h has a predetermined width (for example, about 5 μm), and the fan-shaped chord portions of the respective light spots P _{1 to} P ₄ are located on the center line of the dividing lines 17g · 17h and the dividing lines 17g · 17h. Above it is desensitized or attenuated to the optical signal. In the state shown in FIGS. 1 (a) and 4, the light spots P ₁ and P ₃ are separated from the light spots P ₂ and P ₄ by the dividing line 17
Since the proportion (area ratio) protruding over g / 17h is large, the output signals Sa / Sc of the photodetectors 17a / 17c are
・ It becomes smaller than the output signal Sb ・ Sd of 17d.

On the other hand, when the optical disc 16 is too far from the objective lens 15 and a focus error occurs, the light spots P ₁ and P ₃ expand while the light spots P ₂ and P ₄ shrink, as shown in FIG. 1 (c). Therefore, the output signals Sa / Sc of the photodetectors 17a / 17c become larger than the output signals Sb / Sd of the photodetectors 17b / 17d.

Therefore, the focus error signal FES is the sum of the output signals Sa and Sc of the photodetectors 17a and 17c corresponding to the two regions 13a and 13c at one diagonal position of the diffraction element 13 and the other diagonal position of the diffraction element 13. Photodetector corresponding to the two areas 13b and 13d of
It is obtained by the difference between the output signals Sb and Sd of 17b and 17d and the sum (hereinafter referred to as the diagonal difference signal). That is, the focus error signal FES is obtained by the calculation of FES = (Sa + Sc) − (Sb + Sd) by the focus error detection means (not shown), and the objective lens 15 is moved by the focus servo system (not shown) so that this FES becomes “0”. Driven. on the other hand,
The recording information RF recorded as pits is an output signal of all the photodetection units 17a to 17d by a recording information detection unit (not shown).
As the sum of Sa to Sd (hereinafter referred to as the sum signal), RF = Sa + Sb
It is obtained by the calculation of + Sc + Sd.

As will be described later, the bright and dark pattern of the light flux E (see FIGS. 7A to 7C) of the reflected light from the optical disc 16 on the diffraction element 13 is a light spot D on the optical disc 16 (see FIG. 6). (See (a) to (c)) varies depending on the position on the pit C when passing over the pit C in the direction of the arrow A, and as a result, the values of the output signals Sa to Sd of the photodetection units 17a to 17d are also changed. Light spot D
Fluctuates as it moves on pit C. Therefore, in generating the focus error signal FES, the values of the output signals Sa to Sd of the photodetectors 17a to 17d may be, for example, average values during the passage of the light spot D through the pit C.

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

That is, as shown in FIG. 6 (b), a light spot D is formed at the center of the track where the pits C on the optical disk 16 are aligned.
When the light spot D is approaching the pit C,
In other words, the optical disc at the time when it started passing over the pit C
The bright and dark pattern of the light flux E on the diffraction element 13 of the reflected light from 16 is bright in the upper and lower parts in the figure as shown in FIG.
Darkens in the center. In this case, since the light-dark pattern of the light flux E is bilaterally symmetrical, the above-mentioned diagonal line difference signal is "0".

As shown in FIG. 6 (a), when the optical spot D on the optical disc 16 is displaced from the track center to the left side in the figure to cause a tracking error, the optical spot D is diffracted on the pit C on the diffractive element 13. As shown in FIG. 7 (a), the light-dark pattern of the light flux E in FIG.
Darkens in the center. At this time, the photodetector 17 on the photodetector 17
The amount of light received by a and 17c is relatively large, while the light detector
Since the light receiving amounts of 17b and 17d are relatively small, the diagonal line difference signal (Sa + Sc)-(Sb + Sd) has a positive value.

Further, the light-dark pattern of the light beam E on the diffraction element 13 at the time when the light spot D has finished passing through the pit C in the state where the light spot D is displaced from the center of the track to the left is FIG. 7 (c).
As shown in the figure, the upper right part and lower left part in the figure are bright, and the central part is dark. At this time, the amount of light received by the photodetectors 17a and 17c is relatively small, and the amount of light received by the photodetectors 17b and 17d is relatively large. Therefore, the diagonal difference signal (Sa + Sc)-(Sb + Sd) is negative. Becomes the value of.

Therefore, when the light spot D on the optical disc 16 is displaced to the left with respect to the pit C, the diagonal line difference signal (Sa + S
c)-(Sb + Sd) draws a substantially sinusoidal curve as shown in (b) of FIG. 8 as the light spot D on the optical disc 16 moves on the pit C in the direction of arrow A.

On the other hand, as shown in FIG. 6C, when the optical spot D shifts from the track center to the right side in the figure on the optical disc 16 and a tracking error occurs, the diffraction element at the time when the optical spot D approaches the pit C. The light-dark pattern of the light flux E on 13 is as shown in FIG. 7 (c). At this time, the light detection unit 17a
・ The light receiving amount of 17c becomes relatively small,
Since the amount of received light of d becomes relatively large, the above diagonal difference signal has a negative value.

Further, the light-dark pattern of the light beam E on the diffraction element 13 at the time when the light spot D has finished passing through the pit C in the state where the light spot D is deviated from the track center to the right is shown in FIG. 7 (a).
It becomes like. At this time, the amount of light received by the photodetectors 17a and 17c is relatively large and the amount of light received by the photodetectors 17b and 17d is relatively small, so that the above-mentioned diagonal line difference signal has a positive value.

Therefore, when the light spot D on the optical disc 16 is shifted to the right with respect to the pit C, the above-mentioned diagonal line difference signal (Sa + S
c)-(Sb + Sd) draws a substantially sinusoidal curve as shown in (c) of FIG. 8 as the light spot D moves on the pit C in the direction of arrow A. However, the phase of the sine wave in this case is different from that in the case where the light spot D is shifted to the left side with respect to the pit C by 180 °.

On the other hand, the sum signal Sa + Sb + Sc + Sd draws a sinusoidal curve as shown in FIG. 8A as the light 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. Then, the sine wave ((b) in FIG. 8) drawn by the diagonal line difference signal when the light spot D is displaced to the left on the optical disc 16 becomes a sine wave ((a) in FIG. 8) of the sum signal. On the other hand, the sine wave ((c) in FIG. 8) drawn by the diagonal line difference signal when the light spot D on the optical disc 16 is shifted to the right is the sine wave of the sum signal. On the other hand, the phase is advanced by 90 °.

Therefore, by comparing the phases of the diagonal line difference signal and the sum signal with a tracking error detecting means (not shown), it is possible to detect which side the light spot D is deviated from.
The above phase comparison can be performed by, for example, a heterodyne detection circuit. On the other hand, when no tracking error occurs, the diagonal line difference signal becomes "0" as described above. The bright and dark pattern in FIG. 7 is for the case where the depth of the pit C is 1/4 of the wavelength of the laser light used.

Here, due to the fluctuation of the wavelength of the laser light emitted from the semiconductor laser 11, the wavelength of the laser light is greater than the reference wavelength set so that the light beam diffracted by the diffraction element 13 converges at the points f ₁ and f _2. When the length becomes shorter, the diffracted light from the regions 13a and 13c converges at a position closer to the photodetector 17 than the point f ₁ , and the region 13b
Since the diffracted light from 13d converges at a position closer to the photodetector 17 than the point f ₂ , each of the light spots P _{1 to} P ₄ on the photodetector 17
Both are smaller than at the reference wavelength. for that reason,
The fluctuation of the wavelength of the semiconductor laser 11 does not affect the focus error signal FES. Similarly, when the wavelength of the laser light becomes longer than the reference wavelength, each light spot P ₁ ~
Since both P _{4 and} P ₄ are larger than those at the reference wavelength, no error occurs in the focus error signal FES.

Further, when the laser light fluctuates in frequency, as shown in FIGS. 5A and 5B, the light spots P _{1 to} P ₄ are in the X direction on the photodetector 17, that is, in the diffraction element 13. Move in the diffraction direction. However, in this case, 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 optical detection Since the increase / decrease amount of the output signal Sd of the portion 17d cancels each other out, no error occurs in the focus error signal FES as a whole.

In this embodiment, each photodetector 17a to 17d of the photodetector 17 is
Are formed close to each other, and focus error detection and tracking error detection are performed by the common photodetection units 17a to 17d to reduce the number of photodetection units 17a to 17d. It becomes possible to reduce the area occupied by the detection units 17a to 17d and to reduce the manufacturing cost.

Further, since the photodetection units 17a to 17d are close to each other, the diffraction angles in the respective regions 13a to 13d of the diffraction element 13 become substantially equal to each other, so that the cross-sectional shapes of the gratings 13e, 13e, ..., 13h, 13h ,. When the blazed shape shown in FIG.
Since the pitches of e ・ 13e ... to 13h ・ 13h ... can be made almost equal, processing of the diffractive element 13 can be performed smoothly, and there is no difference in the light use efficiency, and it is possible to obtain a sufficiently high use efficiency. It can be formed into a fine blaze shape.

Since the diffracted light from the diffractive element 13 has a pseudo astigmatism property, a known astigmatism method may be used as the focus control method.

Second Embodiment Next, a second embodiment will be described based on FIGS. 9 and 10.

As shown in FIG. 9, in the second embodiment, as in the first embodiment, the photodetector 17 has four photodetection sections 17a by dividing lines 17h and 17g extending in the track direction and the radial direction of the optical disk 16, respectively. It is divided into ~ 17d. However, each light detector
The widths of 17a to 17d in the X direction are expanded as compared with the first embodiment. The diffractive element 13 is configured such that the light spots P ₁ and P ₂ and the light spots P ₃ and P ₄ are separated by a distance in the X direction at the photodetectors 17a to 17d.

That is, as in the first embodiment, the diffractive element 13 is divided into four regions 13a to 13d by the dividing lines 13i and 13j extending in the track direction and the radial direction of the optical disc 16, as shown in FIG. As shown in FIG. 10, the area of the diffraction element 13
The light beam diffracted by 13a is the light detection unit 1 in the photodetector 17.
After focusing at the focus position f _1b on the front side of 7a and 17b, it is inverted to form the light spot P ₁ on the light detection unit 17a.
The lattices 13e, 13e ... of the region 13a are designed.

Further, the light beam diffracted by the region 13c of the diffractive element 13 is focused on the front focus position f _1a of the photodetector sections 17c and 17d of the photodetector 17 and then inverted to be on the photodetector section 17c. It is adapted to form a light spot P ₃ .

Further, the region 13b of the diffractive element 13 is formed so that the focal position of the light beam diffracted in this region 13b is the point f _2b behind the photodetection units 17a and 17b of the photodetector 17, and thereby the region 13b
The diffracted light from is not inverted and forms a light spot P ₂ on the photodetector 17b. Also, the diffractive element 13
The regions 13d, are formed as the focal position of the diffracted light from the region 13d becomes f _2a point on the rear side of the light detecting section 17c · 17d of the photodetector 17, the diffracted light from the region 13d is inverted Instead, the light spot P ₄ is formed on the photodetector 17d of the photodetector 17.

In the second embodiment, the focus error signal FES is obtained by the diagonal line difference signal (Sa + Sc)-(Sb + Sd) with the output signals of the photodetectors 17a-17d being Sa-Sd, as in the first embodiment.

The tracking error signal RES is also the same as in the first embodiment.
It is obtained by comparing the phase of the diagonal difference signal and the phase of the sum signal Sa + Sb + Sc + Sd, and the reproduction signal RF of the recorded information recorded as pits is obtained by the sum signal.

Further, in the second embodiment, the light spots P ₁ and P ₂ and the light spots P ₃ and P ₄ are separated at intervals in the X direction. Therefore, the light spots P ₁ and P ₄ are separated by the frequency variation of the laser light from the semiconductor laser 11. _{Even if 1 to} P ₄ move in the X direction as indicated by imaginary lines, the respective light spots P _{1 to} P ₄ will be focused in the corresponding photodetection sections 17a to 17d. In the second embodiment, the area of the diffraction element 13 is
The diffraction angles in 13a and 13b are slightly different from the diffraction angles in the regions 13c and 13d, but the difference in diffraction angle is considerably smaller than that of the conventional one.

Third Embodiment Next, a third embodiment will be described based on FIG.

In the third embodiment, the photodetector 20 is moved in the Y direction by a dividing line 20i extending in the X direction, which is the radial direction of the optical disc 16.
Eight photodetection sections 20a to 20h are provided by being divided into four in the X direction by three dividing lines 20j to 20l extending in the Y direction which is the track direction of the optical disc 16.

On the other hand, as in the first embodiment, the diffractive element 13 is divided into four as shown in FIG. 3, and the diffracted light diffracted in the region 13a is once focused at the focal position f ₁ (FIG. 2). The light spot P ₁ is formed on the photodetectors 20h and 20g on the photodetector 20 by being inverted.

The diffracted light diffracted by the region 13c of the diffractive element 13 is once focused at the focal position f ₁ and then inverted to form a light spot P ₃ on the photodetection units 20a and 20b on the photodetector 20. To form.

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 f ₂ . Therefore, the diffracted light diffracted in the region 13b is not inverted, and the photodetector 20c
The light spot P ₂ is formed on 0d, and the diffracted light diffracted by the photodetection unit 20d is not inverted, and the light spot P ₄ is formed on the photodetection units 20e and 20f.

Now, assuming that the output signals of the photodetectors 20a to 20h are Sa to Sh, respectively, the focus error signal FES is generated inside the two photodetectors corresponding to the respective regions 13a to 13d of the diffraction element 13. FES = (Sc + Sf) − (Sb by the diagonal line difference signal by the output signal of the located photodetector 20b / 20c / 20f / 20g
+ Sg), and the pit signal RF is calculated by the sum signal RF = Sa + Sb + Sc + Sd + Se + Sf + Sg + Sh.

Next, the tracking error signal RES is transmitted to the diffraction element 13
Of the diagonal line difference signal (Sc + Sf)-(Sb + Sg) due to the output signals of the photo-detecting sections 20b, 20c, 20f, 20g located inside the two photo-detecting sections corresponding to the respective regions 13a to 13d of And the phase of the sum signal are compared. Even in this case, no error occurs in the focus error signal RES even if the light spots P _{1 to} P ₄ move in the X direction due to the frequency variation of the laser light.

Fourth Embodiment Next, a fourth embodiment will be described based on FIG.

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

On the other hand, the diffractive element 13 has the four-division structure of FIG. 3 as in the first embodiment, and the diffracted light from the region 13a is inverted as in the third embodiment to form a light spot on the photodetection portions 21g and 21h. Form P ₁ ,
The diffracted light from the region 13c is inverted to form the light spot P ₃ on the photodetection portions 21a and 21b.

Further, the diffracted light from the region 13b of the diffractive element 13 does not invert, the light spot P ₂ is formed on the photodetection portions 21c and 21d of the photodetector 21, and the diffracted light from the region 13d does not invert, A light spot P ₄ is formed on the light detection portions 21e and 21f.

Assuming that the output signals of the respective photodetectors 21a to 21h are Sa to Sh, the focus error signal FES is the respective regions 13a to 13d of the diffraction element 13.
Of each of the two photodetector sections of the photodetector 21 corresponding to, as a diagonal difference signal of the photodetector sections 21b, 21c, 21f, and 21g located inside, by the calculation of FES = (Sc + Sf)-(Sb + Sg) Desired.

When the optical system is in focus, Sa + Sd + Se + Sh = Sb + Sc + Sf +
If the diameters of the light spots P _{1 to} P ₄ on the photodetector 21 are adjusted so as to be Sg, FES = (Sd−Sc) + (Se−Sf) + (Sg
-Sh) + (Sb-Sa) = (Sd + Se + Sg + Sb)-(Sc + Sf +
The focus error signal FES can also be obtained by calculating (Sh + Sa). Also in this case, even if the light spots P _{1 to} P ₄ move in the X direction due to the frequency variation of the laser light, no error occurs in the focus error signal FES.

On the other hand, the reproduction signal of the recorded information recorded as pits is RF
Is a sum signal, RF = Sa + Sb + Sc + Sd + Se + Sf + Sg + Sh
Is calculated by.

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

[Fifth Embodiment] Next, a fifth embodiment will be described with reference to FIG.

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

On the other hand, the diffraction element 13 is divided into four regions 13a to 13d as shown in FIG. Then, the diffracted light in the region 13a is temporarily focused at the focus position on the front side of the photodetection units 22a to 22c of the photodetector 22, and after being inverted, a light spot P ₁ is formed on the photodetection units 22b and 22c. The lattices 13e, 13e ... Of the region 13a are designed to be formed. Further, the diffracted light in the region 13c of the diffractive element 13 is once focused at the same focal position as described above, and is inverted to form a light spot P ₃ on the photodetection portions 22a and 22b of the photodetector 22. Has become.

On the other hand, the focal position of the diffracted light diffracted by the regions 13b and 13d of the diffractive element 13 is set to the far side from the photodetection units 22d to 22f of the photodetector 22, and therefore the diffracted light in the regions 13b and 13d is inverted. Light spots P ₂ and P ₄ on the photodetectors 22d to 22f without
Are formed.

In this embodiment, the output signals of the photodetectors 22a to 22f are Sa to Sf, and the focus error signal FES is FES.
= Sb−Se or FES = (Sb + Sd + Sf) − (Sa + Sc + Se). On the other hand, the reproduction signal RF of the recorded information recorded as pits is RF = Sa + Sb + Sc + Sd as the sum signal.
Calculated by + Se + Sf.

Next, the tracking error signal RES is, for example, a diagonal line difference signal (Sa + Sc) − of the output signals of the photodetection units 22a, 22c, 22d, and 22f, which are the photodetection units corresponding to the respective regions 13a to 13d of the diffraction element 13. It is obtained by comparing the phase of (Sd + Sf) with the phase of the sum signal.

In the present embodiment, since the light spots P ₁ and P ₃ and the light spots P ₂ and P ₄ are separated at intervals in the X direction, the light spots P _{1 to} P ₄ move in the X direction due to the frequency fluctuation of the laser light. Even if you move
The light spots P ₁ and P ₃ are received by the photodetectors 22a to 22c, and the light spots P ₂ and P ₄ are received by the photodetectors 22d to 22f.

When embodying the present invention, the division of the diffraction element 13 and the photodetectors 17, 20, 21, and 22 may be performed by a method other than those exemplified in the above embodiments.

Further, in each of the above embodiments, the optical pickup device for the read-only type optical disc has been described, but the present invention is also applicable to a so-called write-once type optical disc optical pickup device.

〔The invention's effect〕

As described above, the optical pickup device according to the present invention includes a light generating unit, an optical system that collects the light emitted from the light generating unit on the optical disc, and guides the reflected light from the optical disc to the diffraction element. In an optical pickup device including a diffractive element that diffracts the reflected light from the optical disc toward the photodetector side and a photodetector that receives the diffracted light from the diffractive element and converts the diffracted light into an electrical signal, the diffractive device is almost the same. The optical disc is divided into four regions with a dividing line extending in the track direction of the optical disc and a dividing line extending substantially 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 determined. The focus positions of the diffracted light in two areas of one diagonal position are detected when the focus error is not generated while the settings are made so that they match each other. It is set so that the focal position of the diffracted light in the two areas of the other diagonal position is located farther than the photodetector, and the photodetector is located at an intermediate position between both focal positions. The photodetector is provided with at least four photodetector sections including at least one photodetector section corresponding to each region of the diffraction element, and all photodetectors of the photodetector are provided. Information detection means for detecting the information recorded on the optical disc based on the sum of the output signals of the optical disc, and the sum of the output signals of the photodetector corresponding to each of the two diagonal positions of the diffraction element. Focus error detecting means for detecting a focus error based on the difference between the two, and the difference between the sums of the output signals of the photodetecting sections respectively corresponding to the two regions of the diagonal position in the diffraction element, and all the photodetecting sections. A configuration in which a tracking error detecting means for detecting a tracking error by comparing the phases of the sum of the output signal.

As a result, when the optical system is focused, the diffracted light from the two regions at one diagonal position in the diffraction element forms a focus on the front side of the photodetector, and the diffracted light from the two regions at the other diagonal position is Since the focal point is formed on the side farther from the photodetector, a light spot having a predetermined area is formed on the photodetector when the optical system is focused. Then, when a focus error occurs, the light spots due to the diffracted light from the two regions at one diagonal position expand or contract, and the light spots due to the diffracted light from the two region pairs at the other diagonal position contract or conversely. Since the amount of light received at each photodetector of the photodetector changes due to enlargement,
The focus error is detected based on this.

Further, when no tracking error occurs, the light-dark pattern of the reflected light from the optical disc generated on the diffraction element by the recording information such as the pits on the optical disc becomes symmetrical with the dividing line extending in the track direction of the optical disc as a boundary. , The sums of the output signals of the photodetector corresponding to the two diagonal positions are equal, and the difference between them is “0”.

On the other hand, when a tracking error occurs and the light spot on the optical disc deviates in either direction from the track center, the light-dark pattern on the diffractive element of the reflected light from the optical disc has a dividing line in the track direction of the optical disc as a boundary. It becomes asymmetrical. Therefore, the sums of the output signals of the photodetector corresponding to each of the two diagonal positions are different, and the difference has a positive or negative value. In that case, the light-dark pattern on the diffractive element is inverted depending on the direction in which the light spot on the optical disc deviates from the center of the track.
The polarity of the difference between the sums of the output signals of the photodetector corresponding to each of the two diagonal positions of the diffractive element is reversed depending on the direction in which the light spot on the optical disc deviates from the track center.

When a tracking error occurs, the bright-dark pattern on the diffraction grating changes as the light spot on the optical disc moves along with recorded information such as pits,
Along with that, the difference between the sums of the output signals of the photodetector corresponding to the respective two regions of the diagonal position of the diffraction element draws a sine wave. The phase of this sine wave changes according to the direction in which the light spot on the optical disc deviates from the center of the track. On the other hand, the sum of the output signals of all the photodetectors also draws a sine wave as the light spot on the optical disc moves along with the recorded information such as pits. Is the phase of this sine wave a tracking error? It is almost constant regardless of whether or not. Therefore, the sine wave drawn by the difference between the sums of the output signals of the photodetector and the sine wave drawn by the sum of the output signals of all the photodetectors corresponding to the two diagonal regions of the diffraction element. Tracking error can be detected by comparing the phases.

Further, in the above configuration, each photodetector of the photodetector that receives the diffracted light from each photodetector of the diffraction element can be provided at a position relatively close to each other, and the focus error and the recorded information Since the detection of the tracking error and the detection of the tracking error are performed by the common photodetector, the number of photodetectors can be reduced, so that the area occupied by the photodetector and the manufacturing cost can be reduced.

Further, since the photodetectors of the photodetector are provided at relatively close positions, it is possible to sufficiently reduce the difference in diffraction angle between the regions of the diffraction element. Thereby, when the cross-sectional shape of the grating in each region of the diffraction grating is a blazed shape, the blazed shapes of the respective regions can be made substantially equal to each other, so that the grating can be easily manufactured and the grating can be easily manufactured in each region. Light utilization efficiency is high enough, and
The difference in utilization efficiency can be made sufficiently small.

Further, in the above configuration, the focus error and the tracking error are detected without splitting the outgoing light of the light generating means into the main beam and the sub beam, so that the outgoing light is split into the main beam and the sub beam. Since the diffraction element is unnecessary, the number of parts can be reduced.

[Brief description of drawings]

1 to 8 show an embodiment of the present invention. FIGS. 1 (a) to 1 (c) are schematic explanatory views 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 view showing an enlarged main part of FIG. 1 (a). FIGS. 5 (a) and 5 (b) are schematic explanatory views showing a case where a frequency variation occurs in the laser light of the semiconductor laser. FIGS. 6A to 6C are explanatory views showing the positional relationship between the optical pot and the pit on the optical disk. FIGS. 7A to 7C are explanatory views showing the light-dark pattern of the light spot on the diffraction element. FIG. 8 is a graph showing the transition of the reproduction signal and the like when the light spot moves on the pit. 9 and 10 show the second embodiment. FIG. 9 is a schematic explanatory view showing a photodetector. FIG. 10 is a partial front view of the optical pickup device. 11 to 13 are schematic explanatory views showing photodetectors in the third to fifth embodiments, respectively. 14 to 16 show a conventional example. 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 view of the photodetector. 16 (a) and 16 (b) are partial vertical cross-sectional views showing the cross-sectional shape of the grating of the second diffraction element. 12 is a semiconductor laser (light generating means), 13 is a diffraction element, 13a
〜13d is a region, 13i ・ 13j is a dividing line, 14 is a collimating lens (optical system), 15 is an objective lens (optical system), 16 is an optical disk, 17 ・ 20 ・ 21 ・ 22 is a photodetector, 17a〜17d ・20a-20h
-21a to 21h and 22a to 22f are photodetection units.

Claims (1)

[Claims] 1. A light generating means, an optical system for condensing light emitted from the light generating means on an optical disk and guiding reflected light from the optical disk to a diffractive element, and a light detector for detecting reflected light from the optical disk. In an optical pickup device including a diffractive element for diffracting light to the side and a photodetector for receiving diffracted light from the diffractive element and converting the diffracted light into an electric signal, the diffractive element includes a dividing line extending substantially in the track direction of the optical disc. , Is divided into four regions with a dividing line extending substantially in the radial direction of the optical disc as a boundary, and the distances to the focal point positions of the diffracted light in the two diagonal regions are set to be substantially the same. Also, when there is no focus error, one of the two diagonal positions is
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 farther than the photodetector. The photodetector is set to be located at an intermediate position, and the photodetector is provided with at least four photodetection units including at least one photodetection unit corresponding to each region of the diffraction element. And recording information detecting means for detecting information recorded on the optical disc based on the sum of the output signals of all the photo-detecting sections of the photo-detector, and two areas of diagonal positions in the diffraction element. The focus error detecting means for detecting a focus error based on the difference between the sums of the output signals of the photodetecting sections respectively corresponding to, and the photodetecting sections respectively corresponding to the two diagonal positions of the diffraction element. An optical pickup device, comprising: a tracking error detecting means for detecting a tracking error by comparing the position of the difference between the sums of the output signals and the position of the sum of the output signals of all the photo detectors.