JP3438688B2 - Optical disc pre-pit signal detection method and optical disc apparatus - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a land (LAN).
D: Convex) and groove (groove: concave) Optical disc device for recording / reproducing an optical disc having prepits shifted in the radial direction (radial direction of optical disc) with respect to the optical disc, particularly defocusing in optical head and optical disc The present invention relates to a pre-pit signal detection method and an optical disc device capable of stably obtaining a pre-pit signal even with respect to the inclination of the.

[0002]

2. Description of the Related Art With the advent of DVDs, expectations for optical discs are increasing in the field of multimedia. DV
Following a read-only optical disc such as a D-ROM, a DVD
-A large-capacity rewritable 2.6 GB / single-sided optical disk such as RAM has appeared on the market. Such an optical disc has a pre-pit area including address information indicating a recording position in addition to the recording area. The position is Nikkei Electronics (No. 700), 31
As described on page 5, it is displaced from the land and groove of the optical disc by 1/2 track pitch in the radial direction. For example, FIG. 18 shows an area in which pre-pits are arranged in the optical disk. This arrangement is CAPA (Comp
lementary Allocated Pit Address), which has four A addresses 202, B addresses 203, and C addresses 20.
4. The D address 205 is displaced by 1/2 track pitch in the radial direction with respect to the land and groove, and uneven pits indicating the address are formed in the area of each address. With this arrangement, the address information can be shared by the land and the groove, and the prepit area can be reduced as compared with the optical disc in which the address pit is formed in each of the land and the groove.

A method for detecting the above-mentioned CAPA pre-pit signal has been proposed, and the method is shown below. FIG. 19 is a configuration diagram of a conventional optical head that detects a prepit. First, the overall configuration will be described. The linearly polarized light beam emitted from the semiconductor laser 1 becomes a parallel light beam by the collimator lens 2, and the polarization beam splitter 3
Incident on. The polarization beam splitter 3 is designed to transmit P-polarized light (polarized light parallel to the paper surface) and reflect S-polarized light (polarized light perpendicular to the paper surface). It is adjusted so that the light beam passes through the polarization beam splitter 3. The light beam that has passed through the polarization beam splitter 3 has its direction bent 90 degrees by the rising mirror 4, becomes circularly polarized light by the quarter-wave plate 5, and is condensed on the recording surface of the optical disk 7 by the objective lens 6. The light beam reflected by the optical disk 7 becomes a parallel light beam by the objective lens 6, and becomes a linearly polarized light by the quarter wavelength plate 5. The polarization direction is rotated 90 degrees with respect to the outgoing light flux, and becomes S-polarized light which is perpendicular to the paper surface. After that, the reflected light from the optical disc
The rising mirror 4 bends its optical path by 90 degrees, reflects it by the polarization beam splitter 3, and makes it enter the re-focusing lens 8. Then, the light beam is split by the beam splitter 9 into two light beams while being focused by the refocusing lens 8.

The light beam transmitted through the beam splitter 9 passes through the cylindrical lens 10 and then enters the focus error signal photodetector 213 to generate a focus error signal by the astigmatism method. Based on this signal, focus control is performed by an objective lens control mechanism (not shown). On the other hand, the light beam reflected by the beam splitter 9 enters the reproduction signal / track error signal photodetector 215.

FIG. 20 is a view of the reproduction signal / track error signal photodetector 215 seen from the beam splitter 9 side. As shown in the figure, the reproduction signal / track error signal photodetector 215 is composed of a first photodetection element 216 and a second photodetection element 217 which are divided into two by a central dividing line 215a. The optical disk reflected light 219 reflected by the beam splitter 9 is incident on the center of the photodetector 215. The outputs from the first photo-detecting element 216 and the second photo-detecting element 217 are amplified by a first amplifier circuit 220 and a second amplifier circuit 221, respectively, and the signals thereof are I220 and I22.
Set to 1. The subtraction amplifier circuit 222 subtracts these signals to generate the track error signal 32. That is, the track error detection method is the push-pull method. From this signal,
Track control is performed by an objective lens control mechanism (not shown). The reproduced signal 33 is the amplified signals I220 and I22.
1 is added by the addition amplification circuit 223 to obtain.

There are mainly two methods for detecting the pre-pit signal in the above optical head, one of which is the amplified signal I220 in which the amplified signal is added like the reproduced signal 33.
+ I221 is the method to obtain. Here, the added amplified signal I220 + I221 is used as the pre-pit signal 34, and the detection method is called sum signal detection. In this detection method, the pre-pit signal 34 obtained when the focused spot 199 scans the groove as shown in FIG.
It becomes like (a). The other pre-pit signal detection method is a method of individually detecting the amplified signals I220 and I221. Pre-pit signal 3 with amplified signal I220
5 and the amplified signal I221 is the pre-pit signal 36, the pre-pit signal 35 and the pre-pit signal 36 obtained when the focused spot 199 scans the groove 201.
Is as shown in FIG. This method is based on ISOM
'98, listed in TECHNICAL DIGEST, 170, Single Hea
It is called der Detection Method (hereinafter referred to as single channel signal detection). In this case, A address 20
2, the B address 203 is detected from the pre-pit signal 36, and the C address 204 and the D address 205 are detected from the pre-pit signal 35.

[0007]

DISCLOSURE OF THE INVENTION In the above-described conventional pre-pit signal detection system, that is, the pre-pit detection system by the sum signal detection system and the one-channel signal detection system, the pre-pit signal is disturbed. One of the causes is that there is a leak from the prepit adjacent to the scanning prepit. That is, in FIG. 18, the focused spot 199 is the A address 202 and the B address 2
When scanning 03, at the same time, E address 206,
The F address 207 is partially scanned. As a result, the read signals of the E address 206 and the F address 207 are included in the prepit signal. In particular, the increase in the focused spot diameter due to defocus is caused by the E address 206 and the F address 207.
Will increase the signal leaking in. Another factor that disturbs the pre-pit signal is a decrease in the resolution of the pre-pit signal due to an increase in the focused spot diameter.

FIG. 22 shows a leak signal component and a pre-pit signal 3 from an adjacent pre-pit for defocus when the pre-pit signal is detected by the sum signal detection method.
It is the result of having calculated the change of the resolution of 4 by the scalar analysis. This result is for the case where there is no astigmatic difference in the focused spot of the optical head, and the conditions shown in Table 2 are used in the calculation. In the same figure, the leakage signal component of the adjacent pre-pits is indicated by "adjacent long pit signal amplitude / scanning length pit signal amplitude (dB)" and the resolution is indicated by "short pit signal amplitude / long pit signal amplitude (dB)". There is. Defocus 0 μm is the focus position where the peak intensity of the focused spot is maximum. As shown in the figure, in the optical head with an astigmatic difference of 0 μm, the resolution decreases as the absolute value of defocus increases, and the leak signal component increases, causing disturbance in the prepit signal during defocus. There is.

In an actual optical head, the converging spot of the optical head has an astigmatic difference due to the astigmatic difference of the semiconductor laser, the astigmatism of the lens and the like, and the deviation of the optical element when the head is manufactured. Due to the magnitude of this astigmatic difference, the defocus characteristics of the two prepit signal quality deterioration factors are different from those in FIG. Astigmatic difference +0.5
FIG. 23 shows the calculated results at μm and −0.5 μm.
Shown in (a) and (b). As shown in the figure, when the absolute value of the astigmatic difference increases, the focus position where the resolution becomes maximum and the focus position where the leak signal of the adjacent pre-pit becomes minimum move in opposite defocus directions. Then, the resolution and the leak signal are deteriorated around the respective best focus positions. As a result, the disturbance of the pre-pit signal at the time of defocusing is further increased.

Further, FIG. 24 is a scalar analysis of the change in the resolution of the leakage signal component from the adjacent pre-pits and the pre-pit signal 35 or the pre-pit signal 36 with respect to the defocus when the pre-pit signal detection is performed by the one-channel detection. This is the result of calculation. Note that this result is for the case where there is no astigmatic difference in the focused spot of the optical head, as in FIG. 22, and the same conditions as shown in Table 2 are used in the calculation. As shown in FIG. 24, unlike the sum signal detection, the focus positions at which the resolution is maximum and the leak signal components of the adjacent pre-pits are minimum are different, and neither is in agreement with defocus 0 μm. With the deviation from each best focus position, the resolution deteriorates and the leak signal component increases.

Next, the astigmatic difference +0.5 μm, −0.5 μm
The calculated results for m are shown in FIGS. As shown in the figure, when the astigmatic difference increases toward the "+" side, the focus position with the maximum resolution moves in the "-" side, and the focus position with the minimum adjacent pre-pit leak signal moves in the "+" side defocus direction. On the other hand, the astigmatic difference is "-".
As the focus position increases toward the side, the focus position with the maximum resolution moves toward the "+" side, and the focus position with the minimum adjacent pre-pit leakage signal moves toward the "-" side. Then, from the astigmatic difference of 0 μm for one-channel detection, the increase of the leak signal with respect to defocus is steep.

On the assumption of the leak signal characteristics due to defocus and the resolution as described above, in consideration of the actual manufacturing process of the optical head, it is necessary to manufacture the optical head with the standard having the astigmatic difference. However, for this reason, the above-described deterioration of the prepit signal at the time of defocusing always occurs, which not only narrows the defocus margin of the prepit signal, but also causes variations in prepit signal characteristics among the optical heads. Also, when the optical disc is tilted with respect to a plane perpendicular to the optical axis, the prepit signal is disturbed for the same reason. As a result, the efficiency of reading the address information in the pre-pits is reduced. Incidentally, JP-A-11-273083 and JP-A-11-273084.
In the publication, in order to obtain a pre-pit signal, a beam spot is formed at a position displaced from the center line of the pit row of the pre-pit by a predetermined distance in the disc radial direction, and
A technique for detecting the pre-pit signal by detecting the reflected light from the optical disc with a dividing line that is parallel to the track tangential direction and shifted in the radial direction is described, but in this technique, control for shifting the beam spot is described. Is required, and the control becomes complicated, and it is doubtful whether or not it effectively acts on the defocus and the tilt of the optical disc.

An object of the present invention is to stably and satisfactorily deal with defocus in an optical head and inclination of an optical disc when scanning an optical disc having prepits that are shifted in the radial direction with respect to a land and a groove. It is an object of the present invention to provide a pre-pit signal detection method and an optical disc device that can obtain various pre-pit signals.

[0014]

In the optical disk pre-pit detection method of the present invention, a light beam emitted from a light source is projected onto a land or groove of the optical disk, and the reflected light beam is received, and an error signal is output from the light reception output. In an optical disc device that detects pre-pit signals and reproduced signals, split the reflected light flux of the optical disc at a position that is offset from the center line in the radial direction, and receive the split one-side light flux.
Wherein the obtaining et before Symbol pre-pit signal.

As an optical disk device for realizing such pre-pit detection of the present invention, an output optical system that guides a light beam emitted from a light source to a land or a groove of the optical disk, and a reflected light beam of the optical disk is received, and a light reception output thereof is received. From the error signal, the pre-pit signal, and the reproduction signal, and the light receiving optical system divides the reflected light flux of the optical disc in the radial direction at a position displaced from the center line in the radial direction, and divides it. characterized in that with the one side of the light detection system to obtain an output or found before Symbol prepit signal received light flux.

As a form of the optical disc apparatus of the present invention, firstly, the optical disc reflected light beam is divided into two at a position deviated from the center line in the radial direction, and the pre-pit signal is detected from the light beam having a large amount of optical disc reflected light among the two divided light beams. It is characterized by doing. Secondly, the optical disc reflected light beam is divided into three in the radial direction, and the two division lines are arranged at positions evenly displaced in the radial direction about the radial direction center line of the optical disc reflected light beam. It is characterized in that the pre-pit signal is detected from the sum of the central light beam and either one of the outer light beams. Thirdly, the optical disc reflected light flux is divided into four in the radial direction, and among the three division lines, the central division line coincides with the radial direction center line of the optical disc reflected light flux, and the radial direction is uniform about the division line. It is characterized in that the remaining two dividing lines are arranged at positions displaced from each other, and the pre-pit signal is detected from the sum of the two central light beams and either one of the outer light beams.

With regard to the first embodiment, the optical flux reflected from the optical disk is split into two light fluxes, and two split light detection is performed so that a split line is located at a position displaced from the radial center line in the radial direction for each light flux. Place the vessels, each 2
It is also a feature that the pre-pit signal is detected from the photo-detecting element that receives a large amount of the reflected light flux from the optical disc among the split photo-detectors. Further, the hologram optical element is arranged such that the division line comes to a position displaced in the radial direction from the radial center line with respect to the optical disc reflected light beam divided into the two light beams, and the hologram optical elements are divided by the respective hologram optical elements. 2
It is also a feature that the pre-pit signal is detected from the output of the photo-detecting element that receives a light beam having a large amount of reflected light from the optical disc, out of the two light beams.

Regarding the second embodiment, in the photodetector which divides the optical disc reflected light beam into three in the radial direction, the division line is located at a position which is evenly displaced in the radial direction around the radial center line of the optical disc reflected light beam. Another feature is that the pre-pit signals are arranged and the pre-pit signal is detected from the sum of the central photo-detecting element and either one of the photo-detecting elements on the outer side. Further, in a hologram optical element that divides an optical disk reflected light beam into three in the radial direction, two division lines are arranged at positions that are evenly displaced in the radial direction from the radial direction center line of the optical disk reflected light beam, and the central region of the hologram optical element. It is also a feature that the pre-pit signal is detected from the output sum of either one of the photodetection element that receives the light beam diffracted by the light receiving element and the light detection element that receives the light beam diffracted by the outer region of the hologram optical element.

With respect to the third embodiment, in a photodetector that divides an optical disc reflected light beam into four in the radial direction, the center dividing line coincides with the radial center line of the optical disc reflected light beam, and the radial line is centered on the dividing line. Another feature is that the remaining two dividing lines are arranged at positions that are evenly displaced in the direction, and the prepit signal is detected from the sum of the outputs of the two central photodetecting elements and one of the outer photodetecting elements. .
Further, in the hologram optical element that divides the optical disc reflected light beam into four in the radial direction, the center dividing line coincides with the radial direction center line of the optical disc reflected light beam, and the positions are evenly displaced in the radial direction around the dividing line. , 2 more
One of a photodetector element that receives two light beams diffracted by the two central areas of the hologram optical element and one that receives a light beam diffracted by the outer area of the hologram optical element. Another feature is that the pre-pit signal is detected from the output sum.

Further, the hologram optical elements in the second and third embodiments may be configured to transmit the light flux emitted from the light source and diffract the light flux reflected by the optical disk.

According to the present invention, the reflected light beam from the optical disk is split at a position deviated from the center line in the radial direction, and the pre-pit signal is detected from the split light beam. The leakage signal component of the adjacent pre-pits is suppressed in a wide range. Further, the deviation between the focus position where the leak signal component of the adjacent pre-pit is the minimum and the focus position where the resolution is the maximum is smaller than the one-channel detection. Therefore, even in an optical head having an astigmatic difference, it is possible to suppress a decrease in the resolution of the pre-pit signal due to defocusing or disk tilt, and to reduce the leakage signal component of the adjacent pre-pits.

Further, in the present invention, a two-division photodetector or a two-division hologram optical element is arranged so as to divide the reflected light flux of the optical disk into two at a position displaced in the radial direction from the radial centerline. By detecting the pre-pit signal from the light flux having a large amount of reflected light from the optical disk, it is not necessary to dispose the dividing line at a position deviated from the center line of the hologram optical element or the photodetector. The element and the two-division photodetector can be used.

Further, according to the present invention, in the photodetector or the hologram optical element which divides the optical disc reflected light beam into three in the radial direction, the two division lines are equally distributed in the radial direction with the center line of the optical disc reflected light beam in the radial direction as the center. The pre-pit signal detection system detects a pre-pit signal by detecting the pre-pit signal from the output sum of either the central light beam or the outer light beam of the three divided light beams.
As a result, the number of optical head components can be reduced. Also,
Not only the pre-pit signal but also the track error signal can be detected from the detection system.

Further, in the present invention, in the photodetector or the hologram optical element which divides the optical disc reflected light beam into four in the radial direction, the center division line coincides with the radial direction center line of the optical disc reflected light beam, and the division line is The remaining two division lines are arranged at positions evenly displaced in the radial direction at the center, and the central two light fluxes of the four light fluxes are divided into four,
By detecting the prepit signal from the output sum of either one of the outer light fluxes, one prepit signal detection system is provided, and the number of components of the optical head can be reduced. Further, not only the pre-pit signal but also the track error signal can be detected from the detection system.

Further, in the present invention, the hologram optical element which is divided into three or four is provided with a function of transmitting the light flux emitted from the light source and diffracting the light flux reflected from the optical disk, thereby separating the light flux emitted from the light source and the optical flux reflected from the optical disk. It becomes possible to remove the optical element and integrate the emitting optical system and the receiving optical system.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a first embodiment of an optical disk device of the present invention. The linearly polarized light beam emitted from the semiconductor laser 1 becomes a parallel light beam by the collimator lens 2 and enters the polarization beam splitter 3. The polarization beam splitter 3 is designed so as to transmit P-polarized light (polarized surface parallel to the paper surface) and reflect S-polarized light (polarized surface perpendicular to the paper surface). Since it is adjusted to be P-polarized light, it passes through the polarization beam splitter 3. The light beam that has passed through the polarization beam splitter 3 has its direction bent 90 degrees by the rising mirror 4, becomes circularly polarized light by the quarter-wave plate 5, and is condensed on the recording surface of the optical disk 7 by the objective lens 6. The light beam reflected by the optical disk 7 becomes a parallel light beam by the objective lens 6, and becomes a linearly polarized light by the quarter wavelength plate 5. The polarization direction is rotated by 90 degrees with respect to the outgoing light flux and becomes S-polarized light. After that, the optical disc 7
The reflected light from is reflected by the polarization beam splitter 3 after its optical path is bent 90 degrees by the rising mirror 4, and enters the re-focusing lens 8. Then, the light beam is split by the beam splitter 9 into two light beams while being collected by the re-focusing lens 8.

The light beam that has passed through the beam splitter 9 passes through a cylindrical lens 10 and then enters a focus / track error signal photodetector 11 to generate a focus error signal by the astigmatism method and a track error signal by the push-pull method. To do. Based on this signal, focus / track control is performed by an objective lens control mechanism (not shown). On the other hand, the light beam reflected by the beam splitter 9 is split into two light beams by the half mirror 14 and is incident on the first and second reproduction signal / pre-pit signal photodetectors 12 and 13, respectively.

FIG. 2 is a view showing the first and second reproduction signal / pre-pit signal photodetectors 12 and 13 viewed from the half mirror 14 side on the same plane for convenience. As shown in the figure, each of the two reproduction signal / pre-pit signal photodetectors 12 and 13 is composed of a photodetector that is divided into two in the radial direction.
7 enters the reproduction signal / pre-pit signal photodetectors 12 and 13, respectively. Here, the two reproduction signal / pre-pit signal photodetectors 12 and 13 are divided lines 12a and 13 extending in a tangential direction perpendicular to the radial direction.
Two photo-detecting elements 20 which are equal in the radial direction by a
It is divided as a, 20b, 21a, 21b,
The dividing lines 12a and 13a are reflected by the optical disk reflected light 17
Of the reproduction signal so as to be displaced from each other with respect to the center line 18 of the light flux of
The pre-pit signal photodetectors 12 and 13 are arranged. Then, the reproduction signal / pre-pit signal photodetectors 12, 1
Amplifier circuits 26a, 26b, 27a, 27b are connected to the respective photodetector elements 20a, 20b, 21a, 21b of No. 3, and each amplifier circuit 26a, 26b, 27a, 2b.
The outputs amplified in 7b are added in the addition amplification circuit 29 and output as a reproduction signal 33. The outputs of the amplifier circuits 26a and 27a of the amplifier circuits are output as prepit signals 30 and 31, respectively.

Next, the operation of detecting the pre-pit signal by the optical head having this structure will be described. The astigmatic difference of the optical head at this time is 0 μm. As shown in FIG. 18, when the focused spot 199 scans the groove 201, the pre-pit signal 30 and the pre-pit signal 31 are as shown in FIG.
It becomes like (a). At this time, the address information of the A address 202 and the B address 203 is read from the prepit signal 30, and the address information of the C address 204 and the D address 205 is read from the prepit signal 31. Further, when one focused spot 199 scans the land 200 on the inner peripheral side, that is, the focused spot 199 indicates the E address 20.
6, the F address 207, the C address 204, and the D address 205 are scanned, and the pre-pit signal 30 and the pre-pit signal 31 are as shown in FIG. At this time,
The address information of the E address 206 and the F address 207 is read from the pre-pit signal 31, and the C address 204,
The address information of the D address 205 is the pre-pit signal 30.
Read more.

FIG. 4A shows the calculation result regarding the defocus characteristics of the leak signal component of the adjacent prepit and the resolution of the prepit signal for the prepit signal read from each address. In the calculation, the conditions in Table 2 were used as in the sum signal detection. In the figure, the dividing lines 12a and 13a of the reproduction signal / pre-pit signal photodetectors 12 and 13 are respectively 87.5% (optical disk reflected light radius to the optical disk inner peripheral side with respect to the optical disk reflected light center line 18). 100
%), And a case where the photodetector is arranged so as to be shifted to the outer peripheral side of the optical disk by 87.5%. The astigmatic difference is 0 μm. Here, the defocus allowable range in the case of the leakage signal component of adjacent pre-pits ≦ −30 dB and the resolution ≧ −6 dB will be compared between the conventional example and the present embodiment. The results are shown in Table 1. It can be seen from Table 1 that the defocus allowable range that simultaneously satisfies the above two conditions is expanded as compared with the sum signal detection and the one-channel detection. As a result, the defocus margin of the prepit signal can be improved. The reproduction signal 33
Are amplified by the amplifier circuits 26a, 26b, 27a, 27b from all the photodetector elements 20a, 20b, 21a, 21b of the reproduction signal / prepit signal photodetectors 12, 13 and added by the addition amplifier circuit 29. Obtained by amplification.

Also in an optical head having an astigmatic difference, by moving the reproduction signal / pre-pit signal photodetectors 12 and 13 in the same manner as described above, the defocus margin in the optical head having an astigmatic difference is improved. Can be achieved. Figure 5
(A), (b) is the figure which showed the calculation result regarding the defocus characteristic of the leak signal component of an adjacent prepit and the resolution of a prepit signal in astigmatic difference ± 0.5 micrometer. The amount of movement of the dividing line is the same as when the astigmatic difference is 0 μm. Table 1 also shows the results of estimating the defocus allowable range in the same manner as above from FIG. From Table 1,
Similar to the case of the astigmatic difference of 0 μm, the defocus allowable range that simultaneously satisfies the above two conditions is expanded by the sum signal detection and the one-channel detection.

Here, in the first embodiment, since the division lines of the reproduction signal / pre-pit signal photodetectors 12 and 13 are located at the center of the photodetector, the two-division photodetection which is usually commercially available. The vessel can be applied as it is. Further, the light flux condensed on the optical disc 7 does not need to be displaced in the radial direction with respect to the groove or the land, and can be applied to the existing optical disc device as it is.

Further, in the first embodiment, the optical disk reflected light 17 is split and received by the two-split photodetectors 12 and 13, but the method of splitting the light flux is not limited to this.
You may use the hologram etc. which can divide a light beam into two. That is, any optical element that can divide the optical disk reflected light 17 in the radial direction may be used. In that case, the dividing optical elements are respectively arranged between the half mirror 14 and the two photodetectors for the reproduction signal and the prepit signal, and the dividing line of each optical element is a radial line in the optical disc with respect to the optical disc reflected light center line 18. Slide in opposite directions. Then, the light beam split by each optical element is received by the reproduction signal / pre-pit signal photodetector, and the pre-pit signal is detected.
The technique using this split optical element will be described in detail as an example using a hologram in the fourth and subsequent embodiments described later.

FIG. 6 is a diagram showing a second embodiment of the present invention. The second embodiment is the same as the first embodiment except for the reproduction signal / pre-pit signal photodetection system. Here, the optical disk reflected light 1 reflected by the beam splitter 9
On the other hand, the half mirror is not used, and the light enters the reproduction signal / pre-pit signal photodetector 55 as it is. FIG. 7 shows the reproduction signal as seen from the beam splitter 9 side.
It is a block diagram of the photodetector 55 for pre-pit signals. As shown in the figure, the reproduction signal / pre-pit signal photodetector 55
Is divided into three in the radial direction, and a dividing line 60 between the photodetector element 56 on the outer peripheral side of the optical disk and the photodetector element 57 in the center is formed.
Is shifted toward the outer circumference of the optical disk in the radial direction with respect to the center line 18 of the reflected light 17 of the optical disk, and the dividing line 6 between the central photodetector 57 and the inner photodetector 58 of the optical disk is separated.
1 is displaced toward the inner peripheral side of the optical disc in the radial direction with respect to the center line 18 of the optical disc reflected light 17. Then, the outputs of the photodetector elements 56, 57 and 57 are amplified by amplifier circuits 59a, 59b and 59c, respectively. When the respective outputs are I56, I57, and I58, the pre-pit signal 30 is obtained by adding I56 and I57 by the addition amplification circuit 62, and the pre-pit signal 31 is obtained by adding I57 and I58 by the addition amplification circuit 63. Further, I56, I57, and I58 are added by the addition amplifier circuit 66 to obtain the reproduction signal 33.

According to the second embodiment, as in the first embodiment, the optimum deviation amount of the dividing lines 60 and 61 with respect to the optical disk reflected light center line 18 in the optical head is investigated in advance, and the optimum deviation amount is taken into consideration. A photodetector. In addition, with respect to the optical disk reflected light center line 18, the dividing line 6
The optimum shift amounts of 0 and 61 are the same. From this, a pre-pit signal equivalent to that of the first embodiment can be obtained. Also, if this configuration is adopted, only one photodetector for the reproduction signal / pre-pit signal is required, and
This is advantageous in reducing the size and cost of the optical head as compared with the above embodiment.

In the second embodiment, the reproduction signal / pre-pit signal photodetector 55 is arranged behind the refocusing point of the optical disk reflected light 17 reflected by the refocusing lens 8. The same effect as described above can be obtained by disposing the photodetector 55 before the condensing point.

FIG. 8 is a diagram showing a photodetector according to the third embodiment of the present invention. In the third embodiment, only the reproduction signal / prepit signal photodetector has a structure different from that of the second embodiment, and the other structures are the same as those of the second embodiment. Therefore, in FIG. 8, the reproduction signal / pre-pit signal photodetector 68 viewed from the beam splitter 9 (the reproduction signal / pre-pit signal photodetector 55 in the second embodiment is shown.
Are replaced). As shown in the figure, the reproduction signal / pre-pit signal photodetector 68 includes four photodetection elements 69, 70 in the radial direction.
It is divided into four as 71 and 72, and the two center photodetection elements 70 and the division line 74 of the photodetection elements 71 coincide with the optical disc reflected light center line 18, and the photodetection elements 69 and photodetection elements on the outer peripheral side of the optical disc. The dividing line 73 of 70 is displaced from the center dividing line 74 to the outer peripheral side of the optical disk, and the dividing line 7 of the photodetecting element 71 and the inner peripheral side of the optical detecting element 72 is divided.
5 is displaced from the dividing line 74 toward the inner circumference of the optical disc. In this configuration, the detection signals of the photodetector 69, the photodetector 70, the photodetector 71, and the photodetector 72 are amplified by the amplifier circuit 76, the amplifier circuit 77, the amplifier circuit 78, and the amplifier circuit 79, respectively. These signals are I69, I70, I71, I
72, I69, I70, I in the summing amplifier circuit 82
71 is added to obtain the prepit signal 30, and I70, I71, and I72 are added by the addition amplification circuit 83 to obtain the prepit signal 31. The reproduced signal 33 is I69, I7.
It is obtained by adding and amplifying 0, I71, and I72 in the adding and amplifying circuit 81.

Also in the third embodiment, similarly to the second embodiment, the optimum deviation amount of the dividing lines 73 and 75 with respect to the optical disk reflected light center line 18 is investigated in advance, and the photodetector based on the value is examined. 68 is produced. The optimum shift amounts of the dividing lines 73 and 75 with respect to the optical disk reflected light center line 18 are the same. From this, a pre-pit signal equivalent to that of the first embodiment can be obtained. Further, since the dividing line 74 is coincident with the optical disc reflected light center line 18, I69 and I70, I71 and I72 are respectively added and subtracted by the subtraction amplifier circuit 80 to obtain a track error signal by the push-pull method. Therefore, since it can be matched with the track error signal obtained from the focus / track error signal photodetector 11 (see FIG. 6), the amount of light distribution to the focus / track error signal photodetector 11 side is reduced and reproduction is performed. It is possible to increase the light amount distribution to the signal / pre-pit signal photodetector 68 side.
As a result, the S / N ratio of the reproduction signal and the prepit signal can be improved. Moreover, if this configuration is adopted, the second
As in the above embodiment, it is advantageous for downsizing and cost reduction of the optical head.

In the third embodiment, the reproduction signal / pre-pit signal photodetector 68 is arranged behind the re-focusing point of the optical disk reflected light 17 by the re-focusing lens 8. Even if the photodetector 68 is arranged before the light spot, the same effect as the second embodiment can be obtained.

FIG. 9 is a diagram showing a fourth embodiment of the present invention. The fourth embodiment is the same as the second embodiment except for the error signal, reproduction signal, and pre-pit signal photodetection system. In the fourth embodiment, the beam splitter 9, the cylindrical lens 10 and the like are unnecessary, and instead, the hologram 135 is arranged on the optical path of the reflected light of the polarization beam splitter 3. Then, the optical disk reflected light 127 reflected by the polarization beam splitter 3 enters the hologram 135.
After that, it is diffracted by the hologram 135 and the re-focusing lens 8
And then enters the photodetector 136.

FIG. 10 is a sectional view of the hologram 135 in the radial direction. As shown in the figure, hologram 1
Reference numeral 35 is a glass substrate 137 and a SiO ₂ film 1 having a lattice pattern.
It is made by depositing 38, and has a function of diffracting incident light in the radial direction. Further, FIG. 11 is a view of the hologram 135 seen from the refocusing lens 8. As shown in the figure, the hologram 135 is divided into two regions having different diffraction grating widths by the tangential dividing line 130, and each divided region is further divided into three by the radial dividing lines 132 and 133. Six areas in total from 1 to 6, namely, the first area 121, the second area 122, the third area 123, the fourth area 124, and the fifth area 1.
25 and the sixth area 126. Hologram 1
The optical disk reflected light 127 that has entered 35 is reflected in each area 121.
Diffracted at ~ 126, and after passing through the re-focusing lens 8, 2
The light is incident on the photodetector 136 as two focused spots. As a result, 12 focused spots are formed on the photodetector 136. Further, in the hologram 135, the hologram radial direction dividing line 132 is displaced to the inner side of the optical disc in the radial direction with respect to the optical disc reflected light center line 128, and the hologram radial direction dividing line 133 is radial to the optical disc reflected light center line 128. Is shifted toward the outer circumference of the optical disc.

FIG. 12 is a diagram showing an example of the configuration of the photodetector 136. The figure is viewed from the side of the re-focusing lens 8, and in the left side area of the figure, four photo-detecting elements 100, 101, 102, 103 are arranged facing each other with a minute interval in the radial direction and the tangential direction, respectively. Six photodetector elements 104, 105, 106, 10 arranged in series in the radial direction at minute intervals in the right region of FIG.
It is composed of ten photodetector elements 7, 108 and 109. The optical disk reflected light 127 is diffracted by the hologram 135 and re-focused by the refocusing lens 8 as described above, and 12 light spots 94 to 99 and 110 to 1 are obtained.
15 is formed and is irradiated to each of the photodetection elements 100 to 109. That is, the region 121 of the hologram 135
The light flux diffracted by becomes the light spots 94 and 115. Similarly, the diffracted light beam in the region 122 is divided into the light spots 95 and 114.
In addition, the diffracted light beam in the region 123 has the light spots 96 and 113.
In addition, the diffracted light beam in the region 124 has the light spots 97 and 112.
In addition, the diffracted light beam in the region 125 has the light spots 98 and 111.
In addition, the diffracted light beam in the region 126 has the light spots 99 and 110.
become.

Here, the light spot 94 and the light spot 9
5, the light spot 96 to the light detecting element 100 and the light detecting element 1
On the division line of 01, the light spot 97, the light spot 98,
The light spot 99 is converted into the light detecting element 102 and the light detecting element 103.
Place each on the dividing line. Although not shown, the detection signals of the photodetector 100, the photodetector 101, the photodetector 102, and the photodetector 103 are I10.
0, I101, I102, I103, (I10
The focus error signal is detected from 0 + I103)-(I101 + I102). That is, the focus error signal is detected by the knife edge method. Also, the light spot 11
0, the light spot 111, the light spot 112, the light spot 113, the light spot 114, and the light spot 115, respectively, are the photodetector 104, the photodetector 105, the photodetector 106, the photodetector 107, the photodetector 108, and the light. The detection element 109 receives the light. The detection signal at that time is I104,
I105, I106, I107, I108, I109, and (I106 + I109)-(I104 + I107)
The track error signal is detected. That is, the track error detection is performed by the push-pull method similar to the above-described embodiments. Based on these signals, an objective lens control mechanism (not shown) performs focus / track control. The reproduced signal is (I104 + I105 + I106 + I107 +
I108 + I109).

On the other hand, the pre-pit signal is (I104 + I1
05 + I107 + I108) and (I105 + I106 +
I108 + I109). Hologram radial direction dividing line 132 with respect to the optical disk reflected light center line 128,
By preliminarily investigating the optimum deviation amount of 133 and producing the hologram 135 based on the value, a good pre-pit signal can be obtained as in each of the above embodiments. In addition, in the fourth embodiment, the error signal photodetector and the prepit signal photodetector can be integrated, and it is not necessary to separately provide an error signal detection system.
The embodiment is more advantageous in cost reduction and size reduction.

Further, in the third embodiment, the pre-pit signal is obtained by taking the form in which the hologram 135 divides the optical disk reflected light 127 into three in the radial direction, but the optical disk reflected light 127 is divided into four in the radial direction. A good pre-pit signal can be detected even with a hologram that is displayed. In that case, the center dividing line of the hologram coincides with the optical disc reflected light center line 128, and the remaining two dividing lines are
The center line 128 of the reflected light of the optical disc is shifted by the same amount in mutually opposite radial directions of the optical disc. From this, one of the light beam diffracted by the central two regions of the hologram and the light beam diffracted by the outer region is detected, and the pre-pit signal is detected from the sum of the outputs.

FIG. 13 is a diagram showing a fifth embodiment of the present invention. The polarization beam splitter 3 used in each of the above-described embodiments is not required, while the module 85 having the semiconductor laser and the photodetector integrated and the polarization hologram 86 are provided. In this configuration, the light flux emitted from the module 85 becomes a parallel light flux by the collimator lens 2 and enters the polarization hologram 86. Polarizing hologram 86
Is designed to transmit ordinary light (polarized light parallel to the paper surface) and diffract extraordinary light (polarized light perpendicular to the paper surface). The light flux emitted from the module 85 is adjusted to be ordinary light. Therefore, the light passes through the polarization hologram 86. The light flux that has passed through the polarization hologram 86 rises to the mirror 4
The direction is bent by 90 degrees, and it becomes circularly polarized light by the quarter-wave plate 5 and is condensed on the recording surface of the optical disk 7 by the objective lens 6. The light beam reflected by the optical disk 7 becomes a parallel light beam by the objective lens 6, and becomes a linearly polarized light by the quarter wavelength plate 5. The polarization direction is rotated by 90 degrees with respect to the outgoing light flux to become extraordinary light.
After that, the reflected light from the optical disk is reflected by the rising mirror 4
Then, the optical path is bent by 90 degrees and is incident on the polarization hologram 86. Since the optical disk reflected light is extraordinary light, it is diffracted by the polarization hologram 86. The diffracted light flux is module 8
Incident on 5.

FIG. 14 is a block diagram showing an example of the configuration of the module 85. As shown in FIG. 8A, the module 85 has a semiconductor laser 87 mounted on a photodetector 88. The light flux emitted from the semiconductor laser 87 is directed upward in the figure and enters the collimator lens 2 shown in FIG. Then, the reflected light flux from the optical disk 7 is the polarization hologram 8
The light is diffracted at 6, collimated by the collimator lens 2 and re-focused, and enters the photodetector 88. As an arrangement configuration example of the semiconductor laser and the photodetector in such a module 85, FIG.
The configurations shown in (b) and (c) are adopted. 14B and 14C are cross-sectional views taken in the direction perpendicular to the plane of the drawing with the semiconductor laser emitted light flux of FIG. 14A as a reference. FIG. 14B shows a case where a glass mirror is used.
The semiconductor laser element 90 (87) is installed on the photodetector 88 via a heat sink 91. The light beam emitted horizontally from the semiconductor laser element 90 is a glass mirror 89.
It is reflected at and goes upward in the figure. The diffracted reflected light 139 from the optical disk 7 is received by the photodetector 88 on both sides of the semiconductor laser element 90 and the glass mirror 89. On the other hand, FIG. 14C shows a case where a mirror formed by etching is used for the photodetector 92. Photo detector 92
To form a concave portion 92a and a mirror surface 93 by etching,
The semiconductor laser device 90 (87) is installed in the recess 230. As a result, the light flux emitted from the semiconductor laser element 90 in the horizontal direction is reflected by the mirror surface 93 and travels upward in the drawing.

FIG. 15 is a sectional view of the polarization hologram 86 in the radial direction. As shown in the figure, the polarization hologram 86 is a lithium niobate substrate 1 having birefringence.
18 has a structure in which a lattice-shaped pattern is formed by the proton exchange region 120 and the phase compensation film 119, and has a function of transmitting all ordinary light among incident light and diffracting all extraordinary light. 16 is a view of the polarizing hologram 86 seen from the collimator lens 2 side. Note that this figure has the same configuration as the hologram 135 shown in the fourth embodiment. Therefore, the divided areas are indicated by the same symbols as in FIG. 11, and six areas, that is, the first area 121, the second area 122, the third area 123, the fourth area 124, and the fifth area 1 are shown.
25 and the sixth area 126. The optical disk reflected light 139 that has entered the polarization hologram 86 is diffracted in each region and enters the photodetector 88 via the collimator lens 2. At that time, 12 focused spots are formed on the photodetector 88, similarly to the fourth embodiment. In the polarization hologram 86, the polarization hologram radial direction dividing line 132 is displaced to the optical disk outer peripheral side in the radial direction with respect to the optical disk reflected light center line 142, and the polarization hologram radial direction dividing line 133 is the optical disk reflected light center. It is displaced to the inner circumference side of the optical disc in the radial direction with respect to the line 142.

FIG. 17 is a diagram showing an example of the configuration of the module 86 shown in FIG. 14A, which is a plan view seen from the collimator lens 2 side. Regarding the configuration of the photodetector 88, the photodetector 136 of the fourth embodiment shown in FIG.
Therefore, the light spots and the light detection elements are indicated by the same symbols as in FIG.
The mounting form of the semiconductor laser device 90 is shown in FIG.
In this case, the light flux emitted from the semiconductor laser element 90 travels in the direction perpendicular to the plane of the drawing by the mirror 89 and travels toward the collimator lens 2. Further, the optical disk reflected light flux is divided by the polarization hologram 86, re-focused by the collimator lens 2, and 12 light spots 94 to 9 are formed on the photodetector 88.
It becomes 9,110-115. At this time, the relationship between each divided area of the polarization hologram 86 and the light spot formed by diffracting and condensing is the same as in the fourth embodiment.

Here, the light spot 94 and the light spot 9
5, the light spot 96 to the light detecting element 100 and the light detecting element 1
On the division line of 01, the light spot 97, the light spot 98,
The light spot 99 is converted into the light detecting element 102 and the light detecting element 103.
Place each on the dividing line. Also, the light spot 11
0, the light spot 111, the light spot 112, the light spot 113, the light spot 114, and the light spot 115, respectively, are the photodetector 104, the photodetector 105, and the photodetector 1.
The light is received by 06, the light detection element 107, the light detection element 108, and the light detection element 109. From this, the error signal, the reproduction signal, and the pre-pit signal are detected as in the fourth embodiment.
The optimum amount of deviation of the polarization hologram radial direction division lines 132 and 133 with respect to the optical disk reflected light center line 142 is investigated in advance, and the polarization hologram 8 is calculated based on the value.
By producing No. 6, a good pre-pit signal can be obtained also in this embodiment. Further, since the hologram has a function of separating the light flux emitted from the light source and the light flux reflected from the optical disk, optical elements such as a polarization beam splitter can be removed, and the number of components of the optical head can be reduced.

Here, in the description of each of the above-described embodiments, the effect on the phenomenon of defocus has been described. However, a sufficient effect can be obtained even when the optical disk is tilted with respect to the optical axis of the optical head.

Although the optical head of the present invention uses the astigmatism method and the knife edge method for the focus error detection method, the present invention is not limited to this, and the spot size method or the like can be used. Other error detection methods can also be applied. Further, although the reproduction signal is obtained from the photodetector or the photodetector used for detecting the pre-pit signal, it is also possible to obtain the reproduction signal by the sum of all the photodetectors or the photodetectors. Furthermore, it is possible to detect not only the prepits shifted to both sides of the scanning track as in the CAPA method but also the prepits shifted to only one side of the track.

[0053]

As described above, according to the present invention, the following effects can be obtained. A first effect is that even in an optical head having an astigmatic difference, a reduction in resolution of a prepit signal due to defocus or disc tilt is suppressed, and a leak signal component of an adjacent prepit is reduced.
The reason is that the reflected light beam from the optical disk is split at a position deviated from the center line in the radial direction, and the pre-pit signal is detected from the split light beam. As shown in FIGS. This is because the leak-in signal component of the adjacent pre-pits can be suppressed in a wider defocus range as compared with the detection. Further, the one-channel detection reduces the deviation between the focus position where the leak signal component of the adjacent pre-pit is minimum and the focus position where the resolution is maximum, which is also a reason for the above effect.

The second effect is that it is not necessary to dispose the dividing line at a position deviated from the center line of the hologram optical element or the photodetector.
A two-part photodetector can be used. The reason is,
A two-division photodetector or a two-division hologram optical element is arranged so as to divide the optical disc reflected light beam into two at a position displaced in the radial direction from the radial center line, and among the two divided light beams, the optical disc reflected light amount is large. This is because the pre-pit signal is detected from.

The third effect is that the number of constituent parts of the optical head can be reduced. The reason is that in a photodetector or hologram optical element that divides the optical disc reflected light beam into three in the radial direction, the two dividing lines are evenly displaced in the radial direction around the radial center line of the optical disc reflected light beam. This is because one pre-pit signal detector can be provided by detecting the pre-pit signal from the output sum of either the central light flux or the outer light flux of the three light fluxes arranged and divided into three. Further, in the photodetector or the hologram optical element that divides the reflected light flux of the optical disc into four in the radial direction, the center division line coincides with the center line of the reflected light flux of the optical disc in the radial direction, and the division line is evenly distributed in the radial direction. By arranging the remaining two division lines at the shifted positions and detecting the prepit signal from the output sum of either the central two light fluxes of the four light fluxes or the outer light fluxes, the prepit signal is detected in the same manner as described above. This is because the number of signal detectors can be one.

The fourth effect is that one photodetector can detect not only the prepit signal but also the track error signal.
The reason is that in a photodetector or a hologram optical element that divides an optical disc reflected light beam into three in the radial direction,
The two split lines are arranged at positions that are evenly displaced in the radial direction around the radial center line of the optical disc reflected light flux, and the output sum of either the central light flux or the outer light flux of the three split light fluxes This is because the pre-pit signal is detected from. Further, in the photodetector or the hologram optical element that divides the optical disc reflected light beam into four in the radial direction, the center dividing line coincides with the radial center line of the optical disc reflected light beam, and the radial lines are evenly distributed around the dividing line. This is because the remaining two division lines are arranged at the shifted positions, and the pre-pit signal is detected from the sum of the outputs of either the central two luminous fluxes of the four luminous fluxes or the outer luminous flux.

The fifth effect is that the optical element for separating the luminous flux emitted from the light source and the reflected luminous flux of the optical disk can be removed.
The reason is that the hologram optical element that is divided into three or four can be provided with a function of transmitting the light flux emitted from the light source and diffracting the light flux reflected from the optical disk.

[Table 1]

[Table 2]

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical system according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a reproduction signal / prepit signal photodetector according to the first embodiment of the present invention.

FIG. 3 is a pre-pit signal waveform diagram according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a defocus characteristic of a prepit signal quality deterioration factor at an astigmatic difference of 0 μm in the first embodiment of the present invention.

FIG. 5 is an astigmatic difference of ± 0.5 μ in the first embodiment of the present invention.
It is a figure which shows the defocus characteristic of the pre-pit signal quality deterioration factor in m.

FIG. 6 is a configuration diagram of an optical system according to a second embodiment of the present invention.

FIG. 7 is a configuration diagram of a reproduction signal / pre-pit signal photodetector according to a second embodiment of the present invention.

FIG. 8 is a configuration diagram of a reproduction signal / pre-pit signal photodetector according to a third embodiment of the present invention.

FIG. 9 is a configuration diagram of an optical system according to a fourth embodiment of the present invention.

FIG. 10 is a sectional view of a hologram according to a fourth embodiment of the present invention.

FIG. 11 is a plan view of a hologram according to the fourth embodiment of the present invention.

FIG. 12 is a configuration diagram of a photodetector according to a fourth embodiment of the present invention.

FIG. 13 is a configuration diagram of an optical system according to a fifth embodiment of the present invention.

FIG. 14 is a configuration diagram of a module according to a fifth embodiment of the present invention.

FIG. 15 is a sectional view of a polarization hologram according to a fifth embodiment of the present invention.

FIG. 16 is a plan view of a polarization hologram according to a fifth embodiment of the present invention.

FIG. 17 is a configuration diagram of a photodetector according to a fifth embodiment of the present invention.

FIG. 18 is an enlarged view of a pre-pit area of a CAPA type optical disc.

FIG. 19 is a configuration diagram of an optical system showing an example of a conventional optical head.

FIG. 20 is a configuration diagram of a reproduction signal / track error signal photodetector in a conventional optical head.

FIG. 21 is a diagram showing an example of a pre-pit signal waveform when a pre-pit signal is detected from a CAPA type optical disc by a conventional head.

FIG. 22 is a diagram showing a defocus characteristic of a prepit signal quality deterioration factor when a prepit signal is obtained by sum signal detection in a conventional optical head having an astigmatic difference of 0 μm.

FIG. 23 is a diagram showing a defocus characteristic which is a factor of quality deterioration of a prepit signal when a prepit signal is obtained by sum signal detection by a conventional optical head having an astigmatic difference of ± 0.5 μm.

FIG. 24 is a diagram showing a defocus characteristic of a prepit signal quality deterioration factor when a prepit signal is obtained by one-channel detection by a conventional optical head having an astigmatic difference of 0 μm.

FIG. 25 is a diagram showing a defocus characteristic which is a factor of quality deterioration of a prepit signal when a prepit signal is obtained by one-channel detection with a conventional optical head having an astigmatic difference of ± 0.5 μm.

[Explanation of symbols]

1 Semiconductor Laser 2 Collimator Lens 3 Polarizing Beam Splitter 4 Standing Mirror 5 1/4 Wave Plate 6 Objective Lens 7 Optical Disk 8 Refocusing Lens 9 Beam Splitter 10 Cylindrical Lens 11 Focus / Track Error Signal Photo Detector 12, 13 Playback Signal / pre-pit signal photodetector 14 Half mirror 17 Optical disc reflected light 18 Optical disc reflected light center line 20a, 20b, 21a, 21b Photodetector 21 Photodetector 26a, 26b, 27a, 27b Amplifier circuit 29 Summing amplifier circuit 30, 31 pre-pit signal 32 track error signal 33 reproduction signal 34, 35, 36 pre-pit signal 55 reproduction signal / pre-pit signal photodetector 56, 57, 58 photodetector 60, 61 dividing line 62, 63, 66 adder amplifying circuit 68 reproduction Signal / pre-pit signal photodetector 69, 70, 71, 72 Photodetection elements 73, 74, 75 Dividing lines 76, 77, 78, 79 Amplification circuit 80 Subtraction amplification circuits 81, 82, 83 Addition amplification circuit 85 Module 86 Polarizing hologram 87 Semiconductor laser 88 Photodetector 89 Mirror 90 Semiconductor laser element 91 Heat sink 92 Photodetector 93 Mirror surface 94, 95, 96, 97, 98, 99 Light spot 100, 101, 102, 103 Photodetector element 104, 105, 106, 107, 108, 109 Photodetection Element 110, 111, 112, 113, 114, 115 Light spot 118 Lithium niobate substrate 119 Phase compensation film 120 Proton exchange region 121, 122, 123, 124, 125, 126 First to sixth region 127 Optical disc reflected light 128 Optical disc Reflected light center line 130 Hologram tangen Chal direction dividing lines 132, 133 Hologram radial direction dividing line 135 Hologram 136 Photodetector 137 Glass substrate 138 SiO ₂ 139 Optical disc reflected light 142 Optical disc reflected light center line 198 Pre-pit (CAPA) area 199 Condensing spot 200 land (LAND) 201 Grooves 202, 203, 204, 205, 206, 207, 2
08,209 A address to H address 213 Focus error signal photodetector 215 Playback signal / track error signal photodetector 216,217 Photodetection element 219 Optical disk reflected light 220,221 Amplification circuit 222 Subtraction amplification circuit 223 Addition amplification circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields investigated (Int.Cl. ⁷ , DB name) G11B ^7/ 09-7/013 G11B 7/09-7/10

Claims (12)

(57) [Claims] 1. An emission from a light source for recording / reproducing information on / from an optical disc in which a pre-pit area having address information separately from a recording area is arranged in a radial direction with respect to a land and a groove. In an optical disk device that projects a light beam onto a land or groove of the optical disk, receives the reflected light beam, and detects at least a prepit signal from the received light output, the position where the reflected light beam of the optical disk is displaced from the center line in the radial direction. in divided pre-pit signal detection method of the optical disc, characterized in that to obtain the divided one side of the output <br/> or found before Symbol prepit signal received light flux. 2. An optical disk device for recording / reproducing information on / from an optical disk in which a pre-pit area having address information separate from a recording area is arranged in a radial direction with respect to a land and a groove. The light receiving optical system includes an emitting optical system that guides a light beam emitted from a light source to a land or a groove of the optical disc, and a light receiving optical system that receives a reflected light beam of the optical disc and detects at least a prepit signal from the light reception output. In the system,
The reflected light beam of the optical disk is separated in the radial direction at a position deviated from the radial center line, characterized by having the divided one side of the light detection system to obtain an output or found before Symbol prepit signal received light beams Optical disk device. 3. The light detection system divides the reflected light flux of the optical disc into two in the radial direction at a position displaced from the center line in the radial direction, and detects a pre-pit signal from a light flux having a large reflected light amount in the two-divided light flux. The optical disk device according to claim 2, wherein: 4. The two-part photodetector for splitting the reflected light beam into two in the radial direction such that the split line is located at a position displaced in the radial direction from the radial centerline of the reflected light beam of the optical disc. 4. The optical disk device according to claim 3, wherein the pre-pit signal is detected from a photodetecting element that receives a large amount of the optical disc reflected light flux among the divided photodetecting elements. 5. The hologram optical element for arranging the reflected light beam into two in the radial direction is arranged in the photodetection system so that a dividing line is located at a position displaced from the radial direction center line of the reflected light beam of the optical disc in the radial direction. 4. A pre-pit signal is detected from the output of a photodetector element that receives a light beam with a large amount of reflected light from the optical disc, of the two light beams that are split in the radial direction by each hologram optical element. Optical disk device. 6. The light detection system divides the reflected light flux of the optical disc into three in the radial direction by two dividing lines that are evenly displaced on both sides in the radial direction around the radial center line of the reflected light flux of the optical disc. 3. The optical disk device according to claim 2, wherein the pre-pit signal is detected from the sum of the outputs of the central light beam and the outer one of the three divided light beams. 7. The photodetection system directs the reflected light flux in the radial direction such that the two dividing lines are located at positions evenly displaced on both sides in the radial direction with respect to the radial centerline of the reflected light flux of the optical disk. 7. The optical disc according to claim 6, wherein a three-division photodetector for dividing into three is disposed, and the prepit signal is detected from the sum of the divided photodetection element in the center and one of the photodetection elements on the outside. apparatus. 8. The light detection system detects the reflected light flux of the optical disc such that two split lines are located at positions evenly displaced on both sides in the radial direction around the center line of the reflected light flux of the optical disc in the radial direction. A photo-detecting element, in which a hologram optical element that divides the hologram optical element into three is arranged, and which receives a light beam diffracted in the divided central region of the hologram optical element,
7. The optical disk device according to claim 6, wherein the prepit signal is detected from the output sum of either one of the photodetection elements that receive the light beam diffracted in the divided outer region of the hologram optical element. 9. The photodetection system has a center dividing line which coincides with a radial centerline of a reflected light beam of an optical disc, and two dividing lines are respectively arranged at positions which are evenly displaced in the radial direction with respect to the dividing line. The reflected light flux of the optical disc is divided into four in the radial direction by the three divided lines arranged, and the pre-pit signal is detected from the sum of the two central light fluxes and either one of the outer light fluxes. The optical disk device according to claim 2. 10. The photodetection system has a center dividing line that coincides with a radial centerline of the reflected light flux of the optical disc, and is evenly displaced on both sides in the radial direction about the center dividing line. A four-division photodetector that divides the reflected light flux into four in the radial direction is arranged so that the two division lines respectively come to different positions, and the outputs of the two photodetection elements in the center and one of the photodetection elements on the outside The optical disk device according to claim 9, wherein the pre-pit signal is detected from the sum. 11. The photodetection system has a center dividing line that coincides with a radial centerline of a reflected light flux of the optical disc, and is evenly displaced on both sides in the radial direction about the center dividing line. A holographic optical element that divides the reflected light beam into four in the radial direction is arranged so that two division lines come to different positions.
A light detecting element that receives a light beam diffracted in two central regions,
10. The optical disk device according to claim 9, wherein the pre-pit signal is detected from the sum of the outputs of either one of the photo-detecting elements that receive the light beam diffracted in the area outside the hologram optical element. 12. The light-emitting optical system and the light-receiving optical system are integrally formed, and the hologram optical element is configured to transmit a light beam emitted from a light source and diffract a light beam reflected from an optical disk. Item 12. An optical disk device according to item 8 or 11.