JPH0778877B2 - Optical disk device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disc apparatus including an optical disc and an optical head for recording or reproducing information on the optical disc.

Conventional Technology As a conventional technology, for example, Applied PHYSICS LETTERS (VOLUMU 42 NUMBE
R 2) High Density Optical Disc Shape Glugs (“High densi
ty optical disk with V-shaped grooves "). First, the configuration of a conventional optical disk device will be described with reference to the drawings.

FIG. 9 shows a reflecting surface of a conventional optical disc, in which pits 101 are formed on the slope 100 of a V-shaped periodic groove. This V
In the case of a grooved optical disk, the track corresponds to a slope and the track pitch is 1/2 of the groove pitch.

FIG. 10 shows a principle diagram of a conventional optical head. Light (wavelength 830 nm) emitted from the semiconductor laser 102 is separated into three light fluxes by the diffraction grating 103, passes through the polarization beam splitter 104 and is converted into parallel light by the condenser lens 105, and the reflection prism 106,
After passing through the quarter-wave plate 107, it is narrowed down by the diaphragm lens 108 to the optical disk reflecting surface 109 on which the V-shaped pre-groove is formed. The return light reflected from the optical disk reflecting surface 109 is separated into three light fluxes and again the diaphragm lens 108 and the quarter-wave plate 10
7. After passing through the reflection prism 106, the light is condensed by the condenser lens 105 and reflected by the polarization beam splitter 104. Out of the three light fluxes, the outer two light fluxes are received by the photodetectors 111 and 112 and become reproduction signals. The central light beam passes through the cylindrical lens 110 and is received by the photodetector 113, and becomes a signal for focus and tracking control.

FIG. 11 shows the arrangement of beam spots on the reflection surface of the optical disk. The beam spots 114 and 115 corresponding to the two outer light fluxes scan the inclined surface of the V groove, and the top of the V groove (or the bottom of the valley). ) Is the beam spot 116 corresponding to the central light flux.
Scans.

FIG. 12 shows the light intensity distribution of the return light of the light scanning on the V-groove slope, which is shown on the aperture surface of the diaphragm lens, and the intensity of the return light from the V-groove slope 100 when there is no pit on the adjacent track. 118, and if there is a pit 117 in the adjacent track, the intensity distribution changes to 119. If there is a reproduced signal detector on the aperture surface, the crosstalk component (disturbance due to the signal on the adjacent track) on the photodetector 120 is canceled by appropriately selecting the gap δ0 with respect to the optical axis with respect to the aperture diameter R0. can do.

FIG. 13 shows how the crosstalk is related to the gap between the photodetector and the optical axis, and the gap δ should be appropriately selected with respect to the diameter R of the returning light on the photodetector 121. Can significantly reduce crosstalk. Therefore, the track pitch can be made dense, and the high density of the optical disc can be realized.

Problems to be Solved by the Invention In such a conventional optical disk device, there are the following problems.

FIG. 14 (a) shows the beam spot 122 and the scanning track center 1
Deviation from 23 (defocus amount εF, off-track amount ε
(B) shows the relationship between the crosstalk and the defocus amount εF when the track pitch is 1 μm.
(C) shows the relationship between the crosstalk and the off-track amount εT. The crosstalk is a value when there is a pit on the adjacent track on one side, the defocus amount εF is positive in the direction in which the reflecting surface moves away from the diaphragm lens 10, and the off-track amount εT approaches the adjacent track on the side with the pit 124. The direction is negative, and the direction on the opposite side, that is, the direction approaching the adjacent track on the side without pits is positive.

Defocus and off-track are inevitably caused by various error factors during adjustment and aging.
The system quality must be guaranteed for at least a defocus amount of ± 1 μm and an off-track amount of ± 0.2 μm. As shown in FIG. 14, the conventional optical disk device has just focus (εF = 0) and just tracking (εT =
In 0), the crosstalk is small, but it significantly deteriorates when defocus and off-track occur. The cross-talk drops to −28 dB when the defocus amount is ± 1 μm, and the crosstalk drops to −21 dB when the off-track amount is ± 0.2 μm.

The optical head has a structure in which the three light beams separated by the folding grating are narrowed down and accurately arranged on the reflecting surface of the optical disc, and the three return lights are received by the three photodetectors, respectively, which complicates the structure of the optical system. . In addition, 3 on the reflective surface of the optical disk
Since one beam spot is formed, it is limited to reproduction only, and is not suitable for additional recording, recording, or erasing. Further, since the grooves are V-shaped to form the grooves and the signal pits of the optical disk, the method of applying resist hardening cannot be applied, and the V-grooves are formed by the cutting method which is not technically well established. Since the signal pits are formed by utilizing the curing and ion milling, the construction method is complicated.

In view of the above problems, the present invention suppresses crosstalk deterioration due to error factors such as differential focus, off-track, etc., the optical head and the optical disc have a simple structure and construction method, and are not only for read-only but also for write-once, recording, or erasing. It is an object of the present invention to provide a high density optical disk device that can be applied to.

Means for Solving the Problems The present invention is directed to a semiconductor laser, a first condensing means for condensing light from the laser into parallel light, and the condensed laser light in a pre-groove or a pre-pit. Second condensing means for condensing the return light from the optical disk reflecting surface while condensing on the formed optical disk reflecting surface,
A detection unit that divides the return light that has passed through the second condensing unit into a plurality of regions along a dividing line corresponding to the radial direction of the optical disc and detects each of the regions, and a differential signal that obtains a difference signal from the pair of the detection units. An optical amplifier is provided, the difference signal is used as a reproduction signal, and the light spot condensed on the optical disc reflection surface by the second condensing means has astigmatism, and the first focal line generated by the astigmatism is almost The optical disk device is on the reflection surface of the optical disk and is parallel to the radial direction of the optical disk.

Operation With the above configuration, crosstalk is canceled by adding astigmatism to the light spot on the reflecting surface, dividing the return light and detecting it, and using the difference as the reproduction signal, defocus, off-track, etc. Since it is possible to suppress the deterioration of crosstalk due to the error factor of, it is possible to make the track pitch dense. In addition, the laser light is not separated but is condensed as one light flux on the optical disc reflection surface,
The configuration for detecting the returning light simplifies the configuration of the optical system. Also, the beam spot on the reflecting surface of the optical disk is 1
It is not limited to playback only, but for additional recording or recording,
It can also be applied to erase. Further, since the groove of the optical disk is U-shaped, a method applying resist curing can be applied to form the groove, and since the depth of the groove and the signal pit is uniform, the groove and the pit can be formed at the same time, which simplifies the method. .

Embodiment An embodiment of the present invention will be described below with reference to FIGS. 1 to 8.

FIG. 1 shows a reflecting surface of an optical disk according to the first embodiment of the present invention, in which a track groove 1 is sandwiched by a U-shaped guide groove 3 which is convex toward the laser irradiation side, and a pit 2 is in contact with the U-shaped guide groove 3. On the track groove 1, and the recording dots 4 are also formed on the track groove 1. The optical depth of the U-shaped guide groove 3 and the bit 2 corresponds to about 1/8 of the laser wavelength, and the width of the track groove 1 is about 1/2 of the track pitch. In the case of this optical disc, unlike the V-groove optical disc,
The track pitch is equal to the groove pitch. Since the tracking sensitivity is generally inversely proportional to the pitch of the periodic groove, the optical disc of this embodiment has a higher tracking sensitivity than the V-groove optical disc.

FIG. 2 shows a principle diagram of the optical head in the first embodiment of the present invention. Light emitted from semiconductor laser 5 (wavelength 830 nm)
Is collimated by a condenser lens 6 and collimated by a magnifying prism 7 into a circular cross section.
After passing through the quarter-wave plate 9, it is narrowed down to the optical disk reflection surface 11 by the diaphragm lens 10. The return light reflected from the optical disk reflection surface 11 passes through the aperture lens 10 and the quarter-wave plate 9 again, is reflected by the polarization beam splitter 8, and is condensed by the convex lens 12. The converged return light is reflected by the half mirror 13 and is received by the photodetector 17 in front of the focal point 15.
The light passing through 13 and reflected by the half mirror 14 is received by the photodetector 18 located after the focal point 16, and the light passing through the half mirror 14 is received by the photodetector 19.

FIG. 3 shows a principle diagram of the optical head signal detecting section in the first embodiment of the present invention. The photodetector 19 has a dividing line 19L parallel to the disc rotation direction and a dividing line 19m perpendicular to the dividing line 19L,
It is divided into four areas 19B, 19C and 19D (a). Dividing line 1
The intersection of 9L and 19m coincides with the center of the return light 20. Summing amplifiers 21A, 21B, 21C and 21D are photodetectors 19A and 19C, respectively.
The detection outputs of 19A and 19B, 19C and 19D, 19B and 19D are added, and differential amplifiers 22A and 22B are added amplifiers 21A, 21B and 21C, respectively.
And the differential of the output of 21D is taken. The output of the differential amplifier 22A is the tracking error (TE) signal, and the output of 22B is the reproduction signal. Since the difference signal is used as the reproduction signal, the crosstalk is canceled and can be kept small. The photodetectors 17 and 18 detect a part of the return lights 23 and 24 along the direction corresponding to the normal direction of the junction surface of the semiconductor laser 5, and the differential amplifier 25 obtains a focus error (FE) signal. (B). The normal direction of the bonding surface of the semiconductor laser 5 is orthogonal to the expansion direction of the expansion prism 7, but it does not have to coincide with the disk radial direction.

FIG. 4 (a) shows the displacement (diffocus amount εF, off-track amount εT) between the beam spot F1 and the scanning track center 26 in the first embodiment of the present invention, and FIG. 4 (b) shows when the track pitch is 1 μm. Shows the relationship between the crosstalk and the defocus amount εF, and (c) shows the relationship between the crosstalk and the off-track amount εT. The crosstalk is a value when there is a pit on the adjacent track on one side, the defocus amount εF is positive in the direction in which the reflecting surface moves away from the diaphragm lens 10, and the offtrack amount εT approaches the adjacent track on the side with the pit 27. The direction is negative, and the direction on the opposite side, that is, the direction approaching the adjacent track on the side without pits is positive.
In addition, assuming that the convergent light 28 has astigmatism, the above-mentioned beam spot F1 is a focal line in the disc radial direction, and FIGS. 4 (b) and 4 (c) show F1 and another focal line F2. Interval a χ
(That is, the astigmatic difference amount) is used as a parameter. (It is assumed that aχ is positive when F2 is closer to the diaphragm lens 10 than F1.) From FIGS. 4 (b) and 4 (c), when astigmatism difference aχ = 0.0 μm, aχ = 0.5 μm Is the just focus (ε
The crosstalk in F = 0) and just tracking (εT = 0) is small, and deterioration is caused by defocus and off-track, but it is considerably improved compared to the conventional example. (Crosstalk -32 with defocus amount ± 1μm
Crosstalk of -27 dB is maintained at dB and off track of ± 0.2 μm. ) Therefore, the track pitch can be made dense, and the high density of the optical disc can be realized. Since the beam spot F1 is the focal line in the disc radial direction, the beam spot on the reflecting surface is well focused in the scanning direction (disc rotation direction), and the signal density in the disc rotation direction does not drop.

FIG. 5 shows a state of a focal line (or a focal point) near a reflection surface of an optical disc when the condenser lens is moved along the optical axis and the returning light on the focus control photodetector in the first embodiment of the present invention. It is an explanatory view showing the distribution of.

In FIG. 5 (a), the laser light is imaged in an aberration-free state, the convex lens 12 is moved in the optical axis direction so that the focal point is located on the ξ-η plane, and the photodetectors 17 and 18 are adjusted. This is the state, and at this time, the return lights 29 and 30 on the photodetectors 17 and 18 are both circular with a diameter a. Therefore, the FE signal which is the differential output of the photodetectors 17 and 18 is 0, and control is performed so that the optical disk reflection surface coincides with the ξ-η plane.

FIG. 5B shows the case where the condenser lens 6 is moved away from the magnifying prism 7 by Δ along the optical axis from the state of FIG. 5A, and the laser light causes an astigmatic difference at the image forming point, and the disc radial direction. The focal line F1 of ( ² ) is away from the aperture lens 10 by (fo / mfc) ² Δ from the ξ-η plane, and the focal line F2 in the disc rotation direction is (fo / fc) ² Δ. Therefore, the astigmatic difference amount aχ is (fo / fc) ² Δ (1
−1 / m ² ). (However, fo: focal length of aperture lens, f
c: focal length of condensing lens, m: magnifying prism magnifying power) Generally, magnifying power m> 2, and if astigmatic difference aχ is small, the focal line
It is considered that F1 almost coincides with the ξ-η plane. When the optical disk reflection surface coincides with the ξ-η plane, that is, the focal line F1, the return light 31, 32 on the photodetectors 17, 18 has an elliptical shape, and the former is short and the latter is long in the normal direction of the bonding surface, The diameter a is maintained in the direction orthogonal to the joining surface normal. Therefore, the FE signal, which is the differential output of the photodetectors 17 and 18, is almost 0,
Control is performed such that the focal line F1 is on the reflection surface of the optical disc.

FIG. 5 (c) shows the case where the condenser lens 6 is moved closer to the magnifying prism 7 along the optical axis by Δ from the state of FIG. 5 (a), the laser light causes an astigmatic difference at the image forming point, and the disc radial direction. Focal line
F1 approaches the diaphragm lens 10 by (fo / mfc) ² Δ from the ξ-η plane, and the focal line F2 in the disc rotation direction approaches (fo / fc) ² Δ. Therefore, the astigmatic difference aχ is (fo / fc) ² Δ (1-1 /
m ² ). If the astigmatic difference aχ is small, the focal line F1 is ξ−
It is considered that the reflection surface almost coincides with the η plane, so when the optical disk reflection surface coincides with the ξ−η plane, that is, the focal line F1,
The return light 33, 34 on the photodetectors 17, 18 has an elliptical shape, and the former is short and the latter is long in the direction of the joining surface normal, but both diameters are kept in the direction orthogonal to the joining surface normal. Therefore photo detector
The FE signal which is the differential output of 17 and 18 is almost 0, (b)
The control is performed so that the focal line F1 is on the reflection surface of the optical disk as in the above.

Therefore, in order to control the focal line F1 on the reflection surface of the optical disc and add the astigmatic difference amount aχ such that the crosstalk becomes small, the condensing lens 6 may be brought close to the magnifying prism 7 along the optical axis. , There is no need to readjust the detection system. As another example of adding the astigmatic difference amount aχ that reduces the crosstalk, it can also be realized by setting a transparent parallel plate between the semiconductor laser 5 and the condenser lens 6 with the optical axis inclined.

FIGS. 6A and 6B are explanatory diagrams showing the relationship between the difference between the reproduction signal interval and the crosstalk signal interval for the same pit and the amount of defocus. When the beam spot 35 scans on the track 37 having the pit 36, reproduction signals 38 and 39 are generated at the start and end of the pit 36, and the interval between them is t ₁ . When the beam spot 40 scans on an adjacent track 41 having no pit, crosstalk signals 42 and 43 are generated at the start and end of the pit 36, and the interval is t ₂ . The difference between the reproduction signal interval and the crosstalk signal interval t ₂ −t ₁ is not 0, and the defocus amount ε
It depends on F. FIG. 6A shows the astigmatic difference amount aχ =
The state when 0.5 μm is shown. Generally, in the case of a digital signal, the pit length and the pit interval of adjacent tracks are an integral multiple of a certain unit length, and if t ₂ −t ₁ = 0, once the reproduction signal and the Crowtalk signal are synchronized between adjacent tracks, The read signal and the crosstalk signal overlap with each other with a considerable probability and the read error rate of the signal increases. However, according to the present invention, since t ₂ −t ₁ ≠ 0, even if the crosstalk signal at the start end becomes a disturbance of the reproduced signal, the crosstalk signal at the end does not become a disturbance and the read error rate becomes small.

In the first embodiment, the laser beam is not separated but is condensed as a single light flux on the optical disc reflecting surface and the return light is detected. Therefore, the configuration of the optical system is simpler than that of the conventional example.
Further, since there is only one beam spot on the reflection surface of the optical disc, the beam spot is not limited to reproduction only, but can be applied to additional recording, recording or erasing. Further, since the groove of the optical disk is U-shaped, a method applying resist curing can be applied to form the groove, and since the depth of the groove and the signal pit is uniform, the groove and the pit can be formed at the same time, which simplifies the method. .

FIGS. 7 (a) and 7 (b) show the principle of the optical head signal detector in the second embodiment of the present invention. Photodetector 19 is 19E, 19
The light is divided into two regions of F, and the zero-order diffracted light 20C and the ± first-order diffracted lights 20R, 20L generated by the groove diffraction in the return light are received mainly. Differential amplifier 22C includes photodetectors 19E and 19E.
It takes the differential of the output of F. The output of the differential amplifier 22C is TE
Signal. The return light on the photodetector has a greater degree of intensity change due to off-track than the amount of received light, and the quality of the TE signal is better than that of the first embodiment.

The photodetectors 17 and 18 are divided into three regions of 17R, 17C, 17L and 18R, 18C, 18L, respectively, and the photodetectors 17C and 18C include return lights 23 and 24 along the direction corresponding to the disk radial direction. A part is detected, and a focus error (FE) signal is obtained by the differential amplifier 25. If the normal direction of the bonding surface of the semiconductor laser 5 and the disk radial direction are made to coincide with each other, as described with reference to FIG.
By moving the condenser lens 6 along the optical axis, the focal line F1 is controlled on the optical disc reflection surface, and an astigmatic difference amount aχ that reduces crosstalk can be added. The photodetectors 17R, 17L and 18R, 18L are sandwiched around the photodetectors 17C, 18C, respectively, and the outputs of 17L, 18R and 17R, 18L are added by summing amplifiers 21E, 21F, respectively, and a differential amplifier
The difference between the outputs of the summing amplifiers 21E and 21F is taken by 22D to obtain a reproduction signal. The crosstalk in this case is also the same as that of the first embodiment, and as shown in FIG. 4, by adding the astigmatic difference, it can be considerably improved compared to the conventional example.

FIG. 8 shows a reflecting surface of an optical disk in a third embodiment of the present invention, in which a convex track groove 1A on the laser irradiation side is sandwiched by lands 3A, and a pit 2A is formed as a discontinuous portion of the track groove 1A. Has been formed. The recording dots 4 are also formed on the track groove 1A. The optical depth of the track groove 1A corresponds to about 1/8 of the laser wavelength, and the width of the track groove 1 is about 1/2 of the track pitch. Also in the case of this optical disk, unlike the V-groove optical disk, the track pitch is equal to the groove pitch. Therefore, the optical disc of this embodiment is V
Greater tracking sensitivity than grooved optical disks.

Depending on whether the track groove is concave or convex with respect to the laser irradiation side, the crosstalk and the defocus amount ε shown in FIG.
F, the astigmatic difference amount a in relation to the off-track amount εT
Since the polarity of χ is inverted, in order to add the astigmatic difference amount aχ such that the focal line F1 is controlled on the reflection surface of the optical disk and the crosstalk is reduced, the condenser lens 6 is expanded along the optical axis. You must stay away from 7. Others are the same as in the first embodiment, and the same effect can be expected. Further, the second embodiment may be applied to the third embodiment.

EFFECTS OF THE INVENTION As described above, according to the optical disk device of the present invention, crosstalk is canceled even if the track pitch is made dense, and deterioration of crosstalk due to error factors such as defocus and off-track can be suppressed. Can be realized. The optimum adjustment can be easily realized by moving the condenser lens along the optical axis. Further, since the laser light is not separated but is condensed as one light flux on the optical disk reflection surface and the return light is detected, the structure of the optical system is simplified. Further, since there is only one beam spot on the reflection surface of the optical disc, the beam spot is not limited to reproduction only, but can be applied to additional recording, recording or erasing. Further, since the groove of the optical disk is U-shaped, the method of applying the effect of the resist can be applied to the formation of the groove, and since the depth of the groove and the signal pit is uniform, the groove and the pit can be formed at the same time, which simplifies the method. .

[Brief description of drawings]

FIG. 1 is a principle diagram of a reflecting surface of an optical disk according to the first embodiment of the present invention, FIG. 2 is a principle diagram of an optical head according to the first embodiment of the present invention, and FIG. 3 is a view of the first embodiment of the present invention. FIG. 4 (a) is an explanatory view showing the position of the beam spot in the first embodiment of the present invention, and FIG. 4 (b) is an explanation showing the relationship between the crosstalk and the defocus amount εF. FIG. 5C is an explanatory diagram showing the relationship between the crosstalk and the off-track amount εT, and FIG. 5 is the state of the focal line (or focus) near the optical disc reflecting surface and the focus control light in the first embodiment of the present invention. FIG. 6 is an explanatory view showing the distribution of the returning light on the detector, FIG. 6 is an explanatory view showing the relationship between the difference between the reproduction signal interval and the crosstalk signal interval by the same pit, and the defocus amount, and FIG. Optical head signal detection in two embodiments FIG. 8 is a principle diagram of a reflecting surface of an optical disc in a third embodiment of the present invention, FIG. 9 is a principle diagram of a reflecting surface of a conventional optical disc, and FIG. 10 is a principle diagram of a conventional optical head. FIG. 11 is a layout diagram of the beam spots in FIG. 10, and FIG. 12 is an explanatory view of a light intensity distribution on the aperture surface of the aperture lens where the return light of the light scanning on the slope of the V groove is shown.
FIG. 13 is an explanatory diagram showing the relationship between crosstalk and the gap of the photodetector, and FIG. 14 is a schematic diagram showing the operation of the conventional example. 1 ... Track groove, 3 ... U-shaped guide groove, 2 ... Pit, 4 ... Recording dot, 5 ... Semiconductor laser, 6 ...
Condensing lens, 7 ... Enlarging prism, 8 ... Polarizing beam splitter, 9 ... 1/4 wavelength plate, 10 ... Aperture lens, 11 ...
… Optical disc reflection surface, 12 …… Convex lens, 13,14 …… Half mirror, 17,18,19 …… Photodetector.

Claims (9)

[Claims] 1. A semiconductor laser, a first condensing means for condensing light from this laser into parallel light, and the condensed laser light on an optical disk reflecting surface on which pregrooves or prepits are formed. Second condensing means for condensing and condensing the return light from the optical disk reflecting surface,
A detection unit that divides the return light that has passed through the second condensing unit into a plurality of regions along a dividing line corresponding to the radial direction of the optical disc and detects each of the regions, and a differential signal that obtains a difference signal from the pair of the detection units. An optical amplifier is provided, the difference signal is used as a reproduction signal, and the light spot condensed on the optical disc reflection surface by the second condensing means has astigmatism, and the first focal line generated by the astigmatism is almost An optical disk device, which is on the optical disk reflection surface and is parallel to a radial direction of the optical disk. 2. The optical disk device according to claim 1, wherein the pitch of the pre-grooves or pre-pits in the disk radial direction is smaller than 1.5 times the wavelength of the laser light. 3. The optical disk device according to claim 1, wherein the amount of astigmatic difference due to astigmatism is larger than 0.3 times and smaller than 1 times the wavelength of the laser light. 4. The cross section of the pre-greave is rectangular or U-shaped, and the optical depth of the pre-groove or pre-pit is approximately 1 / the wavelength of the laser beam.
8. An optical disk device characterized in that 5. The optical disk device according to claim 4, wherein the width of the pre-groove or the pre-pit in the disk radial direction is about 1/2 of the pitch. 6. The optical spot according to claim 1, wherein the light spot focused on the optical disc reflecting surface by the second focusing means follows the track sandwiched by the convex pregrooves toward the second focusing means. In this case, the second focal line generated by the astigmatism is on the side of the second condensing means when viewed from the optical disc reflecting surface, and the light spot is concave toward the second condensing means. An optical disk device, wherein the second focal line is on the opposite side of the second light converging means when viewed from the optical disk reflecting surface when following the track sandwiched by the pregrooves. 7. A semiconductor laser, first condensing means for condensing light from the laser into parallel light, and light beam shaping means for expanding one beam width of the condensed laser light. A second condensing means for condensing the shaped laser light on an optical disc reflecting surface on which pregrooves or prepits are formed and condensing return light from the optical disc reflecting surface; and the second condensing means. The difference signal is provided with a detection unit that divides the returned return light into a plurality of regions by dividing lines corresponding to the radial direction of the optical disc and detects the divided regions, and a differential amplifier that obtains a difference signal from the pair of detection units. Is a reproduction signal, the light spot condensed on the optical disc reflection surface by the second condensing means has astigmatism, and the first focal line caused by the astigmatism is almost on the optical disc reflection surface. Optical disc apparatus according to claim is parallel to the radial direction of the optical disc. 8. The third condensing means for converging the return light passing through the second condensing means, wherein the junction surface of the semiconductor laser is parallel to the disk radial direction, and the third converging means. Separation means for separating the return light that has passed through the light means into two light beams, first detection means for detecting one of the separated return lights before the focus position, and the other of the separated return light after the focus position. And a second detection means for detecting, the first and second detection means are formed along a direction corresponding to the normal direction of the bonding surface, and each part of the separated return light. An optical disk device, which detects and uses the difference signal as a focus control signal. 9. The optical disk device according to claim 8, wherein the light spot focused on the optical disk reflecting surface is provided with astigmatism by moving the first light focusing means close to or away from the light beam shaping means. .