JP2004158150A - Optical head and optical disk device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the following problems: an error occurs in a spherical aberration detection signal when misalignment occurs in a photodetector in the conventional spherical aberration detection system and correction effect may not be obtained sufficiently. <P>SOLUTION: Reflection light from an optical disk is divided into eight and arrangement is made on the photodetector so that the error in the detection signal is canceled even in the misalignment of the photodetector, thus reducing the detection error of the spherical aberration detection signal. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical head for an optical disk device or the like, and more particularly, to an optical head for high-density recording and reproduction that reduces the influence of a displacement of a detector.
[0002]
[Prior art]
Currently used optical disc apparatuses are required to reproduce a plurality of types of optical discs with a high recording density. Currently used optical discs are detected by a diffracted light differential method, a three-spot method, a DPD method, and the like. The optical head corresponding to a recording DVD disk or a read-only DVD disk uses a diffracted light differential method and a DPD method. It is necessary to provide a tracking error detection optical system of the type. (Refer to Patent Document 1 as an example of such an optical head optical system.) In general, in order to increase the recording density in an optical disk device, it is necessary to increase the numerical aperture (NA) of an objective lens for condensing light on the optical disk. In addition, it is necessary to shorten the wavelength of light used for recording and reproduction. In recent years, in order to realize such a large capacity, development of a numerical aperture of about 0.8 and a wavelength of about 410 nm has been advanced. Here, when the numerical aperture is increased, a thickness error of the cover layer of the optical disc and a spherical aberration caused by an increase in the thickness of the cover layer by the two-layer disc become a problem.
[0003]
Therefore, means for measuring and correcting the amount of spherical aberration is required. As a means for measuring the amount of spherical aberration, for example, there are techniques described in Patent Literature 2 and Patent Literature 3.
[0004]
The prior art will be described with reference to FIG. 5 by taking JP-A-2000-171346 of Patent Document 2 as an example. The light emitted from the semiconductor laser 1 as the light source enters the collimator lens 2 as the zero-order light of the diffraction grating 11, becomes parallel light, and reaches the objective lens 7 via the spherical aberration correction element 4. The objective lens 7 converges the light on the optical disk 8 to form a light spot. The information on the optical disk 8 is reproduced or the information is written on the optical disk 8 using the light spot. Here, as the spherical aberration correction element 4, a liquid crystal element or the like that generates a phase shift between the central portion and the outer peripheral portion of the light beam can be used. Alternatively, a so-called immersion lens and its actuator may be arranged between the objective lens 7 and the optical disk 8. The reflected light from the optical disk 8 reaches the diffraction grating 11 again through the objective lens 7, the spherical aberration correction element 4, and the collimator lens 2. The reflected light is diffracted by the diffraction grating 11 and enters the photodetector 12.
[0005]
Next, the pattern of the diffraction grating 11 and the light receiving pattern of the photodetector 12 will be described with reference to the drawings. FIG. 6 shows a conceptual diagram of a pattern of the diffraction grating 11. The pattern of the diffraction grating 500 (the same as the diffraction grating 11) is formed in a region larger than the light beam 505 and is divided into three regions. The region is divided into two regions by a straight line AA set so as to pass through the center of the light beam 505, and one of the regions is divided by a semicircle around a point designed to be the center of the light beam 505. ing. The divided regions are referred to as a region 501, a region 502, and a region 503, respectively. The division line AA dividing the region 501 and the regions 502 and 503 is set to a direction perpendicular to the tangential direction of the guide groove of the optical disk 8.
[0006]
The light diffracted by the diffraction grating 11 is condensed on the photodetector 12, and its light receiving pattern will be described with reference to FIGS. 7 (a), (b) and (c). The photodetector 600 (same as the photodetector 12) and the diffraction grating 500 are arranged so that the directions of the respective division lines AA coincide. FIGS. 7A, 7B, and 7C show an example in which the distance between the optical disk 8 and the objective lens 7 is larger than the focal length, and FIGS. An example in the case of being smaller than the position is shown as (c). The photodetector 600 is divided into five regions as shown in FIG. Assuming that the respective regions are q, r, s, t, and u, the diffracted light from the region 501 of the diffraction grating irradiates substantially the center of q. The diffracted light from the region 503 is applied to the center between r and s.
Further, the diffracted light from the region 502 is applied to the center between t and u. If the outputs from the respective detectors are Sq, Sr, Ss, St, and Su, the focus detection signal FE is FE = (Sr-Ss) (1)
Is obtained. FIG. 7B shows that the output of Sr and the output of Ss are equal when the focus is on the optical disk 8. In FIG. 7A, the distance between the optical disk 8 and the objective lens 7 is larger than the focal length, and FE <0. Conversely, in the case of FIG. 7C where the distance between the optical disk 8 and the objective lens 7 is smaller than the focal length, FE> 0, and the defocus amount including the polarity can be detected.
[0007]
Further, the signal SA for detecting the amount of spherical aberration utilizes the characteristic that the focus is shifted near the center of the light beam and near the outer periphery thereof,
SA = (Sr−Ss) −K1 × (St−Su) (2)
Is obtained. Here, K1 is a constant. The spherical aberration correction is performed by controlling the correction amount by the spherical aberration correction element using the spherical aberration amount signal SA.
[0008]
[Patent Document 1]
JP-A-10-340461 [Patent Document 2]
JP 2000-171346 A [Patent Document 3]
JP 2001-307349 A
[Problems to be solved by the invention]
Generally, a position shift of the photodetector occurs due to thermal expansion around the detector, a change in the state of the adhesive, or the like. In the above-described related art, there is a problem that an error easily occurs in a detection signal when the photodetector is displaced.
[0010]
When the position shift of the photodetector 600 occurs in a direction perpendicular to the division line AA in FIG. 6, an error occurs in the focus detection signal FE and the spherical aberration detection signal SA. For example, if the photodetector 600 is shifted upward in the drawing in FIG. 7B, FE = (Sr-Ss) <0 (3)
SA = (Sr−Ss) −K1 × (St−Su) <0 (4)
Thus, even if the focus is on the optical disk 8, the focus detection signal becomes negative, and the position of the objective lens 7 is corrected so that the focus detection signal FE returns to zero. Similarly, spherical aberration correction is performed even if spherical aberration has not occurred. Here, the allowable positional deviation amount of the photodetector 600 depends on the focal length of the lens focused on the photodetector 600, but is approximately several μm.
[0011]
Furthermore, the above-mentioned prior art does not consider the tracking error detection and needs further improvement from a practical viewpoint.
[0012]
[Means for Solving the Problems]
The object is to provide four or more light beams capable of detecting a focus detection signal formed by reflected light beam splitting means for splitting a reflected light beam from a medium, and at least four pairs of detectors. The focus detection is divided into two sets of opposite polarities, and focus detection is performed by taking the difference between the two sets.
Focus detection is performed on a pair of divided areas on the detector corresponding to one light beam by a difference in the amount of light irradiated by the light beam, and the division lines corresponding to each detected light beam are made parallel. This can be achieved by:
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described with reference to FIGS.
FIG. 3 is an explanatory diagram of a configuration of an optical head according to an embodiment of the present invention. In the following description, the same elements as those described in the description of the related art will be denoted by the same reference numerals. FIG. 1 is a diagram illustrating a polarizing diffraction grating according to the present invention, and FIG. 2 is a diagram illustrating a division method of a photodetector and a light receiving pattern.
[0014]
As shown in FIG. 3, the light emitted from the semiconductor laser 1 is converted into parallel light by a collimating lens 2, passes through a polarizing beam splitter 3, a spherical aberration correction element 4 and a polarizing diffraction grating 5, and passes through a quarter-wave plate 6. Reach. The light changes from linearly polarized light to circularly polarized light by passing through the 波長 wavelength plate 6. The light transmitted through the wavelength plate 6 is focused on the optical disk 8 by the objective lens 7. The reflected light from the optical disk 8 again passes through the objective lens 7 and reaches the quarter-wave plate 6 and the polarizing diffraction grating 5. The polarization direction of the light is changed from circularly polarized light by the １ ／ wavelength plate 6 to linearly polarized light in a direction perpendicular to the polarization direction on the outward path, and is diffracted by the polarizing diffraction grating 5. The polarizing diffraction grating 5 is designed not to diffract linearly polarized light on the outward path, but to diffract linearly polarized light on the return path in a direction orthogonal to the outward path. The diffracted light is reflected by the polarization beam splitter 3 and narrowed down on the photodetector 10 by the detection lens 9.
[0015]
Next, a method of dividing the area of the polarizing diffraction grating 5 and a pattern of a light beam on the photodetector 10 will be described with reference to FIGS. FIG. 1 is an explanatory diagram showing the area division of the polarizing diffraction grating 100. The polarizing diffraction grating 100 is the same as the polarizing diffraction grating 5, and is given another number for explanation. The region of the polarizing diffraction grating 100 is divided into eight. The area of the diffraction grating 100 is divided into four by a straight line AA passing through the set center and perpendicular to a tangent direction of the guide groove of the optical disk 8 and a straight line BB, and further passing through the set center. It is divided inside and outside by a circle. As a result, eight regions from the region 101 to the region 108 are formed on the polarizing diffraction grating 100. In each area, a grating having a different pitch and direction is formed, and a light spot is formed at a predetermined position of the photodetector 200 described below.
[0016]
FIGS. 2A, 2B, and 2C are explanatory views showing the light receiving pattern of the photodetector 200 and the light pattern formed thereon. FIG. 2B shows a case where the optical disk 8 is in focus, FIG. 2A shows a case where the distance between the optical disk 8 and the objective lens 7 is larger than the focal length, and FIG. The case where the distance of the objective lens 7 is smaller than the focal length is shown.
[0017]
The relationship between the region of the polarizing diffraction grating 100 and the light pattern on the photodetector 200 will be described with reference to FIG. The photodetector 200 and the polarizing diffraction grating 100 are arranged so that the directions of the respective division lines AA coincide. The light diffracted in the four regions inside the polarizing diffraction grating, that is, the regions 101, 102, 103, and 104, is such that the + 1st-order diffracted light of the region 101 is on the dividing line between e and f on the detector, and -1. A second order diffracted light term illuminates n on the detector. Similarly, the region 102 is irradiated on the dividing lines e and f and p, the region 103 is irradiated on the dividing lines g and h and m, and the region 104 is irradiated on the dividing lines g and h and o. On the other hand, in the light diffracted in the outer four regions, that is, the region 105, the region 106, the region 107, and the region 108, the + 1st-order diffracted light in the region 105 is detected on the dividing line of i and j on the detector, and the -1st term is detected. It is irradiated to n on the vessel. Similarly, the region 106 is irradiated on the dividing lines a and b and p, the region 107 is irradiated on the dividing lines k and l and m, and the region 108 is irradiated on the dividing lines c and d and o. FIG. 8 schematically shows a state in which a light beam from each region of the polarization diffraction grating 100 reaches each detection unit of the photodetector 200, focusing on a focus detection system. The region 101 and the region 103 of the polarization diffraction grating 100 show + 1st-order diffracted light and -1st-order diffracted light, and only the + 1st-order diffracted light is shown in other regions to avoid being difficult to see. In order to make the light beam split by the polarizing diffraction grating 100 into a predetermined position on the detector as described above, the pitch and direction of the diffraction grating in each of the regions 101 to 108 of the diffraction grating are set. .
[0018]
The focus detection signal is created based on the knife edge method. Here, if the output from the detector a is Sa, and similarly the outputs from the detectors are Sb, Sc, Sd, Se... Sp, the focus detection signal FE is FE = (Se−Sf) + (Sh -Sg) ... (6)
Is obtained.
[0019]
Further, the signal SA for detecting the amount of spherical aberration utilizes the characteristic that the focus is shifted near the center of the light beam and near the outer periphery thereof,
SA = {(Se-Sf) + (Sh-Sg)}-K * [{(Sa-Sb) + (Sd-Sc)} + {(Si-Sj) + (Si-Sk)}] (7)
Is obtained. Here, K is a constant.
[0020]
Further, two signals used for the track servo signal can be obtained as follows. First, the push-pull signal is TRpp = (Sm + Sp)-(Sn + So) (8)
Secondly, the DPD signal is TRdpd = (Sm + Sn)-(So + Sp) (9)
Is obtained.
[0021]
With such a configuration, since the light beam used for detecting the track servo signal is incident inside each divided area of the photodetector, there is practically no problem in the displacement of the position of the detector.
[0022]
Further, it is possible to reduce the occurrence of errors in the focus detection signal FE and the spherical aberration detection signal SA due to the position shift of the photodetector, which is a problem in the related art. FIG. 4 shows how the occurrence of errors is reduced. FIG. 4 is a view corresponding to (b) of FIG. 2 and shows a case where the focus is on the optical disk. Further, for the sake of explanation, the light spot on the photodetector is drawn larger than FIG. FIG. 4B shows a state in which the photodetector has not been displaced. On the other hand, (a) shows a case where the photodetector is shifted downward in the drawing.
When the photodetector is displaced as shown in FIG. 4A, the first term of equation (6) increases and the second term decreases, but the number of light fluxes where the detection value increases is 2 and the number of light fluxes where the detection value is decreased is 2. Yes, the increment and decrement are equal. Therefore, the focus detection signal does not change. The same applies to the spherical aberration detection signal. That is, the output of the first and second terms of the equation (7) increases and decreases in accordance with the amount of displacement, but is canceled because the increase and decrease amounts are equal. The third and fourth terms and the fifth and sixth terms are similarly canceled. Therefore, the spherical aberration detection signal expressed by the equation (7) does not change. This is because the direction of increase or decrease of the position shift direction of the photodetector changes even in the case above, but the focus detection signal does not change because the change amounts are similarly equal. FIG. 4C shows a case where the photodetector is shifted to the left in the drawing. In this case, the focus detection signal FE and the spherical aberration detection signal SA do not change because the ratio of the light spot irradiated to each area of the photodetector does not change. As described above, even when the photodetector is displaced, each light spot moves to the same degree by the positive and negative terms of the focus detection signal FE and the spherical aberration signal SA, thereby canceling the error as a whole.
[0023]
The following is a summary of the concept for reducing the influence of the position shift of the detector on the focus detection error, the spherical aberration detection error, and the track servo signal detection error. Note that, in the case of this patent, spherical aberration detection is performed in combination with focus detection, so that spherical aberration detection will not be particularly described here.
(1) Each detection region of the detector is sufficiently larger than the size of the light beam incident thereon, and there is sufficient margin from the outer edge of the light beam to the edge of the detection region. ············································································································· Alternatively, when the outputs of the set of detectors are combined, there is a direction in which the combined output does not change. ... In the case of focus detection (3) There is a direction in which the output of the detector does not change when the detection light beam and the detector relatively move within the plane of the detection surface. ... In the case of focus detection (4) The direction of (2) and the direction of (3) are orthogonal directions in the plane of the detection surface.
[0024]
Although (1) is self-evident and need not be described, (2) and (3) will be described more specifically.
In order to embody the above (2), in the above embodiment, there are eight luminous fluxes capable of detecting the focus detection signal, there are six detector sets, and six sets have opposite focus detection polarities. By taking the difference between the two sets, the focus detection output is increased and the relative displacement between the detector and the detected light beam is reduced. In the present embodiment, the number of detector sets is six as described above, but the same effect can be expected if four sets are used in principle. However, in the case of four sets, for example, the polarizers are set so that the light beams incident on the detection units a, b, c, and d of the detector shown in FIG. 2 are incident on the detection units i, j, k, and l. It is necessary to change the diffraction grating 5. In this case, the + 1st-order light in the region 106 is incident on the i and j division lines of the detector, and the + 1st-order light in the region 108 is incident on the k and l division lines of the detector. Further, if the light beams incident on the four sets of detectors are each one, it is possible to detect a small error of the focus detection signal FE and the spherical aberration detection signal SA due to the displacement of the detectors with a minimum of four light beams. is there.
[0025]
In addition, in order to realize (3), (3-1) focus detection is performed by detecting a difference between the amounts of light irradiated by the light beam in two divided regions on the detector corresponding to one light beam. And the dividing lines corresponding to the respective detection light beams are made parallel.
[0026]
Another characteristic required of the focus detection system other than the above is the balance of the S-shaped characteristic.
This is a name representing a characteristic in which the detection signal shifts from 0 as the distance between the objective lens and the optical disc surface deviates from the focal length, reaches a maximum at a predetermined positional shift amount determined by the optical system, and gradually decreases. It is. When the distance between the objective lens and the optical disk surface coincides with the focal length, the focus detection signal becomes 0, and the polarity is reversed when the distance is larger than the focal length and when the distance is smaller than the focal length. It is desired that the absolute values on the small side substantially coincide with each other, and such a state is called that the S-shaped signal is balanced. In the present embodiment, as described above, the luminous flux passing through the region 103 and the region 104 intersects and enters the detection unit as shown in FIG. 8, thereby improving the balance of the S-shaped signal. The effect obtained in this manner will be described with reference to FIGS.
[0027]
FIG. 10 is different from this embodiment in that the distance between the objective lens and the optical disk surface greatly deviates from the focal length when the light beam passing through the regions 103 and 104 is not crossed in the same manner as the light beam passing through the regions 101 and 102. Shows the case where FIG. 10A shows a case where the distance between the objective lens and the optical disk surface is shorter than the focal length, and FIG. 10B shows a case where it is far. In FIG. 10A, both of the detection units e and f and the detection units g and h that perform focus detection have a part of the incident light beam protruding from the detection unit, and the absolute value of the focus detection signal becomes small. Is shown. On the other hand, in FIG. 10B, the incident light flux is present in both the detection units e and f and the detection units g and h, and the absolute value of the focus detection signal does not decrease. As described above, when the light beam enters the detection unit as shown in FIG. 10, the absolute value of the output of the focus detection system is different depending on whether the distance between the objective lens and the optical disk surface is smaller than the focal length or larger. Differently, the S-shaped signal becomes unbalanced.
[0028]
On the other hand, FIG. 9 shows a state on the photodetector when the distance between the objective lens and the optical disk surface largely deviates from the focal length in the case of the present embodiment. FIG. 9A shows the case where the distance between the objective lens and the optical disk surface is shorter than the focal length, and FIG. 9B shows the case where it is far. In FIG. 9A, a part of the incident light beam protrudes from the detection unit on the detection units e and f that perform focus detection, and the incident light beam is inside the detection unit on the detection units g and h. On the other hand, in FIG. 9 (b), the incident light beams are inside the detecting unit on the detecting units e and f sides, and a part of the incident light beams protrude from the detecting units on the detecting units g and h sides. As described above, in the case of the present embodiment, even when the distance between the objective lens and the optical disk surface is shorter or longer than the focal length, the focus detection signal outputs the same absolute value even when the distance is longer. It turns out to be good.
[0029]
Since the light beam passing through the regions 105, 106, 107, and 108 outside the polarization diffraction grating 100 has a large outer diameter, the distance between the objective lens and the optical disk surface is slightly different from the focal length as can be seen from FIG. 9 or FIG. It is not suitable for use when the focus control is not performed, because it protrudes from the detection units a, b, c, and d or the detection units i, j, k, and l due to the deviation.
[0030]
When a + 1st-order diffracted light and a -1st-order diffracted light that have passed through a certain region n of the polarization diffraction grating 100 shown in FIG. And the size of the detector 100 is set to a predetermined size. When the wavelength of the laser changes due to a temperature change or the like, the diffraction angle at the diffraction grating changes, and the luminous flux of the + 1st-order and -1st-order diffracted light moves on the straight line. Since the direction of movement of the light flux in the region 101 and the region 103 is opposite to the dividing line AA, it appears as an error with respect to the focus detection signal. Since the light beams on the opposite side to the dividing line AA have the same relationship as described above, the angle θn needs to be within a predetermined range in order to suppress the error of the focus detection signal.
[0031]
Further, according to this method, the polarizing diffraction grating 100 divides the light into a straight line passing through the center of the light beam and perpendicular to the tangential direction of the guide groove and a straight line passing through the center of the light beam and parallel to the tangential direction of the guide groove. Since the light beam can be independently detected by each of the m, n, o, and p sections of the photodetector 200, a track detection signal of the DPD system can be obtained by the calculation of the above equation (9). Further, the division of the diffraction grating is effective to suppress the influence of the convergent light condensed by the objective lens on the focus detection signal when the converged light crosses the guide groove on the optical disk.
[0032]
FIG. 11 is a plan view showing an outline of a disk device on which the optical head according to the present invention is mounted.
The chassis 60 includes a spindle motor 61 as a means for engaging the disk 69 and rotating the disk at a predetermined number of revolutions, a pickup case member 13 on which an optical head or the like according to the present invention is mounted, and the pickup case member 13. The pickup case member 13 is driven in the radial direction of the disk 69 through an engagement member 72 fastened by a fastening member 73 to the seek motor 62 and a lead screw 63 as means for moving the pickup case member 13 to a desired position. Further, guide shafts 64 and 65 for holding the pickup case member 13 and guiding the moving operation are mounted. Usually, the chassis 60 is connected to an external housing (not shown) by connecting members such as 66, 67, and 68.
[0033]
A member 74 protruding from the pickup case member 13 transmits various electric signals and the like necessary for operating elements in the pickup and various electric signals detected by the pickup to an external circuit system (FIG. (Not shown).
Here, the positioning member 14 has its positioning posture adjusted by members 71a, 71b, 71c in the pickup case 13 and is fastened and held.
By having such a structure, the disk device can avoid the objective lens and the disk from being damaged due to external vibrations and shocks, etc., thereby improving the reliability of the disk device performance. You can do it.
[0034]
【The invention's effect】
As described above, according to the present invention, it is possible to reduce the error of the spherical aberration detection signal due to the displacement of the photodetector. In addition, it is possible to detect a DPP method, which is a track detection signal method used in a DVD-ROM.
[Brief description of the drawings]
FIG. 1 is an explanatory view of a polarizing diffraction grating showing one embodiment of the present invention. FIG. 2 is an explanatory view of a photodetector showing one embodiment of the present invention. FIG. 3 is a light showing one embodiment of the present invention. FIG. 4 is an explanatory diagram showing a state when a detector is shifted in one embodiment of the present invention. FIG. 5 is an explanatory diagram showing a configuration of a conventional optical head. FIG. FIG. 7 is an explanatory view showing a conventional photodetector. FIG. 8 is an explanatory view showing the relationship between a polarizing diffraction grating and a photodetector according to an embodiment of the present invention. FIG. 10 is an explanatory diagram of an arrangement of light beams for balancing an S-shaped signal according to an embodiment of the present invention. FIG. 10 is an explanatory diagram of an arrangement of light beams for not balancing an S-shaped signal. FIG. 11 is a plan view of an embodiment of a disk device of the present invention. Explanation of code]
DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser, 2 ... Collimate lens, 4 ... Spherical aberration correction element, 5 ... Polarizing diffraction grating, 6 ... Optical disk, 7 ... Objective lens, 8 ... Optical disk, 9 ... Detection lens, 10 ... Photodetector, 100 ... Polarizing diffraction grating (same as 5), 101 to 108: divided regions of polarizing diffraction grating, 200: photodetector (detection surface shape)

Claims (9)

A light source,
Light collecting means for collecting light emitted from the light source on a medium,
In an optical head having divided light converging means for condensing reflected light from a medium on a photodetector and light beam dividing means for dividing the reflected light beam,
The optical head, wherein the reflected light beam splitting means is split into eight regions. The said reflected light beam division | segmentation means is divided into four in the circumferential direction centering on a predetermined point, and each said area | region divided | segmented into the area | region near and distant from the said point is divided into two. 1 optical head. The reflected light beam splitting means is divided into four by two straight lines orthogonal to each other about a predetermined point, and each of the divided areas is divided into two by a circle centered at the point. 3. The optical head according to 1 or 2. A light source,
Light collecting means for collecting light emitted from the light source on a medium,
In an optical head having divided light converging means for condensing reflected light from a medium on a photodetector and light beam dividing means for dividing the reflected light beam,
Focus detection is performed on a pair of divided regions on a detector corresponding to one light beam of the light beam, based on a difference in light amount irradiated by the light beam;
The dividing lines corresponding to the respective detection light beams are parallel to each other, and include four or more light beams capable of detecting the focus and at least four pairs of detectors,
An optical head, wherein the four pairs of detectors are divided into two sets of mutually opposite focus detection polarities, and focus detection is performed by taking the difference between the two sets. The said reflected light beam division | segmentation means is divided into four in the circumferential direction centering on a predetermined point, and each said area | region divided | segmented into the area | region near and distant from the said point is divided into two. 4 optical head. The reflected light beam splitting means is divided into four by two straight lines orthogonal to each other about a predetermined point, and each of the divided areas is divided into two by a circle centered at the point. 6. The optical head according to 4 or 5. The optical head according to claim 1, wherein the medium has a guide groove, and at least one of the division lines is parallel to a tangent of the guide groove. 8. The optical head according to claim 1, wherein said reflected light beam splitting means is a polarizing diffraction grating. An optical disk device using the optical head according to claim 1.

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