JP2005251293A - Optical head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical head which is compact and has inexpensive constitution and in which spherical aberration can be corrected highly accurately. <P>SOLUTION: In the optical head having an objective lens 7 converging a light beam emitted from a light source 1 on an optical recording medium 8, a spherical aberration correcting means 11 arranged at an optical path between the light source 1 and the objective lens 7 and provided with lens groups 11a, 11b correcting spherical aberration of the light beam, the spherical aberration correcting means 11 has a lens holder 12 holding at least one lens 11a out of the lens groups, a yoke 13 comprising a magnetic substance supporting the lens holder 12 movably in the direction of optical axis, coils 15a-15d attached to the lens holder 12, and magnets 14a, 14b attached to the yoke 13 so that a magnetic field operates to the coils 15a-15d, and the lens holder 12 is moved in the direction of optical axis by electromagnetic operation of magnets 14a, 14b by making current to flow through the coils 15a-15d, and then spherical aberration is corrected. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical head provided in an optical recording / reproducing apparatus such as an optical disk apparatus that optically records / reproduces information, and more particularly to an optical head having a spherical aberration correction function that adjusts the distance between lens groups that correct spherical aberration. It is about.

  In recent years, in an optical disc apparatus, in order to increase the recording density of an optical disc, the laser wavelength has been shortened and the objective lens has a high numerical aperture. In such an optical disc apparatus, since the influence of the spherical aberration caused by the deviation of the substrate thickness of the optical disc is great, a means for correcting the spherical aberration is necessary.

As the spherical aberration correcting means, conventionally, at least one lens of a relay lens system for correcting spherical aberration is held by a relay lens holder, and this relay lens holder is supported on a guide rail so as to be movable in the optical axis direction, The gap of the relay lens system can be varied by meshing with a feed screw extending parallel to the axial direction and rotating the feed screw with a stepping motor and moving the relay lens holder along the guide rail in the optical axis direction. A device that corrects spherical aberration is known (see, for example, Patent Document 1).
JP 200345068 A

  However, in the optical head having the spherical aberration correcting means disclosed in Patent Document 1, the guide rail, the feed screw, and the stepping motor are required, and the guide rail fixing portion and the feed screw receiving portion are required to be provided. Therefore, there is a concern that the apparatus becomes large and the cost increases.

  Accordingly, an object of the present invention made in view of such a point is to provide an optical head capable of correcting spherical aberration with high accuracy with a small and inexpensive configuration.

The invention according to claim 1, which achieves the above object, is disposed in an optical path between an objective lens for condensing a light beam emitted from a light source on a recording surface of an optical recording medium, and the light source and the objective lens. In an optical head having spherical aberration correcting means comprising a lens group for correcting the spherical aberration of the light beam,
The spherical aberration correction means is
A lens holder for holding at least one lens in the lens group;
A yoke made of a magnetic material that supports the lens holder so as to be movable in the optical axis direction;
A coil attached to the lens holder;
A magnet attached to the yoke so as to apply a magnetic field to the coil;
By passing an electric current through the coil, the lens holder is moved in the optical axis direction by electromagnetic action with the magnet to correct spherical aberration.

  According to a second aspect of the present invention, in the optical head according to the first aspect, a flag provided in the lens holder and a position detection sensor for optically detecting a position of the lens holder in the optical axis direction via the flag. It is characterized by having.

  According to a third aspect of the present invention, in the optical head according to the second aspect, the flag has a hypotenuse that is non-parallel to the moving direction of the lens holder, and the position detection sensor detects a displacement of the hypotenuse. The position of the lens holder in the optical axis direction is detected.

  According to a fourth aspect of the invention, in the optical head according to the second or third aspect of the invention, the current flowing through the coil is controlled based on the output signal of the position detection sensor.

  According to a fifth aspect of the invention, in the optical head according to any one of the first to fourth aspects, at least one other lens of the lens group is directly fixed to the yoke. Is.

  According to a sixth aspect of the present invention, in the optical head according to any one of the first to fifth aspects, the yoke has at least four plane portions, the lens holder has a cylindrical outer shape, and the yoke The cylindrical portion of the lens holder is slidably supported by the four flat portions.

  The invention according to claim 7 is the optical head according to any one of claims 1 to 6, wherein the yoke is formed by bending a plate-like member.

  According to the first aspect of the invention, since the number of parts of the spherical aberration correcting means can be reduced, the spherical aberration can be corrected with high accuracy with a small and inexpensive configuration.

  According to the invention of claim 2, since the position of the lens holder in the optical axis direction is detected, the lens holder can be positioned with high accuracy.

  According to the third aspect of the present invention, the position detection sensor can be reduced in size, the degree of freedom of the arrangement can be increased, and the shape of the peripheral component parts can be reduced accordingly, and the assemblability can be improved. it can.

  According to the invention of claim 4, since the current flowing through the coil is controlled by the output signal of the position detection sensor, the lens holder can be positioned more accurately without being affected by external vibration, and the spherical aberration is always increased. It can be corrected with accuracy.

  According to the invention of claim 5, among the lens groups for correcting spherical aberration, a lens holder to be fixedly arranged is not required, and the number of parts can be further reduced, so that further downsizing and cost reduction can be achieved. .

  According to the invention of claim 6, the yoke can be easily manufactured, the cost can be reduced, and the size can be further reduced.

  According to the invention of claim 7, since the yoke is formed by bending the plate-like member, the price can be further reduced.

  Embodiments of an optical head according to the present invention will be described below with reference to the drawings.

(First embodiment)
1 to 7 show a first embodiment of the present invention. FIG. 1 is a diagram showing a configuration of an optical system of an optical head. FIG. 2 is a perspective view showing a configuration of spherical aberration correcting means shown in FIG. 3 is a perspective view showing a lens holder of the lens driving unit shown in FIG. 2, FIG. 4 is a front view of the lens driving unit, FIG. 5 is a sectional view taken along line AA in FIG. 4, and FIG. FIG. 7 is a perspective view showing the configuration of the detection sensor, and FIG. 7 is a view for explaining the position detection operation by the position detection sensor.

  In the optical head shown in FIG. 1, linearly polarized laser light emitted from a semiconductor laser 1 that is a light source is converted into parallel light by a collimator lens 2 and enters a polarizing beam splitter 3 with, for example, P-polarized light. The polarization beam splitter 3 is formed with, for example, a P-polarized light transmittance of 80%, a P-polarized light reflectance of 20%, and an S-polarized light reflectance of 100%. The laser beam that is received and controlled by the emission power of the semiconductor laser 1 is transmitted through a laser beam whose optical path is bent 90 degrees by the rising mirror 5, passes through the quarter-wave plate 6, and the objective lens 7 forms an optical recording medium 8 such as an optical disk. Is recorded on the recording surface 8a, and information is recorded or reproduced.

  In reproducing information, the reflected light from the recording surface 8a is incident on the polarization beam splitter 3 along the same path as the forward path. Here, the return light from the optical recording medium 8 incident on the polarization beam splitter 3 is transmitted twice through the quarter wavelength plate 6 in the forward path and the return path, so that the polarization direction is orthogonal to the forward path, and the polarization beam splitter. 3 is reflected. The return light reflected by the polarization beam splitter 3 is received by a photodetector 10 through a toric lens 9 having a condensing function and an astigmatism generating function formed by joining a spherical lens and a cylindrical concave lens. Based on the output, a focus error, a tracking error, and an information reproduction signal are obtained by a known method.

  In the present embodiment, in FIG. 1, spherical aberration correction means 11 having a relay lens system including a concave lens 11b and a convex lens 11a is provided in the reciprocating optical path between the polarizing beam splitter 3 and the rising mirror 5. Provide.

  The spherical aberration correcting means 11 moves either one or both of the lenses 11a and 11b in the optical axis direction so as to correct the spherical aberration that occurs when there is an error in the thickness of the cover layer of the optical recording medium 8. Constitute. In the present embodiment, as shown in FIG. 2, the lens 11b on the semiconductor laser 1 side is fixed, and the lens 11a on the objective lens 7 side (not visible in FIG. 2) is placed in the optical axis direction by the lens driving unit 26. Drive to correct spherical aberration.

  For this reason, the lens drive unit 26 is provided with a lens holder 12 as shown in FIGS. 3 and 5, and a hole through which a light beam passes is formed in the lens holder 12, and a large diameter is formed in a stepped shape at one end thereof. The lens 11a is held in this large diameter portion. The outer periphery of the other end of the lens holder 12 is formed in a quadrangular shape, and two coils 15a, 15b, 15c, and 15d for obtaining a driving force are attached to the opposing surfaces. In the present embodiment, a total of four coils 15a to 15d are attached. However, if the driving force is large, a total of two coils, one on each opposing surface, may be used. Further, a flag 16 for guiding the movement of the lens holder 12 in the optical axis direction and detecting the movement position is provided on one surface of the lens holder 12 to which the coils 15a to 15d are not attached. Such a lens holder 12 can be made of a plastic molded part.

  On the outer periphery of the lens driving unit 26, a yoke 13 having a square hole for holding the lens holder 12 slidably in the axial direction (X direction) is disposed. The inner diameter of the square hole of the yoke 13 is set to be, for example, about 5 to 15 μm larger than the outer diameter of the cylindrical portion of the lens holder 12. Grooves are formed at positions facing the centers of the coils 15a and 15b attached to the lens holder 12 and the centers of the coils 15c and 15d on the inner surfaces facing the yoke 13, respectively. As shown in FIG. 5, the magnets 14 a and 14 b are arranged with the opposite poles facing each other. The yoke 13 is manufactured by a method such as sintering of magnetic material or lost wax.

  4 and 5, the S pole of the magnet 14a and the N pole of the magnet 14b are opposed so that the magnetic flux is directed from the magnet 14b to the magnet 14a as indicated by an arrow 31, and the magnetic flux from the magnet 14a is And return to the magnet 14b. As a result, the magnetic fluxes of the magnets 14a and 14b are mainly applied to the coil sides 32a to 32d within the range facing the magnets 14a and 14b of the coils 15a to 15d (indicated by a two-dot chain line 33 in FIG. 5). ing.

  A groove 18 in which the flag 16 protrudes is formed in the yoke 13 in the axial direction, and the outer periphery of the yoke 13 of the groove 18 is formed in a plane, and the position detection sensor 17 is attached so that the flag 16 is sandwiched between the planes. . The width of the groove 18 of the yoke 13 is set to be about 10 to 20 μm larger than the flag width so that the lens holder 12 can smoothly move in the axial direction without tilting.

  As shown in FIG. 6, the position detection sensor 17 is provided with a light emitting element 19 and a light receiving element 20 across the movement path of the flag 16, and emits light in the direction of the light receiving element 20 indicated by the arrow 21 from the light emitting element 19. Let it emit. The light receiving element 20 receives light in the light receiving range 22 shown by a two-dot chain line in FIG. 7 among the light emitted from the light emitting element 19 and outputs a signal proportional to the received light quantity. The light from the light emitting element 19 incident on the element 20 is shielded by the flag 16 to detect the position of the flag 16 in the X direction, that is, the position of the lens 11a held by the lens holder 12 over the entire moving range. .

  That is, in the case of FIG. 7, light does not reach the light shielding area 24 indicated by the oblique lines shielded by the flag 16 in the light receiving range 22 of the light receiving element 20, and light enters the remaining area. From this state, when the flag 16 moves in the X + direction, the area of the light shielding region 24 by the flag 16 is reduced, and the amount of light reaching the light receiving element 20 is increased, so that the output signal is also increased. On the contrary, when the flag 16 moves in the X-direction, the light shielding area 24 by the flag 16 increases, and the amount of light reaching the light receiving element 20 decreases, so the output signal decreases. Thus, since the position of the flag 16, that is, the position of the lens holder 12 and the output signal of the light receiving element 20 are in a proportional relationship, negative feedback control is performed using the output signal of the light receiving element 20 as a position error signal of the lens holder 12. Then, the position of the lens 11a held by the lens holder 12 is controlled.

  Hereinafter, the operation of the present embodiment will be described.

  In the present embodiment, the lens position of the relay lens system that maximizes the amplitude of the information reproduction signal of the optical recording medium 8 is calculated by a dedicated circuit (not shown), and based on the calculated lens position information. A current is passed through the coils 15a to 15d of the lens holder 12 of the lens driving unit 26 to optimally control the position of the lens 11a of the relay lens system. Thus, the spherical aberration is corrected by changing the distance between the lens 11a and the lens 11b and changing the convergence and divergence of the incident light on the objective lens 7. At this time, the position of the lens 11 a is controlled by negatively feeding back the output signal of the light receiving element 20 of the position detection sensor 17 as a position error signal of the lens holder 12.

  According to the present embodiment, compared with the configuration disclosed in Patent Document 1, the relay lens system lens 11a can be driven with a small number of parts, so that the apparatus can be made small and inexpensive. Further, since the position detection sensor 17 detects the position of the lens 11a and performs negative feedback control, the lens 11a can be positioned with high accuracy without being affected by external impact, and spherical aberration can be reduced. It can always be corrected with high accuracy.

  In the first embodiment, the lens 11b on the semiconductor laser 1 side is held by a separate member from the yoke 13, but may be directly fixed to the yoke 13 as shown in FIG. In this way, the number of parts can be further reduced, and further downsizing and cost reduction can be achieved.

(Second Embodiment)
9 to 12 show a second embodiment of the present invention. FIG. 9 is a perspective view showing a configuration of spherical aberration correcting means, FIG. 10 is a perspective view showing a lens holder of a lens driving unit, and FIG. FIG. 12 is a sectional view taken along line BB in FIG. 11. In the present embodiment, elements having the same functions as those of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the present embodiment, the yoke 13 is formed into a shape bent to a pentagonal cross section by pressing an iron plate, and the groove in which the flag 16 moves is formed by opening a gap between the mating portions when the plate is annular. 18 is formed. In addition, the coils 15 a to 15 d are arranged at the center in the X direction of the lens holder 12. The relationship between the outer diameter of the lens holder 12 and the inner dimensions of the yoke 13 is substantially the same as that in the first embodiment.

  Thus, in this embodiment, the yoke 13 is bent into a pentagonal cross section, and the cylindrical lens holder 12 is supported by the four planes so as to be movable in the axial direction. The groove 18 can be easily manufactured by press working, and the cost can be reduced. Further, by making the inner surface of the yoke 13 a plane combination, the outer surface can be easily formed into a flat shape, and can be easily attached to the optical head body. Furthermore, by arranging the coils 15a to 15d in the center portion of the lens holder 12, it becomes possible to further reduce the size, and the driving point of the lens holder 12 by the coils 15a to 15d can be positioned at the center of the lens 11a. Thus, it is possible to more reliably prevent the lens 11a from being tilted and position the lens 11a with higher accuracy.

  Needless to say, the yoke 13 is not limited to a pentagonal cross-sectional shape, and may have a triangular, quadrangular, or hexagonal cross-sectional shape. Also in the present embodiment, as shown in FIG. 8, the lens 11 b on the semiconductor laser 1 side can be directly fixed to the yoke 13.

(Third embodiment)
FIGS. 13 to 15 show a third embodiment of the present invention, FIG. 13 is a perspective view showing a lens holder of a lens driving unit, and FIG. 14 is an enlarged perspective view showing the relationship between a flag and a position detection sensor. FIG. 15 is a diagram for explaining the position detection operation by the position detection sensor. Also in the present embodiment, elements having the same functions as those of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the present embodiment, the flag 16 that detects the position of the lens holder 12 of the lens driving unit 26 has a shape having a hypotenuse 23 that is not parallel to the moving direction (X direction) of the lens holder 12. By detecting the position 23, the position of the lens holder 12 can be detected over the entire movement range.

  In this way, if the oblique side 23 that is not parallel to the moving direction is formed on the flag 16, when the flag 16 moves in the X + direction in FIG. 15, the light is blocked by the low oblique side portion 23 a of the flag 16. Since the area of the light shielding region 24 on the element 20 is reduced, the output signal of the light receiving element 20 is increased. Further, when the flag 16 moves in the X-direction, light is blocked by the high oblique side portion 23b of the flag 16, and the area of the light shielding region 24 on the light receiving element 20 is increased, so that the output signal of the light receiving element 20 is small. Become. Therefore, an output signal proportional to the position of the oblique side 23 of the flag 16, that is, the position of the lens 11 a held by the lens holder 12 is obtained from the light receiving element 20.

  According to the present embodiment, by forming the hypotenuse 23 that is not parallel to the movement direction in the flag 16, the movement of the flag 16 in the X direction is converted into the displacement of the hypotenuse 23 in the Z direction (height direction). Since the position of 11a is detected, the dimension in the X direction of the position detection sensor 17 can be made smaller and smaller than in the first and second embodiments. Accordingly, since the degree of freedom of arrangement of the position detection sensor 17 can be increased, the shape of the peripheral components can be reduced. In addition, for example, the position detection sensor 17 is assembled in advance to the yoke 13 and then the lens holder 12 is inserted into the yoke 13.

  In addition, this invention is not limited only to the said embodiment, Many deformation | transformation or a change is possible. For example, in the first or second embodiment, as shown in FIGS. 16A and 16B, an opening 16a is formed in the flag 16, and the light receiving element 20 of the position detection sensor 17 moves the flag 16. The light receiving areas 20a and 20b divided into two in the direction may be configured to detect the position of the flag 16, that is, the position of the lens 11a based on the output difference between the light receiving areas 20a and 20b. In this way, the position detection sensitivity of the flag 16 can be further increased.

  Also, as shown in FIGS. 17A and 17B, the light emitting element 19 of the position detection sensor 17 is a surface emitting LED, the light receiving element 20 is a PSD (semiconductor position detection element), and the flag 16 has a minute opening 16b. , And the light from the light emitting element 19 is received by the light receiving element 20 through the minute opening 16b of the flag 16, and the position of the flag 16 is detected from the light receiving position. In this case, preferably, a single lens is provided in the minute opening 16 b of the flag 16, thereby condensing the light from the light emitting element 19 on the light receiving element 20. In this way, the position of the flag 16, that is, the position of the lens holder 12 can be detected more accurately.

It is a figure which shows the structure of the optical system of the optical head in 1st Embodiment of this invention. It is a perspective view which shows the structure of the spherical aberration correction means shown in FIG. It is a perspective view which shows the lens holder of the lens drive unit shown in FIG. Similarly, it is a front view of a lens drive unit. It is the sectional view on the AA line of FIG. It is a perspective view which shows the structure of the position detection sensor shown in FIG. Similarly, it is a figure for demonstrating the position detection operation | movement by a position detection sensor. It is a figure which shows the modification of 1st Embodiment. It is a perspective view which shows the structure of the spherical aberration correction means in 2nd Embodiment of this invention. It is a perspective view which shows the lens holder of the lens drive unit shown in FIG. Similarly, it is a front view of a lens drive unit. It is the BB sectional drawing of FIG. It is a perspective view which shows the lens holder of the lens drive unit in the 3rd Example of this invention. It is an expansion perspective view which shows the relationship between the flag and position detection sensor in 3rd Embodiment. Similarly, it is a figure for demonstrating the position detection operation | movement by a position detection sensor. It is a figure which shows the modification of this invention. Similarly, it is a figure which shows the modification of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 Collimator lens 3 Polarizing beam splitter 4 Monitor photo detector 5 Rising mirror 6 1/4 wavelength plate 7 Objective lens 8 Optical recording medium 8a Recording surface 9 Toric lens 10 Photo detector 11 Spherical aberration correction means 11a, 11b Lens 12 Lens holder 13 Yoke 14a, 14b Magnet 15a-15d Coil 16 Flag 17 Position detection sensor 18 Groove 19 Light emitting element 20 Light receiving element 22 Light receiving range 23 Oblique side 23a Low oblique side part 23b High oblique side part 24 Light shielding area 26 Lens drive unit 32a ~ 32d Coil side

Claims (7)

An objective lens that condenses the light beam emitted from the light source on the recording surface of the optical recording medium, and a lens group that is disposed in an optical path between the light source and the objective lens and corrects spherical aberration of the light beam. In an optical head having spherical aberration correction means comprising
The spherical aberration correction means is
A lens holder for holding at least one lens in the lens group;
A yoke made of a magnetic material that supports the lens holder so as to be movable in the optical axis direction;
A coil attached to the lens holder;
A magnet attached to the yoke so as to apply a magnetic field to the coil;
An optical head configured to correct spherical aberration by causing a current to flow through the coil and moving the lens holder in an optical axis direction by electromagnetic action with the magnet.   The optical head according to claim 1, further comprising: a flag provided on the lens holder; and a position detection sensor that optically detects the position of the lens holder in the optical axis direction via the flag.   The flag has a hypotenuse not parallel to the moving direction of the lens holder, and the position detection sensor detects the position of the lens holder in the optical axis direction based on the displacement of the hypotenuse. Item 3. The optical head according to Item 2.   4. The optical head according to claim 2, wherein a current flowing through the coil is controlled based on an output signal of the position detection sensor.   The optical head according to claim 1, wherein at least one other lens in the lens group is directly fixed to the yoke.   The yoke has at least four flat portions, the lens holder has a cylindrical outer shape, and the cylindrical portion of the lens holder is slidably supported by the four flat portions of the yoke. Item 6. The optical head according to any one of Items 1 to 5.   The optical head according to claim 1, wherein the yoke is formed by bending a plate-like member.

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