JP2000304993A - Coupling lens and optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily arrange a coupling lens in an optical pickup housing. SOLUTION: The coupling lens 14 is used for the optical pickup device which performs at least one of the recording, reproduction, and erasure of information on an optical recording medium 20 by converging the divergent luminous flux emitted by a semiconductor laser 10 into a spot on the recording surface 21 of the optical recording medium 20. This coupling lens is formed of one kind of material into a single body and has aspherical surfaces as both the surfaces and different positive focal lengths in mutually orthogonal directions crossing the optical axis at right angles; and the coupling lens is arranged in the optical pickup device so that the minor-axis direction of the elliptic intensity distribution of the luminous flux emitted by the semiconductor laser matches the direction of the longer focal length, and the lens peripheral surface part has at least one flat part 14A parallel to the optical axis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coupling lens and an optical pickup device using the same.

[0002]

2. Description of the Related Art A light beam from a semiconductor laser is coupled to a subsequent optical system by a coupling lens, and the coupled light beam is collected as a light spot on a recording surface of an optical recording medium such as a CD or DVD by an objective lens. Optical pickup devices that emit light and perform at least one of recording, reproducing, and erasing of information on a recording medium are widely known. As a coupling lens for coupling a divergent light beam from a semiconductor laser to a subsequent optical system, one having a beam shaping function and configured as a single lens is intended.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to facilitate the arrangement of the above coupling lens in an optical pickup housing. Another object of the present invention is to reduce the size, cost, and ease of assembly of the optical pickup device.

[0004]

A coupling lens according to the present invention "condenses a divergent light beam radiated from a semiconductor laser as a light spot on a recording surface of an optical recording medium via a coupling lens and an objective lens. An optical pickup device for performing at least one of recording, reproducing, and erasing of information (that is, recording or reproducing or erasing, recording and reproducing, recording and erasing, reproducing and erasing, or recording and reproducing and erasing) on the optical recording medium. The coupling lens used in the present invention is characterized by the following points. That is, the coupling lens is formed as a single piece of one kind of material, has aspheric surfaces on both sides, has a different positive focal length in two directions orthogonal to the optical axis and orthogonal to each other, and is radiated from the semiconductor laser. The light beam is arranged in the optical pickup device such that the minor axis direction of the elliptic intensity distribution of the light beam coincides with the longer one of the different focal lengths. The coupling lens has “one or more flat portions parallel to the optical axis” on the lens surface. The coupling lens may have "two or more flat portions". In this case, a plurality of flat portions can be formed symmetrically with the optical axis as a symmetric axis (claim 2). The flat portion can be formed so that the cross-sectional shape of the cross section orthogonal to the axis becomes a “regular polygonal shape”. The coupling lens according to the first, second, or third aspect can be "disposed in an optical pickup housing without using a lens cell." (Claim 4). The coupling lens according to any one of claims 1 to 4 can have “a collimating function for converting a light beam from a semiconductor laser into a parallel light beam and a beam shaping function for making a light beam cross-sectional shape substantially circular” ( Claim 5). Of course, it goes without saying that the flat portion of the coupling lens is formed outside the “effective diameter at which the lens function of the coupling lens functions effectively”. The optical pickup device according to the present invention provides an optical pickup device comprising: "a divergent light beam from a semiconductor laser is coupled to a subsequent optical system by a coupling lens, and the coupled light beam is collected as a light spot on a recording surface of an optical recording medium by an objective lens. Lights and records information on the recording medium.
An optical pickup device for performing at least one of reproduction and erasure ", wherein the coupling lens according to any one of claims 1 to 5 is used as a coupling lens (claim 6). In the optical pickup device according to the sixth aspect, a receiving surface for receiving one of the flat portions of the coupling lens is formed in the optical pickup housing, and the flat portion is brought into close contact with the receiving surface, so that the coupling lens is optically driven. A predetermined attitude around the axis can be set (claim 7).

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1A, a divergent light beam emitted from a semiconductor laser
The light enters the coupling lens 14 through the optical system, and is coupled to the subsequent optical system. The light beam transmitted through the coupling lens 14 has its optical path bent by the deflecting mirror 16, enters the objective lens 18, is converted into a focused light beam by the objective lens 18, passes through the substrate of the optical recording medium 20, and is transmitted onto the recording surface 21. To form a light spot. The optical recording medium 20 is a CD, a DVD, or the like. The light beam reflected by the recording surface 21 becomes a “return light beam”, and the objective lens 18 and the deflecting mirror 1
6. Return to the focused luminous flux via the coupling lens 14,
The light is diffracted by the hologram 12 and enters the light receiving means 24. The light receiving unit 24 generates a focus error signal, a track error signal, a reproduction signal, and the like according to the light receiving state. Servo control for focusing and tracking is performed based on the focus error signal and the track error signal. FIGS. 1B and 1C are diagrams for explaining the optical characteristics of the coupling lens 14. FIG. 1 (b),
In (c), the Z direction is the optical axis direction of the coupling lens 14. As is well known, the divergence angle of a divergent light beam emitted from a semiconductor laser is the largest in the direction perpendicular to the active layer and the smallest in the direction parallel to the active layer, and the light intensity distribution on the light beam cross section is elliptical. Shape. FIG. 1 (b)
In FIG. 1, the Y direction is a direction parallel to the minor axis direction of the elliptical light intensity distribution, and in FIG. 1C, the X direction is a direction parallel to the major axis direction of the light intensity distribution. The X and Y directions are both orthogonal to the Z direction, and are orthogonal to each other. The coupling lens 14 is formed as a single piece of a single material, and has different positive focal lengths in the X direction and the Y direction. The focal length in the Y direction: f _Y is the focal length in the X direction: f. Greater than _X. In order to realize such optical characteristics, the coupling lens 14 is formed with an aspheric surface on both surfaces. As shown in FIGS. 1B and 1C, the light beam emitted from the coupling lens 14 toward the objective lens 18 is a “parallel light beam”, and the light beam diameter is substantially equal in the X direction and the Y direction. Therefore, the light beam cross-sectional shape of the light beam emitted from the coupling lens 14 toward the objective lens 18 is substantially circular. Therefore, by using the coupling lens 14, the light beam from the semiconductor laser can be taken in very efficiently, and a light spot close to a circular shape can be formed on the recording surface. Thus, the coupling lens 14
Since the use efficiency of light energy can be improved by using the information recording, information can be easily recorded, and the speed of reproduction and erasure can be increased. As shown in FIG. 1D, the coupling lens 14 has a flat portion 14A parallel to the optical axis on the peripheral surface of the lens.

That is, the coupling lens 14 described in the embodiment with reference to FIG. 1 transmits the divergent light beam radiated from the semiconductor laser 10 to the optical recording medium 20 via the coupling lens 14 and the objective lens 18. A coupling lens used in an optical pickup device that focuses as a light spot on the recording surface 21 of the optical pickup medium and performs at least one of recording, reproducing, and erasing of information on the optical recording medium 20. And both surfaces are aspherical, and the optical axis (Z direction)
Orthogonal and two orthogonal directions (X, Y directions) from each other in different positive focal distance: f _X, has a f _Y, the semiconductor laser 10
Is disposed in the optical pickup device such that the minor axis direction (Y direction) of the elliptic intensity distribution of the light beam emitted from the lens coincides with the longer one of the different focal lengths, and is disposed on the lens surface. One or more flat portions 14 parallel to the optical axis
A (claim 1). In addition, the coupling lens 14 has a collimating function for converting a light beam from the semiconductor laser 10 into a parallel light beam and a beam shaping function for making the light beam cross-sectional shape substantially circular. The optical pickup device described in the embodiment with reference to FIG. 1 couples a divergent light beam from a semiconductor laser 10 to a subsequent optical system by a coupling lens 14 and converts the coupled light beam into an objective lens 18. The optical recording medium 20
Is condensed as a light spot on the recording surface 21 of the optical recording medium 2.
In an optical pickup device which performs one or more of recording, reproducing and erasing of information with respect to 0, the coupling lens according to claims 1 and 5 is used as the coupling lens 14 (claim 6). By forming the flat portion 14A, the handling of assembling the coupling lens 14 to the optical pickup housing becomes easy. For example, FIG.
(A) shows a case where the coupling lens 14 is pressed against a corner of the optical pickup housing 30. When pressing is performed with the pressing jig 40, the flat portion 14A
By pressing, a stable pressing force can be exerted (compared to a case where a cylindrical peripheral portion is pressed).
FIG. 2B shows a case in which a jig 50 having a suction portion 51 is used, and strong adhesion is achieved by suctioning the flat portion 14A (compared to suctioning a cylindrical peripheral portion). Property is obtained. As shown in FIG. 2B, while the coupling lens 14 is being suctioned and held by the jig 50, the direction of the coupling lens 14 around the optical axis is changed to “the shorter the elliptical intensity distribution of the luminous flux emitted from the semiconductor laser. The axial direction coincides with the direction with the longer focal length ".
It can be fixed to the optical pickup housing 30 by bonding. At this time, by setting the coupling lens 14 as a “thick lens”, the coupling lens 14 can be stably installed without a lens cell. As shown in FIG. 1A, the thickness of the optical pickup device (the vertical dimension in FIG. 1A) is defined by the lens diameter of the coupling lens 14. For this reason, when the coupling lens 14 is set to “installed in the optical pickup housing using a lens cell”, the thickness of the optical pickup device is increased by the thickness of the lens cell. By disposing in an optical pickup housing without using a lens cell (claim 4), the lens cell becomes unnecessary, the thickness of the optical pickup device can be reduced, and the optical pickup device cost can be reduced by reducing the number of parts. Can be reduced.

[0007] Since the coupling lens of the present invention is "both surfaces are aspherical", resin molding is suitable for its production. In this case, if only one flat portion is formed on the peripheral surface portion, asymmetrical distortion may occur in the optical axis of the coupling lens during molding, which may deteriorate the lens function. The two flat portions 13A and 13B are formed symmetrically with the optical axis as the symmetry axis as in the coupling lens 13 shown in FIG. Flat portions 15A, 15B,
By forming 15C and 15D symmetrically with the optical axis as the symmetry axis, that is, generally, "by forming a plurality of flat portions symmetrically with the optical axis as the symmetry axis" (claim 2),
By making the “distortion” symmetrical with respect to the optical axis, the influence of the distortion can be made symmetrical with respect to the optical axis, and the deterioration of optical characteristics can be prevented from being concentrated only in a specific direction. Further, like a coupling lens 140 shown in FIG.
When the flat portion is formed so as to surround the lens peripheral surface and the “cross-sectional shape by a cross-section orthogonal to the optical axis” of the coupling lens 140 is a regular polygonal shape (claim 3).
Distortion can be reduced, and the distribution of distortion can be made uniform around the optical axis.

In FIG. 2, the coupling lens 14
Of the jigs 40 and 50 for disposing the coupling lens 14 in the optical pickup housing 30.
5 is used as the “work surface by
As shown in (1), "the position of the coupling lens is adjusted by the flat portion 14A". That is, the flat portion 1 of the coupling lens is provided on the optical pickup housing 31.
When the receiving surface 31A for receiving the 4A is formed and the flat portion 14A is brought into close contact with the receiving surface 31A, the attitude around the optical axis of the coupling lens 14 is uniquely determined. By adjusting the inclination and the inclination of the flat portion 14A in advance, and disposing the coupling lens 14 in close contact with the receiving surface 31A, the attitude around the optical axis is set to a desired attitude. (Claim 7). In FIG. 5, reference numeral 10A denotes a laser chip of a semiconductor laser. The minor axis direction η of the light intensity distribution of the divergent luminous flux emitted from the laser chip 10A is a direction parallel to the active layer, and the major axis direction 方向 is a direction orthogonal to the active layer. In the coupling lens 14, if the X and Y directions are set as shown in FIG.
The direction is the “direction with the longest focal length”, and the X direction is the “direction with the shortest focal length”. Therefore, the receiving surface 31A of the optical pickup housing 31 is set as a surface inclined by 45 degrees with respect to the directions of ξ and η as shown in FIG.
Is formed parallel to the Z axis and inclined at 45 degrees to both the X and Y axes, and the flat portion 14A is brought into close contact with the receiving surface 31A.
The attitude around the optical axis of the coupling lens 14 is changed to a desired attitude, that is, “the minor axis direction of the elliptic intensity distribution of the light beam emitted from the semiconductor laser: η is the longer of the focal lengths of the coupling lenses. Direction: coincides with Y ”, so that the coupling lens 14 is extremely easy to assemble. Of course, the inclination of the receiving surface and the inclination of the flat portion may be any as long as the attitude around the optical axis of the coupling lens can be uniquely realized, and the setting thereof is appropriate.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The coupling lens 14 in the embodiment described with reference to FIG. 1 is formed as a single body from a single material, has different positive focal lengths in the X direction and the Y direction, and Focal length in the direction: f _Y is the focal length in the X direction:
greater than f _X, are formed in both surfaces aspheric.
As a specific example of such a coupling lens,
f _X = 25 mm, at f _Y = 30 mm, given a collimating effect of collimated light beam from the semiconductor laser, the data of which has a beam shaping function of the light beam cross-section in a substantially circular shape below. This coupling lens has an effective diameter of 5 mm, an outer diameter of the lens of 6.5 mm, and a center thickness of:
8.33682 mm. Further, the flat portion is formed on an outer portion of the effective diameter. Each surface is "aspheric"
As described above, the optical axis direction is the Z axis, the two directions orthogonal to the optical axis and orthogonal to each other are the X and Y directions, and the paraxial curvature in the XZ plane is R _X ,
The paraxial curvature in the YZ plane is R _Y , the conic constant in the XZ plane is K _X ,
Let K _{Y be} the conic constant in the YZ plane, 4th order from the conical shape, 6
AR, BR, CR, and DR are the rotationally symmetric components of the deformation variables of the order 8, the order 10, and the order 10, respectively.
As BP, CP, and DP, the following equation: Z = (R _X X ² + R _Y Y ² ) / [1 + √ {1- (1 + K _X ) R _X ² X ^2- (1 + K _Y ) R _Y ² Y ² }] + AR [(1-AP) X ² + (1 + AP) Y ² ] ² + BR [(1-BP) X ² + (1 + BP) Y ² ] ³ + CR [(1 -CP) X ² + (1 + CP) Y ² ] ⁴ + DR [(1-DP) X ² + (1 + DP) Y ² ] ⁵ . Lens data (for paraxial curvature above,
The reciprocal (1 / R _X , 1 / R _Y , which gives the “paraxial radius of curvature”) is as follows.

Refractive index for light having a wavelength of 635 nm: N
₆₃₅ = 1.726879, wavelength: 785 nm the refractive index of the relative light: N ₇₈₅ = 1.718770, center thickness: 8.
33682mm first surface (the optical recording medium side) the second surface (light source _{side) 1 / R X (mm)} 31.37083 -24.94260 1 / R Y 6.44850 5.62131 K X -6.55035 0.839450 K Y 0.160280 1.860382 AR -0.509955E-5 -0.179779 E-6 BR -0.119283E-5 0.480492E-7 CR 0.466601E-6 -0.250100E-9 DR -0.360245E-7 0.144679E-6 AP -0.439089E + 1 0.309997E + 2 BP 0.841915E + 0 -0.174237 E + 1 CP 0.458520E + 0 0.560766E + 1 DP 0.436494E + 0 0.160343E +
In the data on 0, for example, "E-7" means "10 to ⁷ ".

[0011]

As described above, according to the present invention, a novel coupling lens and optical pickup device can be realized. Since the coupling lens of the present invention has a flat portion on the peripheral surface parallel to the optical axis, the workability is good and the alignment is easy when assembling into the optical pickup device. Further, the optical pickup device of the present invention can be easily assembled, realized at a small size and at low cost by using the coupling lens.

[Brief description of the drawings]

FIG. 1 is a diagram for describing one embodiment of the present invention.

FIG. 2 is a diagram for explaining a state in which a flat portion of a coupling lens is used for adjusting the position of the coupling lens.

FIG. 3 is a view showing two examples of an embodiment of the coupling lens according to the second embodiment.

FIG. 4 shows a first embodiment of the coupling lens according to claim 3;
It is a figure showing a form.

FIG. 5 is a view for explaining an embodiment of the optical pickup device according to claim 7;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Semiconductor laser 12 Hologram 14 Coupling lens 16 Deflection prism 18 Objective lens 20 Optical recording medium 21 Recording surface

Claims (7)

[Claims] A divergent light beam emitted from a semiconductor laser is condensed as a light spot on a recording surface of an optical recording medium via a coupling lens and an objective lens, and information is recorded on the optical recording medium. A coupling lens for use in an optical pickup device that performs at least one of reproduction and erasure. The coupling lens is formed as a single body from one kind of material, has two aspheric surfaces, and is perpendicular to the optical axis and in two directions perpendicular to each other. It has different positive focal lengths, and is disposed in the optical pickup device such that the minor axis direction of the elliptic intensity distribution of the light beam emitted from the semiconductor laser coincides with the longer one of the different focal lengths. And a coupling lens having at least one flat portion parallel to the optical axis on a peripheral surface of the lens. 2. The coupling lens according to claim 1, wherein the plurality of flat portions are formed symmetrically with the optical axis as a symmetric axis. 3. The coupling lens according to claim 2, wherein a cross-sectional shape of the cross-section orthogonal to the optical axis is a regular polygonal shape. 4. The coupling lens according to claim 1, wherein the coupling lens is provided in an optical pickup housing without using a lens cell. 5. The coupling lens according to claim 1, wherein the coupling lens has a collimating function for converting a light beam from the semiconductor laser into a parallel light beam and a beam shaping function for making a light beam cross-sectional shape substantially circular. A coupling lens. 6. A divergent light beam from a semiconductor laser is coupled to a subsequent optical system by a coupling lens, and the coupled light beam is focused as a light spot on a recording surface of an optical recording medium by an objective lens. An optical pickup device for performing at least one of recording, reproducing, and erasing of information on an optical recording medium, wherein the coupling lens according to any one of claims 1 to 5 is used as a coupling lens. Optical pickup device. 7. The optical pickup device according to claim 6, wherein a receiving surface for receiving one of the flat portions of the coupling lens is formed in the optical pickup housing, and the flat portion is brought into close contact with the receiving surface. An optical pickup device, wherein the coupling lens is set in a predetermined position around the optical axis.