CN100437189C - Beam shaping element and optical pickup employing it - Google Patents
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Abstract
There is provided a beam shaping element BC for converting an elliptical beam of laser light emitted from a semiconductor laser light source into a circular beam. Both of first surface S1 and second surface S2 have a curvature only in the long axis direction on the cross-section of the elliptical beam. One surface is an arcuate cylindrical surface and the other surface is a non- arcuate cylindrical surface.
Description
Technical Field
The present invention relates to a beam shaping element, and more particularly, to a beam shaping element for converting laser light emitted from a semiconductor laser light source from an elliptical beam into a circular beam in an optical pickup device, for example.
Background
A typical light source used for an optical pickup optical system is a laser diode, which emits a divergent beam having an elliptical cross-sectional shape. If the divergent light beam is converged as it is by the objective lens, only a part of the circular recording area is irradiated, or the outside of the recording area is also irradiated, thereby degrading the accuracy of recording and reproduction. Therefore, beam shaping is required so that the cross-sectional shape of the laser light forms a circle on the recording medium.
In addition, in recent years, blue semiconductor lasers have been used as laser light sources, but because of their short wavelength, the accuracy required for recording and reproducing signals is strict. In spite of such a demand, the current blue semiconductor laser has a low output, and therefore, sufficient laser power cannot be secured for high-precision recording/reproduction. This problem can be solved if the efficiency of laser light utilization is improved by converting the laser light from an elliptical beam to a circular beam. Therefore, beam shaping techniques are very important to this point.
Beam shaping is typically a method using a prism. However, to shape the beam using a prism, the laser needs to be collimated in advance. However, if the collimator lens is disposed on the light source side of the beam shaping prism in the case of, for example, a blue laser beam, various restrictions arise such as the inability to correct spherical aberration when the disk substrate has an error due to the movement of the collimator lens.
In order to avoid the above-described problems, a beam shaping element has been proposed in the past which shapes a beam by a lens surface. For example, patent document 1 proposes a beam shaping element having a deformed surface on both surfaces, and patent document 2 proposes a beam shaping element having a cylindrical surface on both surfaces. When these beam shaping elements are used, almost no aberration occurs, and the divergent beam can be directly converted from the elliptical beam into the circular beam.
Patent document 1: japanese unexamined patent publication No. 9-258099
Patent document 2: japanese laid-open patent publication No. 2002-208159
However, as proposed in patent document 1, if the surface shape of the beam shaping element is a double-surface deformed shape, it is difficult to process the metal mold. Therefore, mass production is not facilitated, resulting in an increase in cost. In addition, since the beam shaping element proposed in patent document 2 is of a type in which the beam diameter is enlarged in the minor axis direction of the elliptical beam, na (numerical aperture) of the emitted beam is increased. As a result, the laser light is incident at a large angle on a beam splitter for optical path combining/splitting disposed after the beam shaper, and it is difficult to design a film such as a pbs (polarizing beam splitter) film. Further, since the light beam is rapidly expanded, it is difficult to sufficiently secure the distance between the beam shaper and the collimator lens, and thus it is difficult to arrange the optical components after the beam shaper.
Disclosure of Invention
The present invention has been made in view of the above problems, and an object of the present invention is to provide a beam shaping element which can ensure good performance, can be easily manufactured, and is suitable for an optical pickup optical system, and an optical pickup device using the beam shaping element.
To achieve the above object, a beam shaper according to a first aspect of the present invention is a beam shaper for converting a laser beam emitted from a semiconductor laser light source from an elliptical beam to a circular beam, wherein both of a light incident side surface and a light emitting side surface have curvatures only in a major axis direction of a cross section of the elliptical beam, one surface is a circular cylindrical surface, and the other surface is a non-circular cylindrical surface, and the following conditional expression (1) is satisfied,
1≤T1/T0≤10 ...(1)
wherein T1 denotes: core thickness of the beam shaping element, T0 denotes: the on-axis optical distance between the semiconductor laser light source and the beam shaping element.
A beam shaping element according to a second aspect of the present invention is a beam shaping element for converting a laser beam emitted from a semiconductor laser light source from an elliptical beam to a circular beam, wherein both of the light incident side surface and the light emitting side surface have curvatures only in a major axis direction of a cross section of the elliptical beam, one surface is a circular-arc cylindrical surface, the other surface is a non-circular-arc cylindrical surface, and the following conditional expression (2) is satisfied,
0.05≤R1/R2≤1.1 ...(2)
wherein, for the major axis direction of the elliptical beam cross section, R1 represents: the radius of curvature of the light-incident side of the beam-shaping element, R2, denotes: the radius of curvature of the light exit side of the beam-shaping element,
the curvature radius of a surface that is convex on the light incidence side or concave on the light emission side is positive, and the curvature radius of a surface that is concave on the light incidence side or convex on the light emission side is negative.
A beam shaping element according to a third aspect of the present invention is a beam shaping element for converting a laser beam emitted from a semiconductor laser light source from an elliptical beam to a circular beam, wherein both of the light incident side surface and the light emitting side surface have curvatures only in a major axis direction of a cross section of the elliptical beam, one surface is a circular-arc cylindrical surface, and the other surface is a non-circular-arc cylindrical surface, and the following conditional expression (3) is satisfied,
0.45≤R1/T0≤1.5 ...(3)
wherein, for the major axis direction of the elliptical beam cross section, R1 represents: the radius of curvature of the light-incident side of the beam-shaping element, T0, represents: the on-axis optical distance between the semiconductor laser light source and the beam shaping element,
the curvature radius of a surface that is convex on the light incidence side or concave on the light emission side is positive, and the curvature radius of a surface that is concave on the light incidence side or convex on the light emission side is negative.
A beam shaping element according to a fourth aspect of the present invention is a beam shaping element for converting a laser beam emitted from a semiconductor laser light source from an elliptical beam into a circular beam, alone or according to any one of the first to third aspects, wherein both the light incident side surface and the light emitting side surface have curvatures only in a major axis direction of a cross section of the elliptical beam, one surface is a circular-arc cylindrical surface, and the other surface is a non-circular-arc cylindrical surface, and satisfies the following conditional expression (4),
0.1≤R1/T1≤0.6 ...(4)
wherein, for the major axis direction of the elliptical beam cross section, R1 represents: the radius of curvature of the light-incident side of the beam-shaping element, T1, represents: the core of the beam-shaping element is thick,
the curvature radius of a surface that is convex on the light incidence side or concave on the light emission side is positive, and the curvature radius of a surface that is concave on the light incidence side or convex on the light emission side is negative.
Further, an optical pickup device is provided with: a semiconductor laser light source for emitting an elliptical beam; the beam shaping element according to any one of the first to fourth aspects; and an objective lens for imaging the light from the beam shaping element on a recording medium.
According to the present invention, since both the circular cylindrical surface and the non-circular cylindrical surface have curvatures only in the major axis direction of the elliptical beam cross section, it is possible to realize a light-weight, small-sized, high-performance beam shaping element which is easy to manufacture, suitable for an optical pickup optical system, and capable of obtaining a high shaping magnification. Further, when the beam shaping element of the present invention is used in an optical pickup device, the accuracy of recording/reproduction can be improved, and the utilization efficiency of laser light is improved, so that the present invention can be applied to a blue semiconductor laser.
Drawings
Fig. 1A is an optical configuration diagram showing an embodiment (example 1) of a beam shaping element;
fig. 1B is an optical configuration diagram showing an embodiment (example 1) of a beam shaping element;
fig. 2 is an optical configuration diagram showing a state in which the beam shaping element of fig. 1A, B is disposed in an optical path from the laser light source to the collimator lens;
fig. 3 is a schematic diagram showing the main structure of an optical pickup device equipped with the beam shaping element of fig. 1A, B;
FIG. 4 is a graph showing the effect of core thickness on design performance using the beam shaping element of FIG. 1A, B;
FIG. 5A is an aberration diagram showing the axial wavefront aberration of example 1;
FIG. 5B is an aberration diagram showing the axial wavefront aberration of example 1;
FIG. 6A is an aberration diagram showing the axial wavefront aberration of example 2;
FIG. 6B is an aberration diagram showing the axial wavefront aberration of example 2;
FIG. 7A is an aberration diagram showing the axial wavefront aberration of example 3;
FIG. 7B is an aberration diagram showing the axial wavefront aberration of example 3;
FIG. 8A is an aberration diagram showing the axial wavefront aberration of example 4;
FIG. 8B is an aberration diagram showing the axial wavefront aberration of example 4;
FIG. 9A is an aberration diagram showing the axial wavefront aberration of example 5;
FIG. 9B is an aberration diagram showing the axial wavefront aberration of example 5;
FIG. 10A is an aberration diagram showing the axial wavefront aberration of example 6;
FIG. 10B is an aberration diagram showing the axial wavefront aberration of example 6;
FIG. 11A is an aberration diagram showing axial wavefront aberration of example 7;
FIG. 11B is an aberration diagram showing axial wavefront aberration of example 7;
FIG. 12A is an aberration diagram showing axial wavefront aberration of example 8;
FIG. 12B is an aberration diagram showing axial wavefront aberration of example 8;
FIG. 13A is an aberration diagram showing axial wavefront aberration of example 9;
FIG. 13B is an aberration diagram showing axial wavefront aberration in example 9;
FIG. 14A is an aberration diagram showing axial wavefront aberration in example 10;
FIG. 14B is an aberration diagram showing the axial wavefront aberration of example 10;
FIG. 15A is an aberration diagram showing axial wavefront aberration of example 11;
FIG. 15B is an aberration diagram showing axial wavefront aberration of example 11;
FIG. 16A is an aberration diagram showing axial wavefront aberration of example 12;
FIG. 16B is an aberration diagram showing the axial wavefront aberration of example 12;
FIG. 17A is an aberration diagram showing axial wavefront aberration of example 13;
FIG. 17B is an aberration diagram showing axial wavefront aberration of example 13;
FIG. 18A is an aberration diagram showing axial wavefront aberration of example 14;
FIG. 18B is an aberration diagram showing axial wavefront aberration in example 14.
Detailed Description
Next, a beam shaping element and the like embodying the present invention will be described with reference to the drawings. Fig. 1A, B shows an embodiment of the beam shaper BC in optical cross-section. Fig. 2 shows a state where the beam shaper BC is arranged on the optical path from the laser light source 1 to the collimator lens 6 in an optical cross section, and fig. 3 schematically shows the main configuration of the optical pickup device equipped with the beam shaper BC. In the orthogonal coordinate system (X, Y, Z), if the major axis direction of the elliptical beam cross section of the laser beam is the X direction, the minor axis direction is the Y direction, and the optical axis AX direction is the Z direction, fig. 1A shows the XZ cross section of the beam shaper BC, fig. 1B shows the YZ cross section of the beam shaper BC, and fig. 2 and 3 show the XZ cross section, respectively.
The optical pickup device shown in fig. 3 can record and reproduce optical information on and from the optical information recording medium. As the laser light source 1, for example, a semiconductor laser light source (LD) emitting a laser beam with a wavelength of 407.7nm is used. The laser beam emitted from the laser light source 1 is incident on the beam shaper BC, and is converted from an elliptical beam into a circular beam (the beam cross-sectional shape is circular or quasi-circular) in a divergent state by the beam shaper BC.
The beam shaper BC is a type of beam shaper for reducing the beam diameter in the major axis direction (X direction) of the cross section of an elliptical beam in order to convert a laser beam from an elliptical beam to a circular beam. Therefore, as shown in fig. 1A, B, both the 1 st surface S1 (light incident side surface) and the 2 nd surface S2 (light emitting side surface) of the beam shaper BC have curvatures only in the major axis direction (X direction) of the elliptical beam cross section of the laser light, and the 1 st surface S1 is shaped such that the convex surface faces the light incident side and the 2 nd surface S2 is shaped such that the concave surface faces the light emitting side in the X direction. Further, one of the 1 st surface S1 and the 2 nd surface S2 is a circular cylindrical surface, and the other surface is a non-circular cylindrical surface. That is, the cross section of the cylindrical surface of one surface having the direction of curvature thereof forms an arc, and the cross section of the cylindrical surface of the other surface having the direction of curvature thereof forms a non-arc.
The laser beam shaped into a circular beam by the beam shaping element BC is reflected upward by the mirror 2, passes through the 1/2 wavelength plate 3, and is converted from S-polarized light to P-polarized light. Then, for tracking error detection, the light beam is split by the diffraction grating 4 and then enters the polarization beam splitter 5 for optical path multiplexing/demultiplexing. The light beam is transmitted through a pbs (polarizing beam splitter) film 5a provided inside the polarization beam splitter 5 as it is, and is emitted from the polarization beam splitter 5. Then, the light enters the collimator lens 6, is collimated into parallel light, passes through the 1/4 wavelength plate 10 and the objective lens 11 in this order, and forms an image on the optical recording surface 12a of the optical information recording medium 12. The laser beam reflected by the optical recording surface 12a of the optical information recording medium 12 returns along the optical path and enters the polarization beam splitter 5 again. Since the laser light passes through the 1/4 wavelength plate 10 twice, the laser light is reflected as S-polarized light by the PBS film 5a and then emitted from the polarization beam splitter 5. Then, in order to detect the focus error, the beam is split by the hoe (pharmaceutical optical element)7, and then the beam is passed through the cylindrical lens 8 for condensing the detection light of the tracking and focus error, and the signal light is detected by the photodiode 9.
As in the beam shaping element BC of the present embodiment, in the beam shaping element for converting the laser light emitted from the semiconductor laser light source from an elliptical beam to a circular beam, both the light incident side surface and the light emitting side surface have curvatures only in the major axis direction of the cross section of the elliptical beam, and it is preferable that one surface is a circular cylindrical surface and the other surface is a non-circular cylindrical surface. The light incident side surface and the light exit side surface have curvatures only in the major axis direction (X direction) of the elliptical beam cross section, and thus, a beam having a reduced beam diameter in the major axis direction of the elliptical beam cross section can be shaped, and a beam shaping element having a high shaping magnification and suitable for mass production can be realized. Since the na (numerical aperture) on the light exit side can be reduced by reducing the beam diameter in the major axis direction of the elliptical beam cross section, for example, the curvature of the collimator lens 6 (fig. 3) disposed later can be reduced, and the manufacture of the collimator lens 6 can be facilitated. As for the design of the PBS film 5a (fig. 3) of the polarization beam splitter 5, the number of layers can be greatly reduced/simplified as the incident angle becomes smaller, and the manufacturing cost can be reduced by improving the yield as the manufacturing error of the film design is reduced. Further, since the distance from the beam shaping element to the collimator lens can be increased, a beam splitter, a doe (dispersive optical element) for splitting a beam, and the like can be easily arranged between the beam shaping element and the collimator lens.
As for the surface shape of the beam shaping element, as described above, by using the cylindrical surfaces for both surfaces, the die processing becomes very easy as compared with the case of using the deformed surfaces. Therefore, the yield can be improved, the manufacturing cost can be reduced, and the assembly and adjustment of the beam shaping element are easy. Further, by making one surface a circular cylindrical surface and making the other surface a non-circular cylindrical surface, advantages in optical performance and advantages in manufacturing can be obtained at the same time. If both surfaces are non-circular cylindrical surfaces, the parallel decentering sensitivity requirement becomes strict for the surfaces having different directions of curvature, and therefore the manufacturing yield at the time of lens molding is deteriorated, and it is not suitable for mass production. Further, if both surfaces are cylindrical surfaces, high-order aberrations occur in a large amount, and thus good design performance cannot be obtained, and it is difficult to ensure a high shaping magnification. Therefore, the beam shaping element preferably has a structure having both a circular cylindrical surface and a non-circular cylindrical surface.
The above-described effects can be obtained regardless of whether the light incident side is a non-circular-arc cylindrical surface and the light exit side is a circular-arc cylindrical surface or the light incident side is a circular-arc cylindrical surface and the light exit side is a non-circular-arc cylindrical surface. In addition, as in the present embodiment, in a type in which the beam diameter is reduced in the major axis direction (X direction) of the elliptical beam cross section, it is preferable that the light incident side is a convex surface and the light emitting side is a concave surface. Thus, the beam shaping element with better design performance and easy manufacture can be obtained.
As described above, the light incident side surface and the light exit side surface of the beam shaping element both have curvatures only in the long axis direction of the elliptical beam cross section, and one surface is a circular cylindrical surface and the other surface is a non-circular cylindrical surface, whereby the beam shaping element can be easily manufactured, and a structure suitable for an optical pickup optical system can be realized, and weight reduction, size reduction, and high performance can be realized. Further, when such a beam shaping element is used in an optical pickup device, it can contribute to light weight, miniaturization, and cost reduction of the entire device. Next, conditions for obtaining such an effect in a well-balanced manner and achieving a high shaping magnification, higher optical performance, and the like will be described.
The relationship between the light source position and the beam shaping element preferably satisfies the following conditional expression (1),
1≤T1/T0≤10 ...(1)
wherein,
t1 denotes: the core thickness of the beam shaping element,
T0 denotes: the on-axis optical distance between the semiconductor laser light source and the beam shaping element.
If the upper limit of the conditional expression (1) is exceeded, the beam shaping element becomes very large, which inevitably increases the cost and the size and weight of the entire system. On the other hand, if the lower limit of the conditional expression (1) is exceeded, high-order aberration is greatly generated, and it is difficult to ensure good design performance. In addition, since the radius of curvature of the 1 st surface tends to decrease, it is difficult to manufacture.
Fig. 4 graphically shows the relationship between T1/T0 (shaping magnification is 2.0 times, and T0 is 1.6) and design performance defined by conditional expression (1). The line plotted at ● shows the design performance when NA on the light incident side becomes 0.24 due to wavefront aberration, the line plotted at diamond-solid shows the design performance when NA on the light incident side becomes 0.22 due to wavefront aberration, and the line plotted at a-solidup shows the design performance when NA on the light incident side becomes 0.20 due to wavefront aberration. As can be seen from this graph, a high shaping magnification and good design performance can be achieved at the same time in the condition range specified by the conditional expression (1). In addition, the design performance shown in fig. 4 is such that spherical aberration is disregarded. Since the spherical aberration generated by the beam shaper is removed by combining with the subsequent collimator lens, the spherical aberration is ignored in designing, and the amount of aberration other than the spherical aberration is used to indicate the design performance.
More preferably satisfies the following conditional expression (1a),
1≤T1/T0≤3 ...(1a)
the conditional expression (1a) defines a more preferable range of conditions from the above viewpoint and the like, within the range of conditions defined by the conditional expression (1).
The power on both sides of the beam shaping element preferably satisfies the following conditional expression (2),
0.05≤R1/R2≤1.1 ...(2)
wherein, for the long axis direction of the elliptical beam cross section,
r1 represents: the radius of curvature of the light incident side of the beam shaper,
R2 represents: the radius of curvature of the light exit side of the beam-shaping element,
the curvature radius of a surface that is convex on the light incidence side or concave on the light emission side is positive, and the curvature radius of a surface that is concave on the light incidence side or convex on the light emission side is negative.
If the upper limit of the conditional expression (2) is exceeded, high-order aberrations occur in a large amount, and it is difficult to ensure good design performance. On the contrary, if the lower limit of the conditional expression (2) is exceeded, the beam shaping element becomes very large, which inevitably increases the cost and the size and weight of the entire system.
More preferably satisfies the following conditional expression (2a),
0.35≤R1/R2≤1.1 ...(2a)
the conditional expression (2a) defines a more preferable range of conditions from the above viewpoint and the like, within the range of conditions defined by the conditional expression (2).
The relationship between the power of the light incident side of the beam shaper and the object distance preferably satisfies the following conditional expression (3),
0.45≤R1/T0≤1.5 ...(3)
wherein, for the long axis direction of the elliptical beam cross section,
r1 represents: the radius of curvature of the light incident side of the beam shaper,
T0 denotes: the on-axis optical distance between the semiconductor laser light source and the beam shaping element,
the curvature radius of a surface that is convex on the light incidence side or concave on the light emission side is positive, and the curvature radius of a surface that is concave on the light incidence side or convex on the light emission side is negative.
If the upper limit of the conditional expression (3) is exceeded, the beam shaping element becomes very large, and it becomes difficult to miniaturize the entire optical pickup system. On the other hand, if the lower limit of the conditional expression (3) is exceeded, the radius of curvature of the 1 st surface is too small to be manufactured.
More preferably satisfies the following conditional expression (3a),
0.5≤R1/T0≤1 ...(3a)
the conditional expression (3a) defines a more preferable range of conditions from the above viewpoint and the like within the range of conditions defined by the conditional expression (3).
The relationship between the power and the core thickness of the light incident surface of the beam shaper preferably satisfies the following conditional expression (4),
0.1≤R1/T1≤0.6 ...(4)
wherein, for the long axis direction of the elliptical beam cross section,
r1 represents: the radius of curvature of the light incident side of the beam shaper,
T1 denotes: the core of the beam-shaping element is thick,
the curvature radius of a surface that is convex on the light incidence side or concave on the light emission side is positive, and the curvature radius of a surface that is concave on the light incidence side or convex on the light emission side is negative.
If the upper limit of the conditional expression (4) is exceeded, high-order aberrations occur in a large amount, and it is difficult to ensure good design performance. On the contrary, if the lower limit of the conditional expression (4) is exceeded, the beam shaping element becomes very large, and it becomes difficult to miniaturize the entire optical pickup system.
More preferably satisfies the following conditional expression (4a),
0.3≤R1/T1≤0.6 ...(4a)
the conditional expression (4a) defines a more preferable range of conditions from the above viewpoint and the like, within the range of conditions defined by the conditional expression (4).
The non-circular cylindrical surface constituting one surface of the beam shaping element preferably satisfies the following conditional expression (5),
-0.45≤AR×fx3≤0.45 ...(5)
wherein,
AR represents: from the rotational symmetry component of the 4-order deformation coefficient of the cone,
fx represents: the focal length in the shaping direction of the beam shaping element (i.e., the major axis direction of the elliptical beam cross section of the laser).
The conditional expression (5) defines a preferable range of conditions for achieving high performance of the beam shaping element, and if it exceeds the upper limit or the lower limit of the conditional expression (5), high-order aberration occurs, and thus good design performance cannot be obtained. Further, the non-circular cylindrical surface constituting one surface of the beam shaping element is defined by the following expression (AAS) expressing the surface shape of the non-circular surface,
Z＝(X2/Rx+Y2/Ry)/[1+[1-(1+Kx)·X2/Rx2-(1+Ky)·Y2/Ry2]1/2]+AR·[(1-AP)·X2+(1+AP)·Y2]2+BR·[(1-BP)·X2+(1+BP)·Y2]3+CR·[(1-CP)·X2+(1+CP)·Y2]4+DR·[(1-DP)·X2+(1+DP)·Y3]5 ...(AAS)
wherein,
x, Y denotes: relative to a rectangular coordinate in a plane perpendicular to the optical axis AX,
z represents: the displacement amount (plane vertex reference) in the optical axis AX direction at the position of the coordinate (X, Y),
rx represents: paraxial radius of curvature in the X direction [ ═ Rxi (i ═ 1, 2) ],
ry represents: paraxial radius of curvature in the Y direction [ ═ Ryi (i ═ 1, 2) ],
kx represents: the coefficient of the cone in the X-direction,
ky denotes: the coefficient of the cone in the Y-direction,
AR, BR, CR, DR: from the rotational symmetry components of the 4 th, 6 th, 8 th and 10 th order deformation coefficients of the cone,
AP, BP, CP, DP represent: non-rotationally symmetric components from 4, 6, 8, 10 th order deformation coefficients of the cone.
Further, the above-described embodiments and the examples described later include the following configurations (P1) to (P5) and the like, and according to the configuration of the beam shaping element, since the circular cylindrical surface and the non-circular cylindrical surface are both configured to have curvature only in the major axis direction of the cross section of the elliptical beam, the beam shaping element is lightweight, compact, high-performance, and easy to manufacture, is suitable for an optical pickup optical system, and can realize a beam shaping element capable of obtaining a high shaping magnification. Therefore, the recording/reproducing accuracy can be improved, and the laser light utilization efficiency can be improved, so that the laser light can be applied to a blue semiconductor laser light.
(P1) an optical pickup optical system comprising a beam shaping element for converting a laser beam emitted from a semiconductor laser light source from an elliptical beam into a circular beam, wherein both of a light incident side surface and a light emitting side surface of the beam shaping element have curvatures only in a major axis direction of a cross section of the elliptical beam, one surface is a circular-arc cylindrical surface, and the other surface is a non-circular-arc cylindrical surface, and at least one of the conditional expressions (1), (1a), (2a), (3a), (4a), (5) is satisfied.
(P2) the optical pickup optical system according to the above (P1), wherein a light incident side of the beam shaping element is a non-circular cylindrical surface, and a light exit side of the beam shaping element is a circular cylindrical surface.
(P3) the optical pickup optical system according to the above (P1), wherein a light incident side of the beam shaper is a circular cylindrical surface, and a light emitting side of the beam shaper is a non-circular cylindrical surface.
(P4) the optical pickup optical system according to any one of (P1) to (P3) above, wherein a light incident side of the beam shaper is convex, and a light emitting side of the beam shaper is concave.
(P5) the optical pickup optical system according to any one of (P1) to (P4) above, further comprising a collimator optical system for collimating the laser beam converted into the circular beam by the beam shaping element.
Examples
Next, the optical structure of the beam shaping element according to the present invention will be described in more detail with reference to the structural data and the like. Examples 1 to 14 listed here embody the optical structure corresponding to the above-described embodiment (fig. 1A, B) as a numerical example, and example 1 is also a numerical example having the same shape as the above-described embodiment.
Tables 1 to 14 show the configuration data of examples 1 to 14, and table 15 shows data corresponding to parameters defined by the conditional expressions for the respective examples. In each configuration data, λ is a design wavelength (nm), fx is a focal length in the X direction, fy is a focal length in the Y direction, NAx on the light incident side is a numerical aperture in the X direction on the laser incident side, NAx on the light emitting side is a numerical aperture in the X direction on the laser emitting side, and W is residual aberration (m λ rms). And the X direction is the major axis direction of the elliptical beam cross-section and the Y direction is the minor axis direction of the elliptical beam cross-section.
In each configuration data, Si (i is 0, 1, 2) is the i-th surface from the object side, for example, S0 is the light emitting surface of the laser light source 1 corresponding to the object surface, S1 is the light incident side surface (1 st surface) of the beam shaping element BC, and S2 is the light emitting side surface (2 nd surface) of the beam shaping element BC. In addition, Rxi (i is 0, 1, 2) is a paraxial radius of curvature (mm) in the X direction of the surface Si, and Ryi (i is 0, 1, 2) is a paraxial radius of curvature (mm) in the Y direction of the surface Si. Ti (i ═ 0, 1) is the on-axis surface spacing (mm) between the surface Si and the surface Si +1, and Ni (i ═ 0, 1) is the refractive index for the wavelength λ of the medium located at the on-axis surface spacing Ti. The surface Si with the chevron mark is a non-circular cylindrical surface and is defined by the above expression (AAS) representing the surface shape of the non-circular cylindrical surface. In tables 1 to 14, the data of the non-circular arc surfaces of the respective examples are shown in combination. However, the coefficient of the unmarked term is 0, and E-n is × 10 for all data-n，E+n＝×10+n。
Fig. 5A, B to 18A, B are aberration diagrams corresponding to examples 1 to 14, respectively, and show axial wavefront aberrations for light having a wavelength λ of 407.7 nm. However, in fig. 5A, B to 18A, B, a represents the wave front aberration in the Y direction, and B represents the wave front aberration in the X direction. In addition, the design performance of each aberration diagram representation ignores spherical aberration. Since the spherical aberration generated by the beam shaper is removed by combining with the subsequent collimator lens, the spherical aberration is ignored in designing, and the amount of aberration other than the spherical aberration is used to indicate the design performance.
TABLE 1
TABLE 2
TABLE 3
TABLE 4
TABLE 5
TABLE 6
TABLE 7
TABLE 8
TABLE 9
TABLE 11
TABLE 12
Watch 13
TABLE 14
Claims (10)
1. A beam shaping element for converting laser light emitted from a semiconductor laser light source from an elliptical beam to a circular beam,
both the light incident side surface and the light exit side surface have curvatures only in the major axis direction of the elliptical beam cross section, one surface is a circular arc cylindrical surface, the other surface is a non-circular arc cylindrical surface, and the following conditional expression (2) is satisfied,
0.05≤R1/R2≤1.1 ...(2)
wherein, for the long axis direction of the elliptical beam cross section,
r1 represents: the radius of curvature of the light-incident side of the beam-shaping element,
r2 represents: the radius of curvature of the light exit side of the beam-shaping element,
the curvature radius of a surface that is convex on the light incidence side or concave on the light emission side is positive, and the curvature radius of a surface that is concave on the light incidence side or convex on the light emission side is negative.
2. A beam shaping element for converting laser light emitted from a semiconductor laser light source from an elliptical beam to a circular beam,
both the light incident side surface and the light exit side surface have curvatures only in the major axis direction of the elliptical beam cross section, one surface is a circular arc cylindrical surface, the other surface is a non-circular arc cylindrical surface, and the following conditional expression (1) is satisfied,
1≤T1/T0≤10 ...(1)
wherein,
t1 denotes: the core of the beam-shaping element is thick,
t0 denotes: the on-axis optical distance between the semiconductor laser light source and the beam shaping element,
and
satisfies the following conditional expression (2),
0.05≤R1/R2≤1.1 ...(2)
wherein, for the long axis direction of the elliptical beam cross section,
r1 represents: the radius of curvature of the light-incident side of the beam-shaping element,
r2 represents: the radius of curvature of the light exit side of the beam-shaping element,
the curvature radius of a surface that is convex on the light incidence side or concave on the light emission side is positive, and the curvature radius of a surface that is concave on the light incidence side or convex on the light emission side is negative.
3. A beam shaping element for converting laser light emitted from a semiconductor laser light source from an elliptical beam to a circular beam,
both the light incident side surface and the light exit side surface have curvatures only in the major axis direction of the elliptical beam cross section, one surface is a circular arc cylindrical surface, the other surface is a non-circular arc cylindrical surface, and the following conditional expression (3) is satisfied,
0.45≤R1/T0≤1.5 ...(3)
wherein, for the long axis direction of the elliptical beam cross section,
r1 represents: the radius of curvature of the light-incident side of the beam-shaping element,
t0 denotes: the on-axis optical distance between the semiconductor laser light source and the beam shaping element,
the curvature radius of a surface that is convex on the light incidence side or concave on the light emission side is positive, and the curvature radius of a surface that is concave on the light incidence side or convex on the light emission side is negative.
4. A beam shaping element for converting laser light emitted from a semiconductor laser light source from an elliptical beam to a circular beam,
both the light incident side surface and the light exit side surface have curvatures only in the major axis direction of the elliptical beam cross section, one surface is a circular arc cylindrical surface, the other surface is a non-circular arc cylindrical surface, and the following conditional expression (1) is satisfied,
1≤T1/T0≤10 ...(1)
wherein,
t1 denotes: the core of the beam-shaping element is thick,
t0 denotes: on-axis optical distance between semiconductor laser light source and beam shaping element, an
Satisfies the following conditional expression (3),
0.45≤R1/T0≤1.5 ...(3)
wherein, for the long axis direction of the elliptical beam cross section,
r1 represents: the radius of curvature of the light-incident side of the beam-shaping element,
t0 denotes: the on-axis optical distance between the semiconductor laser light source and the beam shaping element,
the curvature radius of a surface that is convex on the light incidence side or concave on the light emission side is positive, and the curvature radius of a surface that is concave on the light incidence side or convex on the light emission side is negative.
5. The beam-shaping element of claim 1,
satisfies the following conditional expression (3),
0.45≤R1/T0≤1.5 ...(3)
wherein, for the long axis direction of the elliptical beam cross section,
r1 represents: the radius of curvature of the light-incident side of the beam-shaping element,
t0 denotes: the on-axis optical distance between the semiconductor laser light source and the beam shaping element,
the curvature radius of a surface that is convex on the light incidence side or concave on the light emission side is positive, and the curvature radius of a surface that is concave on the light incidence side or convex on the light emission side is negative.
6. The beam-shaping element of claim 2,
satisfies the following conditional expression (3),
0.45≤R1/T0≤1.5 ...(3)
wherein, for the long axis direction of the elliptical beam cross section,
r1 represents: the radius of curvature of the light-incident side of the beam-shaping element,
t0 denotes: the on-axis optical distance between the semiconductor laser light source and the beam shaping element,
the curvature radius of a surface that is convex on the light incidence side or concave on the light emission side is positive, and the curvature radius of a surface that is concave on the light incidence side or convex on the light emission side is negative.
7. A beam shaping element for converting laser light emitted from a semiconductor laser light source from an elliptical beam to a circular beam,
both the light incident side surface and the light exit side surface have curvatures only in the major axis direction of the elliptical beam cross section, one surface is a circular arc cylindrical surface, the other surface is a non-circular arc cylindrical surface, and the following conditional expression (1) and conditional expression (4) are satisfied,
1≤T1/T0≤10 ...(1)
wherein,
t1 denotes: the core of the beam-shaping element is thick,
t0 denotes: the on-axis optical distance between the semiconductor laser light source and the beam shaping element,
in addition, the first and second substrates are,
0.1≤R1/T1≤0.6 ...(4)
wherein, for the long axis direction of the elliptical beam cross section,
r1 represents: the radius of curvature of the light-incident side of the beam-shaping element,
t1 denotes: the core of the beam-shaping element is thick,
the curvature radius of a surface that is convex on the light incidence side or concave on the light emission side is positive, and the curvature radius of a surface that is concave on the light incidence side or convex on the light emission side is negative.
8. A beam shaping element for converting laser light emitted from a semiconductor laser light source from an elliptical beam to a circular beam,
both the light incident side surface and the light exit side surface have curvatures only in the major axis direction of the elliptical beam cross section, one surface is a circular arc cylindrical surface, the other surface is a non-circular arc cylindrical surface, and the following conditional expression (2) and conditional expression (4) are satisfied,
0.05≤R1/R2≤1.1 ...(2)
0.1≤R1/T1≤0.6 ...(4)
wherein, for the long axis direction of the elliptical beam cross section,
r1 represents: the radius of curvature of the light incident side of the beam shaper,
R2 represents: the radius of curvature of the light exit side of the beam shaper,
T1 denotes: the core of the beam-shaping element is thick,
the curvature radius of a surface that is convex on the light incidence side or concave on the light emission side is positive, and the curvature radius of a surface that is concave on the light incidence side or convex on the light emission side is negative.
9. A beam shaping element for converting laser light emitted from a semiconductor laser light source from an elliptical beam to a circular beam,
both the light incident side surface and the light exit side surface have curvatures only in the major axis direction of the elliptical beam cross section, one surface is a circular arc cylindrical surface, the other surface is a non-circular arc cylindrical surface, and the following conditional expression (3) and conditional expression (4) are satisfied,
0.45≤R1/T0≤1.5 ...(3)
0.1≤R1/T1≤0.6 ...(4)
wherein, for the long axis direction of the elliptical beam cross section,
r1 represents: the radius of curvature of the light-incident side of the beam-shaping element,
t0 denotes: the on-axis optical distance between the semiconductor laser light source and the beam shaping element,
t1 denotes: the core of the beam-shaping element is thick,
the curvature radius of a surface that is convex on the light incidence side or concave on the light emission side is positive, and the curvature radius of a surface that is concave on the light incidence side or convex on the light emission side is negative.
10. An optical pickup device includes:
a semiconductor laser light source for emitting an elliptical beam;
a beam-shaping element as claimed in any one of claims 1 to 9;
an objective lens for imaging the light from the beam shaping element on a recording medium.
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Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH04263131A (en) * | 1991-02-18 | 1992-09-18 | Ricoh Co Ltd | Beam shaping apparatus |
| JPH08307006A (en) * | 1995-05-11 | 1996-11-22 | Ricoh Co Ltd | Semiconductor laser |
| US5917660A (en) * | 1994-07-13 | 1999-06-29 | Nikon Corporation | Beam converting optical system |
| JP2002208159A (en) * | 2001-01-12 | 2002-07-26 | Minolta Co Ltd | Light beam irradiating optical system and optical pickup |
| JP2003178480A (en) * | 2001-12-10 | 2003-06-27 | Minolta Co Ltd | Light source device and optical pickup |
| US20030128439A1 (en) * | 2001-12-14 | 2003-07-10 | Minolta Co., Ltd. | Light source device and optical pickup |
-
2005
- 2005-03-14 CN CNB2005800094510A patent/CN100437189C/en not_active Expired - Fee Related
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH04263131A (en) * | 1991-02-18 | 1992-09-18 | Ricoh Co Ltd | Beam shaping apparatus |
| US5917660A (en) * | 1994-07-13 | 1999-06-29 | Nikon Corporation | Beam converting optical system |
| JPH08307006A (en) * | 1995-05-11 | 1996-11-22 | Ricoh Co Ltd | Semiconductor laser |
| JP2002208159A (en) * | 2001-01-12 | 2002-07-26 | Minolta Co Ltd | Light beam irradiating optical system and optical pickup |
| JP2003178480A (en) * | 2001-12-10 | 2003-06-27 | Minolta Co Ltd | Light source device and optical pickup |
| US20030128439A1 (en) * | 2001-12-14 | 2003-07-10 | Minolta Co., Ltd. | Light source device and optical pickup |
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