JPH04362608A - Beam expander and optical head using the same - Google Patents

Abstract

PURPOSE:To expand the beam diameter of parallel light by an afocal optical system which has short overall lens length while holding the light parallel by setting a specific condition for the overall length of the afocal optical system, the expansion rate of the diameter of the beam, and the diameter of the projection beam. CONSTITUTION:In the afocal optical system which expands the parallel incident beam and emits the parallel light, a 1st lens with negative power and a 2nd lens with positive power is arranged from the incidence side. When the incident beam is transmitted through the 1st lens having an aspherical surface and the 2nd lens, the condition shown by an inequality is satisfied. In the inequality, L is the overall length of the lens, D is the emitting beam diameter, and (m) is the expansion rate. This constitution corrects a spherical aberration and a sine condition even when the overall lens length is shortened to hold a wave front aberration within a diffraction limit. Consequently, the compact, high- performance beam expander which consists of one or two lenses and has short overall lens length is obtained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a beam expander that expands the diameter of a beam such as a laser beam, and more particularly to a beam expander that can be made smaller and lighter by utilizing an aspheric surface or a refractive index distribution.

0002

[Prior Art] In an optical disk device, light emitted from a semiconductor laser is converted into parallel light by a collimating lens.
Furthermore, an objective lens focuses the laser beam to read or write information. However, in order to increase the density and store information, it is necessary to use a light source with a short wavelength, and gas lasers and the second harmonic of NdYAG lasers have come to be used instead of conventional semiconductor lasers. . However, unlike semiconductor lasers, these light sources are often parallel lights with a diameter of 1 mm or less. When parallel light with a diameter of 1 mm or less is used, the focal length of the objective lens becomes correspondingly short, making it difficult to maintain a sufficient working distance between the disk and the lens. Therefore, a beam expander is used to expand the diameter of the laser beam while it remains parallel. Conventionally, this beam expander has been made of a combination of multiple spherical lenses. (For example, "How to use optical parts and points to keep in mind" pages 78-81, Optronics Inc.)

00
03]

[Problems to be Solved by the Invention] However, in the beam expander as described above, the total length of the assembled lens becomes long, making it impossible to realize a small and lightweight light source. For example, a beam expander with a beam expansion rate of 10 times and an output beam diameter of 4 mm is constructed using a spherical concave lens and a convex lens.
FIG. 9 shows the change in wavefront aberration due to the change in the total length of the lens when a combination of lenses is used. As the total length of the assembled lens is shortened, wavefront aberration increases rapidly, making it unusable. Furthermore, when the overall length is shortened, attempting to remove aberrations increases the number of lenses, making assembly difficult and expensive.

In view of the above-mentioned problems, the present invention consists of one or two lenses, and has a short overall length.
It provides a compact and high-performance beam expander.

[0005]

[Means for Solving the Problems] In order to solve the above problems, the beam expander of the present invention is an afocal optical system that expands an incident beam that is parallel light and emits it again as parallel light. The first lens is arranged to have a negative power and the second lens has a positive power when counted from the side, and at least one surface of each of the first lens and the second lens is an aspherical surface, The afocal optical system is configured to satisfy the following condition (Equation 1), where L is the total length of the afocal optical system, m is the expansion rate of the beam diameter, and D is the diameter of the output beam.

[0006]

[Function] The present invention is a beam expander having the above-described structure, which corrects spherical aberration and sine conditions and keeps wavefront aberration within the diffraction limit even if the total length of the lens is shortened.

By making at least one surface of the two lenses aspherical, spherical aberration can be favorably corrected even if the total length is shortened. Furthermore, if the lower limit of the condition (Equation 1) is exceeded, the total length of the lens becomes too long relative to the beam expansion rate, making it impossible to achieve a reduction in size and weight. Furthermore, it is necessary to use an aspherical lens, which increases the cost. It becomes a thing. Moreover, if the upper limit is exceeded, the total length becomes too short, making it difficult to correct spherical aberration satisfactorily.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A beam expander according to an embodiment of the present invention will be described below with reference to the drawings. In all examples, m is the beam expansion rate, D is the diameter of the output beam in mm, and L is the total length of the optical system in mm.
, Rn is the radius of curvature of the n-th surface, the unit is mm, when the radius of curvature is 0, it represents a plane, and THn is the radius of curvature of the n-th surface and the n+1-th surface.
The distance from the surface is in mm, θ is the angle of view in degrees, λ is the design wavelength in nm, and W0 is the axial wavefront aberration in r.
msλ, W1 is the wavefront aberration at the angle of view θ, and the unit is rm
sλ. Further, in Examples 1 to 10, an aspherical surface is used. The aspherical shape is

[0009]

[Math 6]

It is expressed as: Where, Rj) CCj
: Conical constants of the j-th surface ADj, AEj, AFj, AGj: 4 each of the j-th surface
Aspheric coefficients of order, 6th, 8th, and 10th. Further, the refractive index of the n-th surface is assumed to be Nn.

In Examples 11 and 12, the refractive index distribution n(r) is expressed by (Equation 4), where r is the distance in the radial direction from the optical axis, n0 is the refractive index on the optical axis, g, h1 , h2
represents the refractive index distribution coefficient. (Figure 1) is Example 1 of the present invention
3 is a configuration diagram of Embodiment 3. FIG. The incident beam 1 is the first
The beam passes through the lens 2 and the second lens 3 and becomes an output beam 4.

Example 1 m=10.1 D=4.04
L=15.2R1=-1.042
R2=0R3=0
R4=-1
0.417TH1=2.0
TH2=11.1394TH3=2.0
N1=1.
69447N2=1.69447
CC4=-0.2606777AD4=0.3
164731×10-4 AE1=0.246094
6×10-6AF1=0.1340275×10-8
AG1=0.6841877×10-11θ=2

λ=532W0=0.000
W1=0.0162 Example 2 m=8.87 D=4.08
L=6.0R1=-0.572
R2=2.859R3=-12
2.619 R4=-2.71
5TH1=1.2
TH2=3.0TH3=1.8
N1=1.69447N2=
1.51900 CC3=
0.404809×103AD3=-0.743675
×10-3 AE3=-0.457463×10-4
AF3=-0.535984×10-5 AG3=-
0.223016×10-5CC4=-0.14338
6 AD4=0.165429×10-2 AE4=
0.143990×10-3AF4=0.125003
×10−4 AG4=0.118034×10−
5θ=1
λ=532W0=0.0035
W1=0.0189 Example 3 m=12.5 D=6.0
L=8.4R1=-0.572
R2=1.645R3
=-36.25 R4
=-5.274TH1=1.2
TH2=5.104TH3=2.1
N1=1.
58708N2=1.79881
CC1=-0.581643AD1=0.70
2641 AE1=0.15374
1AF1=-0.344722×101 AG1
=0.220482×103CC2=0.660719 AD2=0.247758×10−1 AE2=
−0.126129AF2=0.100444×10−
1 AG2=0.14035×101CC3=0
．． 417089×102 AD3=-0.130587×10-3 AE3=-
0.101135×10-5AF3=0.766395
×10-7 AG1=-0.672508×10
-9CC4=-0.686235×10-1AD4=0
．． 134477×10-3 AE1=0.258
854×10-5AF1=0.607374×10-7
AG1=-0.157199×10-8θ=2

λ=633W0=0.0001
W1=0.0128 (FIG. 2) is a configuration diagram of an optical head using Examples 1 to 3 of the present invention. The light emitted from the parallel light source 5 enters a beam expander 6, expands its beam diameter, and enters an objective lens 7. The objective lens 7 focuses a beam onto the disk surface 8, allowing information to be read or written. The light reflected by the disk surface 8 passes through the objective lens 7 again, becomes parallel light, is separated by a beam splitter 9, and enters a photodetector 10, where information can be read. In this optical head, by using the beam expanders of Examples 1 to 3, it is possible to realize a small and lightweight optical head. (FIG. 3) is a configuration diagram of embodiments 3 to 7 of the present invention. The incident beam 11 passes through the first lens 12 and becomes an outgoing beam 13 . In Examples 4 to 7, the beam expander is composed of a single lens. In this embodiment, it is necessary to satisfy the condition (Equation 2). If the lower limit of this condition is exceeded, the overall length of the lens becomes long, which not only makes it difficult to manufacture, but also reduces the compactness and lightness of the optical system. Furthermore, there is no need to use an aspherical surface, resulting in an expensive lens. Furthermore, if the upper limit is exceeded, it becomes impossible to satisfactorily correct spherical aberration and sine conditions.

Example 4 m=9.09 D=6.00
L=12.64R1=-0.572
R2=-5.274TH1
=12.6399 N1=1.
59233CC1=-0.840353×10-1AD
1=0.207511 AE1=0
．． 494967AF1=0.787654
AG1=0.491141CC2=-0.13
7465 AD2=0.218793×10-3 AE2=
0.592577×10-5AF2=0.106723
×10−6 AG2=0.738220×10−
8θ=2
λ=532W0=0.0001
W1=0.0386 Example 5 m=6.5 D=6.00
L=8.0R1=-0.645
R2=-4.293TH1=
8.0 N1
=1.81565CC1=-0.245075×10-
2AD1=0.148092AE
1=0.179106AF1=0.767740
AG1=0.240035×101CC
2=-0.150782 AD2=0.253491×10-3 AE2=
0.102999×10-4AF2=0.284908
×10−6 AG2=0.494991×10−
7θ=1
λ=532W0=0.0013
W1=0.0133 Example 6 m=6.12 D=6.00
L=6.0R1=-0.568
R2=-3.471TH1=6
．． 0 N1=
1.93746CC1=-0.967569×10-2
AD1=0.214152 AE1
=-0.205138AF1=0.236108×10
1 AG1=0.126648×102CC
2=-0.161201 AD2=0.341394×10-3 AE2=
0.886352×10-5AF2=0.137872
×10−5 AG2=0.277002×10−
6θ=1
λ=532W0=0.0028
W1=0.0263 Example 7 m=11.11 D=6.00
L=15.0R1=-0.569
R2=-6.244TH1=1
5.0 N1=1
．． 60868CC1=-0.217364 AD1=0.115295 AE1
=0.225670AF1=0.882169
AG1=-0.779746CC2=0.
957262×10-1 AD2=0.247458×10-3 AE2=
0.549325×10-5AF2=0.956466
×10−7 AG2=0.444704×10−
8θ=2
λ=532W0=0.0022
W1=0.0277 Example 4
7 to 7, since the beam expander can be constructed with a single lens, there is no need for assembly or a lens barrel unlike in the case of two lenses.

FIG. 4 is a block diagram of an optical head using embodiments 4 to 7 of the present invention. The light emitted from the parallel light source 14 enters a beam expander 15, expands its beam diameter, and enters an objective lens 16. Objective lens 16 focuses a beam onto disk surface 17, allowing information to be read or written. The light reflected by the disk surface 17 passes through the objective lens 16 again, becomes parallel light, is separated by a beam splitter 18, and enters a photodetector 19, where information can be read. In this optical head, by using the beam expanders of Examples 4 to 7, it is possible to realize a small and lightweight optical head.

(FIG. 5) is a block diagram of embodiments 8 to 10 of the present invention. The incident beam 20 passes through the first lens 2
1 and becomes an output beam 22. In Examples 8 to 10, the beam expander is constructed of a single lens including a reflective optical system. In this embodiment, it is necessary to satisfy the condition (Equation 3). If the lower limit of this condition is exceeded, the overall length of the lens becomes long, which not only makes it difficult to manufacture, but also reduces the compactness and lightness of the optical system. Furthermore, there is no need to use an aspherical surface, resulting in an expensive lens. Furthermore, if the upper limit is exceeded, it becomes impossible to satisfactorily correct spherical aberration and sine conditions.

Example 8 m=7.41 D=4.0
L=3.14R1=0
R2=0.9
51 (reflective surface) R3 = 7.151 (reflective surface)
R4=0TH1=3.1
TH2=3.1TH3=3.14
N=1.6844
2CC2=-0.858735 AD2=-0.205319×10-1 AE2=-
0.166581×10-2AF2=0
AG2=0CC3
=-0.937730 AD3=-0.212851×10-4 AE3=-
0.132593×10-7AF3=0
AG3=0θ=5

λ=633W0=0.0000
W1=0.0001 Example 9 m=16.6 D=4.0
L=3.65R1=0
R2=0
．． 450 (reflective surface) R3=7.65 (reflective surface)
R4=0TH1=3.6
TH2=3.6TH
3=3.65
N=1.81565CC2=-0.921141 AD2=-0.108173 AE
2=-0.211690×10-1AF2=0.470
244×10-2 AG2=-0.2832
67CC3=-0.930785 AD3=-0.193252×10-4 AE3
=-0.114321×10-7AF3=-0.714
709×10-11 AG3=-0.128646×
10-12θ=5
λ=532W0=0.0000
W1=0.0001
Example 10 m=8.7 D=4.0
L=2.85R1=0
R2=
0.815 (reflective surface) R3 = 7.528 (reflective surface)
R4=7.258TH1=2.8
TH2=2
．． 8TH3=2.85
N=1.60868CC2=-0.5336
61 AD2=-0.811492×10-1 AE2
=-0.294350×10-1AF2=0.1505
15×10-1 AG2=0CC3=-0.
123791×101 AD3=-0.118658×10-3 AE3
=0.743753×10-6AF3=-0.4273
85×10-8 AG3=0.299725×1
0-10θ=5
λ=532W0=0.0000
W1=0.0035 Examples 8 to 10 use a reflective optical system, and since a large angle of view can be obtained, alignment with the light source is very easy.

(FIG. 6) shows embodiments 8 to 10 of the present invention.
1 is a configuration diagram of an optical head using an optical head. The light emitted from the parallel light source 23 enters a beam expander 24, expands its beam diameter, and enters an objective lens 25. Objective lens 25 focuses a beam onto disk surface 26, allowing information to be read or written. The light reflected by the disk surface 26 passes through the objective lens 25 again, becomes parallel light, is separated by a beam splitter 27, and enters a photodetector 28, where information can be read. In this optical head, by using the beam expanders of Examples 8 to 10,
A small and lightweight optical head can be realized.

(FIG. 7) is a block diagram of embodiments 11 and 12 of the present invention. The incident beam 29 passes through the first lens 30 and becomes an outgoing beam 31 . Examples 10 and 11 are beam expanders using refractive index distribution. In this embodiment, it is necessary to satisfy the condition (Equation 5). If the lower limit of this condition is exceeded, the overall length of the lens becomes long, which not only makes it difficult to manufacture, but also reduces the compactness and lightness of the optical system. Furthermore, if the upper limit is exceeded, it becomes impossible to satisfactorily correct spherical aberration and sine conditions.

Example 11 m=4.44 D=2.4
L=5.18R1=-0.4
R2=0TH1
=5.184N
0=1.55g=0.25
h1=0.3934θ=0.2

λ=532W0=0.0437
W1=0.0607 Example 12 m=4.82 D=2.12
L=7.29R1=-0.515
R2=0TH1=7.
292 N0=1
．． 742g=0.1852
h1=0.523θ=0.5
λ=53
2W0=0.0006
W1=0.0265 In Examples 11 and 12, since there is no need to use an aspherical surface, the shape can be processed using a conventional polishing method.

(FIG. 8) shows embodiments 10 to 1 of the present invention.
1 is a configuration diagram of an optical head using the optical head 1. The light emitted from the parallel light source 32 enters a beam expander 33, expands its beam diameter, and enters an objective lens 34. Objective lens 34 focuses a beam onto disk surface 35, allowing information to be read or written. The light reflected by the disk surface 35 passes through the objective lens 34 again, becomes parallel light, is separated by a beam splitter 36, and enters a photodetector 37, where information can be read. In this optical head, Example 1
By using 1 to 12 beam expanders, a small and lightweight optical head can be realized.

[0021]

As described above, the present invention is an afocal optical system that magnifies an incident parallel light beam and emits it again as a parallel light, in which the first lens counting from the incident side has a negative
A second lens is arranged to have positive power, at least one surface of each of the first lens and the second lens is an aspherical surface, and the total length of the afocal optical system is L, and the beam When the expansion rate of the diameter of is m and the diameter of the output beam is D, by satisfying the following condition (Equation 1), a beam expander with a short overall length and high magnification using one or two lenses can be created. can be realized.

Furthermore, by manufacturing the beam expander of the present invention using molded glass, a beam expander can be manufactured at low cost.

Furthermore, by using the beam expander of the present invention, a small and lightweight optical head can be realized.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a beam expander according to Examples 1 to 3 of the present invention.

FIG. 2 is a configuration diagram of an optical head using a beam expander according to Examples 1 to 3 of the present invention.

FIG. 3 is a configuration diagram of a beam expander according to Examples 4 to 7 of the present invention.

FIG. 4 is a configuration diagram of an optical head using a beam expander according to Examples 4 to 7 of the present invention.

FIG. 5 is a configuration diagram of a beam expander according to Examples 8 to 10 of the present invention.

FIG. 6 is a configuration diagram of an optical head using beam expanders of Examples 8 to 10 of the present invention.

FIG. 7 is a configuration diagram of a beam expander according to Examples 11 and 12 of the present invention.

FIG. 8 is a configuration diagram of an optical head using the beam expander of Examples 11 and 12 of the present invention.

FIG. 9 is a characteristic diagram showing the relationship between the total length and aberration of a beam expander with a conventional configuration.

[Explanation of symbols]

1 Incident beam 2 First lens 3 Second lens 4 Output beam

Claims (11)

[Claims] Claim 1: An afocal optical system that expands an incident beam that is parallel light and emits it again as parallel light, in which a first lens has a negative power and a second lens has a positive power when counted from the incident side. at least one surface of each of the first lens and the second lens is an aspherical surface, the total length of the afocal optical system is L, the magnification of the beam diameter is m, and the output A beam expander characterized in that, when the diameter of the beam is D, the following condition [Equation 1] is satisfied. 2. A light source that emits parallel light, a beam expander according to claim 1, condensing means for condensing the parallel light emitted from the beam expander onto an information medium surface, and the information medium surface. An optical head comprising information reading means for receiving light reflected or transmitted from the information medium and reading information on the surface of the information medium. [Claim 3] An afocal optical system that expands an incident beam that is parallel light and emits it again as parallel light, which includes a first surface that has a negative power and a first surface that has a positive power in order counting from the incident side. It consists of a single lens consisting of a second surface, and the following condition [Equation 2] is satisfied, where the total length of the afocal optical system is L, the magnification rate of the beam diameter is m, and the diameter of the output beam is D. A beam expander that is characterized by: 4. The beam expander according to claim 3, wherein both the first surface and the second surface are aspherical surfaces. Claim 5: a light source that emits parallel light;
or a beam expander according to claim 4, a condensing means for condensing the parallel light emitted from the beam expander onto an information medium surface, and a condensing means for receiving the light reflected or transmitted from the information medium surface; An optical head comprising an information reading means for reading information on the surface of a medium. 6. An afocal optical system that expands an incident beam that is parallel light and emits it again as parallel light, and is composed of four surfaces having one optical axis, the first surface and the fourth surface. is a boundary surface of the medium, the second surface and the third surface are reflective surfaces, at least one of the reflective surfaces is an aspherical surface, the second surface is a reflective surface with negative power, and the The third surface is a reflective surface with positive power, the third surface is arranged outside the first surface with respect to the optical axis, and the fourth surface is
It is arranged outside the third surface with respect to the optical axis, and when the total length of the afocal optical system is L, the expansion rate of the beam diameter is m, and the diameter of the output beam is D, the following condition [Equation 1] 3
] A beam expander characterized by satisfying the following. 7. The beam expander according to claim 6, wherein at least one of the first surface and the fourth surface is a flat surface. 8. A light source that emits parallel light; a beam expander according to claim 6; and a condensing means for condensing the parallel light emitted from the beam expander onto an information medium surface; An optical head comprising information reading means for receiving light reflected or transmitted from the information medium surface and reading information on the information medium surface. 9. Claims 1, 3, 4, and 6 are characterized in that they are manufactured by glass molding.
Or the beam expander according to claim 7. 10. An afocal optical system that expands an incident beam that is parallel light and emits it as parallel light again, the first afocal optical system consisting of spherical surfaces having negative power in order from the incident side.
In a single lens composed of a surface and a second surface made of a plane, when the refractive index at the center is n0 and the distance in the radial direction from the optical axis is r, the refractive index distribution n(r) is as follows: A beam expander characterized by satisfying the following condition [Equation 5], where the total length of the afocal optical system is L, the expansion rate of the beam diameter is m, and the diameter of the output beam is D. . [Claim 11] A light source that emits parallel light; [Claim 1]
a beam expander according to No. 0, a condensing means for condensing the parallel light emitted from the beam expander onto an information medium surface, and a beam expander for receiving light reflected or transmitted from the information medium surface, An optical head comprising an information reading means for reading information.