JP2000292738A - Beam shaping optical system and recording and reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate the design of a beam shaping optical system by using an anamorphic lens having a focal distance different between a direction parallel corresponding to the active layer of a semiconductor laser and a direction orthogonally corresponding to the active layer. SOLUTION: This beam shaping optical system 20 is used instead of a conventional coupling lens. The optical system 20 has a function to change divergent luminous flux radiated from a semiconductor laser into parallel beams and enlarge the luminous flux in a parallel direction with the active layer of the semiconductor laser. The center thickness D(mm) satisfies an expression: 9<=D<=12.5. It is desirable that the refractive index N and the center thickness D of the material of the anamorphic lens satisfy an expression: 15.5<=N.D<=18.5. Thus, the design of the optical system 20 is facilitated and the optimum anamorphic lens in accordance with a beam shaping magnification is easily and surely optimally designed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a beam shaping optical system and a recording / reproducing apparatus.

[0002]

2. Description of the Related Art A recording / reproducing apparatus for performing at least one of recording, reproducing and erasing of information by condensing a light beam from a semiconductor laser as a light spot on a recording surface of a recording medium by an objective lens is a so-called "optical pickup". It is widely known as a "device." FIG. 7 is a diagram schematically illustrating a typical example of such a recording / reproducing apparatus. Light emitted from the semiconductor laser 1 is converted into a parallel light beam by the coupling lens 2,
The light passes through the beam splitter 3, is converted into a convergent light beam by the objective lens 4, passes through a transparent substrate of a recording medium 5 such as a compact disk or DVD, and is condensed as a light spot on a recording surface 5A. The light beam reflected by the recording surface 5A becomes a "return light beam", passes through the objective lens 4, is returned to substantially parallel light, is reflected by the beam splitter 3, and enters a "signal detection system" (not shown). The signal detection system generates a focus error signal and a track error signal based on the return light beam, and also generates a reproduction signal when information is reproduced. The focus error signal / track error signal is input to control means (not shown), and is used for servo control of focusing and tracking. As is well known, the radiated light flux emitted from a semiconductor laser is divergent, but its intensity distribution is anisotropic, and it is perpendicular to the direction parallel to the junction surface of the semiconductor laser (full width at half maximum: θ _P ). The intensity distributions in the directions (full width at half maximum: θ _N ) are different from each other. Typical values in the far-field image are θ _P ≒ 10 degrees and θ _N ≒ 30 degrees. When a light beam having an anisotropic divergence angle is made substantially parallel light by a normal coupling lens, the light beam cross section of the coupled light beam becomes elliptical.When such a light beam is condensed by an objective lens, The light spot formed on the recording surface has an “elliptical shape”. In this case, if the major axis direction of the elliptical light spot is “perpendicular to the track of the recording medium”, adjacent tracks are irradiated simultaneously with light if the major axis direction length is too large,
Problems such as leakage of information signals from adjacent tracks (crosstalk) and writing to adjacent tracks occur. Conversely, when the major axis direction of the elliptical spot is parallel to the track of the recording medium, if the major axis length is too large, the resolution in the data recording direction is reduced, which may hinder reproduction signal detection and information writing. There is.

[0003] From such a viewpoint, the shape of the light spot formed on the recording surface of the recording medium is “substantially circular” or “elliptical” in which the major axis length / single axis length is in an appropriate range.
Is preferred. For the “long axis length / single axis length” of the light spot, an optimal value is set as a design condition of the recording / reproducing apparatus.
The beam shaping optical system is an “optical system that makes a light beam cross-sectional shape of a light beam incident on an objective lens close to a circular shape” in order to realize a light spot of a desired shape on a recording surface, and reduces a light beam diameter of a light beam from a semiconductor laser. , In the direction parallel to the joining surface. As a beam shaping optical system, a system using a cylinder lens and a system using a prism have been conventionally known.In recent years, a coupling lens has been added to a `` with a function of converting a light beam from a semiconductor laser into a parallel light beam, By providing a function of enlarging the light beam diameter in a direction parallel to the active layer of the semiconductor laser, the coupling lens is intended to "also serve as a beam shaping optical system." The “beam shaping magnification” in the beam shaping optical system also serving as the coupling lens is appropriately set according to the characteristics of the semiconductor laser and the design purpose of the recording / reproducing apparatus. For example, if the beam shaping magnification is increased, high precision is required for adjusting the light source (light emitting portion of the semiconductor laser) and the beam shaping optical system in the optical axis direction, and the assembling of the recording / reproducing apparatus becomes troublesome. In such a case, it is preferable to keep the beam shaping magnification low. Further, depending on the recording / reproducing apparatus, there may be a case where it is desired to realize a “substantially circular” light spot in order to increase the light use efficiency. In such a case, the beam shaping magnification is set to be high. Generally, the setting range of the beam shaping magnification is appropriately 1.5 to 4 times. As described above, in the beam shaping optical system also serving as a coupling lens, individual design of the beam shaping optical system is performed according to the beam shaping magnification set in design.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to facilitate the design of a beam shaping optical system in a recording / reproducing apparatus using a beam shaping optical system that also serves as a coupling lens.

[0005]

According to the beam shaping optical system of the present invention, a light beam from a semiconductor laser is condensed as a light spot on a recording surface of a recording medium by an objective lens to record, reproduce, and erase information. In a recording / reproducing apparatus that performs one or more processes, a beam shaping optical system that converts a light beam from a semiconductor laser into a parallel light beam and expands a light beam diameter in a direction parallel to an active layer of the semiconductor laser ”has the following features. . A direction parallel to the active layer of the semiconductor laser,
It is configured as a single anamorphic lens having focal lengths different from each other in a direction orthogonal to the active layer, and the center thickness: D (mm) is conditioned. (1) 9 ≦ D ≦ 12.5 Is satisfied (claim 1). In the beam shaping optical system according to the first aspect, the refractive index: N and the center thickness: D of the material of the anamorphic lens satisfy the following condition: (2) 15.5 ≦ ND · 18.5 Preferably (claim 2). In the beam shaping optical system according to claim 1 or 2, it is preferable that the refractive index: N of the material of the anamorphic lens satisfies the condition: (3) N ≧ 1.55 (claim 3). Claim 1
Or in the beam shaping optical system according to 2 or 3, when the beam shaping magnification: M is “1.5 ≦ M <2”,
The product of the refractive index of the material of the anamorphic lens: N and the center thickness: D: ND is a straight line: ND = 1.7M + 13
And a straight line: ND = 2.3M + 13 (claim 4). When the beam shaping magnification: M is “2 ≦ M ≦ 4”, the above-mentioned N is set.・ D is
Straight line: ND = 0.47M + 15 and straight line: ND = 0.
Preferably, it is set in a region sandwiched between 43M + 17 (claim 5). According to the recording / reproducing apparatus of the present invention, "a light beam from a semiconductor laser is condensed as a light spot on a recording surface of a recording medium by an objective lens to record, reproduce,
2. A recording / reproducing apparatus which performs one or more erasures, wherein the beam shaping optical system converts a light beam from a semiconductor laser into a parallel light beam and enlarges a light beam diameter in a direction parallel to an active layer of the semiconductor laser. (5) The method according to any one of (1) to (5) is used. According to the recording / reproducing apparatus of the present invention, as described above, one of information recording / reproducing / erasing is performed.
Since the above is performed, it is needless to say that either recording or reproduction or erasing is performed, but recording and reproduction,
Reproduction and erasure, recording and erasure, and recording, reproduction and erasure can be performed. The beam shaping optical system of the present invention can be shared by two or more semiconductor lasers. For example, the wavelengths are different from each other, and a short wavelength semiconductor laser for high recording density and a long wavelength semiconductor laser for low recording density are incorporated in the same recording / reproducing apparatus.
Depending on the recording density of the recording medium (CD-R, DVD, etc.),
The recording / reproducing apparatus can be configured to perform recording, reproduction, and the like by switching the light source to be used. In such a case, the beam shaping optical system can be shared by the two or three or more types of semiconductor lasers. is there.

[0006]

FIG. 1 shows an embodiment of a beam shaping optical system according to the present invention. Reference numeral 20 denotes a beam shaping optical system. The beam shaping optical system 20 is used instead of the coupling lens 2 in FIG. Reference numeral 30 denotes “a transparent parallel plate-shaped optical component provided between the semiconductor laser light source and the beam shaping optical system 20”, that is,
When a cover glass or a diffraction grating of a semiconductor laser (when the return light beam is detected on the light source side with respect to the beam shaping optical system 20, the beam splitter 3 in FIG. 7 is omitted, and the return light beam diffracted by the diffraction grating is incident on the light receiving means. ) Are collectively shown on one transparent parallel flat plate. In the figure, the Z direction is a “direction parallel to the optical axis direction of the beam shaping optical system 20”. The Y direction is a “direction parallel to the active layer” in the semiconductor laser, and the X direction is a “direction orthogonal to the active layer”. Therefore, the divergence angle of the divergent light beam emitted from the semiconductor laser is maximum in a plane parallel to the XZ plane and minimum in a plane parallel to the YZ plane. The beam shaping optical system 20 has a function of converting a divergent light beam emitted from the semiconductor laser into a parallel light beam and expanding a light beam diameter in a direction parallel to the active layer of the semiconductor laser. To achieve this function, the beam shaping optics 20
Focal length in the plane: have f _x, the focal length in the YZ plane: has f _y, these focal length: f _x (>
0), the magnitude relationship of f _y (> 0) has become a f _x <f _y. Beam shaping magnification is M = f _y / f _x.

In a far-field pattern of a general semiconductor laser for an optical device, θ _P : θ _N = 1: 2 to 1: 3, and a recording / reproducing device using a beam shaping optical system is used as described above. The beam shaping magnification: M is determined depending on the characteristics of the semiconductor laser to be used and the purpose of the recording / reproducing apparatus. As the refractive index of the material of the beam shaping optical system 20 by the anamorphic lens,
Refractive index: 3 of n = 1.48595, n = 1.58700, n = 1.83925
The relationship between the center thickness: D and the beam shaping magnification: M when the beam shaping optical system is optimally designed (on-axis wavefront aberration: 0.01 λ or less) assuming the types, is graphed using the refractive index: n as a parameter. The result is shown in FIG. From FIG. 2, it can be seen that the optimum range of the center thickness D in the range of the beam shaping magnification M: 1.5 to 4 is 9 to 12.5 mm (claim 1). Therefore, when the beam shaping optical system is configured as a single anamorphic lens, a good beam shaping optical system can be easily and surely obtained by setting the center thickness: D within the above range and designing. it can.

Next, as the refractive index of the material of the beam shaping optical system 20, n = 1.48595, n = 1.58700, n = 1.83
Assuming three types of 925 and optimally designing the beam shaping optical system as described above, the relationship between the product of the refractive index and the center thickness: ND and the beam shaping magnification: M, and the refractive index: n as a parameter FIG. 3 shows a graph obtained as From FIG. 3, it can be seen that the optimum range of the product: ND is 15.5 to 18.5 in the range of beam shaping magnification: M = 1.5 to 4 (claim 2). Therefore, when the beam shaping optical system is configured as a single anamorphic lens, a good beam shaping optical system can be easily and reliably obtained by designing the product: ND in the above range. it can. That is, the refractive index of the material:
If one of N or center thickness: D is determined, the other optimal range is automatically determined, so that a desired beam shaping optical system can be easily designed based on the optimal range set in this way. can do. FIG. 4 shows the relationship between the refractive index N of the material and the center thickness D in the beam shaping optical system optimally designed as an anamorphic lens, with the beam shaping magnification M as a parameter. As is apparent from FIG. 4, when the refractive index N of the material becomes 1.55 or less, the center thickness D must be rapidly increased regardless of the beam shaping magnification M. As the thickness of the beam shaping optical system increases, the weight of the beam shaping optical system increases,
Since it is difficult to reduce the weight and size of the recording / reproducing apparatus, it is preferable to set the refractive index N of the material of the beam shaping optical system to 1.55 or more in order to reduce the weight and size of the recording / reproducing apparatus. Item 3).

FIG. 5 shows that the beam shaping magnification: M is 1.5 ≦ M.
When ≤2, when the anamorphic lens which is the beam shaping optical system is optimally designed, how the product of the refractive index of the material: N and the center thickness: D: ND changes according to M , The three types of refractive index: n = 1.48595, n = 1.58700, n
= 1.83925 as a parameter. Refractive index: when n = 1.83925, the change in ND is 1.5 ≦ M ≦ 2
Can be approximately expressed by a straight line: ND = 2.3M + 12.9. Refractive index: ND when n = 1.48595
Is approximately a straight line: ND for 1.5 ≦ M ≦ 2
= 2.6M + 11.8, and when the refractive index: n = 1.58700, the change in ND is 1.5 ≦ M ≦ 2
Can be approximately expressed by a straight line: ND = 1.7M + 13. Therefore, beam shaping magnification: M is 1.5 ≦
When M ≦ 2, the product of the refractive index of the material of the anamorphic lens: N and the center thickness: D: ND is a straight line:
ND = 1.7M + 13 and straight line: ND = 2.3M + 1
3 (claim 4), it is possible to easily realize an optimum design. FIG. 6 shows that when the anamorphic lens as the beam shaping optical system is optimally designed with the beam shaping magnification: M being 2 ≦ M ≦ 4, the product of the refractive index of the material: N and the center thickness: D: N · How D changes according to M is determined by the three types of refractive indices: n = 1.4859.
5, n = 1.58700 and n = 1.83925 are shown as parameters. Refractive index: When n = 1.83925, the change of N · D is approximately a straight line for 2 ≦ M ≦ 4: ND = 0.4
It can be expressed as 3M + 16.7. When the refractive index is n = 1.48595, the change in ND is approximately linear for N ≦ M ≦ 4.
D = 0.49M + 16.3, and the refractive index:
When n = 1.58700, the change of N · D is 2 ≦ M ≦ 4,
It can be approximately expressed by a straight line: ND = 0.47M + 15.6. Therefore, beam shaping magnification: M is 2 ≦ M ≦ 4
Is set to, the product of the refractive index of the material of the anamorphic lens: N and the center thickness: D: ND, a straight line: ND
= 0.47M + 15 and straight line: ND = 0.43M + 17
(Claim 4)
Optimal design can be easily realized.

[0010]

EXAMPLES Specific examples will be described. In this embodiment, the beam shaping optical system 20 has f _y = 25 mm and f _x = 1.
This is an anamorphic lens with 0 mm and a beam shaping magnification: M = 2.5. First surface (recording medium side) and second surface
The surface shape of the surface (semiconductor laser side) is represented by the following known aspherical formula (A). ^{_{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 (A) where, Z: sag amount R of surface parallel to Z axis (optical axis direction) _x, R _y: curvature K _x of curvature and the YZ plane in the XZ plane, K _y: conical coefficient of the shape of the XZ plane and YZ plane AR, BR, CR, DR: 4,6,8 from cone , 10th, rotationally symmetric components of deformation coefficients AP, BP, CP, DP: non-rotationally symmetric components of 4, 6, 8, 10th order deformation coefficients from cones. The beam shaping magnification: a M = f _y / f _x.

[0011] The first face the second plane surface coefficient _{R x 0.06029 -0.16932 R y 0.18086 0.38462} K x 13.3716 0.664403E-00 K y 0.15256 0.712653E-00 AR -0.583397E-03 0.161218E-03 BR -0.792109E-05 0.201887E-02 CR -0.104212E-05 -0.767207E-03 DR 0.160470E-08 0.470491E-04 AP -0.203710E-00 -0.206882E + 01 BP -0.177209E-00 0.780332E-00 CP -0.854999E- 01 0.806091E-00 DP -0.933834E-00 0.134193E + 01 Refractive index: n ₆₃₅ (wavelength: refractive index for light of 635 nm)
= 1.58700 Center thickness: 10.687 mm Sum of the thicknesses of the transparent parallel plate optical elements between the semiconductor laser and the beam shaping optical system: t = 5.37 (glass material: BK7) In the above data, for example, E-07 "is, ^10-7
, And this number depends on the number immediately before it.

In the above embodiment, D = 10.687 mm, N
Since 1.58700 and M = 2.5, the above embodiment satisfies the conditions (1) and (3) (claims 1 and 3). Also, N
D = 16.960, which satisfies the condition (2) (claim 2). Beam shaping magnification: M = 2.5 and 2 ≦ M ≦ 4
0.43M + 17 = 18.08, 0.4
Since 7M + 15 = 16.175, ND is a straight line: ND = 0.43M + 17 and a straight line: ND = 0.4
The area is set between 7M + 15 (claim 5). In the case where the beam shaping optical system of the embodiment is used in place of the coupling lens 2 in the recording / reproducing apparatus shown in FIG. 7, the light beam from the semiconductor laser 1 is transferred onto the recording surface 5A of the recording medium 5 by the objective lens 4. A recording / reproducing apparatus which performs one or more of recording, reproducing, and erasing of information by condensing as a light spot, and converts a light beam from a semiconductor laser 1 into a parallel light beam and a light beam in a direction parallel to an active layer of the semiconductor laser. Claim 1 as a beam shaping optical system for expanding the diameter.
A recording / reproducing apparatus using the apparatus described in 2, 3, or 5.

[0013]

As described above, according to the present invention, a novel beam deflection optical system and recording / reproducing apparatus can be realized. According to the present invention, in the recording / reproducing apparatus using the beam shaping optical system also serving as the coupling lens, the design of the beam shaping optical system is facilitated, and the optimum anamorphic lens according to the beam shaping magnification is easily and easily formed. The optimal design can be ensured.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining an embodiment of a beam shaping optical system according to the present invention.

FIG. 2 is a diagram for explaining a condition (1).

FIG. 3 is a diagram for explaining a condition (2).

FIG. 4 is a diagram for explaining a condition (3).

FIG. 5 is a diagram for explaining the invention described in claim 4;

FIG. 6 is a diagram for explaining the invention described in claim 5;

FIG. 7 is a diagram illustrating a recording / reproducing device.

[Explanation of symbols]

20 Beam shaping optical system configured as a single lens 30 Transparent parallel plate optical element between semiconductor laser and beam shaping optical system

Claims (6)

[Claims] 1. A light beam from a semiconductor laser is condensed as a light spot on a recording surface of a recording medium by an objective lens.
In a recording / reproducing apparatus for performing at least one of recording / reproducing / erasing of information, a beam shaping optical system for converting a light beam from the semiconductor laser into a parallel light beam and expanding a light beam diameter in a direction parallel to an active layer of the semiconductor laser. A single anamorphic lens having focal lengths different from each other in a direction parallel to the active layer of the semiconductor laser and in a direction orthogonal to the active layer; Thickness: D (mm): Condition (1) A beam shaping optical system characterized by satisfying 9 ≦ D ≦ 12.5. 2. The beam shaping optical system according to claim 1, wherein the refractive index of the material of the anamorphic lens: N and the center thickness: D are as follows: (2) 15.5 ≦ ND · 18. 5. A beam shaping optical system characterized by satisfying (5). 3. The beam shaping optical system according to claim 1, wherein the refractive index of the material of the anamorphic lens: N satisfies the condition: (3) N ≧ 1.55. Optical system. 4. The beam shaping optical system according to claim 1, wherein the beam shaping magnification M is 1.5 ≦ M <2, and the refractive index of the material of the anamorphic lens is N. The product of the center thickness: D: ND, but the straight line: ND = 1.7M + 13 and the straight line: ND = 2.3
A beam shaping optical system, wherein the beam shaping optical system is set in an area sandwiched by M + 13. 5. The beam shaping optical system according to claim 1, wherein the beam shaping magnification: M is 2 ≦ M ≦ 4, and the refractive index of the material of the anamorphic lens: N and the center thickness. The product of the thickness: D: ND, the straight line: ND = 0.43M + 17 and the straight line: ND = 0.
A beam shaping optical system characterized by being set in an area sandwiched between 47M + 15. 6. A light beam from a semiconductor laser is focused as a light spot on a recording surface of a recording medium by an objective lens.
What is claimed is: 1. A recording / reproducing apparatus for performing at least one of recording, reproducing and erasing of information, comprising: a beam shaping optic for converting a light beam from a semiconductor laser into a parallel light beam and expanding a light beam diameter in a direction parallel to an active layer of the semiconductor laser. A recording / reproducing apparatus using the system according to any one of claims 1 to 5 as a system.