JP2003228000A - Collimator lens, optical pickup and optical disk device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plastic collimator lens installed so that a gate mark projecting part is inclined in an up-and-down direction in an optical pickup, the optical pickup completely thinned by including the collimator lens, and an optical disk device miniaturized by providing the thin optical pickup. <P>SOLUTION: As for the collimator lens 3, its convex refractive surface 3c is not rotationally symmetric to an optical axis A and a maximum curvature meridian Cm is inclined by an angle ϕ to a gate meridian Cg. Thus, a maximum refraction meridian Cx is inclined by an angle θ to the meridian Cg. A plane including the meridian Cx is substantially parallel with the up-and-down direction, and includes the major axis of an ellipse being the cross section Se of the bundle L of laser beams from a laser unit 2. Furthermore, the gate mark projecting part 3a of the lens 3 is arranged lower than the upper surface 1a of a housing 1. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk device, and more particularly to an optical pickup thereof and a collimator lens thereof.

[0002]

2. Description of the Related Art Optical disks such as CDs and DVDs include a recording layer inside. The recording layer records digital data as a variation pattern of a concave-convex shape in a read-only optical disc and a variation pattern of light reflectance in a writable optical disc. The optical disc device uses an optical pickup to detect the uneven shape of the recording layer of the optical disc or the variation pattern of the light reflectance, and converts it into a digital signal. Thus, the optical disc device reads the digital data recorded on the optical disc. Further, the optical disc device can write digital data by changing the optical reflectance of the recording layer in a predetermined pattern by using an optical pickup for a writable optical disc such as a CD-R and a DVD-R. There is also.

FIG. 4 and FIG. 5 are a perspective view and a side view showing an internal optical system of an optical pickup 100 in a conventional optical disk device, respectively. In FIGS. 4 and 5, in order to show the inside of the optical pickup 100, a part of the upper surface and the side surface of the housing 1 are removed. Further, for the purpose of clarifying the arrangement of the optical system inside the optical pickup 100, the illustration of the configuration other than the optical system (for example, a holding portion for each element belonging to the optical system) is omitted.

The laser unit 2 includes a semiconductor laser, a hologram, and a photodetector. The laser unit 2 emits a laser beam bundle L having a predetermined wavelength from the emission port 2a by a semiconductor laser. The chief ray of the laser beam bundle L is a collimator lens 3
It coincides with the optical axis A of 0. The collimator lens 30 is a cylindrical plano-convex lens in the example of FIG. The plane refracting surface and the convex refracting surface 30c have the axis of the cylinder as the optical axis and are substantially rotationally symmetrical with respect to the optical axis. In particular, the convex refracting surface 30c is a substantially spherical surface, and any meridian has substantially the same curvature. Here, the meridian is the line of intersection between the cross section including the optical axis A of the collimator lens 30 (hereinafter referred to as the meridian surface) and the convex refracting surface 30c. The laser beam bundle L incident on the plane refracting surface of the collimator lens 30 is emitted from the convex refracting surface 30c and converted into a parallel ray bundle Lp. The mirror 4 reflects the parallel light flux Lp from the collimator lens 30 upward. The objective lens 5 is a biconvex lens, and focuses the parallel light flux Lp reflected by the mirror 4 on the upper focal point P.

In the optical disk device, a recording layer or a reflective layer (not shown) of the optical disk is arranged at the focal point P of the objective lens 5. Thereby, the laser beam bundle focused at the focal point P is reflected by the recording layer or the reflective layer of the optical disc. The reflected ray bundle passes through the objective lens 5 and the mirror 4 and collimator lens
The light is incident on the convex refraction surface 30c of 30. Further, the collimator lens 30 focuses the light into the emission port 2a of the laser unit 2.
The reflected ray bundle is diffracted by the hologram in the laser unit 2. The photodetector measures the amount of the diffracted light and converts the measured value into an electric signal.

The optical disk is rotated at a predetermined rotation speed by the optical disk device. Therefore, the focus P of the objective lens 5
The light reflectance changes with time according to the uneven shape of the recording layer of the optical disc or the change pattern of the light reflectance. The optical pickup 100 detects the concavo-convex shape of the recording layer of the optical disc or the change pattern of the light reflectance through the temporal change in the amount of reflected light measured.

In a conventional optical pickup, a glass or plastic lens is used as a collimator lens. A glass collimator lens is disclosed in
It can be obtained by molding a glass material by a reheat press, similarly to the glass objective lens disclosed in Japanese Patent Publication No. 48388.

The collimator lens made of plastic is obtained by injection molding from a transparent plastic material such as polymethylmethacrylate (PMMA) or polycarbonate. At the time of injection molding, the gate is set on the ridge of the lens. As a result, on the collimator lens after molding, a convex portion corresponding to a gate trace (hereinafter referred to as a gate trace convex portion) remains at the dent portion. For example, in FIGS. 4 and 5, the collimator lens
The gate mark convex portion 30a remains on the upper ridge portion 30b of the gate 30.

Collimator lenses made of plastic typically include optical distortions when formed by injection molding.
In particular, the refractive index is unevenly distributed such that the refractive index is high near the convex portion of the gate trace. The reason why optical distortion is caused by injection molding is as follows. During injection molding, the hot molten plastic material is filled through the gate into the lens-shaped cavity in the mold at high speed and high pressure. At this time, the molten plastic material flows in the cavity and is cooled and solidified from the portion in contact with the mold wall surface. The previously solidified portion exerts a stress on the other molten portions in the flow direction. The stress causes the molecular chains of the plastic material to be stretched and causes molecular orientation. Further, the stress remains as a residual stress after the plastic material is solidified. As a result of the molecular orientation and residual stress distributed in the collimator lens after molding, optical distortion such as uneven distribution of refractive index occurs.

For example, the collimator lens 3 shown in FIG.
At 0, the refractive index is high in the meridian plane (hereinafter referred to as the gate meridian plane) that passes through the center of the gate mark convex portion 30a. Here, in FIG. 4, on the convex refraction surface 30c of the collimator lens 30, an intersection line (hereinafter, referred to as a gate meridian line) Cg with the gate meridian plane and a meridian line Ct orthogonal to the gate meridian line Cg are shown.

Since the injection-molded plastic collimator lens generally contains optical distortion, astigmatism is particularly generated in the image formation by the collimator lens. When a bundle of rays having a perfect circular cross section is incident on the collimator lens, the cross section of the converted bundle of parallel rays is transformed into an elliptical shape due to its astigmatism. In the collimator lens 30 shown in FIG. 4, when the cross section of the incident laser beam bundle L is a perfect circle, the cross section of the parallel ray bundle Lp converted by the collimator lens 30 is a plane including the gate meridian Cg. It is transformed into an ellipse with a minor axis in the direction of the intersection.

However, the occurrence of astigmatism in the image formation by the plastic collimator lens is advantageous in the conventional optical pickup as follows. In semiconductor lasers, the cross section of the laser beam bundle is generally elliptical. Therefore, in order to use the semiconductor laser as a light source of an optical pickup, it is necessary to correct the cross section of the laser beam bundle into a perfect circle. In a conventional optical pickup, the astigmatism produced by a plastic collimator lens is used to correct a laser beam bundle of a semiconductor laser into a parallel beam bundle and, at the same time, correct the laser beam bundle to have a perfect circular cross section.

For example, the optical pickup 100 shown in FIG.
Then, the laser beam bundle L emitted from the laser unit 2
Has a vertically long elliptical cross section Se. On the other hand, the collimator lens 30 is installed so that the gate meridian Cg is included in the vertical plane. As a result, the cross section Sc of the parallel light beam bundle Lp is corrected into a substantially circular shape.

FIG. 6 is a sectional view showing the vicinity of the collimator lens 30 of the conventional optical pickup 100. Figure 6
The position of the cross section shown in Fig.
Is indicated by the straight line VI-VI and the directions of the arrows at both ends thereof. The collimator lens 30 includes the gate trace convex portion 30a on the housing 1
Inside the upper surface 1a to the concave portion 1c, the lower side surface is the lower surface 1b inside the housing 1
It is fitted into each of the recesses 1d. As a result, the gate meridian Cg is fixed at a position included in the vertical plane.

[0015]

In the conventional optical pickup 100 shown in FIGS. 4, 5, and 6, the upper surface inside the housing 1
The distance between 1a and the lower surface 1b is substantially the same as the diameter of the collimator lens 30. Therefore, the smaller the size of the collimator lens 30, the thinner the optical pickup 100. Since the thinning of the optical pickup is advantageous for downsizing of the optical disc device, the conventional optical pickup 100 requires a device for improving downsizing of the collimator lens 30.

In order to reduce the size of the glass collimator lens, the weight of the glass material must be controlled with high accuracy during the reheat press. However, since the total weight of the glass material is already small, it is quite difficult to keep the weight control error within the allowable range.

In order to reduce the size of the plastic collimator lens, it is preferable to design the overall diameter to be small and the gate trace convex portion to be low. On the other hand, since it is necessary to secure a sufficient effective diameter for the collimator lens,
The width of the ridge is limited to a small width. Therefore, if the height of the convex portion of the gate trace is designed to be too small, the shape of the refracting surface is distorted to within the effective diameter due to the cutting stress when the collimator lens that has been molded is separated. Distortion within the effective diameter impairs the action of the collimator lens itself and must be avoided.
After all, there is a fixed lower limit to the height of the gate mark convex portion, and it is impossible to design lower than the lower limit.

The cross section Se of the laser beam bundle L emitted from the laser unit 2 is usually an ellipse having a long axis in the vertical direction. Therefore, in order to correct the cross section of the laser beam bundle L by utilizing the optical distortion of the collimator lens 30, the gate meridian surface of the collimator lens 30 had to be parallel to the vertical direction. Thereby, the gate trace convex portion 30a
However, it had to be arranged at the top of the collimator lens 30, for example. At that time, as shown in FIG. 6, the gate mark convex portion 30a was fitted into the concave portion 1c of the upper surface 1a in the housing 1. In order to realize fitting of the gate trace convex portion 30a on the upper surface 1a in the housing 1 and to maintain sufficient strength in the vicinity of the concave portion 1c, the thickness of the upper portion of the casing 1 is the height of the gate trace convex portion 30a. Had to be secured large enough compared to. As a result, it was difficult to make the optical pickup 100 thinner.

According to the present invention, a collimator lens made of plastic, in which a gate mark convex portion can be installed in a tilted manner with respect to the vertical direction in an optical pickup, an optical pickup sufficiently thinned by including the collimator lens, and its thin. An object of the present invention is to provide an optical disc device that is downsized by having an optical pickup.

[0020]

A collimator lens according to the present invention is a plastic lens molded into a substantially cylindrical shape by injection molding; (A) a dent portion including a gate mark convex portion formed by injection molding; and , (B) (a) The axis of the cylindrical shape is the optical axis, and (b) the line of intersection with the meridional plane (hereinafter referred to as the gate meridian) that passes through the center of the convex portion of the gate trace (hereinafter referred to as the gate meridian). A convex refraction surface, which intersects at a predetermined angle and includes a meridian having a curvature substantially larger than any of the gate meridian and other meridians (hereinafter referred to as the maximum curvature meridian). Here, the meridian is a cross section including the optical axis of the collimator lens, and the meridian is the line of intersection between the meridian and the convex refracting surface. In this collimator lens, in particular, the convex refracting surface is non-rotationally symmetric with respect to the optical axis.

Astigmatism occurs in the image formation by the above collimator lens. The astigmatism is a combination of a non-uniform distribution of the refractive index in the lens and a non-rotationally symmetric shape of the convex refracting surface. Here, the non-uniform distribution of the refractive index is due to injection molding. In particular, the refractive index is maximum in the meridional plane of the gate. When a ray bundle having a perfect circular cross section is incident on the collimator lens in the optical axis direction, the cross section of the outgoing ray bundle is transformed into an elliptical shape due to astigmatism. The ellipse has a minor axis between the line of intersection with the plane containing the gate meridian and the line of intersection with the plane containing the maximum curvature meridian. Hereinafter, the cross section of the collimator lens formed by a plane including the minor axis direction of the ellipse is referred to as the maximum refraction meridional surface.

The distribution of the refractive index in the collimator lens is
It can be adjusted by injection molding conditions such as injection pressure and mold temperature. Therefore, unlike the conventional collimator lens, the maximum refraction meridional surface is inclined at a predetermined angle with respect to the gate meridional surface depending on the injection molding conditions and the shape of the convex refraction surface.

The optical pickup according to the present invention comprises (A) the collimator lens described above; (B) an upper surface and a lower surface which are separated from each other by a distance substantially equal to the diameter of the collimator lens, and is provided between the upper surface and the lower surface. Holds the collimator lens, aligns the optical axis of the collimator lens in the horizontal direction, and tilts and fixes the meridional surface of the gate with respect to the vertical direction by the angle at which the uppermost part of the convex portion of the gate trace is located below the upper surface. Housing: (C) A semiconductor laser for injecting a bundle of light rays having a predetermined wavelength and a vertically elongated elliptical cross section in the optical axis direction to the collimator lens; (D) Substantially parallel light rays by the collimator lens A mirror for upwardly reflecting the bundle of rays converted into a bundle; (E) an objective lens for focusing the bundle of rays reflected by the mirror onto an optical disc above the housing; and (F) an optical disc In is reflected, the objective lens, a mirror,
And a photodetector for detecting a bundle of rays returning through the collimator lens in order.

In the above collimator lens, the maximum refraction meridional surface is different from the gate meridional surface, so that in the above optical pickup, the gate meridian surface of the collimator lens can be set to be inclined with respect to the vertical direction. Thereby, the uppermost portion of the gate mark convex portion can be arranged below the upper surface in the housing. Therefore, in the above optical pickup, unlike the conventional one, the gate mark convex portion does not have to be fitted into the upper surface in the housing. Therefore, the upper part of the housing is thinner than the conventional one, and particularly thinner than the height of the gate mark convex portion. As a result, the above optical pickup can be made thinner easily than the conventional one.

In the above optical pickup, preferably,
The meridional plane of the gate is inclined at 40 to 70 ° with respect to the vertical direction. If it is within the range of the inclination, the uppermost portion of the gate mark convex portion can be arranged sufficiently below the upper surface in the housing. Along with that
The maximum refraction meridian plane can be set parallel to the vertical direction. Thereby, the cross section of the light beam of the semiconductor laser can be corrected from an elliptical shape to a perfect circular shape.

In the above optical pickup, the meridian plane including the maximum curvature meridian (hereinafter referred to as the maximum curvature meridian) may be substantially parallel to the vertical direction. Some collimator lenses have sufficiently small astigmatism due to injection molding. At that time, the angle between the maximum curvature meridional surface and the maximum refraction meridional surface is substantially negligible. Therefore, even if the maximum curvature meridian plane is set in parallel with the vertical direction instead of the maximum refraction meridional plane, the cross section of the light flux of the semiconductor laser can be sufficiently corrected. An optical disk device according to the present invention has the above optical pickup. Since the above optical pickup is thin enough, the optical disk device can be easily miniaturized.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION The best mode for carrying out the present invention will be described below with reference to the accompanying drawings with reference to its preferred embodiments.

<< Embodiment 1 >> FIG. 1 and FIG. 2 respectively show an optical pickup in an optical disk device according to Embodiment 1 of the present invention.
FIG. 3 is a perspective view and a side view showing an internal optical system of 10. 1 and 2, parts of the top surface and side surfaces of the housing 1 are removed in order to show the inside of the optical pickup 10. Further, for the purpose of clarifying the arrangement of the optical system inside the optical pickup 10, a configuration other than the optical system (for example,
Illustrations of holding parts for each element belonging to the optical system) are omitted.

The laser unit 2 includes a semiconductor laser, a hologram, and a photodetector. The laser unit 2 emits a laser beam bundle L having a predetermined wavelength from the emission port 2a by a semiconductor laser. The chief ray of the laser beam bundle L is a collimator lens 3
Coincides with the optical axis A of.

The collimator lens 3 is a cylindrical plano-convex lens. The two refracting surfaces corresponding to the end faces of the cylinder have the axis A of the cylinder as the optical axis. The convex refracting surface 3c is a curved surface obtained by slightly deforming a spherical surface in a non-rotationally symmetric manner with respect to the optical axis A. Due to the non-rotationally symmetric deformation, the curvature of the meridian changes for each meridian. Here, the meridian is a line of intersection between the cross section including the optical axis A of the collimator lens 3 (hereinafter referred to as the meridian surface) and the convex refracting surface 3c. In particular, one meridian has a substantially larger curvature than the other. Hereinafter, the meridian having the substantially maximum curvature is referred to as the maximum curvature meridian. In FIG. 1, the meridian Cm shown on the convex refracting surface 3c of the collimator lens 3 corresponds to the maximum curvature meridian. The convex refraction surface 3c further has the maximum curvature meridian Cm.
And is symmetric with respect to each of the meridians orthogonal to it. The laser beam bundle L incident on the plane refracting surface of the collimator lens 3 is emitted from the convex refracting surface 3c and converted into a parallel ray bundle Lp.

The mirror 4 reflects the parallel ray bundle Lp from the collimator lens 3 upward. The objective lens 5 is a biconvex lens, and focuses the parallel light flux Lp reflected by the mirror 4 on the upper focal point P.

The optical disc device has a focus P of the objective lens 5.
Then, a reflective layer (not shown) of a writable optical disc such as a CD-R or a DVD-R is arranged. In addition, the recording layer of a read-only optical disc such as a CD or a DVD may be arranged. With the above arrangement, the focus P
The laser beam focused at is reflected on the optical disc. The reflected ray bundle passes through the objective lens 5 and the mirror 4 and enters the convex refracting surface 3c of the collimator lens 3. Further, it is focused by the collimator lens 3 into the emission port 2a of the laser unit 2. The reflected ray bundle is diffracted by the hologram in the laser unit 2. The photodetector measures the amount of diffracted light,
Convert measured values to electrical signals.

The optical disk is rotated at a predetermined rotation speed by the optical disk device. Therefore, the focus P of the objective lens 5
The light reflectance changes with time according to the uneven shape of the recording layer of the optical disc or the change pattern of the light reflectance. The optical pickup 10 detects a concavo-convex shape of the recording layer of the optical disc or a change pattern of the light reflectance through the temporal change in the measured reflected light amount. The detected change pattern is output as an electric signal. Thus, the optical pickup 10
Reads the digital data recorded on the optical disc.

The collimator lens 3 is made of transparent plastic and is obtained by injection molding from PMMA, for example. Alternatively, it may be polycarbonate. Since the collimator lens 3 is obtained by injection molding, it leaves a gate mark on the outer shape and contains a non-uniform distribution of refractive index inside. In fact, the figure
As shown in 1 and FIG. 2, the gate trace convex portion 3a is left on the upper ridge portion 3b. On the other hand, the refractive index is high in the meridian plane (hereinafter referred to as the gate meridian plane) that passes through the center of the gate mark convex portion 3a. Figure 1
Shows a line of intersection Cg with the meridian plane of the gate (hereinafter referred to as the gate meridian) on the convex refracting surface 3c of the collimator lens 3.

Astigmatism occurs in the image formation by the collimator lens 3. The astigmatism is a combination of a non-uniform distribution of the refractive index in the lens and a non-rotationally symmetric shape of the convex refracting surface 3c. A bundle of rays with a perfect circular cross section with respect to the plane refracting surface of the collimator lens 3 is in the optical axis direction A.
When incident on, the transverse section of the ray bundle emitted from the convex refracting surface 3c is transformed into an elliptical shape due to astigmatism. The ellipse has a minor axis between the line of intersection with the plane containing the gate meridian Cg and the line of intersection with the plane containing the maximum curvature meridian Cm. Collimator lens with a plane including the minor axis direction of the ellipse
Hereinafter, the cross section of 3 will be referred to as the maximum refraction meridian plane. Further, the line of intersection between the maximum refraction meridian surface and the convex refraction surface 3c is called the maximum refraction meridian line.

In FIG. 1, the convex refracting surface 3c of the collimator lens 3 is shown.
At the top, the maximum refraction meridian Cx is shown. As shown in FIG. 1, the angle θ between the gate meridian Cg and the maximum refraction meridian Cx is generally smaller than the angle φ between the gate meridian Cg and the maximum curvature meridian Cm. The astigmatic difference due to astigmatism and the angle θ between the gate meridian Cg and the maximum refraction meridian Cx are
It is substantially determined by the distribution of the refractive index in the lens and the shape of the convex refractive surface 3c. The distribution of the refractive index in the lens can be adjusted by injection molding conditions such as injection pressure and mold temperature. Therefore, the astigmatic difference, and the gate meridian Cg and the maximum refraction meridian Cx
The angle θ between and can be adjusted to a predetermined value.

In the optical pickup 10 according to the first embodiment, the angle θ between the gate meridian Cg and the maximum refraction meridian Cx is set to the following value: the maximum refraction meridian plane is substantially parallel to the vertical direction. As described above, the collimator lens 3 is fixed to the housing 1. At that time, the meridional surface of the gate is inclined with respect to the vertical direction by an angle θ, and the gate trace convex portion 3a is arranged below the upper surface 1a in the housing 1.

The fact that the maximum refraction meridional plane is substantially parallel to the vertical direction is advantageous in the following points: As shown in FIG. 1, the laser beam bundle L emitted from the semiconductor laser is L.
The cross section Se of is a vertically long elliptical shape. Therefore, in order to use the semiconductor laser as the light source of the optical pickup, the cross section Se of the laser beam bundle L must be corrected into a perfect circle. In the optical pickup 10, the maximum refraction meridional surface of the collimator lens 3 is substantially parallel to the vertical direction. Thereby, when the laser beam bundle L of the semiconductor laser is converted into the parallel beam bundle Lp by the collimator lens 3, at the same time, the transverse section Sc thereof is corrected into a substantially circular shape. Here, the degree of the correction is adjusted through the astigmatic difference of the collimator lens 3. In this way, in the optical pickup 10 according to the first embodiment, since it is not necessary to particularly provide a correction lens for the cross section of the laser beam bundle L, the scale of the optical system is reduced. Therefore, the fact that the maximum refraction meridian plane is substantially parallel to the vertical direction is advantageous for downsizing the optical pickup 10.

FIG. 3 shows an optical pickup 10 according to the first embodiment.
3 is a cross-sectional view showing the vicinity of the collimator lens 3 with respect to FIG. The position of the cross section shown in FIG. 3 and the direction in which the cross section is viewed are indicated by the line III-III and the directions of the arrows at both ends thereof in FIG. The collimator lens 3 is fixed by fitting the lower side of the side surface into the recess 1d of the lower surface 1b in the housing 1.
At that time, the uppermost part 3d of the side surface is arranged at a slight distance from the upper surface 1a in the housing 1. The interval is preferably about 1/3 of the height of the gate mark convex portion 3a, that is, 0.05 to
It is 0.15 mm. With this arrangement, the distortion of the refracting surface due to the contact between the upper surface 1a in the housing 1 and the collimator lens 3 is avoided, and the distance between the upper surface 1a and the lower surface 1b in the housing 1 is suppressed to be small.

As shown in FIG. 3, the maximum refraction meridian Cx is substantially parallel to the vertical direction, and the gate meridian Cg is inclined by an angle θ with respect to the maximum refraction meridian Cx. As a result, the gate mark convex portion 3a is arranged below the upper surface 1a in the housing 1. In the optical pickup 10, the angle θ is preferably set within the range of 40 to 70 °. Within that range, the laser beam bundle
It is possible to sufficiently maintain the correction effect on the cross section of L and to arrange the gate trace convex portion 3a below the upper surface 1a in the housing 1. Therefore, in the optical pickup 10 according to the first embodiment, unlike the conventional one, the gate mark convex portion 3a of the collimator lens 3 may not be fitted into the upper surface 1a in the housing 1. as a result,
Since the upper part of the housing 1 may be thinner than the conventional one, the thickness of the optical pickup 10 can be reduced as compared with the conventional one. Therefore, the optical pickup 10 according to the first embodiment is advantageous for downsizing the optical disc device.

In the collimator lens 3 according to the above example, the angle φ-θ between the maximum refraction meridian Cx and the maximum curvature meridian Cm is sufficiently large. At that time, the collimator lens 3 is fixed so that the maximum refraction meridian plane is substantially parallel to the vertical direction. However, with respect to the flatness of the cross section Se of the laser beam bundle L by the semiconductor laser, when the astigmatism due to the distribution of the refractive index in the collimator lens 3 is sufficiently small, between the maximum refraction meridian Cx and the maximum curvature meridian Cm. The angle φ-θ is sufficiently small. Then the maximum refraction meridian Cx
Instead of the plane including, the collimator lens 3 may be fixed such that the maximum refraction meridian plane is substantially parallel to the vertical direction.

[0042]

As described above, the collimator lens according to the present invention is made of plastic and can be obtained by injection molding. In the collimator lens, the convex refracting surface is non-rotationally symmetric with respect to the optical axis. In particular, the maximum curvature meridional surface is inclined with respect to the gate meridional surface by a predetermined angle φ. As a result, the maximum refraction meridional plane is inclined with respect to the gate meridional plane by a predetermined angle θ. The angle θ can be adjusted by the shape of the convex refracting surface and the injection molding conditions.

An optical pickup according to the present invention includes the above collimator lens. In the optical pickup, the maximum refraction meridian surface of the collimator lens is substantially parallel to the vertical direction. As a result, when the laser beam bundle emitted from the semiconductor laser is converted into a parallel beam bundle through the collimator lens, at the same time, the transverse section thereof is corrected from the vertically elongated elliptical shape to the perfect circular shape. Therefore, since it is not necessary to specifically include a correction lens for the cross section of the laser beam bundle, the scale of the optical system can be reduced. Therefore, the above optical pickup is advantageous for miniaturization.

In the above collimator lens, the meridional surface of the gate is inclined by the angle θ with respect to the meridional surface of maximum refraction. Therefore, in the above optical pickup, the gate mark convex portion of the collimator lens is arranged below the upper surface in the housing. Above angle θ
Is preferably set within the range of 40 to 70 °. Within this range, it is possible to sufficiently maintain the correction effect on the cross section of the laser beam bundle and to arrange the gate mark convex portion below the upper surface in the housing. Due to the arrangement, in the above optical pickup, the gate mark convex portion of the collimator lens does not have to be fitted into the upper surface in the housing. As a result, since the upper part of the housing may be thinner than the conventional one, the thickness of the optical pickup can be reduced as compared with the conventional one. Therefore, the above optical pickup is advantageous for downsizing the optical disc device.

[Brief description of drawings]

FIG. 1 is a perspective view showing an internal optical system of an optical pickup 10 in an optical disc device according to a first embodiment of the present invention.

FIG. 2 is a side view showing an internal optical system of the optical pickup 10 in the optical disc device according to the first embodiment of the present invention.

FIG. 3 is a cross-sectional view showing the vicinity of the collimator lens 3 of the optical pickup 10 according to the first embodiment of the present invention.

FIG. 4 is a perspective view showing an internal optical system of an optical pickup 100 in a conventional optical disc device.

FIG. 5 is a side view showing an internal optical system of an optical pickup 100 in a conventional optical disc device.

FIG. 6 is a cross-sectional view showing the vicinity of the collimator lens 30 of the conventional optical pickup 100.

[Explanation of symbols]

10 optical pickup 1 case 1a Top surface inside housing 1 1b Lower surface inside housing 1 2 Laser unit 2a Outlet 3 Collimator lens 3a Gate mark convex part 3b Koba part 3c convex refraction surface 4 mirror 5 Objective lens A optical axis L laser beam bundle Cross section of Se laser beam bundle L Lp parallel ray bundle Sc Cross section of parallel ray bundle Cg Gate Meridian Cx maximum refraction meridian Cm maximum curvature meridian

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Claims (5)

[Claims] 1. A plastic lens molded into a substantially cylindrical shape by injection molding; (A) a bar portion including a gate mark convex portion formed by the injection molding;
And, (B) (a) the axis of the cylindrical shape as an optical axis, (b) the meridian plane passing through the center of the gate trace convex portion (hereinafter,
A meridian that intersects with a gate meridian (hereinafter referred to as a gate meridian) at a predetermined angle and has a curvature substantially larger than any of the gate meridian and other meridians (hereinafter referred to as a maximum curvature meridian). Including a convex refracting surface;
Collimator lens having. 2. (A) The collimator lens according to claim 1; (B) The upper surface and the lower surface which are separated by a distance substantially equal to the diameter of the collimator lens are included inside, and between the upper surface and the lower surface. Holds the collimator lens, the optical axis of the collimator lens is aligned in the horizontal direction, and the gate meridian surface in the vertical direction by an angle at which the uppermost portion of the gate trace convex portion is arranged below the upper surface. (C) A semiconductor laser for injecting a bundle of light rays having a predetermined wavelength and a vertically long elliptical cross section in the optical axis direction with respect to the collimator lens; A mirror for upwardly reflecting the bundle of rays converted into a bundle of substantially parallel rays by a collimator lens; (E) focusing the bundle of rays reflected by the mirror on an optical disc above the housing To let (F) the objective lens reflected by the optical disc,
An optical pickup comprising: the mirror, and a photodetector for detecting the light flux that has returned through the collimator lens in order. 3. The optical pickup according to claim 2, wherein the inclination of the meridional surface of the gate with respect to the vertical direction is 40 to 70 °. 4. The optical pickup according to claim 2, wherein a meridian plane including the meridian of maximum curvature is substantially parallel to a vertical direction. 5. An optical disk device having the optical pickup according to claim 2.