JP2001076372A - Optical pickup and beam shaping optical element in optical pickup - Google Patents

Abstract

PROBLEM TO BE SOLVED: To miniaturize the constitution of an optical pickup and to make contributable to miniaturization of a note personal computer or the like. SOLUTION: A divergent luminous flux radiated from a semiconductor laser 2 is made to be a parallel luminous flux and is made to be shaped (nearly made circular) by an anamorphic lens 6 as a beam shaping optical element. Thereafter, a light spot is formed on an optical information recording medium by being reflected with a deflecting prism 8 and by being condensed with an objective lens 10. The anamorphic lens 6 is integrally formed into the shape that the optical axis of a first surface on which light is made incident crosses the optical axis of a second surface from which light is emitted at a certain angle, and incident light is reflected by a reflecting surface 6a to bend the optical path. Thus, the objective lens 10 side is arranged in parallel to the anamorphic lens 6, the distance between seek rails 16 for moving the optical information recording medium in a direction orthogonal to a data recording direction is narrowed, and thereby, the constitution of a light pickup is miniaturized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an optical pickup and a beam shaping optical element in the optical pickup.

[0002]

2. Description of the Related Art A light beam emitted from a semiconductor laser (hereinafter simply referred to as "light" or "light beam" as appropriate) is converted into a parallel light beam, which is condensed as a light spot on a recording surface of an optical information recording medium by an objective lens. An optical pickup for recording and / or reproducing information has been conventionally known. An example of this optical pickup will be described with reference to FIG. The light emitted from the semiconductor laser 100 is converted into a parallel light beam by the coupling lens 102, and the beam splitter 1
The light passes through the objective lens 106 and is condensed by the objective lens 106 to form a minute light spot on the optical information recording medium 108. The light reflected from the optical information recording medium 108 is again
6 and collimated into a parallel beam, and the beam splitter 104
The optical path is bent by this to enter a signal detection element (not shown). It is possible to detect the focus of the objective lens 106, the track control signal, and the information signal of the optical information recording medium 108 from the output of the signal detection element.

[0003] The light beam emitted from the semiconductor laser 100 is divergent. In other words, the light emission distribution is anisotropic, and as shown in FIG. 7, a direction PL (parallel to the bonding plane) parallel to the bonding plane (active layer) of the semiconductor laser 100.
And the direction NL perpendicular to the bonding surface (the direction perpendicular to the bonding surface) NL has a different light intensity distribution. This is because the divergence angle of the divergent light beam is not uniform, the divergence angle is small in the direction parallel to the joint surface, and large in the direction perpendicular to the joint surface. Typical values of the far-field image are a divergence angle θ _PL ≒ 10 ° in the direction parallel to the bonding surface and a divergence angle θ _NL ≒ 30 in the direction perpendicular to the bonding surface.
°.

[0004] Such an anisotropic light beam is converted into a parallel light beam by the coupling lens 102, and the objective lens 106 is left as it is.
When the light is condensed, the spot shape of the disk surface becomes an elliptical shape whose major axis is in the joining surface direction. As shown in FIG. 8A, the major axis direction of the elliptical spot 110 is the optical information recording medium 1.
When the light is irradiated in a state perpendicular to the track 108a, the light is irradiated to the plurality of tracks 108a. Therefore, the information signal from the adjacent track 108a is embedded (crosstalk) and the light is irradiated to the adjacent track 108a. Inconvenience such as writing occurs. As shown in FIG. 8B, the major axis direction of the elliptical spot 110 corresponds to the optical information recording medium 1.
08 in parallel with the track 108a,
The resolution in the data recording direction (longitudinal direction of the track 108a) decreases, and it becomes impossible to detect a good reproduction signal and write information.

[0005] For this reason, attempts have been made to use an optical element having a beam shaping function to expand a beam incident on the objective lens 106 in a specific direction to finally obtain a substantially circular spot. As the system, there are a cylindrical lens system and a prism system. FIG. 9 shows an example of the cylindrical lens system. 9A is a cross-sectional view in a direction parallel to the bonding surface, and FIG. 9B is a cross-sectional view in a direction perpendicular to the bonding surface. Now, it is assumed that the coupling lens 102 captures the laser beam from the semiconductor laser 100 whose relative intensity in the direction parallel to the bonding surface and in the direction perpendicular to the bonding surface is up to X (ratio to the peak intensity). As shown in FIG. 9B, parallel light having a light beam diameter D1 is obtained in the direction orthogonal to the bonding surface. In the direction parallel to the bonding surface, as shown in FIG. 9A, only the diameter of the light flux D0 (D0 <D1) can be obtained only by the coupling lens 102. Therefore, the cylindrical lens 11
The diameter only in the direction parallel to the joining surface is enlarged from D0 to D1 using 2,114. FIG. 10 shows an example of the prism system.
The parallel light having a beam diameter of D0 converted into a parallel light beam by the coupling lens 102 is refracted by the prism 116, so that the beam diameter is enlarged to D1.

However, in the cylindrical lens system, three lenses, that is, a coupling lens 1
02, since the cylindrical lenses 112 and 114 are used, there is a problem that high precision is required in their alignment. Further, in the prism type, there is a problem that the optical path needs to be bent to a predetermined angle by refraction, so that the degree of freedom of the shape of the optical system is lost.

In recent years, in order to address such a problem, a beam shaping optical element using an anamorphic lens having a simpler configuration has been proposed. In this configuration, a beam shaping optical element is configured only by a single anamorphic lens, and the configuration is simplified. One example will be described with reference to FIG. FIG. 11A shows an anamorphic lens 11.
8 shows the YZ cross-sectional shape, FIG. 11B shows the XZ cross-sectional shape of the anamorphic lens 118, and reference numeral 120 denotes a hologram element. The YZ section is a cross-sectional view in a direction parallel to the bonding surface, and the XZ section is a cross-sectional view in a direction orthogonal to the bonding surface. The focal length f _{Y of the} anamorphic lens 118 in the direction parallel to the bonding surface and the focal length f _{X in the} direction perpendicular to the bonding surface are different.
It is a _Y> f _X.

FIG. 12 shows an anamorphic lens 118.
1 shows an optical system using the method. FIG. 12A shows a cross section in a direction parallel to the bonding surface, and FIG. 12B shows a cross section in a direction perpendicular to the bonding surface. The light radiated from the semiconductor laser 100 passes through the hologram element 120 and the anamorphic lens 11
The beam is shaped at 8 and is converted into a parallel light beam. Then, the light is reflected by the deflecting prism 122 and
The light is focused on the recording surface of the optical information recording medium 108 as a light spot by 6. The light reflected from the optical information recording medium 108 is collimated again by the objective lens 106 and converged by the anamorphic lens 118,
The light is diffracted by the hologram element 120 and enters the signal detection light-receiving element 124. Thereby, the light receiving element 1 for signal detection
From 24, information signal, servo (focus, track)
The signal can be detected. As described above, when the anamorphic lens 118 is used as a beam shaping optical element, the parallel light beam formation and shaping (substantially circularization) of light are performed in one lens block. High alignment accuracy between the lenses can be eliminated, and productivity and reliability can be improved.

In FIG. 12, reference numeral 126 denotes an optical system housing, and reference numeral 128 denotes an entire optical system.
A seek rail for moving in a direction perpendicular to the data recording direction 08 is shown. 12, optical system housing 1
26 has a seek rail 128 in the through hole 126a.
Is inserted and supported slidably, and a right end portion is a convex portion 126 b formed integrally with the optical system housing 126.
Are placed and supported on a seek rail 128.

[0010]

In recent years, with the spread of notebook personal computers, information reproducing / recording devices have also been incorporated in notebook personal computers. The information reproducing / recording device for a built-in notebook personal computer is required to be miniaturized, and the interval W between the seek rails 128 is generally 45 mm or less. In order to shape (substantially circularize) the light of the semiconductor laser 100 with the anamorphic lens 118,
A focal length ratio of about f _Y : f _X = (1.5 to 3): 1 is required. That is, the far-field pattern of a general semiconductor laser for an optical device is such that the bonding plane parallel direction: the bonding plane orthogonal direction = 1: 2 to 3. In order to make the intensity distribution of the laser beam incident on the objective lens substantially equal in the direction parallel to the bonding surface and in the direction perpendicular to the bonding surface, the magnification of the beam shaping is as follows: parallel direction to bonding surface: orthogonal direction to bonding surface = 1:
2-3. However, if the magnification of the beam shaping is excessively increased, an error in adjusting the distance between the light source and the anamorphic lens in the optical axis direction becomes severe. Therefore, in consideration of the adjustment, it is desirable to suppress the beam shaping to a low value. On the other hand, depending on the device, there are cases where it is desired to increase the light use efficiency as much as possible and obtain a substantially circular spot. In such a case, the focal length of the anamorphic lens in the direction perpendicular to the cementing surface is shortened, and the magnification of beam shaping is increased. Therefore, in an optical system using an optical element for beam shaping, the magnification of beam shaping is determined by the characteristics of the semiconductor laser to be used and the purpose of the device, and the magnification is generally 1.5 to 3 times. is there.

To realize such magnification with a single optical element (single lens), an anamorphic lens 1
18 has a thickness t of about 10 mm or more. When this thick anamorphic lens 118 is used in the configuration shown in FIG. 12, it is difficult to make the interval W between the seek rails 128 equal to or less than 45 mm. If the entire optical system is rotated by 90 °, the seek rails 128 are located on both sides of the optical system housing 126 in the longitudinal direction.
Although the distance between the seek rails 128 can be reduced, there is a problem that the configuration of the optical system in the longitudinal direction of the seek rail 128 becomes large.

Accordingly, the present invention provides an optical system using an anamorphic lens, which can reduce the seek rail span,
An object of the present invention is to provide an optical pickup and a beam shaping optical element in the optical pickup which can contribute to miniaturization of a notebook personal computer or the like.

[0013]

SUMMARY OF THE INVENTION The present invention is based on the idea that the optical system can be made compact only by changing the conventional arrangement of the light source, the anamorphic lens and the deflecting prism in series. While maintaining the characteristics of the anamorphic lens that can obtain the function of the lens in a single lens block, the optical path is bent to obtain the degree of freedom of arrangement on the objective lens side.

More specifically, according to the first aspect of the present invention, a light beam emitted from a semiconductor laser is transmitted from an anamorphic lens having a different focal length in a direction perpendicular to a direction parallel to an active layer of the semiconductor laser. In an optical pickup for recording and / or reproducing information by converting a parallel light beam by a beam shaping optical element into a light spot on a recording surface of an optical information recording medium by an objective lens, The optical axis of the surface and the optical axis of the second surface are not on the same straight line.

According to a second aspect of the present invention, in the beam shaping optical element according to the first aspect, a configuration is adopted in which the beam shaping optical element is constituted by a single anamorphic lens.

According to the third aspect of the present invention, the first or second aspect is provided.
The described beam shaping optical element employs a configuration in which the optical axis of the first surface and the optical axis of the second surface intersect at a certain angle.

According to a fourth aspect of the present invention, in the beam shaping optical element according to the third aspect, a reflecting surface is provided at an intersection where the optical axis of the first surface and the optical axis of the second surface intersect at an angle. When the minimum incident angle of the light beam incident on the reflecting surface is θmin, and the refractive index of the material of the anamorphic lens is n,
The configuration satisfies the condition of sin θmin ≧ 1 / n.

According to the fifth aspect of the present invention, the light beam emitted from the semiconductor laser is converted into a parallel light beam, and is converged as a light spot on a recording surface of an optical information recording medium by an objective lens, thereby recording and / or reproducing information. In the optical pickup to be performed, a light beam is converted into a parallel light beam by the beam shaping optical element according to claim 4, and a light beam satisfying a condition of sin θ <1 / n is also incident on the reflection surface.

According to a sixth aspect of the present invention, in the optical pickup according to the fifth aspect, a light receiving element is disposed at a position where a light beam transmitted through the reflection surface is incident.

According to the seventh aspect of the present invention, the light beam emitted from the semiconductor laser is converted into a parallel light beam, which is condensed as a light spot on a recording surface of an optical information recording medium by an objective lens to record and / or reproduce information. 4. The optical pickup according to claim 1, wherein the light beam is converted into a parallel light beam.
The configuration employs the beam shaping optical element described above.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. As shown in FIG. 1, in the optical pickup according to the present embodiment, the divergent light beam emitted from the semiconductor laser 2 is transmitted through the hologram element 4 to form a single anamorphic lens 6 as a beam shaping optical element. Item 2) beam shaping (substantially circular shape) and parallel light flux in item 2)
In addition, the optical path can be bent at a substantially right angle. Thereafter, the light is reflected by the deflecting prism 8 and condensed as a light spot on the recording surface of an optical information recording medium (not shown) by the objective lens 10. The light reflected from the optical information recording medium is
Is again converted into a parallel light beam, converged by the anamorphic lens 6, diffracted by the hologram element 4, and incident on the light receiving element 12 for signal detection. As a result, an information signal and a servo (focus, track) signal can be detected from the signal detection light receiving element 12.

These optical pickup components are supported in an optical system housing 14, and the optical system housing 14 (substantially the entire optical pickup configuration) is supported by two seek rails 16, 16 for an optical information recording medium. It can be moved in a direction perpendicular to the data recording direction (the longitudinal direction of the seek rail). In FIG. 1, the left end of the optical system housing 14 is slidably supported by a seek rail 16 inserted through a through hole 14a, and the right end is a convex portion 14b formed integrally with the optical system housing 14. Are placed and supported on the seek rail 16.

As shown in FIG. 2, the anamorphic lens 6 is a first anamorphic lens 6 into which light emitted from the semiconductor laser 2 enters.
A shape in which the optical axis LS1 of the surface intersects with the optical axis LS2 of the second surface at a certain angle α, from which the beam shaped and parallelized light is emitted;
That is, the optical axis LS1 and the optical axis LS2 are integrally formed so as not to be on the same straight line as in the related art.
3, 7) A reflection surface 6a is formed at a position where the two optical axes LS1 and LS2 intersect. When the optical path is bent at a substantially right angle by the anamorphic lens 6, the deflecting prism 8 and the objective lens 10 can be arranged in parallel with the anamorphic lens 6, as shown in FIG. Can be made narrower than before.

Next, a modified example of the anamorphic lens 6 as a beam shaping optical element will be described with reference to FIG. The anamorphic lens 18 in this embodiment is
When the refractive index of the material of the anamorphic lens 18 is n, the angle between the normal 20 of the reflecting surface 18a of the anamorphic lens 18 and the light beam incident on the reflecting surface 18a is θ, and the minimum incident angle is θmin, sin θmin It is formed so as to satisfy the condition of ≧ 1 / n (claim 4). sin
The angle θ at which θ = 1 / n is a critical angle. Therefore, si
When the condition of nθmin ≧ 1 / n is satisfied, the reflection surface 18
All of the angles of the light beams incident on a are greater than or equal to the critical angle, and all the incident light is totally reflected. By setting such conditions, it is not necessary to provide a coating layer for increasing the reflection on the reflection surface 18a, which is advantageous in terms of productivity and cost. Anamorphic lens 1 shown in FIG.
8 can be similarly used in the optical pickup configuration shown in FIG.

Next, another embodiment of the optical pickup will be described with reference to FIG. Note that the overall configuration is the same as that shown in FIG. In the optical pickup of this embodiment, the anamorphic lens 18 shown in FIG. 3 is used.
A light beam incident on the first surface of the anamorphic lens 18 is also incident on the first surface of the anamorphic lens 18, that is, a light beam that satisfies the condition of sin θ <1 / n (claim 5).
Is smaller than the critical angle, the light rays incident at such an angle are not totally reflected by the reflecting surface 18a, but are refracted by the reflecting surface 18a and transmitted through the reflecting surface 18a as shown by hatching. If the transmitted light 22 is monitored by a monitor (not shown), the emission power of the laser light can be controlled. As a specific example, as shown in FIG. 5, a light receiving element 24 as monitoring means is provided at a position where the transmitted light 22 is incident (claim 6), and based on a signal from the light receiving element 24, the emission power of the semiconductor laser 2 is determined. Control.

[0026]

According to the first, third or seventh aspect of the present invention, the optical axis of the first surface and the optical axis of the second surface of the anamorphic lens are not on the same straight line. The optical system can be miniaturized by the degree of freedom of arrangement on the side, which can contribute to miniaturization of notebook computers and the like.

According to the second aspect of the present invention, since the beam shaping optical element is constituted by a single anamorphic lens, the size of the optical system can be further reduced.

According to the fourth aspect of the present invention, since the light incident on the reflecting surface of the anamorphic lens is totally reflected, it is not necessary to provide a coating layer for increasing the reflection on the reflecting surface. The productivity can be improved and the cost can be reduced as compared with the case where a coat layer is provided.

According to the fifth aspect of the present invention, since a light beam whose incident angle is smaller than the critical angle is incident on the reflecting surface, the light emission power of the laser beam can be controlled with a simple structure.

According to the sixth aspect of the present invention, since the light receiving element is arranged at the position where the light beam transmitted through the reflecting surface is incident, the light emission power of the laser light can be controlled with a simple structure.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an optical pickup according to one embodiment of the present invention.

FIG. 2 is a plan view of an anamorphic lens.

FIG. 3 is a plan view of an anamorphic lens according to another example.

FIG. 4 is a plan view showing a use state of an anamorphic lens in an optical pickup according to another embodiment.

FIG. 5 is a plan view showing another use state of an anamorphic lens in an optical pickup according to another embodiment.

FIG. 6 is a schematic diagram showing a configuration of a conventional optical pickup.

FIG. 7 is a graph showing a relationship between an emission angle and light intensity.

8A and 8B are diagrams showing a relationship between a track of an optical information recording medium and an elliptical spot, wherein FIG. 8A is a diagram in a case where irradiation is performed in a state where the major axis direction of the elliptical spot is orthogonal to the track, and FIG. FIG. 5 is a diagram in a case where irradiation is performed in a state where a major axis direction of a spot is parallel to a track.

9A and 9B are schematic diagrams of an optical system of a cylindrical lens system, in which FIG. 9A is a cross-sectional view in a direction parallel to the bonding surface, and FIG. 9B is a cross-sectional view in a direction perpendicular to the bonding surface.

FIG. 10 is a cross-sectional view of a prism type optical system in a direction orthogonal to a bonding surface.

11A and 11B are schematic diagrams of an optical system using an anamorphic lens, wherein FIG. 11A is a cross-sectional view in a direction parallel to the bonding surface, and FIG. 11B is a cross-sectional view in a direction perpendicular to the bonding surface.

12A and 12B are schematic views of an optical pickup using an anamorphic lens, where FIG. 12A is a cross-sectional view in a direction parallel to a bonding surface,
(B) is a cross-sectional view in a direction orthogonal to the bonding surface.

[Explanation of symbols]

 2 Semiconductor laser 6, 18 Anamorphic lens 6a, 18a Reflecting surface 10 Objective lens 24 Light receiving element LS1 Optical axis of first surface LS2 Optical axis of second surface

Claims (7)

[Claims] A light beam emitted from a semiconductor laser is converted into a parallel light beam by a beam shaping optical element comprising an anamorphic lens having a different focal length in a direction perpendicular to a direction parallel to an active layer of the semiconductor laser and a direction perpendicular thereto. In an optical pickup for recording and / or reproducing information by condensing a light spot on a recording surface of an optical information recording medium by a lens, an optical axis of a first surface of the anamorphic lens and an optical axis of a second surface of the anamorphic lens Beam shaping optical element characterized in that the light beams are not on the same straight line 2. A beam shaping optical element according to claim 1, wherein said beam shaping optical element is constituted by a single anamorphic lens. 3. The beam shaping optical element according to claim 1, wherein the optical axis of the first surface and the optical axis of the second surface intersect at a certain angle. 4. A beam shaping optical element according to claim 3, further comprising a reflection surface at an intersection where the optical axis of the first surface and the optical axis of the second surface intersect at an angle, and a light beam incident on the reflection surface. The beam shaping optical element satisfies the condition of sin θmin ≧ 1 / n, where θmin is the minimum incident angle of θmin and n is the refractive index of the material of the anamorphic lens. 5. An optical pickup for recording and / or reproducing information by converting a light beam emitted from a semiconductor laser into a parallel light beam and converging the light beam as a light spot on a recording surface of an optical information recording medium by an objective lens. Item 5. An optical pickup, wherein a light beam is converted into a parallel light beam by the beam shaping optical element according to Item 4, and a light beam satisfying a condition of sin θ <1 / n is also incident on the reflection surface. 6. The optical pickup according to claim 5, wherein a light receiving element is arranged at a position where a light beam transmitted through the reflection surface is incident. 7. An optical pickup for recording and / or reproducing information by converting a light beam emitted from a semiconductor laser into a parallel light beam and converging it as a light spot on a recording surface of an optical information recording medium by an objective lens. An optical pickup characterized by using the beam shaping optical element according to claim 1, 2 or 3 for converting a light beam into a parallel light beam.