JP2001154153A - Optical element and optical device, and recording and reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical element having a beam shaping function constituted so that the performance of anamorphic lens can be prevented from being deteriorated even when a fluctuation of wavelength is generated. SOLUTION: In the optical element constituted of an anamorphic lens 11 having a beam shaping function having different focal distances in a direction vertical to the direction in parallel with the active layer of the semiconductor laser 10 for turning lights from a semiconductor laser 10 into almost parallel lights, the anamorphic lens 11 is integrally constituted of plural materials 12 and 13, and at least the first face and final face (third face) of the anamorphic lens 11 is formed like an aspheric shape. Thus, it is possible to realize an optical element (collimate lens for shaping beams) whose wavefront deterioration is small against wavelength fluctuation by allowing the optical element to have an achromatic action.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention is used for an optical pickup optical system of an optical disk drive, and a laser scanning optical system of an image forming apparatus such as a digital copying machine, a laser printer, a laser plotter, and a laser facsimile.
An optical element that converts light from a semiconductor laser into substantially parallel light, and an optical device such as an optical pickup including the optical element,
And a recording / reproducing device such as an optical disk drive provided with the optical device.

[0002]

2. Description of the Related Art As an optical element which is used in an optical pickup optical system of an optical disk drive, a laser scanning optical system of an image forming apparatus such as a digital copier, a laser printer, etc., and converts light from a semiconductor laser into substantially parallel light, 2. Description of the Related Art An optical element including an anamorphic lens (also referred to as an anamorphic lens) having a beam shaping function having different focal lengths in a direction parallel to and perpendicular to an active layer of a semiconductor laser is known. Hereinafter, an example of an optical system using the optical element is shown in FIG.

[0005] The optical system shown in FIG. 5 is an example of an optical pickup optical system of an optical disk drive. In this optical system, light emitted from a semiconductor laser 1 is converted into a parallel beam by a coupling lens 2. The light passes through the splitter 3 and is condensed by the objective lens 4 to form a minute light spot on a recording medium 5 such as an optical disk. The light reflected by the recording medium 5 passes through the objective lens 4 again, is converted into substantially parallel light, the optical path is bent by the beam splitter 3, and is incident on a signal detection element (not shown). From the output of the signal detecting element, a focus control signal of the objective lens 4, a track control signal, and an information signal of the recording medium 5 are detected. The semiconductor laser 1 has a non-uniform emission distribution, and as shown in FIG. 6, the intensity in a direction (θ //) parallel to the bonding surface (active layer) of the semiconductor laser and a direction (θ⊥) perpendicular thereto. The distribution is different. Typical values of the far-field image are θ // − 10 ° and θ⊥−30 °. When such an anisotropic light beam is converted into substantially parallel light by the coupling lens 2 and condensed by the objective lens 4 as it is, the light spot formed becomes an ellipse. As shown in FIG. 7, when the long axis direction of the elliptical spot 6 is irradiated in a state perpendicular to the track 7 of the recording medium, a plurality of tracks 7 are irradiated with light. Problems such as leakage (crosstalk) and writing to an adjacent track occur. Further, as shown in FIG. 8, when the elliptical spot 6 is irradiated in a state where the major axis direction is parallel to the track 7 of the recording medium, the resolution in the data recording direction is reduced, so that a good reproduction signal detection and information Writing becomes impossible.

Therefore, there has been attempted a method of obtaining a substantially circular light spot by expanding a beam incident on an objective lens in a specific direction by using a beam shaping optical system. As a beam shaping optical system, there is one in which a beam shaping optical system is configured with only an optical element including a single anamorphic lens, and the optical system is simplified. 9A and 9B are diagrams showing an example of a beam shaping optical system using a conventional anamorphic lens 8, in which FIG. 9A is a YZ sectional view of the beam shaping optical system, and FIG.
Is an XZ sectional view of the beam shaping optical system. The direction (θ) in which the YZ section is parallel to the bonding surface (active layer) of the semiconductor laser
//), the XZ section is a direction (θ⊥) perpendicular to the bonding surface (active layer) of the semiconductor laser, and reference numeral 9 is a hologram element. In the anamorphic lens 8, the focal length fy in the direction parallel to the active layer of the semiconductor laser is different from the focal length fx in the direction perpendicular to the active layer, and fy> fx.

[0005]

The disadvantages of the above-mentioned conventional anamorphic lens are described below. The refractive index of the material (glass, resin, etc.) that forms the lens is determined by the wavelength of light. The wavelength of the semiconductor laser changes depending on the temperature of the laser chip (for example, a change in laser output due to a change in ambient temperature). Therefore, when an anamorphic lens is used with a semiconductor laser as a light source,
Changes in the refractive index of an anamorphic lens are inevitable.
The anamorphic lens has a focal length fy parallel to the active layer of the semiconductor laser and a focal length fx perpendicular to the active layer.
Are different, a change in the refractive index causes a difference between the focal length changes Δfy and Δfx in the respective directions, resulting in astigmatism. For example, when an optical pickup of an optical disk drive is configured using an anamorphic lens, wavelength fluctuation causes astigmatism in a light spot on the disk surface, and good signal reproduction / recording cannot be performed.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and a first object of the present invention is to provide an optical element having a configuration in which the performance of an anamorphic lens does not deteriorate even if a wavelength variation occurs. A second object of the present invention is to provide an optical device such as an optical pickup in which spot performance is not degraded at the time of switching between reproduction / recording and a change in wavelength due to environmental temperature change. A third object of the present invention is to provide a recording / reproducing apparatus such as an optical disk drive having a stable performance with respect to a wavelength change due to a change in reproduction / recording or an environmental temperature change.

[0007]

According to a first aspect of the present invention, there is provided an optical element for converting light from a semiconductor laser into substantially parallel light, comprising an active layer of the semiconductor laser. An optical element comprising an anamorphic lens having a beam shaping function having different focal lengths in directions parallel to and perpendicular to the anamorphic lens, wherein the anamorphic lens is made of a plurality of materials.
According to a second aspect of the present invention, in the optical element according to the first aspect, the anamorphic lens is integrally formed of a plurality of materials, and a first surface and a final surface thereof are aspherical. I do. According to a third aspect of the present invention, in the optical element according to the second aspect, the cemented surface of the anamorphic lens is an aspherical surface. According to a fourth aspect of the present invention, in the optical element according to the first, second or third aspect, the anamorphic lens includes two lenses made of different materials, and is formed in a plane parallel to an active layer of the semiconductor laser. The basic curvature in the order from the semiconductor laser side, negative, positive, negative, the basic curvature in a plane perpendicular to the active layer of the semiconductor laser, in order from the semiconductor laser side. , Positive, positive, and negative. According to a fifth aspect of the present invention, in the optical element of the first, second, third or fourth aspect, the Abbe number of the material of the anamorphic lens on the side where the semiconductor laser light is incident is νd1, and the light of the semiconductor laser is When the Abbe number of the material on the side from which light exits is νd2, νd1 <νd2.

[0008] In order to achieve the second object, claim 6
In the invention according to the invention, an optical device for converting light from a semiconductor laser into substantially parallel light with an optical element and then condensing the light on an information recording medium with an objective lens, wherein the optical element is any one of claims 1 to 5. An optical element according to any one of the above aspects is provided.

[0009] In order to achieve the third object, a seventh aspect is provided.
In the invention according to the invention, after the light from the semiconductor laser is converted into substantially parallel light by an optical element, the optical device includes an optical device that focuses the light on an information recording medium with an objective lens, recording of the information recording medium,
In a recording / reproducing apparatus for reproducing or erasing, an optical device according to claim 6 is provided as the optical device.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the illustrated embodiments.

(Embodiment 1) First, a first embodiment (embodiments of claims 1, 2, 4, and 5) of the present invention will be described.
FIG. 1 is a view showing one embodiment of a beam shaping optical system using an anamorphic lens 11 of the present invention, wherein (a) is parallel to a bonding surface (active layer) of a semiconductor laser chip of the beam shaping optical system. (B) is a cross-sectional view (XZ cross-section) orthogonal to the bonding surface (active layer) of the semiconductor laser chip of the beam shaping optical system. Reference numeral 9 denotes a hologram element. Light emitted from the semiconductor laser 10 (only the emission point is shown) passes through the hologram element 9 and passes through the anamorphic lens 11 to become parallel light. In this embodiment, the anamorphic lens 11 is 2
It is constituted integrally by the kinds of materials 12 and 13,
The first surface and the third surface (final surface) are aspherical. Here, the wavelength variation of the conventional anamorphic lens 8 made of one kind of material shown in FIG. 9 and the anamorphic lens 11 made of two kinds of materials 12 and 13 of this embodiment shown in FIG. FIG. 2 shows the values of the wavefront aberration. 2 is a conventional anamorphic lens, and the two-piece ball A is an anamorphic lens of the present embodiment. As is clear from FIG. 2, by forming the anamorphic lens with a plurality of materials, it is possible to have an achromatizing effect, and it is possible to suppress wavefront deterioration due to wavelength fluctuation.

Here, the anamorphic lens 11
Is represented by the following equation. Z = [{(1 / RX ) · x 2 + (1 / RY) y 2} / {1 + √ {1- (1 + KX) · (1 / RX) 2 · x 2 - (1 + KY)・ (1 / RY) 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 ... (1) Z: Z axis Sag on parallel surfaces. RX, RY: Curvature radius in x and y directions. KX, KY: Conical coefficients in the x and y directions. AR, BR, CR, DR: Represents deformed rotationally symmetric parts of order 4, 6, 8, and 10 from a cone. AP, BP, CP, DP: Represents deformed non-rotationally symmetric parts of order 4, 6, 8, 10 from the cone.

Table 1 below shows an example of specific lens data of the conventional single-lens anamorphic lens 8. Table 2 shows the data of the two-lens A anamorphic lens 11 of the present embodiment. An example of specific lens data is shown. FIG.
9 (conventional example), in the optical system of FIG. 9 (conventional example), the hologram element 9 disposed before the anamorphic lens 11 has a thickness of 5.37 (mm) and a glass type of BK7. In the conventional single-lens anamorphic lens 8 shown in FIG. 9, the glass type is BACD5 and the wall thickness is 10.680169 (mm). Further, in the two-lens A anamorphic lens 11 of the present embodiment of FIG. 1, the material 12 is glass type 1: LAFL2 (Abbe number: 48.5) and thickness D1: 5.
843753 (mm), and the material 13 is glass type 2: BACD12 (Abbe number: 59.5), wall thickness D2:
6.189598 (mm). In Tables 1 and 2 below, “E” after the numerical value indicates “power of × 10”.
-04 "is" ^{x10 -04} ".

[0014]

[Table 1]

[0015]

[Table 2]

As is clear from the above-mentioned lens constituent material, lens surface shape (Equation (1)) and lens data (Table 2), the anamorphic lens 11 of this embodiment has two lenses 12 of different materials. , 13 and the basic curvature (the radius of curvature RY of the reciprocal of the curvature in Table 2) in a plane parallel to the active layer of the semiconductor laser 10 (in the YZ section) is the first curvature when viewed from the semiconductor laser 10 side. In the order of the surface, the second surface, and the third surface, negative, positive, and negative are the basic curvatures in the plane perpendicular to the active layer of the semiconductor laser 10 (in the XZ cross section) (in Table 2, the curvature is the inverse of the curvature). The radius RX) is positive, positive, and negative in the order of the first surface, the second surface, and the third surface when viewed from the semiconductor laser 10 side (claim 4). In the anamorphic lens 11 of the present embodiment, the Abbe number νd1 of the material 12 on the light incident side of the semiconductor laser 10 is νd1 = 48.5, and the Abbe number of the material 13 on the light emitting side of the semiconductor laser 10 is νd1 = 48.5. Since the number νd2 is νd2 = 59.5, νd1 <νd2 (claim 5).

(Embodiment 2) Next, a second embodiment of the present invention (an embodiment of claims 3, 4 and 5) will be described. In this embodiment, the configuration of the beam shaping optical system using the anamorphic lens 11 is the same as that shown in FIG.
2 and 13 are integrally formed, and the joint surface (second surface) is aspherical. FIG. 3 shows the wavelengths of the bonding surface (second surface B) of the present embodiment having an aspherical surface (two-piece ball B) and the wavelength of the bonding surface (second surface A) of Example 1 having a spherical bonding surface (second surface). 9 shows a wavefront aberration with respect to fluctuation. Generally, a semiconductor laser has a chip temperature that rises due to light emission, and the wavelength shifts to a longer wavelength side. Therefore, the anamorphic lens is made of two materials 1
When the joint surface (second surface) when integrally formed by the components 2 and 13 is made aspherical, the wavefront deterioration on the long wavelength side can be further suppressed.

Here, since the surface shape of the anamorphic lens of the present embodiment is also represented by the equation (1), Table 3 shows specific lens data of the anamorphic lens of the two-piece ball B of the present embodiment. An example is shown below. The anamorphic lens 11
The hologram element 9 disposed in the preceding stage is 5.37 (mm) in thickness and BK7 in glass type. Two-ball B anamorphic lens 1 of the present embodiment
In the case of No. 1, the material 12 is glass type 1: LAFL2 (Abbe number: 48.5) and thickness D1: 5.
843753 (mm), and the material 13 is glass type 2: BACD12 (Abbe number: 59.5), wall thickness D2:
6.189598 (mm). That is, the configuration is the same as that of the first embodiment except for the lens data of the surface shape.

[0019]

[Table 3]

As is clear from the above-mentioned lens constituent material, lens surface shape (Equation (1)) and lens data (Table 3), the anamorphic lens 11 of this embodiment has two lenses 12 of different materials. , 13, the first surface, the second surface, and the third surface are aspherical surfaces, and the basic curvature (in the YZ cross section) in a plane parallel to the active layer of the semiconductor laser 10 (in the YZ section). The reciprocal radius of curvature RY) is the semiconductor laser 1
When viewed from the 0 side, the first surface, the second surface, the third surface in the order of negative, positive,
The basic curvature (the radius of curvature RX which is the reciprocal of the curvature in Table 3) in a plane perpendicular to the active layer of the semiconductor laser 10 (in the XZ section) is the first curvature when viewed from the semiconductor laser 10 side.
The order of the surface, the second surface, and the third surface is positive, positive, and negative (claim 4). Also, in the anamorphic lens of the present embodiment, the material 12 on the light incident side of the semiconductor laser 10 is also used.
Number νd1 is νd1 = 48.5, and the semiconductor laser 1
The Abbe number νd2 of the material 13 on the side where the light of 0 is emitted is νd2 =
Since 59.5, νd1 <νd2 (claim 5).

(Embodiment 3) Next, FIG. 4 shows an example in which the anamorphic lens of the present invention is mounted on an optical device (optical pickup) of an optical disk drive which is one of recording and reproducing devices.
Shown in 4A is a cross-sectional view of the optical pickup in a direction (θ //) parallel to the bonding surface (active layer) of the semiconductor laser, and FIG. 4B is a direction perpendicular to the bonding surface (active layer) of the semiconductor laser. FIG. 4 is a cross-sectional view of the optical pickup at (θ⊥).
This optical pickup includes a semiconductor laser 101, a hologram element 102, an anamorphic lens 103 having a beam shaping function, a deflecting prism 104, an objective lens 10
5. A light receiving element 107 for signal detection is provided, and these components are mounted on an optical system housing 108.
The optical system housing 108 is connected to the seek rail 1.
The optical system housing 108 is moved by a drive mechanism (not shown).
, And the entire optical system is configured to be moved in a direction perpendicular to the data recording direction (track direction (circumferential direction)) of the optical recording medium 106. Although not shown, the objective lens 105 is supported by an actuator for tracking and focusing, and the direction of the optical axis and the optical axis and the optical recording medium 10 are controlled by the actuator.
The track 6 is moved in a direction perpendicular to the track 6 to perform tracking and focusing control. In FIG. 4, the hologram element 102
The anamorphic lens 103 has the same configuration as the beam shaping optical system shown in FIG. 1, and the configuration of the anamorphic lens 103 is the configuration of the first or second embodiment.

In the optical pickup having the structure shown in FIG. 4, the light emitted from the semiconductor laser 101 passes through the hologram element 102, is shaped by the anamorphic lens 103, and is converted into substantially parallel light. The light is reflected and condensed by the objective lens 105 as a minute light spot on the recording surface of the optical recording medium 106. Then, the light reflected by the optical recording medium 106 is converted into parallel light again by the objective lens 105, converted into convergent light by the anamorphic lens 103, diffracted by the hologram element 102, and incident on the light receiving element 107 for signal detection. And
From the output signal of the signal detection light receiving element 107, an information signal,
Servo signal (focus control signal, track control signal)
Is detected. The servo signal (focus control signal, track control signal) is fed back to the above-described actuator for tracking and focusing via a control system (not shown), and tracking control and focusing control of the objective lens 105 are performed.

In the optical pickup of this embodiment, the anamorphic lens composed of a plurality of materials shown in the first or second embodiment is used as a collimating lens for beam shaping, so that an achromatic effect is obtained. And the wavefront deterioration due to the wavelength fluctuation can be suppressed, so that the deterioration of the spot performance can be prevented. Therefore, according to the present embodiment, it is possible to realize an optical disk drive with stable performance against wavelength fluctuation due to switching between reproduction and recording or a change in environmental temperature.

[0024]

As described above, according to the first to fifth aspects of the present invention, there is provided an optical element for converting light from a semiconductor laser into substantially parallel light, wherein the optical element has a direction parallel to an active layer of the semiconductor laser. An optical element comprising an anamorphic lens having a beam shaping function having different focal lengths in vertical directions, wherein the anamorphic lens is integrally formed of a plurality of materials, and at least a first surface of the anamorphic lens is provided. The final surface has an aspherical shape and has an achromatizing effect in addition to the beam shaping function. Therefore, an optical element that minimizes wavefront degradation due to wavelength fluctuations (such as when switching between reproduction and recording and changes in environmental temperature) (A beam shaping collimating lens) can be realized.

Further, in the invention according to claim 6, in an optical device for converting light from a semiconductor laser into substantially parallel light with an optical element and condensing the light on an information recording medium with an objective lens, By using an optical element (a beam shaping collimating lens) having an achromatic effect in addition to the beam shaping function according to any one of claims 1 to 5, wavelength fluctuation (when switching between reproduction and recording, , An optical device such as an optical pickup which has a small wavefront deterioration with respect to environmental temperature change and does not deteriorate the spot performance.

Further, in the invention according to claim 7, after the light from the semiconductor laser is converted into substantially parallel light by an optical element,
7. A recording and reproducing device for recording, reproducing or erasing the information recording medium, comprising an optical device for condensing the light on an information recording medium with an objective lens, wherein the optical device is an optical device.
Equipped with an optical device that uses an optical element (collimating lens for beam shaping) that has an achromatizing effect in addition to the beam shaping function described, it can be used for wavelength fluctuations (such as when switching between reproduction and recording, and changes in environmental temperature). On the other hand, it is possible to realize a recording / reproducing apparatus such as an optical disk drive having stable performance without deteriorating the spot performance.

The optical element according to any one of claims 1 to 5 can be used in a digital copying machine, a laser printer, a laser plotter, a laser facsimile, or the like, in addition to an optical device (optical pickup or the like) of a recording / reproducing device (optical disk drive or the like). It can also be used in a laser scanning optical system for writing of an image forming apparatus, and when used as a collimating lens for beam shaping in a laser scanning optical system to convert light from a semiconductor laser into substantially parallel light, it can be used on an image carrier. Can be suppressed from deteriorating due to wavelength fluctuation of the light spot for scanning, and image writing with stable spot performance can be performed.

[Brief description of the drawings]

FIG. 1 is a view showing one embodiment of a beam shaping optical system using an anamorphic lens according to the present invention, wherein (a) is parallel to a bonding surface (active layer) of a semiconductor laser chip of the beam shaping optical system. (B) is a cross-sectional view (XZ cross-sectional view) orthogonal to the bonding surface (active layer) of the semiconductor laser chip of the beam shaping optical system.

FIG. 2 is a diagram illustrating values of wavefront aberration with respect to wavelength fluctuation of the anamorphic lens (two-piece ball A) according to the first embodiment of the present invention and the conventional anamorphic lens (single-piece ball).

FIG. 3 is a diagram illustrating values of wavefront aberration with respect to wavelength fluctuation of the anamorphic lens (two-piece ball A) of the first embodiment of the present invention and the anamorphic lens (two-piece ball B) of the second embodiment. .

FIGS. 4A and 4B are explanatory diagrams of the configuration of an optical device (optical pickup) of a recording / reproducing apparatus showing one embodiment of the present invention. FIG. 4A shows an optical pickup in a direction parallel to a bonding surface (active layer) of a semiconductor laser. FIG. 2B is a cross-sectional view of the optical pickup in a direction perpendicular to the bonding surface (active layer) of the semiconductor laser.

FIG. 5 is a diagram showing an example of an optical pickup optical system of a conventional optical disk drive.

FIG. 6 is a diagram showing a light emission distribution (a relationship between an emission angle and an intensity) of a semiconductor laser.

FIG. 7 is a diagram showing a state in which the major axis direction of an elliptical spot focused on a recording medium is orthogonal to a track.

FIG. 8 is a diagram showing a state in which the major axis direction of an elliptical spot focused on a recording medium is parallel to a track.

FIG. 9 is a diagram showing an example of a conventional beam shaping optical system using an anamorphic lens, wherein (a) is a cross-sectional view parallel to a bonding surface (active layer) of a semiconductor laser chip of the beam shaping optical system. (YZ sectional view), (b) is a sectional view (XZ sectional view) orthogonal to the bonding surface (active layer) of the semiconductor laser chip of the beam shaping optical system.

[Explanation of symbols]

9, 102: hologram element 10, 101: semiconductor laser (emission point) 11, 103: anamorphic lens (optical element having beam shaping function) 12, 13: constituent material of anamorphic lens 104: deflection prism 105: Objective lens 106: Optical recording medium 107: Light receiving element for signal detection 108: Optical system housing 109: Seek rail

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H087 KA13 LA25 LA26 LA28 NA14 PA01 PA17 PA18 PB01 PB02 QA02 QA03 QA07 QA14 QA15 QA19 QA21 QA22 QA31 QA34 QA37 QA41 QA42 RA05 RA08 RA12 RA13 RA45 5D119 A0111A50 FA05 JA06

Claims (7)

[Claims] An optical element for converting light from a semiconductor laser into substantially parallel light, said anamorphic having a beam shaping function having a different focal length in a direction perpendicular to a direction parallel to an active layer of said semiconductor laser. An optical element comprising a lens, wherein the anamorphic lens is composed of a plurality of materials. 2. The optical element according to claim 1, wherein said anamorphic lens is integrally formed of a plurality of materials, and a first surface and a final surface thereof are aspherical. 3. The optical element according to claim 2, wherein a cemented surface of said anamorphic lens is an aspherical surface. 4. An optical element according to claim 1, wherein said anamorphic lens is composed of two lenses made of different materials, and is formed in a plane parallel to an active layer of said semiconductor laser. The curvature is negative, positive, negative in the order from the semiconductor laser side, and the basic curvature in a plane perpendicular to the active layer of the semiconductor laser is positive, positive, in the order from the semiconductor laser side. An optical element characterized by being negative. 5. An optical element according to claim 1, wherein the Abbe number of the material of the anamorphic lens on the side where the semiconductor laser light enters is νd1, and the side where the semiconductor laser light exits. An optical element characterized in that, when the Abbe number of the material is νd2, νd1 <νd2. 6. An optical device for converting light from a semiconductor laser into substantially parallel light with an optical element and then condensing the light on an information recording medium with an objective lens. An optical device comprising the optical element described in any one of the above. 7. An optical device for converting light from a semiconductor laser into substantially parallel light with an optical element and condensing the light on an information recording medium with an objective lens, wherein recording, reproduction or erasing of the information recording medium is performed. A recording / reproducing apparatus, comprising: the optical apparatus according to claim 6 as the optical apparatus.