JP2007115301A - Optical pickup device - Google Patents

Abstract

Even if astigmatism occurs in a half mirror, a light beam can be incident in a state where the direction of astigmatism is deviated by 45 degrees with respect to a dividing line of a light receiving element, and thus accurate focus control is achieved. An optical pickup device capable of performing the above is provided.
A light projecting optical system for condensing a light beam emitted from a light source to an optical disc, a light receiving optical system for forming an image of the light beam reflected by the optical disc on a light receiving element, and a light beam traveling through the light receiving optical system and light projection In the optical pickup device 1 having a parallel plate-shaped half plate mirror 23 that separates a light beam traveling in the optical system in a housing, the light receiving optical system is astigmatism on the optical path β after passing through the half plate mirror 23. The correction plate 26 emits light at a predetermined angle δ determined at least according to the thickness of the half-plate mirror with respect to the optical axis immediately before entering the correction plate 26. By arranging with the shaft rotated, astigmatism generated in the half plate mirror 23 can be corrected.
[Selection] Figure 2

Description

  The present invention relates to an optical pickup device that records and / or reproduces optical information on an optical disc (hereinafter referred to as recording and reproduction).

  Conventionally, various optical pickup devices have been developed to perform optical recording and reproduction on optical disks such as CDs and DVDs. This optical pickup device uses an objective lens to project light from a light source onto an optical disc, and guides reflected light from the optical disc to a light receiving element to read various information recorded on the optical disc. By the way, in this optical pickup device, there is known a device in which a light beam separating means (for example, a beam splitter or a half plate mirror) is provided between a light source and a light receiving element to separate the light paths of the light projecting optical system and the light receiving optical system. (For example, refer to Patent Document 1).

  That is, as shown in FIG. 7, for example, this optical pickup device includes a semiconductor laser 101, a diffraction grating 102, a half plate mirror (hereinafter referred to as “half mirror”) 103, a collimator 104, a rising mirror 105, a diaphragm 106, and A projection optical system including an objective lens 107, a diaphragm 106, an objective lens 107, a rising mirror 105, a collimator 104, a half mirror 103 for separating an optical path of reflected light after being reflected by the objective lens 107, a transparent flat plate 108, And a light receiving optical system including the light receiving element 109 and the like.

  In the optical pickup device having such a configuration, for example, the laser beam is divided into three beams by the diffraction grating 102 and tracking control is performed by the three-spot method or the differential push-pull method, and the reflection of the optical disk is performed by the astigmatism method. Since the focus control is performed using light, astigmatism is generated on the transparent flat plate 108 described above.

By the way, since the half mirror 103 is arranged in parallel to the mapping direction R of the pit row P of the optical disk, the reflected light from the optical disk passes through the half mirror 103 and enters the light receiving element 109. Astigmatism occurs in the same direction as the direction of the dividing line to be divided into four, and an error signal for performing focus control cannot be generated. Therefore, in the optical pickup device described in Patent Document 1, the above-described transparent flat plate 108 is arranged to be rotated by 45 degrees with respect to the optical axis, whereby the direction of astigmatism with respect to the dividing line of the light receiving element 109 is set to 45. It is structured so as to be shifted.
JP 2005-18870 A

  In the optical pickup device having such a configuration, the light beam reflected by the optical disc is incident on one surface of the half mirror 103 when traveling toward the light receiving element 109 after passing through the collimator 104. At this time, since the half mirror 103 is inclined with respect to the central axis of the light beam that has passed through the collimator 104, astigmatism occurs in the light beam that has passed through the half mirror 103 described above. In this case, as long as the half mirror 103 is sufficiently thin, the amount of astigmatism that occurs is very small that can be ignored approximately.

  However, since the half mirror 103 normally has a finite thickness, the amount of astigmatism is a finite value that cannot be ignored. For this reason, the light beam incident on the light receiving element 109 causes astigmatism in a direction in which the directions of astigmatism generated in the half mirror 103 and the transparent flat plate 108 are combined in vector. Therefore, when the optical axis of the transparent flat plate 108 is simply rotated 45 degrees with respect to the optical axis immediately before entering the transparent flat plate 108, the direction of astigmatism with respect to the dividing line of the light receiving element 109 is 45. It will not be out of position.

  The present invention has been made in view of the above circumstances. Even if astigmatism occurs in the half mirror, the astigmatism direction of the light beam incident on the light receiving element with respect to the dividing line of the light receiving element is 45. It is an object of the present invention to provide an optical pickup device that can be incident in a state shifted by approximately 45 degrees or approximately 45 degrees and that can accurately control an optical disc.

  An optical pickup device of the present invention includes a light projecting optical system that condenses a light beam emitted from a light source onto an optical disc, a light receiving optical system that forms an image of the light beam reflected by the optical disc on a light receiving element, and the light receiving optical system. In an optical pickup device having a housing with a parallel plate-shaped half plate mirror that separates a traveling light beam and a light beam traveling in a light projecting optical system, the light receiving optical system is configured such that the light beam traveling through the light receiving optical system is A correction plate for correcting the direction of astigmatism is provided on the optical path after passing through the half plate mirror, and the correction plate has at least the half axis with the optical axis of the light beam immediately before entering the correction plate as the rotation center. The optical axis of the correction plate is rotated by a predetermined angle δ determined according to the thickness of the plate mirror.

  In addition, the light receiving element has a dividing line that is divided into four substantially in a square shape, and the correction plate has an astigmatism direction that intersects the dividing line at an angle of 45 degrees or approximately 45 degrees. It is arranged.

  Further, the half plate mirror and the correction plate are installed in an arrangement relationship in which the directions of inclination with respect to the optical axis are opposite to each other.

  The light receiving optical system includes a reflecting mirror on the optical path after passing through the half plate mirror, and the reflecting surface of the reflecting mirror is the other end closer to the floor surface of the housing. Inclined by a predetermined angle toward the floor surface of the housing in a state of being closer to the correction plate than the end portion of the housing.

  According to the present invention, even when affected by the astigmatism generated in the half mirror, the astigmatism can be incident with the direction of the astigmatism deviated by 45 degrees or approximately 45 degrees with respect to the dividing line of the light receiving element. As a result, it is possible to provide an optical pickup device capable of performing accurate control on the optical disk.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
1 and 2 show an optical pickup device 1 according to an embodiment of the present invention. The optical pickup device 1 is roughly divided into an optobase 2 that is a casing and an objective lens actuator 3. . In the figure, symbol D indicates an optical disk.

  The opt base 2 includes a main optical system excluding a diaphragm and an objective lens 31 (not shown), which will be described later. Specifically, a light source 21 using a semiconductor laser, a grating (diffraction grating) 22, A half mirror 23 that is a light beam separating means for separating the optical paths α and β in the forward path and the return path, a collimator 24 that forms parallel light, and an optical path α of the laser light that is projected from the light source 21 and travels. A rising mirror 25 that is bent toward the optical disk D, a reflection mirror 26 that is disposed on the optical path β (after passing through the half mirror 23) of the light receiving optical system in which the laser light reflected and returned by the optical disk D travels, and AS (Astigmatism; A correction plate (hereinafter referred to as “AS correction plate”) 27 for correcting the direction of astigmatism, a light receiving element 28 and the like are arranged.

  As the light source 21, a semiconductor laser that emits laser light having a predetermined wavelength necessary for reading or writing on the optical disk D is used. The diffraction grating 22 generates diffracted light in order to use ± first order light for tracking.

  The half mirror 23 reflects the laser light incident from the light source 21 side to bend the optical path α of the light projecting optical system by 90 degrees, and transmits the laser light reflected by the optical disc D to project the optical path β of the light receiving optical system. A dielectric multilayer film is formed on the surface to be a reflection surface on the optical path α of the light projecting optical system.

The AS correction plate 27 corrects astigmatism generated in the half mirror 23 and forms an image of reading light (reflected light) on the light receiving surface of the light receiving element 28. Specifically, the AS correction plate 27 of the present embodiment is an angle in which the direction of astigmatism of the reflected light from the optical disc D is shifted by 45 degrees with respect to a dividing line provided on a light receiving surface of a light receiving element 28 described later. As shown, the angle δ with respect to the optical axis of the light beam immediately before entering the AS correction plate 27 (60 degrees in this embodiment, but is not particularly limited to this angle in the present invention). Only the optical axis is rotated. Note that there is a fixed relationship between the AS correction plate 27 and the half mirror 23 with respect to the thickness, the incident angle of the laser beam, the direction of the generated astigmatism (AS), and the amount of astigmatism. As described above, the optical axis of the AS correction plate 27 is rotated by an angle δ. This relational expression will be described later.
Further, the AS correction plate 27 is installed in an inclined direction in the opposite direction to the half mirror 23 in the optical path when the reflection mirror 26 is removed, and the coma in the opposite direction to the half mirror 23. (Coma) An aberration is generated. Thereby, the coma aberration generated in the half mirror 23 is canceled.

  As the light receiving element 28, a PIN photodiode as a photoelectric conversion element or the like is used. For example, as shown in FIG. 3, the light receiving surfaces 28A and 28B for focus / reproduction signals and the light receiving surfaces 28C and 28D for tracking are used. And. The light receiving surfaces 28 </ b> A and 28 </ b> B generate a focus signal and a reproduction signal from a substantially square-shaped region that is symmetrically divided into four by a dividing line 281. The light receiving surfaces 28C and 28D receive the ± first-order light diffracted by the diffraction grating 22 and generate a track signal. The light receiving surfaces 28C and 28D are each divided by a dividing line 282. You may use what is used, or you may use what is not divided | segmented, respectively.

  On the other hand, the objective lens actuator 3 is a kind of objective lens 31 and filter means (spatial filter) for condensing a laser beam on a track (pit) of an optical disc D that records and reads information in FIGS. An unillustrated restricting portion or the like is provided. Although not shown, the objective lens actuator 30 of the present embodiment can be displaced in the radial (R) direction of the optical disk D to apply tracking servo, and is displaced in the thickness direction of the optical disk D to apply focusing servo. And a yoke part that supports the movable part in a displaceable state. By having such a configuration, the fine movement of the objective lens 31 for causing the light beam from the light source 21 (semiconductor laser) to follow the track of the optical disk D is performed by the servo mechanism during tracking control, and the servo mechanism follows. In the case where it is necessary to move beyond a predetermined distance, the opt base 2 is moved using a traverse mechanism.

  In the present embodiment, the light projecting optical system includes the light source 21, the diffraction grating 22, the half mirror 23, the collimator 24, the rising mirror 25, the objective lens 31, the diaphragm portion, and the like. On the other hand, the light receiving optical system includes an objective lens 31, a diaphragm, a raising mirror 25, a collimator 24, a half mirror 23, a reflecting mirror 26, an AS (Astigmatism) correction plate 27, a light receiving element 28, and the like. ing.

  The reflection mirror 26 is installed on the optical path after passing through the half mirror 23 of the light receiving optical system. Further, the reflection mirror 26 is directed toward the AS correction plate 27 by an angle ε with respect to the floor surface 2A of the opto base 2 as shown in FIG. 5 in order to reduce the dimension of the opto base 2 in the thickness direction. And tilted. Note that the inclination angle ε of the reflection mirror 26 of the present embodiment is set to about +3 degrees.

  Next, the mounting state of the half mirror 23, the reflection mirror 26, and the AS correction plate 27 on the opt base 2 (which constitutes the casing of the optical pickup device 1) will be described with reference to FIGS.

  In the case of the present embodiment, the half mirror 23 is configured by a parallel plate having a thin plate shape with a glass having a refractive index n as shown in FIG. 1, and reflects the laser light in the light projecting optical system, In order to refract and transmit the laser beam of the light receiving optical system, the surface portion is coated with a dielectric multilayer film or the like.

The half mirror 23 has a constant thickness, and when the reflected light beam from the disk D is obliquely incident on this surface, astigmatism is generated during transmission. For example, in the half mirror 23 of this embodiment, as shown in FIG. 4, the thickness is d ₁ , the refractive index is n ₁ , and the incident angle (however, the oblique incident light to the half mirror 23 is a very narrow convergent light. Assuming that θ ₁ is θ ₁ , an astigmatism amount γ ₁ represented by the following equation is generated.

  Here, in order to cross the dividing line 281 of the light receiving element 28 at an angle of 45 degrees (or may be substantially 45 degrees), in order to correct the direction of astigmatism on the optical path β after being reflected by the reflecting mirror. An AS correction plate 27 is provided. That is, this AS correction plate 27 also has a relational expression similar to the above-described expression (1a),

Is transmitted through the AS correction plate 27 having an astigmatism amount γ ₂ that is uniquely determined by the above, so that γ ₁ and γ ₂ are combined as shown in FIG. Astigmatism amount γ is obtained (here, direction S and direction T in FIG. 6 coincide with direction S and direction T in FIG. 3).

  That is, the synthesized astigmatism amount γ is

Can be obtained.
Further, the angle formed between the direction in which the synthesized astigmatism γ occurs and the direction in which the astigmatism γ ₁ generated in the half mirror 23 occurs is π / 4.

And δ is uniquely determined from these equations (1) to (3). Here, the AS correction plate 27 is set in a state in which the optical axis of the AS correction plate 27 is rotated by a predetermined angle δ with reference to the optical axis of the light beam immediately before entering the AS correction plate 27. By arranging, the astigmatism intersects with the dividing line 281 of the light receiving element 28 at an angle of 45 degrees (or may be approximately 45 degrees).

  In the optical pickup device 1 of the present invention, the direction of the astigmatism of the light beam incident on the light receiving element 28 shown in FIG. 3 is an angle of 45 degrees (or approximately 45 degrees) with respect to the dividing line 281 of the light receiving element 28. As described above, the AS correction plate 27 uses the optical axis of the light beam immediately before entering the AS correction plate 27 as a reference, and the optical axis of the AS correction plate 27 is set at a predetermined angle δ (this embodiment). In this case, the arrangement is rotated by 60 degrees. A method for calculating the angle δ will be described next.

As shown in FIG. 6, the astigmatism amount γ of the light beam when it is received by the light receiving element 28 is astigmatism amount γ ₁ generated by the half mirror 23 and the astigmatism amount γ generated by the AS correction plate 27. ₂ is generated by combining them in vector, and the direction of astigmatism and its absolute value (astigmatism amount γ) at the light receiving element 28 can be calculated using simple elementary mathematics. It is.
That is, with respect to γ, γ ₁ , γ ₂ , and angle δ, the following equations (2) and (3):

Meet. As a result, the angle δ can be uniquely calculated by combining the equations (1a), (1b), (2), and (3).

Next, the operation of this embodiment will be described.
In FIG. 2, the laser light emitted from the light source 21 travels on the optical path α as coherent divergent light having an elliptical cross section, enters the diffraction grating 22, and is split by the diffraction grating 22 (of which 0th order light and 1st order light). And travels toward the optical disc D on the optical path α that is reflected by the half mirror 23 and goes to the right. The laser light, which is divergent light, is converted into parallel light by the collimator 24, and the optical path is deflected (bent) by 90 ° by the rising mirror 25, and then passes through the diaphragm and the objective lens 31 and enters the optical disk D. To do.

  On the other hand, the light beam (reading light) reflected by the optical disk D travels in the direction opposite to the optical path α and enters the collimator 24 in a substantially parallel state. Further, the light beam transmitted through the collimator 24 is incident on the half mirror 23, refracted and transmitted. Then, the read light in which the above-mentioned astigmatism and coma aberration are generated by the half mirror 23 is regularly reflected by the reflection mirror 26, the optical path β is bent, and enters the AS correction plate 27.

  Here, as described above, the AS correction plate 27 is installed to be inclined in a direction opposite to the inclination direction of the half mirror 23 with respect to the optical axis along the optical path β. For this reason, the coma aberration generated in the opposite directions when the reflected light transmitted through the AS correction plate 27 passes through the half mirror 23 and the AS correction plate 27 cancels each other.

  Further, since the AS correction plate 27 is arranged with the optical axis rotated by a predetermined angle (60 degrees), the reflected light after passing through the AS correction plate 27 was generated by the half mirror 23. The direction of astigmatism is corrected, and the light enters the light receiving element 28 while intersecting the dividing line of the light receiving element 28 at an angle of exactly 45 degrees.

  Thus, in the present embodiment, since the half mirror 23 has a finite thickness of d, the amount of astigmatism is considered to have a finite value γ1 that cannot be ignored. An angle δ that simultaneously satisfies equations 1a) to (3) is calculated, and the optical axis of the AS correction plate 27 is rotated by this angle δ. Therefore, by rotating the optical axis of the AS correction plate 27 about the optical axis of the light beam just before entering the AS correction plate 27 by an angle δ, astigmatism is generated with respect to the dividing line of the light receiving element 28. Since the direction can be shifted by 45 degrees, accurate focus control can be performed.

  In addition, the half mirror 23 and the AS correction plate 27 are installed with the inclination directions inclined in directions opposite to each other with respect to the optical axis. For this reason, coma aberration of a non-negligible size that occurs in the half mirror 23 having a finite thickness d, the AS correction plate 27 causes coma aberration in the opposite direction to the coma aberration that occurs in the half mirror 23. By generating it, both coma aberrations can be canceled out.

  The present invention is not limited to the above-described embodiment, and can be implemented in various forms without departing from the spirit of the invention.

  In the optical pickup device of the present invention, even if astigmatism occurs in the half mirror, it can be incident with the astigmatism direction shifted by 45 degrees with respect to the dividing line of the light receiving element. Since focus control can be performed, a high-quality optical pickup device or the like can be realized.

Explanatory drawing which shows the structure of the optical system of the optical pick-up apparatus which concerns on embodiment of this invention. The top view which shows arrangement | positioning of the optical system of the optical pick-up apparatus which concerns on embodiment of this invention Explanatory drawing which shows the structure of the light receiving element of the optical pick-up apparatus which concerns on embodiment of this invention. Explanatory drawing which shows the relationship of the astigmatism in the half mirror of the optical pick-up apparatus which concerns on embodiment of this invention. Explanatory drawing which shows the arrangement state of the reflective mirror, AS correction board, and light receiving element of the optical pick-up apparatus which concerns on embodiment of this invention. Explanatory drawing which shows the synthesis | combination of astigmatism by the half mirror and AS correction plate of the optical pick-up apparatus which concerns on embodiment of this invention. The perspective view which shows the structure of the conventional optical pick-up apparatus. Explanatory drawing which shows arrangement | positioning of the optical system of the conventional optical pick-up apparatus.

Explanation of symbols

1 Pickup device 2 Opt-base (housing)
2A Floor surface (mounting surface)
21 Semiconductor laser (light source)
22 Diffraction grating 23 Half mirror (Flux separation means)
24 Collimator 25 Rising mirror 26 Reflecting mirror 27 AS correction plate 28 Light receiving element 3 Objective lens actuator 31 Objective lens D Optical disk α Optical path of the projecting optical system β Optical path of the receiving optical system γ Combined astigmatism amount γ _{1 In the} half mirror Astigmatism amount γ ₂ Astigmatism amount at AS correction plate δ Rotation angle of AS correction plate ε Tilt angle of reflection mirror θ Incident angle at half mirror

Claims (4)

A light projecting optical system for condensing the light beam emitted from the light source onto the optical disc, a light receiving optical system for forming an image of the light beam reflected by the optical disc on a light receiving element, and a light beam traveling through the light receiving optical system and the light projecting optical system In an optical pickup device provided in a housing with a parallel plate-shaped half plate mirror that separates a light beam traveling through
The light receiving optical system includes a correction plate that corrects the direction of astigmatism on the optical path after the light beam traveling through the light receiving optical system passes through the half plate mirror,
The correction plate has the optical axis of the correction plate at a predetermined angle δ determined at least according to the thickness of the half plate mirror, with the optical axis of the light beam immediately before entering the correction plate as the rotation center. An optical pickup device that is rotated. The light receiving element has a dividing line that is divided into four substantially in a letter shape,
2. The optical pickup device according to claim 1, wherein the correction plate is arranged so that the direction of astigmatism intersects the dividing line at an angle of 45 degrees or approximately 45 degrees.   3. The optical pickup device according to claim 1, wherein the half plate mirror and the correction plate are disposed in an arrangement relationship in which directions of inclination with respect to the optical axis are opposite to each other. The light receiving optical system includes a reflecting mirror on the optical path after passing through the half plate mirror,
The reflection surface of the reflection mirror is such that one end far from the floor surface of the casing is closer to the correction plate than the other end close to the floor surface. The optical pickup device according to claim 1, wherein the optical pickup device is inclined by a predetermined angle toward the head.

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