JP3101504B2 - Optical pickup device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device for a magneto-optical disk, and more particularly to an integrated optical pickup device for a small-sized magneto-optical disk.

[0002]

2. Description of the Related Art FIG. 11 is a block diagram showing an example of a conventional optical pickup device for a magneto-optical disk. In FIG. 11, a laser beam emitted from a laser diode 20 passes through a diffraction grating 21, a collimator lens 22, a beam splitter 23, and an objective lens 24, and the magneto-optical disk 2
5 is irradiated. A magnetic field is applied to the magneto-optical disk 25 from a magnetic coil 26, thereby recording and erasing signals on the magneto-optical disk 25. The laser light reflected by the magneto-optical disk 25 is applied to the beam splitter 23.
And is reflected toward a beam splitter 27 installed in a direction orthogonal to the incident direction. A part of the laser beam incident on the beam splitter 27 passes through the beam splitter 27, and the condenser lens 28, the cylindrical lens 2
The light passes through 9 and is incident on the photodiode 30 divided into four parts, and is used for focus servo and tracking servo. Further, a part of the reflected light incident on the beam splitter 27 is reflected in a direction orthogonal to the incident direction,
The light enters the half-wave plate 31 and the polarization beam splitter 32. The reflected light incident on the polarizing beam splitter 32 is separated according to the polarization angle here, and one of the reflected light is incident on a photodiode 34 after passing through a condenser lens 33. The other transmitted light is incident on the photodiode 36 after passing through the condenser lens 35. Then, the difference between the detection outputs of the photodiodes 34 and 36 is obtained, and the information recorded on the magneto-optical disk 25 is detected.

The conventional optical pickup device for a magneto-optical disk as described above has a complicated structure and a very high manufacturing cost. In addition, the large number of parts makes the device large, which hinders miniaturization of the magneto-optical disk. Therefore, an optical pickup device as disclosed in Japanese Patent Application Laid-Open No. 4-247348 has been proposed. FIG. 12 is a block diagram showing another example of a conventional integrated optical pickup device for a magneto-optical disk. In FIG. 12, laser light incident from a laser diode 41 hits a semi-transmissive reflection surface of a prism 42 provided on the same circuit board as the laser diode 41, passes through a collimator lens 43 and an objective lens 44, and The light is applied to the disk 45. The laser beam reflected by the magneto-optical disk 45 again passes through the objective lens 44 and the collimator lens 43, and then passes through the half-wave plate Y for rotating the polarization plane arranged on the semi-transmissive reflection surface of the prism 42, and the prism 42
It is incident inside. One of the laser beams incident on the inside of the prism 42 is incident on the first photodiode 46 by the polarizing film X formed on the first photodiode 46, and the other is reflected by the polarizing film X, and further, is totally reflected on the film 48. After the light is totally reflected by the second photodiode 47, the light passes through the total transmission film 49 and enters the second photodiode 47. When there is no rotation of the polarization on the magneto-optical disk 45, the amounts of light incident on the first photodiode 46 and the second photodiode 47 become equal. A difference occurs in the amount of light incident on each of the photodiodes 46 and 47. Therefore, the detection signal _{SMO of the} information recorded on the magneto-optical disk can be obtained by the following equation. _SMO = (A + B + C)-(A '+ B' + C '), and for the tracking error signal _STE and the focus error signal _SFE , _STE = (A' + C)-(A +
C ′), S _FE = (A + C + B ′) − (A ′ + C ′ + B)
Can be obtained from

In addition, instead of the half-wave plate Y, it has been proposed to incline the emission point of laser light by 45 °.

[0005]

In the above configuration, the optical film X is provided on the surface of the first photodiode 46 for detecting an information signal, and the surface of the second photodiode 47 is different from the optical film X. An optical film must be provided. However, in this configuration, since the above-described prism is very small, providing an optical film on a part of the substrate requires a precise operation.

In this method, a signal for performing a focusing servo or a tracking servo is basically obtained from a magneto-optical signal having a level difference. Therefore, a difference occurs in the amount of light incident on the first and second photodiodes due to polarization, and an appropriate signal cannot be detected. To correct this, for example, it is conceivable to perform offset correction, but even in that case, correction cannot be performed if birefringence occurs in the magneto-optical disk.

Further, since the signal of the magneto-optical disk is very small, in order to obtain a high C / N, the polarization direction of the laser light incident on the first photodiode 46 is inclined by 45 ° and the differential detection method is used. You have to detect the signal. Also, if the S-polarized light component and the P-polarized light component of the laser light are significantly different, it becomes difficult to detect the servo signal, so that the polarization direction of the laser light incident on the first photodiode 46 is inclined by 45 °. It is necessary to be. Therefore, in the above-described method, the polarization direction of the laser light incident on the prism 42 is changed to 45 by using a tilted submount or devising a method of manufacturing a laser diode.
° tilted. However, the above-described methods require elaborate operations and involve difficult operations such as changing the method of manufacturing a laser diode. Further, providing a half-wave plate or a half mirror on the inclined surface of the minute prism also requires precise work.

Further, the half-wave plate Y provided for rotating the polarization plane cannot obtain its effect sufficiently unless it is in a parallel light beam. Therefore, in the above-described configuration arranged in the convergent light, a phase difference component other than a predetermined polarization angle is generated, and the extinction ratio of polarization separation is significantly deteriorated.

[0009]

Means for Solving the Problems To solve the above problems,
Therefore, in the optical pickup device of the present invention, the polarization plane is different.
A first light receiving element and a second light receiving element for receiving a laser beam
And a substrate mounted on the substrate,
Laser light that is incident and reflected by the interface
A first prism for entering the first light receiving element;
The first prism having a boundary surface in contact with the boundary surface of the prism.
The second pre-light for transmitting the transmitted laser light to the second light receiving element
And each boundary between the first prism and the second prism
A polarizing film interposed on the surface of the first pre-printer.
Laser beam incident on the interface between the prism and the second prism
Is characterized by being tilted in the direction of rotating the polarization plane by 45 °.
Sign. Further, in the above configuration, furthermore, the substrate
A third light receiving element is provided thereon, and the first prism is divided into two.
Split and form a half mirror between the divided surfaces,
The laser light reflected by the half mirror is applied to the third light receiving element.
It is characterized by leading . In addition, the optical pickup of the present invention
Pump device receives a laser beam having a different polarization plane.
A substrate provided with a light receiving element and a second light receiving element, and
Laser light reflected from the disc
The laser light reflected at the interface is incident on the first light receiving element.
A first prism and a boundary surface in contact with a boundary surface of the first prism
Receiving a laser beam transmitted through the first prism in a second manner
A second prism for entering the element, and the first prism
A polarizing film interposed at each boundary surface of the second prism;
The first prism is an optically anisotropic substance
Rotate the polarization plane of the passing laser light by 45 °
It is characterized in that dimensions are set. Also, in the above configuration,
And further providing a third light receiving element on the substrate,
Laser light incident on the first prism is applied to the third light receiving element.
It is characterized by leading.

[0010]

The optical film can be easily manufactured by interposing a polarizing film on the boundary between the first and second prisms.
Also, by specifying the angle of the division plane, the polarization plane can be set to 4
A rotation of 5 ° is realized, or the plane of polarization is rotated by 45 ° by rotating the plane of polarization by the first prism having anisotropy. Further, by causing the laser light to be incident on the third light receiving element, it is possible to simultaneously detect a servo signal and a signal having polarization characteristics.

[0011]

FIG. 1 is a block diagram of an optical pickup according to a first embodiment of the present invention. FIG. 2 is an arrangement diagram of the light receiving element of the first embodiment of the optical pickup device of the present invention. In FIG. 1, a laser diode 1 and a monitor diode 2 are arranged on a submount 3. Submount 3,
The first prism 4, the second prism 5, the first light receiving element 7, the second light receiving element 8, and the third light receiving element 6 are arranged on a circuit board 9.

The laser light emitted from the laser diode 1 is reflected by the inclined surface 4a of the first prism 4, enters the objective lens 10, and irradiates the magneto-optical disk 11. The laser beam reflected by the magneto-optical disk 11 returns to the inclined surface 4a of the first prism 4. The laser light, which is reflected light from the magneto-optical disk 11, passes through the half mirror 12, which is an optical film (a) provided on the inclined surface 4a of the first prism 4, and enters the inside of the first prism 4. It reaches the entering inclined surface 4b. Further, a part of the laser light is transmitted through the optical film (b) by the half mirror 13 as the optical film (b) provided on the inclined surface 4b of the first prism 4 and is incident on the third light receiving element 6. . This third
Signal detection for performing focus servo and tracking servo is performed by the laser light incident on the light receiving element 6. For example, as shown in FIG.
If divided, the focus error can be detected by the astigmatism method or the beam size method, and the tracking error signal can be detected by the push-pull method.

On the other hand, the laser light reflected by the inclined surface 4b is totally reflected by the total reflection film 14 which is an optical film (c) provided on the upper surface of the first prism 4, and the first prism 4
To the boundary 4c. A polarizing film 15, which is an optical film (d), is provided on the boundary surface 4c, and a part of the light is reflected by the polarization characteristics of the reflected light to enter the first light receiving element 7, and the other is transmitted and becomes the second light receiving element. The light passes through the inside of the prism 5 and enters the second light receiving element 8. By making the inclination of the inclined surface 4b appropriate, the incident angle of the laser beam incident on the optical film (d) can be optimized, and the formation of the polarizing film 15, which is the optical film (d), becomes easy. Servo signals and signals having polarization characteristics can be performed simultaneously.

On the third light receiving element 6, the first light receiving element 7, and the third light receiving element 8, a total transmission film (not shown) which is an optical film (e) is provided. All the laser beams incident on the first light receiving element 7 and the second light receiving element 8 are transmitted. Table 1 shows the characteristics of the optical film provided in the optical pickup device of the first embodiment thus configured.
Shown in

[0015]

[Table 1]

FIG. 3 is a perspective view showing the inclination of the prism and the polarization plane in the first embodiment of the optical pickup device of the present invention. As shown in FIG. 3, in the first embodiment, the inclined surface 4c is inclined by, for example, 45 ° in the X direction and 45 ° in the Y direction with respect to a plane perpendicular to the traveling direction of the laser beam. Then, the laser light transmitted and reflected by the inclined surface is rotated by 45 ° in the polarization plane as shown in the figure. This allows the laser light to be emitted from the light emitting substrate (light emitting chip) as in the case of a compact disk.
And the same as the first light receiving element 7 and the second light receiving element 8 by the polarizing film 15 which is the optical film (d) even if the reflected light from the disk has only a single mode. The amount of light comes in. The magneto-optical disk 1
When the polarization is rotated at 1, the light amount incident on the first light receiving element 7 and the second light receiving element 8 is different, and the magneto-optical disk 11
Can be detected.

In the first embodiment, the first prism and the second prism
Providing the third light receiving element with a polarizing film interposed between the prism boundary surfaces facilitates fabrication of the optical film, and enables simultaneous detection of a servo signal and a signal having polarization characteristics. FIG. 4 is a configuration diagram showing a second embodiment of the optical pickup device of the present invention. In FIG. 4, a laser beam emitted from a laser diode is
Is reflected on the inclined surface 4a of the
The light is irradiated onto the magneto-optical disk 11. Next, the laser beam reflected by the magneto-optical disk 11 returns to the inclined surface 4a of the first prism 4. Then, the reflected light from the magneto-optical disk 11 passes through the half mirror 12 which is the above-mentioned optical film (a) provided on the inclined surface of the first prism 4, and is reflected by the first mirror 4.
The light enters the prism 4 and reaches the inclined surface 4b. The inclined surface 4b is provided with the above-mentioned total reflection film 16 which is the optical film (c), the reflected light is totally reflected by the inclined surface 4b, and further the above-mentioned optical film provided on the upper surface of the first prism 4. (C)
And the first prism 4
To the surface 4c. The half mirror 13 which is the optical film (b) described above is provided on the surface 4c, whereby a part of the half mirror 13 is reflected and enters the third light receiving element 6, and the other is transmitted and enters the inside of the first prism 4d. Incident. The boundary surface 5c between the first prism 4d and the second prism 5 is inclined by 45 ° in the X direction and 45 ° in the Y direction as described with reference to FIG. Is provided,
Due to the polarization characteristics of the reflected light, a part is reflected and enters the first light receiving element 7, and the rest passes through the inside of the prism 5 b and enters the second light receiving element 8. This embodiment has the same advantages as the first embodiment.

FIG. 5 shows a third embodiment of the optical pickup device of the present invention. This pickup device includes a submount 53 on which a laser diode 51 and a monitor photodiode 52 are disposed, and a second prism 54 and a first prism 55 mounted on a circuit board 56. Further, first and second light receiving elements 60 and 61 are formed on the circuit board 56. The second prism 54 is a prism made of an optically isotropic material such as glass, and the first prism 55 is a prism made of an optically anisotropic material such as quartz. The second prism 5
4. Between the first prism 55, a polarizing film 59 is formed. The polarizing film is an alternating multilayer film composed of a high-refractive-index film and a low-refractive-index film, and reflects S-polarized light and transmits P-polarized light. Also, a half mirror 67 is provided on the inclined surface 55a of the first prism 55.
Is provided.

The laser light radiated from the laser diode 51 is condensed by the objective lens 57 and is irradiated on the magneto-optical disk 58. The light reflected by the magneto-optical disk 58 passes through the objective lens 57 and the first prism 5
5 returns to the inclined surface 55a. Then, the reflected light from the magneto-optical disk 58 passes through the half mirror 67 attached to the inclined surface 55a, enters the inside of the first prism 55, and reaches the polarizing film 59. Here, since the first prism 55 is optically anisotropic, the polarization direction is rotated by 45 ° before the laser beam reaches the polarizing film 59. The size of the first prism 55 depends on the S-polarized light component of the laser
The polarization component is adjusted so as to generate a phase difference of (2m + 1) π. The light that has reached the polarizing film 59 is S
The light is separated into polarized light and P-polarized light and reaches the first and second light receiving elements 60 and 61, respectively.

Accordingly, an information detection signal can be obtained from a difference between signal components depending on the amount of light incident on the first and second light receiving elements 60 and 61. Further, by forming the first and second light receiving elements 60 and 61 by the divided light receiving elements, it is possible to detect a servo signal such as focus or tracking from the sum or difference of the light amounts of light incident on these light receiving elements. Will be possible.

As an example of signal detection and servo detection, one of the first and second light receiving elements 60 and 61 is divided into five light receiving elements,
The case where the other is constituted by a three-division light receiving element will be described. In this case, the focus error signal is detected by the beam size method, and the tracking error signal is detected by the three beam method.
Further, a diffraction grating for splitting the laser light is provided in the optical path of the laser light.

FIG. 6 is a configuration diagram showing a first example of the arrangement of the light receiving elements in the third embodiment of the optical pickup device. In FIG. 6, (a) is the second light receiving element 61, (b)
Is a view of the first light receiving element 60 as viewed from above. Each is constituted by three light receiving elements A ', B', C 'and five light receiving elements A, B, C, E, F. Therefore, the information detection signal is S = (A + B + C)-(A '+ B').
+ C ').

Further, in this optical pickup device, when the magneto-optical disk is located at the focal point of the beam, the first and second light receiving elements 60 and 61 are controlled so that the beam has a constant size. The size of the prism 55 is determined. Therefore, the size of the beam on the light receiving element increases or decreases as the magneto-optical disk deviates from the focal point of the beam. Therefore, the focus error signal is S _FE = (A + C) -B or S _FE = (A ′).
+ C ')-B'. The tracking error signal can be obtained from S _TE = E−F.

In this embodiment, the tracking error
The three-beam method is used for signals, but the push-pull method
Can be detected. In the push-pull method, the first and second light receiving elements 6
Both or one of 0 and 61 is constituted by three-division light reception.
The racking error signal is S _TE= AC or S_TE=
It can be obtained from A'-C '. In this case, the times
No folding grid is required.

FIG. 7 is a configuration diagram showing a second example of the arrangement of the light receiving elements in the third embodiment of the optical pickup device. FIG. 7 is a top view of the first and second light receiving elements 60 and 61 when the astigmatism method is used for focus error signal detection and the three-beam method is used for tracking error signal detection. One of the light receiving elements constitutes a six-divided light receiving element as shown in FIG. Further, a cylindrical lens and a diffraction grating for dividing laser light into three are provided in the optical path of the laser light. In this case, the information signal and the servo signal are S = (A
+ B + C + D) -G, S _FE = (A + C)-(B + D),
It can be obtained from S _TE = E−F.

FIG. 8 is a block diagram showing a fourth embodiment of the optical pickup device of the present invention. This optical pickup device includes a submount 53 on which a laser diode 51 and a monitor photodiode 52 are disposed,
, A first prism 55 and a third prism 62 are provided on a circuit board 56. The circuit board 56 includes first, second, and third light receiving elements 60, 6
1, 63 are formed. Further, on the third light receiving element 63, a transflective film 64, which is the optical film (b) described above, is provided. The second prism 54 and the third prism 62 are prisms made of an optically isotropic material such as glass, and the first prism 55 is a prism made of an optically anisotropic material such as quartz. The second prism 5
A polarizing film 59 is formed between the fourth and third prisms 62. The polarizing film 59 is an alternate multilayer film composed of a high-refractive-index film and a low-refractive-index film, and reflects S-polarized light and transmits P-polarized light. Also,
On the upper surface of the third prism 62, a total reflection film 66 is provided. Laser light emitted from the laser diode 51 is condensed by the objective lens 57 and is irradiated on the magneto-optical disk 58. The light reflected by the magneto-optical disk 58 passes through the objective lens 57 and returns to the inclined surface 55a on which the half mirror 67 of the first prism 55 is provided. The reflected light from the magneto-optical disk 58 passes through the half mirror 67 attached to the inclined surface 55a, enters the inside of the second prism 55, and reaches the third prism 62. Here, since the first prism 55 shows optical anisotropy, the polarization direction is rotated by 45 ° before the laser beam reaches the third prism 62. The size of the first prism 55 is such that the S-polarized component and the P-polarized component of the laser beam are (2m + 1) π
Are adjusted to produce a phase difference of The light that reaches the third prism 62 and enters the inside reaches the third light receiving element 63. A semi-transmissive reflective film 64 is formed on the prism-side surface of the third light receiving element 63, and a part of the light is incident on the third light receiving element 63 and the remaining light is reflected. The reflected light is reflected by the total reflection film 66 provided on the upper surface of the third prism 62 and reaches the polarizing film 59. The light that reaches the polarizing film 59 is separated into S-polarized light and P-polarized light by the polarizing film 59, and the light is separated into first and second polarized lights, respectively.
The light reaches the second light receiving elements 60 and 61.

The information detection signal is transmitted to the first and second light receiving elements 6.
It can be obtained from the difference between the signal components due to the amount of light incident on 0 and 61. Further, by forming the third light receiving element 63 with the divided light receiving elements, the focus and tracking servo signals can be detected from the sum or difference of the amounts of light incident on these light receiving elements. In this embodiment, it is not necessary to devise a half-wave plate or a laser diode.

FIG. 9 is a diagram showing the arrangement of light receiving elements in a fourth embodiment of the optical pickup device. FIG. 9 is a diagram of the first, second, and third light receiving elements 60, 61, and 63 when the astigmatism method is used for the focus error signal and the three-beam method is used for the tracking error signal, as viewed from above. The third light receiving element 63 is constituted by a six-division photodiode as shown in FIG. Further, a cylindrical lens and a diffraction grating for dividing laser light into three are provided in the optical path of the laser light. In this case, the information signal and the servo signal are S = GH,
_SFE = (A + C)-(B + D) and _STE = _EF can be obtained.

The use of the above configuration has the advantage that servo signals for focusing and tracking are not affected by information detection signals. Also, if astigmatism generated by the transmission of convergent light or divergent light in the prism is used, the focus signal can be detected by the astigmatism method without using a cylindrical lens.

In the above embodiment, the beam size method, the astigmatism method, the tracking error signal detection, the three-beam method, and the push-pull method are used for detecting the focus error signal. The effect of is obtained. When a tracking error signal is detected by a three-beam method, a diffraction grating is provided in an optical path of laser light to split a beam. However, if a three-beam laser diode is used,
Detection is possible without a diffraction grating.

FIG. 10 is a block diagram showing a fifth embodiment of the optical pickup device of the present invention. This optical pickup device has a total reflection film 6 instead of the third light receiving element 63 in FIG. 8 and the semi-transmissive reflection film 64 as the optical film (b) described above.
5 is installed.

[0032]

The optical film can be easily manufactured by interposing a polarizing film at the boundary between the first prism and the second prism. In addition, since the rotation of the polarization plane is realized by specifying the angle of the division plane, the polarization plane is rotated by 45 °, a half-wave plate is not required, and the method of manufacturing the laser diode is not changed. Further, by rotating the polarization plane by the anisotropic prism, the polarization plane
Rotation by an angle makes the half-wave plate unnecessary, and the method of manufacturing the laser diode is not changed. Further, by causing the laser light to be incident on the third light receiving element, it is possible to simultaneously detect a servo signal and a signal having polarization characteristics.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of an optical pickup device of the present invention.

FIG. 2 is a configuration diagram showing an arrangement of light receiving elements of the first embodiment of the optical pickup device of the present invention.

FIG. 3 is a perspective view showing the inclination of a prism and a polarization plane in the first embodiment of the optical pickup device of the present invention.

FIG. 4 is a configuration diagram showing a second embodiment of the optical pickup device of the present invention.

FIG. 5 is a configuration diagram showing a third embodiment of the optical pickup device of the present invention.

FIG. 6 is a configuration diagram showing a first example of an arrangement of light receiving elements in a third embodiment of the optical pickup device of the present invention.

FIG. 7 is a configuration diagram showing a second example of the arrangement of light receiving elements in a third embodiment of the optical pickup device of the present invention.

FIG. 8 is a configuration diagram showing a fourth embodiment of the optical pickup device of the present invention.

FIG. 9 is a configuration diagram showing an arrangement of light receiving elements in a fourth embodiment of the optical pickup device of the present invention.

FIG. 10 is a configuration diagram showing a fifth embodiment of the optical pickup device of the present invention.

FIG. 11 is a configuration diagram showing an example of a conventional optical pickup for a magneto-optical disk.

FIG. 12 is a configuration diagram showing another example of a conventional integrated optical pickup for a magneto-optical disk.

[Explanation of symbols]

 Reference Signs List 1 laser diode 4 first prism 4c boundary surface 5 second prism 6 third light receiving element 7 first light receiving element 8 second light receiving element 9 substrate 11 disk 15 polarizing film

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-67452 (JP, A) JP-A-4-177643 (JP, A) JP-A-5-174441 (JP, A) JP-A-6-176 333289 (JP, A) JP-A-6-4928 (JP, A) JP-A-7-65429 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 11/105 G11B 7 / 135

Claims (4)

(57) [Claims] 1. A substrate provided with a first light receiving element and a second light receiving element for receiving a laser beam having different polarization planes, and a laser beam placed on the substrate and reflected by a disk to enter the boundary. A first prism for making the laser light reflected by the surface incident on the first light receiving element; and a first prism having a boundary surface in contact with a boundary surface of the first prism.
A second prism that causes the laser light transmitted through the prism to enter a second light receiving element; and a polarizing film interposed at each boundary surface between the first prism and the second prism, and further includes the first prism and the second prism. Interface between two prisms
In the direction to rotate the polarization plane of the incident laser light by 45 °
An optical pickup device characterized by being inclined . 2. The method according to claim 1, further comprising:
A third light receiving element is provided, and the first prism is divided into two.
And a half mirror is formed between the divided surfaces.
An optical pickup device for guiding a laser beam reflected by a mirror to the third light receiving element . 3. A method for receiving a laser beam having a different polarization plane.
A substrate provided with the first light receiving element and the second light receiving element, and a laser beam mounted on the substrate and reflected from the disk
Incident on the first light-receiving element,
A first prism to be projected, and a boundary surface in contact with a boundary surface of the first prism.
Making the laser beam transmitted through the prism incident on the second light receiving element
A second prism interposed at each boundary between the first prism and the second prism.
And a polarizing film was allowed, the first prism guess of a material having optical anisotropy
To rotate the plane of polarization of the passing laser beam by 45 °
The optical pickup apparatus is characterized in that set. 4. The method according to claim 3, further comprising:
A third light receiving element, and a ray incident on the first prism;
An optical pickup device for guiding the light to the third light receiving element .