JPH0573984A - Light pickup device - Google Patents

Abstract

(57) [Abstract] [Purpose] To reduce the size, weight and cost of optical pickup devices. [Structure] Between the semiconductor laser 11 and a condensing optical system composed of a collimating lens 12 and an objective lens 13, glass plates 14 and 15 are arranged so as to be inclined with respect to the optical axis. A half-wave plate or a polarizing plate 18 is provided between the semiconductor laser 11 and the glass plate 14. The polarization direction of the emitted light of the semiconductor laser 11 is adjusted by the ½ wavelength plate or the polarizing plate 18.
The emitted light emitted from the semiconductor laser 11 is condensed on the optical disc 20 by the condensing optical system. The reflected light from the optical disc 20 is condensed by the condensing optical system, and the glass plate 14,
Each of the light beams is reflected at 15, and is received by the photodetectors 21 and 22 through the analyzers 31 and 32, respectively. A data read signal, a tracking error signal, and a focusing error signal are created based on the output signals of the photodetectors 21 and 22.

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 recording / reproducing information on / from a magneto-optical recording medium such as a magneto-optical disk or a magneto-optical card.

Recording / reproducing of information in the present invention means
It includes recording information on a magneto-optical recording medium, reproducing information recorded on the magneto-optical recording medium, and recording and reproducing.

[0003]

2. Description of the Related Art A conventional optical pickup device is a first optical system for collimating the divergent light from a semiconductor laser, collecting the collimated light on an optical recording medium, and reflecting the light from the optical recording medium. A second optical system for collimating the light, a first polarization beam splitter for polarization separating the reflected light collimated by the second optical system,
A second polarization beam splitter for further separating the polarization-separated light into tracking control light and focusing control light, and further separating the separated light on the light receiving surface of the tracking control photodetector. A third optical system for collecting the separated light, a fourth optical system for collecting the separated light on the light receiving surface of the focusing control photodetector, a third optical system or a fourth optical system for reading a read signal. It is composed of a fifth optical system and the like for guiding light to a photodetector for obtaining.

Since such a conventional optical pickup device uses many optical parts, its weight is large,
Therefore, there is a problem that the access time is slow.
In addition, since many optical components are used, the cost of the components is high, and the assembly and adjustment of the components are troublesome and time-consuming, and the final cost is also high from this point.

[0005]

The object, structure, operation and effect of the present invention is to greatly reduce the size, weight and cost of an optical pickup device.

According to the present invention, there is provided a light provided with a light emitting element and a condensing optical system for converging divergent light emitted from the light emitting element on a magneto-optical recording medium and condensing reflected light from the magneto-optical recording medium. In the pickup device, it is arranged on the optical path of the divergent light between the light emitting element and the condensing optical system, inclined with respect to the optical axis of the condensing optical system, and transmits a part of the incident light. And at least one pair of transparent plates (for example, dielectric plates) that partially reflects, and among the light reflected by the magneto-optical recording medium and condensed by the condensing optical system, reflected by the transparent plate. At least two photodetectors for respectively receiving light are provided, and the pair of transparent plates are tilted in directions in which line segments generated by intersecting the planes perpendicular to the optical axis intersect these transparent plates. Is arranged as Serial emitting element, characterized in that the half-wave plate or a polarizing plate between the transparent plate on the side closer to the light emitting element is provided.

[0007] Preferably, the inclination angle of the transparent plate is set to a Brewster angle at which a polarization component having a specific polarization plane is completely transmitted.

If necessary, an analyzer having polarization directions different from each other by 90 ° is arranged in front of the photodetector.

The divergent light emitted from the light emitting element is focused on the magneto-optical recording medium by the focusing optical system. The reflected light from the magneto-optical recording medium is condensed by the condensing optical system, a part of which is reflected by the transparent plate and received by at least two photodetectors.

The information recorded on the magneto-optical recording medium is read by detecting the change (Kerr effect) in the rotation angle of the polarization plane of the reflected light from the magneto-optical recording medium.

When light is obliquely incident on one surface of the transparent plate, its reflectance and transmittance have polarization plane selectivity, and the reflectance is 0% and the transmittance is 100% for the light of a specific polarization component. There is an incident angle (Brewster angle).

By setting the inclination directions of the two transparent plates as described above, the reflected light of the two transparent plates can contain only or a large amount of polarization components orthogonal to each other.

Therefore, without using the above-mentioned analyzer, or by using it in an auxiliary manner, the above-mentioned photodetector detects the optical components contained in the reflected light from the magneto-optical recording medium and having mutually orthogonal polarization planes. Therefore, the read signal of information can be created based on the output signals of the two photodetectors.

Further, a tracking error signal and a focusing error signal are obtained from at least two photodetectors described above.

According to the present invention, by arranging at least two transparent plates between the light emitting element and the condensing optical system, an optical pickup device having a minimum required optical structure can be realized, which is small in size. And weight reduction.

Indispensable optical parts in the optical pickup device of the present invention are a light emitting element, a condensing optical system, a transparent plate and a photodetector. If necessary, an analyzer can be provided. Can be planned.

In addition, a half that is provided in front of the light emitting element
The polarization direction of the light emitted from the light emitting element can be adjusted by the wave plate or the polarizing plate. Since the polarization direction of the light emitted from the light emitting element can be adjusted only by the half-wave plate or the polarizing plate, it is necessary to change the positions of other parts of the optical system, especially the parts of the light emitting element and the condensing optical system. Adjustment is very easy because it is unnecessary. Also, the above 1/2
The output signal level of the photodetector can also be adjusted by adjusting the polarization direction of the emitted light with a wave plate or a polarizing plate.

Another optical pickup device according to the present invention is a condensing optical system for condensing a light emitting element and divergent light emitted from the light emitting element on a magneto-optical recording medium and condensing reflected light from the magneto-optical recording medium. In the optical path of the divergent light between the light-emitting element and the condensing optical system, the one of the incident light is arranged at an angle with respect to the optical axis of the condensing optical system. At least two transparent plates that pass through a part and reflect a part of the light that is reflected by the magneto-optical recording medium and that is condensed by the condensing optical system has passed through the transparent plate or is reflected by the transparent plate At least two photodetectors for receiving the emitted light, analyzers respectively arranged between the photodetectors and the corresponding transparent plates for transmitting polarization components orthogonal to each other, the light emitting element, and Luminescent element Characterized in that it includes a half-wave plate or a polarizing plate disposed between the transparent plate is positioned closer to.

The divergent light emitted from the light emitting element is focused on the magneto-optical recording medium by the focusing optical system. The reflected light from the magneto-optical recording medium is condensed by the condensing optical system, a part of which is transmitted through the transparent plate or is reflected by the transparent plate and passes through the analyzer for at least 2
Received by two photodetectors. Since at least two photodetectors have analyzers whose polarization directions are different from each other by 90 degrees, the difference between the output signals of these photodetectors is used to reflect the recorded information on the magneto-optical recording medium. The polarization plane rotation angle of the light is detected. A tracking error signal and a focusing error signal are obtained from the at least two photodetectors.

Also in this optical pickup device, since at least two transparent plates are arranged between the light emitting element and the condensing optical system, the optical pickup device having the minimum required optical structure can be realized. Its smaller size, lighter weight,
The cost can be reduced.

In addition, a 1/2 placed in front of the light emitting element
The wavelength plate or the polarizing plate can adjust the polarization direction of the light emitted from the light emitting element and the level of the output signal of the photodetector.

[0022]

1 and 2 show an embodiment of the present invention.

The optical pickup device includes a semiconductor laser 11
And a condensing optical system for converging the divergent light emitted from the semiconductor laser 11 on the magneto-optical disk 20. The condensing optical system is a collimating lens that collimates divergent light.
It includes an objective lens 13 for condensing the collimated light.

On the optical path of the divergent light between the semiconductor laser 11 and the collimating lens 12, two glass plates 14 and
15 is arranged in a state of being inclined with respect to the optical axes of the semiconductor laser 11 and the focusing optical system.

A half-wave plate (half-wave plate or optical rotator) or a polarizing plate 18 is provided on the front surface of the semiconductor laser 11, that is, between the semiconductor laser 11 and the glass plate 14 on the side close to the semiconductor laser 11. There is.

The divergent light emitted from the semiconductor laser 11 is 1 /
The light is transmitted through the two-wavelength plate or the polarizing plate 18, the two glass plates 14 and 15, and is condensed on the magneto-optical disk 20 by the condensing optical system. A part of the divergent light emitted from the semiconductor laser 11 is reflected by the glass plate 14 and received by the photodetector 23.
The emitted light intensity of the semiconductor laser 11 is controlled based on the light reception signal of the photodetector 23.

The reflected light from the magneto-optical disk 20 is condensed by the condensing optical system. A part of the condensed reflected light is reflected by the glass plate 15 and is incident on the photodetector 22, and a part of the light transmitted through the glass plate 15 is further reflected by the glass plate 14 and is detected by the photodetector 21. Incident on.

Since the reflected light from the magneto-optical disk 20 is condensed by the condensing optical system, the glass plate 15 and the photodetector 22
It is not always necessary to provide a condenser lens or the like between the glass plate 14 and the photodetector 21.

FIG. 3 shows the incident angle dependence of the reflection coefficient and the transmission coefficient of light when the light is obliquely incident on the surface of the glass plate (refractive index = 1.5).

T _p is the transmission coefficient of the P polarization component, T _s is the transmission coefficient of the S polarization component, R _p is the reflection coefficient of the P polarization component, R _s
Is the reflection coefficient of the S-polarized component. The component parallel to the glass surface is the S-polarized component, and the vertical component is the P-polarized component.

As can be seen from FIG. 3, at a certain angle α _B (this is called Brewster's angle), R _p becomes 0% and T _p becomes 100%. At this time, R _s and T _s take values other than 0 or 100%.

Therefore, if the glass plate is tilted with respect to the incident light at the Brewster angle α _B , the reflected light from the glass plate will be only the S-polarized component. Even if the inclination angle of the glass plate is other than Brewster's angle, the reflected light from the glass plate contains more S-polarized component than P-polarized component.

The glass plates 14 and 15 are arranged so that the line segments formed by intersecting the planes perpendicular to the optical axis of the condensing optical system with these glass plates 14 and 15 are orthogonal to each other,
Moreover, if the incident angle of the reflected light condensed by the condensing optical system is tilted so as to be the Brewster angle, the glass plate 14
The reflected light from 15 and 15 contains only polarization components orthogonal to each other, and only these lights are detected by photodetectors 21 and 22.
Respectively detected by.

Even if the inclination angles of the glass plates 14 and 15 with respect to the incident light are other than the Brewster angle, the glass plates 14 and 15 are
The reflected light from 1 contains more polarization components orthogonal to each other. By disposing analyzers 31 and 32 arranged such that their polarization directions are orthogonal to each other so that only these orthogonal polarization components pass respectively, the polarization components orthogonal to each other are provided. Only are detected by photodetectors 21 and 22, respectively.

The ½ wavelength plate or polarizing plate 18 is emitted from the semiconductor laser 11 and is projected onto the magneto-optical disk 20 by the focusing optical system through the ½ wavelength plate or polarizing plate 18. The polarization direction of the linearly polarized light is used for adjusting so as to form an angle of 45 degrees with the above-mentioned polarization directions (the polarization directions of the light passing through the analyzers 31 and 32) orthogonal to each other.

Since the light emitted from the semiconductor laser 11 is linearly polarized light, it is necessary to form an angle of 45 degrees with the above-mentioned mutually orthogonal polarization directions even without the half-wave plate or the polarizing plate 18. It is possible to set. However, in the actual assembly of the optical system, the positions of the semiconductor laser 11 and the focusing optical system must be adjusted so that the emitted light of the semiconductor laser 11 forms a spot on the magneto-optical disk 20 correctly. The semiconductor laser 11
It is difficult to correctly adjust the polarization direction of the emitted light of the.

Therefore, the polarization direction of the emitted light of the semiconductor laser 11 is roughly determined, and the position adjustment with the focusing optical system is first performed. Then, if the polarization direction of the projected light is adjusted by rotating the ½ wavelength plate or the polarization plate 18, it is not necessary to adjust the position of the semiconductor laser 11 or the condensing optical system in adjusting the polarization direction, and the polarization direction is adjusted. It is possible to determine only correctly.

The half-wave plate or polarizing plate 18 can also be used to adjust the levels of the output signals of the photodetectors 21 and 22. It is preferable that the transmittance or reflectance of the glass plates 14 and 15 be adjusted in advance so that the amounts of light incident on the photodetectors 21 and 22 become equal. However, the amounts of light incident on the photodetectors 21 and 22 are not always equal, and the detectors 31 and 32 are provided on the front surfaces of the photodetectors 21 and 22 as necessary, so that twenty two
It is difficult to design the level of the output signal of strictly in advance.

Therefore, a mirror is placed at the position of the magneto-optical disk 20 instead of the magneto-optical disk 20. Light reflected from the mirror is received by photodetectors 21 and 22. The plane of polarization of the reflected light from the mirror is not rotated. Therefore, the 1/2 wavelength plate or the polarizing plate 18 may be rotated and adjusted so that the levels of the output signals of the photodetectors 21 and 22 become equal. The magneto-optical disk 20 may be left as it is without a mirror, and the levels of the centers of the signals obtained from both photodetectors 21 and 22 may be adjusted to be equal.

With the above configuration, the change in the polarization plane rotation angle caused by the information recorded on the magneto-optical disk 20 is detected by the difference between the output signals of the photodetectors 21 and 22.

The output signals of the photodetectors 21 and 22 are also used for producing a focusing error signal and a tracking error signal.

The focusing error signal is generated by, for example, the beam size method or the astigmatism method. In the beam size method, photodetectors 21 and 22 are arranged at positions before and after the focal position of reflected light when focusing is performed correctly (as shown in FIG. 2). The photodetectors 21 and 22 are arranged so that signals representative of the sizes of the light beams received by the photodetectors 21 and 22 are obtained.
22 is formed, and the focusing error signal is created by taking the difference between the output signals of the photodetectors 21 and 22.
Each of the photodetectors 21 and 22 includes, for example, a three-divided photodiode, and the difference between the output signal of the central photodiode and the sum signal of the output signals of the photodiodes on both sides becomes the output signal of the photodetector.

Aberrations including astigmatism occur in the reflected light from the glass plate arranged obliquely with respect to the optical axis. By utilizing this astigmatism, a focusing error signal based on the astigmatism method can be obtained. For example, one of the photodetectors 21 and 22 is composed of a four-division photodiode, and a focusing error signal is generated by adding and subtracting the output signals of these four photodiodes.

The push-pull method, for example, is used to create the tracking error signal. That is, the photodetector
21 or 22 is configured to include a photodiode divided into two in the direction perpendicular to the track direction of the magneto-optical disk 20, and the difference signal between the output signals of these photodiodes becomes the tracking error signal.

If necessary, arrange three or more glass plates,
Focusing error detection for each glass plate,
A photodetector for tracking / error detection or the like may be provided.

As described above, the reflectance and the transmittance of the glass plate are appropriately adjusted in advance as needed. In this adjustment, at least one surface of the glass plate has a non-reflective coating,
It is advisable to apply a coating such as a semi-mirror surface coating. The antireflection coating is particularly useful when it is necessary to obtain the reflected light from only one of the two surfaces of the glass plate.

If necessary, the thickness of the glass plate
On the magneto-optical disk 20, the thickness is made thin (for example, about 100 μm or less) so that the influence of wavefront aberration can be ignored.
Alternatively, the shape of the collimator lens 12 or the like may be a shape (for example, an aspherical surface or an asymmetrical lens) in which the light spot formed on the magneto-optical disk 20 is hardly affected by the wavefront aberration.

Further, between the semiconductor laser 11 and the collimating lens 12 of the condensing optical system, a light beam shaping optical system for correcting the light of the elliptical cross section emitted from the semiconductor laser 11 into the light of the circular cross section is provided. You can also In addition, semiconductor laser 11
The emitted light of the semiconductor laser 11 passes between the glass plate 14 and the glass plate 14, and the semiconductor laser 11 emits the reflected light from the magneto-optical disk 20.
An isolator optical system may be provided to prevent the light from entering the device. If necessary, a condensing optical system can be provided between the glass plate and the photodetector.

FIG. 4 shows a modification.

Comparing with those shown in FIGS. 1 and 2,
Instead of the glass plate, a half mirror 14 having a relatively high reflectance and a relatively low transmittance is arranged. Further, the positions of the semiconductor laser 11 and the photodetector 21 are exchanged. 1/2
The wave plate or polarizing plate 18 is a semiconductor laser 11 and a half mirror.
It is provided between 14 and.

The light emitted from the semiconductor laser 11 is a half mirror 14.
Is reflected by the laser beam and guided to the condensing optical system.
Focused on 20. Magneto-optical disk 20
A part of the light that has been transmitted through the glass plate 15 of the reflected light from is transmitted through the half mirror 16 and enters the photodetector 21.

Further, in FIG. 4, the half mirror 14 and the glass plate 15 are arranged so that the line segments generated by intersecting the plane perpendicular to the optical axis are parallel to each other.
Also with this configuration, light including many polarization direction components orthogonal to each other is reflected by the glass plate 15 and transmitted through the half mirror 14. Then, these lights are incident on the photodetectors 21 and 22 through the analyzers 31 and 32, respectively, which allow the lights of the polarization directions orthogonal to each other to pass.

FIG. 5 shows still another modification.

The collimating lens 12 is removed from the condensing optical system to further reduce the size. The objective lens 13 collects the divergent light emitted from the semiconductor laser 11 on the magneto-optical disk 20. Further, the reflected light from the magneto-optical disk 20 is condensed by the objective lens 13.

FIG. 6 shows still another embodiment.

The glass plates 14 and 15 are these glass plates.
The line segments generated by the intersection of 14 and 15 with the plane perpendicular to the optical axis are arranged parallel to each other (not necessarily arranged in this way). Since both the P polarized component and the S polarized component are reflected on the glass plates 14 and 15,
It is necessary to dispose the analyzers 31, 32 in front of the photodetectors 21, 22. These analyzers 31 and 32 are each orthogonal to each other, and only allow passage of light in polarization directions having an angle of 45 ° with respect to the polarization direction of the projected light on the magneto-optical disk 20, respectively.

[Brief description of drawings]

FIG. 1 shows an embodiment of an optical pickup device according to the present invention and is a plan view of an optical configuration of the optical pickup device.

2 is a perspective view showing an embodiment of the optical pickup device according to the present invention and showing a part of the optical system shown in FIG. 1. FIG.

FIG. 3 is a graph showing the incident angle dependence of the reflection coefficient and the transmission coefficient of a glass plate.

FIG. 4 shows a modification of the optical pickup device.

FIG. 5 shows another modification of the optical pickup device.

FIG. 6 shows another embodiment of the optical pickup device.

[Explanation of symbols]

 11 Semiconductor laser 12 Collimating lens 13 Objective lens 14, 15 Glass plate 18 1/2 wavelength plate or polarizer 20 Magneto-optical disk 21, 22 Photodetector 31, 32 Analyzer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hironobu Kiyomoto 10 Odoron-cho, Hanazono, Ukyo-ku, Kyoto City Omron Corporation

Claims (9)

[Claims] 1. An optical pickup device comprising a light emitting element and a condensing optical system for converging divergent light emitted from the light emitting element onto a magneto-optical recording medium and condensing reflected light from the magneto-optical recording medium. In the optical path of the divergent light between the light emitting element and the condensing optical system, the optical system is tilted with respect to the optical axis of the condensing optical system and transmits a part of the incident light. A set of at least two transparent plates, and at least two of the lights reflected by the magneto-optical recording medium and condensed by the condensing optical system, respectively, which receive the light reflected by the transparent plate. And a pair of the transparent plates are arranged such that line segments generated by a plane perpendicular to the optical axis intersecting these transparent plates are inclined in directions substantially orthogonal to each other. , Close to the above light emitting device 1/2 between the transparent plate and the transparent side
An optical pickup device provided with a wave plate or a polarizing plate. 2. An optical pickup device comprising a light emitting element and a converging optical system for converging divergent light emitted from the light emitting element on a magneto-optical recording medium and condensing reflected light from the magneto-optical recording medium. In the optical path of the divergent light between the light emitting element and the condensing optical system, the optical system is tilted with respect to the optical axis of the condensing optical system and transmits a part of the incident light. At least one pair of transparent plates that reflect light from a portion, and a photodetector that receives light reflected by one of the transparent plates reflected by the magneto-optical recording medium and condensed by the condensing optical system. And a photodetector that receives the light transmitted through the other transparent plate,
Between the light emitting element and the transparent plate on the side close to the light emitting element, the planes perpendicular to the optical axis intersect the transparent plates and are arranged so as to be inclined in a direction in which line segments are substantially parallel to each other. An optical pickup device in which a half-wave plate or a polarizing plate is disposed in the optical pickup device. 3. The optical pickup device according to claim 1, wherein the transparent plate is arranged at an angle at which an incident angle of reflected light from the magneto-optical recording medium becomes equal to a Brewster angle. 4. The optical pickup device according to claim 1, wherein an analyzer is arranged between the photodetector and a transparent plate corresponding to the photodetector. 5. An optical pickup device comprising a light emitting element and a converging optical system for converging divergent light emitted from the light emitting element on a magneto-optical recording medium and condensing reflected light from the magneto-optical recording medium. In the optical path of the divergent light between the light emitting element and the condensing optical system, the optical system is tilted with respect to the optical axis of the condensing optical system and transmits a part of the incident light. Of at least two transparent plates that reflect light at a portion, and receive the light that is transmitted by the transparent plate or is reflected by the transparent plate among the lights that are reflected by the magneto-optical recording medium and are condensed by the condensing optical system. At least two photodetectors, analyzers respectively arranged between the photodetectors and the corresponding transparent plates, which transmit polarization components orthogonal to each other, the light emitting element, and a position close to the light emitting element. Above transparent An optical pickup device comprising a half-wave plate or a polarizing plate arranged between the plate and the plate. 6. The optical pickup device according to claim 1, wherein a tracking error signal and a focusing error signal are created using the output signal of the photodetector. 7. The optical pickup device according to claim 1, wherein a read signal is created using an output signal of the photodetector. 8. A photodetector is provided, which receives light emitted from the light emitting element and reflected by the transparent plate, and outputs a signal for controlling the light emission intensity of the light emitting element. The optical pickup device according to any one of 1 to 7. 9. The coating for adjusting the reflectance is applied to at least one surface of the transparent plate.
9. The optical pickup device according to any one of items 1 to 8.