JPH0547003A - Optical pickup device - Google Patents

Abstract

PURPOSE:To obtain a correct focusing error, etc. CONSTITUTION:In an optical system consisting of transparent plates 14 and 15 placed obliquely against the optical axis of the optical path of convergence light and photodetectors 21 and 22 which receive the reflected light from this transparent plate, the photodetector includes light receiving elements 21a-21c and 22d-22f which are divided into at least three sections by a straight line. In addition, reflected light spots SP11 and SP21 coming from the surface of the transparent plate and reflected light spots SP12 and SP22 from the back side are arranged in the direction of a dividing straight line. The thickness of the transparent plate is set within the range in which the reflected light spot coming from a surface and that from the above stated back side do not overlap each other on the photo reception surface of the light receiving element, and in addition, the diameter of the smaller spot between two reflected light spots is larger than the width of central light receiving elements 21b and 21e.

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 an optical recording medium.

In the present invention, the optical recording medium includes not only an optical recording medium such as an optical disc and an optical card, but also a magneto-optical recording medium such as a magneto-optical disc and a magneto-optical card.

In the present invention, recording / reproducing information includes recording information on an optical recording medium, reproducing information recorded on the optical recording medium, and recording and reproducing.

[0004]

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 components, 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.

[0006]

DESCRIPTION OF THE INVENTION OF THE PRESENT INVENTION The applicant has already proposed an optical pickup device having a novel structure in order to solve such problems and to make the optical pickup device much smaller, lighter and less expensive.

The optical pickup device proposed by the applicant in Japanese Patent Application No. 2-411850 collects a light emitting element and divergent light emitted from the light emitting element on an optical recording medium and reflects light from the optical recording medium. And a condensing optical system for condensing light, 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. At least two transparent plates (for example, dielectric plates) that transmit a part of the incident light and reflect a part thereof, and the light reflected by the optical recording medium and condensed by the condensing optical system. Among them, at least two photodetectors for receiving the light transmitted through the transparent plate or reflected by the transparent plate are provided.

The divergent light emitted from the light emitting element is condensed on the optical recording medium by the condensing optical system. The reflected light from the optical recording medium is condensed by the condensing optical system, a part of which is transmitted through the transparent plate or reflected by the transparent plate and is received by at least two photodetectors. A tracking error signal and a focusing error signal are obtained from the at least two photodetectors. In the case of reproduction, an information read signal is obtained based on the output signal of one or both of the at least two detectors. When the optical recording medium is a magneto-optical recording medium, an analyzer having polarization directions different from each other by 90 degrees is placed in front of the at least two photodetectors, and the polarization plane rotation angle of the reflected light is detected by the recorded information. To be done.

According to the invention of the prior application, an optical pickup device having a minimum required optical structure is realized by disposing at least two transparent plates between the light emitting element and the condensing optical system. It is possible to reduce the size and weight.

Indispensable optical parts in the optical pickup device of the invention of the prior application are a light emitting element, a condensing optical system, a transparent plate and a photodetector, and in the case of a magneto-optical recording medium, an analyzer may be provided on this. Since it is sufficient, the cost can be significantly reduced.

The optical pickup device proposed by the applicant in Japanese Patent Application No. 2-411851 collects a light emitting element and divergent light emitted from the light emitting element onto a magneto-optical recording medium and reflects light from the magneto-optical recording medium. And a condensing optical system for condensing light, 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. At least two transparent plates (for example, dielectric plates) that transmit a part of the incident light and reflect a part of the incident light, and are reflected by the magneto-optical recording medium and condensed by the condensing optical system. At least two photodetectors for respectively receiving the light reflected by the transparent plates among the above-mentioned light beams, and the planes perpendicular to the optical axis intersect these transparent plates. The resulting line segments are Characterized in that it is tilted in the direction crucible orthogonal.

[0012] 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 of light of a specific polarization component is 0% and the transmittance is 100%. 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.

A tracking error signal and a focusing error signal can be obtained from at least two photodetectors.

According to the invention of the prior application, the optical pickup device having the minimum required optical configuration is realized by disposing at least two transparent plates between the light emitting element and the condensing optical system. It is possible to reduce the size and weight.

Indispensable optical parts in the optical pickup device of the invention of the prior application are a light emitting element, a condensing optical system, a transparent plate and a photodetector. It is sufficient to provide an analyzer if necessary, so that the cost is greatly reduced. Can be planned.

[0022]

In these prior inventions, a transparent plate is arranged obliquely with respect to the optical axis on the optical path where the reflected light from the optical recording medium converges.
Since the transparent plate has a finite thickness, reflection of incident light occurs on its front and back surfaces. Both the reflected light from the front surface and the reflected light from the back surface of the transparent plate enter the photodetector.

The photodetector generally includes a plurality of divided photodiodes, and a focusing error signal, a tracking error signal, and an information read signal are generated based on the output signals of these photodiodes. Therefore, these various signals may be adversely affected depending on the incident positions and sizes of the two reflected lights.

The present invention proposes an arrangement configuration in which a correct focusing error signal, tracking error signal, and read signal can be obtained even when two reflected lights are incident on the photodetector.

[0025]

According to the present invention, in the above-mentioned optical pickup device of the prior invention, the photodetector includes a light receiving element divided into at least three parts by a straight line, and the surface of the transparent plate. The reflected light spot from the back surface and the reflected light spot from the back surface are arranged side by side in the direction along the dividing line, and the thickness of the transparent plate is such that the reflected light spot from the front surface and the reflected light spot from the back surface. Are not overlapped on the light receiving surface of the light receiving element, and the diameter of the smaller spot of the two reflected light spots is set to a range larger than the width of the central light receiving element. To do.

[0026]

When the thickness of the transparent plate is thin, the reflected light spot from the front surface and the reflected light spot from the back surface of the transparent plate overlap on the light receiving surface of the photodetector. When the two lights overlap, interference fringes occur. This interference fringe changes with changes in temperature and wavelength. Therefore, the various signals described above become unstable.

When the thickness of the transparent plate is large, the diameter of either one of the two reflected light spots from the front and back surfaces becomes extremely small. This small reflected light spot is incident only on the central one of the light receiving elements divided into at least three and does not enter the other light receiving elements. Since the various signals are generated by adding and subtracting the output signals of the plurality of light receiving elements, if the reflected light is incident on only one specific light receiving element, the addition and subtraction result is adversely affected, and it becomes difficult to obtain a correct signal.

[0028]

According to the present invention, the thickness of the transparent plate is such that the two reflected light spots from the front surface and the back surface do not overlap each other on the light receiving surface and the smaller one of the two reflected light spots. Since the diameter of the spot is set to be larger than the width of the light receiving element in the center, the problem described above does not occur, and an accurate focusing error signal,
A tracking error signal and a read signal (particularly a focusing error signal) can be obtained.

Further, since the two reflected light spots are aligned in the direction of the dividing straight line of the light receiving element, these spots contribute to all the light receiving elements in the same manner, so that various correct signals can be generated without causing an error. can get.

[0030]

[First Embodiment] First, the invention of the prior application and the Japanese Patent Application No. 2-411850 will be described through its embodiments.

FIG. 1 shows an embodiment of Japanese Patent Application No. 2-411850.
1 shows the configuration of an optical pickup device for recording / reproducing information on / from an optical disc.

The optical pickup device includes a semiconductor laser 11
And a condensing optical system that condenses the divergent light emitted from the semiconductor laser 11 onto the optical disc 20. The condensing optical system is a collimating lens 12 that collimates divergent light.
And an objective lens 13 that collects 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.

The divergent light emitted from the semiconductor laser 11 passes through the two glass plates 14 and 15 and is focused on the optical disk 20 by the focusing 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 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 optical disk 20 is condensed by the condensing optical system, a condenser lens or the like is provided between the glass plate 15 and the photodetector 22 and between the glass plate 14 and the photodetector 21. Need not always be provided.

The output signals of the photodetectors 21 and 22 are used for producing a focusing error signal, a tracking error signal and a read signal, as will be described in detail later.

To briefly explain, focusing
The error signal is created 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 focus position of reflected light when focusing is performed correctly. The photodetectors 21 and 22 are provided so that a signal representative of the size of the light beam received is obtained.
21 and 22 are 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 of 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-divided photodiode, and a focusing error signal is generated by adding and subtracting the output signals of these four photodiodes.

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

The read signal of the information recorded on the optical disk 20 can be created by adding the output signals of the photodetectors 21 and 22. Of course, the output signal of either one of the photodetectors 21 and 22 may be used as the read signal.

If necessary, arrange three or more glass plates,
You may make it provide a photodetector corresponding to each glass plate. Further, if necessary, the shape of the collimator lens 12 or the like may be set to a shape (for example, an aspherical surface or an asymmetrical lens) so that the light spot formed on the optical disk 20 is hardly affected by the wavefront aberration.

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
An isolator optical system that allows the emitted light of the semiconductor laser 11 to pass therethrough and blocks the reflected light from the optical disc 20 from entering the semiconductor laser 11 may be provided between the glass 11 and the glass 11. If necessary, a condensing optical system can be provided between the glass plate and the photodetector.

FIG. 2 shows the structure of an optical pickup device suitable for recording / reproducing on a magneto-optical disk. The same components as those shown in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted.

Analyzers 31 and 32 are provided in front of the light receiving surfaces of the photodetectors 21 and 22, respectively. These analyzers 31 and 32 are arranged so that the polarization directions of light passing therethrough are orthogonal to each other. Further, the polarization direction of the linearly polarized light emitted from the semiconductor laser 11 forms an angle of 45 degrees with the polarization direction of the light passing through the analyzers 31 and 32.

With the above configuration, the change in the polarization plane rotation angle caused by the information recorded on the magneto-optical disk 30 is detected by the difference between the output signals of the photodetectors 21 and 22.

It goes without saying that a polarizer may be provided on the front surface of the semiconductor laser 11.

FIG. 3 shows a modification.

Compared with the one shown in FIG.
Instead, a half mirror 16 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.

The light emitted from the semiconductor laser 11 is a half mirror 16.
Is reflected by the laser beam and guided to the condensing optical system.
Focused on 30. Magneto-optical disk 30
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. Other configurations are the same as those shown in FIG.

FIG. 4 shows another modification.

The collimating lens 12 is removed from the condensing optical system to further reduce the size. The objective lens 13 condenses the emitted light emitted from the semiconductor laser 11 onto the magneto-optical disk 30. Further, the reflected light from the magneto-optical disk 30 is condensed by the objective lens 13. Other configurations are the same as those shown in FIG.

Also in the optical pickup device shown in FIG. 1, the positions of the semiconductor laser 11 and the photodetector 21 are changed as shown in FIG. 3, or the collimating lens 12 is removed from the condensing optical system as shown in FIG. It goes without saying that it can be removed.

Next, the prior invention disclosed in Japanese Patent Application No. 2-411851 will be described through its embodiments.

5 and 6 show an embodiment of this prior invention.

The optical pickup device includes a semiconductor laser 11
And a converging optical system for converging the divergent light emitted from the semiconductor laser 11 on the magneto-optical disk 30. 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.

The divergent light emitted from the semiconductor laser 11 passes through the two glass plates 14 and 15 and is focused on the magneto-optical disk 30 by the focusing optical system. A part of the divergent light emitted from the semiconductor laser 11 is reflected by the glass plate 14 and is detected by the photodetector.
Received by 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 30 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. 7 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. 7, R _p becomes 0% and T _p becomes 100% at a certain angle α _B (this is called Brewster's angle). 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 tilt 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 polarization directions of the linearly polarized light emitted from the semiconductor laser 11 are orthogonal to each other (analyzer 31,
The polarization direction of the light passing through 32) and the angle of 45 degrees.

With the above configuration, the change in the polarization plane rotation angle caused by the information recorded on the magneto-optical disk 30 is detected by the difference between the output signals of the photodetectors 21 and 22.

It goes without saying that a polarizer may be provided on the front surface of the semiconductor laser 11.

As described above, the output signals of the photodetectors 21 and 22 are also used for producing the focusing error signal and the tracking error signal.

FIG. 8 shows a modification.

Compared with those shown in FIGS. 5 and 6,
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.

Light emitted from the semiconductor laser 11 is emitted from the half mirror 14.
Is reflected by the laser beam and guided to the condensing optical system.
Focused on 30. Magneto-optical disk 30
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. 8, the half mirror 14 and the glass plate 15 are arranged so that the line segments generated by intersecting with 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. 9 shows another modification.

The collimator 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. 10 shows only the glass plate 15 and the photodetector 22 in the optical pickup device according to the above-mentioned prior invention. The analyzer 32 is not shown. Light reflected from the optical disk 20 or the magneto-optical disk 30 is reflected on the surface of the glass plate 15 and enters the photodetector 22, and is also reflected on the back surface of the glass plate 15 and detected by the photodetector.
It is incident on 22. Similarly, reflected light from both the front and back surfaces of the glass plate 14 also enters the photodetector 21.

FIG. 11 shows a configuration example of the photodetectors 21 and 22. Each of these photodetectors 21 and 22 is composed of a three-divided photodiode. That is, the photodetector 21 is composed of three photodiodes 21a, 21b and 21c which are electrically insulated from each other, and the width of the central photodiode 21b is set to be the smallest. The straight line dividing the photodiodes 21a, 21b and 21c extends in the track direction of the optical disk or the magneto-optical disk in all the embodiments described above. Also, a glass plate
Spots SP ₁₁ and S formed on the photodiodes 21a to 21c by reflected light from the front and back surfaces of 14
The photodetector 21 is arranged so that P _{12 is} also arranged along a straight line dividing the photodiodes 21a to 21c.

The photodetector 22 likewise has three electrically isolated photodiodes 22d, 22e and 22f.
The width of the central photodiode 22e is set to be the smallest. The straight line dividing the photodiodes 22d, 22e and 22f extends in the track direction of the optical disk or magneto-optical disk in the embodiment shown in FIGS. 1 to 4 and 8, and in the embodiment shown in FIGS. 5, 6 and 9, the optical disk. Alternatively, it extends in a direction orthogonal to the track direction of the magneto-optical disk. In addition, the photodiodes 22d to 22f are reflected by the light reflected from the front and back surfaces of the glass plate 15.
The photodetector 22 is arranged so that the spots SP ₂₁ and SP ₂₂ formed above are arranged along a straight line dividing the photodiodes 22d to 22f.

Since the photodetector 22 is arranged in front of the focal position of the reflected light from the glass plate 15, the spot SP ₂₁ due to the reflected light from the front surface of the glass plate 15 is the spot due to the reflected light from the back surface. Greater than SP ₂₂ . Since the photodetector 21 is arranged after the focal point of the reflected light from the glass plate 14, the reflected light spot SP ₁₁ from the front surface of the glass plate 14 is smaller than the reflected light spot SP ₁₂ from the back surface.

The push-pull method is used to detect tracking errors, and the double-pull method is used to detect focusing errors.
The beam size method is used respectively. Due to the double beam size method, when the focusing is performed correctly, as described above, the photodetector 21 is located behind the focal position of the reflected light from the glass plate 14 (see FIG. 6, for example). The photodetectors 22 are arranged in front of the focal position of the reflected light from the glass plate 15.

The tracking error signal is created by the subtracter 49 taking the difference between the output signal of the photodiode 21a of the photodetector 21 and the output signal of the photodiode 21c. Photodetector 22 photodiodes 22d and 22
Tracking can also be performed by taking the difference between the output signals of f
An error signal can be created.

Photodiodes 21a, 21b, 21c, 22
The output signals of d, 22e and 22f are respectively a, b, c,
Represented by d, e and f. Adders 41 and 44 and subtractor 4
Depending on 3,46,47, (a + c + e)-(b + d + f)
Is calculated to generate a focusing error signal.

Read signals are created by calculating (a + b + c)-(d + e + f) by the adders 41, 42, 44, 45 and the subtractor 48.

Even if the reflected light from both the front and back surfaces of the glass plate 14 or 15 is incident on the photodetector 21 or 22, the spots SP ₁₁ and SP ₁₂ or SP ₂₁ and SP ₂₂ due to the reflected light are detected by the photodiodes 21a to 21d. Since they are arranged in the direction of the straight line that divides 21c or 22d to 22f, these reflected light spots contribute to the output signal of each photodiode in the same way, and there is no obstacle (error occurs. (Without) tracking error signal, focusing error signal and read signal can be created.

With reference to FIG. 12, the relationship between the thickness of the glass plate and the reflected light spot will be considered by taking the glass plate 15 and the photodetector 22 as an example.

FIG. 12A shows the case where the glass plate 15 is thin. Reflected light spot SP from the front and back of glass plate 15
₂₁ and SP ₂₂ are photodiodes 22d to 22 of the photodetector 22.
They overlap on the light receiving surface of f. When the two light spots overlap each other in this way, interference fringes occur. The interference fringes change due to changes in temperature and wavelength. Further, due to manufacturing errors of various optical elements, stripes may be obliquely formed with respect to the straight line dividing the photodiodes 22d to 22f. In such a state, the focusing error signal, tracking error signal, and read signal may become unstable. On the other hand, it is preferable that the glass plate 15 is thin in this way, because the aberration on the optical disk or the magneto-optical disk becomes small.

FIG. 12C shows the case where the glass plate 15 is thick. The two reflected light spots SP ₂₁ and SP ₂₂ are separated, but one spot SP ₂₂ is extremely small. When the diameter of the spot SP ₂₂ becomes smaller than the width of the central photodiode 22e, the light from the spot SP ₂₂ contributes only to the output signal of the photodiode 22e, and the output signal of the other photodiodes 22d and 22f. Has no effect at all. Then, in particular, the double
Focusing error detection by the beam size method becomes inaccurate. Here, the spot diameter is 1 / e ² (about 13%) of the maximum value of the light intensity according to the general definition.
The range of light with intensity. The thicker the glass plate 15 is, the larger the aberration is, which makes it difficult to form a correct light spot on the optical disk or the magneto-optical disk.

FIG. 12B shows the case where the thickness of the glass plate 15 is set appropriately. Two light spots SP ₂₁ and S
P ₂₂ is isolated from each other, and these light spots together illuminate all photodiodes 22d-22f.
The optimum glass plate thickness is two reflected light spots SP _21.
It can be said that SP ₂₂ is the thinnest of the thicknesses that do not overlap. Actually, this thickness is 500 μm as one guideline.
It will be about. However, this number is not always correct because the optimum thickness changes depending on the properties of the condensing optical system.

In the present invention, the thickness of the glass plate is set so that the two reflected light spots from the front surface and the back surface of the glass plate do not overlap,
Moreover, since the size of the smaller spot of the two reflected light spots is set to be larger than the width of the central photodiode, a correct focusing error signal or the like can always be obtained. This also applies between the glass plate 14 and the photodetector 21.

[Brief description of drawings]

FIG. 1 shows an embodiment of the invention of the prior application disclosed in Japanese Patent Application No. 2-411850, and shows the configuration of an optical pickup device suitable for recording / reproducing of an optical disc.

FIG. 2 shows another embodiment of the invention of the prior application, showing a configuration of an optical pickup device suitable for recording / reproducing of a magneto-optical disk.

FIG. 3 shows a modification of the optical pickup device shown in FIG.

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

FIG. 5 shows an embodiment of an optical pickup device according to the invention of the prior application disclosed in Japanese Patent Application No. 2-411851, and is a plan view of an optical configuration of the optical pickup device.

FIG. 6 is a perspective view showing an embodiment of the optical pickup device according to the above-mentioned prior invention and showing a part of the optical system shown in FIG.

FIG. 7 is a graph showing the incident angle dependence of the reflection coefficient and the transmission coefficient of a glass plate.

FIG. 8 shows a modification of the optical pickup device.

FIG. 9 shows another modification of the optical pickup device.

FIG. 10 shows how light is reflected on both front and back surfaces of a glass plate and is incident on a photodetector.

FIG. 11 shows a circuit for producing a focusing error signal, a tracking error signal and a read signal.

12A to 12C show how reflected light spots from both front and back surfaces of glass plates having different thicknesses are formed on the light receiving surface of the photodetector.

[Explanation of symbols]

11 Semiconductor laser 12 Collimating lens 13 Objective lens 14, 15 Glass plate 16 Half mirror 20 Optical disc 21, 22 Photodetector 21a, 21b, 21c, 22d, 22e, 22f Photodiode 30 Magneto-optical disc 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 an optical recording medium and condensing reflected light from the 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 light that is transmitted by the transparent plate or is reflected by the transparent plate among the light that is reflected by the optical recording medium and is condensed by the condensing optical system. At least two photodetectors, the photodetector including a light receiving element divided into at least three by a straight line, and a reflected light spot from the front surface and a reflected light spot from the back surface of the transparent plate. Is above The transparent plates are arranged so as to line up in the direction along the secant, and the reflected light spot from the front surface and the reflected light spot from the back surface do not overlap on the light receiving surface of the light receiving element, and An optical pickup device in which the diameter of the smaller spot of the two reflected light spots is set to be larger than the width of the central light receiving element. 2. An optical pickup device comprising 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 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 so that the line segments generated by the plane perpendicular to the optical axis intersecting these transparent plates are substantially orthogonal to each other. The detector is Of the transparent plate, the reflected light spot from the front surface and the reflected light spot from the back surface of the transparent plate are arranged side by side in the direction along the dividing line. The thickness is such that the reflected light spot from the front surface and the reflected light spot from the back surface do not overlap on the light receiving surface of the light receiving element, and the diameter of the smaller one of the two reflected light spots is the center. The optical pickup device is set in a range larger than the width of the light receiving element of. 3. 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,
The planes perpendicular to the optical axis are arranged so as to be inclined in a direction in which line segments generated by intersecting these transparent plates are substantially parallel to each other, and the photodetector is divided into at least three by a straight line. An element, and the reflected light spot from the front surface and the reflected light spot from the back surface of the transparent plate are arranged so as to be aligned in the direction along the dividing line,
The thickness of the transparent plate is such that the reflected light spot from the front surface and the reflected light spot from the back surface do not overlap on the light receiving surface of the light receiving element, and the smaller of the two reflected light spots. An optical pickup device in which the diameter of is larger than the width of the central light receiving element. 4. 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. 5. The optical pickup device according to claim 1, wherein a read signal is created using an output signal of the photodetector. 6. A photodetector is provided which receives the light emitted from the light emitting element and reflected by the transparent plate and outputs a signal for controlling the emission intensity of the light emitting element. 4. The optical pickup device according to any one of 1 to 3. 7. The optical pickup device according to claim 1, wherein an analyzer is arranged between the photodetector and a transparent plate corresponding to the photodetector. 8. The optical pickup device according to claim 2, 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's angle. 9. A photodetector comprising a transparent plate disposed obliquely with respect to the optical axis of the convergent light on the optical path of the convergent light and a photodetector for receiving the reflected light from the transparent plate. The container includes a light receiving element divided into at least three parts by a straight line, and the reflected light spot from the front surface and the reflected light spot from the back surface of the transparent plate are arranged so as to be aligned in the direction along the dividing straight line, The thickness of the transparent plate is such that the reflected light spot from the front surface and the reflected light spot from the back surface do not overlap on the light receiving surface of the light receiving element, and the smaller one of the two reflected light spots. The diameter of is larger than the width of the light receiving element in the center.
Optical detection optics.