JPH087326A - Optical pickup - Google Patents

Abstract

PURPOSE:To detect a focus error simply and surely. CONSTITUTION:A returning light collected at a lens system 25 is detected by a first and a second photodetecting elements 30 and 28. An optical path length- changing means 31 formed of a transparent plate member is arranged on an optical path from the lens system 25 to the first photodetecting element 30. A collective position of the returning light obtained by the lens system 25 when the transparent plate member 31 is removed from on the optical pat is formed at a separated position from the lens system 25.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup for irradiating a light beam on the information recording surface of a disk-shaped recording medium to record and / or reproduce an information signal and detecting the returning light. In particular, the present invention relates to a structure for focus control in this type of optical pickup.

[0002]

2. Description of the Related Art Conventionally, an optical pickup for a magneto-optical disk device is constructed, for example, as shown in FIG. That is, in FIG. 12, the optical pickup 1 includes a laser light source 3 such as a semiconductor laser device that emits a light beam toward a collimator lens 2 and a beam cross-sectional shape of the light beam converted by the collimator lens 2 into substantially parallel rays. The polarization beam splitter 4
A beam cross-section shaping prism 5 which is emitted toward
A reflection mirror 7 that bends the transmitted light of the polarization beam splitter 4 and emits it toward the magneto-optical disk 6, an objective lens 8 that converges the reflected light of the reflection mirror 7 onto the information recording surface of the magneto-optical disk 6, and a polarized light. Beam splitter 4
Signal detection system 9 sequentially arranged below the optical axis along the optical axis
And have.

Here, the signal detection system 9 reflects the return light reflected by the polarization beam splitter 4 from the magneto-optical disk 6 sequentially through the optical system such as the objective lens 8 under the polarization beam splitter 4. The polarization beam splitter 10 that transmits the light, the half-wave plate 12 that emits the reflected light of the polarization beam splitter 10 toward the lens 11, and the return light that is converted into the converged light by the lens 11 have different polarization planes. Polarized beam splitter 13
, Light receiving elements 14 and 15 which respectively receive the transmitted light and the reflected light of the polarization beam splitter 13, a lens 16 which converts the transmitted light of the polarization beam splitter 10 into a converged light, and a light which is not emitted to the lens 16. It has a cylindrical lens 17 which gives point aberration and a light receiving element 18 which receives the light emitted from this cylindrical lens 17.

The optical pickup 1 configured as described above
According to the light beam emitted from the laser light source 3,
After being converted into parallel rays by the collimator lens 2, the beam cross-section shaping prism 5 shapes the beam cross-section shape,
The light then passes through the polarization beam splitter 4 and is reflected by the reflection mirror 7. Further, this light beam will be focused on the recording surface of the magneto-optical disk 6 which is rotationally driven by the action of the objective lens 8.

When the return light reflected by the information recording surface of the magneto-optical disk 6 is reflected, it receives the Kerr effect according to the magnetization polarity of the information recording surface, and after being reflected by the reflection mirror 7,
It is incident on the polarization beam splitter 4. In the polarization beam splitter 4, the returned light is the polarization beam splitter 4
The light is reflected by the reflecting surface of the polarized beam splitter 10 and emitted toward the polarizing beam splitter 10, and is emitted laterally and downward by the reflecting surface of the polarizing beam splitter 10. The return light reflected by the reflecting surface of the beam splitter 10 and emitted to the side has its oscillation direction rotated by the half-wave plate 12, is converted into convergent light by the following lens 11, and then is polarized by the polarization beam splitter 13. Is decomposed into components with different planes of polarization. The decomposed components are received by the light receiving elements 14 and 15, and the reproduction signal is detected by taking the difference in the light amount between the light receiving elements 14 and 15.

The return light, which has passed through the polarization beam splitter 10 and is emitted downward, is converted into convergent light by the lens 16, is given astigmatism by the cylindrical lens 17, and is received by the light receiving element 18. As a result, the light receiving element 18 detects astigmatism to detect a focus error, and the movement of the beam spot in the direction corresponding to the radial direction of the magneto-optical disk 6 is detected to detect a tracking error. Has become. The above configuration is an example of the configuration of the optical pickup of the conventional optical disc device.

[0007]

However, the optical pickup 1 having such a structure has the following problems.

That is, in this type of optical pickup 1, it is necessary to use the cylindrical lens 17 in order to detect a focus error, and the number of optical components is increased accordingly, and there is a problem that the overall configuration becomes complicated. . On the other hand, there is also a method of detecting a focus error by the knife edge method or wedge prism method, but these methods also require special optical parts, which increases the number of optical parts and complicates the overall configuration. In the case of these methods, there is a problem that it is difficult to surely detect a focus error.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an optical pickup capable of detecting a focus error simply and reliably.

[0010]

According to the present invention, the above object is to irradiate a disk-shaped recording medium with a light beam to record desired information on the disk-shaped recording medium, and / or to record the disk-shaped recording medium. In an optical pickup that reproduces information recorded on a medium, a lens system that collects return light obtained from the disk-shaped recording medium, and a first light receiving element that receives the return light that is collected by the lens system. A second light receiving element for receiving the return light condensed by the lens system, and a transparent plate member arranged on the optical path of the return light from the lens system to the first light receiving element. There
The converging position of the return light is formed at a position separated from the lens system with respect to the converging position of the return light formed by the lens system when the transparent plate member is removed from the optical path. By including the optical path length conversion means,
Achieved.

The optical pickup according to the present invention preferably divides the light beam into first and second light beams and irradiates the disc-shaped recording medium with the first and second light beams.
The return light of the light beam can be received by the first and second light receiving elements, respectively.

In the optical pickup according to the present invention, preferably, the return light is split into first and second return lights, and the return lights of the first and second light beams are respectively divided into the first and second return lights. The light receiving element can receive light.

Further, in the optical pickup according to the present invention, preferably, the optical path length conversion means is arranged for the return light so that a part of the return light is transmitted through the transparent plate member. Good.

In the optical pickup according to the present invention, preferably, the optical path length converting means may be arranged on the light receiving surface of the first light receiving element.

[0015]

According to the above structure, the return light focused by the lens system is received by the first and second light receiving elements, respectively, and at this time, the return light from the lens system to the first light receiving element is detected. An optical path length conversion means composed of a transparent plate-shaped member is arranged on the optical path of the return light, and when the transparent plate-shaped member is removed from the optical path, with respect to the condensing position of the return light formed by the lens system. By forming the condensing position of the return light at a position separated from the lens system, the condensing position of the return light can be detected based on the light reception results of the first and second light receiving elements. .

Particularly, the light beam is divided into a first light beam and a second light beam, and the disc-shaped recording medium is irradiated with the return light beams of the first and second light beams, respectively. Alternatively, if the light is received by the light receiving element, the return light is split into first and second return lights, and the return lights of the first and second light beams are respectively divided into the first and second return lights. If the light receiving element receives the light, the focus position can be easily detected.

Alternatively, even if the optical path length conversion means is arranged for the return light so that a part of the return light is transmitted through the transparent plate member, the light collecting position can be easily adjusted. Can be detected.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described below in detail with reference to the accompanying drawings. The examples described below are
Since it is a preferred specific example of the present invention, various technically preferable limitations are attached, but the scope of the present invention is, unless otherwise stated to limit the present invention, in the following description.
It is not limited to these modes.

FIG. 2 shows an example of a compact disc optical pickup as an embodiment of the present invention. Figure 2
In the optical pickup 20, a laser light source 21 such as a semiconductor laser device, a diffraction grating 22 that decomposes a light beam from the laser light source 21 into 0th-order light, + 1st-order light, and −1st-order light, and the diffraction grating 22. A beam splitter 23 that reflects the emitted light of the beam upward in the drawing, and an objective lens 25 that converges the light beam bent by the beam splitter 23 onto the information recording surface of the optical disc 24.
Contrary to this light beam, the optical disc 24 to the objective lens 2
5. It has a light receiving element 26 which receives the return light of the optical disk 24 which sequentially follows the beam splitter 23 below the beam splitter 23.

Here, the light receiving element 26 is constructed as shown in FIG. That is, in FIG.
6 is formed by three photodetectors 28, 29, 30 integrally formed on a semiconductor substrate, and these photodetectors 28, 29, 30 are respectively formed by the diffraction grating 22.
It is continuously formed on the semiconductor substrate so as to receive the return of the + 1st order light, the 0th order light, and the −1st order light formed in 1.

Here, the photodetector 29 for receiving the 0th order light is divided into four by dividing lines extending vertically and horizontally in the vicinity of the center, and the divided sensor element 29.
Of a, 29b, 29c, and 29d, the sensor elements 29a and 29d and the sensor elements 29b and 29c arranged in the vertical direction.
The sum signal of the output signals is obtained between the two. A tracking error is detected by detecting a difference signal between the sum signals (astigmatism method). The sum signal is further taken from this sum signal to detect the reproduction signal.

Further, the optical pickup 20 has the tracking error signal TE and the focus error signal F.
When E is input, an objective lens control unit 25b that issues a command to the objective lens drive unit 25a in response to this and performs tracking servo and focus servo is included. As the objective lens drive unit 25a, for example, a known biaxial actuator that holds the objective lens and can move the objective lens in the tracking direction and the focusing direction is used. In addition, the objective lens control unit 25
A storage unit 25c for storing necessary information such as a reference value described later is connected to b.

The photodetectors 28 and 30 for receiving the + 1st order light and the -1st order light extend vertically in the vicinity of the center.
The sensor element 28 is divided into three by the dividing line of the book.
a, 28b, 28c and sensor elements 30a, 30b, 3
0c are formed respectively.

Of these, the photodetector 30 which receives the −1st-order light is provided with a glass plate 31 made of a dielectric material so as to cover the light-receiving surface, whereby the + 1st-order light reflected by the optical disk 24 and incident on the photodetector 28. The optical path length of the −1st order light incident on the photodetector 30 is shorter than the optical path length.

That is, as shown in FIG. 3, when light enters from a medium having a small refractive index to a medium having a large refractive index, the light is refracted at this boundary, and at this time, the incident angle θ1 and the outgoing angle θ2 are different from each other. In between, the refractive index of each medium is n1 and n, respectively.
2, the Snell's law expressed by the following equation is established.

[0026]

[Equation 1]

Here, when n1 <n2, the relationship of θ1> θ2 is established. Therefore, on the −1st-order light side, as compared with the + 1st-order light side, the condensing position of the return light is the plate of the glass plate 31. It is formed at a position separated from the objective lens 25 by a distance determined by the thickness and the refractive index. That is, in this embodiment,
For the photodetectors 28 and 30 formed on the same substrate, defocus occurs between the + 1st order light and the −1st order light (see FIG. 4A).

Here, when the objective lens 25 gradually approaches the optical disk 24, the + 1st order light L1 and the -1st order light L
2 and the photo detectors 28 and 30 are shown in sequence in FIGS. When the objective lens 25 is separated from the optical disc 24 and the return light of the 0th order light is defocused,
The return lights of the + 1st order light and the −1st order light are both defocused (FIG. 4A), and large beam spots are formed on the photodetectors 28 and 30 (FIG. 4B). Further, in this case, since the photodetector 30 side has a shorter optical path length than the photodetector 28 side,
The photo detector 30 compared to the photo detector 28 side
The beam spot on the side is formed in a large size.

On the other hand, when the objective lens 25 approaches the optical disk 24 and the return light of the 0th order light is just focused, the photodetector 28 side is also just focused (see FIGS. 5A and 5B), and the photodetector 3
On the 0 side, the so-called front pin state is maintained.
When the objective lens 25 further approaches the optical disc 24 and the return light of the 0th order light is defocused, the photodetector 28 side is held in the rear focus state and the photodetector 30 side is held in the just focus (FIG. 6).
(See (A) and (B)).

As a result, the photo detectors 28 and 30 are
In the central sensor elements 28b and 30b of FIG.
As shown in, the amount of incident light changes so as to draw a parabola. As a result, the optical pickup 20 detects the focus error based on the change in the light amount.

That is, in the optical disc device to which the optical pickup 20 is applied, the objective lens control section 25 thereof is provided.
b executes the processing procedure shown in FIG. 8 at a predetermined cycle (SP
1) Based on the focus error signal FE, the process proceeds to step SP2 and it is determined whether the output signal of the sensor element 28b is the maximum value MAX detected in advance. If an affirmative result is obtained here (the distance between the disc and the objective lens indicated by the symbol a in FIG. 7), the process proceeds to step SP3, where it is determined to be just focus and the process returns to step SP2. On the other hand, if a negative result is obtained in step SP2, the objective lens control unit 25b moves to step SP4,
The difference signal Δ of the output signals is detected between the sensor elements 28b and 30b, and it is determined whether or not the difference signal Δ is larger than the reference value detected in advance.

Here, this reference value is the sensor element 28b.
Between 30 and 30b, the difference signal (MAX-PD2
0) is detected in advance, and this difference signal (MAX-PD20) is detected.
Is set to this reference value and stored in the storage unit 25c. That is, as described above, in the sensor elements 28b and 30b, when the distance between the optical disk 24 and the objective lens 25 decreases due to the change of the incident light amount so as to draw a parabola, the difference signal of the output signals is increased accordingly. , The signal level increases.

As a result, the objective lens controller 25b
Output signals MAX and PD2 when just focused
By using the difference signal (MAX-PD20) of 0 as a reference, it is determined whether or not the signal level of the difference signal Δ is larger than the reference value, and thus, between the optical disc 24 and the objective lens 25 with respect to the just focus position. It is possible to judge whether or not the distance is large. This allows the optical pickup 2
In 0, the objective lens control unit 25b causes the step SP
If a positive result is obtained in 4 (state indicated by symbol b in FIG. 7), the optical disc 24 is processed in the subsequent step SP5.
On the other hand, the objective lens control unit 25b determines that the objective lens 25 is approaching, and issues an instruction to the objective lens driving unit 25a to separate the objective lens 25, and the objective lens 25 is focus-controlled. Then, the process returns to step SP2.

On the other hand, the objective lens controller 25b
If a negative result is obtained in step SP4 (represented by symbol c in FIG. 7), it is determined that the objective lens 25 is separated from the optical disc 24 in the following step SP6, and the objective lens 25 is approached here. A command is issued to the objective lens drive unit 25a so that the objective lens 25 is focus-controlled, and the process returns to step SP2.

The optical pickup 20 according to the present embodiment is
The light beam emitted from the laser light source is reflected by the diffraction grating 22.
After being decomposed into + 1st order, 0th order, and −1st order light, it is reflected by the beam splitter 23 and emitted toward the optical disc 24, and is converged on the optical disc 24 by the action of the objective lens 25. As a result, the return light obtained from the optical disc 24 is collected by the objective lens 25, and the beam splitter 2
After passing through 3, the light is collected on the light receiving element 26.

At this time, the returned light of the 0th order light is incident on the photodetector 29 at the center to form a beam spot, and the output signals of the sensor elements 29a and 29c and the sensor elements 29b and 29b arranged in the vertical direction are output. After the sum signals are obtained, the difference signal is detected between the sum signals and the tracking error is detected. The sum signal is further taken from this sum signal to detect the reproduction signal.

The + 1st-order and -1st-order return lights are incident on the left and right photodetectors 28 and 30, respectively, to form beam spots. At this time, the -1st-order return lights are transmitted through the glass plate 31. A beam spot is formed by passing through an optical path shorter than the + 1st-order light incident on the photodetector 30. As a result, the focus error can be detected by detecting the amount of incident light on the sensor elements 28b and 30b arranged in the center of the photodetectors 28 and 30.

Thus, according to the optical pickup 20 of the present embodiment, the focus error can be reliably detected with a simple structure in which the glass plate 31 is arranged on the light receiving surface of the photodetector 30, and thus the overall structure is simplified. Can be made smaller and smaller. Further, the positioning of the lens system can be omitted as in the case of using the cylindrical lens, and the assembling work can be simplified accordingly.

In the above embodiment, the case where the tracking error is detected from the returned light of the 0th order light is described, but the present invention is not limited to this, and the photodetector 2 is not limited thereto.
The tracking error may be detected from the output signals of 8 and 30. In this case, the output signals of the sensor elements 28a to 30c are represented by using the reference numerals attached to the sensor elements, and
-28c) or (30a-30c) may be executed to detect the tracking error, and the tracking error may be detected by adding the two calculation results.

Further, in the above-mentioned embodiment, the light emitted from the laser light source is directly separated into the 0th order light, the 1st order light and the -1st order diffracted light, whereby the 0th order light, the 1st order light and the -1st order light are returned. Although the case of forming light has been described, the present invention is not limited to this, and an optical element such as a diffraction grating may be provided in the optical path of return light to decompose the return light into three. Further, when the present invention is applied to an optical pickup of a magneto-optical disk device, the return light is decomposed into two lights having different polarization planes, and a glass plate is interposed in the optical path of the one decomposed return light. Alternatively, the focus error may be detected together with the light receiving element for detecting the reproduction signal.

Further, in the above-mentioned embodiment, the case where the focus error is detected in the photo detectors 28 and 30 based on the output signals of the sensor elements 28b and 30c arranged at the center has been described, but the present invention is not limited to this. , In the photodetectors 28 and 30, respectively, the beam diameter of the return light in each of the photodetectors 28 and 30 is determined by taking the difference in the output signal between the central sensor elements 28b and 30c and the sensor elements 28a, 28c and 30a, 30c on both sides. Alternatively, the focus error may be detected by detecting the difference in beam diameter between the photodetectors 28 and 30. In this case, the alignment of the return light with respect to the photo detectors 28 and 30 can be simplified, and the assembly work can be simplified accordingly.

Further, in the above-mentioned embodiment, the return light of the + 1st order light and the return light of the -1st order light are respectively detected by the photodetector 28.
However, the present invention is not limited to this, and as shown in FIG. 9, the glass plate 31 is arranged so as to divide one return light, thereby detecting a focus error. Good. That is, in FIG. 9, the glass plate 31 is arranged with the optical axis of the return light L as a boundary, and a division line is formed in the photodetector 35 so as to substantially coincide with this boundary. Furthermore, in the photo detector 35,
Form a dividing line on each side of this dividing line,
Thereby, the sensor elements 35a, 35b, 35c, 35d
To form.

As a result, the return light that passes through the glass plate 31 and the return light that directly enters the photodetector 35 are both defocused (FIGS. 9A and 9B), and go through the glass plate 31. The inserted sensor element 35
The amount of incident light is larger in the sensor element 35b than in c. On the other hand, as shown in FIG.
When the focus is just on the 5b side (FIGS. 10A and 10B), the output signal rises to the maximum value on the sensor element 35b side, and when the objective lens is separated from the optical disk, the output signal on the sensor element 35c side changes. When the maximum value is reached and the objective lens is further separated, finally, as shown in FIG. 11, the returning light comes to form a focus in front of the glass plate 31 (FIGS. 11A and 11B). Thereby, the focus error can be detected by taking the difference between the output signals of the sensor elements 35b and 35c, and the tracking error can be detected by taking the difference between the output signals of the sensor elements 35a and 35d.

Also in this case, the sensor elements 35a and 3a
The beam diameter (in this case, the radius) of the directly incident return light is detected by taking the difference between the output signals of 5b, and similarly, the difference between the output signals is taken by the sensor elements 35c and 35d, and through the glass plate 31. The focus error may be detected by detecting the beam diameter of the incident return light and taking the difference between the detection results.

Further, in the above-mentioned embodiment, the case where the glass plate is arranged in the focus detection system has been described, but the present invention is not limited to this, and the glass plate is arranged in the reproduction signal detection system in addition to this focus detection system. You may. In this case, if the thickness of the glass plate of the reproduction signal detection system is selected to be 1/2 the thickness of the glass plate of the focus detection system,
In the focus detection system, focus control is performed so that the beam diameter directly formed on the light receiving surface and the beam diameter formed on the light receiving surface through the glass plate become equal, and just focus can be performed by the reproduction signal detection system. As a result, a focus control system can be formed and focus control can be performed as in the conventional case.

[0046]

As described above, according to the optical pickup of the present invention, the focus error can be easily and reliably corrected by only disposing the transparent plate member on the optical path of the returning light and changing the optical path length. Can be detected.

[Brief description of drawings]

FIG. 1 is a plan view showing a photodetector of an optical pickup according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing the overall configuration of the optical pickup of FIG.

FIG. 3 is a characteristic diagram for explaining optical characteristics of a glass plate used in the optical pickup of FIG.

FIG. 4 is a schematic diagram for explaining the operation of the optical pickup of FIG.

FIG. 5 is a schematic diagram when the optical pickup of FIG. 1 is just focused.

FIG. 6 is a schematic diagram when defocusing is performed in the optical pickup of FIG.

7 is a characteristic curve diagram showing an output signal of a sensor element in the optical pickup of FIG.

8 is a flowchart showing focus control in the optical pickup of FIG.

FIG. 9 is a schematic diagram when defocusing is performed in the optical pickup according to the embodiment of the present invention.

FIG. 10 is a schematic diagram when the optical pickup of FIG. 9 is just focused.

FIG. 11 is a schematic diagram when defocusing is performed in the optical pickup of FIG.

12 is a schematic diagram when defocusing is performed in the optical pickup of FIG.

FIG. 13 is a schematic diagram showing an example of a conventional optical pickup.

[Explanation of symbols]

 1, 20 Optical pickup 3, 21 Laser light source 8, 25 Objective lens 14, 15, 18, 26 Light receiving element 23 Beam splitter 24 Optical disk 28, 29, 30, 35 Photodetector 31 Glass plate

Claims (5)

[Claims] 1. An optical pickup for irradiating a disc-shaped recording medium with a light beam to record desired information on the disc-shaped recording medium and / or reproducing the information recorded on the disc-shaped recording medium. A lens system that collects the return light obtained from the recording medium, a first light receiving element that receives the return light that is collected by the lens system, and a return light that is collected by the lens system A second light receiving element, a transparent plate-shaped member arranged on the optical path of the return light from the lens system to the first light receiving element, the transparent plate-shaped member being removed from the optical path. At this time, an optical path length conversion means is provided for forming a condensing position of the return light at a position separated from the lens system with respect to a condensing position of the return light formed by the lens system. Optics Kkuappu. 2. The optical pickup divides the light beam into first and second light beams and irradiates the disc-shaped recording medium with the return lights of the first and second light beams, respectively. The optical pickup according to claim 1, wherein the first and second light receiving elements are configured to receive light. 3. The optical pickup splits the return light into first and second return lights, and returns the return lights of the first and second light beams by the first and second light receiving elements, respectively. The optical pickup according to claim 1, wherein the optical pickup is configured to receive light. 4. The optical pickup has the optical path length conversion means arranged for the return light such that a part of the return light is transmitted through the transparent plate member. The optical pickup described in. 5. The optical pickup according to claim 1, wherein the optical pickup has the optical path length conversion means arranged on a light receiving surface of the first light receiving element.