JP2001344775A - Optical pickup device - Google Patents

Abstract

(57) [Problem] To obtain a good tracking error signal with a conventional optical pickup device, it is necessary to correct the relative position between the device main body and the objective lens. It must be provided, and an increase in the size of the apparatus body is a problem. SOLUTION: In the optical pickup device according to the present invention,
The light reflected by the disk 5 is received by the light receiving element 6 to detect a tracking error signal by the DPD method, and the light reflected by the reflecting portion 4b provided outside the effective aperture of the objective lens 4 is received by the light receiving element 6 to obtain an object. An objective lens position signal indicating the shift amount of the lens 4 is detected.

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 forming a minute beam spot on an information recording medium such as an optical disk by a light beam from a light source, and recording or reproducing or erasing information.

[0002]

2. Description of the Related Art FIG. 4 is a schematic diagram showing an example of a conventional optical pickup device. The light beam emitted from the semiconductor laser device 1 is converted into a parallel light beam by the collimator lens 2, passes through the beam splitter 3, and enters the objective lens 4. The objective lens 4 converges the incident parallel light beam and forms a beam spot on the recording surface of the optical disk 5. The effective aperture of the objective lens 4 is D.

[0003] The reflected light from the optical disk 5 is
After being converted into a parallel light beam again, the light beam is reflected by the beam splitter 3 toward the light receiving element 6. The light receiving element 6 reads information signals recorded on the optical disk 5 based on the intensity of the detected reflected light flux.

In the optical pickup device having the above configuration, in order to perform an operation of recording / reproducing or erasing information on / from the optical disk 5 with high accuracy, it is necessary to provide an unevenness on a recording surface of the optical disk 5 and a spindle mechanism for rotating the optical disk 5. It is necessary to keep the distance between the objective lens 4 and the recording surface of the optical disk 5 constant without being affected by accuracy or the like. In addition, it is necessary that the beam spot formed on the recording surface of the optical disc 5 be accurately followed along a row in which information is recorded (hereinafter, referred to as an information track).

For this purpose, the light receiving element 6 provided in the optical pickup device not only detects the information signal recorded on the optical disk 5 but also accurately detects the beam spot formed on the recording surface of the optical disk 5. In this case, it is possible to detect whether or not the information track is followed, that is, to detect a tracking error signal (TES).

FIG. 5 is a schematic configuration diagram showing an example of a conventional light receiving element 6, and is a schematic plan view when the light receiving element 6 is viewed from the beam splitter 3 side. Here, the case where the light receiving element 6 is a two-divided light receiving element will be described as an example. As shown in the figure, the light receiving element 6 is constituted by a PIN photodiode or the like whose light receiving surface is divided into two by a central dividing line 6c, and each light receiving surface is composed of a first light receiving surface 6a and a second light receiving surface.
It is referred to as a light receiving surface 6b.

In the light receiving element 6 having the above-described structure, the reflected light flux incident on the light receiving element 6 from the beam splitter 3 is detected by the first light receiving surface 6a and the second light receiving surface 6b, respectively. 6b, the tracking error signal TE is obtained.
S can be obtained. Such a tracking error detection method is called a push-pull method.

If the intensity of the output signal obtained from each of the light receiving surfaces 6a and 6b is Va and Vb, respectively, and the amplification factor of an amplifier (not shown) for amplifying each output signal is k, the tracking error signal described above is obtained. TES is expressed by the following equation (1).

(Equation 1)

First, FIG. 5A shows a case where the center position of the objective lens 4 coincides with the center of the optical axis of the light beam emitted from the semiconductor laser device 1. In this case, the reflected light flux M (the shaded portion in the figure) incident on the light receiving element 6 is symmetric with respect to the center dividing line 6c. Here, if the beam spot formed on the recording surface of the optical disk 5 is accurately formed on the information track,
The light intensity distribution in the reflected light beam M becomes uniform, and the intensities Va and Vb of the output signals obtained from the first light receiving surface 6a and the second light receiving surface 6b become equal to each other. Therefore, the tracking error signal TES becomes 0.

However, if the beam spot is formed at a position shifted from the information track, the reflected light flux M
The light intensity distribution in the inside is biased, and the first light receiving surface 6a
And the intensity Va of the output signal obtained from the second light receiving surface 6b,
Vb has different values (for example, Va <Vb). Therefore, the tracking error signal TES is not 0.

As described above, in the push-pull method, by detecting the value of the tracking error signal TES,
It is determined whether the beam spot accurately follows the information track, and a tracking servo of the optical pickup device is performed according to the result of the determination.

[0012]

However, in the optical pickup device for driving the objective lens 4 in the tracking direction when performing the above-described tracking servo,
The center position of the objective lens 4 may be shifted from the center of the optical axis of the light beam emitted from the semiconductor laser device 1 in some cases.

(2) in FIG. 5 shows a case where the center position of the objective lens 4 is shifted from the center of the optical axis of the light beam emitted from the semiconductor laser device 1. In this case, since the reflected light flux M incident on the light receiving element 6 is asymmetric with respect to the center division line 6c, the tracking error signal TES
Causes an offset. Therefore, even if the beam spot is accurately formed on the information track, the intensities Va and Vb of the output signals obtained from the first light receiving surface 6a and the second light receiving surface 6b have different values (in the case of FIG. Va <Vb), and the tracking error signal TES is no longer 0.

For the above-mentioned reason, in the optical pickup device adopting the push-pull method as the tracking error detection method, the optical pickup device main body and the objective lens 4 are used.
However, there is a problem that accurate tracking servo cannot be performed unless the relative position of the servo is corrected.

In order to correct the relative position between the main body of the optical pickup device and the objective lens 4, in the conventional optical pickup device, a position sensor is attached to the objective lens 4 to detect an objective lens position signal LES (Lens Error Signal). Then, a configuration has been proposed in which the shift amount of the objective lens 4 with respect to the optical pickup device main body is suppressed based on the value.

However, in this method, a light receiving element for detecting the objective lens position signal LES must be separately provided, and there is a problem that the size of the apparatus is increased. Further, since the weight of the holder for holding the objective lens 4 is increased, there is a problem that the sensitivity of the actuator for driving the objective lens 4 is reduced.

On the other hand, even if the objective lens 4 is shifted with respect to the main body of the optical pickup device, a tracking error detection method that is not easily affected by the shift is a DPD (Differential).
Phase Detection) method. Since the DPD method is a well-known technique, a detailed description thereof will be omitted, but the first light receiving surface 6a
And a method of obtaining a tracking error signal TES by obtaining a phase difference from a high-frequency component of each output signal obtained from the second light receiving surface 6b. Regarding the configuration to realize the DPD method using the two-segment light receiving element and its significance, see IEICE Technical Report CPM80-70, p.1
Proceedings of the 58th Annual Conference of the Japan Society of Applied Physics 4p-ZE-
7,4pZE-8, p.1133 to p.1134 (1997.10) and the like have been reported.

As described above, in the DPD method, the first light receiving surface 6a
And the intensity Va of the output signal obtained from the second light receiving surface 6b,
The tracking error signal TES can be obtained without depending on Vb. Therefore, the center position of the objective lens 4 is shifted with respect to the center of the optical axis of the light beam emitted from the semiconductor laser element 1, so that the reflected light flux M incident on the light receiving element 6 is asymmetric with respect to the center dividing line 6c. Even if it is, the tracking error signal TES can be detected without being affected so much.

However, even in an optical pickup device employing the DPD method, if the shift amount of the objective lens 4 with respect to the device body becomes too large, the first light receiving surface 6
It is inevitable that the S / N of the output signal obtained from the second light receiving surface 6b deteriorates and the tracking servo performance deteriorates.

In order to avoid such deterioration of the tracking servo performance, it is necessary to correct the relative position between the optical pickup device main body and the objective lens 4. Therefore, even in an optical pickup device employing the DPD method, a position sensor and a light receiving element for detecting the objective lens position signal LES must be separately provided, which results in an increase in the size of the device body and sensitivity of the actuator. It has the same problem as described above, such as reduction.

The present invention has been made in view of the above problems, and provides an optical pickup device capable of detecting an objective lens position signal with a simple configuration without increasing the size of the device main body and having good tracking servo performance. With the goal.

[0022]

In order to achieve the above object, in an optical pickup device according to the present invention, a light source for emitting a light beam, an optical system for converting the light beam into a parallel light beam, and the parallel light beam And an objective lens that forms a beam spot on the recording surface of the information recording medium by converging the beam spot and the information track formed on the recording surface by receiving reflected light from the information recording medium. And a light receiving element for detecting a tracking error signal indicating a positional deviation of the objective lens. In the optical pickup device adopting the DPD method as a method for detecting the tracking error signal, an effective aperture outside the parallel light beam incident surface of the objective lens is provided. Is provided with a reflecting portion for reflecting the parallel light beam, and by receiving the reflected light from the reflecting portion with the light receiving element. It is configured to detect the objective lens position signal indicating a relative position of the optical pickup apparatus main body and the objective lens.

Further, it is preferable that the light receiving element has a light receiving surface divided into two, and the objective lens position signal is detected as a difference signal between output signals obtained from each light receiving surface. Further, based on the objective lens position signal,
It is preferable that the apparatus has means for controlling a relative position between the objective lens and the apparatus main body. Further, a configuration may be provided including means for detecting an information signal recorded on the information recording medium based on an output signal obtained from the light receiving element.

[0024]

FIG. 1 is a schematic diagram showing one embodiment of an optical pickup device according to the present invention. As shown in (1) in the figure, the light beam emitted from the semiconductor laser device 1 is converted into a parallel light beam having a diameter A by a collimator lens 2, and is transmitted through a beam splitter 3 to be incident on an objective lens 4. The objective lens 4 converges the incident parallel light beam and forms a beam spot on the recording surface of the optical disk 5. The effective aperture of the objective lens 4 is D.

The reflected light from the optical disk 5 is
After that, the light beam is again converted into a parallel light beam, and is then converted into a reflected light beam toward the light receiving element 6 by the beam splitter 3. The optical pickup device according to the present invention employs the DPD method as a tracking error detection method. As mentioned above, D
The PD method is a method of receiving the reflected light flux returning from the optical disk 5 by a light receiving element 6 having a plurality of light receiving surfaces and detecting a phase difference between high frequency signals obtained on each light receiving surface to obtain a tracking error signal TES. It is. Then, tracking servo is performed based on the tracking error signal TES.

Here, in the optical pickup device according to the present embodiment, as a means for detecting an objective lens position signal LES indicating a relative position between the objective lens 4 and the optical pickup device main body, a lens portion 4a (constituting the objective lens 4) ( Outside the effective aperture D), a reflector 4b (width B) having a reflection surface perpendicular to the optical axis of the objective lens is provided.

FIG. 2B is a schematic front view of the objective lens 4 viewed from the beam splitter 3 side. In order to improve the productivity of the objective lens 4, it is desirable to form the reflecting portion 4 b integrally with the main body of the objective lens 4, but it is also possible to integrate the reflecting portion 4 b as a separate body.

By configuring the objective lens 4 as described above, of the parallel light flux (diameter A) incident on the objective lens 4, the parallel light flux (width B) incident outside the effective aperture D of the objective lens 4. Is reflected by the reflector 4b.

FIG. 2 is a schematic configuration diagram showing the light receiving element 6 in the present embodiment, and is a schematic front view of the light receiving element 6 as viewed from the beam splitter 3 side. Here, the case where the light receiving element 6 is a two-divided light receiving element will be described as an example. As shown in the figure, the light receiving element 6 is constituted by a PIN photodiode or the like whose light receiving surface is divided into two by a central dividing line 6c, and each light receiving surface is composed of a first light receiving surface 6a and a second light receiving surface.
It is referred to as a light receiving surface 6b.

First, (1) in FIG. 2 shows a case where the center position of the objective lens 4 coincides with the center of the optical axis of the light beam emitted from the semiconductor laser device 1. In this case, the optical disk 5 returned through the lens portion 4a
Light beam M (hatched portion in the figure) reflected from the light, and the reflection portion 4b
The reflected light flux R (horizontal line in the figure) reflected by
Each is symmetrical with respect to the center dividing line 6c. The reflected light beam R is observed in a ring shape surrounding the reflected light beam M as shown in the figure.

On the other hand, FIG. 2B shows the case where the center position of the objective lens 4 is shifted from the center of the optical axis of the light beam emitted from the semiconductor laser device 1. In this case, the reflected light flux M and the reflected light flux R incident on the light receiving element 6
Are asymmetric with respect to the center dividing line 6c.

For this reason, when the objective lens 4 is shifted with respect to the optical pickup device main body, the light intensity distribution on the light receiving element 6 is biased to either the first light receiving surface 6a or the second light receiving surface 6b. Becomes Therefore, the first light receiving surface 6a
The objective lens position signal LES indicating the shift amount of the objective lens 4 can be obtained by calculating the difference in the intensity of each output signal obtained from the second light receiving surface 6b.

The detection operation of the objective lens position signal LES will be described in more detail. Among the output signals obtained from the first light receiving surface 6a and the second light receiving surface 6b, the reflected light flux M
Are respectively obtained as Va (M),
Vb (M), the intensities obtained by receiving the reflected light flux R are Va (R) and Vb (R), respectively, and the amplification factor of an amplifier (not shown) for amplifying each output signal is α. Then, the objective lens position signal LES is expressed by the following equation (2).

(Equation 2)

As described above, when the objective lens 4 is shifted with respect to the optical pickup device main body, the light receiving element 6
The upper light intensity distribution corresponds to the first light receiving surface 6a or the second light receiving surface 6a.
b. That is, each output signal ΔV obtained from the first light receiving surface 6a and the second light receiving surface 6b
a (R) + Va (M)} and {Vb (R) + Vb (M)}
And a difference in intensity corresponding to the shift amount of the objective lens 4 occurs. Therefore, the objective lens position signal LES can be obtained by detecting the intensity difference.

Here, among the output signal intensities included in the above equation (2), Va (R) and Vb (R) are complementary depending only on the shift amount of the objective lens 4 with respect to the optical pickup device main body. Increase or decrease. Therefore, it can be said that these intensity differences accurately indicate the shift amount of the objective lens 4 with respect to the optical pickup device main body.

On the other hand, among the output signal strengths included in the above equation (2), Va (M) and Vb (M) are:
It varies depending not only on the shift amount of the objective lens 4 with respect to the optical pickup device main body but also on the relative position between the beam spot and the information track on the optical disk 5, that is, the tracking state.

Therefore, when the light quantity of the reflected light flux R is smaller than the light quantity of the reflected light flux M, the objective lens position signal L
Since the influence of the tracking state on the amount of change in ES becomes large, the shift amount of the objective lens 4 cannot be accurately determined. Therefore, in order to accurately detect the shift amount of the objective lens 4 based on the objective lens position signal LES, it is desirable that the light amount of the reflected light beam R be as large as possible with respect to the light amount of the reflected light beam M.

As described above, in the optical pickup device according to the present invention, of the parallel light beams incident on the objective lens 4, the parallel light beams incident outside the effective aperture D of the objective lens incidence surface are converted into the objective lens 4. The light is reflected by the reflecting portion 4b provided on the outer peripheral portion of the light-emitting device, and the reflected light beam is detected by the light-receiving element 6.

With this configuration, the objective lens position signal LES can be easily detected without providing the objective lens 4 with a position sensor or the like. Therefore, the actuator for driving the objective lens 4 can be reduced in size and weight.

In particular, in the optical pickup device according to the present invention, the DPD method is employed as a tracking error detection method, and it is not a difference between the intensity of each output signal obtained by the first light receiving element 6a and the second light receiving element 6b but a difference. The tracking error signal TES is detected from the phase difference between the high-frequency components of each output signal.

Therefore, even if the light receiving element 6 for detecting a tracking error receives the reflected light beam R necessary only for the operation of detecting the objective lens position signal LES, the detection of the tracking error signal TES is hardly affected.

With such a configuration, it is not necessary to add a new light receiving element to detect the objective lens position signal LES, and the tracking error signal TES and the objective lens position signal LES are generated by the single light receiving element 6. Can be detected. Therefore, the tracking error signal TES and the objective lens position signal LES can be obtained with a simple configuration without increasing the size of the optical pickup device.

Further, the optical pickup device according to the present embodiment determines the shift amount of the objective lens 4 with respect to the optical pickup device main body based on the objective lens position signal LES detected by the above configuration, and according to the determination result, 4 and the relative position of the optical pickup device main body.

FIG. 3 is a block diagram showing an example of the configuration of the means for detecting the tracking error signal TES and the objective lens position signal LES, and the position control means for the objective lens 4 and the optical pickup device main body.

Output signals obtained from the first light receiving surface 6a and the second light receiving surface 6b constituting the light receiving element 6 are respectively supplied to current / voltage conversion circuits 7 and 8 (hereinafter referred to as I / V conversion circuits 7 and 8). , And a voltage level required for detecting the tracking error signal TES and the objective lens position signal LES.

Each output signal of the I / V conversion circuits 7 and 8 is sent to a high-pass filter 9 (hereinafter referred to as HPF 9).
Therefore, after removing the low frequency components, the TES generation circuit 1
Sent to 1. TES generation circuit 1 in the present embodiment
In No. 1, the DPD method is adopted as the tracking error detection method, and the tracking error signal TES is detected based on the phase difference between the high frequency components of the output signals of the I / V conversion circuits 7 and 8.

In order to obtain a good tracking signal TES in the TES generation circuit 11, in this embodiment, TE
Although an HPF 9 is provided in a stage preceding the S generation circuit 11, unnecessary low frequency components are removed in advance.
It is also possible to adopt a configuration in which 9 is not provided.

The tracking error signal TES obtained by the TES generation circuit 11 is sent to the objective lens drive circuit 13. The objective lens drive circuit 13 drives the objective lens 4 by controlling the objective lens drive actuator 15 based on the input tracking error signal TES. Thus, the beam spot formed on the recording surface of the optical disk 5 by the objective lens 4 can follow the information track on which the recording information is arranged.

On the other hand, the output signals of the I / V conversion circuits 7 and 8 are also sent to a low-pass filter 10 (hereinafter referred to as LPF 10), where high-frequency components are removed therefrom and then LE
It is sent to the S generation circuit 12. The LES generation circuit 12 detects the objective lens position signal LES based on the intensity difference between the output signals obtained from the I / V conversion circuits 7 and 8.

In order to obtain a good objective lens position signal LES in the LES generation circuit 12, this embodiment uses L
By providing the LPF 10 in the preceding stage of the ES generation circuit 12,
An unnecessary high-frequency component is removed in advance.
A configuration without the PF 10 is also possible.

The objective lens position signal LES obtained by the LES generation circuit 12 is sent to a slide motor drive circuit 14. The slide motor drive circuit 14 controls the slide motor 16 based on the input objective lens position signal LES to drive the optical pickup device main body. Thereby, the relative position between the objective lens 4 and the optical pickup device main body can be corrected, and the shift amount of the objective lens 4 can be suppressed.

With such a configuration, the relative positional deviation between the objective lens 4 and the optical pickup device main body can be automatically reduced based on the objective lens position signal LES, and therefore, the S / S of the tracking error signal TES can be reduced.
N deterioration can be suppressed. Therefore, an optical pickup device having good tracking servo performance can be realized.

Further, in the optical pickup device having the above configuration, it is preferable that the information signal recorded on the optical disk 5 is also read by the light receiving element 6. In order to realize this configuration, after adding the output signals obtained by the first light receiving element 6a and the second light receiving element 6b, a circuit for cutting the DC component by a capacitor and extracting only the AC component is incorporated. I just need.

With such a configuration, in addition to the detection of the tracking error signal TES and the objective lens position signal LES, the detection of the information signal recorded on the optical disk 5 can be performed by the single light receiving element 6. it can. This makes it possible to reduce the size and weight of the optical pickup device.

In the above-described embodiment, an example in which a two-divided light receiving element is used as the light receiving element 6 has been described. However, the number of divisions of the light receiving element 6 is not limited to this. The present invention is also applicable to an optical pickup device having a multi-segment light receiving element such as a four-segment light receiving element.

[0056]

In the optical pickup device according to the present invention, of the parallel light beams incident on the objective lens, a parallel light beam incident outside the effective aperture of the objective lens incident surface is provided on the outer peripheral portion of the objective lens. The reflected light is reflected by the reflecting portion, and the reflected light beam is detected by the light receiving element. The light receiving element has a light receiving surface divided into two,
It is preferable that the objective lens position signal is detected as a difference signal between output signals obtained from the respective light receiving surfaces.

With this configuration, the objective lens position signal can be easily detected without providing a position sensor or the like in the objective lens. Therefore, the actuator for driving the objective lens can be reduced in size and weight.

In particular, since the optical pickup device according to the present invention employs the DPD method as a tracking error detection method, the light receiving element for tracking error detection receives the reflected light flux returning from the reflecting portion of the objective lens. This configuration has almost no effect on tracking error signal detection.

With such a configuration, it is not necessary to add a new light receiving element for detecting the objective lens position signal, and the tracking error signal and the objective lens position signal can be obtained by a single light receiving element. Can be detected. Therefore, it is possible to contribute to reducing the size and weight of the optical pickup device main body.

Further, it is preferable that the apparatus further comprises means for controlling a relative position between the objective lens and the optical pickup device main body based on the objective lens position signal. With this configuration, it is possible to automatically reduce the relative displacement between the objective lens and the optical pickup device main body based on the objective lens position signal, so that the S / N degradation of the tracking error signal is reduced. Can be suppressed. Therefore, an optical pickup device having good tracking servo performance can be realized.

[0061] Further, it may be configured to have means for detecting an information signal recorded on the information recording medium based on an output signal obtained from the light receiving element. With this configuration, in addition to the detection of the tracking error signal and the objective lens position signal, the detection of the information signal can be performed by the single light receiving element. This makes it possible to reduce the size and weight of the optical pickup device.

[Brief description of the drawings]

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

FIG. 2 is a schematic configuration diagram illustrating a light receiving element 6 in the present embodiment.

FIG. 3 is a block diagram illustrating an example of a configuration of a detection unit of a tracking error signal TES and an objective lens position signal LES, and a position control unit of an objective lens 4 and an optical pickup device main body.

FIG. 4 is a schematic configuration diagram illustrating an example of a conventional optical pickup device.

FIG. 5 is a schematic configuration diagram illustrating an example of a conventional light receiving element 6.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 semiconductor laser element 2 collimating lens 3 beam splitter 4 objective lens 4 a lens unit 4 b reflecting unit 5 optical disk 6 light receiving element 6 a first light receiving surface 6 b second light receiving surface 7 current-voltage conversion circuit 8 current-voltage conversion circuit 9 high-pass filter 10 low-pass filter Reference Signs List 11 TES generation circuit 12 LES generation circuit 13 Objective lens drive circuit 14 Slide motor drive circuit 15 Objective lens drive actuator 16 Slide motor

Claims (4)

[Claims] A light source that emits a light beam; an optical system that converts the light beam into a parallel light beam; an objective lens that forms a beam spot on a recording surface of an information recording medium by converging the parallel light beam; A light receiving element for detecting a tracking error signal indicating a positional shift between the beam spot and an information track formed on the recording surface by receiving reflected light from the information recording medium; In an optical pickup device adopting a DPD method as a method of detecting an error signal, a reflecting portion for reflecting the parallel light beam is provided outside an effective aperture on a parallel light beam incident surface of the objective lens, and a reflection from the reflecting portion is provided. By receiving light with the light receiving element, an objective lens position signal indicating a relative position between the objective lens and the optical pickup device main body is detected. An optical pickup device characterized by emitting light. 2. The light receiving device according to claim 1, wherein the light receiving element has a light receiving surface divided into two, and the objective lens position signal is detected as a difference signal of an output signal obtained from each light receiving surface. An optical pickup device according to item 1. 3. An optical pickup device according to claim 1, further comprising means for controlling a relative position between said objective lens and said apparatus main body based on said objective lens position signal. 4. The information processing apparatus according to claim 1, further comprising means for detecting an information signal recorded on said information recording medium based on an output signal obtained from said light receiving element. Optical pickup device.