JP2003162824A - Optical pickup and optical information reproducing apparatus using the same - Google Patents

Abstract

(57) Abstract: In an optical pickup using an astigmatism method for detecting a focus error signal and an optical disk apparatus using the same, contact between an objective lens and an optical disk due to unexpected disturbance, and an objective lens and an optical disk Prevents the occurrence of damage due to contact. An optical pickup capable of outputting a focus error signal based on an astigmatism method by arranging a light receiving area including a light receiving surface divided into four in a cross shape in a photodetector.
A new light receiving surface is arranged in a substantially diagonal direction of the divided light receiving area, and a defocus signal for outputting a signal when the distance between the objective lens and the optical disk becomes smaller than the focused state is output. Further, by monitoring the defocus signal, a situation is detected in which the objective lens and the optical disk are too close to each other due to unexpected disturbance, and the actuator is driven so as to separate the objective lens from the optical disk when an abnormality 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 used for reproducing an information signal recorded on an optical information recording medium (hereinafter referred to as an optical disk) and an optical information reproducing apparatus using the optical pickup (hereinafter, referred to as an optical pickup). Optical disc device)
Regarding

[0002]

2. Description of the Related Art An optical disk device is an information recording / reproducing device characterized by non-contact, large capacity, high speed access, and low cost media. By utilizing these characteristics, it is used as a recording / reproducing device of a digital audio signal or a computer. It is used as an external storage device.

Currently, there are various kinds of optical disks depending on the difference in information recording capacity and the difference in corresponding wavelength.
For example, a CD-ROM or a CD-R uses a laser beam of 780 nm band and has a storage capacity of about 650 MB.
DVD-ROM, DVD-RAM, and the like use laser light in the 650 nm band and have a storage capacity of about 4.7 GB. Further, for the purpose of further improving the storage capacity, many proposals have been made for an optical disk device that realizes a storage capacity of 20 GB or more by increasing the density of the laser light in the wavelength band of 400 nm.

For example, in a high-density optical disk using the 400 nm band, it is necessary to reduce the spot size irradiated on the optical disk in order to improve the recording density. Therefore, there has been proposed an optical disk device configuration in which the NA of the objective lens is increased and the optical disk substrate thickness is reduced. For example, Japanese Patent Laid-Open No. 2001-174697
Japanese Patent Laid-Open Publication No. 2003-242242 discloses a technique for increasing the NA of an objective lens (0.85) by combining two lenses and coping with optical disks having different disk substrate thicknesses without changing the two lens intervals. There is.

On the other hand, cost reduction is also a major issue in optical pickups and optical disk devices. Therefore, in optical pickups, various reduction measures have been implemented for cost reduction, but reduction of the number of parts of the optical system is very effective and effective. In the optical pickup having the reduced number of components as described above, the astigmatism method is mainly used as the detection method of the focus error signal.

[0006]

[Problems to be Solved by the Invention]
(For example, NA 0.85)
By combining two lenses, a high NA is realized and the recording density is improved. Here, NA of the objective lens,
There is a relationship of NA = D / 2f between the focal length f and the aperture (light beam diameter) D. For example, under the condition that the light beam diameter is constant, that is, when the aperture D is constant, N
The focal length f decreases as A increases. For example, in the case of DVD, NA = 0.6, whereas in a high-density optical disc, NA = 0.8 to 0.85, and if the light beam diameter is φ4 mm, then f = 3.33 in DVD.
On the other hand, f = 2.
It becomes 5 to 2.35 mm. Further, in a configuration in which two lenses that are often used in high density optical discs are combined, the aperture D of the objective lens on the side closer to the optical disc is substantially reduced, so the focal length f is further reduced. As a result, as the optical disc has a larger NA, the distance WD between the optical disc and the objective lens also tends to become smaller, and the objective lens approaches the optical disc when it is out of focus due to an unexpected disturbance, and in some cases, contacts the optical disc. The higher the NA of an optical disk, the greater the concern that an accident will occur. Here, the contact accident between the optical disc and the objective lens causes damage to the optical disc, the objective lens, and the objective lens driving means, and has a great influence on the recording or reproducing performance of the information signal in the optical pickup or the optical disc device. It's a problem.

In view of the above situation, the problem to be solved by the present invention is to provide an unexpected disturbance in an optical pickup for detecting a focus error signal by an astigmatism method effective for cost reduction and an optical disc apparatus using the same. The object is to realize a means for preventing the contact between the objective lens and the optical disk with a simple configuration.

[0008]

In order to solve the above-mentioned problems, according to the present invention, in an optical pickup and an optical information reproducing apparatus using the same, a laser light source and a light beam emitted from the laser light source are optically converted. Objective lens for condensing on the objective information recording medium, objective lens driving means for driving the objective lens, a first light receiving region composed of four light receiving surfaces arranged in a substantially square shape, and the first light receiving area. A photodetector provided with a second light receiving region arranged outside the light receiving region and arranged at a position where a light beam reflected from the optical information recording medium is irradiated, and a photoelectric conversion signal obtained from the photodetector. In an optical pickup capable of generating a focus error signal by the astigmatism method from the first light receiving region by performing a predetermined calculation, and an optical information reproducing device using the optical pickup, Serial to the first light receiving substantially on the extension line pair of the light receiving surface in the corner direction of the region, so as to place said second light receiving region.

Further, in order to solve the above-mentioned problems, in the present invention, a signal is output from the second light receiving area when the objective lens approaches the optical information recording medium side from the in-focus position. The second light receiving area is arranged.

In order to solve the above-mentioned problems, in the present invention, when the output signal is detected from the second light receiving area, the objective lens driving means is driven so that the objective lens is optically moved. It should be separated from the information recording medium.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The configuration and operation of an optical pickup according to a first embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, the laser light source 2 is 400 nm.
The laser light source 2 oscillates at a band wavelength, and the laser light source 2 is in a turned-on state. The light beam emitted from the laser light source 2 passes through the diffraction grating 3 and reaches the half mirror 4. Here, the light beam transmitted through the diffraction grating 3 is at least three light beams of the 0th-order light which is directly transmitted by the diffraction groove formed on the grating and the ± 1st-order diffracted light which separates and advances from the 0th-order light at a predetermined diffraction angle. It is a beam structure. Half mirror 4
Is arranged so as to form an angle of 45 ° with respect to the optical axis of the light beam.
It is an optical element that reflects about 80% of laser light having a wavelength in the nm band and at the same time transmits about 20%. The light beam is reflected by the reflection film of the half mirror 4 and then converted into a parallel light beam by the collimator lens 5, and reaches the first objective lens 6 and the second objective lens 7. Here, the first objective lens 6 and the second objective lens 7 are integrally held by the actuator 8, and the first objective lens 6
And NA = 2 depending on the combination of the second objective lens 7.
Achieved 0.85. Here, by energizing the drive coil 9, the light beam that has passed through the second objective lens 7 is focused on the information recording surface of the optical disc 1 and the zero-order light and ±
It has a configuration capable of forming three light spots of the first-order diffracted light. The light beam reflected by the optical disc 1 traces the same optical path as the outward light in the reverse direction, passes through the second objective lens 7, the first objective lens 6, and the collimator lens 5 and reaches the half mirror 4, where About 20% of the returned light amount passes through the half mirror 4. Since the light beam passing through the half mirror 4 has already been converged by the collimator lens 5, it is 4
Astigmatism is imparted to the light beam when passing through the half mirror 4 tilted in the 5 ° direction, and thereafter, the light beam is focused on a predetermined position of the photodetector 10. . The optical pickup 11 is composed of these optical components.

Here, the light spot on the optical disk 1 will be described.

FIG. 2 shows the spot arrangement on the optical disk according to the first embodiment of the present invention. Figure 2
In the optical disc 1, the guide grooves 202 are alternately formed with the guide groove intervals 201 at the track pitch Tp2. The recording marks 200 are arranged in the track direction of the optical disc 1 at an interval corresponding to Tp2.
The light beam is diffracted by the diffraction grating 3 as described with reference to FIG. 1, and becomes three spots of the 0th order light and the ± 1st order diffracted lights on the optical disc 1. The 0th-order light spot 100, the + 1st-order diffracted light spot 101, and the -1st-order diffracted light spot 102 are arranged on the optical disc 1 at an interval Tp1 corresponding to approximately half the track pitch Tp2, as shown in FIG. .

Next, the shape of the detection surface of the photodetector 10 will be described.

FIG. 3 is a plan view and a block diagram of the photodetector and the signal processing circuit according to the first embodiment of the present invention. In the package 20 of the photodetector 10, as shown in the figure, each divided light receiving surface is provided with a light receiving region 210 which is divided into four in a square shape represented by symbols a, b, c and d. b
Light receiving areas 220 and 230 formed of light receiving surfaces e and f are arranged so as to sandwich the light receiving surfaces b and d on an extension line connecting the lines a and d. Further, at the upper and lower positions of the light receiving area 210, the two light receiving areas 2 whose divided light receiving surfaces are represented by the symbols g and h are shown.
11 and the light receiving surface represented by the symbols i and j 2
A divided light receiving area 212 is arranged. Here, on the light receiving region 210, the disc reflected light of the on-disc light spot 100 is condensed to form a detection light spot 110. Similarly, the disk reflected light of the on-disk light spot 101 is condensed on the light receiving area 211, and the disk reflected light of the on-disk light spot 102 is condensed on the light receiving area 212 to form detection light spots 111 and 112. There is.

Each detected current photoelectrically converted and detected on each of the light receiving surfaces a, b, c, d is a current-voltage conversion amplifier 40, 41 provided in the package 20 of the photodetector 10.
It is converted into a voltage by 42 and 43 and sent to the output terminal of the photodetector 10, respectively. Similarly, the light receiving surfaces e, f, g,
The output lines of h, i, j are current-voltage conversion amplifiers 44, 4
5, 46, 47, 48, 49. (Hereinafter, for simplification of description, these voltage-converted detection signals are denoted by the same symbols as the light-receiving surface on which the detection signals are detected.) Eventually, the ten output terminals of the photodetector 10 , A, b, c, d, e, f, g,
h, i, j will be output.

Next, the arithmetic circuit will be described. Of the 10 detection signals output from the output terminal of the package 20 of the photodetector 10, the output signals a, b, c, d are added by the adders 51, 52 and the subtractor 58 to obtain the signal (a + c)-.
(B + d) is output, and the adders 53 and 54 and the subtracter 59
Outputs a signal (a + d)-(b + c). Here, the signal (a + c)-(b + d) is the optical spot 100 on the disc detected by the so-called astigmatism method.
Corresponds to the focus error signal of. Also (a + d),
(B + c) corresponds to the amount of detected light in each area when the detected light spot 110 is divided into two in the tracking direction (radial direction) of the disc, and the difference signal (a + d)-(b + c) between these two signals is This corresponds to the tracking error signal of the optical spot 100 on the disc detected by the so-called push-pull method.

The adder 55 outputs the output signals a, b,
By generating the sum signal RF of c and d, the information signal recorded on the optical disk can be reproduced by a predetermined signal reproducing circuit. Although not shown in this embodiment, the adder 55 is provided in the package 20 of the photodetector 10.
And the sum signal (a
A configuration in which an output terminal of + b + c + d) is added may be used.

Further, from the output signals e and f, the adder 5
6, the defocus signal e + f is output.
This defocus signal will be described later.

Further, a subtracter 60 is used for the output signals g and h.
The output signal i-j is output by the subtractor 61 and the output signal i, j is output by the subtracter 61.
The signals g-h and i-j are added to the signal (g +
i)-(h + j), and the amplifier 6
3 has been amplified at a predetermined amplification factor K1. The amplification factor K1 of the amplifier 63 is set so that the signal (g + i)-(h + j) has almost the same signal amplitude as the signal (a + c)-(b + d). The signal output from the subtractor 62 is {(a + d)-(b + c)}-K1 · {(g + i)-
(H + j)}. This signal is calculated from the tracking error signal of the spot 100 on the disc obtained from the light receiving area 210.
The tracking error signal corresponds to a signal obtained by subtracting the tracking error signals of the spots 101 and 102 on the disk obtained from the light receiving areas 211 and 212, and is a tracking error signal by a so-called differential push-pull method, and an offset due to the displacement of the objective lens It is possible to obtain a good tracking error signal that is largely eliminated.

Next, the positional relationship between the optical disk and the objective lens will be described with reference to FIG. In FIG. 4, (a)
Shows a focused state, (b) shows a state closer to the disc side than the focused state, and (c) shows a state separated from the focused disc. In FIG. 4A, the distance L between the surface of the optical disc 1 and the objective lens 7 is the working distance WD of the combination lens composed of the objective lens 6 and the objective lens 7.
This allows the light beam to be focused on the optical disc 1 and the information signal recorded on the optical disc 1 to be reproduced. The interval L is smaller than WD in FIG. 4B, and the interval L is larger than WD in FIG. 4C. In any case, the information signal recorded on the optical disc 1 is recorded. Is difficult to reproduce.

Next, the relationship between the position of the objective lens and the light spot on the detector will be described with reference to FIG. FIG. 5 (a),
The positional relationship between the optical disc 1 and the objective lens 7 in (b) and (c) corresponds to each state of FIGS. 4 (a), (b), and (c). In FIG. 5 (a), a detection light spot is provided in the light receiving region 210 which is arranged in the photodetector 10 and is formed by the light receiving surfaces represented by the symbols a, b, c, and d that are divided into four in a square shape. 110 is illuminated. As described above, in the first embodiment of the present invention, the detected light spot 110 is provided with astigmatism, so that the objective lens 7 is applied to the optical disc 1 as shown in FIGS. 5B and 5C. On the other hand, when deviated from the in-focus position, the detection light spot 110 has an elliptical shape whose major axis substantially coincides with the diagonal line of the four-divided light receiving region 210 as shown in the figure. Where (b)
When the optical disc 1 and the objective lens 7 shown in FIG.
A part of 0 is irradiated onto the light receiving regions 220 and 230, that is, the light receiving surfaces e and f. On the other hand, in the state shown in (c), since the major axis direction of the detection light spot 110 and the direction connecting the light receiving surfaces e and f are substantially orthogonal to each other, part of the detection light spot 110 is part of the light receiving surfaces e and f. Will not be irradiated. That is, according to the first embodiment of the present invention,
Only when the optical disc 1 and the objective lens 7 shown in (b) are closer to each other than the focus position, the light receiving surfaces e and f are irradiated with a part of the light amount of the detection light spot 110. as a result,
As shown in FIG. 3, the sum e + f of the outputs from the light receiving surfaces e and f
Is used as the defocus signal, the output can be obtained only in the state where the objective lens 7 is close to the optical disc 1.

Next, the relationship between the objective lens position and the defocus signal will be described with reference to FIG. FIG. 6 shows the position of the objective lens 7 with respect to the optical disc 1 and the light receiving surfaces e and f.
3 shows the relationship of the signal level of the defocus signal which is the sum of the outputs from the. As described above, in the first embodiment, since the defocus signal is output only when the position of the objective lens 7 is closer to the optical disc 1 than the focused state, the defocus signal can be monitored. The case where the position of the objective lens 7 is close to the optical disc 1 can be detected. That is, an unexpected disturbance causes out-of-focus, and the objective lens 7
Even when the lens is deviated from the in-focus state and an abnormal operation is caused, the objective lens 7 and the optical disc 1 are abnormally approached by setting the optimum lens position abnormality detection level with respect to the signal level of the defocus signal. Can be detected. Here, by appropriately energizing the drive coil 9 of the actuator 8, the objective lens 7 is separated from the optical disc 1, the collision between the objective lens 7 and the optical disc 1 is avoided, and the optical disc 1 and the optical pickup 11 are prevented from being damaged. It is possible.

FIG. 7 is a schematic block diagram of an optical disk device equipped with the optical pickup of the present invention. Various detection signals detected by the optical pickup 11 are sent to the defocus error detection circuit 74, the servo signal generation circuit 75, and the information signal reproduction circuit 76 in the signal processing circuit. The defocus error detection circuit 74 generates a defocus error signal from the outputs from the light receiving surfaces e and f, and the control circuit 70 monitors the positional relationship between the objective lens 7 and the optical disc 1 based on this signal. When the control circuit 70 determines that the defocus error signal has exceeded the lens position abnormality detection level, the actuator drive circuit 73 drives the objective lens 7 in the direction of retracting from the optical disc 1, and the objective lens 7 and the optical disc 1 are driven.
To prevent collisions. Further, the servo signal generation circuit 75 generates a focus error signal and a tracking error signal suitable for the optical disc 1 from various signals detected by the optical pickup 11, and these servo signals are sent to the control circuit 70. The control circuit 70 uses these servo signals to drive the actuator 8 in the optical pickup 11 via the actuator drive circuit 73 to control the position of the objective lens 7. In the information signal reproducing circuit 76, the information signal recorded on the optical disk 1 is output from the detection signal to the reproduction signal output terminal. The control circuit 70 also has a function of driving the laser lighting circuit 77 to light the laser light source 2 of the optical pickup 11 with an optimum light output. Further, an access control circuit 72 and a spindle motor drive circuit 71 are connected to the control circuit 70, and the access direction position control of the optical pickup 11 and the rotation control of a spindle motor 78 on which the optical disc 1 is mounted are respectively performed.

In the first embodiment, the second light receiving area is composed of two light receiving surfaces. However, the number of light receiving surfaces may be at least one, and a plurality of light receiving surfaces may be provided. May be internally connected.

In the first embodiment, the NA of the objective lens is 0.85 and the oscillation wavelength of the laser light source is 40.
Although the description has been made by setting the wavelength in the 0 nm band, the present invention is not limited to NA.
The oscillation wavelength of the laser light source is not limited, and it can be applied to various optical disks.

[0028]

As described above, according to the present invention, the photodetector is provided with the light receiving area composed of the light receiving surface divided into four in the shape of a square, and the focus error signal by the astigmatism method can be output. Defocusing such that a new light-receiving surface is arranged in a diagonal direction of the four-divided light-receiving area in a simple optical pickup, and a signal is output when the distance between the objective lens and the optical disk becomes smaller than the in-focus state. The signal can be output. By monitoring this defocus signal, it is possible to detect an abnormality when the objective lens and the optical disk are too close to each other due to an unexpected disturbance. Furthermore, by driving the actuator so as to separate the objective lens from the optical disc when an abnormality is detected, it is possible to prevent the occurrence of damage due to the contact between the objective lens and the optical disc. At this time, since at least one light receiving surface on the photodetector is added to the configuration of the conventional optical pickup, the optical pickup can be realized at substantially the same cost as the conventional one.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a spot arrangement on an optical disc according to the first embodiment of the present invention.

FIG. 3 is a plan view and a block diagram of a photodetector and a signal processing circuit according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a positional relationship between an optical disc and an objective lens according to the first embodiment of the present invention.

FIG. 5 is a diagram showing a relationship between an objective lens position and a light spot on a detector in the first embodiment of the present invention.

FIG. 6 is a diagram showing a relationship between an objective lens position and a defocus signal according to the first embodiment of the present invention.

FIG. 7 is a schematic block diagram of an optical disc device equipped with an optical pickup according to the first embodiment of the present invention.

[Explanation of symbols]

1 ... Optical disc, 2 ... Laser light source, 3 ... Diffraction grating, 4 ...
Half mirror, 5 ... Collimating lens, 6, 7 ... Objective lens, 8 ... Actuator, 9 ... Drive coil, 10 ... Photodetector, 11 ... Optical pickup, 20 ... Package, 4
0-49 ... Current-voltage conversion amplifier, 51-57 ... Adder, 58-62 ... Subtractor, 63 ... Amplifier, 100, 10
1, 102 ... Optical spot on disk, 110, 111,
112 ... Detection light spot, 200 ... Mark, 201 ... Between guide grooves, 202 ... Guide grooves, 210, 211, 212, 2
20, 230 ... Light receiving area, 70 ... Control circuit, 7
1 ... Spindle motor drive circuit, 72 ... Access control circuit, 73 ... Actuator drive circuit, 74 ... Defocus error detection circuit, 75 ... Servo signal generation circuit, 76 ...
Information signal reproducing circuit, 77 ... Laser lighting circuit, 78 ... Spindle motor.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masayuki Inoue             292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa             Ceremony Hitachi Digital Media Development Book             Department F term (reference) 5D117 AA02 BB05 DD15 FF03 HH10                 5D118 AA24 BA01 CA11 CA22 CC02                       CC14 CD02 CF02 CF05 CF08                       DA06

Claims (3)

[Claims] 1. A laser light source, an objective lens for condensing a light beam emitted from the laser light source onto an optical information recording medium, an objective lens driving means for driving the objective lens, and a substantially square shape. A first light-receiving area formed of four light-receiving surfaces and a second light-receiving area arranged outside the first light-receiving area, and a position where a light beam reflected from the optical information recording medium is irradiated. And a light capable of generating a focus error signal by the astigmatism method from the first light receiving region by performing a predetermined calculation on a photoelectric conversion signal obtained from the photodetector. A pickup and an optical information reproducing apparatus using the same, wherein the second light receiving area is arranged on a substantially extended line of a light receiving surface in a diagonal direction in the first light receiving area. -Up and optical information reproducing apparatus using the same. 2. A laser light source, an objective lens for condensing a light beam emitted from the laser light source onto an optical information recording medium, an objective lens driving means for driving the objective lens, and a substantially square shape. A first light-receiving area formed of four light-receiving surfaces and a second light-receiving area arranged outside the first light-receiving area, and a position where a light beam reflected from the optical information recording medium is irradiated. And a light capable of generating a focus error signal by the astigmatism method from the first light receiving region by performing a predetermined calculation on a photoelectric conversion signal obtained from the photodetector. In a pickup and an optical information reproducing apparatus using the pickup, a signal is output from the second light receiving area when the objective lens approaches the optical information recording medium side from a focus position. Serial optical information reproducing apparatus using an optical pickup and it is characterized in that arranging the second light-receiving region. 3. When the output signal is detected from the second light receiving area, the objective lens drive means is driven to separate the objective lens from the optical information recording medium. An optical pickup according to claim 1 or 2, and an optical information reproducing apparatus using the same.