JP2002157766A - Optical head for optical disk device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical head for an optical disk device that can attain excellent recording and reproduction by always forming a focus of a converged light stopped by an objective lens on a recording face of an optical disk through the detection of a focus error signal. SOLUTION: The optical head for the optical disk device provided with a mechanism that collimates a laser beam emitted from a light source by a collimation lens, focuses the laser beam with the objective lens in a moving part and emits the focused light onto the optical disk, is characterized in that the objective lens is mounted on a slider, at least two lenses are placed between the collimate lens and the objective lens, the two lenses are arranged in a way that at least either of the two lenses at the light source side or the moving part side is moved in a direction of the optical axis on the basis of the focus error signal to conduct focus control, and the optical disk device is provided with an output adjustment mechanism that adjusts an output of the laser beam by interlocking with the focus control.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an optical head for an optical disk device provided with a floating head mechanism.

[0002]

2. Description of the Related Art Functions required for an optical head constituting an optical disk device include a focus function for irradiating a beam spot narrowed by an objective lens onto a recording surface of the optical disk, and a beam for a desired track position on the optical disk. And a magneto-optical signal reading function for reading information written on the recording surface. FIG. 9 shows a schematic view of a conventional optical head. Light emitted from the semiconductor laser 1 is collimated by the collimator lens 2, passes through the beam splitter 3 and the objective lens 4,
The beam is irradiated on the recording surface of the optical disk in a state where the beam is narrowed. Light reflected from the recording surface 6 of the optical disk is guided by the beam splitter 3 to a return path detection system.

Conventionally, as one of the techniques for increasing the density of an optical disk, the NA (aperture diameter) of an objective lens is increased,
It has been proposed to reduce the beam diameter on the recording surface of an optical disc. However, when NA is increased, coma due to tilt of the optical disk (proportional to the cube of NA) and spherical aberration due to fluctuations in the distance (working distance) between the objective lens and the recording surface 6 of the optical disk (NA to the fourth power). Proportional) increases, making it difficult to record and reproduce information signals on an optical disk.

Therefore, as a method of solving the above problem,
In recent years, a method of mounting a lens on a slider used for a hard disk and floating the lens has been proposed (see FIG. 9). When the slider 5 is used, the fluctuation amount of the flying height of the slider can be stabilized by the rotation of the optical disk, that is, the working distance can be stabilized, and the wavefront aberration can be suppressed because the slider can be used for the tilt of the optical disk. Becomes possible.

Here, in order to stabilize the working distance, the rotation control method of the optical disc uses a variable linear velocity of the optical disc and a constant linear velocity (CLV).
locity), ZCLV (Zoned Constant Linear Velocit)
y) The method is desirable. However, in the case of the CLV and ZCLV systems, it takes time to control the rotation speed. Therefore, for optical disks that require high-speed access and high-speed transfer, CAV (Constant Angular Velocity), in which the rotation speed is constant and the linear velocity fluctuates,
ZCAV (Zoned Constant Angular Velocity) is more suitable.

[0006]

In recent years, with the spread of the Internet, an optical disk has been actively used as a storage medium for data handled by making full use of the Internet. Optical discs are required to have even larger capacities, and high-speed access and high-speed transfer are also required. As described above, an increase in the capacity of an optical disk can be realized by using a slider equipped with an objective lens (NA: 0.7 to 0.9) having a high NA.

On the other hand, in order to satisfy high-speed access and high-speed rotation, it is desired to control the rotation of the optical disk to CAV or ZCAV. However, when the speed is set to CAV or ZCAV, the rotation speed becomes constant, so that the linear velocity fluctuates from the inner side to the outer side of the optical disk. Therefore, when the slider on which the objective lens is mounted is sought, the flying distance changes by changing the floating pressure of the slider, and the working distance changes. Therefore, the convergent light converged by the objective lens cannot be focused on the recording surface of the optical disc, and defocus occurs. Therefore, it is difficult to record and reproduce an accurate information signal on the optical disk. In particular, in the case of a high NA optical system, the depth of focus becomes shorter, so that the influence is more serious. Further, wavelength fluctuation occurs due to the environmental temperature of the semiconductor laser and the like, and as a result, chromatic aberration also occurs. This is also more serious in high NA advanced schools.

According to the present invention, even if the rotation control method of the optical disk is CAV or ZCAV, the convergent light converged by the objective lens when the slider is sought always detects the focus error signal so that the recording surface of the optical disk is always detected. It is an object of the present invention to provide an optical head for an optical disk device capable of focusing on the optical disk. It is another object of the present invention to provide an optical head for a high-NA optical disk device that can suppress chromatic aberration and perform tracking control, and can perform good recording and reproduction.

[0009]

Thus, according to the present invention, an optical head for an optical disk apparatus having a mechanism for collimating a laser beam emitted from a light source with a collimating lens, condensing the laser beam with an objective lens in a movable section, and irradiating the optical disk with the laser beam. In the above, the objective lens is mounted on a slider, at least two lenses are arranged between the collimating lens and the objective lens, and at least one of the two lenses on the light source side or the movable part side is An optical adjustment device for an optical disc device, comprising: an output adjusting mechanism arranged to perform focus control by moving in the optical axis direction based on a focus error signal, and adjusting an output of a laser beam in conjunction with the focus control. A head is provided.

Further, according to the present invention, in the optical head for an optical disc apparatus, there is provided a mechanism for collimating a laser beam emitted from a light source with a collimating lens, converging the laser beam with an objective lens in a movable part and irradiating the optical disc with the objective lens. Is mounted on a slider, at least two lenses are arranged between the collimating lens and the objective lens, and at least one of the two lenses on the light source side or the movable unit side is moved by a seek amount of the slider. A temperature detecting unit, a film thickness detecting unit, and a seek position detecting unit so as to be able to move along the optical axis direction based on the information on the temperature and the film thickness. At least one of the lenses on the side is moved in the optical axis direction based on signals obtained from the temperature detecting means, the film thickness detecting means and the seek position detecting means. Te is arranged to be carried out focus control, the optical disc apparatus optical head characterized by comprising an output adjusting mechanism for adjusting the output of the laser light is provided in conjunction with the focusing control.

Further, according to the present invention, in an optical disk optical system including a light source, a collimating lens, an objective lens mounted on a slider, and a medium, light emitted from the collimating lens incident on the objective lens mounted on the slider Is an optical head for an optical disk device, wherein is a convergent light.

[0012]

FIG. 1 is a schematic diagram (part 1) of an optical head for an optical disk device according to the present invention. As shown in FIG. 1, the laser light emitted from the light source (semiconductor laser 1)
The light is collimated by the collimating lens 2. The collimated light passes through one unit including a plurality of lenses called a beam expander 11 disposed between the movable unit 14 and the beam splitter 3. The transmitted light is converged by the objective lens 4 mounted on the slider, and
Focuses on the recording surface.

The beam expander 11 shown in FIG. 1 uses two lenses to simplify the explanation. Further, the effective diameter of the light beam emitted from the beam expander 11 is made smaller than the effective diameter of the light beam collimated by the collimator lens 2. Objective lens 4 mounted on slider 5
It is desirable that the effective diameter be as small as possible because of load restrictions and the like.
In the case of A, assembly and adjustment errors of parts become severe. Therefore, if at least the effective light beam diameter before being incident on the beam expander 11 is increased, there is an advantage that the existing optical system can be easily used for the fixed optical unit.

The focus control is performed by the beam expander 1
1. Either the light source side or the movable part side lens in 1.
The defocusing is performed in the optical axis direction based on the focus error signal. It is preferable that the effective diameter of the emitted light beam is smaller than the effective diameter of the light beam collimated by the collimating lens 2. In the tracking control, the beam can be applied to a desired position in the radial direction by swinging the galvanomirror 13 disposed between the beam expander 11 and the beam splitter 3. As a tracking means, there is a push-pull method utilizing diffraction from a guide groove of a recording film of an optical disk, a three-beam method of converting an incident beam into three beams using a diffraction grating, and detecting the reflected light. If a rotation mechanism is added to the slider 5, the tracking control can be performed without using the galvanometer mirror 13 by eccentrically moving the slider 5 in the direction perpendicular to the optical axis direction.

Although the beam expander 11 is disposed between the movable section 14 and the beam splitter 3, the beam expander 11 may be disposed within the movable section 14. When the slider is mounted in the movable section 14, even if the slider on which the objective lens 4 is mounted is sought, the light beam collimated by the collimator lens 2 does not change on the incident surface of the beam expander 11 due to vignetting. , NA can be controlled. In FIG. 1, 6 is a recording surface of the optical disk, 8 is a spindle rotation axis, 9 is a first lens, 10
Denotes a second lens, 12 denotes a rising mirror, 15 denotes a light amount detector, 16 denotes a light amount detection circuit, and 17 denotes a semiconductor laser driving circuit.

By the way, the rotation control method of the optical disk is C
AV and ZCAV. In this case, since the rotation speed of the optical disk is constant, the linear velocity varies from the inner to the outer. Then, when the slider is sought, the floating pressure is not constant, and the flying amount varies, so that it is difficult to focus on the recording surface 6 of the optical disk. Therefore,
FIG. 2 shows the wavefront aberration of the light beam when the first lens 9 in the beam expander 11 is shifted in the optical axis direction and transmitted through the beam expander. The horizontal axis represents the shift amount of the focus point, the left vertical axis represents the shift amount of the first lens 9, and the right vertical axis represents the wavefront aberration value. The positive direction of the left vertical axis is the first
The direction in which the lens 9 approaches the second lens 10.
Note that the focus shift amount on the horizontal axis corresponds to the flying fluctuation amount of the slider 5.

As shown in FIG. 2, even if the focus point shifts, the wavefront aberration can be considerably reduced by shifting the first lens 9 of the beam expander 11 of FIG. 1 in the optical axis direction. It is possible to focus almost on. Therefore, if the rotation control method is CAV, ZC
Even in the case of AV, the convergent light converged by the objective lens when the slider is sought can always substantially focus on the recording surface of the optical disc, so that good wavefront aberration can always be obtained.

Generally, the diameter of a light beam incident on an objective lens from a beam expander is larger than the aperture of the objective lens. This is because an assembly error of the objective lens (actuator) and a margin for an adjustment deviation are considered. Therefore, in the present invention, at this time, the light amount detector 15 is disposed in the aperture of the objective lens 4 as shown in FIG. Then, the amount of light due to vignetting can always be detected.

For example, at the center of the optical disk 7,
It is assumed that the light beam incident on the objective lens 4 is parallel light (FIG. 3). At this time, if the objective lens 4 seeks to the outer side, the beam expander 11
The distance between the first lens 9 and the second lens 10 is reduced, and the light incident on the objective lens 4 becomes divergent light (FIG. 4). On the other hand, when the objective lens 4 seeks to the inner side, the distance between the two lenses of the expander 11 moves in a direction to increase, so that the light incident on the objective lens 4 becomes convergent light (FIG. 5). Therefore, when the objective lens 4 seeks from the center to the outer, vignetting increases, and the amount of light in the photodetector 15 increases. When seeking to the inner side, the vignetting becomes small and the light amount in the photodetector 15 decreases.

The light amount detector 15 shown in FIG. 1 detects an increase or decrease in light amount due to vignetting.
The D power is detected, and the laser driving output is corrected by the semiconductor laser driving circuit 17. With this configuration, it is possible to reduce errors in recording and reproduction due to insufficient light quantity.
Here, the first lens 9 is shifted along the optical axis direction, but the second lens 10 may be shifted similarly.

The above optical head is preferably used for the CAV and ZCAV systems in which the flying height is liable to fluctuate, but can also be applied to the CLV and ZCLV systems. In other words, even in the latter method, the flying height may fluctuate due to flapping during rotation of the optical disc or fluctuation in the thickness of the optical disc itself. In such a case, the optical head of the present invention can be used effectively. it can.

FIG. 6 is a schematic diagram (part 2) of an optical head for an optical disk device according to the present invention. In FIG. 2, the focus control is performed by moving the lens 1 in the optical axis direction according to the focus error signal. On the other hand, in FIG. 6, (1) the seek amount of the slider is calculated, and (2) the seek position detection circuit
Calculation of the radial position of the slider by the drive circuit 18 (calculation of the flying height from the linear velocity); (3) protective film thickness on the optical disk surface;
The temperature / thickness sensor 20 and the temperature / thickness detection circuit 19 detect the fluctuation of the protective thickness due to the temperature and the thickness unevenness of the thickness from the inner to the outer, and the first from (4), (2) and (3). The shift amount of the lens 9 is calculated by the shift amount calculating circuit 21, and (5) the first lens driving circuit 22
The lens 9 is shifted along the optical axis direction, and as a result (6) it becomes possible to focus on the recording surface of the optical disk. In such a flow, it is also possible to perform focus correction based on a predicted value in advance without using a focus error signal. In this case, it is possible to reduce the components and circuits of the focus servo system. Here, the first lens 9 is shifted in the optical axis direction, but the second lens 10 may be shifted similarly.

The beam expander 1 described above
1 is arranged between the movable part and the beam splitter,
It may be arranged in the movable part as shown in FIG. Then,
Even if you seek the slider equipped with the objective lens,
The collimated light beam always enters the beam expander 11, and it is possible to suppress the fluctuation of vignetting on the incident surface of the beam expander 11. Therefore, it is possible to suppress the fluctuation of NA.

Further, in FIGS. 1, 6 and 7, the first
When the combination of the lens 9 and the second lens 10 is a combination of a plano-convex lens and a plano-concave lens, one surface is flat, so that the focal length can be lengthened under the restrictions imposed by the external dimensions of the optical disk device. As a result, it is possible to further secure a margin for errors in the optical axis direction and the direction perpendicular to the optical axis during assembly and errors during adjustment.

Since the oscillation wavelength of the semiconductor laser shifts with temperature, the refractive index of the objective lens 4 changes accordingly. If the wavelength shifts, the focus position is blurred, and the wavefront aberration is deteriorated, so that it is difficult to record and reproduce data on the optical disk. Therefore, two types of lenses having different dispersion characteristics are used for the first lens 9 and the second lens 10. For example, a combination of the above-described plano-convex lens and plano-concave lens is also an example. When a plano-convex lens is used, the shorter the wavelength, the faster the light collection.However, combining a plano-concave lens makes it possible to make the divergence faster, and it is possible to achromatize by canceling colors outside the specified range. Becomes Further, by forming a diffraction grating on the lens surface, it is possible to correct a focus position shift due to a wavelength shift, and it is also possible to perform achromatism. In the description so far, two lenses, the first lens 9 and the second lens 10, have been used. However, even if the number of lenses is increased, tracking control and focus control are performed by relatively displacing a plurality of lenses. Can be performed, and when a plurality of lenses are displaced in the optical axis direction, it is also possible to suppress the wavefront aberration.

FIG. 8 is a schematic diagram (part 3) of the optical head for an optical disk device according to the present invention. As shown in FIG. 8, a beam expander is not used, and the light emitted from the collimator lens 2 is converted into convergent light. The rotation system of the optical disk 7 is CAV,
In the case of the ZCAV method, the flying height is smaller at the inner side than at the outer side. For example, when the slider 5 is floating on the inner side, the curvature of the wavefront incident on the objective lens 4 mounted on the slider 5 needs to be larger than when the slider 5 is floating on the outer side. That is, it is necessary to make the light emitted from the collimator lens 2 into convergent light. Regarding the degree of convergent light at this time, the convergent light may be optimized so as to match the degree of curvature of the wavefront of the convergent light from the collimating lens in consideration of the difference in the flying height between the inner and outer parts. For example, when the distance between the collimator lens 2 and the objective lens 4 is 91 mm for the inner and 51 mm for the outer, and the convergent lens 2 emits convergent light having a focal length of 250 mm ahead, the wavefront aberration is as follows. Inner 0.015λ (rms) Center 0.006λ (rms) Outer 0.028λ (rms)

From the above results, even if focus correction is not performed without using a beam expander, defocus components caused by flying fluctuations are automatically corrected by inputting convergent light. By using this method, it is also possible to suppress aberrations caused by unevenness in the thickness of the protective film on the optical disk surface.

[0028]

As is apparent from the above description, according to the present invention, a slider equipped with an objective lens is used, for example,
Even if the optical disc rotation control method is CAV or ZCAV, the convergent light focused by the objective lens when the slider is sought should always be focused on the recording surface of the optical disc by an optical system using a beam expander. Can be. Therefore, good wavefront aberration can be obtained.

The beam expander at the time of seeking can also suppress the fluctuation in the amount of light generated by vignetting generated in the objective lens. Can be suppressed by the beam expander. Therefore, good recording and reproduction can be obtained.

Further, in the present invention, the defocus component caused by the fluctuation of the inner and outer levitation is automatically corrected by making the light emitted from the collimating lens into convergent light without using a beam expander, thereby achieving good recording. Reproduction becomes possible. And not only focus control but also tracking control becomes possible. Therefore, not only can the recording density of an optical disk be increased by a high NA optical system, but also high-speed access,
It becomes possible to realize an optical head for an optical disk device capable of high-speed transfer.

[Brief description of the drawings]

FIG. 1 is a schematic view of an optical head for an optical disk device according to the present invention.

FIG. 2 is a graph showing a relationship between a shift amount of a focus point, a shift amount of a first lens, and a wavefront aberration.

FIG. 3 is a schematic view of an optical head for an optical disk device according to the present invention.

FIG. 4 is a schematic view of an optical head for an optical disk device according to the present invention.

FIG. 5 is a schematic view of an optical head for an optical disk device according to the present invention.

FIG. 6 is a schematic view of an optical head for an optical disk device according to the present invention.

FIG. 7 is a schematic view of an optical head for an optical disk device according to the present invention.

FIG. 8 is a schematic diagram of an optical head for an optical disk device of the present invention.

FIG. 9 is a schematic view of a conventional optical head for an optical disk device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 Collimating lens 3 Beam splitter 4 Objective lens 5 Slider 6 Recording surface of optical disk 7 Optical disk 8 Spindle rotation axis 9 First lens 10 Second lens 11 Beam expander 12 Start-up mirror 13 Galvano mirror 14 Moving part 15 Light amount detection Device 16 Light amount detection circuit 17 Semiconductor laser drive circuit 18 Seek position detection circuit / drive circuit 19 Temperature / thickness detection circuit 20 Temperature / thickness sensor 21 Shift amount calculation circuit 22 First lens drive circuit

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[Procedure amendment]

[Submission date] April 3, 2001 (2001.4.3)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction contents]

The focus control is performed by the beam expander 1
1. Either the light source side or the movable part side lens in 1.
The defocusing is performed in the optical axis direction based on the focus error signal. It is preferable that the effective diameter of the emitted light beam is smaller than the effective diameter of the light beam collimated by the collimating lens 2. In the tracking control, the beam can be irradiated to a desired position in the radial direction by swinging the galvanomirror 13 disposed between the beam expander 11 and the movable unit 14 . As a tracking means, there is a push-pull method utilizing diffraction from a guide groove of a recording film of an optical disk, a three-beam method of converting an incident beam into three beams using a diffraction grating, and detecting the reflected light. The tracking control can be performed by adding a rotation mechanism to the slider 5 so that the slider 5 is decentered in a direction perpendicular to the optical axis direction.
3 can be used for tracking control.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tsuyoshi Matsumoto 4-1-1, Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Prefecture Inside Fujitsu Limited (72) Kazufumi Uno 4-chome, Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa No. 1 No. 1 Fujitsu Limited F term (reference) 5D118 AA13 BA01 CA11 CD02 CF30 DC04 EA08 5D119 AA09 AA21 BA01 CA06 DA01 DA05 EA03 FA02 HA36 JA49 LB05

Claims (5)

[Claims] 1. An optical head for an optical disk device comprising a mechanism for collimating a laser beam emitted from a light source with a collimator lens, condensing the laser beam with an objective lens in a movable portion, and irradiating the optical disk with the objective lens, wherein the objective lens is mounted on a slider, At least two lenses are disposed between the collimating lens and the objective lens, and at least one of the two lenses on the light source side or the movable unit side is one of the two lenses.
An optical head for an optical disc device, comprising an output adjusting mechanism arranged so as to be able to perform focus control by moving in the optical axis direction based on a focus error signal and adjusting an output of a laser beam in conjunction with the focus control. . 2. The optical head for an optical disk device according to claim 1, wherein two lenses between the collimator lens and the objective lens are arranged in a movable portion. 3. An optical head for an optical disk drive, comprising: a mechanism for collimating a laser beam emitted from a light source by a collimating lens, condensing the laser beam by an objective lens in a movable part, and irradiating the optical disk with the objective lens. At least two lenses are arranged between the collimating lens and the objective lens, and at least one of the two lenses on the light source side or the movable part side,
A temperature detecting means, a film thickness detecting means and a seek position detecting means are provided so that the slider can be moved along the optical axis direction based on information on a seek amount, a temperature and a film thickness of the slider. At least one of the lens on the side and the movable portion side is arranged so as to be able to perform focus control by moving in the optical axis direction based on signals obtained from the temperature detection means, the film thickness detection means and the seek position detection means, An optical head for an optical disk device, comprising an output adjusting mechanism for adjusting an output of a laser beam in conjunction with the optical head. 4. In an optical disc optical system including a light source, a collimating lens, an objective lens mounted on a slider, and a medium, light emitted from the collimating lens incident on the objective lens mounted on the slider is convergent light. An optical head for an optical disk device, comprising: 5. The optical disk device according to claim 1, further comprising a light amount detector having an opening having a predetermined diameter on the light source side of the objective lens and capable of detecting a light amount other than the light transmitted through the objective lens. Optical head.