JPH1031820A - Initialization head for optical disk and initialization device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain a simple and reliable initialization in a short time by giving a longitudinal direction of a linear light beam image an angle in the radial direction or the normal direction of an optical disk. SOLUTION: When the angle between the longitudinal direction of a stripe like beam image and a track is defined θ, and a width of its image is W, and a length is I, the equivalent length I' of this image in the disk radial direction becomes I'=Isinθ, and the width W' in the track direction becomes W'=W/sinθ. In such a manner, by giving the longitudinal direction of the stripe like beam image, the angle for the track, beam irradiation range and irradiation time per one revolution of a disk are set without reducing the peak intensity of the beam image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an initialization head and an initialization apparatus for initializing a phase change optical disk by irradiating a laser beam.

[0002]

2. Description of the Related Art A phase change type optical disk is amorphous when a phase change type recording material is formed on a disk substrate by a sputtering method or the like at the time of factory manufacturing. It is crystallized by irradiating it with a laser beam to enable recording and reproduction of information before being shipped.

At the time of initialization (crystallization), the medium surface is selectively heated, and the other portion is rotated by rotating the disk substrate so that the temperature is not so high, and the light spot is reduced to φ1 to 2 (μm). And a method of irradiating a linear light beam having a width of 1 to 2 (μm) and a length of 50 to 100 (μm) with the longitudinal direction thereof directed in the radial direction of the optical disk. Have been.

[0004]

However, in the former case,
The range that can be initialized at once is small, and it takes time to initialize the entire disk. In the latter case, the range that can be initialized at a time is wide, but a high-output laser light source is required,
A high-power semiconductor laser having a stripe-shaped light emitting point has a problem in that the conditions for performing uniform initialization are narrow because the near-field pattern has uneven intensity.

[0005] In addition, since the near-field pattern of this type of semiconductor laser changes over time and the intensity unevenness also changes, it is necessary to periodically reset initialization conditions and replace the semiconductor laser element. There has been a problem that occurrence of intensity unevenness can be recognized only after initialization unevenness occurs.

The present invention has been made to solve the above problems. That is, an object of the present invention is to provide an initialization head and an initialization device for an optical disk which can be easily initialized in a short time and have high reliability.

[0007]

The object of the present invention is achieved by adopting the following constitution.

That is, a light beam emitted from a semiconductor laser having a stripe-shaped light emitting portion is condensed as a linear light beam image on a medium surface of a phase-change optical disk by an objective lens.
An apparatus for initializing an optical disk for initializing the medium, wherein a longitudinal direction of the linear light beam image has an angle with respect to a radial direction or a tangential direction of the optical disk. .

An optical disc for initializing the medium by condensing a light beam emitted from a semiconductor laser having a stripe-shaped light emitting portion on a medium surface of a phase-change optical disc with an objective lens as a linear light beam image. The initialization head according to claim 1, further comprising an element for reducing unevenness in intensity distribution of a near-field pattern of the semiconductor laser.

An optical disk for initializing the medium by condensing a light beam emitted from a semiconductor laser having a stripe-shaped light emitting portion on a medium surface of a phase-change optical disk with an objective lens as a linear light beam image. The optical disc initialization apparatus according to claim 1, wherein the light beam emitted from the objective lens is vibrated substantially in the longitudinal direction.

An optical disk for initializing the medium by condensing a light beam emitted from a semiconductor laser having a stripe-shaped light emitting portion on a medium surface of a phase-change optical disk with an objective lens as a linear light beam image. A beam splitter for guiding a light beam emitted from a semiconductor laser to an optical path different from an objective lens, a lens for condensing the light beam, and a multi-splitting light detection arranged on a converging point by the lens. An optical disk initialization device, comprising: a detector; and detecting intensity unevenness by a signal from the photodetector.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of the present invention will be described with reference to the attached drawings and FIGS. However, the present invention is not limited to the embodiment described below.

FIG. 1 shows the main structure of the mechanism of the initialization device. The optical disk 17 to be initialized is attached to a disk rotation motor 33, and is rotated at a predetermined rotation speed. The optical head 10 irradiates the medium surface of the optical disk 17 with a linear light beam, and is driven by the moving stage 32 between the inner circumference and the outer circumference.

FIG. 2 is a diagram showing the main configuration of the optical head. High power semiconductor laser 11 having a stripe-shaped light emitting portion
The emitted light beam is converted into a parallel light beam by the collimator lens 12, passes through the polarizing beam splitter 13, the 波長 wavelength plate 14, and the image rotating prism 15 and passes through the objective lens 16.
And is condensed as a stripe-shaped light beam on the medium surface via the transparent substrate of the optical disk 17. For example, Tp = 95%, R
It has a characteristic of s = 99%, and 95% of the light flux incident in the p-polarized direction is transmitted toward the objective lens 16 and 5% is reflected and condensed on the power monitor photodiode 25 by the condensing lens 22. Is done. The output power of the power monitor photodiode 25 can control the laser emission power to a predetermined value.

The light beam condensed on the medium surface of the optical disk 17 is reflected on the medium surface, returns to the objective lens 16, the image rotating prism 15, the quarter-wave plate 14, and the polarization beam splitter 13, and is reflected there. , Foucault prism 2
1. Condensing lens 22, Filter 23 for adjusting light amount
Error detection photodetector 24 via
Incident on. Due to the output from the detector 24, the focusing actuator 31 always controls the objective lens 1
6 is driven to focus a light beam on the medium surface of the optical disk 17.

FIG. 3 is a diagram showing the relationship between the light emitting portion of the stripe semiconductor laser and the stripe light beam image formed on the optical disk. The length of the light emitting portion of the laser chip 111 is L, and the focal length of the collimator lens 12 is f.
c, where fo is the focal length of the objective lens 16 and I is the length of the light beam image to be formed, I = (fo / fc) × L. L = 200 μm, fc = 5.8 mm, fo = 6.
If 2 mm, I ≒ 214 μm.

The image width w is mainly determined by the light source wavelength (λ) and the numerical aperture (NAo) of the objective lens.
If NAo = 0.40, w ≒ 2 μm. Here, if the aperture of the objective lens is Ao, NAo = (Ao / 2) /
fo.

This type of semiconductor laser emits an elliptical beam having a divergence angle of about 10 ° (full width at half maximum) in the direction parallel to the junction of the laser chip and about 30 ° (full width at half maximum) in the vertical direction. The length of the light emitting portion varies depending on the type, but is about L = 100, 200, 500 μm.

The effective numerical aperture (NA) of the collimator lens
c) is given by NAc = (Ao / 2) / fc. It is necessary to set the effective numerical aperture NAc so that the laser emission light can be effectively guided to the objective lens. If the effective numerical aperture NAc is taken into the range of the intensity 1 / e ² of the elliptical beam, NAc = si
n (30 ° × 1.7 / 2) ≒ 0.43 is required.

In such an optical system, once the type of the semiconductor laser and the focal length and the effective numerical aperture of the collimator lens are set, the length and width of the stripe-shaped light beam image are determined by the focal length of the objective lens. Proportional. If w = 4μ
In order to obtain m, the focal length of the objective lens fo = 12.4m
m and the numerical aperture NAo = 0.20, but at this time I = 428 μm, and the peak intensity of the light beam image is reduced to １ ／ of that at w = 2 μm.

FIG. 4 shows the relationship between the optical disk and the direction of the stripe beam image. Assuming that the angle between the longitudinal direction of the beam image and the track is θ and the beam image has a predetermined angle, and the width of the image is w and the length is I, an equivalent disk radius of this image The direction length I ′ is Isin θ,
The width w ′ in the track direction = w / sin θ (FIG. 4
(B)).

When I = 214 μm and w = 2.0 μm, when θ = 45 °, I ′ = 151 μm and w ′ = 2.8 μ.
For m, θ = 30 °, I ′ = 107 μm, w ′ = 4 μm
Becomes

By setting the longitudinal direction of the striped beam image at an angle to the track, the beam irradiation range and irradiation time per one rotation of the disk can be set without lowering the peak intensity of the beam image. it can.

In this embodiment shown in FIG. 2, an image rotating prism 15 is provided between the collimator lens 12 and the objective lens 16 so that the image rotating prism 15 is rotated about the optical axis with respect to the optical head device main body. By doing so, the angle between the longitudinal direction of the stripe-shaped light beam image and the track can be arbitrarily set.

Thus, as initialization parameters,
In addition to the rotation speed of the disk, the feed speed of the optical head, and the laser power, the equivalent beam length in the radial direction and the equivalent beam width in the tangential direction can be set, and various phase change optical disks can be easily initialized. The angle between the longitudinal direction of the stripe light beam image and the track may be set by rotating the optical head body on a moving stage.

A stripe-shaped semiconductor laser often has uneven intensity distribution in the length direction (for example, 200 μm), and usually has a high intensity at the end and a certain periodicity at the center (FIG. 5). . When such a laser is used and focused by the optical system shown in FIGS. 2 and 3, unevenness in the intensity of the laser appears as it is on the medium surface of the optical disk,
This may cause unevenness in initialization, and the setting of conditions for initialization without unevenness becomes narrow. In order to obtain a semiconductor laser with less intensity unevenness, sorting is required and the cost becomes higher. Therefore, an element for reducing unevenness is provided in a path from the semiconductor laser to the optical disk so that the optical system can reduce intensity unevenness.

More specifically, as shown in FIG. 6, a cylindrical lens 26 is placed in the optical path so that its generatrix direction is substantially parallel or substantially perpendicular to the laser stripe direction. On the medium surface of the optical disk, the narrow direction of the stripe light beam image is condensed by the objective lens so that the longitudinal direction having intensity unevenness is defocused and the intensity of each intensity is reduced. Is done.

A beam shaping prism is provided on the path from the collimator lens to the objective lens to correct the far-field pattern of the elliptical beam and, at the same time, convert the light beam incident on the shaping prism into divergent or convergent light. Thus, astigmatism is generated here, and an effect equivalent to the use of the cylindrical lens can be obtained (FIG. 9).

Alternatively, as shown in FIGS. 7 and 8, a Wollaston prism 27 of a birefringent prism and a diffraction grating 28 are arranged in the optical path, the beams are separated into a plurality of beams, and the beams are gathered in such a manner that they are shifted from each other substantially in the longitudinal direction. Lighting can alleviate individual intensity unevenness. The lateral shift amount of the beam image is preferably set to be の of the period P in accordance with the periodicity of the intensity unevenness of the near field pattern of the semiconductor laser.

Utilizing this periodicity, a knife-shaped shield (knife edge 18) can be placed at the edge of the beam, and the intensity unevenness can be reduced by diffraction from the knife edge 18 (FIG. 11). When the knife edge 18 is placed at the edge of the beam, Fresnel diffraction occurs from this portion. This diffraction pattern is a periodic intensity distribution, and the position at which the light beam of the knife edge 18 is cut is set so that the intensity of the intensity distribution is opposite to the intensity of the original laser beam and cancels out.

As an arrangement of these unevenness reducing elements, it is easy to enhance the effect by temporarily condensing the light beam emitted from the semiconductor laser and disposing it at or near this condensing point.

[0032] In FIG. 12, a light beam emitted from the semiconductor laser 112 is focused at the position of the figure F ₁ at the coupling lens. The imaging magnification at this time is -b / a, and if a = 5.8 mm and b = 11.6 mm, L =
The image length of a 200 μm stripe light source is 400 μm
Becomes

[0033] 'When, at the position of the _{F 1 (b / a) L} ' width between the intensities across the peak in near-field pattern shown in FIG. 5 L is the width, wherein the width w _S ≒ (b /
a) By arranging the slit of L ', the intensity peaks at both ends can be cut.

Similarly, as shown in FIG. 10, a filter 2 having a density distribution proportional to the image intensity distribution
3 can be arranged to remove this unevenness.

This will be described with reference to FIG. FIG. 15 (a) laser beam intensity distribution at the position of the F _1, (b) is a filter density distribution. Assuming that the minimum intensity of the laser light intensity distribution is I _L and the maximum intensity is I _H , the filter density D
Is chosen to be I _H -I _L.

By passing the light through this filter, a laser light intensity distribution as shown in FIG.

[0037] The filter was placed a photosensitive material such as photographic plates having sensitivity to a light source wavelength in the position of the F _1, to emit a laser beam at a predetermined intensity, can be created by exposing and developing. By returning the developed dry plate to the same position as at the time of exposure, it is possible to obtain a non-uniformity reduction filter adapted to each laser.

Alternatively, the near-field pattern of the laser beam is observed with a TV camera or the like, and its intensity distribution is obtained.
A pattern similar to this intensity distribution can be created by a mask writing device or the like to provide a non-uniformity reduction filter. In this case, it is preferable to make the pattern long in one direction as shown in FIG. 16 so as to facilitate positioning in the optical path. When placing the filter 23 to the distant position not the F ₁ or in the vicinity thereof, the pattern of the filter 23 becomes Fresnel diffraction pattern of the near-field pattern. By departing from Matashu point F _1, it is possible to reduce the return light from the filter surface of the semiconductor laser.

As such a filter, a combination of a multi-segment variable phase liquid crystal element and a polarizer can be used.

FIG. 17 is a diagram in which a multi-segment variable phase liquid crystal element and a polarizer are arranged in an optical path from a semiconductor laser.

The multi-segment variable phase liquid crystal element 30 can vary the phase difference applied to a light beam passing through each element by variably controlling the voltage applied to each divided liquid crystal element. By disposing the polarizer 19 after this element,
Only the light amount corresponding to the phase difference given by each element,
A variable intensity filter that transmits this polarizer 19 is obtained.

As such a multi-divided phase variable liquid crystal element, for example, there is “Shape Shifter” manufactured by Meadowlark Optics.

The light emitted from the semiconductor laser is generally linearly polarized light having an electric field component in a direction parallel to the bonding direction of the chip, and the fast axis of the liquid crystal element is set at 45 °. Or, between the semiconductor laser and the liquid crystal element,
A half-wave plate is provided to adjust the polarization direction of the light beam incident on the liquid crystal element.

When a birefringent double image element such as a Savart plate or a Wollaston prism, a cylindrical lens, a diffraction grating, or the like is used as a non-uniformity reducing element, it is arranged in a non-parallel light beam from the coupling lens to the objective lens, By adjusting in the direction, the amount of lateral shift and the amount of defocus can be optimized according to each semiconductor laser.

As shown in FIG. 13, the Nd: YAG crystal 2
It is also possible to excite a solid-state laser light-excited crystal such as 9 with a semiconductor laser beam and use the output light from this crystal.

By exciting the Nd: YAG crystal 29 at a wavelength near 808 nm, laser outputs with wavelengths of 1064 nm and 946 nm can be obtained. In the course of this excitation, the spatial distribution of the luminous flux from the semiconductor laser 112 having the stripe-shaped light-emitting portion as the excitation light can be improved.

These methods directly improve the spatial distribution of the intensity distribution unevenness of the laser light by adding an element for reducing the unevenness. Separately, or in combination with these methods, the linear beam image irradiated on the medium surface of the optical disk is vibrated in the longitudinal direction to make the intensity distribution viewed on a time average uniform, Initialization unevenness can be reduced.

As a means for oscillating, a two-dimensional actuator which can be driven in both the focusing direction and the longitudinal direction of the linear light beam is used as an actuator for driving the objective lens. For example, a galvanomirror is disposed on an optical path from a semiconductor laser to an objective lens to be driven, and the galvanomirror is driven by a sine wave signal to oscillate a light beam. An acousto-optic element is disposed in the optical path, and this is modulated at a high frequency. If the drive frequency is synchronized with the rotation frequency of the optical disk, there is a possibility that unevenness may occur in a specific area of the optical disk. The rotation speed of the optical disk depends on the optical disk to be initialized.
0 to 4000 rpm. The frequency is about 20-7
It is 0 Hz, and it is desirable to set the driving common wave number higher than 150 Hz or more. This method can be used in combination with the unevenness reducing element. Further, the unevenness reducing element may be not only one kind but also a combination of two or more kinds.

The intensity distribution of the near-field pattern of the semiconductor laser can be reduced by the above-described method. However, the intensity distribution of the semiconductor laser changes with time with use. It also changes depending on the setting of the output power. Therefore, when used as an initialization device, it is preferable that initialization conditions can be set while observing the beam intensity and intensity distribution. Further, it is preferable to provide a function for preventing occurrence of initialization failure such as issuing a warning when a change over time occurs and the unevenness exceeds a predetermined value.

For this reason, a beam splitter for guiding the emitted light from the semiconductor laser to an optical path different from the objective lens, a lens for condensing this light beam, and a multi-segmented photodetector arranged on the condensing point by this lens are provided. The intensity non-uniformity is detected based on the output from the photodetector. As such a multi-segmented photodetector, a one-dimensional CCD line sensor can be used. For example, if a cell having 14 μm × 14 μm and 128 to 256 elements is used, it is converted into a light source of a stripe laser having L = 200 μm. A resolution of 1-2 μm is obtained.

By subjecting the output of the CCD line sensor to signal processing, detecting the maximum and minimum of the intensity distribution, and comparing the detected value with a predetermined value, a change with time can be detected.

The beam splitter may be placed anywhere in the optical path from the semiconductor laser to the objective lens. However, when the above-mentioned unevenness reducing element is used together, it is actually better to place the light beam after passing through this element. The correspondence with the light beam condensed on the medium surface is improved. Further, the unevenness reducing element can be adjusted while observing the output from the CCD line sensor, and maintenance is easy.

When the multi-segment variable phase liquid crystal element is used, the output from the CCD line sensor is fed back so that the unevenness reduction control can be always performed.

[0054]

According to the present invention, an initialization head and an initialization apparatus for an optical disk which can be easily initialized in a short time and have a high reliability are provided.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a main configuration of a mechanism of an initialization device.

FIG. 2 is a main configuration diagram of an optical head.

FIG. 3 is a diagram illustrating a relationship between a laser light emitting unit and a light beam image.

FIG. 4 is a diagram showing the relationship between the direction of an optical disc and the direction of a stripe beam image.

FIG. 5 is a diagram showing an intensity distribution of a stripe beam image.

FIG. 6 is a diagram in which a cylindrical lens is arranged in an optical path.

FIG. 7 is a diagram in which a Wollaston prism is arranged in an optical path.

FIG. 8 is a diagram in which a diffraction grating is arranged in an optical path.

FIG. 9 is a diagram in which a beam shaping prism is arranged in an optical path.

FIG. 10 is a diagram in which a filter is arranged in an optical path.

FIG. 11 is a diagram in which a knife edge is arranged at an edge portion of a beam in an optical path.

FIG. 12 is an explanatory diagram related to the arrangement of the unevenness reducing elements.

FIG. 13 is a diagram in which an Nd: YAG crystal is arranged in an optical path.

FIG. 14 is a layout diagram of a multi-split sensor.

FIG. 15 is a view for explaining removal of intensity unevenness of a laser beam intensity distribution by a filter.

FIG. 16 is a diagram of a filter pattern.

FIG. 17 is a layout diagram of a multi-segment phase variable liquid crystal element and a polarizer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Optical head 11 Stripe high power semiconductor laser 12 Collimator lens 13 Polarization beam splitter 14 1/4 wavelength plate 15 Image rotation prism 16 Objective lens 17 Optical disk 18 Knife edge 19 Polarizer 20 Beam shaping prism 21 Foucault prism 22 Condensing lens 23 Filter 24 Focus error detection photodetector 25 Power monitor photodiode 26 Cylindrical lens 27 Wollaston prism 28 Diffraction grating 29 YAG crystal 30 Multi-segment variable phase liquid crystal element 31 Focusing actuator 32 Moving stage I Length of light beam image to be formed L Light emitting length of laser chip

Claims (15)

[Claims] 1. An optical disk for initializing the medium by condensing a light beam emitted from a semiconductor laser having a stripe-shaped light emitting portion on a medium surface of a phase-change optical disk with an objective lens as a linear light beam image. In the initialization device of
An apparatus for initializing an optical disk, wherein the longitudinal direction of the linear light beam image has an angle with respect to a radial direction or a tangential direction of the optical disk. 2. The optical disk initialization apparatus according to claim 1, wherein the azimuth of the linear light beam image in the longitudinal direction is adjustable with respect to a radial direction or a tangential direction of the optical disk. 3. The optical disk initialization apparatus according to claim 2, further comprising an image rotating means for adjusting an azimuth of the linear light beam image in a longitudinal direction with respect to the optical head body. . 4. An optical disk for initializing said medium by converging a light beam emitted from a semiconductor laser having a stripe-shaped light emitting portion on an optical disk medium surface of a phase change optical disk with an objective lens. The initialization head according to claim 1, further comprising an element for reducing unevenness in intensity distribution of a near-field pattern of the semiconductor laser. 5. The initialization head for an optical disk according to claim 4, wherein the unevenness reducing element is a cylindrical lens having a generatrix direction substantially parallel or substantially perpendicular to a laser stripe direction. 6. The optical disk initialization head according to claim 4, wherein the unevenness reducing element is a beam shaping prism, and a light beam incident thereon is adjusted to be a non-parallel light beam. 7. The optical disk initialization head according to claim 4, wherein the unevenness reducing element is a birefringent double image element that divides a light beam into a plurality of light beams. 8. The optical disk initialization head according to claim 4, wherein the unevenness reducing element is a diffraction grating that divides a light beam into a plurality of light beams. 9. The optical disk initialization head according to claim 4, wherein the unevenness reducing element is a filter having a density distribution corresponding to the intensity distribution of the light beam. 10. The optical disk initialization head according to claim 4, wherein the unevenness reducing element is a phase variable liquid crystal filter divided into a number of regions in at least one direction. 11. The non-uniformity reducing element is a knife edge arranged on both sides of an end of a light beam.
An optical disk initialization head according to claim 1. 12. The optical disk initialization head according to claim 4, wherein the light beam emitted from the semiconductor laser is once focused before entering the objective lens. 13. The device according to claim 12, wherein the unevenness reducing element is arranged at or near the light converging point.
An optical disk initialization head according to claim 1. 14. An optical disc for initializing the medium by converging a light beam emitted from a semiconductor laser having a stripe-shaped light emitting portion on a medium surface of a phase-change optical disc with an objective lens as a linear light beam image. The optical disc initialization apparatus according to claim 1, wherein the light beam emitted from the objective lens is vibrated substantially in the longitudinal direction. 15. An optical disk for initializing the medium by condensing a light beam emitted from a semiconductor laser having a stripe-shaped light emitting portion on a medium surface of a phase-change optical disk with an objective lens as a linear light beam image. A beam splitter for guiding a light beam emitted from a semiconductor laser to an optical path different from an objective lens, a lens for condensing the light beam, and a multi-splitting light detection arranged on a converging point by the lens. An optical disk initialization device, comprising: a detector; and detecting intensity unevenness by a signal from the photodetector.