JPH11120610A - Optical disk device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To record or reproduce a large capacity of information to and from an optical recording medium by perpendicular resonator surface light emitting semiconductor lasers, etc., of an optical disk device. SOLUTION: This optical disk device is provided with a perpendicular resonator surface light emitting semiconductor laser array 1 constituted by arranging perpendicular resonator surface light emitting semiconductor laser elements 14 to a grid form, a solid immersion lens 9 for receiving the laser beam emitted by this perpendicular resonator surface light emitting semiconductor laser array 1 and a regenerative signal detecting means 10 for detecting the light reflected from the optical recording medium 12 as a regenerative signal. The perpendicular resonator surface light emitting semiconductor laser array 1 inclines at a slight angle with the tangent direction of the rotation of the optical recording medium 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a vertical cavity surface emitting semiconductor laser (Vertica1 Capaci).
ty Surface Emitting Race
r; hereinafter referred to as “VCSEL”. An optical disk capable of recording a large amount of information on an optical recording medium by using a laser beam emitted from an element and a solid immersion lens, and reproducing a large amount of information recorded on the optical recording medium; Related to the device.

[0002]

2. Description of the Related Art In a conventional large-capacity optical disk device such as a compact disk (CD) player, an optical video disk (VD) player, and a so-called digital video disk (DVD) player, a single semiconductor device is used. A laser light source emits a laser beam to form a beam spot, and the beam spot is formed on the CD,
In general, information is recorded by irradiating a recording layer of an optical recording medium such as a VD or DVD, or information is recorded and reproduced by detecting reflected light.

In order to irradiate a beam spot on a predetermined portion of the recording layer of the optical recording medium with a predetermined accuracy, an optical element for irradiating the beam spot is usually 0.1 [μm] by an actuator. And a focus control in the order of 1 [μm], and a single semiconductor laser element typified by a laser diode (hereinafter referred to as “LD”) is used as a light source. ing. More specifically, a beam spot having a diameter of about 1 [μm] is used to form a beam spot of 10 ⁸ to 10.
⁹ [bit / cm ^2] C., i.e., an optical disk apparatus which enables reading information at a recording density of about 1Gb / cm ⁸ from 0.1 GB / cm ⁸ have been put into practical use, in particular, there is a state of the art The optical disk device of the DVD player uses a so-called DVD-RAM, and only achieves a recording capacity of about 2.7 GB per disk.

The light source of the optical pickup disclosed in Japanese Patent Application No. 8-166167 uses a single VCSEL element instead of the LD. Despite the use, in order to realize large-capacity recording and reproduction with such an optical pickup, the beam waist size is reduced by further shortening the used wavelength (closer to the ultraviolet region), or the light source is used. Only by narrowing the beam waist size or beam spot size by further reducing the distance (focal length) between a single VCSEL element and the objective lens,
It is considered that an optical disk device capable of recording and reproducing data with a larger capacity than before can not be realized.

The optical memory head disclosed in Japanese Patent Application No. 8-298981 has a VCSEL in which a plurality of the VCSEL elements are arranged in a lattice as shown in FIG.
An optical memory head 53 using the L array 51 as a light source has been proposed. However, the optical memory head 53 and the optical recording medium 54 are optically recorded by the meniscus 52 of a lubricant thin film liquid formed on the contact surface between the optical memory head 53 and the optical recording medium 54. Since the recording is carried out only by the contact head method in which the medium 54 is always kept in contact with the medium 54, when producing the optical recording medium required for the operation, it is necessary to manufacture the recording layer, the protective film and the like extremely flat. As a result, the production cost of the optical recording medium may be increased.

[0006]

However, if the operating wavelength of a semiconductor laser element or the like as a light source is brought close to (shortened) the ultraviolet region in order to narrow the beam waist size or beam spot size, the laser oscillation efficiency deteriorates with time. However, there is a problem that the life of the semiconductor laser element as a light source is shortened, and an inconvenience that the optical head has to be replaced in a short cycle occurs. Therefore, improvement of such a problem is an urgent issue. I was

[0007] Similarly, if the operating wavelength is brought closer (shortened) to the ultraviolet region, there is a theoretical disadvantage that the transmittance of laser light in the optical element is reduced.
Even if a semiconductor laser element such as an SEL element is used as a light source, there is a difficult problem that large-capacity information cannot be recorded or reproduced on an optical recording medium until the theoretical limit of the optical element is overcome. Was.

In the means for further reducing the focal length between the semiconductor laser element as a light source and the objective lens to reduce the beam waist size or the beam spot size, the objective lens is infinitely limited to the surface of the recording layer of the optical recording medium. Optical recording media mass-produced,
Usually, since many layers such as a reflective layer, a recording layer, and a protective layer are formed by a vacuum evaporation method, a sputtering method, or the like, the thicknesses of these layers are not necessarily uniform. Therefore, it is inevitable that minute irregularities are formed on the surface of the optical recording medium, and the irregularities come into contact with the objective lens of the optical head portion due to the rotation of the optical recording medium and cause abrasion. There has been a problem that the life is shortened, or a fatal scratch in the reading / writing process is caused on the surface of the recording layer or the protective film of the optical recording medium. Therefore, there has been a long-awaited demand for an entirely new optical disk device capable of recording or reproducing a large amount of information on or from an optical recording medium by means that does not depend on the policy of shortening the focal length to the minimum. .

In the near future, FTTH (Fiber
If To The Home) is realized gradually,
The combination of the penetration of optical fiber as a communication infrastructure and the spread of personal computers and the Internet, an optical disc having a data transfer rate of at least 1 [Gb / s] or a recording capacity of at least 30 [GB] The device is a personal computer recording device or VOD (Video On Demand)
It is considered that the configuration will be indispensable, centering on the corresponding communication device. However, conventionally, there has been no optical disc device capable of recording or reproducing such a large amount of information at a high speed as described above. There is a strong desire for a new optical disk device.

[0010]

Means for Solving the Invention Accordingly, the present inventor has proposed:
In order to solve the above problems, as a result of intensive studies, a vertical cavity surface emitting semiconductor laser array in which vertical cavity surface emitting semiconductor laser elements are arranged in a grid pattern, and a vertical cavity surface emitting semiconductor laser array, A solid immersion lens for irradiating the emitted laser light to the optical recording medium and receiving light reflected from the optical recording medium; and a reproduction signal detection for detecting the light reflected from the optical recording medium as a reproduction signal. Means for providing an optical disk device or the like wherein the vertical cavity surface emitting semiconductor laser array is inclined at a small angle with respect to a tangential direction of rotation of the optical recording medium. It is.

An object of the present invention is to use a VCSEL array in which VCSEL elements are arranged in a lattice pattern as a light source, and to form an image formed by a very small beam spot composed of a plurality of laser light bundles through a solid immersion lens. By irradiating on the optical recording medium, while maintaining a substantially constant interval with the optical recording medium without using the contact head method,
It is an object of the present invention to provide an optical disk device capable of recording or reproducing a large amount of information on an optical recording medium, which has not been available before.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a configuration of an embodiment including an optical system of an optical disk apparatus according to the present invention. The projected image in the tangential direction of the rotation of the optical recording medium 12, in other words, the tangential direction. VC as a surface light source having a number of point light sources arranged at a small angle with respect to the reference line as a reference line
SEL array 1, grating holographic optical element 2, polarization beam splitter 3, λ /
Four plates 4, collimator lens 5, objective lens actuator 6, objective lens 7, solid immersion lens actuator 8, solid immersion lens 9, reproduction signal detecting means 10 tilted by the same tilt as VCSEL array 1, optical recording It comprises a medium rotating mechanism 11, an optical recording medium 12, and an optical recording medium rotating mechanism support member 13.

First, recording processing in the above optical system will be described. In FIG. 1, a traveling optical path of a laser beam or the like in recording or reproducing information is indicated by a broken line. First,
VC inclined by a small angle with respect to the tangential direction of the optical recording medium 12
The laser light emitted from the SEL array 1, ie, VC
The laser light emitted in the vertical direction from the SEL array 1 is
The light passes through the grating holographic optical element 2 and enters the polarization beam splitter 3.
Then, the laser light is incident on the λ / 4 plate 4.
Since the λ / 4 plate 4 is made of a birefringent crystal having two refractive indices, the laser beam has two wave components having a slight transit time difference at the time of exiting the λ / 4 plate 4. Will be. Therefore, the laser light obtained by combining these two waves becomes elliptically polarized light whose polarization plane rotates with time. If the thickness of the λ / 4 plate 4 is set so that the time difference between the elliptically polarized lights becomes π / 2 of the laser light, the laser light emitted from the λ / 4 plate 4 is converted into elliptically polarized light. And can be circularly polarized light.

The circularly polarized laser light enters the collimator lens 5 and exits as a parallel light. Thereafter, the laser beam incident on the objective lens 7 while being a parallel light beam is narrowed down in beam waist size until it is limited by the diffraction limit, and a minute beam spot is formed.

In order to irradiate the optical recording medium 12 with a very small beam spot whose beam waist size is further reduced, a laser beam is passed through the solid immersion lens 9 here. In the present invention, the “solid immersion lens” refers to a hemispherical lens or a super hemispherical lens formed of a material that is transparent at a wavelength equivalent to the infrared region, for example, a semiconductor such as Si, GaAs, or InP. Or any other equivalent material. In this embodiment, in particular, GaAs
The case of a hemispherical lens made of s or super hemispherical lens will be described. In this embodiment, a case where the solid immersion lens 9 is a super hemispheric lens will be particularly described.

FIG. 2 shows the solid immersion lens 9.
Fig. 2 (A) shows the state of refraction of laser light at
Shows a case of a hemispherical lens, and FIG. 2B shows a case of a super hemispherical lens. The super hemispherical lens is a kind of hemispherical lens formed so that a spherical portion is slightly larger than a normal hemispherical lens. Assuming that each of the hemispherical lenses has a refractive index of n, in the hemispherical lens of FIG.
In the case of the super hemispherical lens shown in FIG. 2B, it can be reduced to 1 / n ² times. That is, since the laser light is incident along the radial direction of the solid immersion lens 9, the laser light can be narrowed down to an extremely small beam spot without generating spherical aberration. The solid immersion lens 9
The laser beam can enter the optical recording medium 12 without reflection loss if the distance between the flat surface portion and the optical recording medium 12 is kept at λ / 4 or less of the used wavelength.

As described above, the VCSEL
By irradiating the laser beam emitted from the array 1 onto the optical recording medium 12 rotated by the optical recording medium rotating mechanism 11 as an extremely small beam spot, recording of a large amount of information is realized on the optical recording medium 12. is there. That is, the VC
If the image of each light spot of the SEL array 1 is projected onto the optical recording medium 12 and the light wave from each light spot of the VCSEL array 1 is light-intensity-modulated according to the information to be written, the information is thereby optically recorded. It will be recorded on the medium 12.

Next, the case of the reproducing process will be described.
In FIG. 1, the reflected light from the optical recording medium 12 enters the polarization beam splitter 3 in the reverse course of the above-described recording. This reflected light wave is divided by the polarization beam splitter 3 into a light beam which is refracted by the reproduction signal detecting means 10 and polarized and separated, and a light beam which returns directly to the VCSEL array 1. However, the returned light wave, that is, the reflected light is λ
Because of the reciprocation of the / 4 plate 4,
The deflection surface is rotated by π / 2 as compared with the light wave traveling from the L array 1 to the λ / 4 plate 4, and almost all of the light is polarized by the polarization beam splitter 3.
Is reflected toward the reproduction signal detecting means 10.

The reproduction signal detection means 10 comprises, for example, a detection optical system including a convex lens 10a and an astigmatism lens 10b, and a signal detection section 10c. What is performed is detected by the signal detection unit 10c after passing through an optical element such as the convex lens 10a. The signal detector 10c
May be constituted by a photodiode or a CCD, and the number of the elements is sufficient if it is at least about twice the number of the VCSEL elements of the VCSEL array 1, and more preferably a stepping actuator using a stepping motor or the like. For example, the entire surface tracking can be performed. However, the signal detector 10c needs to be tilted by the same small angle as the VCSEL array 1 is tilted. This is because the laser light emitted from the VCSEL array 1 is reflected on the optical recording medium 12 to accurately read an image of the light obtained.

As described above, the signal detecting section 10c reads an image composed of an extremely small beam spot reflected from the optical recording medium 12, thereby obtaining a large-capacity image recorded on the optical recording medium 12. Information can be reproduced.

Next, focus control of the solid immersion lens 9 and the like in a recording or reproducing process will be described. The beam spot irradiated onto the optical recording medium 12 and reduced to an extremely small size is preferably one whose focus is always controlled by the actuator 6 for the objective lens and the actuator 8 for the solid immersion lens shown in FIG. I do. Specifically, a two-stage actuator system is adopted, the tracking signal is band-separated, and the low-frequency component is distributed to a coarse actuator (not shown) and the high-frequency component is distributed to a fine actuator (not shown). Follow operation. Therefore, even in the case of random access, the irradiation of the beam spot on the target track is driven by the coarse actuator. However, when the target track is within several tens of target tracks, the fine actuator can work together to perform accurate positioning. In this case, in order to keep the distance between the solid immersion lens 9 and the objective lens 7 constant, it is desirable to control the displacement using a capacitance displacement meter.

Next, a light source for a recording process or a reproducing process according to the present invention will be described with reference to FIG. As a light source according to the present invention, a VC that emits laser light having a wavelength equivalent to that of an infrared region having a wavelength of about 0.98 [μm] is used.
The VCSEL array 1 in which the SEL elements 14 are arranged in a lattice is used. FIG. 3 is a perspective view of the VCSEL array 1. In the present embodiment, the VCSEL array 1 uses a total of 64 VCSEL elements 14 of 8 rows and 8 columns arranged in a grid pattern. Rows and columns may be used. However,
The term “arranged in a lattice” means that the elements are arranged in a lattice for the sake of simplicity of description. Sometimes, 64 VCSEL elements are formed in layers as if they were arranged in a lattice.

Each VCSEL element 14 has an output window 15 for emitting laser light to the outside.
Paying attention to only a specific row, a total of eight laser beams emitted from the output window 15 and forming one column form eight beam spots on the optical recording medium 12 not shown in FIG. Form. The rotation of the optical recording medium 12 is suppressed to a certain level or less by the optical recording medium rotating mechanism support member 13, so that the locus of eight beam spots is eventually formed on the optical recording medium. In this specification, “row” refers to one column along the direction of the tangent line of rotation of the optical recording medium 12, and “column” refers to one column along the radial direction of the optical recording medium 12.

First, in FIG. 3, focusing only on the laser light emitted from one column of VCSEL elements 14 provided in the eighth row, the eighth row and first column of the eight-row and eight-column VCSEL array 1 in FIG. 8 V arranged in the 8th column from
From the CSEL element 14, a total of eight laser beams are emitted from the output window 15 vertically upward in the drawing. However, in FIG. 3, the VCSEL element 14
The laser light emitted from is drawn diagonally. More specifically, 8 emitted from the VCSEL element 14
This laser beam passes through optical elements such as a grating holographic optical element 2 and a polarizing beam splitter 3 and is applied to the optical recording medium 12 shown in FIG.
Forming eight beam spots (forming an image consisting of eight beam spots). Since the optical recording medium 12 rotates to record or reproduce information, the locus of eight laser beams is drawn on the surface thereof as described above.
However, the tangent of rotation of the optical recording medium 12 and the VCS
When the optical recording medium 12 and the VCSEL array 1 are arranged so that the row direction in the EL array 1 is parallel, the trajectories drawn by the eight beam spots on the optical recording medium 12 are in the same column. As a result,
It becomes one locus.

Therefore, as shown in FIG.
The L array 1 is inclined by a small angle with respect to the tangential direction of rotation of the optical recording medium 12. Therefore, the eight beam spots fall between the two beam spots formed by the two VCSEL elements 14 arranged in the same column and adjacent rows. That is, in the case described above, the seventh
Between the two beam spots formed by the VCSEL elements 14 located in the first row and the eighth row and the first column, all the beam spots (eight) emitted by each VCSEL element 14 in the eighth row are located. It fits without difficulty. However, one beam spot formed by the VCSEL element 14 located at the eighth row and first column, which is the end point, is included in the eight beam spots. Accordingly, when the optical recording medium 12 rotates, eight continuous non-overlapping trajectories can be drawn on the surface thereof, so that information can be recorded or reproduced by eight tracks.

In the VCSEL array 1 having eight rows and eight columns in FIG. 3, a total of 64 laser beams are emitted, so that information can be recorded or reproduced on 64 tracks. Specifically, an image (image) of a beam spot formed when these 64 laser beams enter the grating holographic optical element 2 is composed of 64 beam spots. As described above, this image is narrowed down until it is limited by the diffraction limit when passing through the solid immersion lens 9 of FIG. 1. At this time, the image composed of the 64 beam spots is formed by the VCSEL array 1 or The grating holographic optical element 2
The original image is reduced to the same ratio as it is and irradiated onto the optical recording medium 12. Therefore, even if the size of the laser beam spot is not controlled by the diameter of the output window 15 provided in each VCSEL element 14 of FIG. 3, an image (image) composed of a plurality of beam spots can be obtained by using the solid immersion lens 9. Can be greatly reduced in size.

FIG. 4 is an enlarged view of a main part of the VCSEL array 1. The diameter of the output window 15 or the V
The diameter of each output laser beam of the CSEL array 1 is 1 [μ
m], the output windows 15 are formed so as to be adjacent to each other as much as possible, and when the VCSEL array 1 is tilted by a small angle, the reduced 64 light beams irradiated onto the optical recording medium 12 by the configuration of FIG. If the refractive index is 3.5 and θ in FIG. 2 is 30 degrees when the super hemispheric lens in FIG. 2 is used as the solid immersion lens 9, the wavelength λ of the beam spot image is 0.98 [μ].
m], λ / (2 × n ² ) which is a general optical type
× sin θ), it can be seen that an extremely small image of about 80 [nm] square is obtained. However, the output window 15 is approximately 8 [μ].
m] to 10 [μm] or more.

In FIG. 1 and FIG.
Assuming that the operating wavelength of the EL element 14 is λ, the distance between the surface of the solid immersion lens 9 and the protective film of the optical recording medium 12 is about λ / 4, that is, about 0.25 in this embodiment.
If the distance between the objective lens 7 and the solid immersion lens 9 is controlled so as to be [μm] or less, the 64 laser beams whose beam spot size has been reduced from the principle of near-field (near-field) optics It is possible to reach the recording layer of the optical recording medium 12 without being subjected to reflection loss by the solid immersion lens 9 or the protective film formed on the surface of the optical recording medium 12. for that reason,
Ideally, as shown in FIG. 1, the objective lens actuator 6 and the solid immersion lens actuator 8 are provided, the objective lens 7 and the solid immersion lens 9 are appropriately adjusted in distance, and the beam spot is focused. The distance between the solid immersion lens 9 and the optical recording medium 12 is kept substantially constant. As a result, the solid immersion lens 9 does not contact the uneven surface of the optical recording medium 12 and the optical recording medium 1
2, a high-density track composed of 64 beam spots having a width of about 100 [nm] can be formed, so that a large amount of information can be recorded.
Further, if an image composed of a high-density beam spot reflected from the optical recording medium 12 is traced by the reproduction signal detecting means 10, a large amount of information can be reproduced.

Therefore, the configuration of the optical disk apparatus according to the present invention is similar to that of the contact head system shown in FIG.
The EL array 51 does not need to be brought into contact with the optical recording medium 54, and the distance between the optical recording medium and the objective lens (about 250 [μm]) is maintained at about the same level as in the conventional optical disk apparatus. If possible, it is enough for recording or reproduction.

As a matter of course, a structure in which the distance between the optical recording medium and the objective lens is smaller than about 250 [μm] and is closely adhered from about 100 nm to about 200 nm corresponding to approximately λ / 4 of the wavelength of the laser used. Can be. In a device in which the distance between the optical recording medium and the objective lens is maintained at about 250 [μm], an optical disk can be replaced. In a device in which the distance is approximately 100 nm, such a device as the current hard disk is used. An optical disk as a recording medium is basically realized as a device that cannot be replaced.

In particular, when the present invention is implemented for reproduction only, the output of the laser light emitted from the VCSEL array 1, which is a light source, needs to be weaker than that used for recording. This is because, in the case of reproduction, an output is not necessary to perform pit formation or phase change on the recording layer of the optical recording medium 12.

In this embodiment, the wavelength is about 0.98 [μ
m] is used because the solid immersion lens 9 of this embodiment is made of GaAs, and has a fundamental absorption edge wavelength of about 0.919 [m]. μm],
In the case of Si or InP, the wavelength becomes longer. given that,
The basic absorption edge wavelength used in this embodiment is GaAs.
In the case of the solid immersion lens 9 having an s of about 0.919 [μm], when light having a wavelength shorter than about 0.92 [μm] is transmitted, the light turns black and absorbs the light. It becomes impossible to record or reproduce information on the medium 12. Therefore, in this embodiment, it is necessary to use the VCSEL array 1 which emits a laser beam having a wavelength equal to or longer than the fundamental absorption edge wavelength of the material of the solid immersion lens 9, and preferably, the solid immersion lens 9 9 is made of any material other than GaAs used in this embodiment, which is transparent at least in a wavelength in the infrared region. The VCSEL element 14 does not use a wavelength in the ultraviolet region in order to maintain durability.
2 and the objective lens 7 (approximately 250
[Μm]) while recording or reproducing a large amount of information.

In the optical system shown in FIG. 1, the solid immersion lens 9 as the second objective lens is used.
Is preferably made of GaAs (gallium arsenide), which is a semiconductor material that transmits only infrared rays. When the solid immersion lens 9 is made of such a material, if the wavelength of infrared light of 980 nm is adopted as the oscillation wavelength of each semiconductor laser of the VCSEL element 14, the solid immersion lens 9 is opaque to visible light. The lens 9 can collect the infrared rays in a very small size with little absorption of the infrared rays like a glass lens in the visible light. Here, the solid immersion lens 9 has a radius r of a hemispherical lens as shown in FIG.
This is a super hemispherical lens in which the thickness t0 of the lens is larger than (t0> r), and therefore has the following problem. Therefore, the objective lens 7 as the first objective lens has the following problem.
It is necessary to optimize the lens surface of the lens.

(1) When a plastic aspherical lens used in a compact disk player or a DVD player is used as the first objective lens 7, a commercially available aspherical lens has a wavelength of 780 nm ± 10n.
These lenses are designed to converge a laser beam of this wavelength optimally in the wavelength region of m or in the visible region of 650 nm ± 10 nm.
When used in, a large spherical aberration occurs.

(2) When the thickness t0 of the second objective lens 9 is larger than the radius r of the hemispherical lens, spherical aberration is also generated from the second objective lens 9. In particular, when a GaAs semiconductor material having a large refractive index (refractive index n 3.6 to 3.5) is used as the material of the super hemispherical lens,
Large spherical aberration is generated. That is, the size of the beam waist obtained by the second objective lens is an ideal value (= λ / 2n ² sin) for spherical aberration and field curvature aberration.
θ).

In consideration of the above, the first objective lens 7 as the first objective lens is used to optimize the lens surface so as to correct the aberration of the image plane of the objective lens 9.
It has been found that it is preferable that the aspherical lens as the first objective lens is designed so that the working wavelength and the design wavelength are within a range of ± 10 nm.

A method for optimizing the shapes of the first and second lens surfaces of the first objective lens 7 will be described below with reference to FIG.

That is, as shown in FIG. 6, a plurality of laser beams corresponding to the number of light spots incident on P5 of the first lens surface 41a of the first objective lens 7 When the light is emitted from the second lens surface 41b, the light is emitted from the range indicated by P4. The laser light emitted from the first objective lens 7 is incident on the first lens surface 42a of the second objective lens 9 at P1, and the second lens surface 42b
Through the recording medium layer on the recording surface of the optical disc 12,
It is converged at the beam diameter of Po. Therefore, the optical disk 12
The laser beam passing through the first and second objective lenses 7 and 9 is optimized at points P5 to P1 so that the cross-sectional beam diameter of the laser beam on the recording medium layer on the recording surface becomes Po. The beam diameter at the recording medium layer is
By finding the shape of the lens surface that can be set to o,
The influence of the spherical aberration by the second objective lens 9 can be removed.

More specifically, the first lens surface 42a of the second objective lens 9 is a spherical surface defined by a radius of curvature r,
Since the second lens surface 42b is a flat surface, the lens surfaces that can be used for removing spherical aberration are the first lens surface 41a and the second lens surface 41b of the first objective lens 7. . Therefore, the two lens surfaces 41a and 4
1b, a radius of curvature Rc defining a lens surface is determined for each position where a laser beam passes, and a conditional expression capable of reproducing the radius of curvature Rc at an arbitrary position on the lens surface is defined as the shape of the lens surface. , A condition indicating the shape of the lens surface (aspheric surface) can be obtained. Actually, the direction in which the laser beam travels is indicated by the Z-axis direction, and the direction of the recording surface of the optical disc 12 is indicated by two-dimensional coordinates including the X axis and the Y axis, respectively.
With the recording area layer of the recording surface of the optical disk 12 as the origin, the shape of each lens surface will be considered based on the position (Z-axis direction) of each lens surface.

In FIG. 6, reference numeral 12a denotes a protective film of the optical disk, and the optical path length of the air gap from the flat surface of the second objective lens 9 including the protective film 12a to the recording surface of the disk, that is, The optical length g is set to be smaller than λ / 4 (g <λ / 4).

In FIG. 6, the first of the second objective lens 9
Of the lens surface 42a of the optical disk D farthest from the recording area layer (the top of the first lens surface 42a, X
= 0, Y = 0) and the recording area layer, TD,
The position of the objective lens 9 farthest from the optical disk 12 (the top of the first lens surface 42a; X = 0, Y = 0) and the position of the first objective lens 7 closest to the optical disk D (the second lens The distance between the top of the surface 41b; X = 0, Y = 0) is WD, and in the first objective lens 7, the top of the first lens surface 41a (X = 0, Y = 0) and the second The distance between the top of the lens surface 41b (X = 0, Y = 0), that is, the thickness of the first objective lens 7 in the optical axis (Z-axis) direction is represented by T
When S is replaced by coordinates in the Z-axis direction, Z1 = TD, Z2 = TD + WD, and Z4 = TD + WD + TS.

Here, the ray vector A1 (11, n1)
^{Is, l1 = X1 / (X1 2} + Z1 2) 1/2 n1 = Z1 / (X1 2 + Z1 2) 1/2 The maximum value L1max of l1 is, L1max =
Since NA / nD, the maximum value X1max of X1 is: X1max = (NA · TD / nD) / (1− (NA /
nD) ² ) ^1/2 .

Next, the ray vector A2 (l2, n2)
Is, l2 = (X2-X1) / [(X2-X1) 2 + (Z
^{2-Z1) 2] 1/2 n1} = (Z2-Z1) / [(X2-X1) 2 + (Z
2-Z1) ² ] ^1/2 .

On the other hand, from the law of refraction, since l2 = nD · l1, X2 is calculated as follows: X2 = X1 + [nD · l1 (Z2-Z1)] / (1
−nD2 · 112) ^1/2 .

Next, in order to obtain P3 (X3, Z3), if X3 = X2 + 12.ΔZ3 = Z2 + n2.Δ is defined, Δ = F / [G + (G2-F / Rc) ^{1 / 2} ] where F = X22 / Rc, G = n2- (l2 / X2 /
Rc).

Next, considering refraction on a spherical surface, the ray vector A3 (13, n3) is calculated as follows: l3 = (l2-K.X3) / nsn3 = [n2-K (Z3-Z2-Rc)] ns K is: K = 1 / RC [(ns2-1 + G2-F / Rc)
¹ / 2- (G2-F / Rc) ^1/2 ].

Hereinafter, P4 is a ray vector A3 (13,
n3), it can be expressed as X4 = X3 + Δ '· L3 Z4 = Z3 + Δ' · n3. From Z4, X4 becomes X4 = X3 + 13 (Z4-Z3) / n3.

As described above, the coordinates (Xn, Yn to Xn) of each laser beam crossing the first and second lens surfaces 41a and 41b of the first objective lens 7 respectively.
n, Yn). The optical path length L is L = L1 + L2 + L3, respectively, L1 = nd (X12 + Z12 ), L2 = [(X3-X1) 2 + (Z3-Z
^{1) 2] 1/2, L3 =} n3 [(Z4-X3) 2 + (Z4-Z3) 2]
^1/2 , where X4 = rm and Z4 = mλ, so that L− (nd · TD + WD + ns · TS) =
From mλ, the radius of the grating ring at each of m = 0, 1, 2,..., in other words, the radius of the aspherical surface can be obtained.

As described above, by obtaining "X1" and obtaining "X4" using "X1", each radius of curvature Rc of the m-th lens surface can be obtained. An optimized lens surface can be determined by obtaining these radii of curvature Rc one after another by computer analysis.

The lens surface of the objective lens 7 can be optimized by obtaining each radius of curvature Rc as described above. By optimizing the lens surface of the objective lens 7, many light spots of the VCSEL array 1 as a surface light source are imaged with a large number of minute beam spots on the recording surface without causing spherical aberration and field curvature aberration. Can be projected as

Here, the VCSEL array 1 is not limited to the case where a large number of VCSEL elements are formed on one semiconductor substrate. The structure may be such that they are arranged in an array. When such an edge emitting semiconductor laser is used, the reproduction signal generating means
Naturally, it is composed of a light detection array having a detection sensitivity corresponding to the oscillation wavelength of the semiconductor laser.

In the above-described embodiment, the VCS
EL array 1 is made of gallium nitride (GaN) or II-V
A laser that emits a laser in the blue and ultraviolet regions made of a Group I compound semiconductor may be used.
Glass or a polymer material that transmits a light wave of 50 to 300 nm) is selected as the material of the solid immersion lens as the second objective lens 9, and as described above, the first objective lens is provided for the second objective lens 9. The lens 7 may be optimized.

[0054]

According to the first aspect of the present invention, the vertical cavity surface emitting semiconductor laser array 1 in which the vertical cavity surface emitting semiconductor laser elements 14 are arranged in a lattice, and the vertical cavity surface emitting semiconductor laser array 1 are provided. Irradiates the optical recording medium 12 with the laser light emitted by the optical recording medium 1 and
A solid immersion lens 9 for receiving the light reflected from the optical recording medium 2 and reproduction signal detecting means 10 for detecting the light reflected from the optical recording medium 12 as a reproduction signal; Since the laser array 1 is an optical disk device that is inclined at a small angle with respect to the tangential direction of rotation of the optical recording medium 12, the laser beam emitted from the VCSEL array 1 is not directly irradiated as in the contact head system. Since the solid immersion lens 9 is used, a very small beam spot can be formed on the optical recording medium 12 by irradiating the optical spot on the optical recording medium 12 as a reduced image. This has the effect that information of a remarkable capacity can be recorded or reproduced on the conventional optical recording medium 12.

Further, in the invention of claim 2, according to claim 1, the vertical cavity surface emitting semiconductor laser array 1 is an optical disk device which emits laser light having a wavelength equivalent to that of an infrared region. As a result, it is not necessary to bring the wavelength used closer to the ultraviolet region (shortening) as in the prior art, so that the semiconductor laser as a light source, that is, in the present invention, the durability of the VCSEL array 1 is not shortened unnecessarily, and the optical disk device is durable. There are advantages that can be used. Similarly, since the distance from the optical recording medium surface 12 to the surface of the solid immersion lens 9 does not need to be short as in the related art, there is a concern that the surface of the solid immersion lens 9 may contact the protective film of the optical recording medium 12 or the like. Therefore, even if the protective film of the optical recording medium 12 has some irregularities, there is an advantage that a large amount of information can be recorded or reproduced without being affected by the irregularities.

Further, in the third aspect of the present invention, in the first aspect, the vertical cavity surface emitting semiconductor laser array 1 emits laser light having a wavelength longer than or equal to the fundamental absorption edge wavelength of GaAs. In particular, the solid immersion lens 9 has a G
In the case of using aAs, it is not necessary to bring the wavelength used closer to the ultraviolet region (shortening) as in the prior art.
There is an advantage that the optical disk device can be used with high durability without unnecessarily shortening the life of the array 1. Similarly, the distance from the optical recording medium surface 12 to the surface of the solid immersion lens 9 does not need to be as short as in the related art, so that the surface of the solid immersion lens 9 may be in contact with the protective film or the like of the optical recording medium 12. In addition, even if the protective film of the optical recording medium 12 has some irregularities, there is an advantage that a large amount of information can be recorded or reproduced without being affected by the irregularities.

Further, according to the invention of claim 4, according to claims 1 and 2,
Or 3, in which the solid immersion lens 9 is an optical disk device made of a material that is transparent at a wavelength equivalent to the infrared region, so that the oscillation efficiency and oscillation output of the VCSEL element 14 are most stable at present. 0.98 [μm] and the wavelength in the infrared region around it can be used, and there is an advantage that the optical disk device according to the present invention can be manufactured at extremely low cost by using existing facilities and the like.

According to the fifth aspect of the present invention, the first aspect is provided.
5. In the above 2, 3, or 4, the solid immersion lens 9 is an optical disk device made of a material that is transparent at a wavelength longer than or equal to the GaAs fundamental absorption edge wavelength. An output laser wavelength of 0.98 [μm], which is considered to have the most stable efficiency and oscillation output, can be used, and the optical disk device according to the present invention can be manufactured at extremely low cost using existing equipment. is there.

Further, according to the invention of claim 6, according to claim 1,
2, 3, 4, or 5, wherein the solid immersion lens 9 is an optical disk device made of GaAs, so that the output laser whose oscillation efficiency and oscillation output of the VCSEL element 14 are the most stable at the present time is considered. The wavelength of 0.98 [μm] can be used, and there is an advantage that the optical disk device according to the present invention can be manufactured at extremely low cost using existing facilities and the like.

Further, according to the invention of claim 7, according to claim 1,
In 2, 3, 4, 5, or 6, the solid immersion joy lens 9 is an optical disk device including a super hemispherical lens, so that the laser light can be refracted more than when a hemispherical lens is used. , Resulting in a smaller beam spot image,
It is possible to dramatically record or reproduce a large amount of information.

Further, in the invention of claim 8, according to claim 1,
2, 3, 4, 5, 6, or 7, wherein the solid immersion lens 9 is an optical disk device whose focus is controlled by a solid immersion lens actuator 8, so that the optical recording medium fluctuates in the optical axis direction. In such a case, the focus of the beam spot can be accurately and instantaneously adjusted, so that the information transfer bit error rate can be kept good, and a large amount of information can be recorded or reproduced with high reliability.

According to a ninth aspect of the present invention, a vertical cavity surface emitting semiconductor laser array in which vertical cavity surface emitting semiconductor laser elements are arranged in a grid pattern, and a laser beam emitted by the vertical cavity surface emitting semiconductor laser array And an objective lens system for irradiating the optical recording medium with light and receiving light reflected from the optical recording medium, and reproduction signal detection means for detecting the light reflected from the optical recording medium as a reproduction signal, In an optical disk drive, wherein the vertical cavity surface emitting semiconductor laser array is inclined at a small angle with respect to a tangential direction of rotation of the optical recording medium, the objective lens optical system comprises a laser beam from the vertical cavity surface emitting semiconductor laser array. A first objective lens for converting the collimated laser light into a convergent laser light again, and exiting the first lens. A second objective lens that further converges the laser light, wherein the second objective lens is a hemispherical lens having a thickness t of the lens larger than a radius r defining the lens surface. The first lens is an aspheric lens in which both the light entrance surface and the light exit surface are aspheric, and the lens surface substantially corrects the second spherical aberration and the field curvature aberration. Since the optical disk device is fixed to the surface, the laser beam emitted from the VCSEL array 1 is not directly irradiated as in the contact head method, but the image in which the beam spot is reduced due to the use of the solid immersion lens 9 is used. By irradiating the optical recording medium 12 with a light beam, an extremely small beam spot can be formed on the optical recording medium 12 as compared with the related art. An effect that can record or reproduce the amount of information in the conventional optical recording medium 12. Moreover, it is possible to prevent spherical aberration and field curvature aberration from occurring in a minute beam spot, and to reduce the size to a size close to an ideal size. In other words, the vertical cavity surface emitting semiconductor laser device is not a point light source,
As described above, this is a kind of surface light source in which a large number of point light sources are arranged in a plane having a certain area, and this may cause field curvature aberration at the focal point of the solid immersion lens. Since the first objective lens capable of correcting the field curvature aberration of the solid immersion lens as the objective lens is provided, the image of the planar point light source is converted into spherical aberration and field curvature aberration. Can be formed on the recording surface without any Further, by providing a collimator lens between the objective lens and the vertical cavity surface emitting semiconductor laser element as a light source, a laser beam is collimated from the light source and is incident on the objective lens. This also reduces the field curvature aberration.

According to a tenth aspect of the present invention, in the ninth aspect, the vertical cavity surface emitting semiconductor laser array generates a laser beam in a substantially infrared region, and the second objective lens transmits the laser beam in the infrared region. Since the optical disk device is made of a transparent material, it is possible to effectively transmit light energy to a recording medium.

According to an eleventh aspect of the present invention, in the ninth aspect, the vertical cavity surface emitting semiconductor laser array generates laser light in a blue to near ultraviolet range, and the second objective lens emits the blue to near ultraviolet range. Since the region is made of a material that transmits laser light, light energy can be effectively transmitted to the recording medium. An optical disc device characterized by the above-mentioned.

According to a twelfth aspect of the present invention, in the ninth aspect, the vertical cavity surface emitting semiconductor laser array has a structure in which edge emitting semiconductor lasers are arranged such that light emitting surfaces thereof are arrayed. Since the signal detecting means includes a photodetector array corresponding to laser oscillation generated from the edge emitting semiconductor laser, the vertical cavity surface emitting semiconductor laser array can be easily realized from current technology, A high-density recording device and a reproducing device can be easily realized.

[Brief description of the drawings]

FIG. 1 is an optical principle diagram of an optical disk device according to the present invention.

FIG. 2 (A) is a state diagram of light traveling when the solid immersion lens is a hemispherical lens. FIG. 2 (B) is a state diagram of light traveling when the solid immersion lens is a super hemispherical lens.

FIG. 3 is a perspective view of an 8 × 8 VCSEL array according to the present invention.

FIG. 4 is an enlarged view of a principal part of the VCSEL array.

FIG. 5 is a diagram showing an optical recording medium contact mode of a contact head type optical memory head.

FIG. 6 is a view for explaining a method of optimizing a curved surface of the objective lens shown in FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Vertical cavity surface emitting semiconductor laser array 8 ... Solid immersion lens actuator 9 ... Solid immersion lens 10 ... Reproduction signal detecting means 12 ... Optical recording medium 14 ... Vertical cavity surface emitting semiconductor laser element

Claims (12)

[Claims] 1. A vertical cavity surface emitting semiconductor laser array in which vertical cavity surface emitting semiconductor laser elements are arranged in a lattice, and a laser beam emitted by the vertical cavity surface emitting semiconductor laser array is applied to an optical recording medium. A solid immersion lens for irradiating and receiving light reflected from the optical recording medium, and reproduction signal detecting means for detecting the light reflected from the optical recording medium as a reproduction signal; An optical disk device, wherein the cavity surface emitting semiconductor laser array is inclined at a small angle with respect to a tangential direction of rotation of the optical recording medium. 2. The optical disk apparatus according to claim 1, wherein said vertical cavity surface emitting semiconductor laser array emits laser light having a wavelength equivalent to that of an infrared region. 3. The optical disk apparatus according to claim 1, wherein said vertical cavity surface emitting semiconductor laser array emits laser light having a wavelength longer than or equal to a fundamental absorption edge wavelength of GaAs. 4. The optical disk device according to claim 1, wherein said solid immersion lens is made of a material which is transparent at a wavelength equivalent to an infrared region. 5. The method according to claim 1, wherein the solid immersion lens is GaAs.
2. A material which is transparent at a wavelength longer than or equal to the fundamental absorption edge wavelength of s.
2, 3 or 4 optical disk devices. 6. The solid immersion lens is made of GaAs.
6. The optical disk device according to claim 1, wherein the optical disk device comprises s. 7. The solid immersion lens according to claim 1, wherein said solid immersion lens comprises a super hemispherical lens.
2, 3, 4, 5 or 6 optical disk devices. 8. The optical disk drive according to claim 1, wherein the focus of said solid immersion lens is controlled by a solid immersion lens actuator. 9. A vertical cavity surface emitting semiconductor laser array in which vertical cavity surface emitting semiconductor laser elements are arranged in a lattice, and a laser beam emitted by the vertical cavity surface emitting semiconductor laser array is applied to an optical recording medium. An objective lens system for irradiating and receiving light reflected from the optical recording medium, and reproduction signal detecting means for detecting the light reflected from the optical recording medium as a reproduction signal; In an optical disk drive wherein the surface emitting semiconductor laser array is tilted by a small angle with respect to the tangential direction of rotation of the optical recording medium, the objective lens optical system is formed by collimating laser light from a vertical cavity surface emitting semiconductor laser array. A first objective lens for converting the laser light into a convergent laser light again, and a laser emitted from the first lens A second objective lens for further converging, consists, the second objective lens is a large hemispherical lens than the radius r of the thickness t of the lens defines its lens surface,
The first lens is an aspheric lens in which both a light incident surface and a light exit surface are aspheric, and the lens surface is a surface that substantially corrects a second spherical aberration. An optical disk device characterized by being used. 10. The vertical cavity surface emitting semiconductor laser array generates a laser beam in a substantially infrared region, and
10. The optical disk device according to claim 9, wherein the objective lens is made of a material that transmits the laser light in the infrared region. 11. The vertical cavity surface emitting semiconductor laser array generates laser light in a blue to near ultraviolet region,
10. The optical disk device according to claim 9, wherein the second objective lens is made of a material that transmits the laser light in the blue to near ultraviolet range. 12. The vertical cavity surface emitting semiconductor laser array has a structure in which edge emitting semiconductor lasers are arranged so that light emitting surfaces thereof are arrayed, and the reproduced signal detecting means includes an edge emitting semiconductor laser. 10. The optical disk device according to claim 9, further comprising a photodetector array corresponding to laser oscillation generated by a laser.