JP3288733B2 - Optical disk device for recording - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk apparatus using a diffusion optical system for an optical head, and more particularly to an optical disk apparatus capable of overwriting.

[0002]

2. Description of the Related Art As an optical disk apparatus using a conventional diffusion optical system, there is a reproduction-only apparatus such as a compact disk (CD).

[0003] Regarding an optical head of a diffusion optical system used for a CD, for example, Shigeo Kubota, "Small, lightweight and simplified optical disk pickup", Optics Vol.
) Has been put to practical use. Light emitted from a semiconductor laser as a light source is guided to an objective lens by a half mirror, and is focused on an optical disk. The light reflected from the optical disk is
It is detected by a detector through a half mirror. Such an optical system from a semiconductor laser to an objective lens is not referred to as a parallel light because the light is not made into parallel light.

[0004]

SUMMARY OF THE INVENTION In an optical disk device,
Rotational shake due to rotation of optical disk (runout and eccentricity)
Exists. For this reason, a focus control mechanism for constantly adjusting the light condensing point to the recording surface of the optical disk and a tracking control mechanism for controlling light to follow the same track are required. Focusing and tracking are performed by moving the objective lens in two axial directions with a two-dimensional actuator.
A signal for this control needs to be obtained from the light reflected from the optical disk.

However, in the diffusion optical system, since the lens is moved in the diffused light, aberration occurs due to focusing and tracking, and the light cannot be sufficiently focused. Further, there is a problem that the collected light is deformed. further,
The diffusion optical system has a problem that the light utilization efficiency changes and the light energy on the recording surface changes. For this reason,
A diffusion optical system cannot be used in an optical disk device such as a write-once type or rewritable type device that requires a large light energy on the recording surface of the optical disk.

An object of the present invention is to provide an optical disk device that can be overwritten using a diffusion optical system.

[0007]

According to the present invention, there is provided an optical disk apparatus having a diameter of 1 to which light emitted from a light source is incident as diffused light.
An optical head having an objective lens of up to 4 mm and recording at least information on a disc with light collected by the objective lens is mounted.

Also, the optical disk apparatus of the present invention comprises a light source, an objective lens for condensing light on the disk, a beam splitter for guiding light from the light source to the objective lens as diffused light, the beam splitter and the objective lens And a λ / 4 plate for polarizing light on an optical path between the optical head and the optical head.

[0009] The optical disk apparatus of the present invention is an optical memory in which an optical recording medium for storing information formed on a disk substrate having transparency to light is rotatably housed so as to restrict vertical rotation shake. Irradiating the optical recording medium with light condensed by an objective lens having a diameter of 1 to 4 mm, the light being irradiated as diffused light, and recording information on the optical recording medium; An optical head for performing at least one of reproducing information recorded on a medium and erasing information recorded on the optical recording medium; and positioning the optical memory in a predetermined relationship with the optical head. And a rotation circuit for rotating the optical recording medium, and a drive circuit for controlling the operation of the optical head and the rotation of the rotation means.

An optical disk apparatus according to the present invention comprises: an optical head that collects incident light as light diffused from a light source and irradiates the disk with light to record at least information; and means for rotating the disk. Means for suppressing rotational fluctuation of the disk due to rotation; means for accommodating the disk in a recordable positional relationship with respect to the optical head; and a drive circuit for controlling the operation of the optical head and the rotation of the rotating means. And

Further, the optical disk device of the present invention can rotate an optical recording medium for storing information formed on a disk substrate having a light-transmitting property so as to restrict rotational shake in a vertical direction. Irradiates the optical recording medium with light condensed by an objective lens having a diameter of 1 to 4 mm, which irradiates light as diffused light, and records information on the optical recording medium. An optical head for performing at least one of the following operations: reproducing information recorded on the optical recording medium; and erasing information recorded on the optical recording medium; Means for accommodating the optical recording medium at a predetermined position relative to the head; rotating means for rotating the optical recording medium; and a drive circuit for controlling the operation of the optical head and the rotation of the rotating means.

[0012] It is preferable that the case has a portion having a light transmitting property, and information is recorded, reproduced and / or erased by light irradiated through the portion.

Further, the optical disk device of the present invention is capable of rotating an optical recording medium for storing information formed on a disk substrate having a light transmission property in a vertical direction of 0.10 to 0.1.
Works for optical memory stored to be 25mm,
An objective lens that emits light from a light source as diffused light.
Condensing light and irradiating the optical recording medium to record information on the optical recording medium; reproducing information recorded on the optical recording medium; and recording information recorded on the optical recording medium. Performing at least one of erasing, an optical head having an optical path distance between the light source and the objective lens of 5 to 20 mm, means for housing the optical memory in a predetermined relationship with the optical head, A rotation unit for rotating the optical recording medium; and a drive circuit for controlling the operation of the optical head and the rotation of the rotation unit.

Further, the optical disk device of the present invention functions for an optical memory in which an optical recording medium for storing information formed on a disk substrate having a light transmitting property is rotatably housed. Irradiating the optical recording medium with light condensed by an objective lens having a diameter of 1 to 4 mm, which is irradiated as diffused light, and 25 to 5 of light emitted from the light source.
An optical head for recording, reproducing and / or erasing information by irradiating the optical recording medium with 0% light; a means for accommodating the optical memory at a predetermined position relative to the optical head; Rotating means for rotating the optical head, a drive circuit for controlling the operation of the optical head and the rotation of the rotating means,
Having.

Further, the optical disk apparatus of the present invention functions for an optical memory in which an optical recording medium for storing information formed on a disk substrate having a light transmitting property is rotatably housed. Is operated in the range of 0.25 to 1.00 mm by irradiating an object lens as diffusion, and the light is condensed and irradiated on the optical recording medium, and 25 to 50% of the light emitted from the light source. An optical head for recording, reproducing, and / or erasing information by irradiating the optical recording medium with light, a unit for storing the optical memory at a predetermined position relative to the optical head, and rotating the optical recording medium. And a drive circuit for controlling the operation of the optical head and the rotation of the rotating means.

Further, the optical disk apparatus of the present invention can rotate an optical recording medium for storing information formed on a disk substrate having a light transmitting property, and an optical recording medium for storing information rotatably stored therein. Function as to the optical memory housed in the storage area, and the numerical aperture for irradiating light as diffused light is 0.5 to 0.5.
An optical head for operating the objective lens of No. 6 in the range of 0.25 to 1.00 mm, condensing light and irradiating the optical recording medium, and recording, reproducing and / or erasing information; and the optical memory And a drive circuit for controlling the operation of the optical head and the rotation of the rotating means.

Further, the optical disk device of the present invention functions for an optical memory in which an optical recording medium for storing information formed on a disk substrate having a light transmitting property is rotatably housed, and a light of a certain wavelength is provided. Is condensed by an objective lens having a constant numerical aperture, which is irradiated as diffused light, and irradiates the optical recording medium to record, reproduce, and / or erase information. The ratio between the wavelength and the numerical aperture is 0. .65 to 1.66, means for accommodating the optical memory in a predetermined relationship with the optical head, rotating means for rotating the optical recording medium, operation of the optical head, and operation of the rotating means. A drive circuit for controlling rotation.

Further, the optical disk device of the present invention functions as an optical memory that rotatably stores an optical recording medium for storing information formed on a disk substrate having a light-transmitting property. Magnification is 0.20
An optical head for recording, reproducing, and / or erasing information by condensing light with an objective lens of 0.35 and irradiating the optical recording medium with a light intensity of 5 to 25 mW; The apparatus includes means for accommodating the optical recording medium at a predetermined position, rotation means for rotating the optical recording medium, and a drive circuit for controlling the operation of the optical head and the rotation of the rotation means.

Also, the optical disk apparatus of the present invention condenses diffused light from a light source on an optical disk and at least records information, an optical head for rotating the disk, and suppresses vibration caused by the rotation. Means for accommodating the disc holding information at a predetermined relative position with respect to the head, and a drive circuit for controlling the operation of the head and the rotating means. .

The optical head used in the optical disk apparatus of the present invention comprises a light source comprising a semiconductor laser or the like, an objective lens for condensing diffused light emitted from the light source on the optical disk,
An optical separator for guiding the light reflected by the optical disc to the photodetector, a photodetector for detecting the light reflected by the optical disc,
It is preferable to have

As the semiconductor laser used in the present invention, a wavelength of 400 to 850 nm, an output of 10 to 50 mW, and a light diffusion angle of 8 to 32 ° are preferably selected and used as appropriate.

The objective lens used in the present invention has a numerical aperture of 0.5 to 0.6 on the optical disk side and a numerical aperture of 0.1 to 0.1 on the light source side.
18, a magnification of 0.2 to 0.35, an effective diameter of 1 to 4 mm and the like are suitably selected and used.

As the light separator used in the present invention, it is preferable to use a polarizing beam splitter and a quarter wavelength (λ / 4) plate, or to use a half mirror.

When a half mirror is used as the light separator, the reflectance is R and the transmittance is T. When light from the light source is reflected by the half mirror and reaches the optical disk, the relationship of R ≧ T is satisfied. When the light from the light source passes through the half mirror and reaches the optical disk, it is preferable to satisfy the relationship of R ≦ T.

In addition, it is preferable to suppress the converged light on the disk from forming a recording spot with respect to the surface vibration of the disk caused by the rotation.

Further, the optical disk apparatus of the present invention focuses the diffused light from the light source on the optical disk, and at least records the information, an optical head for rotating the disk, and suppresses the shake accompanying the rotation. Means, means for accommodating the disk at a predetermined relative position with respect to the head, and a drive circuit for controlling operations of the head and the rotating means.

According to the present invention, it is possible to use a diffusion optical system for an optical head, to reduce the amount of surface vibration or eccentricity of an optical disk, and to increase the light use efficiency.

By using the method of the present invention for reducing the amount of surface vibration or eccentricity of an optical disk, an optical disk device recordable by an optical head using a diffusion optical system can be realized.

As one method of reducing the amount of surface vibration, the optical disk is placed in a case, the distance between the case and the optical disk is reduced, and the optical disk is not physically shaken beyond this distance.

Alternatively, it is preferable that a device for inserting the optical disk be provided with a retainer for limiting surface runout. By doing so, the amount of surface vibration of the optical disk can be limited.

Further, by providing a projection or a groove for preventing eccentricity on at least one of the case and the optical disk, the amount of eccentricity can be limited.

Alternatively, a frame may be provided in the optical disk device to limit the amount of eccentricity. By doing so, the amount of eccentricity can be limited.

Further, when the flatness of the disk is good or the warp is small, when the shaft of a drive device for rotating the disk is small, when the surface of the disk is small, and when the position of the track center and the rotation center If the position coincides, the shaft deflection of the rotary drive device is small, and the standard amount of wobble and eccentricity is satisfied, the present invention can be implemented without using a mechanism for limiting the amount of wobble and eccentricity. An optical head using a diffusion optical system can be used.

Further, the optical disk apparatus of the present invention functions for an optical disk which is housed in a case having a transparent portion and holds information by light illuminated through the transparent portion of the case, and diffuses light from a light source. An optical head that focuses light on a disk and guides light reflected by the disk to a photodetector to perform at least one of recording, reproducing, and erasing of information; and housing the disk at a predetermined position relative to the head. And means for performing the operation.

Further, in the present invention, it is preferable to form a flexible support member between the optical disk and the case, and it is preferable that the support member and the optical disk rotate while being in contact with each other.

By rotating the optical disk in contact with the support member, stable rotation of the optical disk can be achieved, and dust and the like attached to the recording portion of the optical disk can be prevented.

Further, it is possible to provide a projection on the optical disk to stably rotate the optical disk and prevent surface runout.

When the optical disk is housed in a case, an opening may be provided in the case to irradiate the light emitted from the light source onto the optical disk, and the case may be provided with a transparent portion to provide the light. Irradiation may be performed.

The light-transmitting optical member constituting the transparent portion is preferably a light-transmitting material such as glass, polycarbonate (PC), and polymethyl methacrylate (PMMA).

Even if the entire transparent case is formed of a light-transmitting material, only the portion corresponding to the optical head is formed of a light-transmitting material, and the other portions are made of a light-transmitting material. It may be formed of a material that is not used.

The objective lens used in the present invention is designed in consideration of the optical thickness of an optical member such as a substrate existing up to the recording surface of the optical disk. Therefore, when light is incident through the optical member forming the transparent portion of the case, the design is made in consideration of the thickness of the optical member and the substrate of the optical disk. Therefore, when a conventional objective lens is used, it is preferable to make the thickness of the optical member and the substrate of the optical disk equal to the thickness of the conventional optical disk substrate. In the case of the present invention, since there is a case in addition to the substrate of the optical disk, light is incident through the case, so that the substrate of the optical disk can be made thinner when a conventional objective lens is used.

Also, the optical disk device of the present invention holds information while rotating, and the shake accompanying the rotation is 0.25 mm.
The following functions for an optical disk and collects at least the information on the disk by condensing a diffused light from a light source on a lens, and an optical path distance between the light source and the lens is 5 to 20 mm. An optical head, means for rotating the disk, and means for accommodating the disk at a predetermined relative position with respect to the head are provided.

The amount of run-out due to rotation of the optical disk according to the present invention can be determined, for example, by the method described in "Key Points of Optical Disk Process Technology", supervised by Yoshihiro Okino, pages 166 to 172 (edited by Hitachi Industrial Technology Center). Stipulated.

In order to increase the light use efficiency in the diffusion optical system, it is preferable to reduce the distance between the light source and the objective lens.

Further, the optical disk apparatus of the present invention functions for an optical disk that holds information while rotating, and that diffuses light from a light source with a numerical aperture of 0.5 to 0.6 and a working distance of 0. An optical head for recording at least the information on the disc by condensing the light with a lens having a diameter of 0.25 to 1.0 mm; a means for rotating the disc; Means for housing.

Here, the relationship between the numerical aperture and the beam (light) diameter will be described. The distance from the principal point of the lens to the recording surface of the optical disk is f, the radius of the lens is D, and the relationship between these and the optical disk side numerical aperture NA is: NA = D / f. The beam diameter d at the focal point is determined by the numerical aperture NA of the optical disk and the wavelength λ of the beam, and at the diffraction limit, d = λ / NA.

When recording, reproducing or erasing information using an optical head, it is necessary to keep the beam diameter constant. Therefore, it is preferable to keep the numerical aperture NA of the lens constant. It can be seen that the lens diameter D decreases when the focal length f is reduced while maintaining a constant.

In order to obtain compatibility with the conventional apparatus, it is necessary to make the beam diameter the same, and when a semiconductor laser having a wavelength of 830 nm is used as a light source, the numerical aperture NA must be 0.5 or more. Understand. It can be seen that when the numerical aperture NA is increased and the beam diameter d is reduced, the energy density increases, and recording can be performed with less film surface power.

As the numerical aperture NA increases, the aberration increases due to the movement of the lens during focusing and tracking. In addition, considering the lens manufacturing conditions, the upper limit of the effective numerical aperture NA of the lens on the optical disk is 0.6. preferable.

Even if the wavelength λ is shortened, the beam diameter d can be reduced, which is preferable for recording.

As the light source, a semiconductor laser having a wavelength of 780 to 830 nm or a light source of 390 to 415 nm whose wavelength is halved by the second harmonic can be used.
At this time, the beam diameter d is preferably 0.65 μm to 1.66 μm.

The numerical aperture on the light source side of the objective lens is
0.1 or more is necessary, and the higher the numerical aperture, the higher the light use efficiency. Considering that the light emitted from the semiconductor laser is elliptical and that the intensity distribution of the light from the light source can be formed in the objective lens, and that the manufacturing conditions of the lens are taken into consideration, the numerical aperture on the light source side is preferably 0.18 or less.

The light use efficiency at the numerical aperture of 0.18 on the light source side is 50%. Since the divergence angle of the semiconductor laser beam depends on the type of laser, it can be seen that the same light use efficiency can be obtained by using an objective lens having a small numerical aperture on the light source side if a semiconductor laser having a small divergence angle is used.

When the magnification of the objective lens is m and the distance A from the objective lens to the light condensing point and the distance from the light source to the objective lens are B, there is a relationship of A = mB. The distance A between the objective lens and the optical disk is determined by the amount of surface wobble of the optical disk, and A and B are large for an optical disk having a large amount of wobble. That is, the size of the optical head can be determined by the amount of surface vibration of the disk.

Further, it is preferable to increase the numerical aperture on the light source side in order to increase the light use efficiency in the diffusion optical system as in the present invention.

When the numerical aperture is increased, the aberration caused by the displacement of the objective lens when focusing and tracking are performed becomes larger than when the numerical aperture is small. The change in light use efficiency is also large.

In the present invention, the amount of movement of the objective lens during focusing and tracking can be reduced even if the numerical aperture of the light source of the objective lens is increased by reducing the amount of surface vibration or the amount of eccentricity. The aberration can be made equal to that of the conventional optical system. Therefore, the light use efficiency of the diffusion optical system can be increased, and the light can be used for a recordable optical head.

The light use efficiency of the diffusion optical system can be determined by the numerical aperture and magnification of the objective lens on the optical disk side.

The relationship between the magnification m and the light use efficiency in the diffusion optical system will be described. The magnification m is expressed as m = NA ₂ / NA ₁ by the numerical aperture NA _{2 of the} lens viewed from the light source and the numerical aperture NA _{1 of} the lens viewed from the optical disk side.

Here, NA ₁ = 0.52, and the spread of light in the direction parallel to the bonding surface of the semiconductor laser as the light source is θ // = 1.
The light use efficiency was calculated assuming that the light spread in the vertical direction was 1 °, and θ⊥ = 25 °. When an inorganic material is used for a recording film of an optical disc, a power of 10 mW or more is required for recording. In order to use a semiconductor laser having a power of 40 mW as a light source, a light use efficiency of 25% or more is required. is there. Calculations show that a magnification m of 0.2 or more is necessary to obtain a light utilization efficiency of 25% or more.

The working distance of the lens will be described.

When the optical disk is housed in a case and light enters through the optical member, there is a case between the objective lens and the optical disk, and there is no possibility that the rotating optical disk and the objective lens come into direct contact with each other. The distance (working distance) between the objective lens and the optical disk can be reduced. Corresponding to the surface vibration amount of 0.25 mm or less,
The working distance is preferably 0.25 mm or more and 1 mm or less.

By reducing the working distance, the distance between the principal point of the lens and the focal point can be reduced. In the present invention, since the amount of surface vibration can be set to ± 0.5 mm or less, the distance from the principal point of the lens to the recording surface of the optical disk can be set to 4 mm or less, and the objective with a magnification of 0.2 can be used. Even if a lens is used, the distance between the light source and the lens can be made 20 mm or less.

The optical disk apparatus of the present invention functions for an optical disk that holds information while rotating, and collects the diffused light from a light source of a fixed wavelength by a lens with a fixed numerical aperture, so that the information is recorded on the disk. At least
An optical head having a ratio of the wavelength to the numerical aperture of 0.65 to 1.66 μm and a light use efficiency of 25 to 50%, and the disk being housed in a predetermined relative position with respect to the head And means for performing the operation.

The optical disk apparatus of the present invention holds information while rotating, and functions for an optical disk in which the shake caused by the rotation is 0.25 mm or less, and diffuses light from a light source with a diameter of 1 to 4 mm. An optical head for recording at least the information on the disk by irradiating the disk with 25-50% of the light emitted from the light source and condensing the light by a lens, and means for rotating the disk When,
Means for accommodating the disk at a predetermined relative position with respect to the head.

The optical disk device of the present invention holds information while rotating, and functions for an optical disk having a shake of 0.25 mm or less due to the rotation, and diffuses light from a light source at a working distance of 0.25 mm. An optical head for recording at least the information on the disk by condensing light with a lens having a diameter of about 1.0 mm, means for rotating the disk, and housing the disk at a predetermined position relative to the head Means.

The optical disk apparatus of the present invention functions for an optical disk that holds information while rotating, and uses a lens having a magnification of 0.2 to 0.35 to diffuse light from a light source. By focusing at 5-25mW,
An optical head for recording at least the information, and means for accommodating the disk at a predetermined relative position with respect to the head are provided.

An optical head according to the present invention irradiates an optical disk with diffused light from a light source and guides light reflected by the disk to a photodetector, and a light separator between the separator and the disk. A lens formed on a road and condensing the diffused light on the disk, wherein information is recorded on at least the disk.

According to the present invention, the optical path distance between the light source and the lens is reduced, and the utilization efficiency of light emitted from the light source is increased. This makes it possible to record data on an optical disk even with an optical head using a diffusion optical system.

[0070]

The light use efficiency can be increased in an optical head using a diffusion optical system by reducing the amount of surface vibration and the amount of eccentricity.

Also, since the amount of surface vibration is small, the working distance of the objective lens can be reduced, and the optical head can be downsized by reducing the distance between the light source and the objective lens.

[0072]

An embodiment of the present invention will be described below.

FIG. 1 is a partial configuration diagram of an optical disk device showing an optical head and an information recording medium of the present invention.

The optical head includes a semiconductor laser 1 as a light source, a compound prism 11, an objective lens 4, a detector 8, and a two-dimensional (not shown) for moving the objective lens 4 in the focusing direction and the tracking direction. It consists of an actuator and a chassis 12 for fixing these components.

On the other hand, a disc-shaped information recording medium (hereinafter referred to as
The optical disk 6 is housed in a transparent case 5.

FIG. 2 is a sectional view of the components shown in FIG. Beam 9 emitted from semiconductor laser 1 as a light source
Is transmitted through the polarizing beam splitter 2 and is turned on.
The light is raised by 0, becomes circularly polarized light by the λ / 4 plate 3, enters the objective lens 4, and is condensed on the recording surface of the optical disk 6. The optical disk 6 is housed in a transparent case 5, and the beam 9 is focused on the recording surface of the optical disk 6 through the transparent case 5. The light reflected from the optical disk 6 becomes linearly polarized light rotated by 90 ° with respect to the light incident from the λ / 4 plate 3, reflected by the polarization beam splitter 2, and detected by a detector. This optical head has a length of 2
5 mm, width 15 mm, height 5.5 mm.

Incidentally, the semiconductor laser changes its oscillation state when its own emitted beam returns slightly, and noise is generated in the oscillation intensity. In an optical disk device, a beam of a semiconductor laser is condensed on an optical disk and its reflected light is detected, so that the reflected light returns to the semiconductor laser to generate noise. In an optical head in a read-only optical disk device using a finite magnification objective lens, as described above, an inexpensive half mirror is used as an optical separator for separating the light irradiated to the optical disk and the reflected light from the optical disk,
It has a simple configuration. Therefore, it cannot be avoided that the reflected light from the optical disk returns to the semiconductor laser. For this reason, a read-only optical disk device uses a so-called gain-guided laser element that is resistant to return light noise due to multimode oscillation. However, a gain-guided laser cannot be used for a recordable optical disc device because a high-output element cannot be manufactured. As a laser with high output, there is a so-called refractive index waveguide type laser element. However, the index guided laser is a single mode oscillation, and noise is likely to be generated by the return light. Therefore, it is necessary to prevent reflected light from the optical disk from returning to the semiconductor laser.

Here, means for preventing the reflected light from the optical disk 6 from returning to the semiconductor laser 1 in FIGS. 1 and 2 will be described. Polarizing beam splitter (PBS)
No. 2 has a property of transmitting P-polarized light and reflecting S-polarized light. The P-polarized light from the semiconductor laser 1 is transmitted through the PBS 2 and λ / 4
The plate 3 becomes circularly polarized light. The circularly polarized light reflected by the optical disk is λ
The beam becomes S-polarized light by the / 4 plate 3 and is reflected by the PBS 2 in the direction of the detector 8, so that the beam hardly returns to the semiconductor laser 1.

Here, the thickness of the quarter-wave plate used in the present invention will be described. A quarter-wave plate changes the conversion rate from linearly polarized light to circularly polarized light depending on the length of the optical path passing through it. When the refractive index of the quarter-wave plate for ordinary light is n ₀ , the refractive index for extraordinary light is n _e , the thickness of the quarter-wave plate is d, and the wavelength of the laser beam is λ, the thickness of the wave plate d is processed so as to satisfy _{d = λ / (n o -n} e) (2k + 1) to k is a natural number. The laser beam incident at an angle θ with respect to the perpendicular to the quarter-wave plate is a quarter.
An extra pass through the wave plate by Δd = d (1 / cos θ −1) reduces the conversion rate from linearly polarized light to circularly polarized light. In the diffusion optical system, a quarter-wave plate is used in the diffused light, so that the peripheral light enters the beam center at an angle to the quarter-wave plate, and the semiconductor The amount of light returning to the laser increases.
In particular, when k is large, the optical path difference between the vertically incident light and the light incident at an angle increases, and the rate of increase of the return light is large. Therefore, a quarter used in diffused light
As a wave plate, a so-called single mode 4 with k = 0
A one-half wave plate is desirable.

FIG. 31 shows the measurement results of the ratio of the amount of light returning to the semiconductor laser through the polarizing plate with respect to the number of modes k of the quarter-wave plate of quartz. The amount of returning light increases as k increases. In order to minimize the return light, the mode number k of the quarter-wave plate is desirably k = 0.

As the material of the quarter-wave plate, a biaxial crystal or a triaxial crystal such as quartz, mica, calcite or the like can be used. Alternatively, it can be realized by a hologram in which grooves are cut at a period equal to or less than the wavelength. When a hologram is used, a quarter-wave plate capable of efficiently performing circular polarization conversion on peripheral light of diffused light of a semiconductor laser can be manufactured by changing the pitch from the center to the outer periphery.

FIGS. 32 and 33 show another embodiment of the optical head used in the present invention. The laser beam 9 from the semiconductor laser 1 passes through a circular polarizer 14 and a quarter-wave plate 3 which are adjusted in a predetermined direction so that the transmitted beam becomes circularly polarized and bonded together. The laser beam 9 transmitted through the quarter-wave plate 3 is reflected by the half mirror 25, changed its direction by the rising mirror 10, enters the finite magnification objective lens 4, and is focused on the optical disk 6. The laser beam 9 reflected by the optical disk 6 passes through the finite magnification objective lens 4, a part of which passes through the half mirror 25, enters the detector 8, and returns the rest toward the semiconductor laser 1. The beam 9 reflected in the direction of the semiconductor laser is converted into linearly polarized light by 90 ° from the polarization of the light emitted from the semiconductor laser 1 by the quarter-wave plate 3, and does not pass through the polarizing plate 14. The objective lens 4 is driven by a two-dimensional actuator to perform focusing and tracking.
The semiconductor laser 1, the polarizing plate 14, the quarter-wave plate 3, the half mirror 25, the rising mirror 10, and the two-dimensional actuator are fixed on the same chassis 12. The half mirror 25 used had a reflectance of 80%. After assembling the optical head, the member in which the polarizing plate 14 and the quarter-wave plate 3 were bonded was rotated and fixed so that the amount of light transmitted through the objective lens 4 was maximized. In advance, the polarizing plate 14 and a quarter
Since the wave plates 3 are attached to each other, it is not necessary to adjust them separately, so that the time required for the adjustment is reduced.
A finite magnification lens having a numerical aperture of 0.15 on the light source side, a numerical aperture of 0.52 on the optical disk, and an effective lens diameter of 2 mmφ was used as the objective lens 4. For the quarter-wave plate 3, a single-mode crystal having a thickness of 100 μm was used. As the polarizing plate 14, a film in which a dye such as an iodine compound was put in a polymer film of polyvinyl alcohol and stretched in a certain direction was used.

FIG. 34 shows the measurement results of the laser noise with respect to the return light rate. The return light rate is the ratio of the amount of light returning to the semiconductor laser to the output light of the semiconductor laser. Return light rate is 0.
Laser noise is small at less than 02%. In addition, there is a small noise area with a return light rate of 0.5% to 7%. From this result, the light rate returned to the semiconductor laser is desirably 0.02% or less, or 0.5% to 7%. In the embodiment of FIG. 32, the return light rate is set to 3%, and the noise is reduced.

As the polarizing plate, a film in which a dye such as an iodine compound is put in a polymer film such as polyvinyl alcohol and stretched in a certain direction can be used. Alternatively, a thin metal film in which thin lines are arranged in the same direction may be used. Alternatively, a so-called polarizing beam splitter that obliquely enters light into a film in which dielectrics having different refractive indices are stacked in multiple layers may be used.

FIG. 35 shows an embodiment in which a polarizing plate and a quarter-wave plate are incorporated in a semiconductor laser package. In the semiconductor laser 1, a package for enclosing the semiconductor laser chip 15 has an optically transparent member for extracting the laser beam 9. A polarizing plate 14 and a quarter-wave plate 3 were used as the optically transparent member and bonded. As the quarter-wave plate 3, a single-mode quartz crystal having the same thickness as that of the cover glass used in the conventional semiconductor laser and having a thickness of 0.3 mm was used. An anti-reflection coating was applied to these surfaces to suppress the return light due to reflection. By using this semiconductor laser, the optical head was miniaturized.

FIG. 3 shows an embodiment of an optical disk housed in a case. An optical disk 200 (hereinafter, referred to as an "optical disk in card") incorporating the optical disk shown here is one in which a rotating optical disk 6 is housed in a fixed protective case 5 to reduce the runout of the optical disk 6.

As a result, the amount of movement of the objective lens for focusing is reduced, and aberration caused by movement of the objective lens for focusing is reduced. The outer shape is the size of a credit card, 84 mm long,
The width was 54 mm and the thickness was 1.5 mm. As the disk substrate, a glass substrate having a diameter of 1.9 inches and a thickness of 0.5 mm was used.
A C substrate or a PMMA substrate may be used.

By reducing the diameter of the optical disk, the relative amount of surface deflection becomes smaller even at the same surface deflection angle. 5.25 inch (133mm) diameter optical disc and diameter comparison
In the case of a 1.9-inch optical disk, the amount of surface vibration is 2/5 or less. In consideration of the amount of surface vibration, the smaller the diameter of the optical disk is, the better the diameter is 2.5 inches (127 mm).

The case 5 was made of a PMMA plate.

The thickness of the light incident portion 201 was 0.3 mm. The sum of the thicknesses of the substrate and the case was 0.8 mm. The distance between the substrate and the case was 0.2 mm above and below. As a result, the surface runout of the substrate can be suppressed to ± 0.2 mm at the maximum.

FIG. 4 shows one round (3 rotations) when the glass substrate optical disk housed in this case is rotated at 3600 rpm.
3 shows a measurement result of the amount of surface vibration of 3 ms).

In this case, the amount of surface vibration was ± 0.015 mm. From this result, it can be seen that the distance between the optical disk and the case can be reduced to 0.015 mm up and down.

In an optical disk device in which only an optical disk is inserted without being accommodated in a case, projections or flat surfaces are provided on both sides of the disk in the disk device so that the optical disk can be accommodated in the case even if surface deviation of the optical disk is limited. The same effect can be obtained.

As a recording medium, a phase-change rewritable recording film of an InSbTe alloy was used. The power required for recording is
A medium having a recording surface of 10 mW was used.

In this embodiment, an objective lens having an effective ratio of 2 mmφ, a working distance of 0.4 mm, an NA of 0.52, and a magnification of 0.3 was used. With this magnification, it was possible to achieve a utilization efficiency of 40%, which is almost the same as the light utilization efficiency realized in the parallel optical system.

The light source has a wavelength of 830 nm and an output of 30 mW.
Was used. As a result, a light energy of 12 mW was obtained on the film surface of the recording medium.
The distance between the objective lens and the light emitting point of the light source could be 6.4 mm. The thickness of the optical head is the bottom thickness of the chassis.
The thickness from the bottom of the chassis to the tip of the objective lens, including the mm, was 5.5 mm.

As an optical disk medium, a write once type and a phase change rewritable type in which a recording state is reproduced by a change in the amount of reflected light can be used. As a phase change type medium, a medium using an amorphous-crystalline phase change such as an InSbTe system, a GeSbTe system, and a GeTe system, an AgZn system, an InSb system
FIG. 5 shows the relationship between the magnification of the objective lens and the light use efficiency.

It can be seen that in order to realize an optical disk device having a light use efficiency of 25% or more, the magnification of the objective lens used for the optical head needs to be 0.2 or more. Considering the manufacturing conditions of the objective lens, the upper limit of the magnification is 0.35, and the upper limit of the light use efficiency is 50%.

FIG. 6 shows the relationship between the beam diameter and the working distance.
The numerical aperture of the objective lens is 0.52. FIG. 6 shows that the working distance is reduced by reducing the distance between the objective lens and the optical disk, and the diameter of the objective lens (light beam diameter) can be reduced. FIG. 7 shows the relationship between the beam diameter and the thickness of the optical head. FIG. 7 shows that the optical head can be made thinner by reducing the beam diameter. There is no danger of the objective lens being in direct contact with the rotating optical disc due to the case, and the amount of surface vibration can be made 0.4 mm or less, so that the working distance can be made 0.4 mm.

Further, when the thickness of the substrate is reduced to 1.2 mm, the diameter of the light beam can be reduced. For example, if the sum of the thickness of the optical disk and the thickness of the case is from 1.2 mm to 0.8 mm, the beam diameter becomes 2 mm at a working distance of 0.4 mm. When the light beam diameter is 2 mm, the thickness of the optical head is 6 mm. The sum of the thickness of the optical disk and the thickness of the case is 0.8 mm
In this case, by further suppressing the amount of surface vibration, the thickness of the optical head can be reduced to 5 mm. According to these relationships, the thickness of the optical head can be further reduced by reducing the thickness of the optical disk and the thickness of the case.

FIG. 8 shows the relationship between the amount of movement of the objective lens for focusing and the light use efficiency. The movement in the positive direction indicates that the objective lens has moved toward the optical disk. The numerical aperture of the objective lens is 0.52, the aperture diameter is 2 mm, and the magnification is 0.3.

If the light energy on the optical disk fluctuates when information is recorded, the light energy becomes excessive or insufficient, resulting in poor recording. Therefore, the fluctuation of the light energy on the recording surface of the optical disk is desirably 10% or less. For this purpose, the moving amount of the objective lens for focusing needs to be ± 0.25 mm or less according to FIG.

At this time, the light utilization efficiency at the design value is 50%. When the light use efficiency is 50% or less, the allowable amount of surface deflection with respect to the change in the light use efficiency increases, but the beam diameter increases due to an increase in aberration due to movement of the lens, and recording becomes impossible. In order to perform recording with a diffusion optical system, it is necessary to make the surface runout ± 0.25 mm or less. The cause of the runout depends on the shaft runout of the motor, the warpage of the board, and the mounting accuracy of the hub. However, even if the accuracy is increased, it is not possible to reduce the runout to ± 0.01 mm or less without using the runout prevention measures. Have difficulty.

Further, with respect to the lens diameter, the lens diameter can be reduced by reducing the surface deflection. Since the apparatus can be made smaller by reducing the lens diameter, the lens diameter is preferably 4 mm or less. However, a lens with a small diameter cannot be manufactured with high accuracy, and a lens with a diameter of 1 mm is the limit.

Next, an example of measurement of surface runout will be described.

FIG. 9 shows the results of measuring the disk runout using a motor with a small motor shaft runout by accurately attaching the hub to a board with little warpage. A 2-inch diameter glass substrate was rotated at 3600 rpm, and the surface vibration amount at the outermost circumference was 1
The measurement was performed on 0 disks. The amount of surface wobble was ± 10 μm even if it was small. ± 60 for most discs
μm or less, 1 ns even without taking measures to prevent runout
Overwriting was possible on the bTe phase change optical disk. The surface vibration of a 2-inch diameter PC board is ± 150 μm to ±
It was 400 μm, and was placed in a case to suppress surface runout.

FIG. 10 shows the relationship between the amount of movement of the objective lens for tracking and the amount of aberration. The aberration other than the aberration due to the movement of the objective lens is 0.03λ, the numerical aperture of the objective lens is 0.5, the aperture diameter is 2 mm, and the magnification is 0.2.

As a criterion that light can be condensed to the diffraction limit, there is a Marshall limit, which needs to be 0.07λ (RMS) or less.

From FIG. 10, it is preferable that the amount of movement of the objective lens be ± 0.3 mm or less so that the Marshall limit is not exceeded when the objective lens moves.

FIG. 21 shows an example of measuring the aberration of the objective lens caused by following the surface runout and eccentricity of the optical disk. The specifications of the objective lens used for the measurement were an effective diameter of 2 mm, a numerical aperture on the optical disk of 0.52, and a numerical aperture on the light source of 0.14. When the objective lens moves to follow the surface deflection and eccentricity of the optical disk, the range in which the aberration caused by the objective lens is 0.045λ or less is shown. The Marshall limit of 0.07 is used as a reference for aberrations that can be focused to the diffraction limit.
λ (RMS). In an optical disk device, since aberrations are generated by both the optical head and the optical disk, the same aberrations are allowed. Therefore, the aberration caused by the optical head needs to be 0.05λ (RMS) or less. In addition to the objective lens, the aberration also occurs due to the semiconductor laser and the optical components. Therefore, the aberration caused by the objective lens needs to be 0.045 λ (RMS) or less. Therefore, a range in which the aberration is equal to or less than 0.045λ was obtained. By the way, when assembling the optical head, an error occurs between the center axis of the semiconductor laser beam and the center axis of the objective lens. Further, an error occurs in the interval between the optical disk and the optical head. Usually, it is difficult to reduce the mounting error to 100 μm or less, so that the moving range of the objective lens with respect to the surface deflection and eccentricity of the optical disk is narrowed. As described above, the surface deflection and eccentricity allowed for the optical disk are indicated by the hatched portions in FIG. The surface runout needs to be ± 340 μm or less, and the eccentricity needs to be ± 200 μm or less. To allow both runout and eccentricity at the same time, runout ± 100 μm or less, eccentricity ± 200 μm
The following is desirable. However, when the entire optical head is moved by the coarse actuator to follow the eccentricity, the allowable eccentricity of the optical disk is widened to ± 300 μm or less. By improving the positioning adjustment accuracy of the optical head with respect to surface runout, the allowable range can be expanded to ± 450 μm.

In the write-once and rewritable optical discs, the light use efficiency needs to be high. When the maximum output power of the light source is small, the optical system is provided with the functions of a polarizing beam splitter and an optical isolator using a λ / 4 plate. It is essential. In addition, when a diffraction grating is used, light use efficiency is reduced. Therefore, a push-pull method or a heterodyne method is used as a tracking method. Focusing methods include a Foucault method using a Foucault prism, an astigmatism method using a cylindrical lens, a critical angle method using a critical angle prism, and a knife edge method using a knife edge. These parts can be made of the same glass or plastic as the material of the prism, such as polarizing prism, λ / 4 plate,
It is possible to produce a composite prism in which a component for obtaining a focus error signal such as a rising mirror and a knife edge and a component for obtaining a stocking error signal are integrally combined.

An embodiment of the compound prism used in the optical head of the present invention will be described with reference to FIG. The knife edge method was used as a focus error signal detection method, and the push-pull method was used as a tracking error signal detection method. The P-polarized beam enters the polarization beam splitter 2, is raised by the rising mirror 10, and becomes circularly polarized by the λ / 4 plate 3. The reflected light from the optical disc is converted into S-polarized light by the λ / 4 plate 3, the polarized beam is reflected by the polarization beam splitter 2, and detected by a four-divided sensor. In the Foucault prism 7, the upper half of the return light is applied to two sensors for tracking signals. The Foucault prism 7 serves as a knife edge, and is detected by a central two-part sensor to obtain a focus error signal. The configuration of the detection optical system can be changed according to the method of detecting a focus error and a tracking error. The composite prism of this embodiment is 5 mm long, 2.5 mm wide, and 2.5 mm high according to the beam diameter.
By using this composite prism, the optical system of the optical head according to the present embodiment was composed of four components: a semiconductor laser, a composite prism, a lens, and a detector. in this way,
By combining optical components, the number of components was reduced, and the number of optical axis adjustment locations that greatly affected the performance of the optical head was significantly reduced, making it possible to easily perform highly accurate optical axis adjustment. In this embodiment, a lens is not used for the detection optical system. However, since the detection sensitivity of the error signal can be adjusted by using the detection lens, a detection lens may be used.

A recording film using an organic material requires less light energy for recording than a recording film using an inorganic material, and recording can be performed with a film surface of 5 mW. When the output of the semiconductor laser is large and the light use efficiency may be small,
There is no need to use a polarizing beam splitter, and a non-polarizing beam splitter such as a half mirror may be used. Further, since the λ / 4 plate is unnecessary, the number of parts is reduced, and the cost can be reduced.

Next, an embodiment of the optical disk will be described.

FIG. 22 shows an embodiment of an optical disk in which a beam is incident through a transparent case. In this embodiment, the rotating optical disk 6 is housed in a case having a small internal space, and the surface deflection of the optical disk 6 is reduced. The optical disk 6 uses a glass substrate, a PC substrate, and a PMMA substrate having a thickness of 0.5 mm for the substrate 151 having a diameter of 2 inches (49 mm).
On top of this, a recording film 160 was formed. The outer shape of the case was 84 mm long and 54 mm wide for easy handling. In this embodiment, a single-sided optical disc for reproduction has a transparent case 5 on the light incident side and an opaque protective case 170 on the opposite side. The transparent case 5 has P
An MMA plate was used. The transparent case 5 may be made of a uniform transparent material such as glass or PC. Transparent case 5
The protective case 170 has a thickness of 0.3 mm, the distance between the case and the optical disk 6 is 0.2 mm, and the thickness of the case is 1.5.
mm. As a result, the surface runout of the substrate is at most ±
It can be reduced to 0.2mm. The sum of the thicknesses of the substrate and the case through which the beam is transmitted was 0.8 mm. A hole was provided in the transparent case on the beam incident side, and the hub 51 was magnetically chucked to the spindle. The data recording range was from the inner circumference of 34 mmφ to the outer circumference of 48 mmφ, and the storage capacity was 40 MB.

FIG. 23 shows an embodiment of an optical disk in card for double-sided reproduction. Two 0.5mm optical disc substrates 1
51, 152 with the recording films 160, 161 inside;
The substrates were bonded with a resin adhesive 165. As for the case, the transparent case 5 is stuck on the optical disk portion of the protection case 170,
A light incident portion was used. The optical disk was rotated by magnetically chucking the hub 51 to the spindle. The thickness of the transparent case 5 and the protective case 170 is 0.3 mm, the distance between the case and the optical disk 6 is 0.2 mm, and the thickness of the case is 2 mm.
mm. The storage capacity became 80 MB.

FIGS. 24 and 25 show the position of the light incident portion facing the optical head. It is desirable to handle the optical disk in card with the center of the optical disk shifted in the longitudinal direction from the center of the case, and to handle the optical disk with a portion opposite to a certain portion of the optical disk. Preferably, the light incident portion is provided in the longitudinal direction of the case with respect to the center of the optical disk. In the embodiment of FIG. 24, the light entrance window 201 is provided from the center of the optical disk to the center of the case. In FIG. 25, the light incident window 201 is provided in the direction opposite to the center of the optical disc from the center of the optical disc. As the transparent case, the entire optical disk may be a transparent case, the optical disk portion may be a transparent case, or only the light incident window may be a transparent case. In consideration of the strength of the case, it is preferable that only the light incident window be a transparent case. Furthermore, since the distance between the protective case and the optical disk is small, they come into contact with each other, and if they are damaged, the recorded information cannot be reproduced.
It is preferable to provide a measure for preventing the information recording portion of the optical disc from contacting the case.

FIGS. 12 and 13 show an optical disc in-card 20 for preventing the information recording section of the optical disc from contacting the case.
0 shows an embodiment.

In the embodiment of the optical disk-in card 200 shown in FIG. 12, a dust-free cloth 31 is provided between the optical disk 6 and the case 5, and the optical disk 6 is rotated while contacting the soft dust-free cloth 31. 6 and the recording medium were not damaged. Since dust adhering to the optical disk 6 is wiped off by the dust-free cloth 31 during rotation of the disk, the beam incident from the light incident portion 201 of the case 5 is not interrupted by the dust. When the disk 6 rotates while contacting the rotation guide member such as the dust-free cloth 31 as in this embodiment, a flexible material such as a plastic substrate is used as the substrate so that the substrate is deformed according to the guide member. Is good.

In the embodiment shown in FIG. 13, a dust-free cloth 31 is used to prevent the area 32 of the optical disk 6 where information is recorded from coming into contact with the case 5. In this embodiment, the dust-free cloth 31 is attached to an area where no information is recorded on the inner peripheral portion of the disk, and the case 5 and the dust-free cloth 31 are rotated while being rubbed. According to the present embodiment, the information recording area 32 at the outer peripheral portion of the disk does not come into contact with the case 5, and the surface deflection of the optical disk 6 is reduced. In this embodiment, since the dust-free cloth does not generate dust and is flexible, a similar effect can be obtained by using dust-free paper, rubber, or the like in addition to the dust-free cloth.

In the present invention, the optical disk is rotated in a case having a small interval to suppress the surface deflection of the optical disk. Therefore, the beam entrance may be a transparent case or an opening.

FIG. 26 shows an embodiment in which an opening is provided in a case without using a transparent case and a beam is incident. Two optical disks 6 each having a diameter of 2 inches (65 mm) and a thickness of 0.6 mm were laminated. The structure of the optical disk was the same as the embodiment of FIG. The optical disk was placed in a protective case 170, and the storage portion was sealed by covering the opening 202 with a protective cover 203 during storage. In use, the protective cover 203 is moved to open the opening 202 and the hub 51 is opened.
Was magnetically clamped to the spindle of the optical disk device and rotated. The beam of the optical head is incident on the optical disk 6 through the opening 202. The outer shape of the protective case 170 was the same as that of FIG.

FIG. 27 shows an embodiment of a double-sided optical disk having a structure in which an opening is provided in a case and a beam is incident thereon. The optical disk 6 used had a diameter of 2 inches (65 mm) and a substrate thickness of 0.6 mm. The optical disk has a protective case 1
70 and the opening 202 with the protective cover 203 during storage.
Was sealed with a lid. During use, the protective cover 203 was moved to open the opening 202, and the hub 51 was magnet-clamped to the spindle of the optical disk device and rotated. The beam of the optical head is incident on the optical disk 6 through the opening 202. The openings 202 are provided on both sides of the protective case 170. When using the back surface, both openings were formed in the same shape so that the optical disc in card was inserted upside down. The outer shape of the protective case 170 was the same as that of FIG. The configuration of the optical disk is the same as that of FIG.

FIG. 28 shows another embodiment of the optical disk and the case. The optical disk 6 used had a diameter of 2.5 inches (65 mm) and a substrate thickness of 0.6 mm. The run-out of this disk was ± 0.2 mm or less. The optical disk is housed in a protective case 170 to prevent scratches and dust, and has a structure in which the opening 202 is closed and sealed with a protective cover 203 during storage. During use, the protective cover 203 was moved to open the opening 202, and the hub 51 was magnet-clamped to the spindle of the optical disk device and rotated. The beam of the optical head enters the optical disc 6 through the opening 202. The outer shape of the protective case 170 was 72 × 72 × 4.5 mm. In this embodiment, the protective case can be made thin by reducing the thickness of the substrate and the surface runout. The protective case 170 has such a structure that the optical disk 6 can be taken out and dust and dirt can be wiped off. FIG. 14 shows another embodiment for preventing the surface deflection of the optical disk. In this embodiment, the beam 9 passes through the case 5 and is incident on the optical disk 6, and the optical disk 6 is provided with a projection 33. 6 was designed to suppress the runout. The substrate was produced by an injection method using PC and PMMA. The projection 33 was formed at the same time when the substrate was formed. There is an advantage that the difference in the amount of contraction of the substrate is reduced and the deformation of the substrate is reduced due to the presence of the projections in the production of the substrate. The protruding portion had a height of 0.1 mm and a width of 3 mm.

FIG. 15 shows a means for reducing the eccentricity of the optical disk in this embodiment. A projection 42 is provided on the optical disk 6 side, and a step 43 for guiding the optical disk 6 is provided on the case 5 side. With the projection 42 and the step 43,
The optical disk 6 has a distance equal to or larger than the distance between the protrusion 42 and the step 43.
It does not move in the in-plane direction of the optical disc 6. As a result, the amount of eccentricity could be suppressed. Since the distance between the optical disk 6 and the case 5 was ± 0.03 mm, the eccentricity of the disk 6 was ± 0.03 mm or less. Projection 42 of disk 6
Was manufactured at the same time when the PC and PMMA substrates were manufactured by the injection method. Therefore, the center of the track and the center of the protrusion 42 could be accurately matched. The hub 41 for fixing the disk to the drive and rotating the disk was mounted on the optical disk 6 such that the deviation between the center of rotation of the disk and the center of the track was ± 0.05 mm or less. When the substrate is manufactured by the injection method, if the hub 41 is attached at the same time, the center of the track and the center of the hub 41 can be accurately adjusted, so that a disk with small eccentricity can be manufactured. in this case,
There is no need to take measures to reduce the amount of eccentricity. Further, in the present embodiment, when the optical disk 6 and the case 5 come into contact with each other due to the surface deflection of the optical disk 6, the surface deflection is reduced because of the protrusion 42 or the central portion of the optical disk.

FIG. 16 shows an embodiment in which there is no deviation between the disk and the rotating shaft of the motor. In the present embodiment, when the hub 51 is attracted by the magnet 53 and is fixed to the fixing portion 54 of the hub 51 in order to fix the optical disk 6 to the motor rotation shaft 52, the motor rotation shaft 52 and the hub 51 are tapered. As a result, no gap is formed between the rotating shaft 52 and the hub 51. In this embodiment, in order to perform recording on both sides of the disk 6, openings for inserting a rotating shaft are provided above and below the case 5, and tapered on both sides of the hub 51. In the case of a single-sided optical disk, a taper may be provided only on the rotation shaft insertion side.

Further, the optical disk device has a course actuator for moving the entire optical head in order to move the optical head in addition to the two-dimensional actuator, and this course actuator can cause the entire optical head to follow eccentricity. As described above, when tracking the eccentricity of the disk by moving the entire optical head by the coarse actuator, the amount of movement of the objective lens is small, and the aberration and the change in light use efficiency are small.

In a 2-inch disk having an eccentricity of 70 μm rotating at 3600 rpm, the eccentricity was followed by the course actuator, and the moving amount of the objective lens was suppressed to ± 10 μm or less. As a result, recording was performed without using means for reducing the eccentricity of the disk such as a taper.

Another embodiment will be described. If a cube-type polarizing beam splitter is used, aberration occurs when diffused light passes, and therefore, it is necessary to correct it in advance when designing a lens. Further, it is necessary to accurately control the thickness of the beam splitter so as to be a design value. As a method of guiding a beam to an objective lens without passing through a thick glass or the like, there is a method of using a reflection type beam splitter. FIG. 17 shows an embodiment using a reflection type beam splitter. The polarization splitting film 23 is provided on the surface of the beam splitter 22.
To reflect only light having a polarization parallel to the surface of the beam splitter 22. The light that has become circularly polarized by the λ / 4 plate 3, transmitted through the case 5, and reflected by the disk 6 becomes polarized in a direction perpendicular to the incident light on the λ / 4 plate 3, passes through the beam splitter 22, and 8 is detected. In order to obtain a focus error signal, astigmatism generated in the beam splitter 22 is used. An aberration compensator and a lens may be provided in order to obtain a more accurate error signal and to obtain a degree of freedom in optical design. In the present embodiment, the detector 8 is placed on the side opposite to the disk 6 with respect to the beam splitter 22.
And the same surface of the beam splitter 22.

Another embodiment will be described with reference to FIG. FIG.
In order to further reduce the optical head of the seventh embodiment, the laser 1 and the detector 8 are arranged in the same direction. A reflection section 24 is provided on the back surface of the beam splitter 22 to reflect the detection light in the direction of the laser 1. The beam from the semiconductor laser 1 is reflected by the polarization separating film 23, passes through the λ / 4 plate 3, and is condensed by the objective lens 4 on the optical disk 6 through the case 5. The reflected light from the optical disk 6 is
3, transmitted through the beam splitter 22, reflected by the reflection unit 24, and detected by the detector 8. The reflected light is condensed at a position different from the light emitting point of the laser 1 due to the refraction of the beam splitter 22, so that the laser 1 and the detector 8 can be installed without interference. However, as described above, in the conventional method, it was impossible to make the distance between the semiconductor laser 1 and the disk 6 less than 20 mm. In this embodiment, the distance between the semiconductor laser 1 and the optical disk 6 is reduced by one by placing the optical disk 6 in the transparent case 5.
It could be 0 mm. According to the present invention, it has become possible to reduce the size of the optical head, which has not been possible conventionally. The size of the optical head in this embodiment is 20 mm in length, 10 mm in width, and 5 mm in height.
It became.

FIG. 19 shows a configuration of an embodiment in which the cost is reduced by using the non-polarizing half mirror 25.

In the optical head shown in FIG. 19, the beam 9 from the semiconductor laser 1 is reflected by the half mirror 25,
The light is condensed by the objective lens 6 and enters the optical disk 6 through the case 5. Therefore, when the reflectance of the half mirror 25 is R, the transmittance is T, and the light collection efficiency of the objective lens is η, the power Pd reaching the optical recording medium among the output powers P of the light source 1 is Pd = ηRP. . Since the power reaching the optical disk increases as the reflectivity R increases, R ≧ T is desirable.

Although not shown, when the beam from the light source passes through the half mirror and enters the optical disk, it is desirable that R ≦ T.

In the case where the ratio between the reflectance and the transmittance of the half mirror 25 reaches the optical disk 6 in a large amount, the power Ps reaching the detector 8 is as follows, where r is the reflectance of the optical disk 6. Since Ps = ηrRTP, and the transmittance T is small, the amount of light reaching the detector decreases, and the reproduction signal decreases. Therefore, it is desirable to increase the output P of the light source during reproduction and make the light amount reaching the detector the same.

In the present embodiment, the power reaching the optical disk 6 is increased by using the half mirror 25 with R = 70% and T = 30%. In FIG. 19, the same effect can be obtained in a configuration in which the positions of the light source 1 and the detector 8 are exchanged and the light emitted from the light source 1 first passes through the half mirror 25. Swap the size of R
≤ T. In this embodiment, since the reflectance of the half mirror 25 is large, the proportion of light reaching the detector 8 is smaller than in the case of using a generally used half mirror of R = T = 50%. Therefore, in this embodiment, the conventional film surface 1
By increasing the reproducing light of mW to 1.7 mW, the amount of light reaching the detector 8 was secured to the same degree as when a half mirror of R = T = 50% was used. The objective lens 4 has C
Use the one with a magnification of 0.24 used for D,
An optical head having a light use efficiency of 30% was manufactured. 5 for light source 1
Using a 0 mW semiconductor laser, a power of 10.5 mW was obtained on the film surface. With this optical head, InSb with a sensitivity of 10 mW
Recording was performed on a Te phase change optical disk medium. As the half mirror 25, not only the reflection type as in the present embodiment but also a cube type may be used. When a recording medium having high recording sensitivity such as one using an organic dye is used, a low-output light source or a half mirror having a small difference between reflectance and transmittance can be used.

This is an embodiment showing the structure of the optical disk apparatus in which the optical disk in card of FIG. 29 and the optical head are combined. The optical head 300 is attached to the course actuator 700 and can move in parallel with the optical disk in card 200. These are built in the optical disk device chassis 800. In this embodiment, the coarse actuator 70 is used.
A stepping motor having a thickness of 6 mm was used as 0. The propulsive force of the course actuator 700 was about 1N. The thickness of the optical head 300 was 6 mm, the weight was 25 g, and the average access time was about 100 ms. The thickness of the optical disc in card 200 capable of recording on one side is 1.5 mm. The thickness of the optical disk device excluding the circuit is 10 mm, and the thickness of the optical disk device is 15 mm when the circuit is added.
By making the circuit LSI, the thickness of the optical disk device can be reduced to 12 mm. In this embodiment, an optical system having a beam diameter of 2 mm is used, but by replacing the optical system with a beam diameter of 1.5 mm, the thickness of the optical head can be 4.5 mm and the thickness of the optical disk device can be 10 mm. . The configuration of the optical disk device of the present embodiment can be used even when a beam is incident from the opening of the optical disk case.

Also in this configuration, by making the thickness of the apparatus 0.5 mm thick, it is easy to use an optical disk in card capable of recording on both sides. In this case, in order to record information on the back surface of the optical disc in card, the optical disc in card may be once taken out of the apparatus, turned over, and inserted into the apparatus.

FIG. 30 shows an embodiment in which the embodiment of FIG. 29 is changed to an apparatus capable of simultaneous recording and reproduction on both sides. The feature of this embodiment is that the first optical head 300 and the second optical head 301 are opposed to each other with the optical disk in card 200 interposed therebetween, and the optical heads 300 and 301 are attached to coarse actuators 700 and 701, respectively. . These are built in the optical disk device 800. With this configuration, the optical disc in card 200 can record information on both sides without having to turn over. The first and second optical heads 3
Since 00 and 301 can be driven independently, two types of information can be reproduced simultaneously. Furthermore, the first and second
By driving the optical heads 300 and 301 in synchronization with each other, the data transfer rate can be effectively doubled. With this configuration, the thickness of the device can be reduced to 20 mm, and the device can be mounted on a laptop or notebook personal computer or workstation. In the double-sided optical disk, the type of the optical disk medium may be changed for each side such as a ROM on one side and a rewritable optical disk on one side.

FIG. 20 shows an embodiment of an optical disk system using the optical head of the present invention. The reproduction signal of the optical head 71 passes through the preamplifier 75 and is
And processed. Focus servo 7 from playback signal
6, and the tracking servo 77 is performed. When modulating the laser output for recording, the laser driver 78 controls the current flowing to the laser. Control of the number of revolutions of the spindle motor 74 and the course actuator 73
Is controlled by the spindle servo 79 and the coarse actuator servo 80, respectively. The drive microcomputer 81 performs signal processing for controlling the focus, tracking, spindle, and course actuators. The control of the optical disk system is performed by the control microcomputer 82. Optical head 7
1, a disk-in card 72 containing an optical disk in a case, a course actuator 73, and a spindle motor 74, a chassis 8 having a length of 100 mm, a width of 60 mm, and a height of 10 mm.
I put it in 3. As the coarse actuator, a linear actuator having a thickness of 5 mm was used. The spindle motor has
Using a disk having a thickness of 5 mm, the rotating shaft of the disk was driven by a belt or directly. Rotation speed is 3600rp
m.

The present invention has been described with reference to a write-once type using perforation and phase change, a rewritable type using phase change, an optical head using a read-only type, and an optical disk apparatus. For the used optical head and optical disk device, the same effect can be obtained only by changing the detection optical system.

The use of a diffusion optical system in the optical head of the present invention reduces the number of constituent parts and facilitates miniaturization of the optical head. The downsizing of the optical head not only reduced the size of the optical disk device, but also reduced the moving time of the optical head and shortened the data transfer time.

In the diffusion optical system, when the objective lens and the optical disk are at a fixed position, aberration is minimized, and light can be collected to the diffraction limit. In the optical disk device, when performing focusing and tracking, the objective lens moves in a direction perpendicular to the disk and in a direction parallel to the disk. In the optical disk device of the present invention, the aberration generated in the light due to this movement is small, and Light is now fully available.

Further, by this focusing and tracking, the light utilization efficiency indicating the ratio of the light energy reaching the recording surface out of the light energy emitted from the light source changes. According to the present invention, the change in the light use efficiency due to the movement of the objective lens is small even in an optical head having a small amount of movement of the objective lens when performing focusing and tracking and having a large light use efficiency. For this reason, an optical head having high light use efficiency could be manufactured.

In the optical disk, the distance between the light source and the objective lens could be reduced because the amount of surface vibration and the amount of eccentricity of the disk were small. An optical head capable of recording information using a diffusion optical system was realized.

[0145]

According to the present invention, the light use efficiency can be increased in the optical head using the diffusion optical system by reducing the amount of surface vibration and the amount of eccentricity of the disk. Therefore, an optical head having a small number of components, a small size, and capable of recording information could be manufactured. In addition, since the magnification of the objective lens is increased in order to increase the light use efficiency, the distance between the light source and the objective lens is reduced, so that the optical head using the conventional diffusion optical system can be downsized. Further, since the amount of surface vibration is small, the working distance of the objective lens can be reduced, and the optical head can be thinned.

The size of the optical head can be reduced by reducing the size of the optical head. By increasing the light use efficiency, an optical information recording / reproducing apparatus using a diffusion optical system could be manufactured.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical head and an optical disk of the present invention.

FIG. 2 is a cross-sectional view of the optical head and the optical disk of the present invention.

FIG. 3 shows an embodiment of an optical disk case.

FIG. 4 is a measurement result of a surface vibration amount of an optical disk placed in a case.

FIG. 5 is a relation between magnification of a diffusion optical system and light use efficiency.

FIG. 6 shows the relationship between the beam diameter and the working distance.

FIG. 7 shows a relationship between a light beam diameter and an optical head thickness.

FIG. 8 shows the relationship between the amount of movement of a lens for focusing and the light use efficiency.

FIG. 9 is a distribution of a surface vibration amount.

FIG. 10 shows the relationship between the amount of movement of the lens for tracking and the wavefront aberration.

FIG. 11 is a perspective view of a composite prism for an optical head according to the present invention.

FIG. 12 shows an embodiment using a dust-free cloth to prevent contact between the disc and the case.

FIG. 13 shows another embodiment using a dust-free cloth to prevent contact between the disk and the case.

FIG. 14 is an embodiment for preventing the disk from oscillating.

FIG. 15 shows an embodiment for preventing eccentricity of a disk.

FIG. 16 shows an embodiment of a hub and a rotating shaft for preventing eccentricity of a disk.

FIG. 17 is a configuration diagram of an optical head optical disc showing another embodiment of the present invention.

FIG. 18 is a configuration diagram of an optical head and an optical disk showing still another embodiment of the present invention.

FIG. 19 shows an embodiment using a half mirror.

FIG. 20 is a block diagram of the optical disc device of the present invention.

FIG. 21 shows measurement results of allowable ranges of surface runout and eccentricity.

FIG. 22 is an embodiment of an optical disk in card in which a beam is incident through a transparent case.

FIG. 23 shows an embodiment of a double-sided reproduction optical disc in card in which a beam is incident through a transparent case.

FIG. 24 is an explanatory diagram of a position of a light incident part.

FIG. 25 is another explanatory diagram showing the position of the light incident part.

FIG. 26 shows an embodiment of an optical disk in card in which a beam is incident from an opening.

FIG. 27 is an embodiment of an optical disc in cart for double-sided reproduction in which a beam is incident from an opening.

FIG. 28 is an embodiment of an optical disk on which a beam is incident from an opening.

FIG. 29 is a configuration diagram of an optical disk device.

FIG. 30 is a configuration diagram of an optical disk device for double-sided reproduction.

FIG. 31 is a measurement result of a relationship between a mode k of a λ / 4 plate and a return light rate.

FIG. 32 shows an embodiment of an optical head using a polarizing plate.

FIG. 33 is an explanatory diagram of positions of a semiconductor laser, a λ / 4 plate, and a polarizing plate.

FIG. 34 shows measurement results of the relationship between the return light rate and laser noise.

FIG. 35 shows an embodiment in which a λ / 4 plate and a polarizing plate are incorporated in a semiconductor laser package.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser, 2 ... Polarization beam splitter, 3 ... λ
/ 4 plate, 4 ... objective lens, 5 ... transparent case, 6 ... optical disk, 7 ... Foucault prism, 8 ... detector, 9 ... beam, 10 ... rising mirror, 11 ... composite prism, 12
... optical head chassis, 22 ... polarizing beam splitter, 2
3 ... polarization separating film, 24 ... reflecting part, 25 ... half mirror,
31: dust-free cloth, 32: information recording area, 33: protrusion, 4
DESCRIPTION OF SYMBOLS 1 ... Hub, 42 ... Eccentricity prevention protrusion part, 43 ... Eccentricity prevention step, 51 ... Hub, 52 ... Rotating shaft, 53 ... Magnet, 54 ... Hub fixing part, 71 ... Optical head, 72 ... Optical disk in card, 72 ... Coarse actuator, 74 ... Spindle motor, 75 ... Preamplifier, 76 ... Focus servo, 7
7: stocking servo, 78: laser drive unit, 79: spindle servo, 80: course actuator servo,
81: drive microcomputer, 82: control microcomputer, 83: chassis, 200: optical disk in card,
201: Light incident part.

──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Nobuyoshi Tsuboi 4026 Kuji-cho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Hiroyuki Minemura 4026 Kuji-cho, Hitachi City, Ibaraki Prefecture Hitachi, Ltd. In-house (72) Inventor Hisashi Ando 4026 Kuji-cho, Hitachi City, Ibaraki Prefecture Hitachi, Ltd. Hitachi Research Laboratory (56) References JP-A-63-142539 (JP, A) JP-A-60-66341 (JP, A) JP-A-61-94285 (JP, A) JP-A-2-210620 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 7/135

Claims (6)

(57) [Claims] 1. An optical disk apparatus for recording on an optical disk, comprising: a rotating unit for rotating the optical disk using a diffusion optical system; a light source; and a light source for condensing diffused light from the light source on the optical disk; An optical disk comprising: an objective lens having a numerical aperture on the side of 0.18 or less and a diameter of 1 mm or more; and a surface vibration suppressing means for suppressing a surface runout due to rotation of the disk to ± 0.25 mm or less. apparatus. 2. An optical disk device according to claim 1, wherein an optical path distance between said light source and said objective lens is 5 to 20 mm. 3. The working distance of the objective lens is 0.25 to 0.25.
3. The thickness is 1.00 mm.
An optical disk device as described in the above. 4. The optical disk device according to claim 1, wherein the diameter of the objective lens is 4 mm or less. 5. The apparatus according to claim 1, wherein a case for accommodating said disk is used as said surface vibration suppressing means.
An optical disk device according to any one of the above. 6. A beam splitter for guiding light from the light source as diffused light to the objective lens, and a quarter-wave plate provided on an optical path between the beam splitter and the objective lens. 6. The method according to claim 1, wherein:
An optical disk device according to any one of the above.