JPH056569A - Optical disk device - Google Patents

Abstract

PURPOSE:To reduce the price of a recording capable optical disk device by introducing an optical head which uses diffused optical system. CONSTITUTION:The disk device utilizes an optical head with a diffused optical system which makes diffused light incident on an objective lens 4. By enclosing the optical disk, which stores information, into a case so as to make the gap between the disk and the case to be 0.1 to 0.25mm top and bottom then, the wobbly surface of the optical disk becomes + or -0.1 to + or -0.25mm. An increase in aberration caused by focusing and a decrease in light effective utilization rate are suppressed and an optical disk device with an optical head which uses a large light effective utilization rate diffused optical system is realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk device using a diffusing optical system for an optical head, and more particularly to an overwritable optical disk device.

[0002]

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

Regarding an optical head of a diffusion optical system used for a CD, for example, Shigeo Kubota, "Small size, light weight and simplification of optical disk pickup", Vol. 16, No. 8 (1987)
Years) has been put to practical use in a simplified optical system. Light emitted from a semiconductor laser as a light source is guided to an objective lens by a half mirror and focused on an optical disc. The light reflected by the optical disk is the objective lens,
It is detected by the detector through the half mirror. From the semiconductor laser to the objective lens, such an optical system is called a diffusion optical system because it does not collimate the light.

[0004]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
Rotational shake due to optical disk rotation (surface runout and eccentricity)
Exists. Therefore, it is necessary to have a focus control mechanism that constantly adjusts the light condensing point to the recording surface of the optical disc, and a tracking control mechanism that controls the light to follow the same track. Focusing and tracking are performed by moving the objective lens in two axial directions with a two-dimensional actuator.
The signal for this control needs to be obtained from the light reflected by the optical disc.

However, in the diffusing optical system, since the lens is moved in the diffused light, aberrations are generated due to focusing and tracking, and the light cannot be sufficiently condensed. In addition, there is a problem that the condensed 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,
The diffusing optical system cannot be used in an optical disk device that requires a large amount of light energy on the recording surface of the optical disk, such as a write-once or rewritable device.

An object of the present invention is to provide an overwritable optical disk device using a diffusing optical system.

[0007]

According to the optical disk device of the present invention, a light emitted from a light source is incident as diffused light with a diameter of 1
It is characterized in that it has an objective lens of ˜4 mm, and is equipped with an optical head for recording at least information on the disc by the light condensed by the objective lens.

Further, the optical disc apparatus of the present invention includes a light source, an objective lens for condensing light on the disc, a beam splitter for guiding the light from the light source to the objective lens as diffused light, the beam splitter and the objective lens. An optical head having a λ / 4 plate that polarizes light on the optical path between and is mounted.

Further, the optical disk device of the present invention is an optical memory in which an optical recording medium for storing information formed on a disk substrate which is transparent to light is rotatably housed so as to regulate rotational shake in the vertical direction. Irradiating the optical recording medium with light condensed by an objective lens having a diameter of 1 to 4 mm, which functions as a diffused light and records 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 a predetermined relation position of the optical memory with the optical head. 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 comprises an optical head for collecting incident light as diffused light emitted from a light source and irradiating the disk to record at least information, and means for rotating the disk. A means for suppressing the rotational shake of the disk due to the rotation, a means for accommodating the disk in a recordable positional relationship with the optical head, and a drive circuit for controlling the operation of the optical head and the rotation of the rotating means. With.

In the optical disk device of the present invention, an optical recording medium for storing information formed on a disk substrate which is transparent to light is rotatably arranged in a credit card size so as to regulate rotation blur in the vertical direction. Which functions as an optical memory housed in a case, and irradiates the optical recording medium with light condensed as an diffused light by an objective lens having a diameter of 1 to 4 mm, and records information on the optical recording medium. An optical head for performing at least one of: reproducing the information recorded on the optical recording medium and erasing the information recorded on the optical recording medium; And a drive unit for controlling the operation of the optical head and the rotation of the rotating unit.

It is preferable that the case has a portion that is transparent to light, and recording, reproduction and / or erasing of information is performed by light irradiated through the portion.

Further, the optical disk device of the present invention uses an optical recording medium for storing information formed on a disk substrate which is transparent to light, and has a vertical rotational shake of 0.10 to 0.
It works for the optical memory stored to be 25 mm,
With an objective lens that emits light from the light source as diffused light,
Recording light on the optical recording medium by condensing light and irradiating the optical recording medium, reproducing information recorded on the optical recording medium, and information recorded on the optical recording medium An optical head having an optical path distance of 5 to 20 mm between the light source and the objective lens, and a means for accommodating the optical memory at a predetermined relation position with the optical head; The optical recording medium includes 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.

Further, the optical disk device of the present invention functions as an optical memory rotatably accommodating an optical recording medium for storing information formed on a disk substrate which is transparent to light, so that the light from the light source is emitted. Of the light emitted from the light source by irradiating the optical recording medium with light condensed by an objective lens having a diameter of 1 to 4 mm, which is emitted as diffused light.
An optical head for irradiating the optical recording medium with 0% of light to record, reproduce and / or erase information, means for accommodating the optical memory at a predetermined relation position with the optical head, and the optical recording medium. Rotating means for rotating the optical head, and a drive circuit for controlling the operation of the optical head and the rotation of the rotating means,
Have.

Further, the optical disk device of the present invention functions as an optical memory rotatably accommodating an optical recording medium for storing information formed on a disk substrate which is transparent to light, so that the light from the light source is emitted. Is operated in the range of 0.25 to 1.00 mm as diffused light to collect light and irradiate the optical recording medium, and 25 to 50% of the light emitted from the light source is collected. Of light to irradiate the optical recording medium to record, reproduce and / or erase information, means for housing the optical memory in a predetermined relation position with the optical head, and the optical recording medium rotating. And a drive circuit for controlling the operation of the optical head and the rotation of the rotating means.

In the optical disk device of the present invention, an optical recording medium for storing information formed on a disk substrate having a light transmitting property and an optical recording medium for rotatably storing information can be rotated. It works for the optical memory stored in and the numerical aperture for emitting light as diffused light is 0.5 to 0.5.
The objective lens of No. 6 is operated in the range of 0.25 to 1.00 mm, and the light is condensed to irradiate the optical recording medium to record, reproduce and / or erase information, and the optical memory. And a drive circuit that controls the operation of the optical head and the rotation of the rotating unit.

Further, the optical disk device of the present invention functions as an optical memory rotatably accommodating an optical recording medium for storing information formed on a disk substrate which is transparent to light, and has a constant wavelength of light. Light is condensed by an objective lens having a constant numerical aperture and is irradiated onto the optical recording medium to record, reproduce and / or erase information, and the ratio between the wavelength and the numerical aperture is 0. Optical head of .65 to 1.66, means for accommodating the optical memory in a predetermined relation position with the optical head, rotation means for rotating the optical recording medium, operation of the optical head, and rotation of the rotation means. A drive circuit for controlling rotation.

Further, the optical disk device of the present invention functions as an optical memory rotatably accommodating an optical recording medium for storing information formed on a disk substrate having a light transmitting property, and diffuses the light. 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 5-25 mW; and the optical memory as the optical head. It has means for accommodating at a predetermined relational 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.

Further, the optical disk device of the present invention condenses the diffused light from the light source onto the optical disk to record at least information, a means for rotating the disk, and a shake caused by the rotation. Means for accommodating the disk for holding information in a predetermined relational 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 device of the present invention comprises a light source composed of a semiconductor laser or the like, an objective lens for converging diffused light emitted from the light source onto the optical disk.
An optical separator for guiding the light reflected by the optical disc to the photodetector, and 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, it is preferable to appropriately select and use a wavelength of 400 to 850 nm, an output of 10 to 50 mW, and a light diffusion angle of 8 to 32 °.

As the objective lens used in the present invention, the numerical aperture on the optical disk side is 0.5 to 0.6, and the numerical aperture on the light source side is 0.1 to 0.1.
It is preferable to appropriately select and use 18, a magnification of 0.2 to 0.35, and an effective diameter of 1 to 4 mm.

As the optical separator used in the present invention, it is preferable to use a polarization 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, and the reflectance is R and the transmittance is T, when the light from the light source is reflected by the half mirror and reaches the optical disc, R ≧ T. When the light from the light source reaches the optical disk after passing through the half mirror, it is preferable to satisfy the relationship of R ≦ T.

Further, it is preferable to suppress the surface vibration of the disk due to the rotation so that the condensed light forms a recording spot on the disk.

Further, the optical disk device of the present invention condenses the diffused light from the light source onto the optical disk to record at least information, a means for rotating the disk, and a shake due to the rotation. Means for accommodating the disk in a predetermined relational position with respect to the head, and a drive circuit for controlling the operation of the head and the rotating means.

In these inventions, a diffusion optical system is used for the optical head, and the amount of surface vibration or eccentricity of the optical disk can be reduced and the light utilization efficiency can be increased.

By using the method of reducing the amount of surface vibration or the amount of eccentricity of the optical disc of the present invention, it is possible to realize an optical disc device which can be recorded by an optical head using a diffusion optical system.

As one of the methods for reducing the amount of surface vibration, etc., the optical disk is housed in a case to reduce the distance between the case and the optical disk so that the optical disk does not shake physically beyond this distance.

Alternatively, it is preferable that a device for inserting the optical disk is provided with a presser for limiting surface wobbling. 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, the optical disc device may be provided with a frame to limit the amount of eccentricity. By doing so, the amount of eccentricity can be limited.

Furthermore, when the disk has good flatness or little warpage, when the shaft of the drive device for rotating the disk has small runout, when the surface runout of the disk is small, and the position of the track center and the rotation center When the positions match, the shaft runout of the rotary drive device is small, and the standard surface vibration amount and eccentricity amount are satisfied, the present invention can be used without using a mechanism for limiting the surface vibration amount and eccentricity amount. An optical head using a diffusion optical system can be used.

Further, the optical disk device of the present invention functions in an optical disk which is housed in a case having a transparent portion and holds information by the light illuminated through the transparent portion of the case, and diffused light from the light source is stored in the optical disk device. An optical head that collects light on a disk and guides the light reflected by the disk to a photodetector to perform at least one of recording, reproduction, and erasing of information, and the disk is housed in a predetermined relation position with respect to the head. And means for doing so.

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

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

It is also possible to provide a protrusion on the optical disc to stably rotate the optical disc and prevent surface wobbling.

When the optical disk is put in a case, in order to irradiate the light emitted from the light source to the optical disk, an opening may be provided in the case to irradiate the light, or a transparent portion may be provided in the case to irradiate the light. It may be irradiated.

The light-transmissive optical member forming the transparent portion is preferably a light-transmissive member such as glass, polycarbonate (PC) or polymethylmethacrylate (PMMA).

Even if the entire transparent case is made of a light-transmissive material, only the portion corresponding to the optical head is made of a light-transmissive material, and the other portions are light-transmissive. You may form with the material which is not.

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 disc. Therefore, when the light is incident through the optical member forming the transparent portion of the case, it is designed in consideration of the thickness of the optical member and the substrate of the optical disk. Therefore, when the conventional objective lens is used, it is preferable that the optical member and the substrate of the optical disc have the same thickness as the conventional optical disc substrate. In the case of the present invention, since there is a case in addition to the substrate of the optical disc, it is possible to make the substrate of the optical disc thin when the conventional objective lens is used by making light incident through the case.

Further, the optical disk device of the present invention holds information while rotating, and the shake due to the rotation is 0.25 mm.
The following functions for an optical disc, and at least the information is recorded on the disc by condensing diffused light from a light source through a lens, and an optical path distance between the light source and the lens is 5 to 20 mm. A certain optical head, means for rotating the disc, and means for accommodating the disc in a predetermined relation position with respect to the head are provided.

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

In order to increase the light utilization 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 device of the present invention functions for an optical disk which holds information while rotating, and diffused light from a light source has 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 with a lens of .25 to 1.0 mm, a means for rotating the disc, and the disc at a predetermined relative position with respect to the head. And a means for accommodating.

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 them and the numerical aperture NA on the optical disk side is NA = D / f. The beam diameter d at the focal point is determined by the numerical aperture NA on the optical disc side and the wavelength λ of the beam, and is d = λ / NA at the diffraction limit.

When recording, reproducing or erasing information using the 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 becomes smaller when the focal length f is made smaller while keeping the value constant.

The beam diameter must be the same for compatibility with the conventional device, and the numerical aperture NA must be 0.5 or more when a semiconductor laser having a wavelength of 830 nm is used as a light source. Recognize. It can be seen that when the numerical aperture NA is increased and the beam diameter d is decreased, the energy density is increased 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 due to focusing and tracking, and considering the manufacturing conditions of the lens, the upper limit of the numerical aperture NA of the effective lens on the optical disk side is 0.6. preferable.

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

As the light source, a semiconductor laser having a wavelength of 780 nm to 830 nm or a light source of 390 nm 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
It is necessary to be 0.1 or more, and the light utilization efficiency increases as the numerical aperture increases. The numerical aperture on the light source side is preferably 0.18 or less in consideration of the fact that the light emitted from the semiconductor laser is elliptical and therefore the intensity distribution of the light from the light source can be formed in the objective lens and the manufacturing conditions of the lens.

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

When the magnification of the objective lens is m and the distance A from the objective lens to the light condensing point is B and the distance from the light source to the objective lens is B, there is a relation of A = mB. The distance A between the objective lens and the optical disk is determined by the amount of surface wobbling of the optical disk, and A and B are large in an optical disk with a large amount of surface wobbling. 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 improve the light utilization efficiency in the diffusion optical system as in the present invention.

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

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

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

The relationship between the magnification m and the light utilization efficiency in the diffusing 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 seen from the light source and the lens numerical aperture NA ₁ seen 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 utilization efficiency was calculated assuming that the light spread in the vertical direction is 1 ° and θ⊥ = 25 °. When an inorganic material is used for the recording film of the optical disk, the recording surface requires a power of 10 mW or more, and in order to use a semiconductor laser having a power of 40 mW as a light source, a light utilization efficiency of 25% or more is required. is there. It can be seen from the calculation that the magnification m must be 0.2 or more in order to obtain the 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 is incident 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 amount of surface vibration is 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. Even if a lens is used, the distance between the light source and the lens can be set to 20 mm or less.

The optical disk device 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 constant wavelength with a lens of a constant numerical aperture, so that the information is recorded on the disk. Record at least
An optical head having a ratio of the wavelength to the numerical aperture of 0.65 to 1.66 μm and a utilization efficiency of the light of 25 to 50%, and the disk accommodated in a predetermined relation position with respect to the head. And means for doing so.

The optical disk device of the present invention holds information while rotating and functions for an optical disk whose shake due to 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 disc by irradiating the disc with 25% to 50% of the light emitted from the light source, and means for rotating the disc. When,
Means for accommodating the disk at a predetermined relational position with respect to the head.

The optical disk device of the present invention retains information while rotating and functions for an optical disk whose shake due to the rotation is 0.25 mm or less, and diffuses light from a light source at a working distance of 0.25. An optical head for recording at least the information on the disk by condensing with a lens of ~ 1.0 mm, means for rotating the disk, and housing the disk in a predetermined relation position with respect to the head. And means.

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

The optical head of the present invention irradiates the optical disc with diffused light from the light source and guides the light reflected by the disc to the photodetector, and the light between the separator and the disc. A lens formed on the road for condensing the diffused light on the disc, and recording information on at least the disc.

According to the present invention, the optical path distance between the light source and the lens is reduced to improve the utilization efficiency of the light emitted from the light source. As a result, even an optical head using a diffusion optical system can record on an optical disc.

[0070]

By reducing the amount of surface vibration and the amount of eccentricity, the light utilization efficiency can be increased in the optical head using the diffusion optical system.

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

[0072]

EXAMPLE An example of the present invention will be described below.

FIG. 1 is a partial block 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 serving 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 focus direction and the tracking direction. It is composed of an actuator and a chassis 12 for fixing these parts.

On the other hand, a disc-shaped information recording medium (hereinafter,
An “optical disk” 6 is housed in a transparent case 5.

FIG. 2 is a cross-sectional view of the components shown in FIG. Beam 9 emitted from semiconductor laser 1 as a light source
Is transmitted through the polarization beam splitter 2 and the startup mirror 1
It is started by 0, becomes circularly polarized 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 which is rotated by 90 ° with respect to the light incident on the λ / 4 plate 3, is reflected by the polarization beam splitter 2, and is detected by the detector. This optical head has a length of 2
It was set to 5 mm, width 15 mm, and height 5.5 mm.

By the way, the oscillation state of the semiconductor laser changes when the beam emitted by itself returns slightly, and noise is generated in the oscillation intensity. In the optical disk device, since the beam of the semiconductor laser is focused on the optical disk and the reflected light is detected, the reflected light is returned to the semiconductor laser and noise is generated. In an optical head in a read-only optical disc device using a finite magnification objective lens, an inexpensive half mirror is used as an optical separator for separating the light irradiating the optical disc and the reflected light from the optical disc as described above.
It has a simple configuration. Therefore, it is inevitable that the reflected light from the optical disk returns to the semiconductor laser. Therefore, the read-only type optical disk device uses a so-called gain-guided laser element that is strong against return light noise by multimode oscillation. However, the gain-guided laser cannot be used for a recordable optical disk device because it cannot manufacture a high-power device. As a laser capable of obtaining high output, there is a so-called refractive index waveguide type laser element. However, the refractive index guided laser is a single mode oscillation, and noise is likely to occur due to the returning light. Therefore, it is necessary to prevent the reflected light from the optical disk from returning to the semiconductor laser.

A means for preventing the reflected light from the optical disk 6 from returning to the semiconductor laser 1 shown in FIGS. 1 and 2 will be described. Polarizing beam splitter (PBS)
2 has a property of transmitting P-polarized light and reflecting S-polarized light. The P-polarized light from the semiconductor laser 1 passes through the PBS 2 and has a wavelength of λ / 4.
The plate 3 becomes circularly polarized light. The circularly polarized light reflected by the optical disk is λ
It becomes S-polarized light by the / 4 plate 3 and is reflected in the direction of the detector 8 by the PBS 2, and the beam hardly returns to the semiconductor laser 1.

The thickness of the quarter-wave plate used in the present invention will be described below. The conversion rate of linearly polarized light into circularly polarized light of the quarter-wave plate changes depending on the optical path length that passes through it. The refractive index for ordinary ray of the quarter-wave plate n _0, d the thickness of the refractive index n _e, quarter wave plate with respect to the extraordinary ray, when the wavelength of the laser beam lambda, 4 minutes 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. A laser beam incident at an angle θ with respect to the perpendicular of the quarter-wave plate is a quarter.
An extra Δd = d (1 / cos θ −1) passes through the wave plate, and the conversion rate from linearly polarized light to circularly polarized light decreases. In the diffusing optical system, since a quarter wavelength plate is used in the diffused light, peripheral light is incident on the quarter wavelength plate at an angle with respect to the center of the beam. 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 incident light at an angle becomes large, and the return light increases at a large rate. Therefore, a quarter used in diffused light
As a wave plate, a so-called single mode 4 with k = 0
A quarter wave plate is desirable.

FIG. 31 shows the measurement results of the ratio of the amount of light transmitted through the polarizing plate and returned to the semiconductor laser with respect to the mode number 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 preferably k = 0.

As the material of the quarter-wave plate, biaxial crystal such as quartz, mica, calcite or triaxial crystal can be used. Alternatively, it can be realized by a hologram in which a groove is formed at a cycle of a wavelength or less. When a hologram is used, a quarter-wave plate that can efficiently convert circularly polarized light to peripheral light of diffused light of a semiconductor laser can be manufactured by changing the pitch from the center to the outer circumference.

32 and 33 show another embodiment of the optical head used in the present invention. A laser beam 9 from the semiconductor laser 1 is transmitted through a circular polarizing plate 14 and a quarter-wave plate 3 that are adjusted and bonded in a predetermined direction so that the beam that has already been transmitted becomes circularly polarized. The laser beam 9 that has passed through the quarter-wave plate 3 is reflected by the half mirror 25, changes its direction by the rising mirror 10, enters the finite-magnification objective lens 4, and is condensed on the optical disk 6. The laser beam 9 reflected by the optical disk 6 passes through the finite-magnification objective lens 4, part of which passes through the half mirror 25, reaches the detector 8, and the rest returns toward the semiconductor laser 1. The beam 9 reflected in the direction of the semiconductor laser becomes linearly polarized light which is deviated from the polarization of the emitted light of the semiconductor laser 1 by 90 ° 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 start-up mirror 10, and the two-dimensional actuator are fixed on the same chassis 12. The half mirror 25 has a reflectance of 80%. After the optical head was assembled, the member in which the polarizing plate 14 and the quarter-wave plate 3 were attached was rotated and fixed so that the amount of light passing through the objective lens 4 was maximized. Polarizer 14 and 1/4 in advance
Since the wave plates 3 are attached to each other, it is not necessary to adjust each separately, so that the time required for the adjustment is shortened.
As the objective lens 4, 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 disc side, and a lens effective diameter of 2 mmφ was used. 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 is put in a polymer film of polyvinyl alcohol and stretched in a certain direction is used.

FIG. 34 shows the measurement result of the laser noise with respect to the return light rate. The return light ratio is the ratio of the amount of light returned to the semiconductor laser to the emitted light of the semiconductor laser. Return light rate is 0.
Laser noise is small below 02%. In addition, there is a small noise region at a return light rate of 0.5% to 7%. From this result, it is desirable that the light rate returning to the semiconductor laser is 0.02% or less, or 0.5% to 7%. In the example of FIG. 32, the return light rate was set to 3% to reduce noise.

As the polarizing plate, a film obtained by placing a dye such as an iodine compound in a polymer film such as polyvinyl alcohol and stretching it in a certain direction can be used. Alternatively, a metal thin film in which thin lines are arranged in the same direction may be used. Alternatively, a so-called polarization beam splitter may be used in which light is obliquely incident on a film in which dielectrics having different refractive indexes are stacked.

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, the package that encloses the semiconductor laser chip 15 has an optically transparent member that extracts the laser beam 9. The polarizing plate 14 and the quarter-wave plate 3 were used as the optically transparent member and bonded. The quarter-wave plate 3 has the same thickness as that of the cover glass used in the conventional semiconductor laser, and a single-mode crystal having a thickness of 0.3 mm is used. An antireflection coating was applied to these surfaces to suppress return light due to reflection. The optical head has been miniaturized by using this semiconductor laser.

FIG. 3 shows an embodiment of the optical disc housed in the case. An optical disc 200 (hereinafter referred to as an "optical disc in card") having the optical disc therein shown has a rotating optical disc 6 housed in a fixed protective case 5 to reduce the surface wobbling of the optical disc 6.

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

By reducing the diameter of the optical disk, the relative amount of surface wobbling becomes small even at the same surface wobbling angle. Compared to 5.25 inch (133 mm) diameter optical disc, diameter
In the case of a 1.9-inch optical disc, the amount of surface vibration is 2/5 or less. In consideration of the amount of surface vibration, it is preferable that the diameter of the optical disc is small, and 2.5 inches (127 mm) or less is desirable.

For Case 5, a PMMA plate was used.

The thickness of the light incident portion 201 was set to 0.3 mm. The sum of the thickness 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 amount of surface deflection of the substrate can be suppressed to ± 0.2 mm at the maximum.

FIG. 4 shows an optical disk of a glass substrate housed in this case, which is rotated by 3600 rpm for one revolution (3
3 ms) shows the measurement result of the amount of surface vibration.

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 in the vertical direction.

In an optical disc device in which only the optical disc is inserted without being placed in the case, the optical disc should be placed in the case even if the surface deviation of the optical disc is limited by providing protrusions or flat surfaces on both sides of the disc in the disc device. The same effect as can be obtained.

As the recording medium, a phase change type rewritable recording film of InSbTe alloy was used. The power required for recording is
A recording medium of 10 mW was used.

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

The light source has a wavelength of 830 nm and an output of 30 mW.
The semiconductor laser of was used. As a result, 12 mW of light energy could be 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 1
Including the mm, the thickness from the bottom surface of the chassis to the tip of the objective lens could be 5.5 mm.

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

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

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

Further, if the substrate thickness is reduced to 1.2 mm, the luminous flux diameter can be reduced. For example, when the sum of the thickness of the optical disk and the thickness of the case is 1.2 mm to 0.8 mm, the luminous flux diameter is 2 mm when the working distance is 0.4 mm. When the luminous flux 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
At this time, the thickness of the optical head can be reduced to 5 mm by further suppressing the amount of surface vibration. According to these relationships, the thickness of the optical head can be further reduced by reducing the thickness of the optical disc 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 utilization efficiency. The movement in the positive direction indicates that the objective lens has moved to the optical disc side. The objective lens has a numerical aperture of 0.52, an aperture diameter of 2 mm, and a magnification of 0.3.

When the optical energy on the optical disk fluctuates when information is recorded, excess or deficiency of the optical energy occurs and recording failure occurs. Therefore, the fluctuation of the light energy on the recording surface of the optical disk is preferably 10% or less. For that purpose, the moving amount of the objective lens for focusing needs to be ± 0.25 mm or less from FIG.

At this time, the light utilization efficiency at the designed value is 50%. When the light utilization efficiency is 50% or less, the permissible amount of surface wobbling with respect to the change in the light utilization efficiency becomes large, but the beam diameter increases due to the increase in aberrations accompanying the movement of the lens, and recording becomes impossible. In order to perform recording with the diffusion optical system, it is necessary that the surface runout be ± 0.25 mm or less. The cause of the surface runout depends on the shaft runout of the motor, the warp of the board, and the hub mounting accuracy. Even if the accuracy is increased, the amount of surface runout should be ± 0.01 mm or less without using the surface runout prevention measures. Have difficulty.

Regarding the lens diameter, it is possible to reduce the lens diameter by reducing the surface runout. Since the device can be made smaller by reducing the lens diameter, the lens diameter is preferably 4 mm or less. However, it is not possible to accurately manufacture a lens having a small diameter, and a lens having a diameter of 1 mm is the limit.

A measurement example of surface wobbling will be described.

FIG. 9 shows the results of measuring the surface runout of the disk by mounting the hub on the substrate with less warp with high accuracy and using a motor with a small axial runout of the motor. Rotate a 2 inch diameter glass substrate at 3600 rpm and set the amount of surface vibration to 1 at the outermost circumference.
Measurements were made on 0 discs. The amount of surface vibration was ± 10 μm even with a small amount. ± 60 for most discs
μm or less, 1 nS even without taking measures for surface wobbling
It was possible to overwrite on a bTe phase change optical disk. The amount of surface vibration of a 2-inch diameter PC board is ± 150 μm to ±
It was 400 μm, and it 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. Aberrations other than those associated with the movement of the objective lens are 0.03λ, and the objective lens has a numerical aperture of 0.5, an aperture diameter of 2 mm, and a magnification of 0.2.

There is a Marshall limit as a criterion that the light can be condensed to the diffraction limit, and it is necessary to be 0.07λ (RMS) or less.

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

FIG. 21 shows an example of measurement of the aberration of the objective lens caused by following the surface deflection and decentering of the optical disk. The specifications of the objective lens used for the measurement are an effective diameter of 2 mm, an optical disk side numerical aperture of 0.52, and a light source side numerical aperture of 0.14. The range in which the aberration caused by the objective lens is 0.045λ or less when the objective lens moves to follow the surface runout and decentering of the optical disk is shown. Marshall's limit of 0.07 as the standard for aberration that can focus light to the diffraction limit
There is λ (RMS). In the optical disc device, aberrations are generated by both the optical head and the optical disc, so that the same aberrations are allowed. Therefore, the aberration caused by the optical head needs to be 0.05λ (RMS) or less. Aberrations are caused not only by the objective lens but also by the semiconductor laser and the optical parts. Therefore, the aberration caused by the objective lens needs to be 0.045 λ (RMS) or less. Therefore, here, a range in which the aberration is 0.045λ or less was obtained. By the way, when the optical head is assembled, an error occurs between the central axis of the semiconductor laser light and the central axis of the objective lens. Further, an error also occurs in the distance between the optical disk and the optical head. Since it is usually difficult to make this mounting error 100 μm or less, the moving range of the objective lens with respect to the surface runout and decentering of the optical disk becomes narrow. From the above, the surface wobbling and eccentricity allowed for the optical disk are shown by the shaded areas in FIG. The surface runout must be ± 340 μm or less and the eccentricity must be ± 200 μm or less. To allow both surface runout and eccentricity at the same time, surface runout ± 100 μm or less, eccentricity ± 200 μm
The following is desirable. However, when the course actuator moves the optical head to follow the eccentricity, the eccentricity allowed for the optical disk is widened to ± 300 μm or less. By improving the positioning adjustment accuracy of the optical head with respect to the surface runout, the allowable range can be expanded to ± 450 μm.

The write-once type and rewritable type optical disks require high light utilization efficiency. When the maximum output power of the light source is small, the optical system functions as a polarization beam splitter and an optical isolator with a λ / 4 plate. It is essential. Further, since the utilization efficiency of light is reduced when the diffraction grating is used, the push-pull method and the heterodyne method are used as the 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 create a composite prism in which parts such as a rising mirror and a knife edge for obtaining a focus error signal and parts for obtaining a toking error signal are integrally combined.

An embodiment of the composite prism used in the optical head of the present invention will be described with reference to FIG. The knife-edge method was used as the focus error signal detection method, and the push-pull method was used as the tracking error signal detection method. The P-polarized beam enters the polarization beam splitter 2, is raised by the raising mirror 10, and is circularly polarized by the λ / 4 plate 3. The reflected light from the optical disk is S-polarized by the λ / 4 plate 3, the polarized beam is reflected by the polarizing beam splitter 2, and is detected by the four-division sensor. The Foucault prism 7 puts the upper half of the returned light into two sensors for tracking signals. The Foucault prism 7 also serves as a knife edge, and is detected by a central two-divided sensor to obtain a focus error signal. The configuration of the detection optical system can be changed according to the method of detecting the focus error and the tracking error. The composite prism of this embodiment has a length of 5 mm, a width of 2.5 mm, and a height of 2.5 mm in accordance with the luminous flux diameter.
By using this composite prism, the optical system of the optical head of this embodiment is composed of four parts, that is, a semiconductor laser, a composite prism, a lens, and a detector. in this way,
By combining optical components, the number of components is reduced and the number of optical axis adjustment points that greatly affect the performance of the optical head is greatly reduced, making it possible to easily and accurately adjust the optical axis. In this embodiment, no lens is used in the detection optical system, but the detection lens may be used because the detection sensitivity of the error signal can be adjusted by using the detection lens.

A recording film using an organic material may require less light energy for recording than a recording film using an inorganic material, and recording is possible with a film surface of 5 mW. When the output of the semiconductor laser is high and the light utilization efficiency is low,
It is not necessary to use a polarization beam splitter, and a non-polarization beam splitter such as a half mirror may be used. Further, since the λ / 4 plate is unnecessary, the number of parts can be reduced and the cost can be reduced.

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

FIG. 22 shows an embodiment of an optical disc in which a beam is incident through a transparent case. In this embodiment, the rotating optical disc 6 is housed in a case having a narrow inner space to reduce the surface runout of the optical disc 6. The optical disk 6 uses a glass substrate, a PC substrate, and a PMMA substrate having a thickness of 0.5 mm as the substrate 151 having a diameter of 2 inches (49 mm).
A recording film 160 was formed on top of No. 1. The outer shape of the case is a credit case size of 84 mm in length and 54 mm in width for easy handling. In this embodiment, an optical disk for single-sided reproduction is used, in which the case on the light incident side is the transparent case 5 and the opposite side is the opaque protective case 170. In the transparent case 5, P
An MMA plate was used. The material of the transparent case 5 may be 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 case has a thickness of 1.5 mm.
mm. As a result, the amount of surface deflection of the board is ±
It can be suppressed to 0.2 mm. The sum of the thickness of the substrate through which the beam is transmitted and the thickness of the case is 0.8 mm. A hole was provided in the transparent case on the beam incident side, and the hub 51 was magnet-chucked to the spindle. The data recording range was 34 mmφ on the inner circumference to 48 mmφ on the outer circumference, and the storage capacity was 40 MB.

FIG. 23 shows an embodiment of an optical disk in card for double-sided reproduction. Two 0.5 mm optical disc substrates 1
51 and 152 with the recording films 160 and 161 inside, and UV
A resin adhesive 165 was used to bond them together. The transparent case 5 is attached to the optical disk part of the protective case 170,
It was used as a light incident part. The optical disk was rotated by magnetically chucking the hub 51 to the spindle. The transparent case 5 and the protective case 170 have 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 2 mm.
It became mm. The storage capacity is 80MB.

24 and 25 show the position of the light incident portion facing the optical head. It is desirable to shift the center of the optical disc in the longitudinal direction from the center of the case and handle the optical disc in card while holding the part opposite to the part where the optical disc is present. It is desirable to insert the optical disc in the optical disc device in the longitudinal direction of the case. The light incident part is preferably provided in the longitudinal direction of the case with respect to the center of the optical disc. In the embodiment of FIG. 24, the light incident window 201 is provided from the center of the optical disc toward 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 for 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. Due to the strength of the case, it is preferable that only the light incident window is a transparent case. Furthermore, since the space between the protective case and the optical disc is small, they come into contact with each other, and if scratched, the recorded information cannot be reproduced.
It is preferable to provide a measure so that the information recording portion of the optical disc does not come into contact with the case.

12 and 13, an optical disk in-card 20 for preventing the information recording portion of the optical disk from coming into contact with the case.
An example at 0 is shown.

In the embodiment of the optical disk in-card 200 of 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 scratched. The dust adhering to the optical disc 6 is wiped off by the dust-free cloth 31 during the rotation of the disc, so that the beam incident from the light incident portion 201 of the case 5 is not blocked by the dust. When the disk 6 rotates in contact with a rotating guide member such as the dust-free cloth 31 as in the present 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 so that the area 32 of the optical disk 6 where information is recorded does not come into contact with the case 5. In this embodiment, the dust-free cloth 31 is attached to the area where no information is recorded on the inner circumference of the disc, and the case 5 and the dust-free cloth 31 are rotated while being rubbed. According to this embodiment, the information recording area 32 on the outer peripheral portion of the disc does not come into contact with the case 5, and the surface wobbling of the optical disc 6 is reduced. In this embodiment, since the dust-free cloth does not generate dust and is flexible, the same effect can be obtained by using dust-free paper, rubber or the like in addition to the dust-free cloth.

In the present invention, since the surface wobbling of the optical disk is suppressed by rotating the optical disk in a case with a narrow interval, the beam entrance may be a transparent case or an opening.

FIG. 26 shows an embodiment in which a transparent case is not used but an opening is provided in the case so that a beam is incident. Two optical discs 6 each having a diameter of 2 inches (65 mm) and a substrate thickness of 0.6 mm were laminated. The structure of the optical disk is the same as that of the embodiment shown in FIG. The optical disk is housed in a protective case 170, and the opening 202 is covered and sealed with a protective cover 203 during storage. At the time of use, the protective cover 203 is moved to open the opening 202, and the hub 51
Was magnetically 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 is the same as that shown in FIG.

FIG. 27 shows an embodiment of a double-sided reproduction optical disc having a structure in which an opening is provided in a case and a beam is incident thereon. The optical disc 6 has a diameter of 2 inches (65 mm) and a substrate thickness of 0.6 mm. Optical disc has a protective case 1
70, and the opening 202 with the protective cover 203 during storage.
The lid was covered and sealed. During use, the protective cover 203 was moved to open the opening 202, and the hub 51 was magnetically 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 openings 202 are provided on both sides of the protective case 170. When the back side is used, both openings have the same shape so that the optical disk in card can be turned over and inserted. The outer shape of the protective case 170 is the same as that shown in FIG. The structure of the optical disk is the same as that of FIG. 22 and is shown by the same symbol.

FIG. 28 shows another embodiment of the optical disc and the case. The optical disk 6 used has a diameter of 2.5 inches (65 mm) and a substrate thickness of 0.6 mm. The surface runout of this disk was ± 0.2 mm or less. The optical disc is housed in a protective case 170 to prevent scratches and dust, and has a structure in which the opening 202 is covered with a protective cover 203 for sealing during storage. During use, the protective cover 203 was moved to open the opening 202, and the hub 51 was magnetically 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 is 72 mm long × 72 mm wide × 4.5 mm thick. In this embodiment, the protective case can be thinned by thinning the substrate and reducing the surface runout. The protective case 170 has a structure in which the optical disk 6 can be taken out and dust and dirt can be wiped off. FIG. 14 shows another embodiment for preventing surface wobbling of the optical disk. In this embodiment, the beam 9 passes through the case 5 and enters the optical disc 6, and the optical disc 6 is provided with a protrusion 33. Even if the optical disc 6 causes surface wobbling, the protrusion 33 first contacts the case 5, and The structure for suppressing the surface runout of No. 6 was adopted. The substrate was manufactured by an injection method using PC and PMMA. The protrusion 33 was formed at the same time when the substrate was formed. In the production of the substrate, the presence of the protrusions has an advantage that the difference in the contraction amount of the substrate is alleviated and the deformation of the substrate is reduced. The protrusion 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 disc in this embodiment. A protrusion 42 is provided on the optical disc 6 side, and a step 43 for guiding the optical disc 6 is provided on the case 5 side. With the protrusion 42 and the step 43,
The optical disc 6 has a space 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 is ± 0.03 mm, the eccentricity of the disk 6 is ± 0.03 mm or less. Protrusion 42 of disk 6
Was produced at the same time when the PC and PMMA substrates were produced by the injection method. Therefore, the center of the track and the center of the protrusion 42 can be accurately matched. The hub 41 for fixing and rotating the disk to the drive device was attached to the optical disk 6 so that the center of rotation of the disk and the center of the track would be ± 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 aligned with each other with high accuracy, and thus a disk with a small eccentricity can be manufactured. in this case,
It is not necessary 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 surface wobbling of the optical disk 6, the surface wobbling is small because it is the protrusion 42 or the center part of the optical disk.

FIG. 16 shows an embodiment in which the disc and the rotation axis of the motor are not displaced. In this embodiment, when the hub 51 is attracted by the magnet 53 and fixed to the fixing portion 54 of the hub 51 in order to fix the optical disk 6 to the motor rotation shaft 52, a taper is provided on the rotation shaft 52 and the hub 51 of the motor. Thus, no gap is formed between the rotary shaft 52 and the hub 51. In this embodiment, in order to perform recording on both sides of the disk 6, openings for inserting the rotary shaft are provided above and below the case 5, and tapers are provided on both sides of the hub 51. For a single-sided optical disc, it is sufficient to provide a taper only on the side where the rotary shaft is inserted.

In addition to the two-dimensional actuator, the optical disk device has a course actuator that moves the entire optical head to move the optical head, and the course actuator can follow the eccentricity of the entire optical head. As described above, when the entire optical head is moved by the coarse actuator to perform tracking with respect to the eccentricity of the disk, the amount of movement of the objective lens is small, and the aberration and the change in light utilization efficiency are small.

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

Another embodiment will be described. When a cube-type polarization beam splitter is used, aberration occurs when diffused light passes, so it is necessary to correct it in advance when designing the lens. Further, it is necessary to accurately control the thickness of the beam splitter so as to reach the designed value. As a method of guiding a beam to an objective lens without passing through 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. A polarization separation film 23 is formed on the surface of the beam splitter 22.
Is attached so that only light having polarized light parallel to the surface of the beam splitter 22 is reflected. The light which has been circularly polarized by the λ / 4 plate 3 and which has been transmitted through the case 5 and then reflected by the disk 6 becomes polarized light in the direction perpendicular to the incident light at the λ / 4 plate 3 and is transmitted through the beam splitter 22 to be detected. Detected at 8. Astigmatism generated in the beam splitter 22 is used to obtain the focus error signal. An aberration compensating plate or a lens may be added in order to obtain a highly accurate error signal or to obtain a degree of freedom in optical design. In this embodiment, the detector 8 is placed on the side opposite to the disk 6 with respect to the beam splitter 22.
And the beam splitter 22 may be on the same surface.

Another embodiment will be described with reference to FIG. Figure 1
In order to further reduce the size of the optical head of the seventh embodiment, the laser 1 and the detector 8 are placed in the same direction. A reflector 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 separation film 23, transmitted through the λ / 4 plate 3, and focused by the objective lens 4 on the optical disc 6 through the case 5. The reflected light from the optical disc 6 is reflected by the polarization separation film 2
3, the light is transmitted through the beam splitter 22, reflected by the reflecting portion 24, and detected by the detector 8. Since the reflected light is condensed at a position different from the light emitting point of the laser 1 by the refraction of the beam splitter 22, the laser 1 and the detector 8 can be installed without interference. However, as described above, it is impossible to set the distance between the semiconductor laser 1 and the disk 6 to 20 mm or less by the conventional method. In this embodiment, the optical disc 6 is housed in the transparent case 5 so that the distance between the semiconductor laser 1 and the optical disc 6 is reduced to 1.
It was possible to make it 0 mm. The present invention enables downsizing of an optical head, which has been impossible in the past. The size of the optical head in this embodiment is 20 mm in length, 10 mm in width, and 5 mm in height.
Became.

FIG. 19 shows the structure 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,
It is condensed by the objective lens 6 and enters the optical disc 6 through the case 5. Therefore, when the reflectance of the half mirror 25 is R, the transmittance is T, and the condensing efficiency of the objective lens is η, the power Pd reaching the optical recording medium in the output power P of the light source 1 is Pd = ηRP. . Since the power reaching the optical disk increases as the reflectance R increases, R ≧ T is desirable.

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

When the ratio of the reflectance and the transmittance of the half mirror 25 is made to reach the optical disk 6 in this way, the power Ps reaching the detector 8 is such that when the reflectance of the optical disk 6 is r. Since Ps = ηrRTP and the transmittance T is small, the amount of light reaching the detector is reduced and the reproduction signal is reduced. Therefore, it is desirable to increase the output P of the light source during reproduction so that the amount of light reaching the detector is the same.

In this embodiment, the half mirror 25 with R = 70% and T = 30% is used to increase the power reaching the optical disk 6. 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, but in that case, the reflectance and the transmittance are reduced. Swap the size of R
≦ T. In this embodiment, since the reflectance of the half mirror 25 is high, the proportion of the light reaching the detector 8 is small as compared with 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 reproduction light of mW to 1.7 mW, the amount of light reaching the detector 8 was secured at the same level as when a half mirror with R = T = 50% was used. The objective lens 4 has a C
With a magnification of 0.24 used for D,
An optical head having a light utilization efficiency of 30% was manufactured. 5 for light source 1
Using a semiconductor laser of 0 mW, 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-based phase change optical disk medium. As the half mirror 25, not only the reflective type as in the present embodiment but also the 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 an optical disk device in which the optical disk in card of FIG. 29 and an optical head are combined. The optical head 300 is attached to the course actuator 700 and can move in parallel with the optical disc in card 200. These are built in the optical disk device chassis 800. In this embodiment, the course actuator 70
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 optical head 300 has a thickness of 6 mm, a weight of 25 g, and an average access time of about 100 ms. As the optical disk in card 200, a one-sided recordable thickness of 1.5 mm was used. The thickness of this optical disk device excluding the circuit was 10 mm, and the thickness of the optical disk device was 15 mm when the circuit was added, making it possible to mount it on a laptop or notebook computer or workstation.
The thickness of this optical disk device can be reduced to 12 mm by advancing the circuit to LSI. In this embodiment, an optical system having a beam diameter of 2 mm was used, but by changing this to an optical system having 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 this embodiment can be used even when the beam is incident from the opening of the case of the optical disk.

Also in this configuration, by increasing the thickness of the device by 0.5 mm, it is possible to easily use the optical disk in card capable of double-sided recording. 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 taken out from the device, turned over, and inserted into the device.

FIG. 30 shows an embodiment in which the embodiment of FIG. 29 is changed to a device capable of simultaneously recording and reproducing on both sides. A 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 the course actuators 700 and 701, respectively. . These are built into the optical disk device 800. With this configuration, the optical disc in card 200 can record information on both sides without having to turn it over. In addition, 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 synchronously driving the optical heads 300 and 301, the data transfer rate can be effectively doubled. With this configuration, the thickness of the device can be reduced to 20 mm, and it can be mounted on laptop or notebook computers and workstations. For the double-sided optical disk, the type of optical disk medium may be changed for each side, such as one side of the ROM and one side of the rewritable optical disk.

FIG. 20 shows an embodiment of an optical disc system using the optical head of the present invention. The reproduction signal of the optical head 71 passes through the preamplifier 75 and the drive microcomputer 81.
Entered and processed. Focus servo 7 from playback signal
6 and the tracking servo 77 are performed. When the laser output is modulated for recording, the laser drive unit 78 controls the current passed through the laser. Control of rotation speed of spindle motor 74 and course actuator 73
The control of the positioning of the optical head 71 is performed by the spindle servo 79 and the course actuator servo 80, respectively. The drive microcomputer 81 performs signal processing for controlling the focus, tracking, spindle, and coarse actuators. The control of the optical disk system is performed by the control microcomputer 82. Optical head 7
1, a disc-in-card 72 in which an optical disc is housed in a case, a course actuator 73, and a spindle motor 74 are 100 mm in length, 60 mm in width, and 10 mm in height.
I put it in 3. A linear actuator having a thickness of 5 mm was used as the course actuator. The spindle motor has
A disk having a thickness of 5 mm was used, and the rotary shaft of the disk was driven by a belt or directly. Rotation speed is 3600rp
m.

The present invention has been described by using the optical head and the optical disk device using the write-once type using phase change, the rewritable type using phase change, and the read-only type. With respect to the optical head and the optical disk device used, the same effect can be obtained only by changing the detection optical system.

Since the optical head of the present invention uses the diffusing optical system, the number of constituent parts is reduced and the optical head can be easily miniaturized. Due to the miniaturization of the optical head, not only the optical disc device can be miniaturized, but also the movement time of the optical head can be shortened and the data transfer time can be shortened.

In the diffusing optical system, the aberration is minimized when the objective lens and the optical disc are at fixed positions, and light can be condensed to the diffraction limit. When performing focusing and tracking in the optical disc device, the objective lens moves in a direction perpendicular to the disc and in a direction parallel to the disc. However, in the optical disc device of the present invention, the aberration generated in the light due to this movement is small, and The light is now fully available.

Further, due to this focusing and tracking, the light utilization efficiency showing the ratio of the light energy reaching the recording surface to the light energy emitted from the light source is changed. According to the present invention, even in an optical head that has a small movement amount of the objective lens when performing focusing and tracking and has a large light utilization efficiency, the change in the light utilization efficiency due to the movement of the objective lens is small. Therefore, an optical head with high light utilization efficiency could be manufactured.

In the case of the optical disc, the distance between the light source and the objective lens can be reduced because the amount of surface vibration and the amount of eccentricity of the disc are small. An optical head capable of recording information using a diffusion optical system has been realized.

[0145]

According to the present invention, the light utilization efficiency can be increased in the optical head using the diffusing optical system by reducing the surface vibration amount and the eccentricity amount of the disk. Therefore, it was possible to manufacture an optical head having a small number of parts, small size, and capable of recording information. Moreover, since the magnification of the objective lens is increased in order to increase the light utilization efficiency, the distance between the light source and the objective lens is reduced and the optical head can be made smaller than the conventional optical head using the diffusion optical system. Further, since the amount of surface vibration is small, the working distance of the objective lens can be shortened and the optical head can be made thin.

The optical disk device can be downsized by downsizing the optical head. Then, by increasing the light utilization efficiency, an optical information recording / reproducing apparatus using the diffusion optical system could be manufactured.

[Brief description of drawings]

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

FIG. 2 is a sectional view of an optical head and an optical disc of the present invention.

FIG. 3 is an example of a case of an optical disc.

FIG. 4 is a result of measuring the amount of surface vibration of an optical disc housed in a case.

FIG. 5 shows the relationship between the magnification of the diffusing optical system and the light use efficiency.

FIG. 6 shows the relationship between the luminous flux diameter and the working distance.

FIG. 7 shows the relationship between the luminous flux diameter and the optical head thickness.

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

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

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 is an embodiment in which a dust-free cloth is used to prevent contact between the disc and the case.

FIG. 13 is another embodiment in which a dust-free cloth is used to prevent contact between the disc and the case.

FIG. 14 is an embodiment for preventing surface wobbling of a disc.

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

FIG. 16 is an example of a hub and a rotating shaft for preventing eccentricity of a disc.

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

FIG. 18 is a configuration diagram of an optical head and an optical disc according to still another embodiment of the present invention.

FIG. 19 is an example using a half mirror.

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

FIG. 21 is a result of measuring the allowable range of surface runout and eccentricity.

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

FIG. 23 is an example of a double-sided reproduction optical disk 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 portion.

FIG. 25 is another explanatory view showing the position of the light incident portion.

FIG. 26 is an example of an optical disk in card in which a beam is incident through an opening.

FIG. 27 is an example of an optical disk incart for double-sided reproduction in which a beam is incident through an opening.

FIG. 28 is an example of an optical disc in which a beam is incident through an opening.

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

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

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

FIG. 32 is an example 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 is a measurement result of the relationship between the return light rate and laser noise.

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

[Explanation of symbols]

1 ... Semiconductor laser, 2 ... Polarization beam splitter, 3 ... λ
/ 4 plate, 4 ... Objective lens, 5 ... Transparent case, 6 ... Optical disc, 7 ... Foucault prism, 8 ... Detector, 9 ... Beam, 10 ... Stand-up mirror, 11 ... Composite prism, 12
… Optical head chassis, 22… Polarizing beam splitter, 2
3 ... Polarization separation film, 24 ... Reflector, 25 ... Half mirror,
31 ... Dust-free cloth, 32 ... Information recording area, 33 ... Projection part, 4
DESCRIPTION OF SYMBOLS 1 ... Hub, 42 ... Eccentricity prevention protrusion, 43 ... Eccentricity prevention step, 51 ... Hub, 52 ... Rotating shaft, 53 ... Magnet, 54 ... Hub fixing part, 71 ... Optical head, 72 ... Optical disk in-card, 72 … Course actuator, 74… Spindle motor, 75… Preamplifier, 76… Focus servo, 7
7 ... Toking servo, 78 ... Laser drive unit, 79 ... Spindle servo, 80 ... Coarse actuator servo,
81 ... Drive microcomputer, 82 ... Control microcomputer, 83 ... Chassis, 200 ... Optical disc in card,
201 ... Light incident part.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hiroyuki Minemura             4026 Kujimachi, Hitachi City, Ibaraki Japan             Tachi Works Hitachi Research Laboratory (72) Inventor Hisato Ando             4026 Kujimachi, Hitachi City, Ibaraki Japan             Tachi Works Hitachi Research Laboratory

Claims (12)

[Claims] 1. An optical head having an objective lens having a diameter of 1 to 4 mm, into which light emitted from a light source is incident as diffused light, and equipped with an optical head for recording at least information on a disc by the light condensed by the objective lens. Optical disk device. 2. A light source, an objective lens for condensing light on a disk, a beam spirit that guides the light from the light source to the objective lens as diffused light, and light between the beam spirit and the objective lens. An optical disk device equipped with an optical head having a λ / 4 plate that polarizes light on the road. 3. An optical recording medium for storing information, which is formed on a disk substrate having a light transmitting property, functions as an optical memory which is rotatably housed so as to regulate a vertical shake. Is emitted as diffused light with a diameter of 1 to 4
irradiating the optical recording medium with light condensed by a mm objective lens, recording information on the optical recording medium, reproducing information recorded on the optical recording medium, and An optical head for performing at least one of erasing recorded information, means for accommodating the optical memory in a predetermined relation position with the optical head, rotating means for rotating the optical recording medium, and An optical disc device comprising: a drive circuit for controlling the operation of an optical head and the rotation of the rotating means. 4. An optical head for condensing incident light as diffused light emitted from a light source and irradiating the disc for recording at least information, means for rotating the disc, and rotation of the disc accompanying the rotation. An optical disk device comprising: a means for suppressing blurring; a means for accommodating a disk in a recordable positional relationship with the optical head; and a drive circuit for controlling the operation of the optical head and the rotation of the rotating means. 5. An optical memory, which is rotatably housed in a credit card-sized case, so as to regulate a vertical shake of an optical recording medium for storing information, which is formed on a disc substrate having a light transmitting property. The optical recording medium is irradiated with light condensed by an objective lens having a diameter of 1 to 4 mm, which functions as a diffused light and functions as a diffused light, and records information on the optical recording medium. An optical head for performing at least one of reproducing the information recorded on the optical recording medium and erasing the information recorded on the optical recording medium, and the optical memory at a predetermined relation position with the optical head. An optical disk device comprising: a housing means, a 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. 6. The optical disk device according to claim 5, wherein the case has a portion having a light transmitting property, and information is recorded, reproduced and / or erased by the light irradiated through the portion. 7. An optical memory in which an optical recording medium for storing information formed on a disk substrate having a light-transmitting property is housed so as to have a vertical rotational shake of 0.10 to 0.25 mm. An objective lens that functions and is irradiated with light from a light source as diffused light, collects light, irradiates the optical recording medium, records information on the optical recording medium, and records the information on the optical recording medium. An optical head having an optical path distance of 5 to 20 mm between the light source and the objective lens, which performs at least one of reproducing information stored in the optical recording medium and erasing information recorded in the optical recording medium, An optical disc device having means for accommodating the optical memory in a predetermined relation position with the optical head, 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. 8. An optical memory, which rotatably accommodates an optical recording medium for storing information, which is formed on a disc substrate having a light transmitting property, functions as a diffused light from a light source. The information collected by the objective lens having a diameter of 1 to 4 mm is irradiated onto the optical recording medium, and 25 to 50% of the light emitted from the light source is irradiated onto the optical recording medium to record information. An optical head for reproducing and / or erasing, a means for accommodating the optical memory in a predetermined relation position with the optical head, a rotating means for rotating the optical recording medium, an operation of the optical head and the rotating means. Drive circuit for controlling the rotation of the optical disc device. 9. An optical memory, which rotatably accommodates an optical recording medium for storing information, formed on a disk substrate having a light-transmitting property, functions as a diffused light from a light source. The objective lens is irradiated in the range of 0.25 to 1.00 mm, the light is condensed and applied to the optical recording medium, and 25 to 50% of the light emitted from the light source is recorded in the optical recording. An optical head for irradiating a medium to record, reproduce and / or erase information, means for accommodating the optical memory in a predetermined relation position with the optical head; rotating means for rotating the optical recording medium; An optical disc device comprising: a drive circuit for controlling the operation of an optical head and the rotation of the rotating means. 10. A numerical aperture for irradiating light as diffused light, which functions as an optical memory rotatably accommodating an optical recording medium for storing information formed on a disk substrate having a light transmitting property. Objective lens of 0.5-0.6 is set to 0.25-
An optical head for operating in the range of 1.00 mm, condensing light to irradiate the optical recording medium to record, reproduce and / or erase information, and the optical memory at a predetermined relation position with the optical head. An optical disk device comprising: a means for accommodating the optical disk, a 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. 11. An optical recording medium for storing information, which is formed on a disk substrate having a light-transmitting property, is rotatably accommodated and is irradiated with light having a constant wavelength as diffused light. The ratio of the wavelength to the numerical aperture is 0.65 to record light with an objective lens having a constant numerical aperture and irradiate the optical recording medium to record, reproduce and / or erase information.
1.66 optical head, means for accommodating the optical memory at a predetermined relation position with the optical head, rotating means for rotating the optical recording medium, operation of the optical head and rotation of the rotating means And an optical disc device having a drive circuit for performing. 12. An optical recording medium for storing information, which is formed on a disk substrate having light transparency, functions rotatably in an optical memory, and the light is irradiated as diffused light at a magnification of 0. The light is condensed by an objective lens of .20 to 0.35 and is irradiated to the optical recording medium with a light intensity of 5 to 25 mW.
An optical head for recording, reproducing and / or erasing information, means for accommodating the optical memory in a predetermined relation position with the optical head, rotating means for rotating the optical recording medium, operation of the optical head and rotation An optical disk device having a drive circuit for controlling the rotation of the means.