JPH07302437A - Optical head device and lens - Google Patents

Abstract

PURPOSE:To execute good reproduction with plural information recording media varying in specifications in spite of the constitution small in size and low in cost by providing an objective lens having functions to form a condensed light spot on the recording surfaces of optical memories varying in specifications. CONSTITUTION:The laser beam emitted from a laser 614 transmits a collimator lens 618 and is introduced to a beam splitter 616. The laser beam reflected by this beam splitter 616 is condensed by an objective lens 600 and the microspots are formed on the signal recording surfaces 620a, 622a of the optical disks 620, 622 having different disk thicknesses. The signal recording surfaces are formed on a transparent substrate. The light beams reflected by the optical disks 620, 622 propagate backward in the same optical paths. Namely, the reflected light beams are made incident via the objective lens 600 and a converging lens 626 on a holographic element(HOE) 624, by which the light beams are diffracted. These light beams are detected by the photodetector 628.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head device,
In particular, the present invention relates to an optical head device capable of easily performing at least reproduction of an optical memory such as a plurality of optical disks having different specifications and standards, and a lens used therein.

[0002]

2. Description of the Related Art A technique for irradiating an optical disc with a light beam and detecting the reflected light to reproduce the information recorded on the optical disc is widely put to practical use as a CD (compact disc), an LD (laser disc) device or the like. Has been done. In such an optical disc reproducing apparatus, a light beam emitted from a light source such as a semiconductor laser is focused on a signal recording surface of the optical disc by an objective lens, and reflected light from the optical disc is detected by a photodetector to be recorded on the optical disc. Play the information that has been recorded.

In such an optical disc, the recording density has been increased, and an optical disc having a standard different from that of the conventional optical disc has come to exist. For example, the size of a pit, which is the unit for recording information, is
Currently it is about 1 micron, but there is a high possibility that it will be reduced to submicron.

The recording density of an optical disk is determined by the size of a recording / reproducing light spot irradiated onto the optical disk by an optical head (pickup) for reading minute pits for recording information formed on the optical disk. .

The diameter of this spot depends on the wavelength of the laser used and the numerical aperture (NA: Numerical Apertur) of the objective lens.
It is determined by e) and is expressed by spot diameter = k × laser wavelength / NA. k is a constant.

Therefore, in order to read a higher density optical disc by using a small spot, it is necessary to use one having a short laser wavelength or a lens having a large NA.

In the conventional optical head device, the objective lens is
Since it has only one optical disk, it is impossible to read a high-density optical disk with an optical head equipped with an objective lens corresponding to the conventional optical disk.

That is, the optical head for high density has a NA
When an objective lens having a large size is used, if the optical disc is tilted with respect to the objective lens, the spot disturbance becomes large, and therefore it cannot be commonly used in many cases. According to the conventional standard, the warp of the optical disc and the like are allowed up to a large value, but the new optical disc allows only the warp with a small value, so that the optical disc with the large warp cannot be read. Because of that.

The spot disturbance is affected by the thickness of the optical disc, and the thin optical disc has a small spot disturbance even if the optical disc is tilted. There is also an example where it is used as a substrate.

In addition, even if the same optical disc is used, the optimum specifications of the objective lens may differ between the time of recording and the time of reproduction, but since it has a configuration having only one objective lens, this cannot be dealt with. There was a problem.

Further, discs having different substrate thicknesses are also emerging as a new standard, and there is a risk that the new device will not be able to record or reproduce information on discs of conventional standards.

The standard is the thickness of the disk substrate.
This type of optical disc generally has a structure in which a reflective film is formed on a transparent substrate (hereinafter referred to as a disc substrate) on which information is recorded in the form of pits, and a protective layer is formed thereon. The light beam is applied to the reflective film, which is the signal recording surface, from the transparent substrate side. In this case, the reproduction characteristic changes depending on the thickness of the disc substrate. Even if the objective lens has the same numerical aperture, the thinner the disc substrate, the smaller the transmitted wavefront aberration due to the disc tilt, and the better the condensing characteristics of the condensing spot on the signal recording surface. Therefore, the quality of the reproduced information signal is high. Is obtained. Therefore, an optical disk device using an optical disk having a thin disk substrate has appeared.

As described above, when a plurality of types of optical discs having different specifications and standards are present, it is naturally demanded that these can be reproduced by the same device. Therefore, a method has been adopted in which one recording / reproducing apparatus is provided with a plurality of optical heads according to the type of optical disk and these are mechanically switched according to the disk used.

This method is reliable, but since it is necessary to prepare a plurality of optical heads and a plurality of mechanisms for driving / switching them, it is the same cost as providing a plurality of recording / reproducing devices. However, the installation space is required, and the original merit of recording / reproducing optical discs having a plurality of specifications with the same device is lost.

On the other hand, as described above, when the NA is increased, the influence of the lens aberration increases in proportion to the cube of the NA, and the influence easily occurs. Although there is a drawback that the distortion of the spot becomes large when tilted, a technique called "super-resolution" has been devised to solve this. For example, as described in US Pat. No. 5,121,378,
It has been reported that when a donut-shaped lens is constructed by blocking the central part of the lens, the spot diameter by the lens is reduced by 10 to 20% as compared with the case where the lens is not covered.

Particularly, when a laser beam is used as a light source, not only a part of the lens is covered but also the thickness of a part of the lens is changed.
It has also been reported that the same effect can be obtained by changing the light phase to an extent that affects the phase of the light and configuring it in a concentric shape.

However, in the above technique, since the shielding member is required, the optical system becomes large and complicated. Moreover, there is a problem that the light efficiency is deteriorated by the shielding member.

As described above, since the conventional optical head device has a configuration having only one objective lens, it is desired to use a plurality of optical discs having different standards such as a difference in recording density, a warp allowable amount, a substrate thickness and the like. In this case, or even with the same optical disc, there is a problem that it cannot be dealt with when the optimum lens specifications differ between recording and reproduction.

It is possible to prepare a plurality of dedicated optical heads using a dedicated objective lens adapted to each standard or specification and switch and use them. In such a case, the mechanism is However, there is a problem in that it cannot be put to practical use because not only it becomes complicated and the device becomes large, but also the cost increases.

[0020]

SUMMARY OF THE INVENTION The present invention has been made to address the above-mentioned circumstances, and its object is to provide a plurality of information recording mediums having different specifications while having a compact and inexpensive structure. The present invention provides an optical head device capable of performing at least good reproduction, and a lens used therein.

[0021]

An optical head device according to the present invention comprises a light source, an objective lens for focusing and irradiating a light beam emitted from the light source onto a recording surface of an optical memory, and light reflected from the recording surface. In the optical head device configured to guide the signal to the detection means and detect the signal, the objective lens is an objective lens having a function of forming a focused spot on the recording surfaces of a plurality of optical memories having different specifications. .

In the optical head device of the present invention, the objective lens is an objective lens having a function of forming a focused spot of the light beam emitted from the light source on the recording surfaces of a plurality of optical memories having different substrate thicknesses. Is characterized by.

In the optical head device according to the present invention, the objective lens has a function of forming the light beam emitted from the light source on the recording surface of a plurality of optical memories having different recording densities and forming a condensed spot having a size suitable for the recording density. It is characterized in that it is an objective lens having.

In the optical head device of the present invention, the objective lens is characterized in that the lens surface is divided into a plurality of areas in the shape of a ring, and each area has a lens surface shape with different specifications.

In the optical head device of the present invention, a plurality of objective lenses designed to form an optimum focused spot on the recording surface for each of a plurality of optical memories having different specifications are divided into a plurality of ring shapes. It is characterized by being arranged in the area.

In the optical head device of the present invention, one of the surfaces of the objective lens has a common lens surface shape. In the optical head device of the present invention, the objective lens is configured to have a lens surface shape that does not cause a step in each of the boundary portions of the plurality of regions divided into the ring shape.

In the optical head device of the present invention, the objective lens forms a focused spot on the recording surface of a plurality of optical memories having different specifications, and the distance (working distance) between the exit surface of the objective lens and the incident surface of the plurality of optical memories. ) Is constant.

In the optical head device of the present invention, when the objective lens is divided into a plurality of regions, the areas are distributed on the basis of the reproduction signal frequency or the information recording density of a plurality of optical memories having different specifications.

In the optical head device of the present invention, a light source,
It is characterized in that it further comprises means for integrally supporting the objective lens and the light detecting means, and the light detecting means detects the reflected light from the recording surface while the supporting means moves.

In the lens according to the present invention, the first light is incident.
And a second surface that emits light, and at least one of the first surface and the second surface is concentrically divided into a plurality of lens surfaces having different optical characteristics. Characterize.

In the lens of the present invention, the width of each of the concentric lens surfaces is larger than the wavelength of light. In the lens of the present invention, the lens surfaces divided into concentric circles have different focal lengths.

In the lens of the present invention, the lens surfaces divided into concentric circles have different numerical apertures. The lens of the present invention is characterized by being formed by molding or injection using plastic or glass. In the lens of the present invention, the number of divisions is 3 or more.

[0033]

According to the present invention, the light source, the objective lens for focusing and irradiating the light beam emitted from the light source onto the recording surface of the optical memory, and the reflected light from the recording surface are guided to the light detecting means to detect a signal. By configuring the objective lens to have a function of forming a focused spot on the recording surface of a plurality of optical memories having different specifications,
In addition, it is possible to perform at least good reproduction with a single optical head device on a plurality of information recording media having different specifications even though the structure is inexpensive.

[0034]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of an optical head device according to the present invention will be described below with reference to the drawings. FIG. 1 is a schematic view of an objective lens used in the optical head device of the first embodiment.
The objective lens 600 is configured such that at least one surface thereof is concentrically divided into a plurality of lens surfaces, and each lens surface has different optical characteristics. FIG. 1A shows a plan view of the objective lens viewed from the light source side, and FIG. 1B shows a sectional view thereof. The surface of the objective lens 600 on the light source (not shown) side has two concentric circles 602 and 604.
Is divided into The inner lens surface 602 has a circular shape, and the outer lens surface 604 has a ring shape (donut shape). The other surface (disk-side surface) 606 is a normal continuous lens surface. The lens surface 602 projects more outward than the lens surface 604, and the lens surfaces 602 and 604 have different focal lengths. Focal plane 6 of inner lens surface 602
08 is farther from the focal plane 610 of the outer lens surface 604. As described above, the objective lens 600 is equivalent to a lens in which two lenses having different focal lengths are concentrically combined.

Although the surface 606 on the disk side is a continuous surface, this surface may also be concentrically divided into two lens surfaces. When using the objective lens 600 of FIG. 1, it is necessary to dispose the signal recording surface of the optical disc on either the focal plane 608 or 610. When the signal recording surface of the optical disc is configured to be located at the focal surface 610, only the light that has passed through the lens surface 604 is focused at the focal surface 610, and the light that has passed through the lens surface 602 is focused farther than the focal surface 610. However, the focal plane 610 is blurred. Therefore, the light passing through the lens surface 602 does not return to the photoelectric conversion element (not shown in FIG. 1) for signal detection. Alternatively,
Even if it returns, the intensity is very weak, so that it does not become an interference signal or a noise signal with respect to the main signal based on the light passing through the lens surface 604. Thus, the lens 600 can be used as a lens having two focal lengths. In the optical disk device, the position of the disk is constant, so that it is necessary to move the objective lens in the focus direction when the position of the signal recording surface of the disk changes.

FIG. 2 is a schematic view of the entire optical head device using the lens 600 of FIG. 1 as an objective lens. The laser light emitted from the laser 614 is collimator lens 61.
8 and is guided to the beam splitter 616. The laser light reflected by the beam splitter 616 is focused by the objective lens 600 shown in FIG. 1, and the signal recording surfaces 620a, 62 of the optical disks 620, 622 having different disk thicknesses.
A minute spot is formed on 2a. The signal recording surface is formed on the transparent substrate.

The light reflected by the optical disks 620 and 622 propagates in the opposite direction along the same optical path. That is, the reflected light is incident on the holographic element (HOE) 624, which is a polarizing element, through the objective lens 600 and the converging lens 626. The light beam that is diffracted by the holographic element 624 is detected by the photodetector 628.

The output signal of the photodetector 628 is input to the signal processing circuit 630 including an amplifier and an arithmetic circuit. The signal processing circuit 630 performs various calculations on the output signal of the photodetector 628 to generate a focus error signal, a tracking error signal and a reproduction information signal. The focus error signal and the tracking error signal are supplied to the focusing coil 632 and the tracking coil 634 via an actuator drive circuit (not shown). These coils 63
The objective lens 600 is moved by 2, 634 to control the position of the light spot on the optical disk in the optical axis direction and the tracking direction. The reproduction information signal is supplied to a data reproduction circuit (not shown).

As shown in FIG. 3, the holographic element 624 has an area dividing line 623 in the same direction as the track direction.
It is divided into two regions 625a and 625b by c. In these areas 625a and 625b, in order to cause a change in the shape of the light beam necessary for focus error detection, one is a pincushion-shaped one, and the other is a barrel-shaped hologram in which gratings at regular intervals are transformed. Are formed. In addition, the diffracted lights of the regions 625a and 625b are separated on the light receiving surface of the photodetector 628,
The average lattice spacing is different between the regions 625a and 625b. As a result, the diffracted light 630a from the region 625a receives the light receiving surfaces 629a and 629b of the photodetector 628.
Diffracted light 630b from the region 625b is condensed in a region that straddles the light receiving surface 629c and 629d of the photodetector 628.
Focus on the area that spans.

Here, the light receiving surface 629 of the photodetector 628.
When the detection signals corresponding to a, 629b, 629c, and 629d are 629A, 629B, 629C, and 629, respectively, the focus error signal Sf, the tracking error signal St, and the reproduction information signal Si are obtained by the calculation of the following equation.

Sf = (629A-629B) + (629C-629)
D) St = (629A + 629B)-(629C + 629)
D) Si = (629A + 629B + 629C + 629D) In the optical head device of FIG. 2, the photodetector 628 is arranged on the focal plane of the converging lens 626. Therefore, the reflected light through the objective lens 600 is a parallel beam both when recording / reproducing the disk 620 and when recording / reproducing the disk 622. When the focus detection is performed by, for example, the astigmatism method, the regions 629a to 629d of the photodetector 628 are detected.
Since it is possible to detect the in-focus point regardless of the thickness of the beam applied to the upper side, it is possible to detect the focus of two disks with the same detector.

On the other hand, regarding the tracking error detection, the conventional three-beam method, push-pull method, etc. can obtain the tracking error signal regardless of the size of the light spot on the photodetector. Therefore, with such a configuration, it is possible to design an optical head that obtains a correct tracking error signal for both disks.

The above is a general example. Next, as a specific example, a case where recording / reproducing of a compact disc (CD) and a high density optical disc are performed by the same optical head device will be described. The standard of the compact disc is that the laser wavelength is 780 nm, the NA is 0.45, and the substrate thickness is 1.2 mm. On the other hand, as a high density optical disc for compressing and recording moving image information, the laser wavelength is 680 nm,
A NA of 0.6 and a substrate thickness of 0.6 mm are considered. If the disc thickness is different, the optical head device is designed so that the distance (working distance) between the disc and the lens is as equal as possible even if the disc changes, and the position of the objective lens changes as the disc changes. There is an effect that it is not necessary to change and the design of the entire mechanical system becomes easy.

FIG. 4A is a perspective view showing an example of a high density optical disk, and FIG. 4B is a view showing the difference in the focal length of the objective lens 600 when a compact disk and a high density optical disk are used. . The compact disc is a transparent substrate 720 having a substrate thickness t2 (= 1.2 mm) and a reflective layer 72.
4 and a protective layer 722.

The high density optical disc 700 has transparent substrates 701 and 702 each having a substrate thickness t2 (= 0.6 mm).
Two discs including the reflection layers 703 and 704 and the protection layers 705 and 706 are provided on the protection layer 705 through the adhesive layer 707.
706 are attached so that they face each other. A transparent resin such as polycarbonate or acrylic is used as the transparent substrate, and aluminum or the like is used as the reflective layer. The adhesive layer 707 is made of a thermosetting adhesive having a thickness of several tens of μm. A hole 708 for clamping is formed in the center of the high density optical disc 700, and a clamping zone 709 is provided around the hole 708.

A reproduction light beam emitted from a laser diode (not shown) and incident through the reproduction optical system is transmitted through the objective lens 600 to the transparent substrates 720 and 70 on the disk.
The light enters from the side of 1, 720 and the reflection films 722, 703, 70
It is focused as a minute beam spot on the surface 4.

Since the high-density optical disc 700 uses the thin substrates 701 and 702 having a thickness of 0.6 mm, it is more susceptible to dust and dirt attached to the surface than a CD using a substrate having a thickness of 1.2 mm. Therefore, it may be housed in a cartridge (not shown). When the high-density optical disc 700 is housed in a cartridge, it is not necessary to pay attention to how to hold the disc, dust, fingerprints, etc. like a CD, and it is advantageous in terms of handling and carrying. When the disc is exposed like a CD, it is necessary to determine the error correction capability in consideration of an unexpected situation such as a scratch, but when a cartridge is used, such consideration is unnecessary. Therefore, as used in an optical disk capable of recording and reproducing, LD
A C-Reed-Solomon error correction scheme can be used. As a result, when the optical disk is formatted in units of 2 K to 4 K bytes, for example, the recording efficiency can be increased by 10% or more as compared with the CD.

As an example, a 4/9 modulation system is used as a modulation system of information recorded on the high density optical disc 700, and the track pitch on the high density optical disc 700 is 0.72 μm and the pit pitch is 0.96 μm.
Compared with the conventional CD format, the pit density ratio is 3.84 times, the modulation method is 20%, and the format efficiency is 1
Since an improvement of 0% is expected, a total capacity increase of about 5.1 times can be expected. S for moving image information such as movies
-When recording / reproducing with a high image quality as high as VHS, the rate including the voice is 4.5 Mbps, so that the capacity required for 2 hours of reproduction is 4 GB. By increasing the capacity 5.1 times as described above, this capacity of 4 GB can be realized on one side of the disk. Furthermore, if the optical disc is double-sided as shown in FIG. 4, recording can be performed for up to 4 hours on a single optical disc.

In general, lens diameter is related to NA. For a high density optical disc having a disc thickness of 0.6 mm, it is preferable to minimize the beam spot on the disc so that the NA becomes large. Further, for a low density CD having a disk thickness of 1.2 mm, it is not necessary to minimize the beam spot on the disk, so that an objective lens with a small NA can be used.

The objective lens of the present embodiment may be modified so as to increase the number of divisions of the lens surface. FIG. 5 shows a lens 640 in which the lens surface is concentrically divided into five areas 640a to 640e. Here, the focus of the odd-numbered areas 640a, 640c, 640e counting from the center is located on the signal recording surface 622a of the thin optical disk 622, and the focus of the even-numbered areas 640b, 640d is the thick optical disk 6.
20 signal recording surfaces 620a. That is, the odd-numbered lens surfaces 640a, 640c, 640e project outward from the even-numbered lens surfaces 640b, 640d. Of course, on the contrary, the odd-numbered lens surface 640
Optical disc 620 having thick focal points of a, 640c, and 640e
Of the even-numbered lens surface 6 located on the signal recording surface 620a of
The focal points of 40b and 640d may be designed so as to be located on the signal recording surface 622a of the optical disc 622.

The width and diameter of each ring region are preferably larger than the wavelength of the laser light used. If the width and diameter are smaller than the wavelength of the laser light, the light beam will be focused on a position other than the signal recording surface of the disk due to diffraction.

As described above, according to the optical head device of the first embodiment, a lens in which at least one surface having a different focal length for each area is concentrically divided into a plurality of areas is used as an objective lens. Therefore, it is possible to reproduce at least the discs of different standards with the same device.

FIG. 6 is a diagram showing an example of an optical head device using a lens 640 according to a modification of the first embodiment shown in FIG. In the above embodiment, the substrate thickness is different (1.2 m
m and 0.6 mm), but in the present embodiment, the case where the substrate thickness is the same but the track pitch is different is targeted. As described above, the lens 640 has two focal points FA and FB (> FA). In this apparatus, a low density disk 650 having a thickness TB and a high density disk 652 having a thickness TA (= TB) are used. Low density disc 6
50 is arranged at the focal length FB, and the beam spot is focused on the signal recording surface 650a. The high-density disc 652 is arranged at the focal length FA, and the beam spot is focused on the signal recording surface 652a. In order to realize this, in this device, the disc tray (not shown) on which the disc is placed moves up and down in the focus direction according to the type of disc, and the working distance between the disc and the lens depends on the disc. It is designed to change between WDA and WDB.

FIG. 7 is a diagram showing another example of the optical head device using the lens 640. In this device, the position of the disc tray is fixed, the lens 640 moves in the focusing direction according to the disc type, and the working distance between the disc and the lens changes between WDA and WDB depending on the disc. There is.

FIG. 8 shows a second embodiment of the lens according to the present invention. The surface of the lens 660 facing the light source (not shown) is concentrically divided into five ring-shaped lens surfaces 660a to 660e. The lens 640 of the first embodiment has a structure in which lenses having two focal points are stacked, and a step is formed at the boundary portion of the ring-shaped lens surfaces. However, in this embodiment, as shown in FIG. The surface shape of each lens surface is determined so as to be smoothly continuous and have no step at the boundary. This consists of a combination of lenses having different focal lengths on each lens surface 660a-660e. That is, the odd-numbered lens surface 66 counting from the center
0a, 660c, 660e are on an arc having a center on the optical axis, and even-numbered lens surfaces 660b, 660d connect the lens surfaces 660a, 660c, 660e at an angle. That is, the example of FIG. 8 is substantially composed of triple concentric lens surfaces 660a, 660c, 660e, and the lens surfaces are continuously connected. Since light can also pass through this continuous portion, it becomes lens surfaces 660b and 660d.

The width of the five lens surfaces 660a-660e,
The diameter and curvature are odd numbered lens surfaces 660a, 660c, 6
The light passing through 60e is focused on the signal recording surface 622a of the thin high-density disc 622, and the even-numbered lens surface 660
b, a low-density disc 620 in which light passing through 660d is thick
It is decided to focus on the signal recording surface 620a. Of course, on the contrary, the odd-numbered lens surface 660
Light passing through a, 660c, 660e is focused on the signal recording surface 620a of the thick low-density disc 620, and light passing through even-numbered lens surfaces 660b, 660d is focused on the signal recording surface 622a of the thin high-density disc 622. Thus, the width, diameter, and curvature of the five lens surfaces 660a to 660e may be determined.

Here, two disks 620 and 622 are used.
Are placed at the same working distance. Low density disc 6
20 is, for example, a compact disc, and the high-density disc 622 is, for example, the disc shown in FIG.

When such a lens is used, as shown in FIG. 9, there is a tendency that a strong light portion called a side lobe is formed concentrically at a position apart from the central main beam. For this reason, there are cases in which the same effect as when the light spot becomes substantially larger is brought about. To prevent this,
It is necessary to strictly design the area of each lens surface 660a to 660e. Such a triple concentric structure is preferable also from the viewpoint of ensuring the degree of freedom in design. Of course, the number of concentric structures is not limited to 3, and may be divided into 4 or 5 lens surfaces.

When the number of divisions is increased as much as possible, the optical characteristics of each lens surface are the same as those of the two lens surfaces 60 shown in FIG.
It is obvious that the characteristics of 2,604 are gradually approached. Therefore, in order to prevent the above-mentioned side lobe effect,
It is preferable that the number of divisions is as large as possible. However, when the width of each split ring-shaped region approaches the wavelength of laser light, the lens exhibits a function as a diffraction grating in addition to its original function,
Since the influence of diffracted light appears, each region cannot be made too small. Therefore, the number of divisions is limited to a range in which the division region can have a width sufficiently large with respect to the wavelength of light.

Of course, conversely, it is also possible to design it as a diffraction grating to serve as an objective lens, but in this case, the utilization efficiency of light is lowered, and therefore another method is required as a design concept. Becomes

Such a concentric structure is usually used in the case of a lens called super-resolution, and in this case, although the side lobes described above are easily formed,
The main beam tends to be smaller and smaller spot sizes are obtained with proper design. Therefore, it is possible to realize a smaller spot size by utilizing this property.

In the above description, the surface of the lens opposite to the disk is divided into a plurality of surfaces, and the surface facing the lens is a continuous surface. However, in the case of FIG. Then, the light may pass through the same surface. For example, if the lens surface on the side opposite to the disc is five lens surfaces 6
When divided into 04a to 604e, the lens surfaces 660a and 6
The light passing through 60c and 660e, the lens surface 660b,
This is because light passing through 660d may pass through the same area on the lens surface facing the disc. However, the configuration of the lens is not limited to this, and the surface facing the disk rather than the opposite side of the disk may be divided into a plurality of lens surfaces, and the surface on the opposite side of the disk may be a continuous surface. Both surfaces of the lens may be divided into a plurality of lens surfaces.

The example of FIG. 8 shows the case where disks having different thicknesses are used at the same working distance. FIG. 10 shows two disks 650 having the same thickness but different track pitches (recording densities).
An optical head for changing the working distance between WDA and WDB in order to focus the beam spot on the recording surfaces 650a and 652a of 652 is shown. The high-density disc 652 having a fine track pitch needs to be arranged closer to the lens than the low-density disc 650 having a coarse track pitch. The signal recording surface 6 of the high density disc 652 in which the light passing through the lens surfaces 660a, 660c, 660e is on the front side
The signal recording surface 6 of the low-density disc 650 in which the light that has been focused on 52a and has passed through the lens surfaces 660b and 660d is distant
Focus on 50a. Therefore, the disc tray (not shown) on which the disc is placed moves up and down in the focus direction according to the type of disc, and the working distance between the disc and the lens changes between WDA and WDB depending on the disc.

FIG. 9 is a diagram showing another example of the optical head device using the lens 660. In this device, the position of the disc tray is fixed, the lens 660 moves in the focus direction according to the disc type, and the working distance between the disc and the lens changes between WDA and WDB depending on the disc. There is.

For the lens of the present invention, it is necessary to cut out the mold with a precision machine tool and mold it by plastic injection or glass molding. This manufacturing method itself is the same as the currently used aspherical lens manufacturing method, and the required accuracy does not change.
There are few manufacturing problems.

FIG. 12 is a plan view of a third embodiment of the optical head device according to the present invention. The disc 101 (optical disc, magneto-optical disc, etc.) used for recording and reproducing information is
The spindle motor 103 is fixed to the base 102 and held by chucking means such as a magnet chuck.
It is driven to rotate stably.

A movable body 104 is arranged at a position close to the lower portion of the disc 101. The movable body 104 is the first
It is composed of a movable body 105 and a second movable body 106, and is supported so as to be movable in the radial direction and the thickness direction of the disk 101, as will be described later.

The first movable body 105 has a substantially elliptical flat blade 105a facing the surface of the disk 101,
It consists of a cylindrical coil bobbin 105b fixed to the lower part of the blade 105a. A sliding bearing 105c is provided at the center of the blade 105a and the coil bobbin 105b.
Is provided.

In the plain bearing 105c, a rotary shaft 107, which is fixed to the second movable body 106 and has one end fixed thereto, has a minute gap (1
The sliding bearing mechanism (shaft sliding mechanism) is configured by being inserted and fitted through (0 micron or less). Then, the first movable body 1
Reference numeral 05 is capable of rotational movement about the rotation axis 107 and translational movement in the axial direction.

On the blade 105a, a counterweight 732 and an objective lens 730 composed of any of the lenses 600, 640 and 660 described above are provided. Objective lens 730 is configured to have a plurality of different optical characteristics. For example, the numerical aperture (NA) is 0.4
It is configured to have 5 and 0.6. The mounting positions of the objective lens 730 and the counter weight 732 are equidistant from the central axis on the diameter passing through the rotation shaft 107 so that the center of gravity of the entire mass of the first movable body 105 substantially coincides with the rotation shaft 107. It is located in. That is, the first movable body 105 has a structure in which the objective lens 730 and the counterweight 732 are well balanced in weight with respect to the rotation shaft 107.

A focus coil 109 is wound around the coil bobbin 105b. Focus coil 1
On the periphery of 09, two rectangular tracking coils 200a and 200b wound in a plane are attached at predetermined intervals. A magnetic circuit 112a composed of permanent magnets 110a and 110b and yokes 111a and 111b is arranged around the focus coil 109 and the tracking coils 200a and 200b and on the second movable body 106 in a positional relationship just symmetrical with respect to the rotation axis 107. ,
112b is provided, and the focus coil 109 and the tracking coil 20 are provided via a magnetic gap of a predetermined length.
0a and 200b are arranged to face each other, and the focus coil 109 and the tracking coils 200a and 200b are arranged.
A magnetic field is applied to. The two magnetic circuits 112a and 112b have the same structure, and the magnetization directions of the permanent magnets 110a and 110b coincide with the thickness direction of the magnetic gap.

When the focus coil 109 is energized and a magnetic flux is received from the magnetic circuits 112a and 112b, a Lorentz force is generated, and the first movable body 105 moves in the thickness direction of the disk 101 (axial direction of the rotating shaft 107). It is slightly translated. Further, the tracking coils 200a and 200b are energized and the magnetic circuit 11 is
Lorentz force is generated by receiving the magnetic flux from 2a and 112b, and the first movable body 105 is slightly rotationally driven in the radial direction of the disk 101 (around the rotation axis 107).

On the tracking coils 200a and 200b at positions separated by 180 ° around the coil bobbin 105b, two magnetic bodies 201a and 201 made of iron pieces or the like are placed on the tracking coils 200a and 200b.
b is provided. The magnetic bodies 201a and 201b are attached to the objective lens 730 and the counter weight 732 at positions separated by 90 ° in a symmetrical relationship with respect to the rotation shaft 107. When the objective lens 730 is in the optical path, these magnetic bodies 201a and 201b are just the magnetic circuit 112.
The magnetic gaps a and 112b are arranged to face each other.

On the other hand, the second movable body 106 is connected to the first movable body 105 via the rotating shaft 107, as described above. A pair of radial coils 113a and 113b are attached to both ends of the second movable body 106 at exactly the same distance from the center of gravity of the second movable body 106. A magnetic field is applied to the radial coils 113a and 113b from the radial magnetic circuits 114a and 114b fixed to the base 102.

The radial magnetic circuits 114a and 114b are
Back yokes 115a and 115b and center yoke 11
6a and 116b and permanent magnets 117a and 117b, and the radial coils 113a and 113b include center yokes 116a and 116b and permanent magnets 117a and 117b.
It is movably inserted in the magnetic gap defined by and. Note that the two radial magnetic circuits 114a, 114
b has the same structure, and permanent magnets 117a, 117a
The direction of magnetization of b coincides with the thickness direction of the magnetic gap.

Two to four slide bearings 119a and 119b are provided on the left and right of the second movable body 106, and two guide rails 118a and 11 are inserted in the slide bearings.
8b are arranged in parallel. The guide rail 118
Both ends of a and 118b are fixed to the base 102.
The second movable body 106 has these guide rails 118a, 11a.
It is movably supported along 8b.

The Lorentz force is generated when the radial coils 113a and 113b are energized and the magnetic flux is received from the radial magnetic circuits 114a and 114b.
The movable body 106 is translationally driven in the radial direction of the disk 101.

As for the magnetic gap width of the radial magnetic circuits 114a and 114b, the second movable body 106 has the guide rail 11
8a, 118b are formed to be long enough in the same direction so that they can be moved by a required distance in the longitudinal direction, in other words, the objective lenses 108a, 108b can be moved in the radial direction from the outermost circumference to the innermost circumference of the disc 101. Has been done.

Regarding the optical system and the signal processing system of this apparatus, Japanese Patent Application No. 6-83788 "Objective lens driving device"
Those described in can be used. FIG. 13 is a plan view of a fourth embodiment of the optical head device according to the present invention. This apparatus has a spindle motor as a disk drive means for holding and rotating an optical disk 10 (only a part of which is indicated by a chain double-dashed line) which is an information recording medium. On the lower surface side of the optical disk 10 rotated by the spindle motor, the counter weight 742 and the lenses 600 and 64 described above are provided.
The pickup 20 is equipped with an objective lens 740 and an optical system, which is composed of 0 or 660, and is linearly movable in the radial direction (direction of arrow A) of the optical disc 10.

The pickup 20 has a carriage 60 as a moving means that is movable in the radial direction of the optical disk 10 (direction of arrow A), which is the tracking control direction, using the linear motor 74 as a drive source.

On both sides of the carriage 60, a plurality of (in this case, two pairs) support rollers 62, which are supported by leaf springs, are provided.
2 ... by rolling contact with two guide shafts 64, 64 arranged horizontally and in parallel along the radial direction of the optical disc 10, the radial direction of the optical disc 10 (direction of arrow A)
It is movably supported by.

Further, radial coils 66, 66 are attached to both sides of the carriage 60. The radial coils 66, 66 are in a state of being externally fitted to inner yokes 68, 68 which are members for forming a magnetic circuit. Has become. The inner yokes 68, 68 are in a state of being connected to outer yokes 70, 70 provided on the outer side.
Magnets 72 are attached to the inside of 0 and 70, respectively, and form a linear motor 74.

By supplying electric power to the radial coils 66, 66, a propulsive force (Lorentz force) is generated, and the carriage 60 can be reciprocated in the tracking control direction.

FIG. 14 shows the structure of the pickup 20 shown in FIG. 13, which is roughly divided into a lens actuator composed of a rotary blade 82 which is a movable supporting member and a magnetic circuit 1411. Rotating blade 8
Reference numeral 2 is provided so as to be rotatable about an axis perpendicular to the recording surface of an optical disk (not shown in FIG. 14) loaded in the optical disk device and to be movable in the optical axis direction of the light beam applied to the optical disk. There is. Light source 140 such as a semiconductor laser
3, a collimating lens 1404 and a beam splitter 1405 constitute a light-transmitting optical system, and a condenser lens 1408 and a diffractive optical element (HOE: Holographic Opt) are used.
The optical element) 1409 and the photodetector 1410 constitute a detection system for detecting the light beam reflected by the optical disc.

The rotary blade 82 has a bottomed cylindrical shape with at least the upper end closed in the figure, and the objective lens 740 and the counterweight 742 are equidistant from the upper end and the weight is balanced about the rotational axis. It is arranged as follows. The magnetic circuit 1411 is composed of a pair of semi-arc-shaped yokes 1412a and 1412b, and the yokes 1412a and 112a and 112b, which are arranged at positions facing each other by 180 ° around the rotary blade 82.
Magnets 1413a, 141 attached to the inner peripheral side of 412b
3b and magnets 1413a, 1413 of the rotating blade 82.
tracking coil 1 disposed at a position that can face b
414a-1414f.

A reflecting mirror 1406 for forming an optical path between the beam splitter 1405 and the objective lens 740 is arranged between the light transmitting optical system and the detecting system. In such a configuration, the light emitted from the light source 1403 becomes a parallel light flux by the collimating lens 1404, passes through the beam splitter 1405 and the reflecting mirror 1406, is condensed by the objective lens 740, and is arranged above the rotary blade 82. A minute beam spot is formed on the information recording surface of the rotating optical disc.

The light reflected by the recording surface of the optical disk is transmitted from the light source 1403 in the outward path, that is, the collimating lens 140.
4, the beam splitter 1405, the reflecting mirror 1406, and the objective lens 740, and the objective lens 740 and the reflecting mirror 1406, which are opposite to the path of the incident light toward the recording surface of the optical disc.
Then, the light is reflected by the beam splitter 1405 and guided to the detection system. The detection system is an error signal for controlling the position of the minute spot focused by the objective lens 740 in the optical axis direction (focus direction) and the optical disc radial direction (tracking direction) with respect to the pit row on the recording surface of the optical disc. And reproducing the information signal recorded on the optical disc.

A detection system for obtaining these three signals (focus error signal, tracking error signal, reproduction information signal) is described in detail in, for example, Japanese Patent Laid-Open No. 3-257, "Optical memory device". Can be composed of Although this detection system itself is not related to the gist of the present invention, its operation will be briefly described. The detection system of this example is
As described above, it is composed of the condenser lens 1408, the HOE 1409, and the photodetector 1410. The reflected light from the optical disc is condensed on the photodetector 1410 by the condenser lens 1408.

The optical disc 142 is mounted on the HOE 1409 disposed between the condenser lens 1408 and the photodetector 1410.
Holograms having different lattice shapes are formed in regions divided by a dividing line having the same direction as the track on the track 0a or 1420b. Specifically, when one of the lattice shapes has a shape that is curved inward in a spool shape, the other one is a hologram that has a shape that is curved outward in a barrel shape. In addition, the diffracted light of each hologram is detected by the photodetector 1.
The grating pitch is made different so as to diffract to different positions on the detection surface of 410. When the hologram on the HOE 1409 is set in such a lattice shape, the photodetector 1410
Since it is possible to cause the upper light beam to change its characteristic shape according to the focus shift, the photodetector 1
The focus error can be detected by configuring 410 of two sets of two-split light receiving elements and differentially detecting each diffracted light by the two-split light receiving element. The tracking error can be detected from the difference between the diffracted lights of the holograms. Furthermore, the reproduction information signal can be easily detected from the total sum of the outputs of the photodetector 1410. Although the detection system using the HOE is used in the present embodiment, the detection system is not limited to this, and any known detection optical system such as a focus error detection system called an astigmatism method in which a condenser lens and a cylindrical lens are combined is similarly used. Can be used.

The four output signals output from the two sets of the two-divided light receiving elements constituting the photodetector 1410 are input to the detection signal processing circuit 1501 where amplification and calculation are performed to perform the above-mentioned operation. As a result, a reproduction information signal, a focus error signal and a tracking error signal are generated.
Of these, the reproduction information signal is output to a signal processing unit (not shown) that performs decoding and the like. On the other hand, the focus error signal and the tracking error signal are input to a control signal generation circuit 1502 connected to a host system (not shown), and a special operation signal is superimposed on the tracking control signal at the time of focus control sequence control and track search. After signal processing such as the above is performed, it becomes a focus control motion signal and a tracking control signal via the actuator control circuit 1503.

In accordance with these focus control signal and tracking control signal, the focus coil 1416 and the tracking coil 1414 in the magnetic circuit 1411.
The current flowing through a to 1414c is controlled. As a result, the rotating blade 82 is driven by the driving force generated by the electromagnetic action.
Are controlled in the optical axis direction (focusing direction) of the light beam with which the optical disk is irradiated and in the radial direction (tracking direction) of the optical disk, so that the light spot is positioned on the track of the optical disk.

The series of configurations and operations are basically the same as those of the conventional optical head. The present invention is not limited to the above-mentioned embodiments, but can be implemented with various modifications. For example, in the above description, the focal length is described as the different optical characteristic of each divided area, but the present invention is not limited to this, and NA or the like may be used. In addition, it is not limited to a plurality of objective lenses suitable for processing a plurality of discs with different standards such as disc recording density, warp tolerance, substrate thickness, etc. Even when the specifications of the objective lens are different, the optical head using the lens of the present invention is effective. Furthermore, the recording medium is not limited to a read-only optical disc, but a write-once optical disc,
A rewritable magneto-optical disk or the like may be used.

[0093]

As described above, according to the present invention, it is possible to perform at least good reproduction on a plurality of information recording media having different specifications of objective lenses while having a compact and inexpensive structure. A head device is provided.

[Brief description of drawings]

FIG. 1 is a schematic view showing a first embodiment of a lens according to the present invention.

FIG. 2 is a diagram showing an outline of an optical head device using the lens according to the first example.

3 is a diagram showing a detection principle of a photodetector used in the optical head device of FIG.

FIG. 4 is a diagram showing a configuration of a high density optical disc reproduced by the optical head device of FIG.

FIG. 5 is a diagram showing a modified example of the lens of Example 1.

FIG. 6 is a diagram showing an example of an optical head device using a lens according to the modification shown in FIG.

FIG. 7 is a diagram showing another example of an optical head device using the lens according to the modification shown in FIG.

FIG. 8 is a schematic view showing a second embodiment of the lens according to the present invention.

FIG. 9 is a diagram showing characteristics of a lens according to Example 2.

FIG. 10 is a diagram showing an example of an optical head device using a lens according to a second example.

FIG. 11 is a diagram showing another example of the optical head device using the lens according to the second example.

FIG. 12 is a plan view of a third embodiment of the optical head device according to the present invention.

FIG. 13 is a plan view of a fourth embodiment of the optical head device according to the present invention.

FIG. 14 is a diagram showing details of an optical system of a fourth embodiment.

FIG. 15 is a diagram showing the principle of reproducing discs having different densities.

FIG. 16 is a diagram showing the principle of tracking control in disks having different densities.

[Explanation of symbols]

600 ... Objective lens, 602, 604 ... Lens surface, 60
8, 610 ... Focal plane, 614 ... Laser, 618 ... Collimator lens, 616 ... Beam splitter, 620, 62
2 ... Optical disc, 620a, 622a ... Recording surface, 626
... Converging lens, 624 ... Holographic element, 628
Photo detector, 630 Signal processing circuit, 632 Focusing coil, 634 Tracking coil.

Claims (16)

[Claims] 1. A light source, an objective lens for focusing and irradiating a light beam emitted from the light source onto a recording surface of an optical memory, and light reflected by the recording surface to a light detecting means for signal detection. In the optical head device configured as described above, the objective lens is an objective lens having a function of forming a focused spot on a recording surface of an optical memory having different specifications. 2. The objective lens is an objective lens having a function of forming a focused spot of a light beam emitted from the light source on a recording surface of a plurality of optical memories having different substrate thicknesses. The optical head device according to claim 1. 3. The objective lens is an objective lens having a function of forming, on a recording surface of a plurality of optical memories having different recording densities, a light beam emitted from the light source, a condensed spot having a size suitable for the recording density. The optical head device according to claim 1, wherein the optical head device is provided. 4. The objective lens is formed by dividing a lens surface into a plurality of areas in a ring shape, and each area has a lens surface shape having different specifications. The optical head device according to claim 1. 5. A plurality of objective lenses, which are designed to form an optimum focused spot on a recording surface for each of a plurality of optical memories having different specifications, are arranged in the plurality of regions divided into ring shapes. Claims 1 and 2, characterized in that
The optical head device according to any one of items 3 and 4. 6. The objective lens according to claim 1, wherein one surface has a common lens surface shape.
The optical head device according to any one of items 4 and 5. 7. The objective lens is configured to have a lens surface shape in which no step is formed at a boundary portion of a plurality of regions divided into a ring shape.
The optical head device according to any one of 2, 3, 4, and 6. 8. The objective lens forms a focused spot on the recording surface of a plurality of optical memories having different specifications, and the distance (working distance) between the exit surface of the objective lens and the incident surface of the plurality of optical memories is constant. The optical head device according to any one of claims 1, 2, 4, 5, 6, and 7, wherein 9. When dividing the objective lens into a plurality of regions, the areas are distributed on the basis of reproduction signal frequencies or information recording densities of a plurality of optical memories having different specifications. 9. The optical head device according to any one of 4, 5, 6, 7, and 8. 10. A means for integrally supporting the light source, the objective lens, and the light detecting means, wherein the light detecting means detects reflected light from the recording surface while the supporting means moves. Claims 1 and 2, characterized in that
The optical head device according to any one of 3, 4, 5, 6, 7, 8, and 9. 11. A first surface on which light is incident and a second surface on which light is emitted are provided, and at least one of the first surface and the second surface has different optical characteristics. A lens characterized by being concentrically divided into a plurality of lens surfaces. 12. The lens according to claim 11, wherein the width of each of the lens surfaces divided into concentric circles is larger than the wavelength of light. 13. The lens surface divided into concentric circles has different focal lengths.
The lens according to 1. 14. The lens according to claim 11, wherein the lens surfaces divided into concentric circles have different numerical apertures. 15. The lens according to claim 11, which is formed by molding or injection using plastic or glass. 16. The lens according to claim 11, wherein the number of divisions is 3 or more.