JPH0660467A - Head device for magnetop0tical recording medium - Google Patents

Abstract

PURPOSE:To put a head device integrally laid with a generating device for magnetic field on an objective lens into practical use by optimizing the shape and the size of the generating device for magnetic field and developing a light receiving optical system capable of removing the influence of an airy pattern. CONSTITUTION:A generating device for magnetic field 3 is coaxially laid in the axial part of an objective lens 10. The ratio of the location area of the generating device for magnetic field 3 occupied in the aperture area of the objective lens is adjusted so that a light quantity transmitted through the objective lens is larger than 50% of the incident light quantity. Also, a pinhole 20 is provided before photodetectors 15, 17 or a point photodetector is used as a photodetector so that only a main beam is received by the photodetectors 15, 17 of the light receiving optical system among reflected light beams converged by a detecting lens.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a head device for a magneto-optical recording medium, and more particularly to the shape and arrangement of a magnetic field generator for an objective lens and the structure of a light receiving optical system.

[0002]

2. Description of the Related Art FIG. 6 shows an example of a conventionally known head device for a magneto-optical disk. As shown in this figure, in the most commonly known head device for a magneto-optical disk, an optical head 2 and a magnetic field generator 3 are arranged to face each other via a magneto-optical disk 1. There is.
The optical head 2 includes a light projecting optical system 4 and a light receiving optical system 5. The projection optical system 4 includes a semiconductor laser 6 and
A collimator lens 8 for converting a laser beam 7 emitted from the semiconductor laser 6 into a parallel beam;
Beam splitter 9 that partially transmits and reflects light, and a laser spot 7a on the information recording surface 1a of the magneto-optical disk 1.
And the objective lens 10 for focusing. On the other hand, the light receiving optical system 5 includes the objective lens 10, the beam splitter 9, a half-wave plate 11 for adjusting the polarization angle of the reflected light, a detection lens 12, and the reflected light into an S polarization component and a P polarization component. It comprises an analyzer 13 for separation, a first photodetector 15 for detecting the S-polarized component 14, and a second photodetector 17 for detecting the P-polarized component 16. Then, as shown in the figure, the magnetic field generator 3 and the objective lens 10 are arranged to face each other.

At the time of recording and erasing information, a high-level laser beam 7 is emitted from the semiconductor laser 6 and the parallel beam is narrowed down by the objective lens 10 to near its diffraction limit, and the information recording surface 1a of the magneto-optical disc 1 is recorded. Focus on. As a result, the magnetic field in the recording direction or the erasing direction is applied from the magnetic field generator 3 to the temperature rising portion while the temperature of the magneto-optical recording film 1b is raised to or near the Curie temperature or near the Curie temperature. Information is recorded or erased by reversing the direction of magnetization. On the other hand, at the time of reproducing information, the semiconductor laser 6 emits a low-level laser beam 7 that does not erase the information, and the parallel beam is narrowed down by the objective lens 10 to near the diffraction limit thereof to record information on the magneto-optical disk 1. Focus on the track. Then, the reflected light signal from the magneto-optical disk 1 is received by the first photodetector 15 and the second photodetector 17, and the difference signal between these first and second photodetectors is an information signal. The magneto-optical signal is reproduced, and the preformatted signal is reproduced from the sum signal.

In the head device having the above-mentioned structure, the laser beam 7 emitted from the objective lens 10 and the control device for always positioning the objective lens 10 with respect to the information recording surface 1a of the magneto-optical disk 1 at a constant interval. In addition to the control device for positioning the magnetic recording medium on the target information recording track, the magnetic field generator 3 is connected to the information recording surface 1 of the magneto-optical disk 1.
Since a device for driving the magnetic field generator 3 in the radial direction of the magneto-optical disk together with a control device for always keeping a constant distance with respect to a and the objective lens 10 is indispensable, the device is complicated. However, there is an inconvenience that the size becomes large and the manufacturing cost becomes high. In order to eliminate such inconvenience, a head device for a magneto-optical recording medium, in which a magnetic field generator is embedded in an objective lens, has been proposed in the past, as disclosed in, for example, Japanese Unexamined Patent Publication No. 3-62343.

On the other hand, as an optical head of a system for increasing the recording density of an optical disk medium, conventionally, for example, ISOM 1
989,27-D17, Y.YAMANAKA `` High Density Optical Record
As described in "ing by Super-Resolution", a mask is applied to the optical axis part of the collimator lens so that a light spot smaller than the value regulated by the diffraction limit of the objective lens is formed on the information recording surface of the optical disc medium. An optical head capable of focusing has been proposed.

[0006]

When the magnetic field generator 3 is embedded coaxially in the objective lens 10, the magnetic field generator 3 is always positioned at a constant distance from the information recording surface 1a of the magneto-optical disk 1. Since the control device and the device for driving the magneto-optical disk 1 in the radial direction are unnecessary, the structure is simplified, and the size and cost of the device can be reduced. Further, since the magnetic field generator 3 has the same function as the mask provided on the optical axis portion of the collimator lens, the recording density can be improved.

However, when the magnetic field generator 3 is embedded in the objective lens 10, the laser beam from the semiconductor laser 6 is blocked by the magnetic field generator 3, so that the amount of light reaching the magneto-optical disk 1 decreases. If the ratio of the magnetic field generator 3 to the diameter of the objective lens 10 becomes too high, the amount of light necessary for recording, erasing, and reproducing information cannot be obtained. How to do is extremely important in putting this kind of head device to practical use. However, this point has not been clarified in the prior art.

When the magnetic field generator 3 is coaxially embedded in the optical axis portion of the objective lens 10, the magnetic field generator 3 determines the diameter D _{1 of the} beam spot irradiated on the magneto-optical disk 1 as shown in FIG. Beam spot diameter D ₂ without
Although the diameter can be made smaller than that, an Airy pattern 19 is generated around the main beam 18 as shown in FIG. Therefore, not only the reflected light of the main beam 18 but also the leaked light of the Airy pattern 19 is received by the photodetectors 15 and 17, and crosstalk occurs. Therefore, unless some measure is taken to eliminate the influence of the Airy pattern 19. However, it is practically difficult to improve the resolution of the reproduced signal.

Therefore, in order to put into practical use a head device in which the magnetic field generator is integrally embedded in the objective lens, the shape and size of the magnetic field generator are optimized, and the light receiving optical system capable of eliminating the influence of the Airy pattern is used. Development is essential.

The present invention has been made to solve the above problems, and its purpose is to have a simple structure and high C
Another object of the present invention is to provide an optical head for high density recording capable of reproducing N ratio information.

[0011]

In order to achieve the above-mentioned object, the present invention has a projection optical system having at least a light source and an objective lens, and is embedded in the optical axis portion of the objective lens coaxially therewith. A head device for a magneto-optical recording medium including a magnetic field generator, a light receiving optical system having at least a detection lens that collects a reflected light beam from the magneto-optical recording medium, and a photodetector arranged on the focal plane of the detection lens. In addition, the ratio of the installation area of the magnetic field generator occupying the opening area of the objective lens is adjusted so that the amount of light transmitted through the objective lens becomes 50% or more of the incident light amount, and the light is condensed by the detection lens. The light receiving optical system is configured such that only the main beam of the reflected light flux is received by the photodetector.

In the above-mentioned light receiving optical system, a point light detector having a light receiving area less than the diffraction limit of the detecting lens is used as the light detector, or a light receiving area sufficiently larger than the diffraction limit of the detecting lens is used. This can be realized by providing a pinhole on the front surface of the photodetector, removing the Airy pattern 19 through the pinhole, and focusing only the main beam 18 on the photodetector.

The magnetic field generator may be composed of a center core, side yokes, and a coil wound around the center core. The center core is small, so that a strong magnetic field can be applied to the magneto-optical recording medium.
It is particularly preferable that the tip portion of the side facing the magneto-optical recording medium is projected outward from the tip portion of the side yoke, and that the tip portion of the center core is made smaller in diameter than other portions.

Further, the objective lens and the magnetic field generator are slidably attached to a support shaft set in a direction orthogonal to the information recording surface of the magneto-optical recording medium to form a shaft sliding type head device. You can also do it. In this case, in order to prevent foreign matter from adhering to the support shaft and to ensure smooth operation, the objective lens has a stroke larger than the operation range for following the magneto-optical recording medium when the magneto-optical recording medium is not driven. Further, it is preferable that the driving method of the objective lens and the magnetic field generator is configured so that the magnetic field generator is driven and the foreign matter attached to the support shaft is discharged to the outside of the following movement range.

[0015]

[Function] The amount of light transmitted through the objective lens is 50% of the amount of incident light
When the area ratio of the objective lens and the magnetic field generator is adjusted as described above, information can be normally recorded, reproduced, and erased using a general magneto-optical recording medium, and the information can be recorded on the magneto-optical recording medium. The spot diameter to be irradiated can be reduced by about 20%. Further, if the light receiving optical system is configured so that only the main beam of the reflected light beam condensed by the detection lens is received by the photodetector, the leaky airy pattern can be prevented, and the high recording density and high Information reproduction with a CN ratio can be realized.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of a head device according to the present invention will be described below with reference to FIGS. 1 is an optical circuit diagram of a head device according to an embodiment, FIG. 2 is a vertical cross-sectional view of an objective lens portion of the head device according to the embodiment, and FIG. 3 is a cross-sectional view of an objective lens portion of the head device according to the embodiment. FIG. 4 is a perspective view of the head device according to the example, and FIG. 5 is an operation explanatory view of the objective lens.

In the head device of this embodiment, as shown in FIGS. 1 and 2, the magnetic field generator 3 is coaxially embedded in the optical axis portion of the objective lens 10, and the first photodetector 15 and the second photodetector 15 are provided. Pinholes 20 are arranged in front of the photodetectors 17 of FIG. Since the other parts are the same as those of the conventional head device shown in FIG. 6, the corresponding parts are designated by the same reference numerals and the description thereof will be omitted.

The objective lens 10 is made of a light-transmissive material such as glass or synthetic resin, emitted from the semiconductor laser 6, converted into a parallel beam by the collimator lens 8, and further converted into a linearly polarized light by the polarizer 9. The converted laser beam 7 is formed in a shape to focus on the information recording surface 1a of the magneto-optical disk 1.

The magnetic field generator 3 includes a center core 21 and
It is composed of a side yoke 22 and a coil 23 wound around the center core 21. The center core 21 is
The ferromagnetic material is formed into a substantially cylindrical shape that is longer than the thickness of the objective lens 10, and one end thereof is cut into a conical shape. After winding the coil 23, the center core 21 has its conical-shaped tip end directed toward the side facing the magneto-optical disk 1 so that its tip and base end project from the objective lens 10, respectively. Then, the objective lens 1
It is buried coaxially with the optical axis of 0. The coil 23 may be projected outward from the medium facing surface of the objective lens 10 or may be configured not to be projected. In any case, the lead 23a of the coil 23 is drawn out from the beam incident side of the objective lens 10.

As described above, when the ratio of the installation area of the center core 21 and the coil 23 to the opening area of the objective lens 10 is too large, the magneto-optical disk 1 cannot be irradiated with the laser beam having the required intensity, and the information is lost. Record, erase,
This causes inconvenience in reproduction. According to experiments, when a general magneto-optical recording medium and a drive device are used, the objective lens 1
If the amount of light passing through 0 is 50% or more of the amount of incident light, information can be recorded, erased, and reproduced without any inconvenience.
Therefore, the dimensions of the center core 21 and the coil 23,
The shape and the mounting position of these members with respect to the objective lens 10 are adjusted so that the amount of light transmitted through the objective lens 10 is 50% or more of the amount of incident light.

The side yoke 22 also serves as a holder for the objective lens 10, and is made of the same ferromagnetic material as the center core 21 and is formed into a cylindrical shape capable of accommodating the objective lens 10 therein.

Since the center core 21 applies a strong magnetic field to the magneto-optical disk 1, it is preferable that the center core 21 is arranged as close to the magneto-optical disk 1 as possible. It is set to project outward. In addition, the center core 21 and the side yoke 2
2 may be formed separately from each other as shown in FIGS. 1 and 2, but in order to improve the magnetic efficiency,
It is more preferable to integrally form a ferromagnetic material as shown in FIG. The connecting portion 24 connecting the center core 21 and the side yoke 22 is formed in a narrow strip shape as shown in FIG. 3 in order to secure a transmitted light amount of 50% or more.

The pinhole 20 has an S polarization component 14 and a P polarization component.
The leaky light of the Airy pattern 19 (see FIG. 7) included in the polarization component 16 is removed, and only the main beam 18 (see FIG. 7) is incident on the photodetectors 15 and 17, It is set at a predetermined position between the analyzer 13 and the first photodetector 15 and between the analyzer 13 and the second photodetector 17.

FIG. 4 shows a shaft sliding type actuator used in the head device. As shown in this figure, the shaft sliding type actuator is capable of rotating and sliding a coil holder 35 in which a tracking coil 33 and a focusing coil 34 are mounted on a support shaft 32 erected on a base yoke 31. Attached to the coil holder 35
The objective lens 10 and the magnetic field generator 3 are mounted on the base yoke 31, and the magnet 36 and the yoke 37 are fixed to the portion of the base yoke 31 facing the tracking coil 33. This actuator is set in the drive device with the support shaft 32 oriented in a direction orthogonal to the information recording surface of the magneto-optical disk. When a tracking control signal from a controller (not shown) is applied to the tracking coil 33, the coil holder 35 causes the support shaft 32 to move.
Is rotated in the direction of the arrow XX ′ around the center of the arrow and the objective lens 10 and the magnetic field generator 3 are positioned on a desired track. When a focusing control signal from a controller (not shown) is applied to the focusing coil 34, the coil holder 35 is slid along the support shaft 32 in the direction of the arrow Y-Y ', so that the magneto-optical disk. Follow the surface runout of.

By the way, in this type of actuator, the coil holder 35 is vertically moved along the support shaft 32 at a high speed during operation. Therefore, when the coil holder 35 is continuously operated for a long time, the lubricating layer coated on the support shaft 32 is operated. And coil holder 35
Abrasion powder is accumulated at both ends of the operation stroke, and it is caught between the coil holder 35 and the support shaft 32, resulting in inconvenience that the operation characteristics of the actuator are deteriorated or the life of the drive device is shortened. Cheap. In order to prevent such an inconvenience, when the magneto-optical disk is not driven, for example, when the drive device is turned on or off, or when the drive device is in the power saving mode, as shown in FIG. The coil holder 35 is driven with a stroke B larger than A, and the support shaft 3
It is preferable that the foreign matter C adhering to 2 is discharged outside the following operation range. The operation of ejecting the foreign matter C can be performed by applying a signal to the focusing coil 34 from a control device (not shown). In the 3.5-inch magneto-optical disk drive device, the focus operation range of the objective lens for following the surface wobbling of the magneto-optical disk is about ± 5.
While the maximum operating range of the coil holder 35 is set to about ± 400 μm, while the coil holder 35 is driven with a stroke of the focus operating range or more and the maximum operating range or less, The foreign matter attached to 32 can be discharged out of the following movement range.

When the coil holder 35 was continuously driven with a stroke of ± 100 μm and the change in the DC sensitivity representing the operating characteristics of the actuator was measured, the DC sensitivity deteriorated by about 20% from the initial value after 90 hours. At this point, the continuous drive operation is stopped and the coil holder 35 is moved to ± 35
Drive for a few seconds with a stroke of 0 μm, and then ± again
When the continuous drive operation with a stroke of 100 μm was restarted, the DC sensitivity was restored to almost the initial value.

In the actuator of the above-described embodiment, the aperture area of the objective lens and the area ratio of the center core 21 and the coil 23 are adjusted so that the amount of light transmitted through the objective lens 10 is 50% or more of the incident light amount. Information can be normally recorded, reproduced, and erased by using a conventional magneto-optical recording medium, and the spot diameter irradiated on the magneto-optical recording medium can be reduced by about 20% or more. Also, the photodetectors 13, 1
Since the pinholes 20 are provided in front of 5 respectively, leakage of the airy pattern 19 can be prevented, and information reproduction with high recording density and high CN ratio can be realized. Further, when the magneto-optical disk is not driven, the coil holder 35 is driven with a stroke B larger than the follow-up operation range A for the magneto-optical disk so that the foreign matter C adhering to the support shaft 32 is discharged outside the follow-up operation range. Therefore, the operating characteristics of the actuator are stable and the durability is excellent.

In the above embodiment, the pinhole 20 is provided in front of the photodetectors 13 and 15 as a means for preventing the airy pattern 19 from leaking.
Instead of such a configuration, as the photodetectors 13 and 15,
A point light detector having a light receiving area equal to or smaller than the diffraction limit of the detection lens 12 may be used.

Further, although the objective lens and the magnetic field generator are incorporated in the shaft sliding type actuator in the above-mentioned embodiment, they may be incorporated in other types of actuators.

Further, the above-mentioned foreign matter discharging operation method is
Not only the actuator in which the magnetic field generating device is embedded in the objective lens, but also a driving method of a normal optical device configured separately from the magnetic field generating device can be adopted.

[0031]

As described above, according to the present invention, the aperture area ratio of the objective lens and the area ratio of the center core and the coil are adjusted so that the amount of light transmitted through the objective lens becomes 50% or more of the amount of incident light. Since the adjustment is performed, information can be normally recorded, reproduced, and erased using a general magneto-optical recording medium, and the spot diameter irradiated on the magneto-optical recording medium can be reduced by about 20% or more. In addition, since the light receiving optical system is configured so that only the main beam of the reflected light beam condensed by the detection lens is received by the photodetector, leakage of the Airy pattern can be prevented, and high recording density can be achieved. Information reproduction with a high CN ratio can be realized.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a head device according to an embodiment.

FIG. 2 is a vertical cross-sectional view of an objective lens portion of a head device according to an example.

FIG. 3 is a cross-sectional view of an objective lens portion of the head device according to the example.

FIG. 4 is a perspective view showing an appearance of a head device according to an embodiment.

FIG. 5 is an operation explanatory diagram of the head device according to the embodiment.

FIG. 6 is an explanatory diagram of a head device according to a conventional example.

FIG. 7 is a graph showing the problems of the prior art.

[Explanation of symbols]

 1 Magneto-optical disk 2 Optical head 3 Magnetic field generator 10 Objective lens 21 Center core 22 Side yoke 23 Coil

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigehisa Suzuki 1-88, Torora, Ibaraki City, Osaka Prefecture Hitachi Maxell Co., Ltd.

Claims (4)

[Claims] 1. A projection optical system having at least a light source and an objective lens, a magnetic field generator embedded coaxially with the optical axis portion of the objective lens, and at least a reflected light flux from a magneto-optical recording medium. In a head device for a magneto-optical recording medium including a light receiving optical system having a detection lens that emits light and a photodetector arranged on the focal plane of the detection lens, the amount of light transmitted through the objective lens is 50% or more of the amount of incident light. The ratio of the installation area of the magnetic field generation device to the aperture area of the objective lens is adjusted so that only the main beam of the reflected light flux condensed by the detection lens is detected by the photodetector. A head device for a magneto-optical recording medium, wherein the light receiving optical system is configured to receive light. 2. The magnetic field generator according to claim 1, comprising a center core, a side yoke, and a coil wound around the center core, wherein the objective lens, the center core, and A head device for a magneto-optical recording medium, wherein the coil is fixed, and a tip of the center core on the side facing the magneto-optical recording medium protrudes further outward than a tip of the side yoke. 3. The head for a magneto-optical recording medium according to claim 2, wherein a tip portion of the center core facing the magneto-optical recording medium has a smaller diameter than other portions. apparatus. 4. The objective lens and magnetic field generator according to claim 1, wherein the objective lens and the magnetic field generator are slidably attached to a support shaft set in a direction orthogonal to an information recording surface of a magneto-optical recording medium, and slid by an actuator. When the magneto-optical recording medium is not driven, the actuator is driven to drive the objective lens and the magnetic field generation device with a stroke larger than the operation range for following the magneto-optical recording medium. A head device for a magneto-optical recording medium, characterized in that the foreign matter attached to the support shaft is discharged outside the following movement range.