JPS63234418A - Multilayered magneto-optical disk device - Google Patents

Abstract

PURPOSE:To accurately focus the light on each of plural recording layers of a layered structure by providing a second laser light source for information recording/reproducing and erasing independently of the servo mechanism of a disk substrate and changing the distance between this laser light source and a fixed lens provided in front of this light source. CONSTITUTION:A second laser light source (the second light source) 13 is provided on an electrostrictive element 11, and the light of the light source 13 is converted to parallel rays of light by a fixed lens 9, and an objective lens 10 is driven by the servo mechanism and is focused on a second recording layer 4. An electric field is applied to the electrostrictive element 11 to expand this element in the thickness direction, and the distance between the second light source 13 and the fixed lens 9 is shortened to set the light in the out-of- focus state. Consequently, the focus position is shifted forward because the position of the objective lens 10 is not changed, and the light is focused on a first recording layer 2. The focus position is controlled by the voltage applied to an electrode 12 of the electrostrictive element 11. Thus, the position of the objective lens 10 is not changed but the position of the second light source is changed to focus the light.

Description

[Detailed Description of the Invention] [Summary] As a method for focusing a laser beam on an arbitrary recording layer of a magneto-optical disk formed with a plurality of recording layers, a first light source is used to focus a laser beam on an arbitrary recording layer of a magneto-optical disk formed with a plurality of recording layers. In addition to performing autofocus servo using the reflected light, a second light source is provided on the electrostrictive element, and a voltage is applied to the electrostrictive element to change the distance between the second light source and the fixed lens, allowing arbitrary recording. Record and focus on layers
A magneto-optical disk device that performs playback and erasing.

[Industrial application field]

The present invention relates to a method for focusing on each recording layer of a multilayer magneto-optical disk.

A magneto-optical disk is a memory that uses laser light to record high-density information. Like an optical disk, it has a large storage capacity, can record and read without contact, and is unaffected by dust. It has certain characteristics.

Such magneto-optical disks have a recording layer made of a thin film of an amorphous rare earth-transition metal alloy on a disk-shaped substrate with concentric or spiral guide grooves, and a protective layer on top of this. In addition to the single-plate type, a sandwich type in which magneto-optical disks are bonded back to back with the protective layer on the inside has also been put into practical use in order to achieve a smaller size and larger capacity.

The present invention also relates to a magneto-optical disk that is even more compact and has a larger capacity.

[Conventional technology]

The inventors have proposed a multilayer magneto-optical disk as shown in FIG. 4 as a method for downsizing and increasing the capacity of magneto-optical disks.

That is, a first recording layer 2. is formed on a transparent substrate l provided with a guide groove. First spacer layer 3. Second recording layer 4. Second spacer layer5. A third recording layer 6..., a recording layer, and a spacer layer are alternately laminated, and the laser beam 7 indicated by the arrow is directed to the surface recording layer (in this figure, the third recording layer 6). )
The laser beam is irradiated from the side of the transparent substrate 1 or from the side of the transparent substrate 1, and the laser beam is focused on any recording layer (in the case of the figure, the first to third recording layers) to record, reproduce, and erase information. This is what we do.

Here, to describe the structure of the multilayer magneto-optical disk, the transparent substrate l is made of glass with a thickness of about 1.2 mm, similar to the optical disk, and is coated with a thickness of 3000 to 5000 mm using a method such as sputtering or electron beam evaporation. Person record Id2, 4.
6 and a spacer layer 3.5 having a thickness of 5,000 to 1 μm.

Here, the constituent material of the recording layer 2.4.6 is γ diiron oxide (
The spacer 3.5 is made of a transparent perpendicular magnetic film such as γ-Pesos) or magnetic garnet, and the spacer 3.5 is made of glass or non-magnetic garnet (Gadolinium-Gallium-Garnet (Ga=GasOt□, abbreviated as GGG)). There is.

A recording layer is formed by stacking multiple perpendicular magnetic films in this way, and a laser beam focused by a lens is irradiated onto any recording layer while applying a magnetic field perpendicular to the substrate as in the conventional method. The temperature of the recording layer in the irradiated area rises and approaches the Curie temperature,
Information is recorded by utilizing magnetization reversal in the direction of the magnetic field.

By recording in this manner, a much larger amount of information can be recorded than with a single layer or sand inch type.

However, the problem in this case lies in how to accurately focus the laser beam on the necessary recording layer for recording, and how to servo a substrate rotating at high speed.

Figure 2 explains the focusing method that has been considered up to now. )
This is the case when focusing on the first recording layer 2.

That is, in the figure (A), after the light from the laser light source 8 is made into parallel light using the fixed lens 9, the objective lens 10 is moved up and down to form a microscopic beam with a diameter of about 1 μm on the second recording layer 4. When the light is focused on a spot, the reflected light from the second recording layer 4 is focused using a two-split detector and a differential amplifier, and the objective lens 10 is driven by a voice coil.

Similarly, (B) in the same figure shows a state in which the servo mechanism is operated by the reflected light from the first recording layer 2, and the objective lens 10 is moved up and down to focus on the first recording layer 2. It shows.

Here, in the case shown in the same figure (A), the refractive index of air and the second
Since the refractive index of the recording layer 4 is different, the amount of reflected light is large,
Therefore, it is easy to detect the reflected light, but in a case like the one shown in the same figure (B), there is almost no difference in the refractive index between the recording layer and the spacer layer (
Since the amount of reflected light is small, focusing is extremely difficult.

[Problem that the invention seeks to solve]

As described above, focusing on each recording layer with a multilayer structure is achieved by detecting the reflected light from the recording layer that performs recording, reproduction, and erasing, and driving the objective lens using this signal current. The problem is that the difference in refractive index between the material constituting the recording layer and the material constituting the spacer is small, making it difficult to detect reflected light.

Means for Solving Problem C] The above problem occurs when a magneto-optical disk is constructed by alternately laminating a plurality of transparent recording layers and spacer layers on a disk-shaped transparent substrate. Autofocus servo is performed using a laser beam irradiated from a light source to the uppermost recording layer, and a second light source is provided on the electrostrictive element, and the laser beam is irradiated through an objective lens that performs autofocus servo. The distance between the light source No. 2 and a fixed lens provided in front of the light source is changed using the electrostrictive effect of the electrostrictive element, and the laser beam is focused on an arbitrary recording layer to record and reproduce information. This problem can be solved by using a multilayer magneto-optical disk that performs erasing and erasing.

[Effect]

It is impossible to perform recording, reproduction, and erasing on an arbitrary recording layer of a multilayer structure by focusing a laser beam onto a spot with a diameter of 1 μm using the conventional FI method.

In other words, a substrate rotating at a high speed of about 10 w/s has undulations of about 100 μm, and the reflected light from the surface layer of the disk substrate is captured and a signal is detected using a two-split detector or the like. A servo a mechanism is used in optical disks, which moves the voice coil to adapt the objective lens to the optimal position, but it is difficult to apply this to focusing on an internal recording layer where the amount of reflected light is small.

Therefore, the present invention provides a second laser light source for recording, reproducing, and erasing information separately from the servo mechanism of the disk substrate, and the distance between this laser light source and a fixed lens provided in front of this light source is By changing the focus of the laser beam from the second light source, the focus of the laser beam from the second light source is changed from the surface position of the multilayer magneto-optical disk, and the focus is accurately focused on each of the plurality of recording layers having a layered structure.

In this case, the thickness of the spacer layer separating each recording layer is 500 mm.
The distance between the second laser light source and the fixed lens must be adjusted with high precision because it is thin, measuring 0 to 111 m1.

The present invention adjusts this position using an electrostrictive element, and uses lanthanum-doped lead zirconate titanate (abbreviated as PLZT).
) or barium titanate (BaTiOs), which deforms due to the piezoelectric effect when an electric field is applied to a piezoelectric material.

FIG. 1 explains the present invention, and FIG. 1A shows a second laser light source (hereinafter abbreviated as second light source) 13 provided on an electrostrictive element 11, and a fixed lens 9 as in the conventional case. The object lens 10 is focused on the second recording layer 4 by driving the objective lens 10 by a servo mechanism (not shown).

Next, the same figure (B) shows a state in which an electric field is applied to the electrostrictive element 11 to cause it to expand in the thickness direction, and the distance between the second light source 13 and the fixed lens 9 is shortened to deviate from the focal length. , since the position of the objective lens 10 is the same as in FIG.

Here, the relationship between the voltage applied between the electrodes 12 and the amount of displacement of the electrostrictive element 11 and the amount of movement of the focusing position of the laser beam when shifted from the focal position of the fixed lens 9 are known, and the recording layer Since the thickness of the spacer layer is known, electrostrictive element 1
The light focusing position can be adjusted by applying a voltage to one electrode 12.

In this way, the present invention provides a second lens without changing the position of the objective lens 10.
Focusing is performed by changing the position of the light source.

〔Example〕

FIG. 3 is a schematic diagram illustrating the driving method according to the present invention, in which a servo system and a signal system for recording, reproducing, and erasing information are formed separately.

That is, the first wave with a wavelength of 780no+ and an output of 5 mW
The light source 15 is used as a servo system light source, while the wavelength 83
A second light source 13 with an output of 10 mW at 0 ns was used as a signal system.

As for the servo mechanism, the first light source 15 is used as before.
Half mirror 16, Gikroic mirror 1
7. A multilayer optical disk 18 is irradiated through an objective lens 10, and this reflected light 19 is reflected by a guichroic mirror 17. The signal is guided through the half mirror 16 to the °ζ half-divided υ1 detector 20, and the two signals obtained from this are input to the differential amplifier 21.
The objective lens lO is adjusted by the voice coil 22 to focus the light onto the surface of the multilayer optical disk 18.

On the other hand, the signal system according to the present invention first places the second light source 13 provided on the electrostrictive element 11 at the focal distance of the fixed lens 9,
After confirming that the laser beam is focused on the surface of the multilayer optical disk 18 using the signal detector 23 provided at the back,
By closing the circuit of the power supply 24, applying an electric field to the electrostrictive element 11, changing the distance from the fixed lens 9, and changing the focusing position as shown in the figure, a laser spot can be focused on any recording layer.

〔Effect of the invention〕

As described above, the servo system and the signal system are separated, and light is focused on each recording layer that makes up the multilayer optical disk by moving the second light source instead of adjusting the fI of the objective lens as in the conventional method. By implementing the present invention, light can be accurately focused on any recording layer even in a multilayer optical disc in which a recording layer and a spacer layer with a small difference in refractive index are laminated.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram explaining the focusing method according to the present invention, FIG. 2 is a schematic diagram explaining the conventional focusing method, FIG. 3 is a schematic diagram explaining the driving method according to the present invention, and FIG. The figure is a schematic cross-sectional view of a multilayer magneto-optical disk. In the figure, 1 is a transparent substrate, 2 is a first recording layer, 3 is a first spacer layer, 4 is a second recording layer, 5 is a second spacer layer, 6 is a third recording layer, and 8 is a laser light source,
9 is a fixed lens, 10 is an objective lens,
11 is an electrostrictive element, 13 is a second light source,
15 is a first light source, 16 is a half mirror 1, 17 is a graphical mirror, 18 is a multilayer optical disk,
20 is a two-split detector, 21 is a differential amplifier, 22
is the voice coil, 23 is the signal detector

Claims (1)

[Claims] In a magneto-optical disk configured by alternately stacking a plurality of transparent recording layers and spacer layers on a disk-shaped transparent substrate, a first light source is provided to the topmost recording layer. Auto-focus servo is performed using the irradiated laser light, and a second light source is provided on the electrostrictive element, and the laser light is irradiated through the objective lens that performs auto-focus servo. The recording/reproducing and erasing of information is performed by changing the distance from a fixed lens provided in the electrostrictive element using the electrostrictive effect of the electrostrictive element, and focusing a laser beam on a required recording layer. A multilayer magneto-optical disk device.