JPH04271040A - Optical head for over-write - Google Patents

Abstract

PURPOSE:To erase/record by using semiconductor laser with high utilization efficiency of light and with relatively small output. CONSTITUTION:This device is constituted of a semiconductor laser 2, a first light irradiator 6 and a second light irradiator 7 irradiating respectively a first light beam 3 and a second light beam 4 emitted from the semiconductor laser 2 to a magneto-optical recording medium 5 and a permanent magnet 10 applying magnetic fields in the opposite directions each other to an ersing part 8 and a recording part 9. While being erased by the first light irradiator, recording is performed by the second light irradiator. Since the first and the second light beams 3, 4 irradiate the magneto-optical recording medium 5 with little loss, the output of the semiconductor laser 2 may be about a half of the output used for a conventional magneto-optical head.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an optical head used in an optical recording/reproducing device that records, reproduces, and erases information on an optical recording medium using a laser beam, and more specifically, the present invention relates to an optical head used in an optical recording/reproducing device that records, reproduces, and erases information on an optical recording medium using a laser beam. The present invention relates to an optical head for overwriting that enables overwriting.

0002

2. Description of the Related Art Conventionally, in order to overwrite a magneto-optical recording medium, for example, as shown in FIG.
The optical head 101 erases information while the other optical head 100 records information. Such an optical head 1
00 and 101 are configured as shown in FIG.
8 , is focused by an objective lens 109 , and is irradiated onto the recording layer 112 of the magneto-optical recording medium 102 .

The light reflected from the magneto-optical recording medium and whose plane of polarization has been rotated by the direction of magnetization is turned into parallel light by an objective lens 109 and reflected by a non-polarizing beam splitter 108 . Furthermore, it is separated into two by a non-polarizing beam splitter 114, and one is detected by a 4-split photodiode 116 through a cylindrical lens 115 in order to obtain a servo signal. On the other hand, the polarizing beam splitter 118 polarizes two orthogonal beams.
divided into two polarization components, each with one photodiode.
Detected at 19 and 120. Photodiode 11
By taking the differential outputs of 9 and 120, the rotation of the polarization plane of the light is detected, and the information recorded on the magneto-optical recording medium is reproduced.

Two such optical heads 100, 10
1 to perform overwriting as follows. That is, the output of the semiconductor laser 105 of the optical head 101 is increased to irradiate the magneto-optical recording medium 102 with laser light,
At the same time as the recording layer 112 is heated to the Curie temperature or higher, an upward magnetic field is applied, for example, by a magnet 114 provided facing the objective lens 109 with the magneto-optical disk 102 in between, so that the magnetization of the recording layer 112 is aligned upward. Next, the semiconductor laser 105 of the optical head 100 is modulated with the recording signal, and the modulated laser beam is irradiated onto the recording layer 112. At the same time, a downward magnetic field is applied using the magnet 115, and the recording layer 112 is
The magnetization of is reversed downward according to the recording signal. In this way, overwriting is performed in which new information is recorded on top of old information while erasing it.

[0005]

However, in the magneto-optical optical head 100, the non-polarizing beam splitter 10
8, half of the light emitted from the semiconductor laser 105 is reflected, and the amount of light irradiated onto the magneto-optical recording medium 102 is reduced by half, resulting in low light utilization efficiency and the need to use a semiconductor laser with high output. was there. Furthermore, half of the light reflected from the magneto-optical recording medium 102 returns to the semiconductor laser 105, causing the semiconductor laser 105 to generate noise. Further, the magneto-optical optical head 100 has a complicated configuration because it needs to detect the rotation of the polarization plane of the light reflected from the magneto-optical recording medium 102, and is difficult to adjust and expensive. A recording/reproducing apparatus using two such devices also has the problem of being extremely expensive. Furthermore, although erasing and recording can be performed at the same time, it is not possible to simultaneously perform verification to confirm whether or not recording has been performed correctly.

The present invention has been made to solve the above-mentioned problems, and its purpose is to erase and record using a semiconductor laser with high light utilization efficiency and relatively low output. An object of the present invention is to provide an optical head for overwriting that can perform overwriting.

[0007]

[Means for Solving the Problems] In order to achieve this object, the overwriting optical head of the present invention includes a light source that emits light in a plurality of directions, and a first light source that irradiates the optical recording medium with the first light. a second light irradiation means that irradiates the optical recording medium with the second light; and a magnetic field that applies magnetic fields in opposite directions to the portions irradiated with the first and second light. and an application means. At this time, semiconductor lasers that emit light from mutually parallel end faces may be used as the light source. Furthermore, in order to perform recording, the first or second light irradiation means may include a light modulator.

[0008]

[Operation] In the overwriting optical head of the present invention having the above configuration, the first light of two lights emitted in opposite directions from a light source such as a semiconductor laser is optically recorded by the first light irradiation means. Erasing is performed by irradiating the medium and applying a magnetic field in a fixed direction using a magnetic field applying means. Also, the second light is
The second light irradiation means irradiates the optical recording medium after being modulated by the optical modulator. Recording is performed because a magnetic field is applied to the area irradiated with the second light by the magnetic field application means in the opposite direction to the magnetic field applied to the area irradiated with the first light that is to be erased. . Since the first and second lights are irradiated onto the same track, recording is performed subsequent to erasing, and overwriting can be performed.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment embodying the present invention will be described below with reference to the drawings.

As shown in FIG. 1, an overwriting optical head 1 to which the present invention is suitably applied is provided with a semiconductor laser 2 as a light source and a first light 3 emitted from mutually parallel end surfaces of the semiconductor laser 2. A first light irradiator 6 and a second light irradiator 7 which are irradiation means for irradiating the magneto-optical recording medium 5 with the second light 4, and the first and second light irradiators 6.
, 7 to which the first and second beams 3, 4 are irradiated, and a permanent magnet 10 which applies magnetic fields in opposite directions to the recording area 9.

In the first light irradiator 6, the first light 3 emitted from the semiconductor laser 2 is linearly polarized light, and after being turned into parallel light by a collimator lens 11, it is split into two by a beam splitter 12. , one is received by the photodiode 13. The other light passes through the polarizing beam splitter 14, becomes circularly polarized light by the λ/4 plate 15, is focused by the objective lens 16, and is irradiated onto the recording layer 18 of the magneto-optical recording medium 5. Note that the polarization direction of the light 3 emitted from the semiconductor laser 2 is
It is adjusted so that it becomes P-polarized light that matches the polarization direction of the light passing through the polarizing beam splitter 14, and the loss in the amount of light in the polarizing beam splitter 14 is extremely small.

The light reflected by the recording layer 18 becomes parallel light by the objective lens 16, and then passes through the λ/4 plate 15 again, so that the plane of polarization is rotated by 90 degrees and becomes S-polarized light. Therefore, the light is reflected by the polarizing beam splitter 14, passes through the cylindrical lens 20, and is received by the 4-split photodiode 21. Using the output of the four-division photodiode 21, focus servo and tracking servo are applied by the well-known astigmatism method, push-pull method, or the like. The light splitting ratio in the beam splitter 12 is, for example, 10:
1, and most of the first light 3 emitted from the semiconductor laser 2 is irradiated onto the magneto-optical recording medium 5, thereby increasing the light utilization efficiency. Further, by monitoring the output of the semiconductor laser 2 with the photodiode 13 and controlling the current flowing through the semiconductor laser 2, the output of the semiconductor laser 2 can be kept constant.

In the second light irradiator 7, the second light 4 emitted from the semiconductor laser 2 is linearly polarized light, and after being turned into parallel light by the collimator lens 23, it is passed through the right angle prism 24.
, and enters the optical modulator 25 . The light modulated by the optical modulator 25 passes through the polarizing beam splitter 26,
The light becomes circularly polarized by the λ/4 plate 27, is focused by the objective lens 28, and is irradiated onto the recording layer 18 of the magneto-optical recording medium 5. In addition,
The polarization direction of the light 4 emitted from the semiconductor laser 2 is also adjusted so that it becomes P-polarized light that matches the polarization direction of the light passing through the polarization beam splitter 26, and the loss in the amount of light in the polarization beam splitter 14 is extremely small.

The light reflected by the recording layer 18 passes through the objective lens 2.
After becoming parallel light at step 8, the light passes through the λ/4 plate 27 again, thereby rotating the plane of polarization by 90 degrees and becoming S-polarized light. Therefore, it is reflected by the polarizing beam splitter 26 and the cylindrical lens 2
9 and is received by the 4-split photodiode 30. Using the output of the four-part photodiode 30, focus servo and tracking servo are applied using the well-known astigmatism method, push-pull method, or the like.

The optical modulator 25 includes, for example, as shown in FIG.
One in which electrodes 32a and 32b are provided so that an electric field is applied in the optical axis z direction of a single crystal 31 of lithium niobate is used. The optical axis z direction is tilted at 45 degrees with respect to the polarization direction of the incident light, and the incident light is divided into two types: light whose electric field oscillates in the z direction, and light whose electric field oscillates in the z direction.
The electric field oscillates in the vertical direction and the light propagates through the crystal. When a voltage is applied to the electrodes 32a and 32b and an electric field is applied in the z direction, light whose electric field oscillates in the z direction and z
Since the phase shift that the light whose electric field oscillates in the direction and the perpendicular direction undergoes is different in the crystal, a phase difference occurs between these lights. By selecting the dimensions of the crystal and the applied voltage so that this phase difference is π/2, the polarization plane of the light emitted from the lithium niobate single crystal 31 is 90° with respect to the incident light.
Rotate degrees.

Therefore, the incident P-polarized light is transmitted to the electrode 32.
By applying a voltage to a and 32b, the plane of polarization is rotated by 90 degrees to become S-polarized light, which is reflected by the polarizing beam splitter 26 and is not irradiated onto the magneto-optical recording medium 5. Electrode 3
When no voltage is applied to 2a and 32b, the plane of polarization of the incident light does not rotate, passes through the polarization beam splitter 26, and is irradiated onto the magneto-optical recording medium 5. That is, by using such an optical modulator 25, the intensity of light irradiated onto the magneto-optical recording medium 5 can be changed depending on the voltage applied to the electrodes 32a and 32b.

In the overwriting optical head 1 as shown in FIG. 1, the first and second lights 3 and 4 emitted from the semiconductor laser 2 are irradiated onto the magneto-optical recording medium 5 with almost no loss. Therefore, the output of the semiconductor laser 2 is
Since it only requires about half of that used in conventional magneto-optical optical heads, the cost is reduced and reliability such as life span is improved. Furthermore, the optical systems of the light irradiators 6 and 7 are simple, making adjustment and the like easier.

Next, the overwrite operation will be explained using FIGS. 3 to 6. As shown in FIG. 3, the overwriting optical head 1 has an erased portion 8 and a recorded portion 9 on the same track 35 where light is irradiated onto the recording layer 18 of the magneto-optical recording medium 5 by objective lenses 16 and 28. be arranged to be located. Note that since the overwriting optical head 1 cannot detect magneto-optical signals, the magneto-optical optical head 36 is arranged so that the portion 38 irradiated with light by the objective lens 37 is located on the same track 35 on which overwriting is performed. It is placed. Since the magneto-optical optical head 36 is used only for reproduction, the output of the semiconductor laser may be low, and there is no need to use an expensive high-output semiconductor laser.

In FIG. 4, when the first light 3 is first focused by the objective lens 16 and irradiated onto the recording layer 18, the erased portion 8 of the recording layer 18 is heated to a temperature higher than the Curie temperature. At this time, it is assumed that the magneto-optical recording medium 18 is moving from left to right. Since an upward magnetic field He is always applied to the erased portion 8 by the permanent magnet 10, the magnetization 40 of the recording layer 18 is always aligned upward.

Next, as shown in FIG. 5, when the second light 4 is focused by the objective lens 28 and irradiated onto the recording layer 18, the recording portion 9 of the recording layer 18 is heated to a temperature higher than the Curie temperature. Since a downward magnetic field Hw is constantly applied to the recording portion 9 by the permanent magnet 10, the magnetization 42 of the recording layer 18 is reversed downward, and recording is performed. Further, when the second light 4 is not irradiated, the recording portion 9 of the recording layer 18 is
Since is not heated, the magnetization 44 is not reversed even if a downward magnetic field Hw is applied. In this way, erasing is followed by recording and overwriting. Furthermore, by reproducing the signals recorded by the magneto-optical head, it is possible to confirm the recording, that is, to verify the recording at the same time.

Although one embodiment of the present invention has been described above in detail based on FIGS. 1 to 6, the present invention can be implemented in other embodiments. That is, the configuration of the light irradiators 6 and 7 is as follows:
The present invention is not limited to the one shown in FIG. 1, but any type that can irradiate the magneto-optical recording medium 5 with a plurality of lights emitted from the semiconductor laser 2 may be used. Also, beam splitter 1
The division ratio of 2 does not need to be 10:1, but 1:1, 10
It may be 0:1 etc. and is not particularly limited. Furthermore, the output of the semiconductor laser 2 may be monitored by providing a beam splitter 12 and a photodiode 13 in the recording side light irradiator 7 instead of the erasing side light irradiator 6.

Furthermore, an optical modulator 25 may be provided between the beam splitter 12 and the polarizing beam splitter 14 of the light irradiator 6 on the erasing side. This can prevent the area between the erased portion 8 and the recorded portion 9 of the recording layer 18 from remaining erased at the end of recording in FIG. That is, at the time when the portion of the recording layer 18 that passes through the recorded portion 9 at the end of recording passes through the erased portion 8, the first light 3 may be prevented from being irradiated onto the erased portion 8 by the optical modulator.

Furthermore, the distance between the objective lenses 16 and 28 is not particularly limited. Further, the magnetic field applying means is not limited, and an electromagnet or a coil may be used instead of a permanent magnet. Furthermore, there is no particular limitation on the direction in which the magnetic field is applied.

[0024] Furthermore, the light source is not limited to a semiconductor laser;
A solid laser, a gas laser, etc., or a second harmonic thereof may be used. Furthermore, the direction in which the light emitted from the light source is emitted is not limited, and as shown in FIG.
You may also bend it 0 degrees and take it out. Alternatively, as shown in FIG. 5B, the light emitted from both end faces of the semiconductor laser 54 may be bent by 90 degrees using mirrors 55 and 56 formed on the same substrate and then extracted.

Furthermore, the optical modulator 25 is not limited to one using lithium niobate, but may also be one using other crystals having an electro-optic effect, an acousto-optic effect, or a magneto-optic effect.

Furthermore, as shown in FIG. 8, the overwriting optical head 1 and the magneto-optical optical head 36 may be combined into one. In addition, the overwriting optical head 1 is attached to the fixing part 6.
2 and the movable part 63, and only the movable part 63 may be moved. The movable part 63 consists of the objective lenses 16, 28, etc., and is lightweight, allowing high-speed access.

Furthermore, the positions to which light is irradiated by the overwriting optical head and the magneto-optical optical head do not necessarily have to be on the same track. That is, information may be recorded on one track and information on another track may be reproduced at the same time.

[0028]

Effects of the Invention As is clear from the above explanation, the optical head for overwriting of the present invention has high light utilization efficiency, so the output of the light source required for erasing and recording can be reduced compared to that of the conventional magneto-optical head. It can be reduced to about half of what was used for optical heads. Furthermore, the optical system of each light irradiator is simple, easy to adjust, and highly productive.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing the configuration of an overwriting optical head embodying the present invention.

FIG. 2 is a perspective view showing the configuration of an optical modulator.

FIG. 3 is a top view showing the arrangement of an overwriting optical head and a magneto-optical optical head.

FIG. 4 is an explanatory diagram showing the principle of overwriting.

FIG. 5 is an explanatory diagram showing the principle of overwriting.

FIG. 6 is an explanatory diagram showing the principle of overwriting.

FIG. 7(a) is a cross-sectional view illustrating the structure of a light source. (b) It is a sectional view explaining the structure of a light source.

FIG. 8 is a top view showing another embodiment of the overwriting optical head.

FIG. 9 is a top view showing another embodiment of the overwriting optical head.

FIG. 10 is a layout diagram when overwriting is performed using two conventional magneto-optical optical heads.

FIG. 11 is a configuration diagram of a conventional magneto-optical optical head.

[Explanation of symbols]

1 Optical head for overwriting 2 Semiconductor laser (light source) 3 First light 4 Second light 6 First light irradiator (light irradiation means) 7 Second light irradiator (light irradiation means) 10 Permanent magnet (magnetic field applying means) 25 Optical modulator

Claims (3)

[Claims] 1. A light source that emits light in a plurality of directions; and a first light irradiation means that irradiates an optical recording medium with the first light;
It consists of a second light irradiation means that irradiates the optical recording medium with the second light, and a magnetic field application means that applies magnetic fields in opposite directions to the portions irradiated with the first and second light. An optical head for overwriting, which is characterized by: 2. The overwriting optical head according to claim 1, wherein the light source comprises a semiconductor laser. 3. The overwriting optical head according to claim 1, wherein the first or second light irradiation means has a light modulator.