JPH03141060A - Magneto-optical information recording, reproducing and erasing device - Google Patents

Abstract

PURPOSE:To enhance the C/N of a reproducing signal by making the diameter of a light stop which is used for reproducing smaller than that of a light spot which is used for performing write. CONSTITUTION:A reproducing head 1 and a recording and erasing head 2 separately perform a seeking action to a magneto-optical disk 3. At the time of reproducing, the light from a semiconductor laser 10 is condensed on the recording surface of the disk 3 through an objective lens 14. Based on the reflected luminous flux from the disk 3, a two-division phtodetector 21 performs the focus detection control in a knife edge system, and the output difference of a two-division photodetetor 19 becomes an information signal. The intensity of light emitted from a semiconductor laser 22 is modulated with a signal in accordance with magneto-optical information by a magnetic head 27 to perform the write of the information. Then, the laser 22 is consecutively lighted to perform the erasing of the information with magnetic field for erasing by the head 27. The oscillation wavelength lambdaR in the laser 10, the numerical aperture NAR of the lens 14, the oscillation wavelength lambdaw in the laser 2, and the numerical aperture NAw of an objective lens 26 satisfy the condition of (lambdaR/NAR)>(lambdaw/ NAw). Therefore, the diameter of the light spot for reproducing is smaller than that of the light spot for recording and erasing.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a magneto-optical information recording/reproducing/erasing device.

[Prior Art] An optical disk system is known as a system for recording and reproducing optical information. Magneto-optical recording media are a type of medium that records optical information, and since magneto-optical recording media can erase previously recorded information and write new information, they have recently become widely used in various fields of information processing. is intended.

Conventionally, a single head has been used to record, reproduce, and erase magneto-optical information on a magneto-optical recording medium.

[Problems to be solved by the invention] When recording, reproducing, and erasing optical information are performed using the same head, the optical path from the light source to the magneto-optical recording medium via the objective lens is common for recording, reproducing, and erasing. However, since the light source and objective lens are common for recording, reproducing, and erasing, the following problems arise.

FIG. 2(I) is an explanatory diagram showing a state in which a laser beam for writing is focused as a light spot on the magneto-optical recording medium 3. The symbol indicates the light intensity distribution at the light spot.

The magneto-optical recording medium 3 has a structure in which a thin layer 31 of magnetic material is provided on a substrate 30 of non-magnetic material.

Writing of magneto-optical recording information to the magneto-optical recording medium 3 is performed as follows.

The thin layer 31 is uniformly magnetized in advance in a predetermined direction in the thickness direction.

During writing, a magnetic field is applied in the thickness direction of the thin layer 31 in a direction opposite to the magnetization direction. In this state, the irradiation of the optical spot is turned on and off using a signal according to the magneto-optical information. When the light spot is irradiated as shown in FIG. 2 (I), the temperature of the thin film 31 in the irradiated area rises, and in the area where the temperature has risen to a certain extent, the previously magnetized state disappears, and from the outside It is newly magnetized according to the direction of the applied magnetic field. In this manner, the direction of magnetization of the thin film 31 in the portion irradiated with the light spot is reversed from that in the portion not irradiated with the light spot. Each part whose magnetization direction is reversed in accordance with the magneto-optical information is called a bit.

As mentioned above, when a bit is formed by a light spot, the direction of magnetization is reversed by using the temperature rise of the thin film caused by the irradiation of the light spot.
This occurs only when the temperature of 1 rises above a certain temperature, so the width of the bit is smaller than the width of the light spot.

To explain this with reference to FIG. 2(I), it is the portion irradiated with light stronger than the light intensity L1 that causes the temperature rise necessary to reverse the direction of magnetization in the thin film 31, and is therefore indicated by reference numeral 32. The direction of magnetization is reversed in some parts.

FIG. 2 (II) shows the relationship between the optical spot SP and the bit PT. When forming one bit, the optical spot SP is irradiated onto the magneto-optical recording medium for a time corresponding to the information, but at this time, the magneto-optical recording medium and the optical spot are moving relative to each other. The bit has a long shape in the direction of movement.

Now, when reproducing the magneto-optical signal recorded in this way, a light spot of a laser beam is irradiated and the reflected beam is guided to the detection section.

The laser beam is linearly polarized in a predetermined direction, but when reflected by a thin film, the plane of polarization rotates depending on the magnetization of the irradiation position. Since the direction of magnetization of the thin film is opposite between the bit portion and the non-bit portion, the direction of rotation of the plane of polarization is opposite between the bit portion and the other portion. Therefore, information can be reproduced based on the polarization state of the reflected light beam.

If the optical path from the light source to the magneto-optical recording medium via the objective lens is shared for recording, reproduction, and erasing, the second
As shown in Figure (II), the light spot SP that irradiates the bit PT has the same spot diameter as that during writing.

Since the direction of magnetization is opposite between the hatched part and the dotted part shown in FIG. 2 (II), when reproducing information, if the light spot SP ideally illuminates only the inside of the bit PT, If possible, for example, a reproduced signal as shown by the solid line in FIG. The reflected light flux from is bit PT
It acts in the direction of weakening the reproduced information from. Therefore, the reproduced signal actually obtained has a low C/N ratio as shown by the broken line in FIG. 2 (III).

The present invention was made in view of the above-mentioned circumstances, and
The objective is to provide a novel magneto-optical information recording/reproducing/erasing device that can improve the C/N ratio of reproduced signals.

[Means to solve the problem] The present invention will be explained below.

The present invention is a "device for recording, reproducing, and erasing magneto-optical information on a magneto-optical recording medium," and includes a "recording/erasing head and a reproducing head."

The "recording/erasing head" records and erases magneto-optical information on a magneto-optical recording medium.

The "reproduction head" reproduces magneto-optical information recorded on a magneto-optical recording medium.

The oscillation wavelength of the laser light source in the recording/erasing head is λ.
1. The numerical aperture of the objective lens of the recording/erasing head is NAW, and the oscillation wavelength of the laser light source in the reproducing head is λR.
, if the numerical aperture of the objective lens of the playback head is MAR, then
These λ1. λR1NAw, NAR satisfies the following condition: (λR/NAR)<(λW/NAW).

In the apparatus of the second aspect, semiconductor lasers are used as laser light sources for both of the heads, and the semiconductor laser with a larger oscillation wavelength is used for the recording/erasing head.

[Function] In the present invention, the recording/erasing head for recording and erasing magneto-optical information on the magneto-optical recording medium and the reproducing head for reproducing the information are separate from each other. The light source and objective lens can be separated.

As is clear from the above explanation, C in the playback information
In order to increase the /N ratio, the diameter of the optical spot used for reproduction is made smaller than the diameter of the optical spot used for writing when recording magneto-optical information, and the amount of protrusion of the optical spot for reproduction from the r bit width is increased. ” should be made smaller.

The diameter φ of the optical spot is the beam waist diameter of the condensed laser beam, and as is well known, it is given by the numerical aperture NA of the objective lens and the wavelength λ, as follows: φ=1.22·(λ/NA).

Therefore, the condition that the diameter φa of the optical spot from the reproducing head is smaller than the diameter φ of the optical spot from the recording/erasing head used for recording/erasing is that the oscillation wavelength λ1 of the laser light source in the recording/erasing head is , numerical aperture NA of the objective lens of the recording/erasing head, , oscillation wavelength λR of the laser light source in the reproducing head, numerical aperture NAi of the objective lens of the reproducing head is (λh/NAR) < (λNV/NAW
) is to satisfy the following conditions.

A semiconductor laser is suitable as such two laser light sources with different wavelengths. Currently, semiconductor lasers include those with an oscillation wavelength of 780 nm and those with an oscillation wavelength of 830 nm. Among these, a semiconductor laser with a wavelength of 830 nm can have a high output and has high reliability such as a long life.

When recording/erasing and reproducing magneto-optical information, greater power is required for recording/erasing. Therefore, it is better to use the one with a larger oscillation wavelength for the recording/erasing head.

[Example] Hereinafter, description will be given based on specific examples.

FIG. 1 schematically depicts an embodiment of the invention.

Reference numeral 1 indicates a reproducing head, reference numeral 2 indicates a recording/erasing head, and reference numeral 3 indicates a magneto-optical disk which is a magneto-optical recording medium.

The magneto-optical disk 3 is rotated around the axis AX.

The reproducing head 1 and the recording/erasing head 2 are separate bodies and perform seek operations separately.

As the reproducing bed 1, an optical pickup configuration conventionally known for magneto-optical recording systems can be used.

FIG. 1 (II) shows one optical arrangement in the reproducing head 1.
This is an example.

Light from a semiconductor laser 10 with an oscillation wavelength λ8 of 780 nm is collimated by a collimator lens 11, and then passed through a beam splitter 12 and a deflection prism 13 to a numerical aperture N.
The light is made incident on the objective lens 14 of A, and is focused by the same lens 14 onto the recording surface of the magneto-optical recording disk 3. The reflected light flux from the magneto-optical recording disk 3 enters the objective lens 14, passes through the deflection prism 13 and the beam splitter 12, and is condensed by the detection lens 15, and then sent to the beam splitter.
16, the beam is separated into two beams.

One of the separated light beams passes through the Naifetsu prisms 20 and 2.
The divided light-receiving element 21 is used for focus detection control using a known knife method.

The other beam separated by the beam splitter 16 is 17
The plane of polarization is rotated by 45 degrees by the two-wavelength plate 17, and further separated into a P-polarized light component and an S-polarized light component by the Wollaston prism 18, and the separated light beams of each component enter each light-receiving part of the two-split light-receiving element 19. do. The difference in output from each of these light receiving sections becomes an information signal.

On the other hand, the recording/erasing head 2 has an oscillation wavelength λ1 of 830
The light from the nm semiconductor laser 22 is collimated by the collimator lens 23, transmitted through the polarizing beam splitter 24 and the 174 wavelength plate 28 to become circularly polarized light, and then passed through the deflecting prism 25 to form a parallel beam with a numerical aperture NA, objective lens 2
6, and the lens 26 focuses the light onto the recording surface of the magneto-optical recording disk 3.

Then, magneto-optical information is written by modulating the emission intensity of the semiconductor laser 22 with a signal corresponding to the magneto-optical information while applying a recording magnetic field by the magnetic head 27, or while continuously lighting the semiconductor laser 22, the magnetic head 27 applies an erasing magnetic field to erase information.

The oscillation wavelength λR1 of the semiconductor laser 10, the numerical aperture NA of the objective lens 14, and the oscillation wavelength λ1 of the semiconductor laser 22, the numerical aperture NA of the objective lens 26, are (λ/NA)
Since the following condition is satisfied: R)<(λW/NAW), the diameter of the optical spot for reproduction is smaller than the diameter of the optical spot for recording/erasing.

[Effects of the Invention] As described above, according to the present invention, a novel magneto-optical information recording/reproducing/erasing device can be provided.

Since this device has the above-described configuration, it is possible to obtain a large C/N ratio when reproducing information.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the present invention in detail, and FIG. 2 is a diagram for explaining the problem to be solved by the present invention. 100. playback head, 200. Recording/erasing head, 30
．． . Magneto-optical disk as a magneto-optical recording medium 14.27.
, . Objective lens, 10.22. ,, Semi-guided light as a laser light source A C = Ko place? ■ (I) (I) CI) (I) (■)

Claims (1)

[Claims] 1. A device for recording, reproducing, and erasing magneto-optical information on a magneto-optical recording medium, comprising a recording/erasing head for recording and erasing magneto-optical information on the magneto-optical recording medium. and a reproducing head for reproducing magneto-optical information recorded on the magneto-optical recording medium, the oscillation wavelength of the laser light source in the recording/erasing head is λ_W, and the numerical aperture of the objective lens of the recording/erasing head is N
Let A_W be the oscillation wavelength of the laser light source in the above reproducing head.
R, the numerical aperture of the objective lens of the read head is NA_R, then these λ_W, λ_R, NA_W, NA_R are (λ
_R/NA_R)<(λ_W/NA_W) A magneto-optical information recording/reproducing/erasing device is characterized in that it satisfies the following condition. 2. The magneto-optical device according to claim 1, characterized in that a semiconductor laser is used as each laser light source in the recording/erasing head and the reproducing head, and the semiconductor laser with a larger oscillation wavelength is used for the recording/erasing head. Information recording/reproducing/erasing device.