JPS61206950A - Pickup for photomagnetic recording and reproducing device of simultaneous erasing and recording type - Google Patents

Abstract

PURPOSE:To record and reproduce information with one pit in the simultaneous erasing and recording type and monitor information at the recording time by using beams different in wavelength at the recording time as well as the reproducing time. CONSTITUTION:A laser light source 1 emits a polarized beam Bw having a wavelength lambdaw, and a laser light source 2 emits a polarized beam Bm having a wavelength lambdam. A beam splitter BS 3 allows optical axes of irradiated light to a recording medium S of beams Bm and Bw to coincide with each other. A quarter-wave plate 4a is provided on the first face of a PBS 4, and a reflecting layer 4b is provided on the outside of this plate 4a and a quarter-wave plate 4c is provided on the second face of the PBS 4, and the first interference filter 4b which permits the beam Bm to transmit through bus reflects the beam Bw is provided on the outside of this plate 4c. The BS 3 and the PBS 4 are so arranged that their azimuth angles gamma to the reference plane of polarization is <=45 deg. and >0, and directions of the PBS 4 and the BS are equalized.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a pickup for a recording/reproducing device used in a simultaneous erasure type magneto-optical recording method.

(Background of the invention) Can be done. This magneto-optical recording method is 1, for example, GdCo.

The direction of magnetization of a magneto-optical recording medium made of a perpendicularly magnetized film such as GdTbFe is aligned in advance either upward or downward relative to the film surface using a strong external magnetic field (this operation is called initialization). Then, by forming pits with opposite perpendicular magnetization in this medium, 2
It records digitized information. To form these pits, a laser beam with a diameter of about 1 to 2 microns is irradiated to raise the temperature of that area to around the Curie point of the magnetized film, thereby reducing the coercive force of that area to zero or When the direction of magnetization is reduced to almost zero, and at the same time a weak external magnetic field (bias magnetic field) in the opposite direction is applied to reverse the direction of magnetization, and then the laser beam irradiation is stopped, it is naturally cooled and returns to room temperature. The orientation is fixed. In this way, pits with opposite magnetization directions are formed.

Therefore.

For example, if the original orientation is rOJ, a pit of "1" is formed, and the binarized information is recorded as the presence or absence of this pit or the bit length.

The binarized information recorded in this way is generated by irradiating the recording medium with linearly polarized light (laser beam).

The state of rotation of the polarization plane of the reflected light and transmitted light is read using the phenomenon (magnetic Kerr effect and Faraday effect) that changes depending on the direction of magnetization. In other words.

Assuming that it is rotated by K degrees, when the direction of magnetization is downward with respect to the incident light, it is rotated by one θ degree. Therefore.

If you place a polarizer (also called an analyzer) at the end of the reflected or transmitted light so that its main axis is approximately perpendicular to -θ, most of the light from the downwardly magnetized part will not pass through the analyzer. The light from the upwardly magnetized part is s
in" 2θ, so if you install a detector (photoelectric conversion means) at the end of the analyzer,
When scanning a recording medium at high speed, current strength signals (electrical information) are generated based on the recorded magnetic information.
is played.

By the way, how can I reuse recorded media?

(b) It is necessary to initialize again with an initialization device, (b) to install a separate head for erasing, or (c) to erase in advance using a recording head as a preliminary process.

However, the initialization device is large and expensive.

It is practically impossible to attach it to a recording device.

Providing a separate erasing head also increases manufacturing costs.

It is also possible to erase the data in advance using a recording device.

Since erasing takes the same amount of time as recording, it has little practical appeal.

Therefore, it would be advantageous if new information could be recorded at the same time as easily erasing recorded information. In order to perform simultaneous erasure in this way, it is necessary to form pits having the desired magnetization direction, regardless of whether the magnetization direction of the recording medium is upward or downward. To do this, the bias magnetic field must be varied not only in one direction, but also upwards or downwards as desired. Moreover, the rate of change (modulation frequency) needs to be about megaHz (10' cycles/second) in order to increase the recording speed. If this were not the case, this magneto-optical recording/playback/digital reproduction method would lose its appeal compared to other recording/playback methods.

On the other hand, to obtain a bias magnetic field, a permanent magnet or an electromagnet is used, but only an electromagnet can be considered to change (modulate) the direction of magnetization at a frequency of mega H2. This is because it is quite difficult to mechanically reverse the permanent magnet at a frequency of mega H2. However, even electromagnets
In order to apply a sufficient magnetic field to the perpendicularly magnetized film of a recording medium in a non-contact manner, a considerably large current must be passed through the electromagnet, and it is extremely difficult to modulate the direction of this current at a frequency of mega H2.

Therefore, at present, only a constant magnetic field method is being considered for the bias magnetic field, and it is considered that simultaneous erasing is not possible with the magneto-optical recording method unless a separate erasing head is provided.

By the way, a magneto-optical recording medium is usually disk-shaped, so it has a concentric or spiral recording area (Aw), and in order to avoid overlapping with adjacent recording areas (A, w),
) and the recording area (Aw), there is a non-recording area (A, m
) (see Figure 2A).

In addition, as shown in Figure 2A, recording grooves are formed to prevent crosstalk between five tracks even on media that does not distinguish between recording areas (A W) and non-recording areas (Am) in advance. Tiffi provides a sufficient non-recording area (A m) between tracks.

When forming a perpendicular magnetization film in the recording area (A w), it is very troublesome to prevent the formation of a perpendicular magnetization film in the non-recording area (A m ), so generally, a perpendicular magnetization film is formed over the entire area. Resulting in. Therefore, the non-recording area (Am)
will always have perpendicular magnetization aligned to one side, and since the non-recording area (Am) is adjacent to the recording area (Aw), the recording area (Aw) will have perpendicular magnetization as shown by the broken line in Figure 2B. A stray magnetic field from the non-recording area (Am) will reach this area.

The present inventor, together with ten other inventors, previously invented a magneto-optical recording system that enabled simultaneous erasure by modulating the temperature of a perpendicularly magnetized film at a frequency of about megaH2, and filed a patent application for this method. (Patent Application No. 59-91360).

However, depending on the material of the perpendicularly magnetized film, when the temperature is set at two levels, high and low, the direction of perpendicular magnetization may be the same at either temperature level, or the compensation temperature may be different between the two temperature levels. Therefore, even if the magnetization directions are different, the magnitude of the perpendicular magnetization in either the upward or downward direction is insufficient, and the stray magnetic field from there is weaker than the recording magnetic field IH,l, which is sufficient for recording. By applying a bias constant magnetic field as an aid, recording becomes possible by the sum of the modulated stray magnetic field. Generally, if the floating magnetic field at high temperature is HI, the floating magnetic field at low temperature is Ho, and the bias constant magnetic field is H5.

lH++H1≧lH,1 1HO+Hb　l≧IH01 Must.

Therefore, in the prior invention, the recording area (A
w) and a non-recording area showing perpendicular magnetization aligned in one direction (
As shown in FIG. 3, for a magneto-optical recording medium having a

While the medium (S) is being rotated by a motor (33), a main beam (Bw) having sufficient light intensity to raise the temperature at which the coercive force of the medium (S) becomes zero or considerably small is applied to the recording area (Aw). is constantly irradiated during recording, and at the same time, if necessary, the recording area (Aw) is
Apply a bias constant magnetic field to.

On the other hand, another sub beam (B m
) between high and low intensities (including zero) (3
9) to modulate the temperature of the non-recording area (Am) between high and low temperatures.

This modulates the perpendicular magnetization of the non-recording area (Am).

The sum of the floating magnetic field from this modulated perpendicular magnetization and the bias constant magnetic field applied as necessary creates recording magnetic fields with mutually different directions, thereby creating a recording area (A
A bit (Po) with upward magnetization and a bit (P+) with downward magnetization are formed in w), and recording is performed using these bits.

(Object of the Invention) An object of the present invention is to provide a pickup for a recording and reproducing device suitable for the above-mentioned simultaneous erasure type magneto-optical recording system.

(Summary of the Invention) The present invention uses beams (Bw) and (Bm) with mutually different wavelengths during both recording and reproduction.1 The features are as follows.

(1) A polarized beam (BW) light source with a wavelength λw that irradiates the recording area (Aw).

(2) A polarized beam (Bm) light source that simultaneously irradiates both the non-recording area (Am) and the recording area (Aw) and has a wavelength λ different from the wavelength λw.

(3) First beam splitter 3 (4) A quarter wavelength plate is provided on the first surface and a reflective layer is provided on the outside thereof, and a quarter wavelength plate is provided on the second surface and a beam (
Bm) and reflects the beam (Bw). Polarizing beam splitter 9 provided with a first interference filter (5) Second beam splitter 9 (6) A second interference filter that transmits the beam (Bw) and does not transmit the beam (Bm).

(7) first photoelectric conversion means for receiving control light; and (8)
It consists of a second photoelectric conversion means that receives information light, both during recording and reproduction.

- The beam (Bw) passes through the second beam splitter, enters the third surface of the polarizing beam splitter, and is reflected by the reflective layer provided on the first surface.

The beam is further reflected by a first interference filter provided on the second surface, and the reflected light is emitted from the fourth surface and is perpendicularly incident on the recording medium through the first beam splitter.

The reflected light (BW) reflected by the medium passes through the first beam splitter and enters the polarizing beam splitter, and the beam (Bw) reflected there is reflected twice by the second beam splitter to form a second interference beam. The first photoelectric conversion means receives the light as control light through a filter.

・Beam (Bm) is the first←h→beam splitter
The beam (Bm) is made perpendicularly incident on the recording medium through the beam splitter, and the beam (Bm) reflected by the medium is received by the second photoelectric conversion means through the fourth polarizing beam splitter. It is found in the pickup of an erasable magneto-optical recording and reproducing device.

EXAMPLES The present invention will be specifically explained below using examples, but the present invention is not limited thereto.

(Example of magneto-optical recording medium) G of 3000 mm thick on a circular glass substrate of 1.2 fi thick.
d, forming a perpendicular magnetization film (first layer) of (FeCo),
It was made by forming a perpendicularly magnetized film (second layer) of T b Fe with a thickness of 2000 nm on top of the film.

Here, for simplicity, no grooves are particularly provided on the substrate, and a recording area (Aw) of 1 micron in diameter is used.

Next to this, a non-recording area (Am) of 3 microns in diameter is set in a spiral shape.

This medium is initialized by applying an external magnetic field in advance.

(Example 1) FIG. 1 is a conceptual diagram (the lens system is omitted) showing the configuration of a pickup of a magneto-optical recording and reproducing apparatus of this example.

In Figure 1, (1) is a laser light source that emits a polarized beam (Bw) with wavelength λ = 780 nm, and (2) is a polarized beam (Bw) with wavelength λ = 830 nn+.
It is a laser light source that emits. (3) is a beam splitter (BS), and (4) is a polarizing beam splitter (PBS).

(PBS) refers to, for example, a Wallaston prism, Rochon prism, Thomson prism, or thin-film polarizing beam splitter; Determined by

A quarter-wave plate (4a) is provided on the first surface of the PBS (4), and when light passes through the quarter-wave plate (4a) twice, the plane of polarization rotates by 90 degrees. A reflective layer (4b) is further provided on the outside of the quarter wavelength plate (4a). Furthermore, on the second surface of the PBS (4), there is also a 1/4 wavelength plate (4C), and on the outside there is a first plate that transmits the beam (B m) and reflects the beam (Bw).
An interference filter (4b) is provided.

(5) is a second BS; (6) is a second interference filter that transmits the beam (Bw) but does not transmit the beam (Bm); (7) is a first photoelectric conversion means that receives control light; (8) is a second photoelectric conversion means that receives information light. (S) is the aforementioned recording medium.

The LBS (3) and the PBS are arranged at an azimuth angle (γ) of 45≧γ>0 with respect to the reference plane of polarization.

(A W), the irradiation surface is designed to be a circle with a diameter of, for example, 1 μm, and the sub beam (Bm) is designed to be a concentric circle with a diameter of, for example, 5 μl (see Figure 4). The beam (Bm) illuminates both the recording area (Aw) and the non-recording areas (Am) provided on both sides thereof. In this case, the recording area (A
, w) illuminates three locations: the portion to be recorded, the portion currently being recorded, and the recorded portion (see FIG. 5).

In the present invention, the reflected light from the recorded portion is used for monitoring during recording and for reproduction.

During recording, a light source (1) oscillates a polarized beam (Bw) having a vibration plane parallel to the plane of the paper in Figure 1.
After transmitting BS (5), the third of PBS (4)
The light is made incident on the PBS (4) from the surface.

The incident beam (Bw) passes 100% through the PBS (4), reaches the quarter-wave plate (4a), is reflected by two reflective layers (4b), and passes through the quarter-wave plate (4a) again. During this time, the beam (Bw) passes through the 1/4 wavelength plate (4a) twice, so the vibration plane rotates 90 degrees and has a vibration plane perpendicular to the plane of FIG. 1. Therefore, the beam (Bw) is now reflected by the PBS (4), passes through the second surface of the PBS (4), reaches the 1/4 wavelength plate (4C), is reflected by the first interference filter (4d), and is again 1 /4 wavelength plate (4C). During this time, the beam (Bw) passes through the 1/4 wavelength plate (4C) twice, so the vibration plane rotates 90 degrees and becomes parallel to the plane of FIG. 1 again. Therefore, the beam (B w) passes through the PBS (4) 100%, exits from the fourth surface, enters the first beam splitter (3), passes through it, and enters the recording medium (S
) at normal incidence.

The beam (Bw) is continuously irradiated at room temperature during recording, and its intensity is such that the temperature of the perpendicularly magnetized film reaches 150 to 160°C. Then, the coercive force of the recording area (Aw) becomes almost zero.

The beam (BW) reflected by the medium (S) is transmitted through the first beam splitter (3) and approximately 100% reflected by the PBS (4) in order to be used as control light. For example, when the polarized beam (Bw) from the light source (1) has a vibration plane parallel to the plane of the paper as shown in FIG.
) also has the same vibration plane, so P
The BS (4) is placed at an angle that reflects almost 100% of the polarized light in its vibration direction. The beam (Bw) reflected by the PBS (4) is further reflected by the second BS (5), and then passed through the second interference filter (+1) and received by the first photoelectric conversion means (7), where it is converted into an electrical signal. .

Drive control such as focusing and tracking is performed using this electrical signal.

On the other hand, a light source (2) oscillates a polarized beam (B m ) having a plane of vibration perpendicular to the plane of FIG.

The intensity of the sub beam (B m ) is modulated according to the binarized information to be recorded by controlling the light source (2) by a modulation means (not shown). The modulation intensity is such that the temperature of the perpendicularly magnetized film in the non-recording area (Am) reaches 100 to 110° C. when the intensity is high, and the minimum intensity required for reproduction when the intensity is low. In addition, if you set it to zero at low intensity,
Monitoring becomes impossible.

As a result, when the intensity of the sub beam (B m) is high, the surrounding non-recording area (A m
) is applied a downward stray magnetic field to form a PI (PI) with downward perpendicular magnetization, and a sub-beam (B
When the strength of m) is low, an upward floating magnetic field is also applied, and the magnetic field is directed upward (p).

) pits are formed. Thus, the upward pit
Desired binary information is recorded by (P, ) and downward pits (Pl) (see FIG. 5).

Note that even if this sub beam (Bm) is reflected by the medium (S), one reflected light is cut by the second interference filter (6),
Since it does not enter the first photoelectric conversion means (7),
There is no risk of drive control being incorrect.

By the way, the sub beam (Bm) reflected by the medium (S) is
As shown in FIG. 5, it includes reflected light from pits (preceding bits) in the area to be recorded and pits (trailing bits) in the area that has just been recorded. Therefore, if these can be distinguished and received, it is possible to monitor the leading and trailing pits. The leading monitor detects a unique signal on the medium that indicates, for example, whether or not that sector or track is allowed to be recorded, and the trailing monitor detects whether the pit that has just been recorded is formed into the desired pit. This is to detect whether or not the

In any case, the sub-beam (Bm) reflected by the medium (S)
) is transmitted through the first beam splitter (3) and the PB
S (4), where information light (first light) and second light
This information light passes through a quarter wavelength plate (4C) and a first interference filter (4d), and then passes through a second photoelectric conversion means (8).
) to receive the light.

The second photoelectric conversion means (8) needs to receive reflected light only from the leading pit and the trailing pit, depending on the leading monitor and trailing monitor. Therefore, first the beam (B
When the real image of the medium surface irradiated in step m) is focused on a surface near the light-receiving surface or an equivalent surface using an imaging or projection optical system (not shown), and only one of the leading and trailing surfaces is to be monitored. teeth.

Only the necessary part of the light is transmitted through a mask placed on the imaging plane and received by the photoelectric conversion means (8), or the photoelectric conversion means (8) with a one-dimensional shape that receives only the necessary part of the light is transmitted.
to receive the light. When receiving light, it is split into two parts by a splitting means,
The light may be received by separate light-receiving elements, converted into an electrical signal, and then differentially determined to generate an information signal.

However, the information signals X (t) and S (t) as the leading and trailing monitors reproduced in this way are both beams (B m) whose intensity is modulated according to the information signals r and (t) being recorded. The information signal as a true advance monitor is obtained by irradiating X (t) with f, (t)
The quotient divided by X (t)/f, (t). This is the unique signal obtained from the preliminary monitor, and it is processed according to conventional methods to find out its meaning.

Similarly, for the trailing monitor, the quotient s (t)/f, (t
) is the true monitor signal, and this is compared with the information signal f, (t - Δt) obtained when recording the trailing monitor pit obtained through the delay circuit.9 If the two match, it means that the recording is correct. I can know.

During reproduction, the main beam (B m ) is oscillated with a lower intensity than during recording, and the reflected light from the medium (S) is used as control light in the same way as during recording.

The sub beam (Bm) is oscillated at a constant intensity without intensity modulation, and the reflected light from the medium (S) is received by the second photoelectric conversion means (8) and converted into an electrical signal in the same way as the recording monitor. do. This signal can be used as it is as a reproduction signal of recorded information.

In this case, since the sub beam (Bm) has a large spot diameter on the medium surface, it is possible to simultaneously irradiate a plurality of pits, for example, three pits. Therefore, an imaging or projection optical system is provided in the reflected optical path from the individual medium to form or project real images of the plurality of pits on the light receiving surface of the photoelectric conversion means (8). At this time, if the means (8) is provided with a plurality of light-receiving elements (8a to 8C) corresponding to the real images of the respective pits, as shown in FIG. Each light receiving element receives light one after another with a time difference.

It will be converted into an electrical signal. If the converted signals are added at a certain time using a delay circuit, the strength of the reproduced signal from one pit will be multiplied by n times, and the S/N
The ratio is improved by E times. This method is disclosed in detail in the specification of Japanese Patent Application No. 152,839/1983 filed by the present applicant.

In addition, the main beam (BW) is not turned on during playback.

It is also possible to use the sub beam (Bm) as reproduction and control light. In other words, without providing the second interference filter (6), the beam (Bm) reflected by the medium (S) is transmitted to the PBS (
4), the first light is divided into information light (first light) and second light, and the first light is directly received by the second photoelectric conversion means (8) as information light, and the second light is used as control light (10 information light). 2nd BS (5)
The reflected light is received by the first photoelectric conversion means (7), and optionally (7).

The information reproduction signal may be obtained by taking the differential of (8).

(Embodiment 2) This embodiment is a modification of Embodiment 1, and its configuration is shown in FIG. 6, and there is no essential difference from Embodiment 1 except for a slight change in arrangement.

(Effects of the Invention) As described above, according to the present invention, simultaneous erasure type recording and reproduction can be performed using one bit, and moreover, it is possible to monitor during recording.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram showing the overall configuration of a pickup according to Embodiment 1 of the present invention. FIG. 2A is a schematic vertical cross-sectional view of the recording medium. Figure 2B shows the recording medium! ! FIG. 2 is a conceptual diagram showing how a floating magnetic field is applied from a non-recording area (Am) to an area (Aw). FIG. 3 is a conceptual diagram showing the overall structure of a simultaneous erasing type magneto-optical recording device according to the invention of the earlier application: Japanese Patent Application No. 59-91360. FIG. 4 is an explanatory diagram showing how the recording medium is irradiated with beams (Bw) and (Bm). FIG. 5 is an explanatory diagram illustrating how recording is performed according to the first embodiment. FIG. 6 is a conceptual diagram showing the overall configuration of the pickup according to the second embodiment. FIG. 7 is an explanatory diagram showing the relationship between the spot shape of the beam (B m) on the light-receiving surface and the light-receiving surfaces of three light-receiving elements. The imaginary line shows the actual image of the projected pit. [Explanation of symbols of main parts] 1.37---- Beam (Bw) light source 1.38---
- Beam (B m ) light source 3 - First beam splitter - 4 - Polarizing beam splitter 5 - Second beam splitter 6 ---Second interference filter 7
----------First photoelectric conversion means 8--------
---1 second photoelectric conversion means 8a, 8b, 8cm-light receiving element

Claims (1)

[Claims] For a magneto-optical recording medium having a recording area (Aw) made of a perpendicular magnetization film and a non-recording area (Am) showing perpendicular magnetization aligned in one direction, (1) the recording area A polarized beam (Bw) light source of wavelength λ_w that irradiates (Aw). (2) Both the non-recording area (Am) and the recording area (Aw) are irradiated with a wavelength λ_m different from the wavelength λ_w.
polarized beam (Bm) light source. (3) a first beam splitter; (4) a quarter-wave plate on the first surface and a reflective layer on the outside thereof, a quarter-wave plate on the second surface and a beam (
Bm) and reflects the beam (Bw). A polarizing beam splitter with a first interference filter. (5) a second beam splitter; (6) a second interference filter that transmits the beam (Bw) but does not transmit the beam (Bm); (7) a first photoelectric conversion means that receives the control light; and (8)
The beam (Bw) is transmitted through the second beam splitter and is incident on the third surface of the polarizing beam splitter, and is provided on the first surface. After being reflected by the reflective layer, the reflected light is further reflected by a first interference filter provided on the second surface, and the reflected light is emitted from the fourth surface and is perpendicularly incident on the recording medium through the first beam splitter. The reflected light (Bw) reflected by the medium passes through a first beam splitter and enters a polarizing beam splitter, and the beam reflected there (Bw) is reflected by a second beam splitter and passes through a second interference filter into a control light. The beam (Bm) is made perpendicularly incident on the recording medium via the first beam splitter, and the beam (Bm) reflected by the medium is received by the first photoelectric conversion means.
Bm) is incident on the fourth surface of the polarizing beam splitter through the beam splitter, and the information light and the second
A pickup for a simultaneous erasing type magneto-optical recording and reproducing device characterized in that the information light is split into light and received by a second photoelectric conversion means through a 1/4 wavelength plate and a first interference filter.