JPS61206952A - Pickup of simultaneous erasing and recording type photomagnetic recording and reproducing device - Google Patents

Abstract

PURPOSE:To make recording and reproducing of simultaneous erasing and recording type by one pickup and to monitor at the time of recording by using beams of different wavelength at the time of recording and reproducing. CONSTITUTION:When recording, a polarized light beam Bm having an oscillation plane perpendicular to the face of paper is oscillated from a light source 1. The beam is reflected by the first beam splitter 3 and projected vertically onto a recording medium S. On the other hand, a beam Bm oscillated from a light source 2 is a polarized light beam B having an oscillation plane parallel to the face of paper and intensity of the sub-beam Bm is modulated according to binary coded information to be recorded by controlling the light source 2. When reproducing, the main beam Bw is oscillated lowering its intensity than the case of recording, and reflected light from the medium S is utilized as controlling light as in the case of recording. The sub-beam Bm is oscillated at a fixed intensity without making intensity modulation, and reflected light from the medium S is received by the second photoelectric converting device similar to the case of monitoring of recording, and converted to electrical signals.

Description

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

(Background of the Invention) The magneto-optical recording method is a term derived from the magneto-optical recording and reproducing method, and can also be called the magneto-optical recording method.

This magneto-optical recording system is9 For example, GdCo, GdTbF.
The direction of magnetization of a magneto-optical recording medium made of a perpendicularly magnetized film such as e is aligned in advance with a strong external magnetic field, either upward or downward relative to the film surface (this process is called initialization). ), and then, by forming pits with opposite perpendicular magnetization on this medium, binarized information is recorded. To form these pits, a laser beam with a diameter of about 1 to 2 microns is irradiated to raise the temperature of the area to around the Curie point of the magnetized film.

Make the coercive force of that part zero or almost zero.

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 when the laser beam irradiation is stopped, it is naturally cooled and returns to room temperature. 2 The reversed direction of magnetization is fixed. Ru.

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.

The presence or absence of this pit or the bit length is recorded.

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 a phenomenon (magnetic Kerr effect and Faraday effect) that differs depending on the direction of magnetization. In other words, when the direction of magnetization is upward relative to the incident light.

If the polarization plane of reflected light or transmitted light is rotated by θ with respect to the polarization plane of incident light, when the direction of magnetization is downward with respect to the incident light, it is rotated by 1 θ. Therefore, if a polarizer (also called an analyzer) is placed in front of the reflected or transmitted light with its principal axis at 1θ and almost perpendicular to the skin surface, the light from the downwardly magnetized part will hardly pass through the analyzer. ,
Since the light from the upwardly magnetized portion is transmitted by the amount equal to sin" 20, if a detector (photoelectric conversion means) is installed at the end of the analyzer, the recording medium can be scanned at high speed. A current strength signal (electrical information) is reproduced based on the generated magnetic information.

By the way, how can I reuse recorded media?

It is necessary to (b) initialize again with an initialization device, (b) install a separate head for erasing, or (c) erase in advance using a recording head as a preliminary process. however,
The initialization device is large and expensive, and it is practically impossible to attach it to the recording device. Providing a separate erasing head also increases manufacturing costs. Furthermore, erasing using a recording device in advance is not practical because it takes the same amount of time to erase as it does to record.

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 changed not only in one direction (but also upwards or downwards as desired).Moreover, the speed of change (modulation frequency) must be changed to increase the recording speed.
Approximately megaHz (10' cycles/sec) is required. If this were not the case, this magneto-optical recording and reproducing method would lose its appeal compared to other recording and reproducing methods.

On the other hand, to obtain a bias magnetic field, a permanent magnet or an electromagnet is used, but an electromagnet is the only option that can be used to change (modulate) the direction of magnetization at a frequency of megahertz. This is because it is quite difficult to mechanically flip a permanent magnet at a frequency of megahertz. 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, it is necessary to flow a considerably large current through an electromagnet, and it is extremely difficult to modulate the direction of this current at a frequency of megallz.

Therefore, at present, only a constant magnetic field system is being considered for the bias magnetic field, and it is considered that simultaneous erasing is not possible in the magneto-optical recording system unless a separate erasing and rad system is installed.

By the way, since magneto-optical recording media are usually disk-shaped, they have concentric circles or spiral ttcSI areas (Aw), and in order to avoid overlapping with adjacent recording areas (Aw), recording areas (Aw) and recording areas (Aw) and the non-recording area (Am
) (see Figure 2A).

Also, as shown in FIG. 2A, the recording area (Aw) and the non-recording area (Am) are not distinguished in advance by forming tracking grooves on the medium.

To prevent crosstalk between tracks, it is common to provide sufficient non-recording areas (Am) between recording tracks.

When forming a perpendicular magnetization film in the recording area (A W), it is extremely troublesome to prevent the perpendicular magnetization film from forming in the non-recording area (Am), so generally a perpendicular magnetization film is formed over the entire area. I end up. Therefore, the non-recording area (A m
) will always have perpendicular magnetization aligned on one side, and since the non-recording area (Am) is adjacent to the recording area (Aw), the recording area (Aw) will have perpendicular magnetization that is always aligned on one side, 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 other inventors, first focused on the fact that it is possible to modulate the temperature of a perpendicularly magnetized film at a frequency of around megahertz, and biased the stray magnetic field from the non-recording area (Am), which changes depending on the temperature. He invented a magneto-optical recording system that enabled simultaneous erasure by using it as a magnetic field, and filed a patent application (Japanese Patent Application No. 91360/1982).

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 both temperature levels.

If the magnitude of perpendicular magnetization in either direction is insufficient and the stray magnetic field from there is weaker than the recording magnetic field IHL, which is sufficient for recording, modulation can be performed by applying a bias constant magnetic field as an auxiliary. Recording is made possible by the sum of the stray magnetic fields. Generally, if the floating magnetic field at high temperature is H1, the floating magnetic field at low temperature is Ha, and the bias constant magnetic field is Hb.

IH, +Hbl≧IHw1 1H・+Hbl≧1HW1 Must.

Therefore, in the prior invention, the recording area (A
4@) and a non-recording area (A m ) exhibiting perpendicular magnetization aligned in one direction.
As shown in the figure.

While the medium (S) is rotated by a motor (33), a main beam (B W ) is constantly irradiated during recording, and at the same time, if necessary, the recording area (
Apply a bias constant magnetic field to Aw).

On the other hand, another sub beam (Bm) is placed in the non-recording area (Am).
between high and low intensities (including zero) (39
) 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 focus (PO) with upward magnetization and a pit (Pl) with downward magnetization are formed in the W), and recording is performed using these pits.

(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) having different wavelengths during both recording and reproduction.

What makes it so special?

(1) A polarized beam (B W) light source with a wavelength λ1 that irradiates the recording area (Aw). (2) A polarized beam (B W) light source that irradiates both the non-recording area (Am) and the recording area (Aw) at the same time and has a wavelength different from λw. Polarized beam (Bm) light source with wavelength λw (3) First beam splitter (4) A quarter-wave plate on the first surface and a reflective layer on the outside thereof, and a quarter-wave plate and a reflective layer on the second surface. The beam (Bw) is transmitted to the outside and the beam (Bm) is reflected. Polarizing beam splitter with first interference filter (5) Second beam splitter 9 (6) Transmits the beam (Bm) and converts the beam (B W)
a second interference filter (7) that does not transmit the control light; and a first photoelectric conversion means that receives the control light; After being reflected by a reflective layer provided on one surface, the light is further reflected by a first interference filter provided on a second surface, and the reflected light is emitted from a fourth surface.

After passing through the first beam splitter, the reflected light (Bm) is vertically incident on the recording medium, and the reflected light (Bm) reflected by the medium passes through the first beam splitter and enters the polarizing beam splitter, where information light (first light ) and a second beam, and the information beam (Bm) emitted from the third surface is sent to a second beam splitter.
Let it reflect.

The light is received by a second photoelectric conversion means through a second interference filter.

- The beam (Bw) passes through the first beam splitter and is vertically incident on the recording medium, and the beam (BW) reflected by the medium passes through the beam splitter and enters the fourth surface of the polarizing beam splitter. A pickup for a simultaneous erasing type magneto-optical recording and reproducing device is characterized in that the light is received by a first photoelectric conversion means through a quarter-wave plate and a first interference filter.

EXAMPLES The present invention will be specifically explained below with reference to Examples, but the present invention is not limited thereto.

(Example of magneto-optical recording medium) Gd of 3,000 people thick on a circular glass substrate of 1° and 2 mm thick.
, (FeCo) perpendicular magnetization film (first layer) is formed, and a TbFe perpendicular magnetization film (1st layer) with a thickness of 2000 μm is formed on it.
2nd layer).

Here, for the sake of simplicity, no grooves are provided on the substrate, and a recording N area (AW) with a width of 1 micron is used.

Adjacent to this, a non-recording area (A m) with a width of 3 microns 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 FIG. 1, (1) is a laser light source that emits a polarized beam (BW) with a wavelength λ of 780 nm.

(2) is a laser light source that emits a polarized beam (B) of λ-=830 nm. (3) is the beam (Bm) and -(
(4) is a polarizing beam splitter (PB).
S).

(P　B　S) means 1, for example, a Wallaston prism.

These are Rochon prisms, Thomson prisms, and thin-film polarizing beam splitters. These are the angle (γ
) is determined by

P B S (1/4 wavelength plate (4a) on the first side of 41
is provided, and when the light passes through the 1/4 wavelength 1 (4a) twice, the plane of polarization rotates 90 degrees. A reflective layer (4b) is further provided on the outside of the quarter wavelength plate (4a). Furthermore, P B S (
Similarly, the second surface of 4) is provided with a 1/4 wavelength plate (4c) and a first interference filter (4d) that transmits the beam (BW) and reflects the beam (Bm) on the outside thereof.

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

The first B S (31 and PBS are arranged at an azimuth angle (T) of 45≧γ〉0 with respect to the reference polarization plane, and the PBS
and the second BS have the same direction.

The main beam (BW) is the recording area (Aw) of the recording medium (S)
The irradiation surface is designed to be a circle with a diameter of, for example, 1 μm, and the sub beam (B m) is a concentric circle with a diameter of, for example, 5 μm.
It is designed to be a circle of m (see Figure 4), and therefore,
The sub beam (Bm) illuminates both the recording area (Aw) and the non-recording areas (A m ) provided on both sides thereof. In this case, the recording area (Aw) illuminated by the sub beam (Bm)
illuminates three locations: the part that is about to be recorded, the part that is being recorded, and the part that has already been recorded (see Figure 5).

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

During recording, the light source (11) oscillates a polarized beam (B m ) having a plane of vibration perpendicular to the plane of the paper in FIG. Make it incident.

The beam (BW) is continuously irradiated 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) to be used as control light, and almost 100% thereof is transmitted through the PBS (4). Light source (1
For example, when the polarized beam (Bw) from the medium (S) has a plane of vibration parallel to the paper plane as shown in FIG.
41 is installed at an angle that transmits almost 100% of the polarized light in the vibration direction.

The beam (Bw) that has passed through PBS (4) passes through the first interference filter (4d) and enters the first photoelectric conversion means (7).
The light is received and converted into an electrical signal. with this electrical signal.

Performs drive control such as focusing and tracking.

On the other hand, the beam (Bm) oscillated from the light source (2) is.

For example, a polarized beam (
B) and after passing through the second B S (5).

P B S (Inject into P B S (41) from the third surface of 41. The incident beam (B m)
(It passes through 41 100% and reaches the 1/4 wavelength plate (4a), is reflected by the 3 reflective layer (4b), and is again 1/4 wavelength plate (4a).
).

During this time, the beam (Bm) 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 (Bm) is now P B
S (41) and passes through the second surface of P ).During this time, the beam (Bm) passes through the 1/4 wavelength plate (4C).
Since the vibration plane passes through twice, the vibration plane rotates 90 degrees and becomes parallel to the plane of the first drawing again. Therefore, the beam (Bm) transmits 100% through the PBS (4), exits from the fourth surface, enters the first beam splitter (3), passes through it, and enters the recording medium (S) perpendicularly. do.

The intensity of the sub beam (Bm) is controlled by controlling the light source (2) by a modulation means (not shown).
Modulate it according to the binary information you want to record.

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.

Note that if you set it to zero when the intensity is low, you will not be able to monitor it.

As a result, when the intensity of the sub-beam (Bm) is high, a downward floating magnetic field is applied to the recording area (Aw) from the surrounding non-recording area (Am).

A pit (Pl) with downward perpendicular magnetization is formed,
When the intensity of the sub-beam (B m ) is low, an upward floating magnetic field is also applied, causing an upward magnetic field (p).

) pits are formed. Thus, the upward pisoto (
Desired binarized information is recorded by the pits (Po) and downward pits (PI) (see FIG. 5).

Incidentally, even if this sub beam (Bm) is reflected by the medium (S), one reflected light is cut by the first interference filter (4d) and does not enter the first photoelectric conversion means (7).
There is no risk of drive control being incorrect.

By the way, as shown in FIG. 5, the sub beam (Bm) reflected by the medium (S) is used to generate pits (leading bits) in the area to be recorded and pits (trailing bits) in the area that has just been recorded. includes reflected light from bits). 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 trunk 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
It enters the Sf41, where it is split into an information light (the first light) and a second light, and this information light is emitted from the third surface, and the second B S (51 and the second interference filter (
6), the light is received by the second photoelectric conversion means (8). Second
The photoelectric conversion means (8) needs to receive reflected light only from the leading pit and trailing pit, depending on the leading monitor and trailing monitor. Therefore, first, beam * (B
The real image of the medium surface irradiated by m) is projected near the light-receiving surface using a formed image or a projection optical system (not shown),
If you want to monitor only one of the leading and trailing lights by forming an image on a fixed point equivalent to that, only the necessary part of the light is transmitted through a mask placed on the imaging surface, and the photoelectric conversion means (
8) or a photoelectric conversion means (8) having a shape and dimensions of 9 that receives only the necessary portion of the light. When receiving light, the light may be split into two parts by a splitting means, received by separate light-receiving elements, converted into electrical signals, and then differentially divided into two parts to be used as information signals.

However, the information signals X (t) and S (t) reproduced in this way as the leading and trailing monitors are both beams (B m) whose intensity is modulated according to the information signal fm (t) being recorded. Therefore, the information signal as a true advance monitor is obtained by irradiating X (t) with fm (
The quotient divided by t) is X (t) /fm (t). This is the solid 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 5(t)/fm(t) is the true monitor signal.

This is compared with the information signal fm (-Δt) obtained when the trailing monitor bit obtained through the delay circuit is recorded, and if the two match, it is known that the information has been recorded correctly.

During field reproduction, the main beam (Bw) 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 (B m ) is oscillated at a constant intensity without varying the intensity, and the reflected light from the medium (S) is received by the second photoelectric conversion means (8) in the same way as the recording monitor, and is converted into an electric signal. Convert to 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 irradiate a plurality of pits (for example, three) at the same time. Therefore, an imaging or projection optical system is provided in the optical path of reflection from the medium to form or project real images of the plurality of pits onto the light receiving surface of the photoelectric conversion means (8). At this time, the means (8) is a plurality of light receiving elements (8a to 8c) corresponding to the real images of the respective pits, as shown in FIG.
When a light receiving element consisting of a pit is installed, each light receiving element receives reflected light from the same pit 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 increases by a factor of fW. This method was applied in the applicant's earlier application:
This is disclosed in detail in the specification of Japanese Patent Application No. 152839/1983.

Note that during reproduction, the main beam (Bw) may be used as reproduction and control light without turning on the sub beam (Bm). In other words, the second interference filter (6) is not provided.

The beam (B w) reflected by the medium (S) is transferred to PBS (4
) is divided into first light and second light, and the first light is reflected as information light by the second B S (5) and converted to the second photoelectric conversion means (8
), and the second light is received by the first light as a control light (+information light).
First photoelectric conversion means (7) via interference filter (4d)
If necessary, the information reproduction signal may be obtained by taking the differential between (7) and (8).

(Example 2) This example is a modification of Example 1, and its configuration is shown in FIG. There is no essential difference from the first embodiment except for a slight change in arrangement.

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

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram showing the overall configuration of a pick amplifier according to a first embodiment of the present invention. FIG. 2A is a schematic vertical cross-sectional view of the recording medium. FIG. 2B is a conceptual diagram showing how a floating magnetic field is applied from a non-recording area (Am) to a recording area (Aw) of a recording medium. 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 a pickup according to the second embodiment. FIG. 7 is an explanatory diagram showing the relationship between the spot shape of the beam (Bm) 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]

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) exhibiting perpendicular magnetization aligned in one direction, (1) the recording area a polarized beam (Bw) light source with a wavelength λ_w that irradiates (Aw);
a polarized beam (Bm) light source, (3) a first beam splitter, (4) a 1/4 wavelength plate on the first surface and a reflective layer on the outside thereof, and a 1/4 wavelength plate on the second surface and the outside thereof. Beam (
a polarizing beam splitter including a first interference filter that transmits the beam (Bw) and reflects the beam (Bm); (5) a second beam splitter; (6) a second interference filter that transmits the beam (Bm) and does not transmit the beam (Bw); 2 interference filters, (7) a first photoelectric conversion means that receives control light, and (8) a second photoelectric conversion means that receives information light, and during both recording and reproduction, the beam (Bm) is the second beam. The light passes through the splitter and enters the third surface of the polarizing beam splitter, is reflected by the reflective layer provided on the first surface, is further reflected by the first interference filter provided on the second surface, and the reflected light is reflected by the first interference filter provided on the second surface. The reflected light (
Bm) passes through the first beam splitter and enters the polarizing beam splitter, where it separates the information light (first light) and the second light beam.
The information light (Bm) emitted from the third surface is divided into two
The beam (Bw) is reflected by a beam splitter and received by a second photoelectric conversion means through a second interference filter, and the beam (Bw) passes through the first beam splitter and is made perpendicularly incident on a recording medium, and the beam (Bw) reflected by the medium is
Bw) is incident on the fourth surface of the polarizing beam splitter through the beam splitter, and is received by the first photoelectric conversion means through a quarter-wave plate and a first interference filter. Pick-up for magnetic recording and playback equipment