JPH0757324A - Recording/reproduction system - Google Patents

Abstract

PURPOSE:To reduce a noise of a reproducing beam obtained from a medium by superposing a high frequency current on a driving current of a recording semiconductor laser. CONSTITUTION:The beam of the semiconductor laser 1 is faced to a magneto- optial recording medium 20 by a PBS 4 through a collimate lens 2 and a diffraction grating 3, and a prescribed track is irradiated by the beam through a lens 5. Magnetic field is applied from the rear side of the medium 20 by a magnetic head 6. The magnetic field is modulated by a modulation circuit 7 according to recording information, and magnetic recording is performed. A part of the laser beam is sent to an LD driver 10 through a detector 8 and an APC circuit 9. Further, a high frequency superposition signal is sent from a control circuit 11 to the LD driver 10, and a sample-and-hold control signal, etc., is outputted to the APC circuit 9. Thus, an LD 1 is output controlled and driven automatically, and further, the presribed high frequency current is superposed at a recording time, and the noise occurrence in the LD 1 due to a return beam from the medium is suppressed. Further, since the laser beam irradiates continuously at the recording time, the verify is the whole area.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording / reproducing system for a magneto-optical recording medium utilizing a magneto-optical effect, and more particularly to a recording / reproducing system for verifying the recorded contents simultaneously with recording.

[0002]

2. Description of the Related Art A magneto-optical recording medium for recording / reproducing information by utilizing the magneto-optical effect, that is, by changing the polarization direction of the reflected light of the light irradiated on the magnetic layer depending on the direction of magnetization of the magnetic layer. In this, various recording / reproducing systems such as a light intensity modulation type and a magnetic field intensity modulation type have been studied.
In any case, in order to improve the reliability of the data from the practical point of view, at the same time, it is essential to record the data and at the same time reproduce the data immediately after the recording to verify the recorded content, so-called verification. It is said that.

As a method of performing this verification, there is a method of reproducing by using reflected light of the same light as the light beam for recording (for example, Japanese Patent Laid-Open No. 5-94649), or a prism or a grating. A method for reproducing a main beam for recording and a sub-spot for verifying by splitting a light beam into, for example, 0th-order light and 1st-order light (for example, Japanese Patent Laid-Open No. 4-123342).
Etc. have been proposed.

For example, when the light from the light source is separated by a grating and applied to the surface of the magneto-optical recording medium, as shown in FIG.
As shown in FIG.
It is possible to verify the recorded content by performing tracking adjustment so that the light is emitted, and by reading the reflected light of, for example, the sub-spot 35 located behind the main spot 33 by the rotation of the optical recording medium 1. 32 is track 3
A groove for controlling both sides of 1 is a so-called groove.

[0005]

By the way, when the reproduction signals of the recorded contents of the magneto-optical recording medium are simultaneously detected by using the laser spot at the time of recording, the recording laser power becomes the laser power at the time of reproduction. Since the intensity is several times higher than that of the laser beam, there is a problem that the laser return light noise increases.

The present invention solves such a problem to improve the quality of a reproduction signal using a laser beam at the time of recording,
By enabling stable data extraction, the recording time can be shortened, the reliability at the time of recording can be improved, and the recording / reproducing characteristics can be improved.

[0007]

According to the present invention, information is recorded by irradiating a magneto-optical recording medium 20 with a laser beam from a semiconductor laser 1 as shown in FIG. At the same time, when reading the recorded information, a high frequency current is superimposed on the drive current for driving the semiconductor laser 1.

According to the present invention, in the above method, laser light is continuously oscillated, and a magnetic field modulated according to recorded information is applied to the laser light irradiation site by the magnetic head 6 to record information. .

Furthermore, the present invention is based on the above-mentioned system,
As shown in FIG. 2 which is an enlarged schematic cross-sectional view of a main part of the example, recording and reproduction are performed using a magneto-optical recording medium 20 including at least two kinds of magnetic layers 23 and 24 exchange-coupled to each other. .

According to the present invention, in each of the above-mentioned methods, the absolute rated output of the semiconductor laser 1 is P _O , the average recording output when a high frequency current is superimposed is P _A , and the semiconductor laser 1 is
Letting a be the ratio of the amount of light reaching the magneto-optical recording medium to the amount of emitted light, b be the split light amount ratio of the return light from the magneto-optical recording medium 20, and d be the pulse duty, P _A <P _O × a Select xbxd.

Furthermore, in the present invention, in each of the above-mentioned systems, the linear velocity of the magneto-optical recording medium 20 is 1.2 to 1.4 m / s.
Recording and reproduction are performed as.

[0012]

According to the present invention, when recording on a magneto-optical recording medium, a high frequency current is added to the driving current of the recording semiconductor laser to add a high frequency current, thereby reducing the noise of reproducing light obtained from the medium. I was able to. It is considered that this is because it is possible to suppress the generation of noise generated in the semiconductor laser due to the returning light.

In particular, when the present invention is applied to a magnetic field modulation type magneto-optical recording in which a semiconductor laser is continuously emitted and the direction of a magnetic field is modulated for recording, the laser light is used for recording. Since the irradiation is continuously performed without being turned on / off corresponding to 1 "and" 0 ", the verification can be performed in the entire area without depending on the recorded contents.

Further, the recording layers are exchange-coupled to each other.
When a magneto-optical recording medium having a structure in which a plurality of magnetic layers are laminated is used for recording and reproducing at the same time, according to the present invention, the signal / noise ratio is increased by 1 dB or more as compared with the case where a high frequency is not superimposed. It was confirmed that the generation of noise could be surely suppressed.

Further, in the above-mentioned present invention, the average recording output P _A when a high frequency current is superposed on the magneto-optical recording medium with respect to the absolute rated output P _{O of} the semiconductor laser 1 and the emitted light amount of the semiconductor laser 1 With respect to the ratio a of the reaching light amount, the split light amount ratio b of the returning light from the magneto-optical recording medium 20, and the pulse duty d, P _A <P _O × a × b × d (1) By selecting it, it is possible to avoid the superposition of high frequencies exceeding the rated output of the semiconductor laser 1. This will be described below.

The power of the laser recording on the magneto-optical recording medium 20 is P _W , and the maximum output when high frequency superimposition is applied is P _M
Then, the power to be recorded on the magneto-optical recording medium 20 must satisfy P _W <P _O × a × b (2).

Further, the average recording output P _A when high frequency superimposition is applied becomes P _M <P _A / d (3) with respect to the pulse duty d. Therefore, the condition that the maximum recording power P _M satisfies the above expression (2) is the above expression (1). by this,
A reliable and reliable recording is possible.

The linear velocity of the magneto-optical recording medium 20 is 1.2.
By selecting a relatively low value of ~ 1.4 m / s, recording can be performed with a substantially lower laser power,
A high frequency can be easily superimposed without exceeding the rated output of the semiconductor laser.

[0019]

Embodiments of the present invention will now be described in detail with reference to the drawings. This example is applied to a so-called magnetic field modulation type magneto-optical recording system in which laser light is continuously oscillated and a magnetic field modulated according to recorded information is applied to the laser light irradiation site to record information. Indicate the case.

In FIG. 1, reference numeral 1 denotes a semiconductor laser. Laser light emitted from the semiconductor laser is directed to a magneto-optical recording medium 20 by a polarization beam splitter (PBS) 4 via a collimator lens 2 and a grating 3, and an objective is obtained. A predetermined track on the surface is irradiated through the lens 5. At this time, a magnetic field is applied by the magnetic head 6 from the back surface side of the magneto-optical recording medium 20 opposite to the side irradiated with the laser beam. This magnetic field is modulated by the magnetic field modulation circuit 7 according to the recorded information, and the magneto-optical recording medium 20 is magnetically recorded in accordance with this modulated magnetic field.

Further, a part of the laser beam directed to the magneto-optical recording medium 20 is separated by the PBS 4 and goes straight to the APC.
It is detected by the detector 8 for the (automatic power control) circuit, is input to the APC circuit 9, and the laser diode (L
D) Send a control signal to the driver 10. A high frequency superposition signal of about 120 MHz is sent from the high frequency superposition circuit set in the LD control circuit 11 to the LD driver 10, and a sample hold control signal or the like is output to the APC circuit 9. As a result, the semiconductor laser 1 is automatically power-controlled and driven, and a predetermined high frequency can be superimposed during recording.

On the other hand, the reproducing light reflected from the surface of the magneto-optical recording medium 20 is adjusted by the PBS 4 so as to go straight through the objective lens 5 and the PBS 4, and the 1/2 wavelength plate (λ /
2 plates) 12, PBS through the cylindrical lens 13
The polarized S wave and the P wave are separated by 14 and detected by detectors 15 and 16, respectively, and converted into an electric signal, and the difference between them is output as an output signal S by a differential amplifier 17.

The beam spot applied to the magneto-optical recording medium 20 is composed of 0th-order light and 1st-order light separated by the grating 3 as described with reference to FIG. The grating 3 is adjusted so that 33 and the sub-spots 34 and 35 are located on the same track. Therefore, only the main beam is used for tracking servo signal detection.

In the above structure, the grating 3
Is omitted to configure an optical system, one beam spot is irradiated on the magneto-optical recording medium 20, and the return light from this is emitted to the PB.
It is also possible to separate and read by S4.

With such an apparatus structure, as an example, the magnetic layer of the magneto-optical recording medium 20 is formed as a two-layer structure,
It was reproduced at the same time as the recording.

In this case, the magneto-optical recording medium 20 has at least two kinds of exchange-coupled mutual couplings as shown in FIG. 2 in consideration of simultaneous detection of reproduced signals at the time of recording by such one beam. The magnetic layers 23 and 24 are provided.

That is, on a transparent substrate 21 made of a non-magnetic material such as polycarbonate, a dielectric layer 22 made of SiN _x or the like and having a thickness of 850 Å and Gd (Fe _0.89 C
o _{0. 07} Cr _0.04) the first magnetic layer having a thickness of, for example, 90Å made of such _{23, Tb (Fe 0.89 Co 0.07} Cr 0.04) second magnetic layer having a thickness of, for example, 150Å consisting like 24, further Si
A protective layer 25 made of N _x or the like and having a thickness of, for example, 300 Å and Al
A reflective layer 26 having a thickness of, for example, 500 Å is sequentially deposited by sputtering or the like.

The Curie temperatures of the magnetic layers 23 and 24 are
The first magnetic layer 23 is 250 ° C. and the second magnetic layer 24 is 19
0 ℃, beam spot temperature during recording is 220 ℃
Since it is below the range, a sufficient signal can be obtained from the first magnetic layer 23 having a relatively high Curie temperature.

Using such a magneto-optical recording medium 20,
First, the reproduction signals at the time of recording were simultaneously detected with one beam spot.

The recording condition for recording and reproduction is a linear velocity of 1.4.
m / s, recording frequency 720 kHz, recording power 5 mW,
The recording magnetic field strength is ± 16 kA / m. The measurement results of the C / N (carrier / noise ratio) of the signal recorded under these conditions are shown in Table 1 as Example 1 and the case where no high frequency current is superimposed is shown as Comparative Example 1.

[0031]

[Table 1]

From this result, in the present embodiment in which the high frequency superposition is applied, 1 dB is compared with the comparative example 1 in which the high frequency is not superposed.
Was observed. The recorded tracks are compared on the same track, and if the noise of the medium is constant, this noise level difference seems to be due to laser noise, and the effect of noise reduction by applying high frequency superposition It was found that

Next, the laser beam was separated into 0th-order diffracted light and 1st-order diffracted light by the grating 3, and reproduction was performed at the time of recording by a sub-beam different from the recording beam, in this case, 1st-order diffracted light. In this case, the sub-spot behind the main spot for recording in the medium rotation direction was used. The split beam intensity ratio of these three spots is 8 for the main beam.
3%, 1st-order diffracted light is about 7%.

The recording condition is the same as the one beam spot described above. Since the recording power is 5 mW, the sub beam power is 0.42 mW.
The C / N measurement results of the signals recorded under these conditions are shown in Table 2 below.
Example 2 will be shown as Comparative Example 2 in which no high frequency current is superposed.

[0035]

[Table 2]

Similar to Example 1 described above, Comparative Example 2 in which high frequency superimposition is not applied even when a plurality of beams are used
On the other hand, a signal increase of 1 dB was observed. Even in this case, the recorded tracks are compared on the same track, and if the noise of the medium is constant, this difference in noise level is considered to be due to laser noise. It was found that the effect of reduction can be obtained.

In each of the above-described embodiments, the average recording power P _A is 5 mW, and the absolute rated output of the semiconductor laser 1 used is 35 mW. The ratio a of the amount of light reaching
%, The split light amount ratio b of the main beam was 85%, and the pulse duty d was 50%.

Therefore, in this case, the above equation (1) can be satisfied. That is, P _O × a × b × d = 35 × 0.35 × 0.85 × 0.50 = 5.21 [mW] <P _A , and high frequency superposition is possible without exceeding the rated output of the semiconductor laser 1. It can be seen that it is.

In each of the above examples, the EFM modulation method is adopted as the recording information modulation method, and its linear velocity is 1.2 to 1.4 m / s, for example, about 1.4 m / s, which is relatively high. Selected low. By applying the present invention to, for example, a mini disk (MD) as a magneto-optical recording medium adopting this modulation method and linear velocity, the quality of the reproduction signal is improved when the verification at the time of recording is performed as described above. Therefore, it is possible to surely confirm the recorded contents, and since the recording beam itself is used, it is possible to shorten the confirmation work time, and thereby to shorten the recording time.

Further, by reducing the laser return light noise at the time of recording, it is possible to suppress the occurrence of jitter due to the fluctuation of the recording power.

The present invention is not limited to the above-mentioned embodiments, and the material configuration of the magneto-optical recording medium used, the optical system configuration of the recording light and the reproducing light, and the like are within the scope of the present invention. It goes without saying that various modifications can be made with.

[0042]

As described above, according to the present invention, in so-called verification for confirming the recorded contents of the magneto-optical recording medium, the confirmed contents can be performed at the same time as the recording, so that the recording time is shortened. In addition to the above, it is possible to reduce the reproduction noise at the time of recording, improve the quality, and stably extract the data.

Further, since the laser return light noise at the time of recording is reduced, it is possible to suppress the occurrence of jitter due to the fluctuation of the recording power, and it is possible to improve the recording / reproducing characteristics.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a schematic configuration of an embodiment of the present invention.

FIG. 2 is an enlarged schematic cross-sectional view of a main part of a magneto-optical recording medium used in an example of the present invention.

FIG. 3 is an explanatory diagram of an example of a recording / reproducing system using three beams.

[Explanation of symbols]

 1 Semiconductor Laser 3 Grating 6 Magnetic Head 7 Magnetic Field Modulation Circuit 10 LD Driver 11 LD Control Circuit 20 Magneto-Optical Recording Medium 21 Base 22 Dielectric Layer 23 First Magnetic Layer 24 Second Magnetic Layer 25 Dielectric Layer 26 Reflective Layer 33 Main spot 34 Sub spot 35 Sub spot

Claims (5)

[Claims] 1. When a magneto-optical recording medium is irradiated with laser light from a semiconductor laser to record information and at the same time the recorded information is read out, a high-frequency current is applied to a drive current for driving the semiconductor laser. A recording and reproducing method characterized by superimposing. 2. The information is recorded by oscillating the laser light continuously and applying a magnetic field modulated according to the recorded information to the laser light irradiation portion to record the information. Recording and playback method. 3. The recording / reproducing system according to claim 1, wherein the recording / reproducing is performed by using a magneto-optical recording medium composed of at least two kinds of magnetic layers exchange-coupled to each other. Wherein the absolute rated output of the semiconductor laser P _O, average recording outputs P _A when superimposed with the high frequency current, the ratio of the arrival quantity to the magneto-optical recording medium with respect to the emission light amount of the semiconductor laser a, a divided light quantity ratio of the return light from the magneto-optical recording medium is b, and a pulse duty is d, P _A <P _O × a × b × d is satisfied. Alternatively, the recording / reproducing method described in 3 above. 5. The linear velocity of the magneto-optical recording medium during recording is 1.2.
2. The above-mentioned claim 1 characterized in that it is set to ~ 1.4 m / s.
Alternatively, the recording / reproducing method described in 2 or 3 or 4.