JPH0927152A - Optical recording and reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely execute an overwrite recording by completely erasing information already recorded on an optical disk in the case of performing an overwrite recording on the optical disk capable of a light intensity modulation overwrite. SOLUTION: The intensity modulation of a laser beam light source 2 is performed by transmitting binary information inputted to an input part 5 to a modulation means 4 and by instructing an optimum recording laser power from an instruction means 10. The beam after the modulation irrdiates the recording surface of a magneto-optical disk D rotated by a motor 1 through an irradiation optical system 3 to be changed into heat. Then, information are recorded on the recording surface by actions of heat and a recording magnetic field impressing means 6. Then, in the reproducing of the information, the laser beam light source 2 is lighten in a reproducing level by the instruction from the instruction means 10 and the laser beam of the reproducing level irradiates the recorded surface of the disk D through the irradiation optical system 3. The reflected beam is converted into the intensity signal of a light by a detector 7 to be outputted to a demodulation means 8 and is demodulated to the form of coded information to be outputted from an output part 9 in original information.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an optical recording / reproducing apparatus.

[0002]

2. Description of the Related Art Recently, an optical recording / reproducing method satisfying various requirements including high density, large capacity, high access speed, and high recording / reproducing speed, and a recording apparatus, reproducing apparatus and recording medium used therefor. Efforts are being made to develop. Among a wide range of optical recording / reproducing methods, the magneto-optical recording / reproducing method has the unique advantage that information can be recorded and then erased, and that new information can be recorded again and again. For, is full of the greatest charm.

A magneto-optical recording disk (medium) used in this magneto-optical recording / reproducing method has a magnetic film composed of one layer or multiple layers as a layer for recording. The magnetic film is a perpendicular magnetic film (perpendicular film) with high recording density and high signal strength.
magnetic layer or layers) have been developed and are being used. Such a magnetized film is made of, for example, amorphous GdFe or
It is composed of GdCo, GdFeCo, TbFe, TbCo, TbFeCo and the like. The perpendicular magnetic film generally has concentric or spiral tracks, and information is recorded on the tracks.

[Principle of Mark Formation] In the formation of marks, the characteristic of the laser, that is, the excellent coherence in terms of space and time is advantageously used, and it is almost the same as the diffraction limit determined by the wavelength of laser light. The beam is narrowed down to a small spot. The narrowed light is irradiated to the track surface, heats the recording film, and the diameter of the recording film is 1 μm.
Information is recorded by forming marks of m or less. In optical recording, theoretically about 108 marks / cm
Recording densities up to 2 can be achieved. This is because the laser beam can be concentrated into a spot with a diameter as small as about its wavelength.

In magneto-optical recording, a laser beam is focused on a perpendicularly magnetized film and heated. Meanwhile, the recording magnetic field Hb in the direction opposite to the initialized direction is externally applied to the heated portion. Then, the coercive force Hc (coersivity) of the locally heated portion decreases and becomes smaller than the recording magnetic field Hb. As a result, the magnetization of that part is
Lined up in the direction of the recording magnetic field Hb. In this way, the oppositely magnetized mark is formed.

[Principle of magneto-optical reproduction] Light is an electromagnetic wave having an electromagnetic field vector normally diverging in all directions on a plane perpendicular to the optical path. When light is converted to linearly polarized light and illuminates a perpendicular magnetized film, the light is reflected on its surface or transmitted through the perpendicular magnetized film. At this time, the polarization plane rotates according to the direction of the magnetization. This rotating phenomenon is
It is called the magnetic Kerr effect or the magnetic Faraday effect.

For example, if the polarization plane of the reflected light is rotated by θK degrees with respect to the magnetization in the initialization direction, it is rotated by −θk degrees with respect to the magnetization in the recording direction. Therefore, if the axis of the optical analyzer (polarizer) is set perpendicular to the plane inclined by θK degrees, the light reflected from the mark magnetized in the initialization direction cannot pass through the analyzer. On the other hand, the light reflected from the mark magnetized in the recording direction is
The amount multiplied by (sin2θk) 2 passes through the analyzer and is captured by the detector (photoelectric conversion means). As a result, the mark magnetized in the recording direction looks brighter than the mark magnetized in the initialization direction, and generates a strong electric signal in the detector. Therefore, the electrical signal from this detector is modulated according to the recorded information,
The information is reproduced.

[Light Intensity Modulation Overwrite] However, in conventional magneto-optical recording, since heat generated by laser light is used for recording, it is necessary to erase the recorded portion once. In magnetic recording, a new signal can be recorded without erasing, that is, so-called overwriting is possible, whereas in magneto-optical recording, there is a drawback that re-recording takes time.

However, if the direction of the recording magnetic field Hb can be freely modulated as required, overwriting is possible. However, it is impossible to modulate the direction of the recording magnetic field Hb at a high speed. For example, the recording magnetic field H
When b is a permanent magnet, it is necessary to mechanically reverse the direction of the magnet, but it is impossible to reverse the magnet at high speed. Even when the recording magnetic field Hb is an electromagnet, it is difficult to modulate the direction of a large-capacity current at such a high speed.

However, the technological progress has been remarkable, and the magneto-optical recording method is capable of overwriting by simply modulating the intensity of the irradiation light beam without modulating the intensity of the recording magnetic field Hb according to the binary information to be recorded. And an overwritable magneto-optical recording medium used therefor and an overwritable recording device also used therein have been invented and applied for a patent. (JP-A-62-175948 = DE3,619,618A1 =
This invention will be described below.

In the basic invention, "a memory layer (hereinafter, M layer) basically consisting of a magnetic thin film capable of perpendicular magnetization and a recording layer (hereinafter W layer) consisting of a magnetic thin film capable of perpendicular magnetization are included, and both layers are exchanged. An overwritable multi-layered magneto-optical recording medium which is coupled and is capable of directing only the magnetization of the W layer to a predetermined direction without changing the magnetization direction of the M layer at room temperature is used.

Then, information is expressed by the direction of magnetization in the M layer and recording is performed. The M layer and W layer are generally composed of an alloy of a rare earth metal and a transition metal. The exchange coupling force acts in the direction of aligning the sublattice magnetizations of the transition metal and the sublattice magnetizations of the rare earth metal. This medium is W
The magnetization direction of the layers can be aligned in one direction. Moreover,
At that time, the magnetization direction of the M layer is not reversed, and further, the magnetization direction of the W layer once aligned in one direction is not reversed even when the exchange coupling force from the M layer is received, and conversely, the magnetization direction of the M layer is reversed. The direction of magnetization is W
It does not reverse even when it receives exchange coupling force from the layers. And W
The layer has a lower coercive force Hc and a higher Curie point T than the M layer.
has c.

According to the recording method of the basic invention, in the recording medium, only the direction of magnetization of the W layer is aligned in one direction by the initialization means before recording. The initialization means may use a magnetic field from the outside, or the medium itself may have the initialization means. Then, the medium is irradiated with the laser beam pulse-modulated according to the binarized information. The intensity of the laser beam has a high level PH and a low level PL. This low level is higher than the reproduction level PR applied to the medium during reproduction. At this time, the recording magnetic field Hb is applied to the medium portion irradiated with the laser beam.

When the initialized medium is irradiated with a laser beam of low level PL, the temperature of the medium rises and M
The coercive force of the layer is very small or extremely zero.
It becomes zero when the temperature of the medium is equal to or higher than the Curie point of the M layer. At this time, the coercive force of the W layer is sufficiently large and is not reversed by the recording magnetic field Hb. Then, since an exchange coupling force acts from the W layer to the M layer, the sub-lattice magnetization of the M layer follows the initialized sub-lattice magnetization of the W layer. When the irradiation of the laser beam is stopped from this state, the temperature of the medium is lowered, but the direction of the sublattice magnetization of the M layer is not changed.

On the other hand, when the laser beam of high level PH is irradiated, the temperature of the medium rises higher than that at the time of irradiation of the PL laser beam, exceeds the Curie point of the M layer, and the coercive force of the M layer becomes zero. The coercive force will be very small or extremely zero. The magnetization of the W layer having a reduced coercive force is reversed by the recording magnetic field Hb. When the irradiation of the laser beam is stopped, the temperature of the medium drops, and when the temperature becomes equal to or lower than the Curie point of the M layer, the magnetization of the M layer appears following the inverted sublattice magnetization of the W layer. Further, even if the medium temperature is lowered, the direction of the sub-lattice magnetization of the M layer does not change. At this time, the direction of the sub-lattice magnetization of the M layer is opposite to that in the case of irradiating the PL level laser beam.

As described above, low level PL and high level P L
By irradiating the laser beam of H 2, the magnetization direction of the M layer is determined without depending on the magnetization direction of the original M layer.
Overwriting is possible because the layers do not have to be erased before re-recording. The medium used in the light modulation overwrite method has a multi-layer structure including an M layer and a W layer. The M layer is a magnetic layer having a large coercive force and a low magnetization reversal temperature at room temperature. The W layer is a magnetic layer having a relatively higher magnetization reversal temperature than the M layer. The M layer and the W layer may themselves be composed of a multilayer film. In some cases, an intermediate layer may be present between the M layer and the W layer. Further, an initialization layer for initializing the W layer may be provided adjacent to the W layer.

[Pulse Train Recording] In optical recording, marks are used as a method of recording and reproducing information. The pit position recording having the mark position as information and the pit edge recording having the mark edge position as information
There are different types of recording methods. Particularly, in pit edge recording, both the front end and the rear end of the mark are used, so that the recording density becomes higher than that in pit position recording.

However, when performing pit edge recording, it is necessary to strictly control the size of the mark. However, since optical recording is thermal recording, with a simple binary pulse, the rear end of the mark becomes larger than the front end due to heat accumulation, and so-called teardrop-shaped marks tend to be formed.
Therefore, pulse train recording was devised as a recording correction method for correcting the mark shape by modulating the recording laser pulse as shown in FIG. In this pulse train recording, the laser power is set to three values of Pa, Pw1 and Pw2, and the recording is performed based on the ratio of the three values determined from the thermal characteristics.

When the pulse train is applied to the above-mentioned light intensity modulation overwrite, Pa is at a low level P.
Equivalent to L laser power, Pw1 and Pw2 are high level P
Equivalent to H laser power.

[0020]

By the way, when recording information on an optical disk, in order to optimize the mark shape, the output of laser power is adjusted to a small value in accordance with the recording temperature of the optical disk and the temperature of the external environment. There was a problem that it had to be adjusted. Therefore, in an optical disc drive device that records information on an optical disc, sensitivity is adjusted by performing test recording before recording information on the optical disc.

In the above-mentioned pulse train recording described above, test recording was performed by changing the power of the laser light while keeping the ratio of the three values Pa, Pw1 and Pw2 constant. In the case of an optical disc that is not a light intensity modulation overwrite, it is 3 of Pa, Pw1, and Pw2.
All three values are relevant for recording only. For this reason,
With the ratio of the three values of Pa, Pw1 and Pw2 being constant,
It suffices to perform a test recording that changes the power of the laser light.

However, when the recording method as described above is used for the light intensity modulation overwrite, a problem occurs. Because Pa is a low level PL laser power, Pa is an important parameter not only for recording but also for erasing. Therefore, if test recording is performed with the value of Pa kept constant with the values of Pw1 and Pw2 as in the prior art, there is a risk of erasing failure. Then, old data remains, and there is a problem that overwrite cannot be performed completely. This is not a problem that occurs only in pulse train recording, but can always be a problem when a binary or higher power of low level and high level is required.

An object of the present invention is to perform overwriting recording on an optical disc capable of light intensity modulation overwriting.
Completely erase the information already recorded on the optical disc,
The point is to enable complete overwrite recording.

[0024]

The invention described in claim 1 can be overwritten by modulating the light intensity of a laser beam for recording information into at least two values of a high level and a low level. In an optical disk drive device for recording / reproducing the information on / from the optical disk, the means for determining the light intensity of the at least two (hereinafter, n) modulated laser beams includes the light intensity of the n laser beams. Means for obtaining a product, means for pre-storing the product of the obtained light intensities of the n laser lights, means for obtaining the light intensities of the respective n-1 laser lights, and the previously stored n The product of the light intensities of the individual laser beams and the obtained n−
Means for obtaining the light intensity of the n-th laser light from the value of the light intensity of each one of the laser lights.

According to a second aspect of the present invention, in the optical recording / reproducing apparatus according to the first aspect, the means for obtaining the light intensity of each of the n-1 laser beams is a trial writing for performing a trial writing on the optical disc. It is characterized by having means. According to a third aspect of the present invention, in the optical recording / reproducing apparatus according to the first aspect, the optical disc is overwritable.

[0026]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a magneto-optical recording / reproducing apparatus according to an embodiment of the present invention. In the figure, the binarized information entered in the information input section 5 is sent to the modulation means 4. The instruction of the proper recording laser power is received from the instruction means 10, converted into the modulation signal of the laser beam light source 2, and the intensity modulation of the laser beam light source 2 is performed. The intensity-modulated beam is applied to the magneto-optical disk D rotated by the motor 1 through the irradiation optical system 3 and converted into heat. Information is recorded on the recording surface of the magneto-optical disk D by the action of the heat and the recording magnetic field applying means 6.

Information reproduction is performed by recording / reproduction control / determination means 1
The laser beam light source 2 is turned on at the reproduction level by the proper reproduction laser power according to the instruction from 0. The emitted reproduction level beam is applied to the disk D through the irradiation optical system 3. The beam reflected by the recording surface of the disk D returns to the irradiation optical system 3 again, is reflected there, and then enters the detector 7. The detector 7 converts the light intensity signal into an electric signal and outputs the electric signal to the demodulation means 8. The demodulation means 8 demodulates it into the coded information and then outputs the original binarized information from the information output unit 9 to the outside.

The procedure of trial writing will be described below. (1) The loaded disc D is rotated by the motor 1 to access the trial writing area of the disc D with the recording / reproducing laser beam. (2) The modulation unit 4 generates a short mark repeating pattern for trial writing, which is controlled by the recording / reproduction control / determination unit 10. Then, according to a command from the recording / reproducing control / determination means 10, the recording power is set in the laser beam light source 2 to determine PW1, and trial writing is performed. Then, Pw1 is changed stepwise without changing the recording power Pa, and test recording is performed on an adjacent sector or track. (3) The recorded test area is reproduced and input to the recording / reproducing / determining means 10 to determine PW1 that minimizes the edge jitter of the recording mark. (4) From the known power product and the obtained Pa and PW1, the recording / reproducing / determining means 10 calculates PW2 using the relationship of PW2 = power product / (Pa · PW1).

The value of the power product is set in advance in the recording / reproducing control / determination means 10 by a method such as reading the information previously recorded in the vendor zone of the disc.

[0030]

As described above, according to the present invention, when recording information on an optical disc capable of overwriting the light intensity modulation, since the power product is known, it is not necessary to obtain powers having different n values, and the work amount is reduced. can do.

[Brief description of drawings]

FIG. 1 is a block diagram of a magneto-optical recording / reproducing apparatus according to an embodiment of the present invention.

FIG. 2 is a conceptual diagram showing recording pulses in conventional pulse train recording.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 motor 2 laser beam light source 3 recording and reproducing optical system 4 modulating means 5 input section 6 recording magnetic field applying means 7 detector 8 demodulating means 9 output section 10 recording / reproducing control / judging means

Claims (3)

[Claims] 1. An optical disk drive device for recording / reproducing information on / from an overwritable optical disk by modulating the light intensity of a laser beam for recording information into at least two values of a high level and a low level. The means for obtaining the light intensities of the modulated at least two (hereinafter referred to as n) laser lights are means for obtaining the product of the light intensities of the n laser lights, and the obtained n lasers. Means for pre-storing the product of the light intensities of the light, means for determining the light intensities of the n-1 respective laser lights, and the product of the pre-stored light intensities of the n laser lights and the determined An optical recording / reproducing apparatus comprising means for obtaining the light intensity of the n-th laser beam from the light intensity values of the n-1 laser beams. 2. The optical recording / reproducing apparatus according to claim 1, wherein the means for obtaining the light intensities of the respective n-1 laser lights comprises a trial writing means for performing trial writing on the optical disc. Characteristic optical recording / reproducing device. 3. The optical recording / reproducing apparatus according to claim 1, wherein the optical disc is overwritable.