JPH0419610B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a thermal information recording device that forms minute pits on a recording medium using heat and records information based on the presence or absence of pits and the length of the pits.

(Background of the invention) With the development of the information society, there is a need for a recording method that can record large amounts of information. A method has been developed in which a delicate pit is formed, for example, a pit of 1 micron in width and 2 microns in length at the minimum, and information is recorded based on the presence or absence of the pit and the length of the pit.

As a means for forming pits, a method has been developed in which a medium is irradiated with a laser beam focused to a minute diameter and the pits are formed using the heat generated. For example, (a) a medium is melted or sublimated by heat to create a depression, and this depression becomes a pit, and (b) a phase transition is caused by heat to change optical properties such as refractive index and reflectance. creates an area different from the original state and makes this area the pit,
(c) The coercive force of the perpendicular magnetization aligned upward or downward in the medium is reduced by heat, and at the same time, a reversal magnetic field is applied to reverse the direction of magnetization, and then the laser beam irradiation is stopped to change the magnetization. Thermal information recording devices have already been proposed, such as those that create an area whose direction is opposite to the original state and use this area as a pit (magneto-optical recording), and some of them have been put into practical use.

On the other hand, due to the immaturity of the mechanical precision of recording devices, the medium may move waves or become eccentric during rotation, so the pickup section that irradiates the laser beam must always maintain a certain distance from the recording surface of the medium. You need to make sure you don't go off course.

Therefore, even when pits are not being formed, the intensity of the laser beam is not reduced to zero, and the laser beam continues to be irradiated with a low-intensity beam, and the reflected light from the medium is used for focusing and maintaining a constant distance from the recording surface of the medium. It is often used as a tracking signal to keep you on course. in this case,
The relationship between the intensity change of the laser beam and the shape of the pit formed is shown in FIG. 1. In the figure,
P _R is the intensity level of the laser beam required for recording, and P _DC is the intensity level required for focusing and tracking.

However, recording media have very thin recording layers and are made of metal materials with good thermal conductivity, such as tellurium.
Because GdCo, GdTbFeCo, etc. are used, the end points of the formed pits tend to trail off carelessly, making it difficult to obtain tight and faithful end points, and the minimum pit length and pit spacing are not 1:1. No. Therefore, during playback, the falling edge of the playback signal pulse is the second
As shown in the figure, the slope was gentle, resulting in a decrease in the S/N ratio and a decrease in recording density.

This drawback is particularly noticeable in thermal information recording devices that continuously irradiate a low-intensity laser beam for focusing or tracking.

(Object of the Invention) Therefore, the object of the present invention is to provide a thermal type that does not have the above-mentioned drawbacks, has a steep falling edge of the reproduced signal pulse, and can therefore make the minimum pit length and pit spacing equal to 1:1. The purpose of the present invention is to provide an information recording device.

(Summary of the Invention) The inventor of the present invention happened to be able to form a pit with a steep falling edge of the reproduced signal pulse by completely stopping the laser beam irradiation for a certain period of time immediately after pit formation, and was able to form a pit with an extremely steep fall. The inventors have discovered that since the inertial force acts for a short period of time, it does not affect focusing and tracking at all, leading to the present invention.

Therefore, the present invention irradiates a recording medium that moves at high speed with a laser beam, forms pits on the medium using the heat generated by the irradiation, records information based on the presence or absence of the pits and the length of the pits, and records information other than when the pits are formed. In a thermal information recording device that continues to irradiate a low-intensity laser beam and uses the beam reflected from the medium as a focusing or tracking signal, the laser beam irradiation is stopped for a certain period of time immediately after pit formation. A thermal information recording device is provided.

The present invention will be specifically explained below using a magneto-optical recording device as an example, but the present invention is not limited thereto.

(Example) FIG. 3 is a schematic diagram showing the overall configuration of a magneto-optical recording device of this example. In the figure, 1 is the driving electric system of the light source, 2 is the semiconductor laser light source, 3 is the collimator lens, 4 is the beam splitter, 5 is the objective lens, and 6 is the spindle motor for rotating the disk-shaped recording medium (Disk). , 7 is a condenser lens, and 9 is a detector. (Disk) is a disk-shaped magneto-optical recording medium that is not included in the constituent elements of the present invention. The recording layer of this recording medium has a thickness
500Å TbFe-based perpendicular magnetization film (Kerr rotation angle 0.35°)
It has been found that irradiation with a laser beam of light intensity P _W =8 mW is optimal for recording (pit formation) on this medium.

On the other hand, this device required irradiation with a laser beam with a light intensity of P _DC =4.5 mW in order to obtain signals for focusing and tracking. Furthermore, the pickup that houses the optical system of this device is designed to track the medium at a constant linear velocity of 13.2 m/sec.

In order to record the information of 1010101... on this device,
The irradiation intensity of the laser beam was varied as shown in FIG. In Fig. 4, the recording pulse width t _W = 4×
10 ⁻⁷ seconds, non-recording pulse interval t _I =4×10 ⁻⁷ seconds, and irradiation stop time t _R =1.33×10 ⁻⁷ seconds. Since the irradiation stop time t _R was extremely short, no effects were observed on focusing and tracking.

In order to change the intensity of the laser beam as shown in FIG. 4, it is sufficient to control the current supplied to the light source as shown in FIG. 4, and such current control itself is easy for those skilled in the art.

When the medium recorded in this way is observed with a polarizing microscope, pits with uniform shapes are lined up in an orderly manner as shown in FIG. The ratio was approximately 1:1. Theoretically, this ratio is 1:1
The reproduction S/N ratio is the highest when .

(Conventional example) Although the overall configuration is almost the same as the apparatus of the embodiment, the apparatus of this embodiment does not stop the laser beam irradiation.

With the device of this example, as in Example 1, now 1010101...
In order to record the information, a laser beam was irradiated as shown in FIG.

When the medium recorded in this way is observed with a polarizing microscope, the end point of the pit becomes long as if it were a tail, as shown in Fig. 5, and the pit length l = approximately 6.
microns, pit spacing l′ = approximately 4 microns,
The ratio between the two was approximately 3:2.

(Effects of the Invention) As described above, according to the present invention, by stopping the irradiation of a low-intensity laser beam for focusing or tracking for a certain period of time immediately after the pit is formed, the end point of the pit can be inadvertently trailed. Therefore, the S/N ratio during reproduction can be improved and the recording density can be increased, while focusing and tracking are not affected.

[Brief explanation of drawings]

FIG. 1 is a waveform diagram showing changes in the intensity of a laser beam, and FIG. 1 is a plan view of a pit shape formed correspondingly thereto (conventional example). Figure 2 is the first
FIG. 3 is a waveform diagram of the reproduced signal strength when the pit recorded in FIG. 2 is reproduced. FIG. 3 is a schematic diagram showing the overall configuration of a magneto-optical recording device which is a type of thermal information recording device according to an embodiment of the present invention. 4. FIG. 4 1 is a waveform diagram showing an example of a laser beam intensity change of the apparatus of the embodiment, 2 is a plan view of a pit shape formed correspondingly, and 3 is a 0 and 1 column diagram of corresponding recorded information. It is. FIG. 5 1 is a waveform diagram showing an example of a laser beam intensity change of a conventional device.
2 is a plan view of the pit shape formed correspondingly, and 3 is the 0 and 1 rows of corresponding recording information.

Claims (1)

[Claims] 1 A recording medium moving at high speed is irradiated with a laser beam, a pit is formed on the medium by the heat generated by the irradiation, and information is recorded based on the presence or absence of the pit and the length of the pit. In a thermal information recording device that continues to irradiate a beam and uses the beam reflected from the medium as a signal for focusing or tracking, the irradiation of the laser beam is stopped for a certain period of time immediately after pit formation. A thermal information recording device.