JPH02199628A - Overwriting method for optical recording medium - Google Patents

Abstract

PURPOSE:To obtain good CN by averting the irradiation of the molten part of the medium by irradiation of laser pulses for information recording by the laser pulses for erasing, thereby forming a recording spot to a prescribed size even in the case of overwriting of a small circumferential speed in the part irradiated with the laser. CONSTITUTION:The irradiation of the low-power laser pulses which are lower in output than the laser pulses for erasing is executed between the irradiation of the laser pulses for information recording and the irradiation of the laser pulses for erasing to be executed right thereafter in the overwriting method for the optical recording medium to be irradiated with the laser pulses of a single beam. The recording spots heated to the m. p. or above by the irradiation of the laser pulses for information recording are, therefore, no longer irradiated by the laser pulses for erasing and the recording spots are rapidly cooled. The recording spots of prescribed sizes are formed in this way even if the relative circumferential speed of the medium is low in the case of overwriting with the single beam laser pulses. The good CN is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for overwriting an optical recording medium, and more particularly to a method for irradiating a laser pulse when overwriting is performed using a single laser beam.

[Conventional technology]

In recent years, there has been an increasing demand for higher density and larger capacity information storage, and research and development has been actively conducted both domestically and internationally.
In particular, optical recording media that use a radar as a light source have a recording density approximately 10 to 100 times that of conventional magnetic recording media, and can record and reproduce information without contact between the recording and reproducing heads and the recording medium. Because of this, there is less damage to the recording medium and it has a long lifespan. For this reason, high-density technology is a means of recording and reproducing huge amounts of information.

Optical recording media, which are large-capacity recording systems, are promising.

This optical recording medium can be roughly divided into three types depending on the purpose: a reciprocating-only type, a write-once type, and a rewritable type.

The read-only type is a read-only recording medium from which information can only be read, and the write-once type allows information to be recorded and reproduced as needed, but the recorded information cannot be erased. On the other hand, the rewritable type is capable of recording and reproducing information, as well as erasing and rewriting already recorded information, and is desired and has the highest expectations for use as a data file for computers.

There are two types of rewritable optical recording media: magneto-optical and phase change. Among these, the phase change type generally focuses a pulsed laser beam on the optical recording material surface of the medium and heats it, and the phase change of the recording material that occurs by controlling the pulse output and pulse width of the laser beam, e.g. By raising the temperature of a crystalline material above its melting point, it transitions to an amorphous state, and information is written using the difference in reflectance in each state.
Information is erased by heating the recording material by irradiating it with a laser beam of lower energy and causing a reverse phase transformation, for example, by annealing the amorphous material to transition to the crystalline state. .

At this time, in phase change type rewriting, overwriting (recording while erasing) is performed. This overwriting method includes a method using two laser beams and a method using a single laser beam. When erasing information, the laser must be irradiated for at least as long as the time required to transition from an amorphous state to a crystalline state, that is, the crystallization time, so in the case of materials with a relatively long crystallization time. For this purpose, overwriting is performed using a laser beam focused into an elliptical shape and a laser beam focused into a circular shape. That is, the portion where old information has been written is passed under an elliptical laser beam, and laser irradiation is performed for a period longer than the required crystallization time. New information can then be written with a circular laser beam. On the other hand, in the case of a material whose crystallization time is relatively short, crystallization is completed just by passing through the circular laser spot, so overwriting can be performed using a single laser beam. As an overwriting method using a single laser beam, a laser output waveform as shown in FIG. 7, for example, has been proposed. In other words, the part of the medium that is irradiated with the laser pulse for information recording is heated to the melting point and then rapidly cooled to become amorphous, forming a recording spot, whereas the part that is irradiated with the laser pulse for erasing becomes crystalline, although it is lower than the melting point. When heated to a temperature higher than the crystallization temperature, it crystallizes and erases information.

[Problem to be solved by the invention]

However, when overwriting with this method, a good recording spot is formed when the rotational speed of the optical recording medium is high and the circumferential speed of the part where the laser irradiation is performed is high, but the relationship with the recording frequency If the rotational speed of the medium becomes slow, overwriting will not work properly.For example, under the conditions of recording frequency 3.7MH2, medium rotational speed 1800rpm, duty ratio 33%, and laser beam diameter 1.2-5.
When overwriting the outermost circumference of an inch-inch medium by irradiating the laser with the pattern shown in Figure 7 (information recording pulse 90 ns, erasing pulse 180 ns), the inside of the trunk 5 of the medium as shown in Figure 8 (al) is used. Recording spot 8 formed on
The area becomes smaller than the predetermined size, which means that the area of the crystalline part with high light reflectance increases among the spots irradiated with the reproduction laser beam, reducing the CN ratio of the medium to 35 dB. The reason why the area of the recording spot becomes small in this case is as follows. Figure 8(b) shows the relationship between the position (μ) of each point on the track of the medium and the laser beam irradiation time (μa) at each point in the case of emotional recording laser pulse irradiation and erasing laser pulse irradiation. FIG. As shown in Figure 8 (bl), each point within the track receives the information recording pulse irradiation and the erasing pulse irradiation in duplicate, so the heating effect of the erasing pulse causes the medium to rapidly cool down after the information recording pulse irradiation. This is because, as a result, amorphization is prevented and a portion of the portion that should become a recording spot changes to a crystalline material with a high reflectance.

The present invention has been made in view of the above-mentioned points, and its purpose is to avoid irradiating the melted part of the medium by the laser pulse irradiation for information recording with the laser pulse for erasing, even in the case of overwriting with a small circumferential speed of the laser irradiated part. The objective is to obtain a good CN ratio (45 dB or more) by forming a recording spot to a predetermined size.

[Means to solve the problem]

According to the present invention, the above-mentioned object is achieved by providing a method for overwriting an optical recording medium in which an optical recording medium is irradiated with a single beam laser pulse for information recording or erasing by adjusting the output power. This is achieved by irradiating a low-power laser pulse with a lower output than the erasing laser pulse between the erasing laser pulse irradiation that is performed immediately thereafter.

The low power laser pulse may be a laser output for reproduction, etc., as long as its output does not hinder the amorphization of the medium. A non-oscillating state of the laser is also used.

[Effect]

The part of the medium that is heated above the melting point by irradiation with the information recording laser pulse is irradiated with a low-power laser pulse during cooling, but is not irradiated with the erasing laser pulse, so it is erased. There is no heating effect due to the laser pulse, and the entire area that should become a recording spot is rapidly cooled to form a recording spot of a predetermined size.

〔Example〕

(Example 1) Next, an example of the present invention will be described based on the drawings. 9th
The figure is a schematic cross-sectional view of an optical recording medium.
SiO retention layer (190 nm thick) 12GeSb on llO
*Tc* g layer (75r++w thickness) 13.310 protective layer (190nm thickness) 14, AJ cooling 1! ! (100n
-thickness) 15 are sequentially laminated.

The size is 5 inches.

FIG. 1 shows the output pattern of a single beam laser pulse according to an embodiment of the present invention. The information recording laser pulse is a 4th order laser pulse emitted for 90 ns with a recording power of 151.
Low power laser pulse is 55ns with 5W reading power
irradiated. An erasing laser pulse is applied for 70 ns with an erasing power of 8. After this, a low power laser pulse is irradiated for 55 ns, and one cycle is completed. This corresponds to a recording frequency of 3.7 M)IZ and a duty ratio of 33%. After initializing a 5-inch optical recording medium, the medium is irradiated with the laser output pattern described above. 1 medium
When rotating at 800 rpm and irradiating the outermost circumference of the medium with a laser beam with a diameter of 1.2 - (laser beam relative circumferential speed 11.1 s/s), the recorded spot is shown in Figure 2 ta+.
The laser pulse irradiation characteristics at each point within the medium track are shown in FIG. 2), and the relative movement characteristics of the laser pulse are shown in FIG. 2 fC). The recording spots 8^ have a diameter of about 1 .mu.m and are arranged within the track 5 at intervals of 3-. The CN ratio during reproduction of the recording spot 8A due to this overwriting is 55 dB. The laser pulse irradiation characteristics shown in FIG. 2 (bl) and the laser pulse relative movement characteristics shown in FIG. 2 ic correspond to the positions of points within the medium track. In FIG. 2 tel, the thick line indicates the irradiation section of the information recording laser pulse or the erasing laser pulse, which is the start of the information recording laser pulse irradiation.
At step s, the information recording laser pulse irradiates an interval from 0- to 1.2- for each point in the medium track. This laser beam moves to the right with a relative speed of 11.111/3 and 9
No position 21 at the end of 0ns information recording laser pulse irradiation
．． Irradiate the 0- and 2.2 μm sections. Within the relative movement time of this laser pulse, the point position 1. Since the section between Otna and 1.2- is constantly irradiated with laser, the laser irradiation time in this section is 90ns as shown in Figure 2 (1)).
In the section between point positions 0 and 1.0 tr-, the laser pulse moves relatively, so the irradiation time increases to the right as shown in Figure 2), and the section between 0 point positions 1.2- and 2.2μ is reversed. As shown in the figure, it becomes a straight line that slopes downward to the right. After irradiation of a 55 ns low power laser pulse, that is, after 145 ns have elapsed from the start, an erasing laser pulse is irradiated to the area between point positions 1.6 μm and 2.8 μm. This erasing laser pulse is also 11.1++
/s, and after the irradiation time of 70 ns elapsed, that is, after 215 ns elapsed from the start, point positions 2.4- and 3 were set.
．． Irradiate the section 6-. The section between point positions 2.4n and 2.8- is irradiated with a writing erasing laser pulse of 70 ns, which is the relative movement time of the erasing pulse. Therefore, the laser irradiation time is Tons, which is the zero point position of 1.6n and 2.4μ.
The laser irradiation time in the section - and the sections 12.8μ and 3.61 without position is as shown in the figure based on the same concept as in the case of laser pulse irradiation for information recording. A low power laser is irradiated for 55n3 after the end of the erasing laser pulse irradiation, and 270 ns after the start, the information recording laser pulse is irradiated again and the same procedure as before is repeated.

As shown in Figure 2), the laser pulse for information recording is 90
The part that should become a recording spot centered on the area between 1.0- and 1.2μ- point positions that were melted by ns irradiation will not be irradiated with an erasing laser pulse (as opposed to the conventional erasing laser pulse irradiation). Since the local heating effect is eliminated, the entire area that should become the recording spot is rapidly cooled, and a recording spot having an amorphous portion of a predetermined size is formed.In addition, the area around the recording spot is erased. Since the irradiation time of the laser pulse for information recording is short, it is not possible to heat the material above the crystallization temperature by irradiating it with the laser pulse for erasing. The old recording spot is erased and overwriting becomes possible even in the vicinity of the recording spot where the erasing laser pulse irradiates for a short time.

An erasing ratio of 30 dB can be obtained for erasing spots (not shown) due to overwriting. This cancellation ratio is 3.7 as mentioned above.
M) Overwrite with IZ conditions, then 2.2NH
It can be determined by overwriting under the conditions of 4 and comparing the two recording spots.

Next, a 5-inch optical recording medium was heated at 1800 rpm in the same manner as above.
The innermost circumference of the medium (laser beam relative circumferential speed 5
．． 5 m/s) with the output pattern shown in FIG. 1, the recording spot is shown in FIG. 3 (al), and the laser irradiation characteristics at each point within the medium track are shown in FIG. 3 (b). The CN ratio during playback of recording spot 8B is 50.
dB is obtained.

(Example 2) FIG. 4 shows different output patterns of a single beam laser pulse. This pattern differs from Example 1 in that low-power laser pulse irradiation is not performed between the erasing laser pulse irradiation and the subsequent information recording laser pulse irradiation.

When a 5-inch medium is rotated at 180 rpm and its outermost periphery is irradiated with a laser beam with a diameter of 1.2 μm using the output turn shown in FIG. 4, the recording spot is shown in FIG. 5 ta+.
The laser pulse irradiation characteristics at each point within the medium track are shown in Fig. 5.Recording spot 8 obtained by one overwriting
By using the same recording power and erasing power as in Example 1, a CN ratio of 53 dB and an erasing ratio of 30 dB are obtained during reproduction of C.

In this example, since the information recording laser pulse is irradiated immediately after the erasing laser pulse irradiation ends, there may be a heating effect due to the erasing laser pulse irradiation in the previous stage, but compared to Example 1, The CN ratio is only reduced by about 2 dB, and the effect is small.

When a 5-inch medium is rotated at 1800 rpm and its innermost periphery is irradiated with a laser beam in the output pattern shown in Figure 4 (
The recording spot at a laser beam relative circumferential velocity of 5.5 m/s) is shown in FIG. 6 fal, and the laser irradiation characteristics at each point in the medium trunk are shown in FIG. 6 rb3. The CN ratio during reproduction of the recording spot 80 obtained by overwriting is 48 dB in this case, which is sufficiently usable.

〔Effect of the invention〕

According to this invention, in the overwriting method for an optical recording medium in which the optical recording medium is irradiated with a single beam laser pulse for information recording or erasing by adjusting the output, the method comprises: irradiating the laser pulse for information recording and erasing performed immediately thereafter. Since a low power laser pulse with a lower output than the erasing laser pulse is irradiated between the information recording laser pulse irradiation and the information recording laser pulse irradiation, the recording spot is heated above the melting point by the information recording laser pulse irradiation due to the interposition of the low power laser pulse. As a result, the entire area that should be irradiated by the erasing laser pulse is not affected by the heating effect of the erasing laser pulse (recording sub-board 7), and as a result, the single beam laser pulse Even when the relative circumferential speed of the medium is slow when overwriting is performed, a recording spot of a predetermined size is formed, making it possible to obtain a good CN ratio.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the output pattern of a laser beam according to an embodiment of the invention, FIG. 2(a) is a plan view showing a recording spot at a relative peripheral speed of 11 m/s according to an embodiment of the invention, FIG. 2(b) is a diagram showing the laser irradiation characteristics at each point in the medium track at a relative circumferential speed of 11 s/s according to the embodiment of the present invention, and FIG. 2(C) is a diagram according to the embodiment of the present invention. FIG. 3 fa+ is a diagram showing the relative movement characteristics of the laser pulse when the relative circumferential velocity is 11 m/s, and the relative circumferential velocity is 5.0 m/s.
5 is a diagram showing the laser irradiation characteristics at each point in the medium trunk at the time of application, FIG. 4 is a diagram showing the output pattern of the laser beam according to another embodiment of the present invention, and FIG. A plan view showing a recording spot at a relative circumferential speed of 11 m/s according to another embodiment, FIG. A diagram showing the irradiation characteristics, FIG. 6 fa) is a plan view showing a recording spot at a relative circumferential speed of 5.5 m/s according to another embodiment of the present invention, FIG. A diagram showing the laser irradiation characteristics at each point in the medium trunk at a relative circumferential speed of 5.5 a/s according to the embodiment, FIG. 7 is a diagram showing the conventional laser beam output pattern, and FIG. 8 ta+ shows the relative circumferential speed. A plan view showing a conventional recording spont at a speed of 11 m/s,
FIG. 8 (bl is a line diagram showing the laser irradiation characteristics at each point in a conventional medium track at a relative circumferential speed of 11.tm/s, and FIG. 9 is a schematic cross-sectional view showing an optical recording medium. 5 Nidrank, 8, 8A, 1311.8C, 80: recording spot, 11: polycarbonate substrate, 12: S
iO protective layer, 13: GeSb, Tea recording layer, 14
: SiO holding fulljl, 15:u cold 1c2 figure 1 rarego-6 17Tftllh direction ffl placement (μm) 31st! ! L-7 family's condolence V! Punishment times 1st rank M (μ7FL) 1$6 The drunkenness of the courage! 91 Layer V (μM)
) Figure 8 Figure 9

Claims (1)

[Claims] 1) An overwriting method for an optical recording medium in which an optical recording medium is irradiated with a single beam laser pulse for information recording or erasing by adjusting the output, comprising: irradiating a laser pulse for information recording and immediately after that; 1. A method for overwriting an optical recording medium, comprising irradiating a low-power laser pulse with a lower output than the erasing laser pulse between the erasing laser pulse irradiation and the erasing laser pulse irradiation.