JPS63113938A - Recording method for optical information - Google Patents

Abstract

PURPOSE:To attain simultaneous erasure/recording capable of obtaining a large reproducing signal without complicating the constitution of a device by applying 3-stage of modulation to a power level of a laser light so as to record a new signal while erasing the recording by one semiconductor laser. CONSTITUTION:A laser light is subject to intensity jodulation by a recording power level PW and the recording onto an optical disk 1 is applied and the intensity modulation is applied with a lower cooling level PC than that of the erasure power level PE, the disk 1 whose temperature rises due to recording is quenched and the recording thin film 3 goes to an amorphous state. In this state, the erasure by the laser whose intensity is modulated by the level PE and the succeeding recording is applied and the reproducing signal is increased by the recording to the thin film 3 of the amorphous state. Thus, a large reproducing signal with simple constitution employing one semiconductor laser and simultaneous erasure/recording is also applied.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is directed to optical information recording members, mainly optical discs, which record, reproduce, or erase optical information at high speed and with high density using laser beams or the like. The present invention relates to a method for recording optical information.

2. Description of the Related Art Techniques for recording and reproducing high-density information using laser beams are already well known, and are currently being widely applied to document file systems, still image file systems, and the like. There are also reports of research and development cases regarding rewritable recording systems. One of these methods is the so-called phase-change optical disk, which mainly utilizes the change in state between amorphous and crystalline Te, Te compounds, or Ss compounds, or the fact that different crystal structures have different volumes. be. For example, when using the state change between amorphous and crystal, the refractive index n can be changed by irradiating a relatively strong and short pulsed light and rapidly cooling the irradiated part from a heated state to an amorphous state. Decrease the optical constant (whitening) to the extinction coefficient, and also
Signals are recorded and erased by irradiating relatively weak and long pulsed light to create a crystalline state, which increases the optical constants (blackens), and generally decreases the optical constants during recording. , the idea is to use the increasing direction when erasing.

The recording erasing method is also the same when using the change in state between crystals, which takes advantage of the fact that the crystal structure changes and the volume changes reversibly between rapid heating and cooling and slow heating and cooling. It is.

One of the features of the phase change optical disc is that it is possible to perform so-called simultaneous erasure, in which a previously recorded signal is erased while the next signal is simultaneously recorded.

To achieve this, multiple semiconductor lasers are installed in the optical head to form multiple beam spots on the signal recording track of the optical disk, and the preceding beam erases the previously written signal while the subsequent beam spots A method was devised to record a new signal using a beam of
-145535).

In this case, the preceding erasing beam removes heat from the recording film.

In order to obtain a crystalline state through slow cooling, the beam shape is shaped into an ellipse that extends toward the trunk, allowing the laser beam to irradiate the same location for a longer period of time than with a circular beam.

In addition, a method for realizing simultaneous erasure using only one laser has also been devised (Japanese Patent Application Laid-Open No. 145530/1983).

This uses a recording thin film that has a fast crystallization rate and can complete crystallization even in the same circular spot as the recording beam, and as shown in Figure 2, the laser beam is used to increase the recording power level Pw and erase power level PE (Pw>PE). ), the laser spot erases the previously recorded signal and records a new signal in just one pass over the track. It is.

Problems to be Solved by the Invention The two methods described above for realizing simultaneous erasing using a phase change optical disk each have their own problems.

First, the method of installing multiple lasers on an optical head requires a high level of optical precision in order to simultaneously form multiple laser spots on one track and accurately track it, which is especially important for mass production. This is a big problem if you think about it. Furthermore, each laser must be controlled separately, making the system complex.

Furthermore, the use of a plurality of expensive semiconductor lasers increases the cost of the device.

On the other hand, what is the record level of one racer? 'F
+Modulating between two power levels of the Hower level PE for simultaneous erasure does not require as much optical precision and complex systems as the method using multiple lasers, but it does Because the erasing beam is irradiated on both the front and the back, it is difficult to achieve rapid cooling to obtain an amorphous state. Therefore, the recording bit may be small, or the recording bit may contain microcrystals and the apparent optical constant may be amorphous. In some cases, the change in reflectance from the crystalline state is small, making it impossible to obtain a large reproduced signal. Further, even when utilizing the state change between crystals, a large reproduced signal could not be obtained if rapid cooling conditions were similarly difficult to obtain.

The present invention has been made in view of the above, and an object of the present invention is to realize simultaneous erasing and erasing of a large reproduced signal using an optical head having a simple configuration.

Means for Solving the Problems In order to solve the above problems, the present invention provides an optical information recording member having a recording thin film that reversibly changes between two optically distinguishable states by irradiation with a laser beam or the like. To,
When simultaneously erasing data using a single laser beam spot, the power level of the laser beam is lower than the recording power level, the erasing power level, and the two power levels instantaneously set immediately after the recording power level. It modulates between levels.

Function: If the method of the present invention is used to perform simultaneous erasing using irradiation light modulated at three power levels, the irradiation power momentarily decreases immediately after the recording light is irradiated, so the temperature of the recording light irradiation area increases. Later, it is easier to obtain rapid cooling, which makes it easier to form large amorphous regions, and it becomes difficult for microcrystals to be included in the recording area, resulting in smaller optical constants and large changes in optical constants.In other words, large reproduced signals can be obtained. be able to obtain it.

Furthermore, since the method of simultaneously erasing signals according to the present invention is executed using only a single laser, the optical head and device configuration are not complicated, and the cost of the device can be kept low.

Example Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is an embodiment showing a method for recording and erasing optical information according to the present invention.

The basic structure of the optical disc 1 is that a recording thin film 3 is provided on a substrate 2. As the substrate 2, polymethyl methacrylate (PMMA) or polycarbonate (P
Resin substrates such as C), glass substrates, etc. can be used, and
The recording thin film 3, which records signals by utilizing a change in state between crystal and amorphous due to light irradiation, is a thin film mainly made of Te, a Te compound, or a Se compound, or a thin film made of Te0x(0 A thin film mainly made of x(2) can be used, but this recording thin film must be erased (crystallized) with the same circular beam spot shape as when recording signals, and a high crystallization speed is required. Therefore, the thin film material consists of Te as the main component, Sn,
Ge, In, Bi, Se, S, Sb, Au.

A material containing at least one of Pd and Pb, or a material containing Sn, Ge, In, Bi,
Ss.

Materials containing at least one of S, Sb, Au, Pd and Pb are particularly suitable.

Further, as a material that can be used as the recording thin film 3 and causes a state change between crystals, an In5bSe compound or the like is suitable.

In this example, a semiconductor laser 4 was used as a light source.

The light with a wavelength of 830 nm emitted from the semiconductor laser 4 is the first
The second lens 7 becomes a condensed thousand-line light 6 through the lens 5.
After being shaped into a round shape, the light is turned into parallel light again by a third lens 8, and is focused onto a spot 11 with a wavelength limit of about 1 μm on the optical disk 1 by a fourth lens 10 via a half mirror 9. Recording and erasure are performed.

The reproduction signal was detected by receiving the reflected light from the optical disc 1 via the half mirror 9, passing it through the lens 12, and using the photosensitive diode 13.

The most distinctive feature of the method for recording and erasing optical information according to the present invention lies in the shape of the intensity-modulated output waveform of the laser light input to the optical disk 1, which is similar to the current waveform input to the semiconductor laser 4. 14, and its effects will be described in detail next.

The output waveform of the semiconductor laser whose intensity is modulated by the current waveform 14 is shown in FIG. 3(a), and the change in the temperature reached by the recording thin film at this time is shown in FIG. 3(b). The state of the recorded bits of the recorded signal is shown in FIG. 3(c). As shown in FIG. 3(, ), the power level of the laser beam continues immediately after the signal recording power level N and the erasing power level PE which is lower than the signal recording power level Pw, and PE is further lower than the signal recording power level Pw. It is modulated into three levels of power level (hereinafter referred to as cooling power level PC). At this time, at the signal recording power level level, the thin film temperature is the melting temperature T! The erase power level PE is selected so that the thin film temperature is equal to or higher than the crystallization (blackening) transition temperature Tx. The upper limit of PE is generally set so that the thin film temperature is below Tm, but if the irradiated part can finally be crystallized, Trn
may exceed. In other words, if you irradiate with Pw and raise the thin film temperature to a temperature sufficiently higher than T, completely melt it, and then rapidly cool it, it will be in an amorphous state, but if you irradiate with PE and raise the thin film temperature to a temperature slightly higher than Tm. Even if it is melted and then cooled, it may not become an amorphous state but may become a crystalline state. This means that even if the recording thin film is melted by a beam spot of the same shape, the melted state (either completely melted or incompletely melted and the solution contains substances that can become crystal nuclei when cooled) This shows that whether the final state becomes amorphous or crystal changes depending on the cooling conditions and the subsequent cooling conditions.

In addition, the cooling power level Pc is determined by the fact that if the time of irradiation with PW is short, the irradiation will be repeated with ~ and PE, and the temperature will also rise due to the conductive heat from the Pw and PE irradiation parts, even if PC = ○. Even if there is, it is possible to make the crystallization transition temperature 11 or higher.

The shape of the recording bit of the signal actually recorded on the track is not a precise oval shape, but an oval shape with a large bulge at the rear, as shown in Figure 3 (C). There is. This is because the power level drops to PC immediately after irradiation with Pw, so it is thought that sufficient rapid cooling conditions were obtained in the latter half of the part irradiated with Pw. This distortion of the recorded bits leads to distortion of the reproduced waveform, but this does not pose a problem when the recording signal modulation method is a pulse position modulation method (PPM) in which signals are recorded and reproduced depending on the positional relationship of the recorded bits.

It is clear that in the optical information recording and erasing method according to the present invention, signals previously recorded on a track are erased when a new signal is recorded. In other words, the area irradiated at the signal recording power level becomes amorphous regardless of whether the previous state was crystalline or amorphous, and the other area becomes crystalline regardless of the previous state. It is from.

Next, the reproduced waveform of the signal recorded by the optical information recording method of the present invention will be explained in comparison with that by the conventional method (FIG. 2).

The optical disc used for the comparative study was a Te5e on a PC board.
An Au-based recording thin film was formed by vapor deposition to a thickness of 1000 mm. Further, the moving speed (linear velocity) of the laser spot on the track was set to 4 m/sec.

Figure 4(a) shows the shape of the irradiated light when using the conventional method, and the recording power level "w = 6 mW (
on the surface of the optical disc), erasing power level PE-3mW
and the irradiation time is 0.5μ East in both cases. Figure 4 (b
) is the reproduced waveform when recorded under these conditions.

FIG. 5 (-) shows the shape of the irradiated light when using the method of the present invention, and the recording power level PW-6mW,
Erasing power level P E = 3 mW, cooling power level PC = 1 mW, and irradiation time was ~1 mW, respectively.
0.5 μSeC, pE: 0.4 psec, Pc:○
+1μ5. Figures 5 to 5) show reproduced waveforms when recording under these conditions.

Comparing the reproduced waveforms in FIG. 4(g)) and FIG. 5(b), it can be seen that when recording by the method according to the present invention, the signal amplitude is large and a large output signal can be obtained. This is considered to be because when recording by the method according to the present invention, the cooling rate after floor irradiation is faster, and thus larger recording bits are formed.

Note that the reproduced waveform according to the present invention shown in FIG. 5(b) includes the following:
Although waveform distortion is observed, this is not a problem if the modulation method is PPM as described above.

Effects of the Invention Since the optical information recording method according to the present invention can be realized with a single semiconductor laser, it is possible to simultaneously erase and erase a large reproduced signal amplitude without complicating the device configuration including the optical head. It is something to do.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) are output waveform diagrams of a semiconductor laser used in the optical information recording method according to the present invention.
b) is a temperature distribution diagram of the recording thin film at that time, and the same figure (C
) is a diagram showing the bits recorded on the signal recording track,
FIG. 4(a) is a diagram showing the irradiated light power in the case of the conventional example, FIG. 5(a) is a diagram showing the irradiated light power in the case of the present invention, FIG. ]) is a signal reproduction waveform diagram. 1... Optical disk, 2... Substrate, 3.
... Recording thin film, 4 ... Semiconductor laser. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 3
figure

Claims (4)

[Claims] (1) A single laser beam spot is used to erase old signals on an optical information recording member that has a recording thin film that reversibly changes between two optically distinguishable states when irradiated with a laser beam, etc. A method of simultaneously recording a new signal, the power level of the laser beam being set between a recording power level, an erasing power level, and a power level lower than the two power levels instantaneously provided immediately after the recording power level. A method for recording optical information characterized by modulating it with. (2) The method for recording optical information according to claim 1, wherein the recording thin film contains a material that causes a reversible state change between amorphous and crystalline states. (3) The power level of the laser beam is modulated between an amorphization power level, a crystallization power level, and a power level lower than the two power levels instantaneously provided immediately after the amorphization power level. A method for recording optical information according to claim 1. (4) When recording, increase the power level of the laser beam,
2. The optical information recording method according to claim 1, wherein the power level is lowered during erasing than during recording, and the power level is instantaneously lowered than the erasing power level immediately after recording.