JPS6238768B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a writing method capable of writing digital signals and the like onto an optical recording medium with high precision.

Conventionally, optical recording media have been known to have a low melting point metal such as bismuth Bi deposited on a glass or ceramic substrate, and information is recorded by irradiating this with a laser beam whose on/off is controlled by an information signal. A fixed memory (ROM) is formed by forming a pit (hole).
used as. In this case, as shown in Fig. 1 a to c, if the signal S ₁ with different pulse widths is shown in Fig. 1 a, the shape of the corresponding pit is near the rising edge of the pulse, as shown in Fig. 1 b. As shown in Figure c, the accumulation of laser light energy is insufficient, so the pit width is narrow and in the subsequent part, a portion of the heat from the laser light irradiated earlier is transferred, resulting in a shape that gradually becomes wider. show. Furthermore, if the pulse is short, it ends while the pit width is narrow, so the pit becomes smaller. With such a pit shape, bit-by-bit accuracy cannot be obtained when reading the pit.

Conventionally, in cases such as long-period image signals or short-period video signals that do not require much precision per bit, the above-mentioned optical recording media can be used as is because the image quality is not significantly degraded. However, it is rarely a problem. but,
In the case of digital data, each bit has a meaning, and if the pit shape is as shown in FIG. 1B, the detection signal will not correspond to the pulse width and a fatal error will occur, so it cannot be used as is.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for writing on an optical recording medium that completely corresponds to the input pulse width and has improved bit-by-bit precision.

In order to achieve the above object, the present invention provides a writing method for an optical recording medium in an optical recording apparatus that writes information by irradiating a laser beam whose on/off is controlled onto an optical recording medium that performs a predetermined relative movement. It is characterized in that the irradiation intensity in a predetermined time width at the rise of the laser beam pulse during pit formation is greater than in other parts.

The present invention will be described in detail below with reference to examples.

FIGS. 2a to 2d are explanatory diagrams of the principle of the present invention. 1A shows a signal pulse _S1 having the same pulse width as that in _FIG . When signal pulse S ₁ and pulse S ₂ are combined, as shown in pulse S ₃ in Figure c, when the pulse width is wide, the amplitude at the beginning is large, and when the pulse width is narrow, the overall amplitude is large. Create a waveform that looks like this, and use this as a write pulse to be applied to the optical recording medium. As a result, a highly accurate pit corresponding to the signal pulse _S1 shown in figure a is formed, as shown in figure d. In other words, since the laser beam intensity is concentrated at the head of each pulse, the pit shape shown in Figure 1b can be corrected, and if the width of the pulse _S2 is appropriately selected, it will be uniform from the front to the rear. Since a pit can be obtained and the correspondence with the signal pulse _S1 is highly accurate, it is possible to sufficiently identify each bit, and writing and reading of digital data can be performed without error.

The ratio of the amplitudes of the signals _S1 and _S2 and the pulse width of the signal _S2 vary depending on the intensity of the laser beam, the type of optical recording medium, the film thickness, etc., but by selecting these, a sufficiently good pit shape can be obtained. .

FIGS. 3a and 3b are explanatory diagrams showing an example of the configuration of an apparatus implementing the present invention.

FIG. 2A shows a circuit for realizing the principle shown in FIGS. 2A to 2D. The signal _S1 is input to a monostable multivibrator (MM) 12, and the rising edge of the pulse is used as a trigger to generate a pulse with a predetermined pulse width τ. This pulse width τ can be changed by a capacitor C ₀ and a resistor R ₀ connected to the bias voltage Vcc of the oscillation circuit. In order to match the timing of the rise of the output pulse S ₂ of the MM 12 and the rise of the signal pulse S ₁ , the signal S ₁ is branched and passed through the delay circuit 11 to give a predetermined delay. And signal S ₁ is line driver 13
and the resistor _R1 , and the signal _S2 passes through the line driver 14 and the resistor _R2 , and the two are combined to obtain the signal _S3 . This signal S ₃ is passed through an amplifier 15 with a sufficiently high input impedance connected with a resistor R ₃ in parallel.
Output S′ ₃ . Each of the line drivers 13 and 14 has a characteristic capable of maintaining a stable output voltage independent of output current.

Now, if the voltages of signals S ₁ , S ₂ , and S ₃ are V ₁ , V ₂ , and V ₃ , then V ₃ =V ₁ Y ₁ +V ₂ Y ₂ /Y ₁ +Y ₂ +Y ₃ (1) Here, Y ₁ = 1/R ₁ , Y ₂ = 1/R ₂ , Y ₃ = 1/R ₃ .

That is, due to the rise of the output pulse S ₂ of the MM 12, the voltage V ₃ of the signal S ₃ expressed by equation (1) becomes V ₂ = 0 after a time τ, and the waveform shown by the signal S ₃ in FIG. 2c is obtained. . And this waveform has resistance R ₁ ,
It can be changed by R ₂ and R ₃ . As mentioned above, MM12
Since the pulse width τ of the signal S ₂ is changed by the capacitor C ₀ and the resistor R ₀ , the waveform of the signal S ₃ changes accordingly.

Next, as shown in FIG. 1B, the output signal S' ₃ of the amplifier 15 is applied to the optical modulator 17 via the driver 16, while the laser light from the laser light source 18 is applied to the optical modulator 17 via the mirror 19. The output signal S' ₃ drives an ultrasonic transducer, that is, modulation is performed by changing the refractive index of the transducer, and the signal S' ₃ is transmitted onto the rotating optical recording disk 20.
A pit corresponding to this is formed.

As explained above, according to the present invention, when the pulse width of the signal pulse is wide, only the voltage at the beginning of the write signal waveform applied to the optical recording medium is increased, and when the pulse width is narrow, the entire voltage is increased. By controlling the modulation of the laser beam, it is possible to obtain a pit that perfectly matches the signal pulse as described above, and writing bit by bit like digital data is performed with high precision, reducing the possibility of read errors. It is possible to realize a small amount of optical fixed memory.

It goes without saying that the present invention can also be applied to pulse width modulation of analog signals.

[Brief explanation of the drawing]

1A to 1C are explanatory diagrams of the drawbacks of the conventional example, FIGS. 2A to 2D are explanatory diagrams of the principle of the present invention, and FIGS. 3A and 3B are explanatory diagrams showing the configuration of the embodiment of the present invention, In the figure, 11 is a delay circuit, 12 is a monostable multivibrator, 13 and 14 are line drivers, and 15
is an amplifier, 16 is a driver, 17 is an optical modulator, 1
8 is a laser light source, 19 is a mirror, and 20 is an optical recording disk.

Claims (1)

[Claims] 1. In an optical recording device that writes information by irradiating a laser beam whose on/off is controlled onto an optical recording medium that performs a predetermined relative movement, the laser beam is irradiated for a predetermined time width at the rising edge of the laser light pulse when forming each pit. A writing method for an optical recording medium, characterized in that the intensity is greater than that of other parts.