JPS58212628A - Disc recording device - Google Patents

Abstract

PURPOSE:To make it possible to form also small bits without a shear between objective and reproducing signals by detecting the pulse width of a pulse signal, changing the output power of a laser beam in accordance with the detected pulse width and reducing the pulse width of the pulse signal. CONSTITUTION:A disc 3 obtained by adhering a transparent acryl base plate 4 to a recording layer 2 is rotated at a constant line velocity, 1.4m/sec e.g., by a spindle motor 5. A laser beam from a laser generator 6 which consists of semiconductor laser is converted into parallel light through a colimeter 7, the parallel light is made incident to a mirror 9 through a beam splitter 8, converted at its optical path by the mirror 9 and focused by an objective lens 10 and then the focused light is irradiated to the recording layer 2. Since the laser beam is moved in the diametral direction of the disc 3, a vortical signal track is formed on the disc 3.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a disk recording device that records pulse signals on a disk using a laser beam.

When a pulse signal is recorded by forming bits in a recording layer made of a thin metal film using the heat generated by laser beam irradiation, as the wavelength of the recording pulse signal becomes shorter, the recorded pulse becomes shorter. First, there is a discrepancy between the reproduced signal and the recording pulse signal during reproduction, making it particularly difficult to record pulse signals with short pulse widths.

By driving a laser light source with the recording signal shown in FIG. 1A, when the laser beam spot moves on the recording layer of the disk as shown in FIG. 1B, pits as shown in FIG. is formed. In other words, small bits that are close to the wavelength of the laser beam are not formed, and the bits are small at the beginning of the laser signal, gradually becoming larger, and then reaching a certain size. However, it is difficult to form small pits unless the power (meaning light intensity) is increased.On the other hand, if the power is sufficient to form small bits, in the case of large pits, there will be holes larger than the input signal. It turns out.

As a method to solve such deterioration in the fidelity of the reproduced signal and the decrease in the recording density, the recording signal shown in Figure 1A is converted into the one shown in Figure 1B, and this waveform is used to control the laser beam power. A control method has been proposed. In the recording area of the recording signal, the power of the laser beam is increased in the section where the pulse inversion interval is short, and in the non-recording area, the power is decreased in the section where the inversion interval is short. It is.

However, in this method, when the small pits are near the wavelength of the laser, the pits formed on the recording layer become too large, making it impossible to obtain a reproduced signal faithful to the recorded signal.

This point will be explained with reference to FIG. When the laser beam 1 is irradiated onto the recording layer 2 of the disk as shown in FIG. Recording layer 2
A hole appears when the energy exceeds the recording threshold. As shown in FIG. 3B, the pulse widths are different: a low level pulse signal S□ with a wide pulse width, and a high level Nohalus signal S with a narrow pulse width. Comparing the case where the laser beam is driven by -, as shown in FIG. 3C, the diameter φ of the beam spot becomes equal between the two. However, since the laser beam generated by the pulse signal s2 has a larger power P, a hole is formed with the same energy in the shape of a diagonal line in FIG. 3 011C. In this case, as shown in the third diagram, the pulse signal S2 has a high power P but a narrow pulse width (short irradiation time), so that the heat diffusion distance in the recording layer is short. In the case of pulse signal days, the trend is opposite to this.

Generally, when a laser beam is focused using a convex lens, the spot diameter φ of the laser beam becomes λ (φ=1r). Here, NA is the numerical aperture of the convex lens, λ is the wavelength of the laser, and K is a constant whose value is 00g2 when the power of the Gaussian distributed laser beam becomes - (e: the base of the natural logarithm). It is. - For example, with a (λ-g30nm) semiconductor laser,
When a convex lens of NA-0, 4t7 is used, a beam spot as shown in Figure B is generated from the power distribution of the laser beam shown in Figure A, and the spot diameter φ is θg2×g3θnm φ−-/, + 5 Pm θhiro7. Therefore, /μ close to the wavelength of the laser beam
It is not possible to form pits of about m size.

If an argon laser is used instead of a semiconductor laser, the wavelength can be shortened and the beam spot diameter can be made small, but in the case of a gas laser, the problem arises that the equipment becomes large-scale. Also, the spot diameter of the laser beam can be reduced by using a convex lens with a large NA value;
Focusing and tracking during recording and playback become difficult, making it impossible to reduce the NA value.

The NA value and the value of λ are the same as above, and 7.4 m/se
The measurement results when pits are formed on a disk rotating at a constant linear velocity of a will be explained with reference to FIG. The recording layer of the disc is a selenium layer with a thickness of 4'50A and a thickness of 1aOA and 21.5A. A laminated structure sandwiched between OA tellurium is used.

First, as shown in Figure S, the pulse width is 490noθ
According to a recording pulse signal with a pulse width of C, 2.2 mW (means the value measured on the recording layer, and the same applies below).
Generates a laser beam of power. This pulse width Bs (/,'l m/ee-a x 4 de On s
The irradiation distance is ea = 0.97/''').However, in this case, the pits formed are too large, and the pulse width of the reproduced pulse signal is as shown in Figure SB. It became 900 naθC.

In addition, as shown in Figure S, when the pulse width is reduced to 'I A On sea' and a laser beam with a large power (2, g m w ) is used as the recording signal, this pulse width and the corresponding irradiation distance is o, b
1Iμm, and the size of the pit formed is 0.
97μ electric current, 1-90 n as shown in diagram S
A pulse signal with a pulse width of sea was regenerated. Furthermore, the pulse width of the recording pulse signal shown in FIG.
If you leave ea as the same value and lower the power, the pits formed will become smaller, but the pits will approach the recording threshold of the recording layer and become susceptible to extremely small dust and scratches on the disc. , a hole was made as a pit,
A phenomenon occurs where it does not warm up.

The present invention is based on the above-mentioned experimental results and studies, and aims to realize a disk recording device that is capable of forming even small pits without any deviation between recorded and reproduced signals.

An embodiment of the present invention will be described below with reference to the drawings. The line in FIG. 6 shows the configuration of the optical system of one embodiment of the present invention.

In FIG. 6, a disk holder indicated by 3 has a transparent acrylic substrate 4 adhered to a recording layer 2, and is rotated by a spindle motor 5 at a constant linear velocity of 1W/8ea. The recording layer 2 is made of selenium with tellurium adhered to both sides as described above, and the thickness of the 1-cryl substrate 4 is /, 2 .

Further, a laser beam from a laser generator 6 consisting of a semiconductor laser is converted into a parallel beam by a collimator lens 7, is incident on a mirror 9 via a beam splitter 8, is converted into an optical path by the mirror 9, and is further , an objective lens (convex lens) 10) and is focused onto the recording layer 2.

The laser beam is moved in the radial direction of the disk 3, and a spiral signal track is formed on the disk 3.

Further, the signal track of the disc 3 is irradiated with a laser beam, and the disc 3 is reproduced. Light for reading signal tracks on the disk 3 is supplied via an objective lens 10, a mirror 9, a beam splitter 8, and a lens 11 to a detector 12 consisting of a photodiode. A reproduced signal is obtained from this detector 12, and error signals for focus servo and tracking servo are formed by processing the output signal of detector i2.

Further, an embodiment of the present invention will be described with reference to FIGS. 7 and 3. FIG. 7B shows an example of a recording pulse signal. In this example, the audio POM signal is converted to predetermined recording data,
Furthermore, the data is EFM modulated and recorded on the disc. KPM
The modulation converts g bits into a preferred pattern of /dabits, as shown in FIG.

In Figure 7B, J T t 'I T *! ;Tt
A recording pulse signal with an inversion interval of 3T is shown. As a clock, for example, '1.32/, g
A frequency of MH2 (approximately a period of l 3 Q n sea) is used.

In FIG. 3, the above-mentioned recording pulse signal is supplied to an input terminal indicated by 13, and is supplied to a pulse width detection circuit 14. At each of the output terminals t1 to tll of this pulse width detection circuit 14, a recording pulse signal having a pulse width of 3T to //T appears. Monostable multivibrators M1 to M are connected to the output terminals tlxt, respectively.

is connected, and the pulse width is reduced. The outputs of the monostable multivibrators M1 to Mg are converted into drive signals at predetermined levels by the level adjusters VR1 to VR and supplied to the laser generator 6.

An example of the reduction and laser beam power for each of the pulse widths of the original recording pulse signal is shown below.

Recording pulse signal after reduction power 3T
l! ;T 3mw+T
2. gT 2. ffmW recording pulse signal
Power after reduction! ;T,? , !
; T2. A m wAT
IIT 2.3mW7T jT
2.5mwgT ATQ
3mWqT 7T:L, 3WL
VI/θT, gT 2. ! ;
mVI//T qT! 3mW Therefore, the recording pulse signal shown in FIG.
3, it is converted into a pulse signal as shown in FIG. 7C and is supplied to the laser generator 6. 0.3 m during the low level period of the recording pulse signal
A collision with the W laser occurs, but this does not cause holes to be made in the recording layer 2.

In this way, the narrower the pulse width of the recording pulse signal, the smaller the pulse width, and when the pulse width is narrower, by increasing the power of the laser beam, it is possible to accurately form the smallest bit. I can do it.

FIG. 9 shows the configuration of another embodiment of the present invention, in which 18 is an input terminal to which the clock (FIG. 7A) is supplied. The recording pulse signal from the input terminal 13 is
A monostable multivibrator M, which is supplied to the level regulator VR1°. supplied to

This monostable i-multivibrator M1° reduces the pulse width of the recording pulse signal by /T from the rising edge. The output of this monostable multivibrator ht1o is supplied to the 7-lip 70-tube 15. This flip 7 fours 15
Solid flops 16 and 17 are connected in cascade to
The recording pulse signal is delayed and inverted by the same amount.

Recording pulse signal and delay from monostable multivibrator M1°.

The inverted recording pulse signal is supplied to the AND gate 19, and the output of this AND gate 19 is supplied to the level adjustment 1□ adjustment amount VR1凰.

One level adjuster VR□. For example, 4.2 m from
A drive signal that generates a laser beam with a power of W appears, and the other level adjuster VR11 outputs, for example, 0.
．． A drive signal appears that generates a laser beam with the power of OtsuIILW. Since the AND gate 19 generates a pulse signal that remains at a high level for a period of 3T from the rising edge of the recording pulse signal, a pulse signal as shown in Figure 7 is generated at the output of the adder circuit 20. The laser generator 6 is driven accordingly. As is clear from the seventh diagram, when the rising edge of the recording pulse signal is reduced by /T, in the first 3T period, 2. A laser beam with a power of grlW is generated. After that, a laser beam with a power of J, 2 mW is generated in a high level period, and a laser beam with a power of (7,5 mW) is generated in a low level period of the recording pulse signal. do.

As can be understood from the description of the embodiments described above, according to the present invention, by reducing the pulse width of the recording pulse signal and increasing the power of the laser beam, a reproduced signal that does not deviate from the recorded signal can be produced. It is possible to form pits on the disk such that □ is obtained. Further, according to the present invention, it is possible to accurately form extremely small pits that are close to the wavelength of a laser beam, and the recording density of the disk can be increased.

Note that, unlike forming pits by heating the recording layer with a laser beam, the refractive index or reflectance may be changed by this heating.

Furthermore, Jin's invention can be applied to the case where a disk is rotated at a constant angular velocity, and also to the case where a gas laser is used as a laser generator.

[Brief explanation of the drawing]

Figure 1 is a route map used to explain recording using a laser.
Figure 2 is a waveform diagram used to explain the previously proposed disk recording device; Figures 3, 3 and S are route maps used to explain problems when recording using a laser; FIG. 6 is a block diagram showing the configuration of an optical system according to an embodiment of this invention, FIG. 7 is a waveform diagram used to explain one embodiment and other embodiments of this invention, and FIG. 3 is a diagram showing one embodiment of this invention. FIG. 9 is a block diagram showing the configuration of an example, and a block diagram showing the configuration of another embodiment of the invention on the line of FIG. 2・・・・・・・・・Recording layer, 3・・・・・・・・・
・・・・・・Disk, 6・・・・・・・・・Laser generator, 10・・・・・・・・・Objective lens, 13・・・・・・・・・...Recording pulse signal input terminal, 14...) (Russ width detection circuit. Representative: Tomo Sugiura, Figure 1, Figure 2, Station 1, Figure 4) Figure 5

Claims (1)

[Claims] In a disk recording device that records pulse signals on a rotating disk using heat generated by laser beam irradiation, the pulse width of the pulse signal is detected, and the output power of the laser beam is changed according to this pulse width. In addition, a disc recording device characterized in that the pulse width of the pulse signal is reduced.