JPS6025032A - Optical information recording device - Google Patents

Abstract

PURPOSE:To form such pits that an excellent reproduction output is obtained, and eliminate the risk of destruction of record due to an irradiating readout light beam by irradiating a recording medium which has high heat conductivity with proper light pulses. CONSTITUTION:The optical recording medium in use has heat diffusivity of >=5mum<2>/mus in the medium surface and recording is carried out while the light intensity of laser light pulses is made larger at the leading edge part than at the trailing edge part. A differential amplifier 20 in a laser driving circuit supplies differential signals to TRs 21 and 22 according to an input signal. A capacitor 38 applies only the variation component of voltage pulses of a variable resistor 26 to a TR23. Then when the signal applied to the TR22 rises and falls, a positive and a negative edge pulse are applied to the base of the TR23 and a laser 3 emits light with large power at the leading edge part of a pulse supplied to the laser 3. When the pulse to the TR22 rises, on the other hand, there is no influence upon the current supplied to the laser 3, so the light power becomes larger at the leading edge of the laser light pulse than at the trailing edge part.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention records information by irradiating a moving recording medium with focused laser light. The present invention relates to optical information recording devices such as optical disk file devices.

An optical information recording device such as a source disk device that records information by irradiating a photosensitive recording medium with a focused laser beam into a minute spot and altering the quality of the original irradiated area of the medium due to a rise in the temperature of the medium. In this case, it is preferable that the laser light source for recording is a shed, and the optical power required for recording is required to be small. In particular, when a compact semiconductor laser that can be directly modulated is used as a light source, there is a limit to the source power that can be generated, so a highly sensitive optical recording medium is desirable. However, highly sensitive recording media are susceptible to deterioration even by weak light; for example, even when irradiated with a laser beam of low power to read out recorded information, the recording of omitted information or There is a high risk of destruction. This tendency is particularly strong when a material with low thermal conductivity is used as a medium in an attempt to improve the recording sensitivity of the medium.

In other words, if heat accumulates in a medium with low thermal conductivity,
When irradiated with light of low power for a long period of time, the temperature of the medium can easily rise to a level where deterioration occurs. In order to avoid such a situation, many optical information recording and reproducing apparatuses employ a method of irradiating the medium with a moving state, even with a weak original beam for reading information.

However, even if such a method is adopted, there is no risk that the light beam will be irradiated with the medium in a stopped state; Restoration is not possible. Also, from the viewpoint of operation when starting and stopping the apparatus, it is desirable to be able to irradiate the readout light beam in order to obtain the focus error signal and the off-track signal while the medium is stopped.

On the other hand, if a material with high thermal conductivity is used as the recording medium, the thermal energy from the irradiated original beam will be diffused quickly, making it difficult for heat to accumulate, so there is a risk of deterioration of the medium due to the original irradiation with a small power. becomes smaller, it becomes possible to irradiate light even in a stopped state, and information storage and security are improved. However, in a medium with high thermal conductivity, thermal energy particles due to the irradiated light ζ are quickly diffused, so that the temperature rise of the medium in response to the irradiated light energy is relatively small, and the apparent recording sensitivity decreases. This trend is
The tip of the pulse (corresponding to the tip of the bit) when irradiating light in a pulsed manner to continuously form an altered information recording area of minute length (hereinafter referred to as a bit) It appears prominently in

This is because when a light pulse is irradiated while the medium is moving, the thermal energy irradiated to the medium at the tip quickly diffuses, and because the medium is moving, the original beam irradiated afterwards This is because the rear part of the medium is irradiated with respect to the moving direction of the medium, and the light energy does not contribute to the temperature rise at the tip of the bit. - At the back of the bit, in addition to the energy from the light irradiated at that point, a part of the thermal energy diffused by the tip of the bit is transmitted6, so the original energy irradiated is reduced. A relatively high temperature rise occurs. Although the original irradiation is applied almost uniformly and continuously to each point within the bit, the amount of thermal energy transmitted by diffusion increases toward the rear of the bit, resulting in higher temperatures than at the tip. You will get an increase. For this reason, the degree of deterioration of the recorded bits is small at the tip and becomes more significant toward the rear.When reading such bits, the level is low at the hanging and tip portions, and the level increases toward the rear. It becomes a waveform. This kind of bit recording state or reproduction waveform is unfavorable for high-density, surface-accuracy recording and reproduction, but this tendency appears more strongly as the thermal conductivity of the recording medium increases, and materials with high thermal conductivity are not suitable for optical recording. This is a major difficulty when using it as a medium.

An object of the present invention is to eliminate the drawbacks of such conventional optical information recording devices and form bits that can provide good reproduction output by irradiating a recording medium with high thermal conductivity with an appropriate light pulse. Another object of the present invention is to provide an optical information recording device that is free from the risk of recording destruction due to irradiation with a reading moonlight beam or the like.

The present invention will be explained in detail below with reference to the drawings.

FIG. 1 is a schematic diagram showing an embodiment of the optical information recording device of the present invention. A signal source 1 supplies a signal corresponding to information to be recorded to a laser drive circuit 2 via a signal line 12. The laser drive circuit 2 supplies a pulsed current to the semiconductor laser 3 via the signal line '13 in response to a signal input from the signal line 12. The semiconductor laser 3 emits light in a pulsed manner from the current ζ supplied from the signal line 13 with an intensity corresponding to the current value. Divergent laser light emitted from the semiconductor laser 3 is converted into a parallel laser beam by a collimating lens 4. The focusing lens 5 focuses the parallel laser beam to form a minute spot of light on the surface of the medium 11 on the record carrier 6. The record carrier 6 has a disk shape and is rotated by a spindle motor 7, so that the medium 11
The information recording tracks formed on the surface are generally concentric circles. The position of the focusing lens 5 is controlled so that a minute light spot is focused and hits a predetermined position on the surface of the medium 11, but this is not directly related to the gist of the present invention, so a description thereof will be omitted.

The temperature of a certain point on the surface of the medium 11 that is irradiated with a minute light spot increases due to the thermal energy of the light, and when the temperature exceeds a threshold value for medium deterioration, recording is performed. In this case, the temperature rise at the target point of the medium 11 is not simply proportional to the amount of original energy irradiated, but because the thermal energy is diffused in all directions by heat conduction of the medium 11,
Above a temperature of 1, the energy of the irradiated light is small compared to l. In particular, in a medium with high thermal conductivity, the diffusion of thermal energy is large, and the temperature of the medium I! The proportion of energy that contributes upward and outward tends to be very small.

The speed of diffusion of this thermal energy can be expressed by the thermal diffusivity T of the medium 11. Thermal diffusion 4 is given by the ratio of the thermal conductivity of the medium 11 to the heat capacity per volume, and is a value indicating how much surface heat spreads per unit time. Example & example tellurium (
Te), the thermal conductivity is OΩ15J4[・”(leg), and the heat capacity is 125J/degcrd, so
The thermal diffusivity is approximately 1.2 μg/μs. Also, iron (Fe
) has a thermal conductivity of Q, 5 J /Cf1bec d6g
And since Atsutani Firefly is 3.6J/degffl,
The thermal diffusivity is approximately 14 μd/μs. Even if the original spot is irradiated for a long time on a medium with a high thermal diffusivity, most of the thermal energy will be diffused and will not contribute to the temperature rise that changes the quality of the medium. It is effective to irradiate light with high power.

Furthermore, even if the moving speed of the medium 11 is increased, the
For each point, it is the same as shortening the time that light is irradiated, and it is possible to achieve the same effect as short-time irradiation. On the other hand, if the original power is small, the temperature rise will be extremely small even if the medium 11 is irradiated with open light for a long time in the figure 11 with a large thermal diffusivity, and even if the medium 11 is stopped, recording will occur, or even if the medium 11 has already been recorded. There is almost no risk of the information being destroyed. In the apparatus of the present invention, by making the medium 11 have a thermal diffusivity of 5 μg/μs or more, deterioration etc. will not occur even when irradiated with the readout source beam for a long time, and the information can be preserved easily. It is said that

Materials for such a medium 11 include Bi, C+Fe.
Although many metals or metalloids such as Or, etc. can be used, Te, which has a thermal diffusivity of 1.2 μm'/μs as described above, is not suitable. Medium 1 with high thermal diffusivity as above
1 has low apparent recording sensitivity when exposed to long-term irradiation with weak light, and therefore there is little risk of deterioration due to readout beams, etc.; For recording when the medium 11 is moved at a crystal velocity, the thermal diffusivity is 1 degree lower (it can exhibit recording sensitivity equivalent to that of the optical material).

When the medium 11 having such a high thermal diffusivity is moved and the original spot is irradiated, the temperature rise at the point on the medium 11 where the irradiation is started becomes relatively small due to the diffusion of thermal energy. - At a point behind the irradiation start point, in addition to the original energy irradiated to that point, thermal energy due to diffusion is transmitted from a point in front, so the temperature rise is relatively high depending on the original energy irradiated. happens.

This phenomenon does not appear clearly when the moving speed of the medium 11 is large compared to the thermal diffusivity of the medium 11 (i.e., the speed of heat conduction), or when the thermal diffusivity of the medium 11 is very small. However, it becomes noticeable when the moving speed of the medium 11 is about the same as or slightly smaller than the thermal diffusivity. For this reason, a bit that is formed long and thin along the moving direction of the medium 11 has a small degree of deterioration at the tip, and the deterioration becomes greater toward the rear, resulting in, for example, a tapered bit. When such bits are read out, a reproduced waveform is obtained in which the level is low at the leading end and the level increases as it approaches the rear. This type of billet recording condition is not favorable for high-precision, high-density recording and reproduction, but such bits are formed when light or light of uniform power is irradiated from the leading edge to the trailing edge of the bit forming area. In this case, the bit forming section (information recording section)
If the tip of the bit is irradiated with a light having a higher power than the back of the bit, a sufficient fAIEl condition can be obtained even at the tip, and almost uniform deterioration occurs from the tip to the rear end of the bit. In the optical coasting information recording system of the present invention, the signal is supplied to the semiconductor laser 3 via the signal line 13. ″
! The light intensity (power) at the tip of the laser light pulse from the semiconductor laser 3 that is irradiated onto the medium can be increased by making the current value at the tip of the lulus current larger than the value at the rear.
The strength of the bit is made stronger than that of the rear part, so that deterioration occurs almost uniformly over the entire bit area. This results in
The waveform of the readout output is at a nearly constant level from the tip to the rear end, and has a high Mll! -1 High-density recording and reproduction is performed.

FIG. 2 is a diagram showing the relationship between the light irradiation time when the medium is stopped and the thermal energy accumulated at the irradiation point of the medium. This figure was created using a computer called Luminion, and the vertical axis of the graph shows the energy per unit surface area (nJ/μ-) of the center area hit by the light spot, which is divided by the heat capacity per unit surface area. , the temperature rise in that area can be obtained.

Curve a shows the properties of a material with a thermal diffusivity of 0.2 μlTl1/μs. If the thermal diffusivity is small, the thermal energy (temperature) increases significantly with the light irradiation time. The curves show the characteristics of a material with a thermal diffusivity of 1.0μ-/μs, the curve C shows the characteristics of a material with a thermal diffusivity of 5μ♂/μS, and the curve d shows the characteristics of a material with a thermal diffusivity of 1.
The characteristics of the material at 0μt111/μS are shown respectively. From this figure, it can be seen that as the thermal diffusivity increases, the slope of temperature rise over time becomes gentler. Immediately, the thermal diffusivity is 1
．． With a medium of 0μd/μs or less, even if the optical power is 4 when recording by irradiating the source with a pulse width of 100ns, recording will be performed if the source is irradiated for 1μs, but if the thermal diffusivity is 5μ
For a medium of ♂/μs or more, if the optical power is 173 or less when recording with a pulse width of 100 ns, there is almost no possibility of recording. Therefore, the thermal diffusivity is 5μrr
? /ltS or more, it is considered that the risk of medium deterioration due to reading moonlight beam irradiation can be eliminated with a sufficient margin.

FIG. 3 is a diagram showing an example of the configuration of the laser drive circuit 2 used in the apparatus shown in FIG. 1. The differential amplifier 20 is connected to the signal line 12
Differential signals having mutually different polarities are supplied to transistors 21 and 22 constituting a differential output device via signal lines 31 and 32, respectively, in accordance with signals inputted through the differential output terminal. Resistors 33 and 34 are for eliminating waveform distortion by impedance matching. The collector of the transistor 22 is connected to the signal line 13 and supplies a current to the semiconductor laser 3 for generation. Transistor 23 and resistor 3
5 constitutes a current control circuit, which controls transistors 21 and 22 according to the voltage applied to the base of transistor 23.
& controls the output current of the differential output device. A constant voltage circuit consisting of a resistor 36 and a constant voltage diode 25ζ generates a constant reference voltage, which is connected to the transistor 2 via a resistor 37.
Apply that reference voltage to the base of 3. As a result, if there is no signal applied to the base of the transistor 23 through the capacitor 38, the transistor 23 will cause the differential output device formed by the transistors 21 and 22 to output a current pulse at a constant level corresponding to the reference voltage. Keep its collector current constant. Transistor 24 is connected to signal line 3
It functions as a voltage buffer that receives the signal supplied to the transistor 22 through the transistor 2 and outputs a pulse of the same polarity. The variable resistor 26 reduces the voltage pulse output from the emitter of the transistor 24 to an appropriate level and connects the capacitor 3.
Add to one end of 8. The capacitor 38 cuts the DC component of the output of the variable resistor 26, and transfers only the voltage pulse change (rising and falling edge portions) to the transistor.
Add to the base. The DC power of this capacitor 38,
The time constant of the differential operation is given by the product of the capacitance value of the capacitor 38 and the value of the resistor 37. Due to the function of the transistor 24 and the capacitor 38, when the signal supplied to the transistor 22 rises and falls,
A positive edge pulse (differential pulse) and a negative edge pulse, respectively, are applied to the base of transistor 23 to change the collector current of transistor 23. Due to the stiffness, a positive pulse is supplied to the transistor 22 and the transistor 22 is turned on to supply a pulse current to the semiconductor laser 3. At the tip of the pulse, a current with a level as large as the positive edge pulse is generated. Semiconductor laser 3
is supplied, and the semiconductor laser 3 emits light with a correspondingly large power. On the other hand, when the pulse supplied to transistor 224 rises, a negative edge pulse is applied to the base of transistor 23 and the collector current of transistor % decreases, but at this time transistor 21 is turned on and transistor 22 is turned off. Because
This decrease in current does not affect the current supplied to the semiconductor laser 3. As a result of such a laser drive circuit 2I, the optical power at the leading end of the laser light pulse irradiated onto the medium 11 is greater than that at the rear end, resulting in uniform deterioration of the medium 11 with a large thermal diffusivity. This makes it possible to form bits in which this occurs. As can be easily seen, the transistor 24 and the capacitor 38 can be omitted or the variable resistor 26 can be changed so that the level of the pulse applied to one end of the capacitor 38 is almost 0, which is supplied to the semiconductor laser 3. The level of the pulse current becomes uniform, and the level of the laser light pulse also becomes uniform.

FIG. 4 (4) is a diagram schematically showing the relationship between the intensity waveform of the laser light pulse and the temperature rise of the light irradiation part on the medium 11 in the apparatus shown in FIG. FIG. 4(2) shows a case where a light pulse of a uniform level is irradiated. Light pulse intensity 1
03 When a changes T in the shape of a rectangular wave as shown in the figure, the temperature of the medium 11 does not rise much at its tip due to thermal diffusion,
The tip of ζ shown in the temperature rise waveform 104a is in a lowered state. When the medium 11 moves and the position of the irradiation light spot advances backward, the temperature of the medium increases at the tip due to the addition of the thermal energy diffused and transmitted from the front of the medium and the energy of the irradiation light. The temperature will rise even more. This tendency becomes stronger as the light spot moves backward, so the temperature rise waveform 104a rises as shown in the figure.
When the 11 bits recorded in this case are read out, this temperature waveform 104. This means that a readout waveform with a rising edge similar to a is output.

FIG. 40 shows the case where the original power of the tip of the laser light pulse is increased and irradiated. If the laser beam is irradiated so that the optical pulse intensity If 103b becomes larger at the tip as shown in the figure, the optical power is greater at the tip where the temperature of the medium 11 is difficult to rise due to thermal diffusion, and the medium 11 is heated. Even at the tip where the bit is formed, the temperature rises rapidly as shown in the temperature rise/external waveform 104b, and there is no longer a state where the temperature of the tip becomes low. Heat diffusion also occurs in this case, and some of the thermal energy in the front of the bit is transmitted to the rear, but the optical power irradiating the back of the bit is smaller than that at the tip, and the temperature rise at the rear of the bit is less than the temperature at the tip. As shown in the figure, the temperature rise in the bit area is approximately equal to the temperature rise in the bit area, and the temperature rise waveform 104b has a rectangular wave (or trapezoidal) shape with an approximately uniform level over the entire bit area, as shown in the figure.

When the bits recorded in this manner are read out, a readout waveform similar to a rectangular wave similar to this temperature rise waveform 104b is output, making it possible to record and reproduce optical information with high density and high precision.

As described above, according to the present invention, there is little risk of medium damage due to a readout light beam, etc., and optical information recording is possible that forms bits with a good quality shape and performs high-density and high-quality recording. A device is realized.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an embodiment of the optical information recording device of the present invention, and FIG. 2 is a diagram showing the light irradiation time when the medium is stopped and the thermal energy accumulated at the irradiation point of the medium to explain the present invention. Figure 3 is a diagram showing an example of the configuration of the laser drive circuit 2 used in the apparatus shown in Figure 1, Figure 4 shows the intensity of the laser light pulse in the apparatus shown in Figure 1 3 is a diagram schematically showing the relationship between a waveform and a temperature rise of a light irradiation part on a medium 11. FIG. In the figure, 1 is a signal source, 2 is a laser drive circuit, 3 is a semiconductor laser, 4 is a collimator lens, 5 is a focusing lens, 6 is a record carrier, 7 is a spindle motor, and 11 is an optical recording medium. [(Entered by Susumu Uchihara 1', Yuj・'' 71-1 Figure 72 Light irradiation time Figure 4 (A)' 41 yen 1 (B) +04b -- Yaichi

Claims (1)

[Claims] Focusing a laser beam and irradiating it onto the surface of the recording medium, altering the surface of the recording medium with the thermal energy of the beam,
In an optical information recording device for recording information, the recording medium has a thermal diffusivity of 5 μg/μ in the in-plane direction of the medium.
s or more, and record information by making the laser light intensity at the tip of each laser light pulse irradiated onto the recording medium for recording greater than the intensity at the rear of the pulse. An optical information recording device characterized by: