JP3381500B2 - Information recording / reproducing apparatus and optical recording medium reproducing method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information recording / reproducing apparatus for recording / reproducing information on / from an optical recording medium, and a reproducing method for reading information from the optical recording medium.

[0002]

2. Description of the Related Art Optical recording media capable of accumulating high-density data and capable of high-speed information processing are attracting attention as audio and image applications and also as computer memories. Read-only CDs are rapidly becoming popular for audio and computers. In addition, the write-once type, which allows information to be written only once, and the magneto-optical type, which allows rewriting of information, have been standardized by the ISO standard for optical discs with a diameter of 5.25 inches or 3.5 inches, and more in the future. It is expected to spread widely. In addition, a phase change type optical disc as a rewritable optical disc is beginning to appear on the market. Under such circumstances, there is an extremely high demand for storing more information in one storage medium, and for that purpose, recording / reproducing of information at a higher density, and therefore various studies have been made.

By the way, when the intensity of the reproducing light emitted from the reproducing device to the optical recording medium is increased, as shown in FIG. 3, C / of the reproducing signal is increased to some extent in response to the increase of the reproducing light amount returning to the photodetector. N (Carrier to Noise ratio) increases. However, when the reproducing light intensity is further increased, the C / N starts to decrease due to the decrease in the Kerr rotation angle due to the temperature rise of the medium. Further, increasing the reproducing light intensity destroys the recorded information. That is, there is an optimum reproducing light intensity with which the highest C / N is obtained. In order to meet the demand for recording information at a high density, it is desirable to set the reproduction light intensity to the optimum level, improve the C / N of the reproduction signal as much as possible, and maximize the capacity of the medium. .

On the other hand, a method has been attempted in which the reproduction light spot is reduced by shortening the light source wavelength of the optical head to enable reproduction of information recorded at high density. The wavelength of the semiconductor laser used is limited, and a short wavelength laser has a problem that the shape and output of laser light are insufficient. Therefore, a super-resolution reading medium has been developed which can read information recorded at high density even if the wavelength of the light source and the size of the reproduction light spot remain unchanged.

This utilizes the temperature distribution of the medium in the light spot caused by the combination of the temperature rise of the medium and the rotational movement of the medium due to the reproducing light, and reproduces a part of the signal of the medium that has entered the light spot. It is a mask so that it is not detected as a signal. As a result, the area of the effective opening from which the signal can be read becomes smaller than the light spot, and it is possible to reproduce the information with higher density. An example of such super-resolution reproduction is shown in FIG.
The t Aperture Detection) method will be briefly described. Figure 4
FIG. 4A is a plan view of an FAD type optical recording medium, and FIG.
FIG. 4 is a sectional view taken along the line AA of FIG.

The optical recording medium 31 of the FAD system is
It has three magnetic layers of a recording layer 32 made of TbFeCo, a cutting layer 33 made of TbFe, and a reproducing layer 34 made of GdFeCo, and signal reproduction is performed from the reproducing layer side. In the initial state, as shown in FIG. 4B, the magnetization direction of each layer is the recording layer 32 on which information (recording mark 38) is recorded.
Are aligned in the direction of magnetization. This is because the exchange coupling force acts on the membranes that are in contact with each other. Then, an external magnetic field Hr is applied during reproduction. When the reproducing light spot 35 moves relative to the medium 31 as shown in FIG. 4A, the front region of the medium 31 entering the light spot 35 becomes a low temperature region 36, and the rear region becomes a high temperature region 37. There is a temperature difference.

When the temperature of the high temperature region 37 reaches the temperature at which the magnetization of the cutting layer 33 disappears (Curie temperature), the magnetization of the reproducing layer 34 and the recording layer 32 via the cutting layer 33.
And the magnetization of the reproducing layer 34 is reversed in the direction of the external magnetic field Hr (in FIG. 4B, the direction of magnetization at the position B is reversed). That is, the high temperature region 37
In the above, the magnetization of the reproducing layer 34 shows a constant state regardless of the presence or absence of the recording mark 38, and becomes a mask that does not contribute to signal reproduction. On the other hand, only the low temperature area 36 which holds the recording state serves as an effective opening portion of the light spot which carries out signal detection, whereby the recording mark 38a in this area 36 is formed.
Can only read.

A medium for super-resolution reading has such an F
In addition to the AD method, a RAD (Rear Aperture Detection) method and a CAD (Center Aperture Detection) method have been invented in which only the high temperature region serves as an opening and the rest serves as a mask. The RAD type medium has a recording layer and a reproducing layer formed thereon. Then, the magnetization direction of the reproducing layer is aligned in a fixed direction by the initialization magnetic field. When a light spot is irradiated in the same manner as described above, the magnetization direction of the reproducing layer is reversed to the magnetization direction of the recording layer due to the exchange coupling force in the high temperature region within the spot, and functions as an opening. In the low temperature region, the magnetization direction of the reproducing layer remains in the initial state and functions as a mask. In this way, super-resolution reproduction can be realized.

Further, the CAD type medium comprises a recording layer and a reproducing layer formed on the recording layer, which exhibits in-plane magnetization (the direction of magnetization is horizontal) at low temperature and perpendicular magnetization at high temperature. When this medium is irradiated with a light spot, in the high temperature region near the center of the spot, the magnetization direction of the reproducing layer becomes the same as that of the recording layer, and the medium functions as an opening. In the other regions, the magnetization direction of the reproducing layer remains in-plane magnetization, and this in-plane magnetization does not give the Kerr effect to the vertically incident light, so that it functions as a mask. In this way, super-resolution reproduction can be realized. Further, the principle of mask generation has been announced, which utilizes the magnetic coupling force, the coercive force, and the change in the magnitude of magnetization as described above, and the change in the transmittance due to the phase change.

[0010]

By the way, the intensity of the reproducing light emitted from the reproducing apparatus to the optical recording medium is constant regardless of the temperature of the medium or surrounding environment. However, in the medium for super-resolution reading as described above, when the temperature of the medium itself changes, the temperature distribution of the medium in the light spot changes even if the reproducing light of the same intensity is irradiated, and the above-mentioned effective opening The shape of will change. Therefore, when the temperature of the medium itself changes, the effect of super-resolution reproduction cannot be sufficiently obtained, and there is a problem in that reading errors of information easily occur.

Further, in a normal medium which is not a super-resolution reading medium, when the temperature of the medium itself changes, the C / N of the reproduced signal changes due to the change in the temperature distribution. Therefore,
Even if the reproducing light intensity is optimally set so that the highest C / N is obtained, the C / N will be lowered when the temperature of the medium itself changes, so that the medium capacity is sufficient at a constant reproducing light intensity. There was a problem that it could not be utilized. Also,
If the temperature of the optical recording medium is always kept constant on the playback device side, the environment temperature of the playback device is limited, and measures such as heat generation inside the device are required, which makes the device large-scaled. was there. The present invention has been made to solve the above problems, and an information recording / reproducing apparatus and a reproducing method capable of always providing a temperature distribution of a medium in a reproduction light spot with a predetermined temperature distribution regardless of the temperature of the medium itself. The purpose is to provide.

[0012]

SUMMARY OF THE INVENTION An information recording / reproducing apparatus of the present invention comprises an irradiating means for irradiating an optical recording medium with a recording light for writing information or a reproducing light for reading information, and a reflected light from the medium. An appropriate light intensity of the recording light is obtained by detecting means for receiving light and converting it into an electric signal, and test writing for recording / reproducing on / from the medium by the irradiating means and the detecting means, estimating the temperature of the medium from this light intensity, and irradiating the medium. The recording / reproducing control means adjusts the light intensity of the reproduction light based on the estimated temperature of the medium so that the light intensity of the reproduction light emitted from the means to the medium becomes appropriate. In this way, the recording / reproducing control means obtains an appropriate recording light intensity from the result of the trial writing,
By estimating the temperature of the medium from this light intensity and adjusting the light intensity of the reproducing light appropriately according to the temperature of the medium, the light intensity of the reproducing light is adjusted appropriately even if the temperature of the optical recording medium changes. Therefore, the temperature distribution of the medium in the reproduction light spot can always be a predetermined temperature distribution regardless of the temperature of the medium itself.

Further, test writing is performed on the optical recording medium, an appropriate light intensity of the recording light for writing information to be irradiated onto the medium is obtained from the result of the trial writing, and the temperature of the medium is calculated from the light intensity of the recording light. Then, the light intensity of the reproduction light is adjusted based on the estimated temperature of the medium so that the light intensity of the reproduction light for irradiating the medium for reading information becomes appropriate.

[0014]

1 is a block diagram of an information recording / reproducing apparatus showing a first embodiment of the present invention. Reference numeral 1 is an optical recording medium, 2 is an optical head, 3 is a recording / reproducing controller serving as recording / reproducing control means for controlling the laser light emitted from the semiconductor laser 21 in the optical head 2 to the medium 1 and performing recording / reproducing signal processing. Is a laser drive circuit for driving the semiconductor laser 21, and 5 is a system controller for controlling the entire information recording / reproducing apparatus.

Further, 22 is a beam splitter for splitting the laser light emitted from the semiconductor laser 21, 23 is a laser beam from the beam splitter 22, and the reflected light of the laser light emitted to the optical recording medium 1 is reflected. A beam splitter to be incident on a photodetector, which will be described later, 24 is an objective lens, 25 is a front monitor for detecting the intensity of laser light with which the optical recording medium 1 is irradiated,
Reference numeral 26 is a photodetector for detecting the reflected light from the optical recording medium 1.

Next, the operation of such an information recording / reproducing apparatus will be described. In the present embodiment, the CAV (Constant A) that rotates the medium 1 at a constant rotation speed regardless of the reproduction radial position.
The case of ngular Velocity) is explained. The system controller 5 of the information recording / reproducing apparatus is the optical recording medium 1
When is inserted, the medium 1 is rotated at a predetermined rotation speed by a spindle motor (not shown).

The recording / reproducing controller 3 controls the laser drive circuit 4 to turn on the semiconductor laser 21. A part of the laser beam emitted from the semiconductor laser 21 is separated by the beam splitter 22 and enters the front monitor 25. Thereby, the light intensity is detected. Based on the detected light intensity, the controller 3 controls the semiconductor laser 21 via the laser drive circuit 4 so that the reproduction light intensity (the power of the laser light irradiated on the medium 1 during reproduction) becomes a predetermined value. Adjust the drive current of.

The reproducing light intensity here is set to such a value that the data recorded at a low density can be reproduced at any temperature as long as the temperature of the medium 1 is within the specifications.
For example, when the medium 1 is the above-described FAD system super-resolution reading medium, it is set to a small value such that a mask hardly occurs in the reproduction light spot, and in the case of the RAD or CAD system, it is sufficiently large in the light spot. Set it to a value large enough to obtain an opening.

Next, the system controller 5 causes the optical head 2 to pass through a focus actuator (not shown).
The objective lens 24 is moved to pull in the focus, and the focus control for adjusting the focus is performed. Further, in order to know where the laser beam is radiated on the medium 1, a tracking actuator (not shown) is controlled to perform a beam track pull-in operation, and tracking control for causing the laser beam to follow the track of the medium 1 is performed. .

Laser light emitted from the semiconductor laser 21 passes through the beam splitters 22 and 23 and the objective lens 24 and enters the medium 1. The reflected light from the medium 1 due to the irradiation of the reproduction light is reflected by the beam splitter 23 and enters the photodetector 26. Then, by demodulating the signal obtained by the photodetector 26, the recording / reproducing controller 3 obtains the address information from the optical recording medium 1.

The system controller 5 seeks to move the optical head 2 to move the laser beam by the difference between the current address obtained by the controller 3 and the address of the control information area which is the first target position. I do. At the location reached by the seek operation, the tracking control is performed again to read the address information and determine whether the laser beam has reached the target address. Then, if there is a deviation between the read address and the target address, the step jump operation of moving the laser beam is repeated.

Thus, by demodulating the signal of the photodetector 26 when it reaches the control information area on the medium 1,
The controller 3 reads the information recorded in the control information area in advance at a low density when the medium is manufactured. As this information, the optimum recording light intensity (power of the laser beam irradiated on the medium 1 at the time of recording) PWref when the temperature of the medium 1 is the reference temperature Tref, the rate of change R of this recording light intensity with respect to temperature, and the medium There is an optimum reproduction light intensity PRref when the temperature of 1 is the reference temperature Tref and the predetermined linear velocity (for example, the linear velocity at the innermost circumference) V0.

After reading the information from the control information area,
The system controller 5 moves the laser beam to the trial writing area of the medium 1 by the seek or step jump operation similar to the above. Next, the recording / reproduction controller 3 performs recording / reproduction in the trial writing area,
The current temperature of the optical recording medium 1 is estimated as follows.

First, the controller 3 gives a recording signal having a frequency f0 and a duty ratio of 50% as shown in FIG. 2 (a) to the laser drive circuit 4, and based on the light intensity detected by the front monitor 25, The laser drive circuit 4 is controlled so that the intensity of the recording light with which the medium 1 is irradiated becomes the optimum recording light intensity PWref. At this time, the frequency f0 is set so that the mark recorded on the medium 1 is sufficiently longer than the laser beam diameter.

Then, the laser drive circuit 4 generates a laser drive signal according to the recording signal to generate a semiconductor laser 2
Give to one. As a result, the recording mark as shown in FIG. 2B is written in the trial writing area of the optical recording medium 1. When the test writing area recorded in this way is irradiated with reproduction light,
The signal as shown in FIG. 2C is detected by the photodetector 26, and the reproduced signal as shown in FIG. 2D is obtained by binarizing this signal.

The recording / reproducing controller 3 is shown in FIG.
When the duty ratio of the reproduction signal is larger than 50% (that is, t1> t2), the intensity of the recording light is reduced and the trial writing is performed again. On the contrary, when the duty ratio is smaller than 50% (t1 <t2) as shown in FIG. 2F, the intensity of the recording light is increased and the trial writing is performed again. Such test writing is performed while changing the recording light intensity to obtain the recording light intensity such that the duty ratio of the reproduction signal becomes approximately 50% (t1 = t2) as shown in FIG. The intensity thus obtained is the optimum recording light intensity PW.

Subsequently, the recording / reproducing controller 3 calculates the temperature T of the medium 1 from the optimum recording light intensity PWref read from the control information area and the rate of change R with respect to the temperature, and the optimum recording light intensity PW obtained by the trial writing. Estimate as. T = {(PWref-PW) / R} + Tref (1)

For example, the reference temperature Tref is 25 ° C., and the optimum recording light intensity PWref at the reference temperature 25 ° C. is 5.
25 mW, the rate of change R of the recording light intensity with respect to temperature is 0.03 mW / ° C., and the optimum recording light intensity PW obtained by trial writing is 4.95 mW, the temperature T of the medium 1 is 35 ° C. from the formula (1). It is estimated to be. That is, the formula (1) is
The present medium temperature T is estimated from the optimum recording light intensity PWref at the current optimum recording light intensity PW and the reference temperature Tref.

Next, the recording / reproducing controller 3 determines the optimum reproducing light intensity PR1 at the current medium temperature T based on the temperature T of the optical recording medium 1 thus obtained and the optimum reproducing light intensity PRref read from the control information area. It is calculated by the following formula. PR1 = {(Tr-T) / (Tr-Tref)} × PRref (2)

When the medium 1 is a medium for super-resolution reading, T
r is an optimum temperature at which the effect of super-resolution reproduction is sufficiently obtained, and in the case of the FAD method described above, the temperature at which the mask is formed in the reproduction light spot, that is, the magnetization of the cutting layer 33 disappears and the reproduction layer The magnetization direction of 34 is set to a temperature at which the direction of the external magnetic field Hr is reversed. In the case of the RAD method, the temperature at which an opening is formed in the light spot, that is, the temperature at which the magnetization direction of the reproducing layer is inverted to the magnetization direction of the recording layer, is set,
In the case of the CAD method, similarly, the temperature at which the opening is formed, that is, the temperature of the reproduction layer facing in the in-plane direction is set to the temperature at which the magnetization is perpendicular.

Further, when the medium 1 is a normal medium such as a magneto-optical disk which is not for super-resolution reading, it is the optimum temperature at which the C / N of the reproduced signal becomes the highest, and, for example, the Kerr rotation angle is significantly reduced. It is set using the starting temperature as a guide.

Subsequently, the system controller 5 calculates the address of the target position where the information to be reproduced is recorded by a command from a host computer (not shown), and the recording / reproducing controller 3 uses the address to read the medium 1 at the target position. The linear velocity V is calculated, and the reproducing light intensity PR1 calculated by the equation (2) is corrected by the following equation. PR2 = (V / V0) ^1/2 × PR1 (3)

Thus, the optimum reproduction light intensity PR2 at the target position can be obtained. The reproducing light intensity is changed depending on the linear velocity V of the optical recording medium 1 because the temperature distribution of the medium 1 formed by the reproducing light is changed if the linear velocity is different even if the same reproducing light intensity is given. By correcting the equation (3), it is possible to prevent the temperature distribution of the medium 1 in the light spot from being different due to the linear velocity. Therefore, CLV (Constant Linear Velocity) with a constant linear velocity
In the case of (city), it is not necessary to correct equation (3).

Next, the controller 3 controls the medium 1 based on the light intensity detected by the front monitor 25.
The optimum reproduction light intensity P calculated by the reproduction light intensity applied to the
The laser drive circuit 4 is controlled so that it becomes R2. Then, the system controller 5 moves the laser beam to the target position to be reproduced by a seek or step jump operation.

When the target position is reached, the recording / reproducing controller 3 demodulates the signal of the photodetector 26 and reproduces information. The calculation of the optimum reproduction light intensity, the setting of the reproduction light intensity, the seek or step jump operation, and the information reproduction as described above are repeated each time a target position to be reproduced is generated by a command from the host computer, and the necessary information is sequentially acquired. Read out. In this way, information can be reproduced with the optimum light intensity.

In the information recording / reproducing apparatus of the present invention, it is necessary to update the temperature T of the medium 1 by carrying out the above-mentioned trial writing and estimating the medium temperature from time to time. However, since the change in the temperature of the medium 1 is usually gradual, the temperature estimation by trial writing may be performed at regular time intervals, and the loss of the time can be set to a level not causing a problem. Until the next measurement, the measured value may be used as it is as the medium temperature. Further, until the next measurement, it is possible to estimate the medium temperature T by predicting the rate of temperature change from that value and the value before that.

Further, in the present embodiment, since the reproducing light intensity is changed by the linear velocity V at the target position of the medium 1, the set reproducing light intensity at that position on the way to the target position is It may be higher than the optimum reproduction light intensity (for example, when the target position is outside the current position). Therefore, in such a case, the reproducing light intensity may be set to a constant value during the seek or step jump operation, and the optimum reproducing light intensity calculated after reaching the target position may be set. Further, in the present embodiment, FAD, RAD, C are used as the super-resolution reading medium.
Although an example of a magnetic super-resolution magneto-optical disk such as an AD system has been described, the same effect can be obtained with other super-resolution media other than the magneto-optical disk.

[0038]

According to the present invention, the recording / reproducing control means obtains an appropriate recording light intensity from the result of the trial writing, estimates the temperature of the medium from this light intensity, and reproduces the reproducing light in accordance with the temperature of the medium. Since the light intensity is properly adjusted, the temperature distribution of the medium in the reproduction light spot can always be a predetermined temperature distribution regardless of the temperature of the medium itself. Therefore, if the optical recording medium to be reproduced is a super-resolution reading medium, the shape of the effective opening of the light spot responsible for super-resolution reproduction can always be an appropriate shape regardless of the temperature of the medium itself. Information recorded at high density can be stably read even when the temperature of the medium is different. If the optical recording medium is a normal medium that is not for super-resolution reading, the C of the highest reproduction signal is obtained.
/ N can always be obtained regardless of the temperature of the medium itself,
The capacity of the medium can be fully utilized. Further, since the temperature of the optical recording medium does not always have to be kept constant in the information recording / reproducing apparatus, the apparatus installation environment temperature is not restricted, and the apparatus does not become complicated due to measures such as heat generation.

Further, an appropriate recording light intensity is obtained from the result of trial writing on the optical recording medium, the temperature of the medium is estimated from this light intensity, and the light intensity of the reproducing light is appropriately adjusted according to the temperature of the medium. By adjusting, the temperature distribution of the medium in the reproduction light spot can always be a predetermined temperature distribution regardless of the temperature of the medium itself. Therefore, if the optical recording medium to be reproduced is a super-resolution reading medium, the shape of the effective opening of the light spot responsible for super-resolution reproduction can always be an appropriate shape regardless of the temperature of the medium itself. Information recorded at high density can be stably read even when the temperature of the medium is different. Further, if the optical recording medium is a normal medium that is not for super-resolution reading, the C / N of the highest reproduction signal can always be obtained irrespective of the temperature of the medium itself, and the capacity of the medium can be fully utilized. .

[Brief description of drawings]

FIG. 1 is a block diagram of an information recording / reproducing apparatus showing a first embodiment of the present invention.

FIG. 2 is a recording signal waveform for measuring the optimum recording light intensity,
It is a figure which shows the mark recorded on the optical recording medium by this signal, and the reproduction | regeneration signal waveform obtained by reproducing this mark.

FIG. 3 is a diagram showing a change in C / N of a reproduction signal with respect to reproduction light intensity.

FIG. 4 is a plan view and a cross-sectional view of an FAD-type optical recording medium that is an example of a super-resolution reading medium.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical recording medium, 2 ... Optical head, 3 ... Recording / reproducing controller, 4 ... Laser drive circuit, 5 ... System controller, 21 ... Semiconductor laser, 22, 23 ... Beam splitter, 24 ... Objective lens, 25 ... Front monitor, 26 ... Photodetector.

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G11B 11/10-11/105 G11B 7/125

Claims (2)

(57) [Claims] 1. An information recording / reproducing apparatus for optically recording / reproducing information on / from an optical recording medium, which comprises an irradiation means for irradiating an optical recording medium with recording light for writing information or reproducing light for reading information. A detecting means for receiving the reflected light from the medium and converting it into an electric signal; and obtaining an appropriate light intensity of the recording light by trial writing for recording / reproducing on / from the medium by the irradiating means and the detecting means. And a recording / reproducing control unit that adjusts the light intensity of the reproducing light based on the estimated temperature of the medium so that the light intensity of the reproducing light irradiated from the irradiating unit to the medium becomes appropriate. An information recording / reproducing apparatus characterized by the above. 2. A reproducing method for optically reading information from an optical recording medium, wherein trial writing is performed on the optical recording medium, and appropriate recording light for writing information is irradiated onto the medium from the result of the trial writing. Then, the temperature of the medium is estimated from the light intensity of this recording light, and the reproduction light is projected based on the estimated temperature of the medium so that the light intensity of the reproduction light for reading information on the medium is appropriate. A method for reproducing an optical recording medium, which comprises adjusting the light intensity of light.