JP4139994B2 - Signal recording apparatus, signal reproducing apparatus, and method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a signal recording apparatus and method for recording a signal on an optical recording medium using near-field light, and a signal reproducing apparatus and method for reproducing the signal from an optical reproduction medium using near-field light.
[0002]
[Prior art]
In an optical recording / reproducing apparatus using near-field light, it is necessary to control (gap control) the gap between the SIL end face and the disk to a distance (near field) where near-field light is generated.
This distance is generally ½ of the wavelength of the input laser beam. For example, when a 400 nm blue-violet laser is used, the thickness is about 200 nm.
For this reason, an overshoot of 1 μm or less at the start of control, which is not particularly problematic in a far field optical system such as a DVD, becomes a problem in an optical recording / reproducing apparatus using near-field light. That is, even if an overshoot of 1 μm or less occurs at the start of control, the SIL collides with the disk, causing damage to both.
[0003]
In order to solve this problem, as a first method, there is a method in which an electrode is provided on the SIL end face and the gap is controlled by the capacitance between the SIL and the disk.
According to this method, gap control is performed at the far field distance, and after the servo is pulled in, the distance is manually brought to the near field distance.
This avoids collision between the SIL and the disk due to overshoot at the start of the gap servo.
[0004]
As a second method, there is a method of performing gap servo after the SIL is brought close to the near field distance in the gap servo method using the total reflected return light amount.
In the gap servo system using the total reflected light, the gap error becomes a constant value independent of the gap length except for the near field distance. Since the gap servo is started from the far field distance due to the non-linear characteristic having the dead zone, the SIL collides with the disk due to overshoot.
Therefore, there is a method in which the SIL is approached slowly to the distance where the near field state occurs, and near field control is started when the near field state is in the linear region (see Japanese Patent Application No. 11-253296).
As a result, the overshoot amount becomes a specific amount corresponding to the step response characteristic of the control system, and the control system is designed so that the overshoot amount is equal to or less than the gap length target value. Avoid collision between SIL and disk.
[0005]
[Problems to be solved by the invention]
However, these conventional techniques have the following problems.
First, the first method has a drawback in that an electrode is basically required to perform gap servo, leading to an increase in the number of parts.
In addition, since the capacitance that is a gap error is inversely proportional to the distance between the SIL and the disk, for example, when a biaxial device used in a DVD as an optical head is used, a wide movable range of the biaxial device, For example, at a distance of 300 μm, the error signal becomes minute and difficult to detect. That is, there is a problem that the wide movable range of the biaxial device cannot be fully utilized.
[0006]
In the second method, depending on the moving speed of the SIL, a speed disturbance occurs when switching from the approaching operation of the SIL to the gap servo, and the SIL also collides with the disk when the gap servo is switched.
In order to avoid this problem, it is conceivable that the SIL approaches the disk at a slow approach speed of several μm / sec. However, a biaxial device is used as the optical head, for example, the initial position of the SIL is 300 μm from the disk. If it is far away, it will take too much time to reach the near field state, and it will not be practical. For example, when the approach speed is 3 μm / sec, it takes about 1.7 minutes.
[0007]
The present invention has been made in view of such a situation, and when the distance between the optical field and the medium moves from a far field distance of several hundred μm to a near field distance of several tens of nanometers, It is an object of the present invention to provide a signal recording apparatus, a signal reproducing apparatus, and a method capable of realizing a short pull-in time of 1 second or less without collision of optical means with a chute.
[0008]
[Means for Solving the Problems]
Since the present invention is to achieve the above object, the signal recording apparatus utilizing near-field light by the light source and optical means for recording a signal on an optical recording medium, a detection means for detecting that a near-field, the two-axis device An approach means for causing the optical means to approach the optical recording medium until it becomes a near field, and a control means for controlling the distance between the optical means and the optical recording medium to be constant after becoming a near field, A switching means for switching between the operation of the approaching means and the operation of the control means by a signal for detecting the near field, and a changing means for changing the control target value of the distance , the approaching means and the control The means operate independently of each other, and the control means does not operate until the control means is switched from the approach means to the control means by a signal for detecting the near field. The distance approaching means is stopped after switching from the approaching means to the control means, and the control target value of the distance is changed every predetermined time after switching from the approaching means to the control means. .
[0009]
According to another aspect of the present invention, there is provided a signal recording method for recording a signal on an optical recording medium using near-field light by a light source and optical means, a detection step for detecting near-field, and the optical means by a biaxial device. An approach step for approaching the optical recording medium until the near field is reached, a control step for controlling the distance between the optical means and the optical recording medium to be constant after the near field is reached, and the near field. A switching step of switching between the operation of the approaching step and the operation of the control step according to a signal to detect that, and a changing step of changing the control target value of the distance , wherein the approaching step and the control step operate independently of each other In addition, the control process is not operated until the approach process is switched to the control process, and the distance approach process is stopped after switching from the access process to the control process. And the control target value of the distance is changed every predetermined time after switching from the approaching step to the control step .
[0010]
The present invention, in the signal reproducing apparatus utilizing near-field light by the light source and optical means for reproducing a signal to the optical recording medium, a detection means for detecting that a near field, the optical means by biaxial device An approach means for approaching the optical reproduction medium until a near field is reached; a control means for controlling the distance between the optical means and the optical reproduction medium to be constant after becoming the near field; and the near field. A switching means for switching between the approach means and the control means in accordance with a signal for detecting this, and a changing means for changing the control target value of the distance, and the approach means and the control means operate independently of each other. The control means is not operated until the control means is switched from the approach means to the control means by a signal for detecting the near field, and the approach means is switched to the control means. The distance approaching means is stopped after switching, and the control target value of the distance is changed every predetermined time after switching from the approaching means to the control means .
[0011]
According to another aspect of the present invention, there is provided a signal reproduction method for reproducing a signal on an optical reproduction medium using near-field light by a light source and optical means, a detection step for detecting near-field, and the optical means by a two-axis device. An approach step of approaching the optical reproduction medium until the near field is reached, a control step of controlling the distance between the optical means and the optical reproduction medium to be constant after the near field is reached, and the near field A switching step for switching between the approach step and the control step according to a signal to detect that, and a change step for changing the control target value of the distance , the approach step and the control step operate independently of each other, The control process is not operated until switching from the approach process to the control process, and the approach process of the distance is stopped after switching from the approach process to the control process, and The control target value of the distance is changed every predetermined time after switching from the approach process to the control process .
[0012]
In the signal recording apparatus, the signal reproducing apparatus, and the method of the present invention, the operation of bringing the optical means closer to the medium until the near field is reached, and the distance between the optical means and the medium is controlled to be constant after the near field is reached. By performing this operation while changing the distance control target value, the optical means can be quickly drawn into the near field without causing the optical means to collide with the medium due to overshoot.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of a signal recording apparatus, a signal reproducing apparatus, and a method according to the present invention will be described.
The embodiments described below are preferred specific examples of the present invention, and various technically preferable limitations are given. However, the scope of the present invention is not limited to the following description. Unless otherwise specified, the present invention is not limited to these embodiments.
[0014]
FIG. 1 is an explanatory diagram showing a configuration of an optical head portion of a near-field reproducing apparatus according to an embodiment of the present invention.
This optical head has a structure in which the SIL 2 and the aspherical lens 3 are accommodated in a lens holder 4 and installed in a biaxial device 5.
Through this optical head, the gap between the SIL 2 and the disk 1 is controlled so that the return light quantity 6 (that is, the total reflected return light quantity) of the incident laser light incident on the disk 1 at an angle causing total reflection is obtained. To do.
[0015]
FIG. 2 is an explanatory diagram showing the relationship between the gap length and the total reflected return light amount 6. The vertical axis indicates the light amount (unit is arbitrary), and the horizontal axis indicates the gap length (nm).
Here, a case where a laser having a wavelength of 400 nm is used as incident light is considered.
The near-field state is generally ½ or less of the wavelength. For this reason, when the gap length is 200 nm or more, that is, in the far field state, all the light incident on the SIL end face at an angle causing total reflection is reflected on the SIL end face, and the total reflected return light quantity 6 is constant.
However, when the gap length is 200 nm or less, that is, in the near-field state, a part of light incident on the SIL end face penetrates the SIL end face at an angle causing total reflection. For this reason, the total reflection return light quantity 6 becomes small.
When the gap length between the SIL and the disk is zero, that is, when the SIL and the disk come into contact with each other, all the light incident on the SIL end face through the angle causing the total reflection penetrates the SIL end face, and the total reflected return light quantity 6 becomes zero.
[0016]
In FIG. 2, in the region 7 where the near field state is entered and the gap length and the total reflected return light amount are linear, the total reflected return light amount that is linearly related to the gap length is obtained. In this linear region 7, gap control is performed using the gap error signal as the total reflected return light amount.
This gap control is performed by a phase compensation filter based on a frequency response, for example, by classical control.
If the initial position of the SIL is in the near field distance, even if the gap servo is operated by the gap servo as it is, the control system is designed so as not to cause an overshoot. Will not collide. However, in this case, the initial position of the SIL before starting the gap servo must be set to 200 nm or less, and the SIL collides with the disk due to vibration disturbances or the like. In addition, it is extremely difficult to install the SIL at a distance of 200 nm or less without gap control, which is not practical.
[0017]
Therefore, it is necessary to perform the gap servo by installing the SIL at the far field distance and moving from there to the near field distance.
In this case, if the gap servo loop is simply operated to control from the far field position to the gap servo target value at the near field position, the SIL collides with the disk. This is because, in the far-field state, the relationship between the total reflected return light quantity 6 with respect to the applied voltage of the biaxial device 5 shows a dead band characteristic, so that an excessive voltage is applied to the biaxial device 5 so that the SIL approaches the disk. Because it will do.
Therefore, when the near field distance is reached and the relationship between the total reflected return light quantity 6 with respect to the applied voltage of the biaxial device 5 reaches the linear characteristic 7, the SIL collides with the disk because of the excessive voltage and cannot be controlled. End up. This is shown in FIG. In the illustrated example, a collision occurs at time t1.
[0018]
Therefore, as shown in FIG. 4, a threshold value (gap servo start threshold value) 8 for determining the near field state is set, and the total reflected return light quantity 6 becomes smaller than the gap servo start threshold value 8, that is, up to the near field distance. There is a method in which the SIL is approached slowly and the gap servo is started only when the near field distance is reached (see, for example, Japanese Patent Application No. 11-253296).
[0019]
This method is not particularly problematic when a piezo element is used as a device for driving a lens. This is because the movable range of the piezo element is several μm, and the initial speed of the SIL when starting the gap servo at the near field distance by moving the lens close to the disk at a very low speed of several μm / sec from this initial position. Is almost zero, and the speed disturbance as described above does not occur. Therefore, the lens does not collide with the disc.
However, in this method, unless the initial position of the SIL is reduced, the time until the target gap length is reached becomes long and is not practical. For example, when a biaxial device such as a DVD is used as a lens driving device and is approached at a very low speed of several μm / sec from a distance of several hundred μm as described above, several hundreds of times are required until the near field state is reached. It takes a second.
[0020]
Therefore, in the present embodiment, a method is provided in which the time required for a lens at a distance of several hundreds of μm to reach the target gap length after approaching the lens is short, and the lens does not collide with the disk when retracted. Is.
[0021]
FIG. 5 is a block diagram showing an outline of a signal recording / reproducing apparatus according to the present embodiment.
In this signal recording / reproducing apparatus, the control target is the biaxial device 5. The controlled amount is the total reflected return light amount 6, which is detected by the photodetector 17. The detected total reflected return light quantity 6 is normalized to 1 V, for example, by a normalization gain 18. The standardized signal is digitized by the AD converter 19.
[0022]
The digitized total reflected return light amount is input to the data processing unit 10. A voltage for causing the SIL to approach the disk is output by the data processing unit 10, converted to an analog signal by the DA converter 14, and output as the approach voltage 14. A gap error signal is input to the filter 13, converted to an analog signal by the DA converter 12, and output as a servo voltage 15. The approach voltage 14 and the servo voltage 15 are added and input to the driver 16 to drive the biaxial device 5 so that the gap error 27 becomes zero.
[0023]
FIG. 6 is a block diagram showing details of the data processing unit 10.
The data processing unit 10 receives a total reflected return light amount 6 and a gap servo switch 9.
The total reflected return light amount 6 is compared with the gap servo start threshold value 8 set by the gap servo start threshold value setting unit 21 in the comparator 20.
The gap servo start threshold value 8 is set as shown in FIG. 4, for example. That is, the gap servo start threshold value 8 is set to a value larger than the gap servo final target value in the near field region. For example, in FIG. 4, when the value of the total reflected return light amount 6 in the far field region is normalized to 1 (V), it is set to 0.8 (V).
[0024]
Next, based on the comparison result of the comparator 20, for example, when the total reflected return light amount 6 is larger than the gap servo start threshold value 8, that is, when the SIL is at the far field distance, the output of the comparator 20 becomes Low.
Further, when the total reflected return light quantity 6 is smaller than the gap servo start threshold value 8, that is, when the head is in the near field distance, it becomes High.
The switch 24 is switched by the output of the comparator 20 as described above, and the operations of the approach speed generation unit 23 and the gap servo target value generation unit 25 are selectively switched.
For example, when the output of the comparator 20 is low, that is, when the SIL is a far field distance, the operation of the approach speed generator 23 is selected by the switch 24, and when the output of the comparator 20 is high, that is, the SIL is near field. When the distance is selected, the operation of the gap servo target value generation unit 25 is selected by the switch 24.
[0025]
FIG. 7 is a block diagram illustrating a configuration example of the approach speed generation unit 23.
The approach speed generator 23 receives the gap servo switch signal 9 and the output signal of the comparator 20. The approach speed generator 23 includes a ramp voltage generator 28 and a sample holder 29, and the approach voltage 14 is output.
Here, when the output of the comparator 20 is Low, the sample holder 29 is in the sample mode. When the gap servo switch 9 is turned on, the ramp voltage generator 28 is turned on, and the voltage on the ramp starts to be generated. This is output as the approach voltage 14.
When the output of the comparator 20 is High, the sample holder 29 is in the hold mode, and is held at the ramp voltage when the output of the comparator 20 changes from Low to High.
[0026]
This is shown in FIG. In FIG. 8, at time t1, the output of the comparator 20 changes from Low to High, and the lamp voltage is held. That is, during time t0 to t1, the ramp voltage is applied to the biaxial device, and the SIL approaches the disk. At time t1, the SIL enters the near field distance, and the operation for bringing the SIL closer to the disk is terminated at that time.
[0027]
On the other hand, until the lens reaches the near field distance at time t1, the switch 26 in FIG. 6 is reset to zero, and the gap error becomes zero. That is, the gap servo does not operate and the servo voltage 15 is zero output.
Next, when the output of the comparator 20 becomes High at time t1, that is, when the SIL becomes the near field distance, the switch 24 is switched from the approach speed generation unit 23 to the gap servo target value generation unit 25. Further, the switch 26 starts to output a gap error 27 from the zero reset state, and the gap servo loop operates.
[0028]
The target value of the gap servo loop is generated by the gap length target value generation unit 25. This is shown in FIG. As shown in the figure, the gap length target value generation unit 25 inputs the output signal of the comparator 20, the gap servo start threshold value 8, and the gap servo final target value 31 to the signal pattern generator 30, and servos based on these values. A pattern signal of voltage 15 is output.
The gap servo final target value 31 is set as shown in FIG. For example, when the value of the total reflected return light amount 6 in the far field is normalized to be 1 (V), it is set to 0.5 (V). This value is set to a value smaller than the gap servo start threshold value 8.
[0029]
The gap length target value generation unit 25 uses the gap servo start threshold value 8 and the gap set as the start pulse at the point where the output of the comparator 20 transitions from Low to High, that is, the point where the SIL moves from the far field distance to the near field distance. A signal that interpolates between the servo final target values 31 is generated from the signal pattern generator 30. This is the gap servo target value.
An example of the gap servo target value is shown in FIG. In the case of FIG. 11, a signal is generated by the signal pattern generator 30 so as to linearly interpolate between the gap servo start threshold 8 and the final gap servo target value 31 between times t1 and t2.
[0030]
The change speed of the gap servo target value is set so as to change at a speed within the gap servo band. As a result, the gap servo changes so as to follow the gap servo target value.
When the gap servo is started, even if there is an initial speed disturbance, it starts to follow the target value and vibrates. However, after that, the SIL does not collide with the disk by following the gap target value line 32 completely. . This is shown in FIG.
As described above, in the present embodiment, the gap servo is pulled in by changing the gap target value at the time of controlling the gap with the optical recording medium every time. It is possible to control the gap from a distance equivalent to an optical disk such as DVD or DVD to a distance of several tens of nanometers without the lens colliding with the disk.
The method according to the present embodiment as described above can be widely applied to signal reproducing apparatuses and signal recording apparatuses using various optical media.
[0031]
【The invention's effect】
As described above, in the signal recording apparatus, the signal reproducing apparatus, and the method of the present invention, the operation of bringing the optical means closer to the medium until the near field is reached, and between the optical means and the medium after becoming the near field. By performing the operation to control the distance constant while changing the distance control target value, the optical means can be quickly brought into the near field without causing the optical means to collide with the medium due to overshoot. Is possible.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a configuration of an optical head portion of a near-field reproducing device according to an embodiment of the present invention.
FIG. 2 is an explanatory diagram showing the relationship between the gap length of the optical head portion shown in FIG. 1 and the total reflected return light amount.
FIG. 3 is an explanatory diagram showing a total reflected return light amount during a gap servo operation when only a conventional gap servo is used.
FIG. 4 is an explanatory diagram showing a gap servo start threshold in a method in which conventional SIL approach control and gap servo control are combined.
FIG. 5 is a block diagram showing a configuration example of a gap servo apparatus according to an embodiment of the present invention.
6 is a block diagram showing a configuration example of a data processing unit of the gap servo apparatus shown in FIG. 5;
7 is a block diagram illustrating a configuration example of an approach speed generation unit of the gap servo apparatus illustrated in FIG. 5;
FIG. 8 is an explanatory diagram showing an example of an approach voltage of the gap servo device shown in FIG. 5;
9 is a block diagram illustrating a configuration example of a gap servo target value generation unit of the gap servo apparatus illustrated in FIG. 5;
10 is an explanatory diagram showing an example of a gap servo final target value of the gap servo device shown in FIG. 5. FIG.
11 is an explanatory diagram showing a change in the target value of the gap servo of the gap servo device shown in FIG.
12 is an explanatory diagram showing an example of a total reflected return light amount during a gap servo operation of the gap servo device shown in FIG. 5;
[Explanation of symbols]
2 ... SIL, 3 ... Aspherical lens, 5 ... Biaxial device, 6 ... Total reflected return light amount, 8 ... Gap servo start threshold, 10 ... Data processing unit, 21 ... Gap servo start threshold setting , 22... Final gap servo target value setting unit, 23... Approach speed generation unit, 25... Gap servo target value generation unit, 28... Ramp voltage generator, 30. Gap servo final target value.

Claims (20)

In a signal recording apparatus for recording a signal on an optical recording medium using near-field light by a light source and optical means,
A detecting means for detecting a near field using the total reflected return light amount ;
Access means for causing the optical means to approach the optical recording medium until it becomes a near field by a biaxial device ;
Control means for controlling the distance between the optical means and the optical recording medium to be constant after becoming a near field;
Switching means for switching between the operation of the approaching means and the operation of the control means by a signal for detecting the near field;
Change means for changing the control target value of the distance ,
The approach means and the control means operate independently of each other, and the control means is not operated until the approach means is switched to the control means by a signal for detecting the near field, and the approach means is not operated. The distance approaching means is stopped after switching from the approaching means to the control means, and the control target value of the distance is changed every predetermined time after switching from the approaching means to the control means.
A signal recording apparatus.   A light source that emits laser light, and an optical unit that is disposed in proximity to a signal surface to the optical recording medium and that condenses near-field light from the laser light on the optical recording medium. The signal recording apparatus according to claim 1, wherein the signal recording apparatus detects a near-field state.   The optical recording medium is provided close to the signal surface of the optical recording medium, and includes optical means for condensing near-field light by the laser light on the optical recording medium, and the optical means and the optical recording medium are controlled by the amount of return light of the laser light. The signal recording apparatus according to claim 1, wherein the distance between them is constant.   2. The signal recording apparatus according to claim 1, wherein the objective lens constituting the optical means comprises an aspherical lens and a SIL (Solid Immersion Lens).   2. The signal recording apparatus according to claim 1, wherein the objective lens constituting the optical means comprises an aspherical lens and a SIM (Solid Immersion Mirror). In a signal recording method for recording a signal on an optical recording medium using near-field light by a light source and optical means,
A detection step of detecting the near field using the total reflected return light amount ;
An approaching step of approaching the optical recording medium until the optical means is in the near field by a biaxial device ;
A control step of controlling the distance between the optical means and the optical recording medium to be constant after becoming a near field;
A switching step of switching between the operation of the approaching step and the operation of the control step by a signal for detecting the near field;
A change step for changing the control target value of the distance ,
The approach step and the control step operate independently of each other, and the control step is not operated until the approach step is switched to the control step, and the distance approach step is performed after switching from the approach step to the control step. And changing the control target value of the distance every predetermined time after switching from the approach process to the control process.
And a signal recording method. The detection step includes returning the laser light by a light source that emits laser light and an optical unit that is disposed in proximity to the signal surface of the optical recording medium and collects near-field light from the laser light on the optical recording medium. 7. The signal recording method according to claim 6, wherein the near-field state is detected by the amount of light. In the control step, the optical means is arranged near the signal surface of the optical recording medium, and the optical means is optically reflected by the return light amount of the laser light by an optical means for condensing the near-field light by the laser light on the optical recording medium. 7. The signal recording method according to claim 6 , wherein a distance from the recording medium is made constant. 7. The signal recording method according to claim 6 , wherein the objective lens constituting the optical means comprises an aspheric lens and a SIL (Solid Immersion Lens). 7. The signal recording method according to claim 6 , wherein the objective lens constituting the optical means comprises an aspheric lens and a SIM (Solid Immersion Mirror). In a signal reproduction apparatus for reproducing a signal on an optical reproduction medium using near-field light by a light source and optical means,
A detecting means for detecting a near field using the total reflected return light amount ;
Access means for causing the optical means to approach the optical reproduction medium until it becomes a near field by a biaxial device ;
Control means for controlling the distance between the optical means and the optical reproduction medium to be constant after becoming a near field;
A switching means for switching between the approaching means and the control means by a signal for detecting the near field;
Change means for changing the control target value of the distance ,
The approach means and the control means operate independently of each other, and the control means is not operated until the approach means is switched to the control means by a signal for detecting the near field, and the approach means is not operated. The distance approaching means is stopped after switching from the approaching means to the control means, and the control target value of the distance is changed every predetermined time after switching from the approaching means to the control means.
A signal reproducing apparatus characterized by the above. A light source that emits laser light and an optical means that is arranged close to the signal surface to the optical reproduction medium and that condenses near-field light by the laser light on the optical reproduction medium, and is closer to the amount of return light of the laser light. 12. The signal reproducing apparatus according to claim 11 , wherein the signal reproducing apparatus detects that the state is a field state. Optical means disposed near the signal surface to the optical reproduction medium, and condensing the near-field light by the laser light on the optical reproduction medium, and the optical means and the optical reproduction medium by the return light amount of the laser light 12. The signal reproducing apparatus according to claim 11 , wherein the distance between the two is constant. 12. The signal reproducing apparatus according to claim 11 , wherein the objective lens constituting the optical means comprises an aspheric lens and a SIL (Solid Immersion Lens). 12. The signal reproducing apparatus according to claim 11 , wherein the objective lens constituting the optical means comprises an aspherical lens and a SIM (Solid Immersion Mirror). In a signal reproduction method for reproducing a signal on an optical reproduction medium using near-field light by a light source and optical means,
A detection step of detecting the near field using the total reflected return light amount ;
An approaching step of bringing the optical means closer to the optical reproduction medium until it becomes a near field by a biaxial device ;
A control step of controlling the distance between the optical means and the optical reproduction medium to be constant after becoming a near field;
A switching step of switching between the approaching step and the control step by a signal for detecting the near field;
A change step for changing the control target value of the distance ,
The approach step and the control step operate independently of each other, and the control step is not operated until the approach step is switched to the control step, and the distance approach step is performed after switching from the approach step to the control step. And changing the control target value of the distance every predetermined time after switching from the approach process to the control process.
A signal reproduction method characterized by the above. The detection step includes returning the laser light by a light source that emits laser light and an optical unit that is disposed in proximity to the signal surface of the optical reproduction medium and collects near-field light from the laser light on the optical reproduction medium. 17. The signal reproduction method according to claim 16, wherein the near-field state is detected by the amount of light. In the control step, the optical means is arranged near the signal surface of the optical reproduction medium, and the optical means is reflected by the return light amount of the laser light by the optical means for condensing the near-field light by the laser light on the optical reproduction medium. 17. The signal reproduction method according to claim 16 , wherein a distance from the reproduction medium is made constant. 17. The signal reproducing method according to claim 16 , wherein the objective lens constituting the optical means comprises an aspherical lens and a SIL (Solid Immersion Lens). 17. The signal reproducing method according to claim 16 , wherein the objective lens constituting the optical means comprises an aspheric lens and a SIM (Solid Immersion Mirror).

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