JP2004030821A - Signal recording device, signal reproducing device, and method - Google Patents

Abstract

A signal recording device, a signal reproducing device, and a method capable of quickly drawing an optical unit into a near field without causing collision of the optical unit with a medium due to overshoot are provided.
A comparator (20) compares a total reflection return light amount (6) with a gap servo start threshold to determine whether the SIL is at a far field distance or a near field distance, and switches the switch (24) according to the comparison result. The switching and the operation of the approach speed generator 23 and the gap servo target value generator 25 are selected. Based on the output of the comparator 20, the gap servo target value generation unit 25 interpolates between the gap servo start threshold set at the point where the SIL moves from the far field distance to the near field distance as the start pulse and the gap servo final target value. Such a gap servo target value is output, and the SIL pull-in control is performed using the time-varying gap servo target value.
[Selection] Fig. 6

Description

[0001]
TECHNICAL FIELD 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 disc to a distance (near field) at which near-field light is generated.
This distance is generally の of the wavelength of the input laser light. For example, when a 400 nm blue-violet laser is used, the wavelength is about 200 nm.
For this reason, an overshoot of 1 μm or less at the start of control, which is not a problem in a far-field optical system such as a DVD, becomes a problem in an optical recording / reproducing apparatus using near-field light. In other words, even if an overshoot of 1 μm or less occurs at the start of the control, the SIL collides with the disk, and both are damaged.
[0003]
In order to solve this problem, as a first method, there is a method in which an electrode is provided on the end face of the SIL and the gap is controlled by the capacitance between the SIL and the disk.
According to this method, the gap control is performed at the far field distance, the servo is pulled in, and then the near field distance is manually set.
This avoids a collision between the SIL and the disk due to overshoot at the start of the gap servo.
[0004]
As a second method, in the gap servo method using the total reflection return light amount, there is a method of performing gap servo after approaching the SIL to a near-field distance.
In the gap servo method using the total reflection light, the gap error has a constant value independent of the gap length except for the near-field distance. Since the gap servo is started from the distance of the far field due to the non-linear characteristic having a dead zone, the SIL collides with the disk due to overshoot.
Therefore, there is a method in which the SIL is slowly approached to a distance at which the near-field state occurs, and near-field control is started when the near-field state becomes a linear region (see Japanese Patent Application No. 11-253296).
As a result, the overshoot amount becomes a characteristic amount according to the step response characteristic of the control system. 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 disadvantage that an electrode is basically required for performing the gap servo, which leads to an increase in the number of components and the like.
Further, since the capacitance as a gap error is inversely proportional to the distance between the SIL and the disk, for example, if a two-axis device such as that used in a DVD as an optical head is used, the wide movable range of the two-axis device, For example, at a distance of 300 μm, the error signal becomes very small and it is difficult to detect the error signal. That is, there is a problem that the wide movable range of the two-axis device cannot be fully utilized.
[0006]
Further, in the second method, depending on the moving speed of the SIL, a speed disturbance occurs when switching from the approach operation of the SIL to the gap servo, and the SIL collides with the disk when the gap servo is switched.
In order to avoid this problem, it is conceivable to approach the SIL to the disk at a slow approach speed of several μm / sec. However, a two-axis device is used as an optical head, and for example, the initial position of the SIL is 300 μm from the disk. If it is far away, it takes too much time to reach the near-field state, which is not 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 unit and the medium moves from the far field distance of several hundred μm to the near field distance of several tens nm, an over-range occurs. It is an object of the present invention to provide a signal recording device, a signal reproducing device, and a method capable of realizing a short pull-in time of 1 second or less without collision of an optical unit with a medium due to a chute.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a signal recording device that records a signal on an optical recording medium using near-field light generated by a light source and an optical unit. Approaching means for approaching the optical means to the optical recording medium until it becomes, a control means for controlling the distance between the optical means and the optical recording medium to be constant after the near field, and Switching means for switching the operation of the approaching means and the operation of the control means in response to a signal for detecting the presence of the signal, and changing means for changing a control target value of the distance are provided.
[0009]
The present invention also provides a signal recording method for recording a signal on an optical recording medium using a near-field light generated by a light source and an optical unit. Approaching the optical recording medium, controlling the distance between the optical unit and the optical recording medium to be constant after the near-field is reached, and detecting the near-field. A switching step of switching the operation of the approach step and the operation of the control step by a signal; and a changing step of changing a control target value of the distance.
[0010]
Further, the present invention provides a signal reproducing apparatus for reproducing a signal on an optical reproducing medium using a near-field light generated by a light source and an optical means. Approaching means for approaching the optical reproduction medium, control means for controlling the distance between the optical means and the optical reproduction medium to be constant after a near field has been reached, and detecting that the optical field is the near field. A switching means for switching between the approach means and the control means by a signal, and a change means for changing a control target value of the distance are provided.
[0011]
Also, the present invention provides a signal reproducing method for reproducing a signal on an optical reproducing medium using a near-field light by a light source and an optical means, wherein a detecting step of detecting that the optical field is a near field; Approaching to the optical reproduction medium, controlling the distance between the optical means and the optical reproduction medium to be constant after the near field is reached, and detecting the near field. A switching step of switching between the approach step and the control step by a signal; and a changing step of changing a control target value of the distance.
[0012]
According to the signal recording device, the signal reproducing device, and the method of the present invention, the operation of bringing the optical unit close to the medium until the near field is reached, and the distance between the optical unit and the medium after the near field is controlled to be constant By performing such an operation while changing the control target value of the distance, the optical unit can be quickly drawn into the near field without causing collision of the optical unit with the medium due to overshoot.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of a signal recording device, a signal reproducing device, 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 added. However, the scope of the present invention is not limited to the embodiments described below. It is not limited to these embodiments unless otherwise specified.
[0014]
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.
This optical head has a structure in which an SIL 2 and an aspheric lens 3 are housed in a lens holder 4 and this is 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 amount of return light 6 of the light incident on the disk 1 (that is, the amount of total reflection return light) at an angle that causes total reflection of the incident laser light is obtained. I do.
[0015]
FIG. 2 is an explanatory diagram showing the relationship between the gap length and the total reflection return light amount 6, with the vertical axis indicating the light amount (arbitrary unit) and the horizontal axis indicating 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 less than half the wavelength. For this reason, in the distance where 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 that causes total reflection is reflected on the SIL end face, and the total reflection return light quantity 6 is constant.
However, when the gap length is 200 nm or less, that is, in a near-field state, a part of light incident on the SIL end face penetrates the SIL end face at an angle that causes total reflection. For this reason, the total reflection return light amount 6 becomes small.
When the gap length between the SIL and the disk is zero, that is, when the SIL comes into contact with the disk, all light incident on the SIL end face at an angle that causes total reflection penetrates the SIL end face, and the total reflection return light quantity 6 becomes zero.
[0016]
In addition, in FIG. 2, in a near-field state where the gap length and the total reflection return light quantity are in a linear state, a total reflection return light quantity having a linear relationship with the gap length is obtained. In the linear region 7, gap control is performed using the gap error signal as the total reflection return light amount.
This gap control is performed by a phase compensation filter based on a frequency response by, for example, classical control.
If the initial position of the SIL is at the near-field distance and the gap servo is operated by the gap servo as it is, if the control system is designed so as not to cause overshoot, the SIL will be disc-shaped when the gap servo is pulled in. Do not collide. However, in this case, the initial position of the SIL before the start of the gap servo must be set to 200 nm or less, and the SIL collides with the disk due to vibration disturbance 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 set the SIL at a far-field distance and move the SIL to a near-field distance to perform gap servo.
In this case, if the gap servo loop is simply operated to control the gap servo target value from the far field position to the near field position, the SIL will collide with the disk. This is because, in the far-field state, the relationship between the applied voltage of the biaxial device 5 and the total reflected return light quantity 6 shows a dead zone characteristic, so that 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 relation of the total reflection return light quantity 6 to the applied voltage of the biaxial device 5 becomes a linear characteristic 7, the SIL collides with the disk without control due to the excess voltage. I will. This is shown in FIG. In the illustrated example, a collision occurs at time t1.
[0018]
Therefore, as shown in FIG. 4, a threshold (gap servo start threshold) 8 for determining the near-field state is set, and the total reflection return light amount 6 becomes smaller than the gap servo start threshold 8, that is, until the near-field distance. , The SIL is slowly approached, 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 has no particular problem 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 bringing 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 hit the disk.
However, this method is not practical unless the initial position of the SIL is reduced, because the time required to reach the target gap length becomes long. For example, if a two-axis device such as a DVD is used as a lens driving device and approached at a very low speed of several μm / sec from a distance of several hundred μm in the same manner as described above, several hundred It takes seconds.
[0020]
In view of this, the present embodiment provides a method for shortening the time from approaching the lens to the target gap length for a lens located at a distance of several hundred μm and preventing the lens from colliding with the disk when retracted. Things.
[0021]
FIG. 5 is a block diagram showing an outline of the signal recording / reproducing apparatus according to the present embodiment.
In this signal recording / reproducing apparatus, the control target is the two-axis device 5. The controlled amount is the total reflection returning light amount 6, which is detected by the photodetector 17. The detected total reflection return light amount 6 is normalized to, for example, 1 V by the normalization gain 18. The signal after the standardization is digitized by the AD converter 19.
[0022]
The digitized total reflection return light amount is input to the data processing unit 10. Then, a voltage for causing the SIL to approach the disk is output by the data processing unit 10, converted into an analog signal by the DA converter 14, and output as the approach voltage 14. The gap error signal is input to the filter 13, converted into an analog signal by the DA converter 12, and output as the 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 illustrating details of the data processing unit 10.
The data processing unit 10 receives the total reflection return light amount 6 and the gap servo switch 9.
The total reflection return light amount 6 is compared by the comparator 20 with the gap servo start threshold 8 set by the gap servo start threshold setting unit 21.
The gap servo start threshold 8 is set, for example, as shown in FIG. That is, the gap servo start threshold value 8 is set to a value within the near field area and larger than the gap servo final target value. For example, in FIG. 4, when the value of the total reflection return light amount 6 in the far field area is normalized to 1 (V), it is set to 0.8 (V).
[0024]
Next, according to the comparison result of the comparator 20, for example, when the total reflection return light amount 6 is larger than the gap servo start threshold 8, that is, when the SIL is at the far field distance, the output of the comparator 20 becomes Low.
When the total reflection return light amount 6 is smaller than the gap servo start threshold value 8, that is, when the head is at the near-field distance, it becomes High.
The switch 24 is switched by the output of the comparator 20, and the operation of the approach speed generator 23 and the gap servo target value generator 25 is selectively switched.
For example, when the output of the comparator 20 is Low, that is, when the SIL is the far field distance, the operation of the approach speed generation unit 23 is selected by the switch 24, and when the output of the comparator 20 is High, that is, when the SIL is near field. In the case of the distance, the operation of the gap servo target value generator 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 outputs the approach voltage 14.
Here, when the output of the comparator 20 is Low, the sample holder 29 enters the sample mode. When the gap servo switch 9 is turned on, the lamp voltage generator 28 is turned on, and the voltage on the lamp 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 enters the hold mode, and is held at the ramp voltage at the time 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, from time t0 to t1, the ramp voltage is applied to the biaxial device, and the SIL approaches the disk. Then, at time t1, the SIL enters the near field distance, at which point the operation of bringing the SIL closer to the disk is terminated.
[0027]
On the other hand, until the lens reaches the near-field distance at time t1, the switch is reset to zero by the switch 26 in FIG. 6, and the gap error becomes zero. That is, the gap servo does not operate, and the servo voltage 15 becomes zero output.
Next, at time t1, when the output of the comparator 20 becomes High, that is, when the SIL becomes the near-field distance, the switch 24 switches from the approach speed generator 23 to the gap servo target value generator 25. Further, the switch 26 is switched from the zero reset state to output the gap error 27, and the gap servo loop is operated.
[0028]
The target value of the gap servo loop is generated by the target gap length 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 8 and the gap servo final target value 31 to the signal pattern generator 30, and performs servo control based on these values. It outputs a pattern signal of voltage 15.
The gap servo final target value 31 is set as shown in FIG. For example, if the value of the total reflection return light quantity 6 in the far field is normalized to be 1 (V), it is set as 0.5 (V). Note that 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 determines the gap servo start threshold 8 and the gap servo start threshold 8 set as a start pulse at the point where the output of the comparator 20 transitions from low to high, that is, the point at which 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.
FIG. 11 shows an example of the gap servo target value. 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 value 8 and the final gap servo target value 31 between times t1 and t2.
[0030]
Further, the changing 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, the SIL does not collide with the disk by virtue of oscillating at the beginning of following the target value, but thereafter following the gap target value line 32 completely. . This is shown in FIG.
As described above, in the present embodiment, the gap target value for controlling the gap with the optical recording medium is changed every time to perform the gap servo pull-in. It is possible to control the gap from a distance equivalent to that of an optical disk such as a DVD or a DVD to a distance of several tens of nm without the lens colliding with the disk.
The method according to the present embodiment as described above can be widely applied to a signal reproducing device and a signal recording device using various optical media.
[0031]
【The invention's effect】
As described above, in the signal recording device, the signal reproducing device, and the method of the present invention, the operation of bringing the optical unit close to the medium until the near field is reached, and the operation of the optical unit and the medium after the near field is reached. By performing the operation of controlling the distance constant while changing the control value of the distance, the optical means can be quickly drawn into the near field without causing the collision of the optical means with the medium due to overshoot. Becomes 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 a relationship between a gap length of the optical head unit shown in FIG. 1 and a total reflection return light amount.
FIG. 3 is an explanatory diagram showing a total reflection return light amount at the time of a gap servo operation when only a conventional gap servo is used.
FIG. 4 is an explanatory diagram showing a gap servo start threshold value in a conventional system combining SIL approach control and gap servo control.
FIG. 5 is a block diagram illustrating a configuration example of a gap servo device 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 device shown in FIG.
FIG. 7 is a block diagram illustrating a configuration example of an approach speed generating unit of the gap servo device 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.
9 is a block diagram illustrating a configuration example of a gap servo target value generation unit of the gap servo device illustrated in FIG.
10 is an explanatory diagram showing an example of a gap servo final target value of the gap servo device shown in FIG.
FIG. 11 is an explanatory diagram showing how a target value of a gap servo of the gap servo device shown in FIG. 5 changes.
12 is an explanatory diagram showing an example of the total reflection return light amount during the gap servo operation of the gap servo device shown in FIG.
[Explanation of symbols]
2... SIL, 3... Aspherical lens, 5... 2-axis device, 6... Total reflected return light quantity, 8... Gap servo start threshold, 10. , 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: signal pattern generator, 31 ... Gap servo final target value.

Claims (36)

In a signal recording device that records a signal on an optical recording medium using near-field light by a light source and optical means,
Detecting means for detecting that it is a near field;
Approaching means for approaching the optical means to the optical recording medium until a near field is reached;
After the near field, control means for controlling the distance between the optical means and the optical recording medium to be constant,
Switching means for switching between the operation of the approach means and the operation of the control means by a signal for detecting the near field,
Changing means for changing the control target value of the distance,
A signal recording device comprising: A light source that emits laser light, and an optical unit that is disposed close to a signal surface to the optical recording medium and condenses near-field light by the laser light on the optical recording medium, and includes a return light amount of the laser light. 2. The signal recording apparatus according to claim 1, wherein the signal recording apparatus detects a near-field state. The optical recording medium is provided in proximity to a signal surface, and includes optical means for converging near-field light by the laser light on the optical recording medium, and the optical means and the optical recording medium are formed by returning light of the laser light. 2. The signal recording apparatus according to claim 1, wherein a distance between the signals is constant. 2. The signal recording apparatus according to claim 1, wherein the signal is switched from the approaching means to the control means in response to a signal for detecting the near field, and then stopped with the approaching means at the distance. 2. The signal recording apparatus according to claim 1, wherein 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. 2. The signal recording apparatus according to claim 1, wherein the control target value of the distance is changed every predetermined time after switching from the approaching means to the control means in response to the signal for detecting the near field. 2. The signal recording apparatus according to claim 1, wherein said approach means and said control means operate independently of each other. 2. The signal recording apparatus according to claim 1, wherein the objective lens constituting the optical means comprises an aspherical lens and SIL (Solid Immersion Lens). 2. The signal recording apparatus according to claim 1, wherein the objective lens constituting the optical means comprises an aspheric lens and a SIM (Solid Immersion Mirror). In a signal recording method of recording a signal on an optical recording medium using near-field light by a light source and optical means,
A detection step of detecting that it is a near field;
An approaching step of bringing the optical means closer to the optical recording medium until a near field is reached;
After the near field, a control step of controlling the distance between the optical means and the optical recording medium to be constant,
A switching step of switching between the operation of the approach step and the operation of the control step by a signal that detects that the field is the near field,
A changing step of changing the control target value of the distance,
A signal recording method comprising: The detecting step includes: returning a laser beam by a light source that emits a laser beam; and an optical unit that is disposed close to a signal surface of the optical recording medium and focuses near-field light by the laser beam on the optical recording medium. 11. The signal recording method according to claim 10, wherein a near-field state is detected based on a light amount. The controlling step includes: placing the optical unit in proximity to the signal surface of the optical recording medium; and concentrating the optical unit on the optical recording medium by the returning light amount of the laser light. 11. The signal recording method according to claim 10, wherein a distance from the recording medium is fixed. 11. The signal recording method according to claim 10, wherein in the switching step, the approaching step of the distance is stopped after switching from the approaching step to the control step by a signal for detecting the near field. The signal recording method according to claim 10, wherein the control step is not operated until the control step is switched from the approach step to the control step by a signal for detecting the near field. 11. The signal recording method according to claim 10, wherein the control target value of the distance is changed every predetermined time after switching from the approach process to the control process by the signal for detecting the near field. The signal recording method according to claim 10, wherein the approaching step and the control step operate independently of each other. 11. The signal recording method according to claim 10, wherein the objective lens constituting the optical means comprises an aspheric lens and SIL (Solid Immersion Lens). 11. The signal recording method according to claim 10, wherein the objective lens constituting the optical means comprises an aspheric lens and a SIM (Solid Immersion Mirror). In a signal reproducing apparatus that reproduces a signal on an optical reproducing medium using near-field light by a light source and optical means,
Detecting means for detecting that it is a near field;
Approach means for approaching the optical means to the optical reproduction medium until a near field is reached;
After becoming a near field, control means for controlling the distance between the optical means and the optical reproduction medium to be constant,
Switching means for switching between the approach means and the control means by a signal for detecting that the near field,
Changing means for changing the control target value of the distance,
A signal reproducing device comprising: A light source that emits laser light; and an optical unit that is disposed close to a signal surface to the optical reproduction medium and condenses near-field light by the laser light on the optical reproduction medium. 20. The signal reproducing device according to claim 19, wherein the signal reproducing device detects that the signal is in a field state. The optical reproduction medium is disposed in the vicinity of a signal surface, and optical means for condensing near-field light by the laser light on the optical reproduction medium is provided. 20. The signal reproducing apparatus according to claim 19, wherein a distance between the two is fixed. 20. The signal reproducing apparatus according to claim 19, wherein after switching from the approaching means to the control means by a signal for detecting the near field, the approaching means at the distance is stopped. 20. The signal reproducing apparatus according to claim 19, wherein 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. 20. The signal reproducing apparatus according to claim 19, wherein the control target value of the distance is changed at predetermined time intervals after switching from the approach means to the control means by a signal for detecting the near field. 20. The signal reproducing apparatus according to claim 19, wherein said approach means and said control means operate independently of each other. 20. The signal reproducing apparatus according to claim 19, wherein the objective lens constituting the optical means comprises an aspherical lens and SIL (Solid Immersion Lens). 20. The signal reproducing apparatus according to claim 19, 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 an optical unit,
A detection step of detecting that it is a near field;
An approaching step of bringing the optical means closer to the optical reproduction medium until a near field is reached;
After becoming a near field, a control step of controlling the distance between the optical means and the optical reproduction medium to be constant,
A switching step of switching between the approaching step and the control step by a signal that detects that the near field,
A changing step of changing the control target value of the distance,
A signal reproducing method comprising: The detecting step includes: returning a laser beam by a light source that emits a laser beam; and an optical unit that is disposed close to a signal surface of the optical reproducing medium and condenses near-field light by the laser beam on the optical reproducing medium. 29. The signal reproducing method according to claim 28, wherein a near field state is detected based on a light amount. The controlling step includes: placing the optical unit in proximity to a signal surface of the optical reproduction medium; and condensing the near-field light by the laser light on the optical reproduction medium. 29. The signal reproducing method according to claim 28, wherein a distance from the reproducing medium is fixed. 29. The signal reproducing method according to claim 28, wherein, in the switching step, the approaching step of the distance is stopped after switching from the approaching step to the control step based on the signal for detecting the near field. 29. The signal reproducing method according to claim 28, wherein the control step is not operated until switching from the approach step to the control step by a signal for detecting the near field. 29. The signal reproducing method according to claim 28, wherein the control target value of the distance is changed every predetermined time after switching from the approach step to the control step by a signal for detecting the near field. 29. The signal reproducing method according to claim 28, wherein the approach step and the control step operate independently of each other. 29. The signal reproducing method according to claim 28, wherein the objective lens forming the optical means comprises an aspherical lens and SIL (Solid Immersion Lens). 29. The signal reproducing method according to claim 28, wherein the objective lens constituting the optical means comprises an aspheric lens and a SIM (Solid Immersion Mirror).

Images