JP2000200431A - Focus jumping method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a correct focus jump by executing a focus jump at a position focused on an optional signal recording surface during reproducing, braking an objective lens when the objective lens reaches a prescribed position of an S shaped curve which is observed from the other signal recording surface and focusing on the other signal recording surface. SOLUTION: Before a focus jump is executed, a switch 65 is connected to the side of a terminal 66, and a coil 63 of an actuator transferring an objective lens is controlled via an amplifier 62 based on a focus error signal. When the focus jump is executed, a jump pulse 64 is applied from a terminal 61, the switch 65 is simultaneously connected to a terminal 67, and the coil 63 of the actuator transferring the objective lens is controlled via the amplifier 62 from the side of the terminal 67. Timing for braking is set to a preliminarily measured time or is set with a time having elapsed after starting of the focus jump.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an apparatus for reproducing a plurality of types of optical disks having different substrate thicknesses.

[0002]

2. Description of the Related Art An optical disk having a thickness of about 1.2 mm, such as a CD-ROM, from which information is read using a semiconductor laser is provided. In this type of optical disk, focus servo and tracking servo are performed on a pickup objective lens to irradiate a pit row on a signal recording surface with a laser beam to reproduce a signal. Recently, the recording density for recording a long moving image has been increasing.

[0003] For example, the same 12 cm diameter as a CD-ROM
A DVD standard for recording 4.7 Gbyte information on one side of an optical disc has been proposed. The thickness of a DVD disk is about 0.6 mm, and 9.4 Gbyte information can be recorded on a single disc by bonding both sides. In order to reproduce the optical disk having the two signal recording surfaces, a method of reproducing two signal recording surfaces from one surface of the disk and a method of reproducing one signal recording surface from both surfaces of the disk can be considered. However, the method of reproducing one signal recording surface from each side requires that the disc be turned over when reproducing the other signal recording surface after the reproduction of one signal recording surface is completed. It is. Also, it is not possible to reproduce another signal recording surface while reproducing one signal recording surface. For this reason, 2
The method of reproducing one signal recording surface has become mainstream.

[0004]

In order to reproduce two signal recording surfaces from one surface of an optical disk, focus of an objective lens in an optical pickup during reproduction of one signal recording surface or after reproduction on another signal recording surface. Needs to be redone.
However, in the conventional method, when refocusing from one signal recording surface to another signal recording surface, a brake is applied to the objective lens when an S-shaped curve from the other signal recording surface starts to be observed, and Although an attempt was made to stop the objective lens at the focal point, the portion where the S-shaped curve began to be observed is usually 1 to the peak-to-peak value of the S-shaped curve.
Since there is about 0% noise, it is not possible to accurately determine whether or not the curve is an S-shaped curve from the signal recording surface to be reproduced, so that there is a problem that an accurate focus jump cannot be performed.

Therefore, the present invention solves such a problem,
An object of the present invention is to provide a method capable of accurately performing a focus jump from an arbitrary signal recording surface to another signal recording surface.

[0006]

The present invention uses an optical pickup for reproducing an optical disk having two or more signal recording surfaces using a laser beam, and focuses on an arbitrary signal recording surface during reproduction. A first step of performing a focus jump at a position, and when the objective lens in the optical pickup reaches a predetermined position of an S-shaped curve observed from another signal recording surface different from an arbitrary signal recording surface, Brake and focus on other signal recording surface 2nd
And the step of:

Further, the present invention uses an optical pickup for reproducing an optical disk having two or more signal recording surfaces by using a laser beam, and performs a focus jump at a position where an arbitrary signal recording surface being reproduced is in focus. And a second step of applying a brake to the objective lens in the optical pickup and focusing on another signal recording surface after a predetermined time has elapsed since the focus jump was performed. And

Further, the present invention uses an optical pickup for reproducing an optical disk having two or more signal recording surfaces by using a laser beam, and performs a focus jump at a position where an arbitrary signal recording surface being reproduced is in focus. A first step of applying a focus jump and a time from when a focus jump is applied until the objective lens in the optical pickup reaches a predetermined position of an S-shaped curve observed from another signal recording surface different from an arbitrary signal recording surface. A time is measured, and a voltage for applying a brake to the objective lens is determined based on the measured time.

Further, the present invention uses an optical pickup for reproducing an optical disk having two or more signal recording surfaces by using a laser beam, and performs a focus jump at a position where an arbitrary signal recording surface being reproduced is in focus. And the time from when the focus jump is applied to when the objective lens in the optical pickup reaches a predetermined position of the S-shaped curve observed from another signal recording surface different from the arbitrary signal recording surface. Is measured, and a time during which a brake is applied to the objective lens is determined based on the measured time.

Further, the present invention is characterized in that the predetermined position is in a range of 0 to 100% of the peak-to-peak value of the S-shaped curve. Further, the present invention is characterized in that the optical pickup is an optical pickup capable of compatible reproduction of optical disks having different substrate thicknesses. Further, the present invention is characterized in that the optical disk is an optical disk having a first signal recording surface and a second signal recording surface.

Further, according to the present invention, the first signal recording surface of the optical disk is at a position of 0.55 to 0.65 mm from the substrate surface, and the second signal recording surface is 40 to 70 μm from the first signal recording surface.
It is characterized by being separated.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to the drawings. According to the present invention, when a two-layer type optical disk having two signal recording surfaces is reproduced by using an optical pickup capable of reproducing interchangeably optical disks having different substrate thicknesses, the focus state of the laser beam is changed from the first signal recording surface. Second
A method for switching to a signal recording surface is disclosed. Referring to FIG. 1, two signal recording surfaces are arranged at a distance of 0.6 from the substrate surface.
A two-layer optical disk 1 located at a position of (tolerance ± 0.05) mm has a pit 3 on one side of a substrate 2 made of a translucent polycarbonate or the like, and a metal reflection formed to cover the pit 3. An optical disk having a substrate thickness of 0.6 mm (with a tolerance of ± 0.05 mm) on which a first signal recording surface 5 made of a film 4 is disposed, and a pit 7 on one of a substrate 10 made of a transparent polycarbonate or the like, An optical disk having a substrate thickness of 0.6 mm (with a tolerance of ± 0.05 mm) provided with a second signal recording surface 9 made of a metal reflection film 8 formed so as to cover the first signal recording surface 5 and the second signal recording surface 9 The two signal recording surfaces 9 are bonded together with the ultraviolet curing resin 6 so as to be inside. The thickness of the ultraviolet curing resin 6 is 40 to 70
μm, and the first signal recording surface 5 and the second signal recording surface 9 are separated by a distance of 40 to 70 μm. In the following, the dual-layer optical disc shown in FIG.
Called D.

Referring to FIG. 2, an optical disk 20 having a signal recording surface located at a position of 1.2 mm (allowable error ± 0.1) mm from the substrate surface is a substrate 21 made of translucent polycarbonate or the like. A signal recording surface 24 composed of a pit 22 and a metal reflection film 23 formed so as to cover the pit 22 is arranged on one of the two sides, and a protective film 25 is formed on the signal recording surface 24. Hereinafter, the optical disk shown in FIG. 2 is referred to as a CD.

FIG. 6 shows the rated values and reproduction conditions of a CD and a dual-layer DVD. The substrate thickness on the signal reading side of the CD is 1.2 (allowable range: 1.1 to 1.3) mm, and the shortest pit length is 0.90 (allowable range: 0.80 to 1.0) μm. Track pitch is 1.6 (allowable range: 1.5-1.7) μm
And the reflectance is 70% or more. In addition, two-layer DV
The substrate thickness on the signal reading surface side of D is 0.6 (allowable range: 0.55).
0.65) mm, the shortest pit length is 0.40 (permissible range: 0.30 to 0.5) μm, and the track pitch is 0.74 (permissible range: 0.73 to 0.75). μm,
The reflectivity is 20-40%.

The reproducing conditions are as follows: the wavelength of the laser beam is 635 (allowable range: 620 to 650) nm;
In this case, the spot diameter of the laser beam is 1.5 (allowable range: 1.4 to 1.6) μm, and the effective numerical aperture of the objective lens is 0.35 (allowable range: 0.30 to 0.40). In the case of a dual-layer DVD, the effective numerical aperture of the objective lens is 0.60
(Allowable range: 0.55 to 0.65).

FIG. 3 shows an optical pickup 60 capable of reproducing a CD and a two-layer DVD in a compatible manner. The optical pickup 60 is
Semiconductor laser 3 that emits a laser beam with a wavelength of 635 nm
1. Polarization plane rotating means 3 for rotating the polarization plane of a laser beam
2, a diffraction grating 35, a half mirror 36, a collimator lens 37, a polarization selecting means 38 for selectively blocking a laser beam, an objective lens 42, and a photodetector 43. The laser beam emitted from the semiconductor laser 31 reaches the half mirror 36 via the polarization plane rotating means 32 and the diffraction grating 35, is half-reflected by the half mirror 36, and is made parallel by the collimator lens 37. The light passes through the polarization selecting means 38, is condensed by the objective lens 42, and irradiates the signal recording surface 5 through the substrate of the optical disk. The laser beam reflected by the signal recording surface 5 returns via the objective lens 42, the polarization selecting means 38, and the collimator lens 37, passes through half by the half mirror 36, and condenses on the photodetector 43. Is detected.

The objective lens 42 has a substrate thickness of 0.6 mm.
The optical disc is designed so that light can be focused on the signal recording surface of the optical disc, and the numerical aperture is 0.6 (permissible range: 0.55 to 0.65). The polarization plane rotating means 32 controls the TN type liquid crystal 34 to 2
When a voltage is applied to the transparent electrode, a voltage is applied to the TN type liquid crystal, and the laser beam does not rotate the polarization plane of the TN type liquid crystal. pass. When no voltage is applied to the transparent electrode, the laser beam is rotated through its polarization plane by 90 degrees and passes through the TN liquid crystal.

The polarization selecting means 38 has a structure in which a polarizing filter 40 provided at a portion corresponding to the outer peripheral portion of a laser beam is sandwiched between two glasses 39, 39. , A filter 41 that does not exhibit polarization characteristics is provided. The polarizing filter 40 has a property of transmitting only a laser beam in a certain polarization direction, and in this embodiment, transmits only a laser beam polarized in a direction parallel to the paper surface. Therefore, the polarization selecting means 38 has the characteristics shown in FIG. That is, the outer peripheral portion 38a of the polarization selecting means 38 allows the polarization filter 40 to transmit only a laser beam polarized in a direction parallel to the paper surface,
The inner peripheral portion 38b transmits the laser beam regardless of the polarization direction of the laser beam. The polarizing filter 40 transmits a laser beam polarized in a direction parallel to the plane of the drawing, but has a transmittance of about 70 to 90%.
If no filter is provided, the transmittance of the laser beam differs between the inner and outer peripheral portions of the laser beam, which causes a reduction in reproduction characteristics. Therefore, it is necessary to provide the filter 41 on the inner periphery of the polarization selecting means 38.

The operation of reproducing a two-layer DVD having a substrate thickness of 0.6 mm on the signal reading surface side will be described. When a two-layer DVD is reproduced, a voltage is applied from the liquid crystal drive circuit 44 to the polarization plane rotating means 32. As a result, the laser beam having a wavelength of 635 nm emitted from the semiconductor laser 31 and polarized in a direction parallel to the plane of the paper is transmitted as it is without rotating the polarization plane by the polarization plane rotating means 32,
The light is half-reflected by the half mirror 36 via the diffraction grating 35 and is made parallel by the collimator lens 37.
The light passes through the entire outer periphery without being shielded by the polarization selecting means 38 and is condensed by the objective lens 42.
The signal is irradiated onto the signal recording surface 5 through the substrate 2 of the layered DVD 1. Subsequent operations are the same as those described with reference to FIG. The spot diameter of the laser beam applied to the signal recording surface 5 is 0.9 (allowable range: 0.80 to 1.0) μ.
m.

Next, the substrate thickness on the signal reading side is 1.2 mm.
Will be described. When a CD is reproduced, no voltage is applied to the polarization plane rotating means 32. As a result, the laser beam having a wavelength of 635 nm emitted from the semiconductor laser 31 and polarized in a direction parallel to the paper surface has its polarization plane rotated by the polarization plane rotating means 32 to 90 degrees.
Through the diffraction grating, is half-reflected by the half mirror 36, is converted into parallel light by the collimator lens 37, and is shielded only at the outer peripheral portion by the polarization selecting means 38. Collected at C
The signal is irradiated on the signal recording surface 24 through the substrate 21 of D20. The subsequent operation is the same as that described with reference to FIG. The diameter of the inner peripheral portion 38b of the polarization selector 38 is 0.6 (numerical aperture: 0.55-0.65),
In the case of an objective lens having an effective luminous flux diameter of 4 mm, a circular shape having a diameter of 2.3 (allowable error ± 0.2) mm so that the effective numerical aperture becomes 0.35 (allowable range: 0.30 to 0.40). I do. Further, when the effective light beam diameter is other than 4 mm, the size of the through hole is proportionally set to a size such that the effective numerical aperture becomes 0.35. The spot diameter of the laser beam applied to the signal recording surface 24 is 1.5 (permissible range: 1.4 to 1.6).
μm.

Referring to FIG. 5, a reproducing apparatus for compatible reproduction of optical disks having different substrate thicknesses will be described. The objective lens 42 in the optical pickup 60 is controlled by the servo mechanism 47 so that a signal to be reproduced is focused on a track formed as a pit row, and the laser beam is focused by the objective lens 42. The light is irradiated to the signal recording surface 5 through the substrate 2 of the optical disk. The laser beam reflected by the signal recording surface 5 is detected by the photodetector 43 and detected as a reproduction signal. The reproduced signal detected by the photodetector 43 is supplied to a preamplifier 45.
After a predetermined amplification is performed, the determination circuit 48 and R
The signal is sent to the F demodulation circuit 53 and the servo circuit 46. The servo circuit 46 controls the servo mechanism 19 based on the tracking error signal sent. Also, the discriminating circuit 4
Reference numeral 8 denotes a command circuit for identifying the type of the optical disk mounted on the reproducing apparatus on the basis of the transmitted signal.
Send to The command circuit 49 switches the numerical aperture of the objective lens 42 so as to match the identified optical disk, based on the received identification result.
Command 0. Further, the command circuit 49 is provided with a characteristic switching circuit 51 based on the transmitted identification result to switch to a demodulation circuit suitable for reproducing the identified optical disk.
Also issue a command. The NA switching circuit 50 switches the effective numerical aperture of the objective lens 42 via the liquid crystal driving circuit 44, and the characteristic switching circuit 51 switches the RF demodulation circuit 53.

When the optical disc is mounted on the reproducing apparatus, after the focus servo and the tracking servo are performed, the optical disc is rotated at a predetermined number of revolutions, and the signal is reproduced. The rotation of the optical disk at the predetermined number of rotations does not have to be performed after the focus servo and the tracking servo are performed, and the rotation of the optical disk may be started after the focus servo is performed. In the reproduction of the dual-layer DVD, one of the first signal recording surface 5 and the second signal recording surface 9 is focused on, for example, the first signal recording surface 5, and the signal is reproduced. When the second signal recording surface is to be reproduced during the reproduction operation from the first signal recording surface, a focus jump from the first signal recording surface 5 to the second signal recording surface 9 is performed. You need to refocus. In this case, the focus jump is performed by the focus jump circuit 4 provided in the servo circuit 46.
6a by controlling the servo mechanism 47. Referring to FIG. 7, usually, when the focus of the optical disk is pulled in, an S-shaped curve is generated while the objective lens 42 moves up and down in the vertical direction under the control of the servo mechanism 47. Point A in FIG.
B is the focus position. Assuming that the S-shaped curve generated from the first signal recording surface 5 is S1 and the S-shaped curve generated from the second signal recording surface 9 is S2, the point A of the S-shaped curve S1 is set during the reproduction of the first signal recording surface. The objective lens 42 is located. When a focus jump is performed in this state, the focus jumps to the position of the point C of the S-shaped curve S2 generated from the second signal recording surface 9, and the S-shaped curve S2 is observed in the direction of the arrow 14. Normally, when the objective lens 42 moves to the point C, the brake is applied to the objective lens 42 so that the objective lens 42 stops at the focal point B of the S-shaped curve S2 from the second signal recording surface 9. Although the control is performed, the region 13 shown in FIG. 7A is actually about 10% when it is larger than the peak value of the S-shaped curve as shown in FIG.
There is a degree of signal variation. Therefore, even when a focus jump is performed from the first signal recording surface 5 to the second signal recording surface 9, the timing for applying a brake to the objective lens 42 is not clear, and it is difficult to stop the objective lens 42 at the in-focus position B. is there. Therefore, in the present invention, the brake is applied at the timing when the objective lens 42 is located between the points C and B of the S-shaped curve S2, and the focus is turned on. The brake may be applied from the point C to the peak value of the S-shaped curve S2, or the brake may be applied from the peak value to the point B. Therefore,
The current value applied to the objective lens 42 differs depending on which of the points C and B applies the brake. That is, when a brake is applied at a point close to the focal point B, more current is applied.

In the above, the case where the focus jump is performed from the first signal recording surface 5 to the second signal recording surface 9 has been described.
Conversely, a focus jump from the second signal recording surface 9 to the first signal recording surface 5 is similarly performed. In order to clearly control the timing of applying the brake, a reference may be set to a predetermined level with respect to the peak-to-peak value of the S-shaped curve, and the brake may be applied based on this reference. In the present invention, the standards 11 and 12 are set in a range of 0 to 100% with respect to the peak-to-peak value of the S-shaped curve. When performing a focus jump from the first signal recording surface 5 to the second signal recording surface 9, the reference 11 is used, the point C is moved in the direction of the arrow 14, and the brake is applied at a timing exceeding the reference 11. When the focus jump is performed from the second signal recording surface 9 to the first signal recording surface 5, the reference 1
2 is used. In this case, a focus jump is performed in the state of the point B, and the objective lens 42 moves to the point D of the S-shaped curve S1 generated from the first signal recording surface. Thereafter, the brake moves in the direction of the arrow 15, so that the brake is applied at a timing exceeding the reference 12. In addition, criteria 11 and 12
Is set after measuring the peak-to-peak value of the s-shaped curve.

When a focus jump is performed, FIG.
The objective lens 42 is controlled by the circuit shown in FIG. This circuit includes a terminal 60 to which a focus error signal is input,
A terminal 61 to which a jump pulse 64 is applied and an amplifier 62
Before the focus jump is performed, the switch 65 is connected to the terminal 66 side, and controls the coil 63 of the actuator that moves the objective lens 42 via the amplifier 62 based on the focus error signal. When the focus jump is performed, the switch 6 is simultaneously turned on when the jump pulse 64 is applied from the terminal 61.
Reference numeral 5 is connected to a terminal 67, and controls a coil 63 of an actuator for moving the objective lens 42 from the terminal 67 side via an amplifier 62.

Further, the voltage value at the time of applying the brake may be determined based on the time from the start of the focus jump. For example, a focus jump is performed from point A, the objective lens 42 moves to point C, and thereafter, the arrow 14
When moving in the direction of, the time to reach the reference 11 for the first time and the time to reach the second time are measured in advance,
The value of the voltage to apply the brake is determined according to the measured time. In this case, when the brake is applied in the state where the reference 11 is reached for the second time, the voltage value is smaller than when the brake is applied in the state where the reference 11 is reached for the first time. In this case, the range of the applied voltage is in the range of 1-2V. This method can also be used when performing a focus jump from the second signal recording surface 9 to the first signal recording surface.

Further, the time for applying the brake may be determined according to the measured time. In this case, if the focus jumps from point A to point C and the brake is applied when the reference 11 is reached for the first time, the braking time is set longer, and the reference 11 is applied for the second time. If you want to apply the brake when it reaches, set the brake application time shorter. In this case, the braking time is on the order of 1 msec. This method can also be used when performing a focus jump from the second signal recording surface 9 to the first signal recording surface.

According to the method of setting the references 11 and 12 and applying a brake as described above, it is possible to determine from which signal recording surface the focus jump is performed. That is, if the brake is applied at a timing exceeding the reference 11, a focus jump from the first signal recording surface to the second signal recording surface is performed, and if the brake is applied at a timing exceeding the reference 12, the second signal recording surface 9 is obtained. Is a focus jump to the first signal recording surface 5.

In the above description, the case of a two-layer DVD having two signal recording surfaces has been described. However, the present invention is not limited to this, and it goes without saying that the present invention can be applied to a DVD having three or more signal recording surfaces.

[0029]

According to the present invention, a focus jump can be accurately performed in an optical reproducing apparatus capable of reproducing a CD and a two-layer DVD in a compatible manner. According to the present invention,
In a multilayer DVD having two or more signal recording surfaces, a focus jump from an arbitrary signal recording surface to another signal recording surface can be accurately performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a cross-sectional structure of a two-layer DVD.

FIG. 2 is a diagram showing a cross-sectional structure of a CD.

FIG. 3 is a diagram showing a configuration of an optical pickup that enables compatible reproduction of optical disks having different substrate thicknesses.

FIG. 4 is a diagram illustrating characteristics of a polarization selection unit.

FIG. 5 is a diagram showing a block diagram of a playback apparatus for compatible playback of optical discs having different substrate thicknesses.

FIG. 6 is a table showing rated values and reproduction conditions of a CD and a dual-layer DVD.

FIG. 7 is an S-shaped curve waveform observed when focusing is performed.

FIG. 8 is a diagram showing a circuit configuration when a focus jump is performed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Double-layer DVD 2 ... Substrate 3 ... Pit 4 ... Reflective film 5 ... 1st signal recording surface 6 ... UV curable resin 7 ... Pit 8 ... Reflection Film 9—second signal recording surface 10—substrate 11—reference 12—reference 13—region where no S-shaped curve is observed 31—semiconductor laser 32—polarization plane rotating means 33 ... Glass with transparent electrode 34 ... TN type liquid crystal 35 ... Diffraction grating 36 ... Half mirror 37 ... Collimator lens 38 ... Polarization selecting means 39 ... Glass 40 ... Polarization Filter 41 ... Filter 42 ... Objective lens

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5D117 AA02 CC01 DD03 FF02 FF27 GG02 5D119 AA09 BA01 BB01 BB13 DA05 DA12 EA03 KA11

Claims (8)

[Claims] An optical pickup for reproducing an optical disk having two or more signal recording surfaces by using a laser beam, wherein a focus jump is performed at a position where an arbitrary signal recording surface being reproduced is in focus. And when the objective lens in the optical pickup reaches a predetermined position of an S-shaped curve observed from another signal recording surface different from the arbitrary signal recording surface, brakes the objective lens, A second step of focusing on the signal recording surface. 2. An optical pickup for reproducing an optical disk having two or more signal recording surfaces by using a laser beam, wherein a focus jump is performed at a position where an arbitrary signal recording surface being reproduced is in focus. And a second step of applying a brake to the objective lens in the optical pickup and focusing on the other signal recording surface after a predetermined time has elapsed since the focus jump was performed. Focus jump method. 3. A first method for performing a focus jump at a position where an arbitrary signal recording surface being reproduced is in focus by using an optical pickup for reproducing an optical disk having two or more signal recording surfaces using a laser beam. And the time from when the focus jump is applied to when the objective lens in the optical pickup reaches the predetermined position of the S-shaped curve observed from another signal recording surface different from the arbitrary signal recording surface. A focus jump method, comprising: measuring and determining a voltage for applying a brake to the objective lens based on the measured time. 4. An optical pickup for reproducing an optical disk having two or more signal recording surfaces by using a laser beam, and performing a focus jump at a position where an arbitrary signal recording surface being reproduced is in focus. And the time from when the focus jump is applied to when the objective lens in the optical pickup reaches the predetermined position of the S-shaped curve observed from another signal recording surface different from the arbitrary signal recording surface. A focus jump method, comprising: measuring, and determining a time during which a brake is applied to the objective lens based on the measured time. 5. The focus jump method according to claim 1, wherein the predetermined position is in a range of 0 to 100% of a peak-to-peak value of the S-shaped curve. 6. The focus jump method according to claim 1, wherein the optical pickup is an optical pickup capable of compatible reproduction of optical disks having different substrate thicknesses. 7. The focus jump method according to claim 6, wherein the optical disk is an optical disk having a first signal recording surface and a second signal recording surface. 8. The optical disk according to claim 7, wherein the first signal recording surface of the optical disk is located at a distance of 0.
55 to 0.65 mm, wherein the second signal recording surface is 40 to 7
A focus jump method characterized by being separated by 0 μm.