JP2003141766A - Device and method for recording/reproducing optical information - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device and a method for recording/reproducing the optical information having the small circuit scale and the simple constitution, while the thickness deviation of a substrate is detectable/correctable also for an optical recording medium whereon an RF signal is not being recorded beforehand. SOLUTION: A collimator lens 2 is moved in the optical axis direction by a driving circuit 14a within the specified range to make the spherical aberration change in the specified range, then the change of the amplitude of a focus error signal with respect to the change of the spherical aberration is observed. After that, the position of the collimator lens 2 in the optical axis direction is adjusted so that the amplitude of the focus error signal becomes maximum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording / reproducing apparatus and method for recording information on an optical recording medium or reproducing the recorded information, and more particularly to a substrate thickness deviation of the optical recording medium. The present invention relates to an optical information recording / reproducing apparatus and method capable of detecting and correcting the.

[0002]

2. Description of the Related Art Conventionally, the recording density in an optical information recording / reproducing apparatus is inversely proportional to the square of the diameter of a focused spot formed on an optical recording medium. That is, the smaller the diameter of the focused spot, the higher the recording density. The diameter of the focused spot is proportional to the wavelength of the light source and inversely proportional to the numerical aperture of the objective lens.

That is, the shorter the wavelength of the light source and the higher the numerical aperture of the objective lens, the smaller the diameter of the focused spot. On the other hand, if the thickness of the substrate of the optical recording medium deviates from the designed value, the shape of the focused spot is disturbed by the spherical aberration caused by the deviation of the substrate thickness, and the recording / reproducing characteristics deteriorate.

Since the spherical aberration is inversely proportional to the wavelength of the light source and is proportional to the fourth power of the numerical aperture of the objective lens, the shorter the wavelength of the light source is and the higher the numerical aperture of the objective lens is, the more the deviation of the substrate thickness of the optical recording medium from the recording / reproducing characteristics becomes. Margin becomes narrow.

Therefore, in the optical information recording / reproducing apparatus in which the wavelength of the light source is short and the numerical aperture of the objective lens is high in order to increase the recording density, in order to prevent the recording / reproducing characteristics from being deteriorated, the deviation of the substrate thickness of the optical recording medium is caused. It is necessary to detect and correct.

FIG. 10 shows a part of a conventional optical information recording / reproducing apparatus capable of detecting and correcting a substrate thickness deviation of an optical recording medium. This optical information recording / reproducing apparatus is described in Japanese Patent Application Laid-Open No. 2000-40237.

Light emitted from a semiconductor laser (not shown) is
2 composed of the first lens 15 and the second lens 16
It is focused on the disk 6 by a set of objective lenses. The first lens 15 is mounted on the first actuator 17, and is driven by the first actuator 17 in the optical axis direction.

A first lens 15 having a first lens 15 mounted thereon
The actuator 17 and the second lens 16 are mounted on the second actuator 18, and are driven by the second actuator 18 in the optical axis direction.

That is, by driving the first actuator 17, the first lens 15 and the second lens 16
Is changed, and by driving the second actuator 18, the distance between the disc 6 and the two objective lenses composed of the first lens 15 and the second lens 16 is changed.

When the distance between the first lens 15 and the second lens 16 changes, the spherical aberration changes, and when the distance between the two objective lenses and the disk 6 changes, the focus offset changes.

When the disc 6 has a substrate thickness deviation, the amplitude of the RF signal recorded on the disc 6 decreases due to spherical aberration caused by the substrate thickness deviation. The focus offset also reduces the amplitude of the RF signal recorded on the disk 6.

Therefore, while observing the amplitude of the RF signal recorded on the disk 6, the first actuator 17 is driven to change the distance between the first lens 15 and the second lens 16 so that the amplitude of the RF signal is changed. The distance between the first lens 15 and the second lens 16 is adjusted so as to maximize the distance.

While observing the amplitude of the RF signal recorded on the disk 6, the second actuator 18 is driven to change the distance between the two objective lenses and the disk 6,
The distance between the two objective lenses and the disc 6 is adjusted so that the amplitude of the RF signal becomes maximum.

That is, the substrate thickness deviation of the disk 6 is detected by observing the amplitude of the RF signal recorded on the disk 6, and the substrate thickness deviation of the disk 6 is corrected by the first lens 15 and the second lens 15. This is performed by adjusting the distance between the lenses 16 to generate spherical aberration in the optical information recording / reproducing apparatus that cancels spherical aberration caused by the substrate thickness deviation.

[0015]

However, in the prior art, when detecting the substrate thickness deviation of the optical recording medium, the RF signal needs to be recorded in advance in order to observe the amplitude of the RF signal. RF in a read-only optical recording medium
Since the signal is recorded in advance, the substrate thickness deviation can be detected. However, in the write-once and rewritable optical recording media, the RF signal is not recorded in advance, so the substrate thickness deviation can be detected. There is a problem that you cannot do it.

A method of detecting the substrate thickness deviation after recording an RF signal for detecting the substrate thickness deviation by the optical information recording / reproducing apparatus is also conceivable. In that case, the optical information recording / reproducing apparatus is a substrate. Since the optical information recording / reproducing apparatus does not correct the thickness deviation, the spherical aberration caused by the thickness deviation of the substrate disturbs the shape of the focused spot, and the RF signal cannot be correctly recorded.

On the other hand, as an optical information recording / reproducing apparatus capable of detecting a substrate thickness deviation even for an optical recording medium in which an RF signal is not recorded in advance, Japanese Patent Laid-Open No. 2000-57.
There is an optical information recording / reproducing device described in Japanese Patent No. 616 and an optical information recording / reproducing device described in Optical Data Storage Topical Meeting 2001 Technical Digest page 97-99.

However, in the former optical information recording / reproducing apparatus, since the reflected light from the optical recording medium is divided into the central portion and the peripheral portion to be received, the photodetector and the current-voltage conversion circuit connected thereto are provided. The scale of the arithmetic circuit is large and the configuration is complicated.

In the latter optical information recording / reproducing apparatus, the light emitted from the light source is divided into five lights by the diffractive optical element, and the five lights reflected by the optical recording medium are separately received. After all, the photodetector and the current-voltage conversion circuit, arithmetic circuit, etc. connected thereto are large in scale and complicated in configuration.

Therefore, the present invention solves the above-mentioned problems in the conventional optical information recording / reproducing apparatus capable of detecting and correcting the substrate thickness deviation of the optical recording medium, and the RF signal is recorded in advance. It is an object of the present invention to provide an optical information recording / reproducing apparatus and method capable of detecting and correcting a substrate thickness deviation even for an optical recording medium that does not exist and having a small circuit scale and a simple configuration.

[0021]

In order to solve the above-mentioned problems, an optical information recording / reproducing apparatus of the present invention comprises a light source, an objective lens for converging light emitted from the light source onto an optical recording medium, A photodetector that receives the reflected light from the optical recording medium, an arithmetic circuit that calculates at least a focus error signal based on the output from the photodetector, and the objective lens based on the focus error signal A means for obtaining a reference signal having an extreme value when the spherical aberration of the light focused on the optical recording medium is 0, a spherical aberration changing means for changing the spherical aberration, and a drive for driving the spherical aberration changing means. And a circuit.

The optical information recording / reproducing method of the present invention uses the above-described optical information recording / reproducing apparatus, and drives the spherical aberration changing means by the first drive circuit to change the spherical aberration. A first step, a second step of observing a change of the reference signal with respect to a change of the spherical aberration, and a third step of driving the spherical aberration changing means so that the reference signal has an extreme value. It is characterized in that recording or reproducing is performed on the optical recording medium in the state of performing the first to third steps.

Further, in the optical information recording / reproducing apparatus and method of the present invention, when the substrate thickness deviation of the optical recording medium is 0 and the spherical aberration caused by it is 0, the reference signal takes an extreme value. The larger the absolute value of the substrate thickness deviation of the optical recording medium and the larger the absolute value of the spherical aberration caused thereby, the larger the reduction amount or the increase amount of the reference signal.

Therefore, by driving the spherical aberration changing means so that the reference signal takes the extreme value, spherical aberration that cancels out the spherical aberration caused by the substrate thickness deviation of the optical recording medium occurs, and the total spherical aberration. Is 0.

That is, the substrate thickness deviation of the optical recording medium is corrected. Since the reference signal is obtained based on the focus error signal, it is possible to detect and correct the substrate thickness deviation even in an optical recording medium in which no RF signal is recorded in advance.

Further, since the reflected light from the optical recording medium and the emitted light from the light source are not divided and received in order to detect the substrate thickness deviation, the photodetector and the current-voltage conversion circuit connected to it, the operation The scale of the circuit is small and the configuration is simple.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 shows Embodiment 1 of the optical information recording / reproducing apparatus of the present invention. The emitted light from the semiconductor laser 1 is collimated by the collimator lens 2 and is incident on the polarization beam splitter 3 as P-polarized light, which is almost 100%.
Is transmitted, is transmitted through the quarter-wave plate 4, is converted from linearly polarized light into circularly polarized light, and is condensed on the disk 6 by the objective lens 5.

The reflected light from the disk 6 passes through the objective lens 5 in the opposite direction, passes through the quarter-wave plate 4 and is converted from circularly polarized light into linearly polarized light whose polarization direction is orthogonal to the forward path, and the polarization beam splitter 3 Almost 100% when incident as S-polarized light on
Is reflected, transmitted through the cylindrical lenses 7 and 8, and received by the photodetector 9. The photodetector 9 is installed in the middle of the two focal lines of the cylindrical lens 7 and the lens 8.

The arithmetic circuit 12 calculates the focus error signal and the focus sum signal based on the output from each light receiving portion of the photodetector 9. Here, the focus error signal is obtained by the astigmatism method. The drive circuit 14a moves the collimator lens 2 surrounded by the dotted line in the drawing in the optical axis direction by an actuator (not shown). When the collimator lens 2 is moved in the optical axis direction, the magnification of the objective lens 5 changes and the spherical aberration changes. When the spherical aberration changes, the amplitude of the focus error signal changes.

Therefore, first, the collimator lens 2 is moved in the optical axis direction within a predetermined range to change the spherical aberration within the predetermined range, and the change in the focus error signal amplitude with respect to the change in the spherical aberration is observed. Then, the position of the collimator lens 2 in the optical axis direction is adjusted so that the amplitude of the focus error signal becomes maximum. As a result, a spherical aberration that cancels the spherical aberration caused by the substrate thickness deviation of the disk 6 is generated in the objective lens 5, and the total spherical aberration becomes zero.

That is, the substrate thickness deviation of the disk 6 is corrected. The drive circuit 13 moves the objective lens 5 surrounded by the dotted line in the figure in the optical axis direction by an actuator (not shown). After the substrate thickness deviation of the disk 6 is corrected, focus servo is performed and the focus error signal becomes 0.
The position of the objective lens 5 in the optical axis direction is controlled so that

Substrate thickness deviation of the disk 6 is corrected, and recording or reproduction is performed on the disk 6 in a state where focus servo is performed. This eliminates adverse effects on the recording / reproducing characteristics.

FIG. 2 shows various focus error signals and focus sum signals. 2A to 2C correspond to the cases where the substrate thickness deviation of the disk 6 is negative (the substrate is thinner than the design), 0, and positive (the substrate is thicker than the design), respectively. In FIG. 2, the horizontal axis represents the defocus amount of the disc 6.

The solid and dotted lines shown in the figure represent the focus error signal and the focus sum signal, respectively. When the substrate thickness deviation of the disk 6 is negative, the zero-cross point of the focus error signal shifts to the right side of the figure and the amplitude of the focus error signal decreases as compared with the case where the disk thickness deviation of the disk 6 is zero.

On the other hand, when the substrate thickness deviation of the disk 6 is positive, the zero-cross point of the focus error signal shifts to the left side of the figure and the amplitude of the focus error signal decreases as compared with the case where the disk thickness deviation of the disk 6 is zero. To do.

FIG. 3 shows the relationship between the spherical aberration and the focus error signal amplitude. When the substrate thickness deviation of the disk 6 is 0 and the spherical aberration caused by it is 0, the amplitude of the focus error signal has a maximum value. The larger the absolute value of the substrate thickness deviation of the disk 6 and the larger the absolute value of the spherical aberration resulting therefrom, the larger the reduction amount of the amplitude of the focus error signal.

From this fact, by adjusting the position of the collimator lens 2 in the optical axis direction so that the amplitude of the focus error signal is maximized, the spherical aberration that cancels the spherical aberration caused by the substrate thickness deviation of the disk 6 is eliminated. It can be seen that the total spherical aberration generated by the objective lens 5 can be reduced to zero.

In this embodiment, instead of observing the amplitude of the focus error signal, the level of the focus sum signal can be observed to correct the substrate thickness deviation of the disk 6. When the spherical aberration changes, the level of the focus sum signal changes when the focus servo is performed.

Therefore, first, the focus servo is performed,
The drive circuit 13 controls the position of the objective lens 5 in the optical axis direction so that the focus error signal becomes zero. After performing the focus servo, the collimator lens 2 is moved in the optical axis direction by the drive circuit 14a within a predetermined range to change the spherical aberration within the predetermined range, and the change of the focus sum signal level with respect to the change of the spherical aberration is observed. .

After that, the position of the collimator lens 2 in the optical axis direction is adjusted so that the level of the focus sum signal is maximized. As a result, a spherical aberration that cancels the spherical aberration caused by the substrate thickness deviation of the disk 6 is generated in the objective lens 5, and the total spherical aberration becomes zero.

That is, the substrate thickness deviation of the disk 6 is corrected. Focus servo is performed, and recording or reproduction is performed on the disk 6 in a state where the substrate thickness deviation of the disk 6 is corrected. This eliminates adverse effects on the recording / reproducing characteristics.

In FIG. 2, when the substrate thickness deviation of the disk 6 is 0, the maximum point of the focus sum signal coincides with the zero cross point of the focus error signal. On the other hand, when the substrate thickness deviation of the disk 6 is negative, the maximum point of the focus sum signal and the zero-cross point of the focus error signal are shifted to the right side of the figure when the substrate thickness deviation of the disk 6 is 0.
The former shift amount is larger than the latter shift amount. Therefore, the level of the focus sum signal at the zero-cross point of the focus error signal decreases as compared with the case where the substrate thickness deviation of the disk 6 is zero.

On the other hand, when the substrate thickness deviation of the disk 6 is positive, the maximum point of the focus sum signal and the zero-cross point of the focus error signal are displaced to the left side of the figure when the substrate thickness deviation of the disk 6 is zero. The former shift amount is larger than the latter shift amount. Therefore, the level of the focus sum signal at the zero-cross point of the focus error signal decreases as compared with the case where the substrate thickness deviation of the disk 6 is zero.

FIG. 4 shows the relationship between the spherical aberration and the focus sum signal level. When the substrate thickness deviation of the disk 6 is 0 and the spherical aberration caused by the deviation is 0, the level of the focus sum signal in the state where focus servo is performed at the zero cross point of the focus error signal has a maximum value. The larger the absolute value of the substrate thickness deviation of the disk 6 and the larger the absolute value of the spherical aberration resulting therefrom, the larger the reduction amount of the level of the focus sum signal.

From this fact, by adjusting the position of the collimator lens 2 in the optical axis direction so that the level of the focus sum signal is maximized, the spherical aberration that cancels the spherical aberration caused by the substrate thickness deviation of the disk 6 is eliminated. It can be seen that the total spherical aberration generated by the objective lens 5 can be reduced to zero.

In the present embodiment, instead of observing the amplitude of the focus error signal, the loop gain of the focus servo can be observed to correct the substrate thickness deviation of the disk 6. When the spherical aberration changes, the loop gain of the focus servo changes when the focus servo is performed.

Therefore, first, the focus servo is performed,
The drive circuit 13 controls the position of the objective lens 5 in the optical axis direction so that the focus error signal becomes zero. After the focus servo is performed, the collimator lens 2 is moved in the optical axis direction by the drive circuit 14a within a predetermined range to change the spherical aberration within the predetermined range, and the change in the focus servo loop gain with respect to the change in the spherical aberration is observed. .

After that, the position of the collimator lens 2 in the optical axis direction is adjusted so that the loop gain of the focus servo becomes maximum. As a result, a spherical aberration that cancels the spherical aberration caused by the substrate thickness deviation of the disk 6 is generated in the objective lens 5, and the total spherical aberration becomes zero. That is, the substrate thickness deviation of the disk 6 is corrected. Focus servo is performed, and recording or reproduction is performed on the disk 6 in a state where the substrate thickness deviation of the disk 6 is corrected.

As a result, the recording / reproducing characteristics are not adversely affected. To observe the loop gain of the focus servo, superimpose the disturbance signal on the loop of the focus servo,
The compression ratio of the disturbance signal may be observed.

In FIG. 2, when the substrate thickness deviation of the disk 6 is negative, the zero-cross point of the focus error signal is shifted to the right side of the drawing and the amplitude of the focus error signal is 0 when the substrate thickness deviation of the disk 6 is zero. Decreases, and the slope at the zero cross point decreases. The loop gain of the focus servo is proportional to the slope of the focus error signal, so
The loop gain of the focus servo at the zero-cross point of the focus error signal decreases as compared with the case where the substrate thickness deviation of the disk 6 is zero.

On the other hand, when the substrate thickness deviation of the disk 6 is positive, the zero-cross point of the focus error signal is shifted to the left side of the figure and the amplitude of the focus error signal is reduced as compared with the case where the disk thickness deviation of the disk 6 is zero. However, the slope at the zero cross point decreases.

Since the loop gain of the focus servo is proportional to the inclination of the focus error signal, the loop gain of the focus servo at the zero cross point of the focus error signal is reduced as compared with the case where the substrate thickness deviation of the disk 6 is zero.

FIG. 5 shows the relationship between the spherical aberration and the focus servo loop gain. When the substrate thickness deviation of the disk 6 is 0 and the spherical aberration caused by it is 0, the loop gain of the focus servo in the state where the focus servo is performed at the zero cross point of the focus error signal has a maximum value. The larger the absolute value of the substrate thickness deviation of the disk 6 and the larger the absolute value of the spherical aberration caused thereby, the larger the decrease amount of the loop gain of the focus servo.

Therefore, by adjusting the position of the collimator lens 2 in the optical axis direction so that the loop gain of the focus servo becomes maximum, spherical aberration that cancels out spherical aberration caused by the substrate thickness deviation of the disk 6 is eliminated. It can be seen that the total spherical aberration generated by the objective lens 5 can be reduced to zero.

In the present embodiment, instead of observing the amplitude of the focus error signal, it is possible to observe the groove crossing noise of the focus error signal and correct the substrate thickness deviation of the disk 6. When the spherical aberration changes, the groove crossing noise of the focus error signal changes when the focus servo is performed.

Therefore, first, the focus servo is performed,
The drive circuit 13 controls the position of the objective lens 5 in the optical axis direction so that the focus error signal becomes zero. After performing the focus servo, the collimator lens 2 is moved in the optical axis direction by the drive circuit 14a within a predetermined range to change the spherical aberration within the predetermined range, and the change of the focus error signal groove crossing noise with respect to the change of the spherical aberration is changed. Observe.

After that, the position of the collimator lens 2 in the optical axis direction is adjusted so that the groove crossing noise of the focus error signal is minimized. As a result, a spherical aberration that cancels the spherical aberration caused by the substrate thickness deviation of the disk 6 is generated in the objective lens 5, and the total spherical aberration becomes zero.

That is, the substrate thickness deviation of the disk 6 is corrected. Focus servo is performed, and recording or reproduction is performed on the disk 6 in a state where the substrate thickness deviation of the disk 6 is corrected. This eliminates adverse effects on the recording / reproducing characteristics.

FIG. 6 shows various focus error signals.
FIGS. 6A to 6C correspond to cases where the substrate thickness deviation of the disk 6 is negative (the substrate is thinner than the design), 0, and positive (the substrate is thicker than the design), respectively. In FIG. 6, the horizontal axis represents the defocus amount of the disc 6.

Also, the thin solid line, thick solid line,
The thick dotted lines indicate the focus error signal when there is no groove on the disk 6 (focus error signal without groove), the focus error signal at the groove recess (land) when there is a groove on the disk 6 (land focus error signal), Focus error signal at the convex portion (groove) of the groove when the disk 6 has a groove (groove focus error signal)
Is represented.

When the substrate thickness deviation of the disk 6 is 0, the zero cross points of the focus error signal of the land and the focus error signal of the groove almost coincide with the zero cross points of the focus error signal without the groove. When the substrate thickness deviation of the disk 6 is negative, the zero-cross points of the land focus error signal and the groove focus error signal deviate to the right side of the figure compared to the case where the disk 6 substrate thickness deviation is 0, but the former deviation amount Is larger than the latter shift amount.

At this time, the focus error signal of the land has a negative offset and the focus error signal of the groove has a positive offset at the zero cross point of the focus error signal without the groove. Since the groove crossing noise of the focus error signal is the difference between these offsets, the groove crossing noise of the focus error signal at the zero cross point of the focus error signal without the groove increases as compared with the case where the substrate thickness deviation of the disk 6 is zero. .

On the other hand, when the substrate thickness deviation of the disk 6 is positive, the zero-cross points of the land focus error signal and the groove focus error signal are shifted to the left side of the figure when the disk thickness deviation of the disk 6 is zero. The former shift amount is smaller than the latter shift amount.

At this time, the focus error signal of the land has a negative offset and the focus error signal of the groove has a positive offset at the zero cross point of the focus error signal without the groove. Since the groove crossing noise of the focus error signal is the difference between these offsets, the groove crossing noise of the focus error signal at the zero cross point of the focus error signal without the groove increases as compared with the case where the substrate thickness deviation of the disk 6 is zero. .

FIG. 7 shows the relationship between spherical aberration and focus error signal groove crossing noise. When the substrate thickness deviation of the disk 6 is 0 and the spherical aberration caused by it is 0, the groove crossing noise of the focus error signal in the state where the focus servo is performed at the zero cross point of the focus error signal without the groove has a minimum value. The larger the absolute value of the substrate thickness deviation of the disk 6 and the larger the absolute value of the spherical aberration caused thereby, the larger the increase amount of the groove crossing noise of the focus error signal.

From this, by adjusting the position of the collimator lens 2 in the optical axis direction so that the groove crossing noise of the focus error signal is minimized, the spherical aberration that cancels the spherical aberration caused by the substrate thickness deviation of the disk 6 is compensated. It is understood that the aberration can be generated by the objective lens 5 and the total spherical aberration can be made zero.

(Embodiment 2) FIG. 8 shows Embodiment 2 of the optical information recording / reproducing apparatus of the present invention. This embodiment is shown in FIG.
In addition to the relay lenses 10a and 10b, the drive circuit 14a is replaced with the drive circuit 14b.

The arithmetic circuit 12 calculates the focus error signal and the focus sum signal based on the outputs from the respective light receiving portions of the photodetector 9. Here, the focus error signal is obtained by the astigmatism method. The drive circuit 14b moves either one of the relay lenses 10a and 10b surrounded by the dotted line in the figure in the optical axis direction by an actuator (not shown).

When either one of the relay lenses 10a and 10b is moved in the optical axis direction, the magnification of the objective lens 5 changes and the spherical aberration changes. When the spherical aberration changes, the amplitude of the focus error signal changes.

Therefore, first, the relay lenses 10a and 10
Either one of b is moved in the optical axis direction within a predetermined range to change the spherical aberration within the predetermined range, and the change of the focus error signal amplitude with respect to the change of the spherical aberration is observed.

After that, the position of one of the relay lenses 10a and 10b in the optical axis direction is adjusted so that the amplitude of the focus error signal becomes maximum. As a result, a spherical aberration that cancels the spherical aberration caused by the substrate thickness deviation of the disk 6 is generated in the objective lens 5, and the total spherical aberration becomes zero.

That is, the substrate thickness deviation of the disk 6 is corrected. The drive circuit 13 moves the objective lens 5 surrounded by the dotted line in the figure in the optical axis direction by an actuator (not shown). After the substrate thickness deviation of the disk 6 is corrected, focus servo is performed and the focus error signal becomes 0.
The position of the objective lens 5 in the optical axis direction is controlled so that

Substrate thickness deviation of the disk 6 is corrected, and recording or reproduction is performed on the disk 6 in a state where focus servo is performed. This eliminates adverse effects on the recording / reproducing characteristics.

In the present embodiment, as in the case of the first embodiment, instead of observing the amplitude of the focus error signal, the level of the focus sum signal, the loop gain of the focus servo, and the groove crossing noise of the focus error signal are observed to disc. It is also possible to correct the substrate thickness deviation of No. 6.

(Embodiment 3) FIG. 9 shows Embodiment 3 of the optical information recording / reproducing apparatus of the present invention. This embodiment is shown in FIG.
In addition to the liquid crystal optical element 11, the drive circuit 14a is replaced with a drive circuit 14c. The liquid crystal optical element 11 is divided into a plurality of concentric regions.

The arithmetic circuit 12 calculates the focus error signal and the focus sum signal based on the output from each light receiving portion of the photodetector 9. Here, the focus error signal is obtained by the astigmatism method. The drive circuit 14c applies a voltage to each region of the liquid crystal optical element 11 surrounded by the dotted line shown in the figure. When the voltage applied to each region of the liquid crystal optical element 11 is changed, the spherical aberration with respect to the transmitted light changes. When the spherical aberration changes, the amplitude of the focus error signal changes.

Therefore, first, the voltage applied to each region of the liquid crystal optical element 11 is changed in a predetermined range to change the spherical aberration in the predetermined range, and the change in the focus error signal amplitude with respect to the change in the spherical aberration is observed. .

After that, the voltage applied to each region of the liquid crystal optical element 11 is adjusted so that the amplitude of the focus error signal becomes maximum. As a result, the spherical aberration that cancels the spherical aberration caused by the deviation of the substrate thickness of the disk 6 becomes a liquid crystal optical element 11.
Occurs, and the total spherical aberration becomes zero.

That is, the substrate thickness deviation of the disk 6 is corrected. The drive circuit 13 moves the objective lens 5 surrounded by the dotted line in the figure in the optical axis direction by an actuator (not shown). After the substrate thickness deviation of the disk 6 is corrected, focus servo is performed and the focus error signal becomes 0.
The position of the objective lens 5 in the optical axis direction is controlled so that

Substrate thickness deviation of the disk 6 is corrected, and recording or reproduction is performed on the disk 6 in a state where focus servo is performed. This eliminates adverse effects on the recording / reproducing characteristics.

In the present embodiment, similarly to the first embodiment, instead of observing the amplitude of the focus error signal, the level of the focus sum signal, the loop gain of the focus servo, and the groove crossing noise of the focus error signal are observed to disc. It is also possible to correct the substrate thickness deviation of No. 6.

The value of the substrate thickness deviation of the disk 6 normally changes gently with respect to the radial position of the disk 6. Therefore, when the disc 6 is inserted into the optical information recording / reproducing apparatus, the position of the collimator lens 2 in the optical axis direction, which is a correction value for correcting the substrate thickness deviation of the disc 6, and the relay lenses 10a and 10b One of the positions in the optical axis direction or the voltage applied to each region of the liquid crystal optical element 11 is obtained at a plurality of radial positions of the disk 6, and interpolation is performed based on these correction values at the other radial positions of the disk 6. By obtaining the correction value, it is possible to obtain the correction value with sufficient accuracy for practical use in all the radial positions of the disk 6 in a short time.

[0084]

As described above, in the optical information recording / reproducing apparatus and method of the present invention, when the substrate thickness deviation of the optical recording medium is 0 and the spherical aberration caused by it is 0, the reference signal has an extreme value. Take The larger the absolute value of the substrate thickness deviation of the optical recording medium and the larger the absolute value of the spherical aberration caused thereby, the larger the reduction amount or the increase amount of the reference signal.

Therefore, by driving the spherical aberration changing means so that the reference signal takes the extreme value, spherical aberration that cancels the spherical aberration caused by the substrate thickness deviation of the optical recording medium occurs, and the total spherical aberration is generated. Is 0. That is, the substrate thickness deviation of the optical recording medium is corrected.

The effect of the optical information recording / reproducing apparatus and method of the present invention is that the substrate thickness deviation can be detected and corrected even for an optical recording medium in which no RF signal is recorded in advance, and the circuit scale can be improved. Is small and the configuration is simple. The former reason is that the reference signal is obtained based on the focus error signal. The latter reason is that the reflected light from the optical recording medium and the emitted light from the light source are not divided and received in order to detect the substrate thickness deviation.

[Brief description of drawings]

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

FIG. 2 is a first embodiment of an optical information recording / reproducing apparatus of the present invention.
6 is a diagram showing various focus error signals and focus sum signals in FIG.

FIG. 3 is a first embodiment of an optical information recording / reproducing apparatus of the present invention.
6 is a diagram showing a relationship between spherical aberration and focus error signal amplitude in FIG.

FIG. 4 is a first embodiment of an optical information recording / reproducing apparatus of the present invention.
6 is a diagram showing the relationship between spherical aberration and focus sum signal level in FIG.

FIG. 5 is a first embodiment of an optical information recording / reproducing apparatus of the present invention.
6 is a diagram showing a relationship between spherical aberration and focus servo loop gain in FIG.

FIG. 6 is a first embodiment of an optical information recording / reproducing apparatus of the present invention.
6 is a diagram showing various focus error signals in FIG.

FIG. 7 is a first embodiment of an optical information recording / reproducing apparatus of the present invention.
6 is a diagram showing a relationship between spherical aberration and focus error signal groove crossing noise in FIG.

FIG. 8 is a second embodiment of the optical information recording / reproducing apparatus of the present invention.
FIG.

FIG. 9 is a third embodiment of the optical information recording / reproducing apparatus of the present invention.
FIG.

FIG. 10 is a diagram showing a part of a conventional optical information recording / reproducing apparatus.

[Explanation of symbols]

1 Semiconductor laser 2 Collimator lens 3 Polarizing beam splitter 4 1/4 wave plate 5 Objective lens 6 discs 7 Cylindrical lens 8 lenses 9 Photodetector 10a, 10b relay lens 11 Liquid crystal optical elements 12 arithmetic circuit 13 Drive circuit 14a, 14b, 14c drive circuit 15 First lens 16 Second lens 17 First Actuator 18 Second Actuator

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 5D118 AA14 AA16 BA01 BC09 CA11                       CD02 DC04 DC05 DC12                 5D119 AA11 AA22 BA01 EA03 EB02                       EC01 JA02 JA09                 5D789 AA11 AA22 BA01 EA03 EB02                       EC01 JA02 JA09

Claims (17)

[Claims] 1. A light source, an objective lens for condensing light emitted from the light source on an optical recording medium, a photodetector for receiving reflected light from the optical recording medium, and an output from the photodetector. A calculation circuit for calculating at least a focus error signal based on the above, and an extreme value when the spherical aberration of the light focused on the optical recording medium by the objective lens based on the focus error signal is 0. An optical information recording / reproducing apparatus comprising: a means for obtaining a signal; a spherical aberration changing means for changing the spherical aberration; and a drive circuit for driving the spherical aberration changing means. 2. The optical information recording / reproducing apparatus according to claim 1, wherein the reference signal is an amplitude of a focus error signal. 3. The optical information recording / reproducing apparatus according to claim 1, wherein the reference signal is a level of a focus sum signal in a state where focus servo is performed. 4. The optical information recording / reproducing apparatus according to claim 1, wherein the reference signal is a loop gain of the focus servo when the focus servo is performed. 5. The optical information recording / reproducing apparatus according to claim 1, wherein the reference signal is a groove crossing noise of a focus error signal in a state where focus servo is performed. 6. A collimator lens is provided between the light source and the objective lens, and the spherical aberration changing means is means for moving the collimator lens in the optical axis direction. The optical information recording / reproducing apparatus according to any one of items. 7. A relay lens is provided between the light source and the objective lens, and the spherical aberration changing means is means for moving one of the two relay lenses in an optical axis direction. The optical information recording / reproducing apparatus according to any one of claims 1 to 5. 8. The liquid crystal optical element is provided between the light source and the objective lens, and the spherical aberration changing means is means for applying a voltage to the liquid crystal optical element. The optical information recording / reproducing apparatus according to any one of items. 9. A light source, an objective lens for condensing light emitted from the light source onto an optical recording medium, a photodetector for receiving reflected light from the optical recording medium, and an output from the photodetector. A calculation circuit for calculating at least a focus error signal based on the above, and an extreme value when the spherical aberration of the light focused on the optical recording medium by the objective lens based on the focus error signal is 0. An optical information recording / reproducing apparatus having a means for obtaining a signal, a spherical aberration changing means for changing the spherical aberration, and a drive circuit for driving the spherical aberration changing means is used, and the spherical aberration changing means is driven by the first driving means. A first process of driving the circuit to change the spherical aberration, a second process of observing a change of the reference signal with respect to the change of the spherical aberration, and the spherical aberration so that the reference signal has an extreme value. Means of change And a third step of driving the optical recording medium, wherein recording or reproduction is performed on the optical recording medium in the state where the first to third steps are performed. 10. The reference signal is the amplitude of a focus error signal, and the third step is a step of driving the spherical aberration changing means so that the amplitude of the focus error signal is maximized. The optical information recording / reproducing method according to claim 9. 11. The reference signal is a level of a focus sum signal in a state where focus servo is performed, and in the third step, the spherical aberration changing means is set so that the level of the focus sum signal is maximized. 10. The optical information recording / reproducing method according to claim 9, wherein the method is a driving process. 12. The reference signal is a loop gain of focus servo in a state of performing focus servo,
10. The optical information recording / reproducing method according to claim 9, wherein the third step is a step of driving the spherical aberration changing means so that a loop gain of the focus servo becomes maximum. 13. The reference signal is a groove crossing noise of a focus error signal in a state where focus servo is performed,
10. The optical information recording / reproducing method according to claim 9, wherein the third step is a step of driving the spherical aberration changing means so that the groove crossing noise of the focus error signal is minimized. 14. A collimator lens is provided between the light source and the objective lens, and the spherical aberration changing means is means for moving the collimator lens in the optical axis direction. The optical information recording / reproducing method according to any one of items. 15. A relay lens is provided between the light source and the objective lens, and the spherical aberration changing means is the second lens.
14. The optical information recording / reproducing method according to claim 9, which is a means for moving one of the two relay lenses in the optical axis direction. 16. A liquid crystal optical element is provided between the light source and the objective lens, and the spherical aberration changing means is means for applying a voltage to the liquid crystal optical element. The optical information recording / reproducing method according to any one of items. 17. A drive amount of the spherical aberration changing means, which is a correction value for correcting the substrate thickness deviation of the optical recording medium, is obtained at a plurality of radial positions of the optical recording medium, and based on these correction values. 17. The optical information recording / reproducing method according to claim 9, wherein a correction value at another radial position of the optical recording medium is obtained by interpolation.