KR100712895B1 - Method for correcting spherical aberration of optical disc and suitable device - Google Patents

Abstract

The present invention relates to spherical aberration correction of an optical disc, and more particularly, to a spherical aberration correction method for coping with an uneven thickness of an optical disc and a device suitable therefor.

According to the present invention, a method of correcting spherical aberration according to a thickness deviation of an optical disc comprises: dividing an optical disc into a plurality of zones in a radial direction and measuring a spherical aberration correction value in each zone; And correcting spherical aberration at any position of the optical disk by linear interpolation of spherical aberration correction values of adjacent zones.

In the spherical aberration correction method according to the present invention, the spherical aberration correction value is measured by dividing the optical disc into a plurality of areas, and the spherical aberration correction is performed by interpolation using the measured spherical aberration correction values at arbitrary positions on the optical disc. Effectively cope with the thickness variation.

Description

Method of correcting spherical aberration of optical disks and a device suitable thereto

1 is a flowchart showing a method of correcting spherical aberration of an optical disk according to a preferred embodiment of the present invention.

2A and 2B schematically show an interpolation method using spherical aberration correction values for each zone in the method shown in FIG. 1.

FIG. 3 schematically shows the principle of a three-point measuring method for measuring spherical aberration correction values in each zone in FIG. 1.

4 is a block diagram showing the configuration of an optical disk drive according to a preferred embodiment of the present invention.

5A and 5B show an example and operation of the spherical aberration corrector shown in FIG. 4.

The present invention relates to spherical aberration correction of an optical disc, and more particularly, to a spherical aberration correction method for coping with an uneven thickness of an optical disc and a device suitable therefor.

Currently, optical recording media mainly used include CDs and DVDs, and recently, a Blu-ray Disc (BD) has been released.

The emergence of new optical record carriers, such as Blu-ray discs, is intended to increase recording density. The size of the light spot incident on the optical disc is proportional to the wavelength [lambda] of the light used and inversely proportional to the numerical aperture (NA) of the objective lens. Therefore, increasing the recording density of the optical recording medium is made possible by shortening the wavelength of the light source or increasing the numerical aperture of the objective lens.

Blu-ray discs use a wavelength of 650 nm and NA 0.6, but Blu-ray discs have a thickness of approximately 0.1 mm (the thickness of the protective layer in the distance from the light incident surface to the information recording surface, here the thickness of the protective layer). It is a standard having a wavelength of around 405 nm and has a recording capacity of about 25 GB.

Due to such a difference in numerical aperture, the effect of spherical aberration on Blu-ray discs is relatively larger than that of DVDs. Spherical aberration means that the light rays passing through the periphery of the lens and the light rays passing through the center are different from each other due to the difference in refractive index between the periphery and the center of the lens. For optical disc drives, spherical aberration is reflected from the recording surface. The energy of the light beam is lowered, that is, the performance is lowered.

As shown in Equation 1, spherical aberration W is proportional to the fourth power of the objective lens numerical aperture, so that the influence of spherical aberration is larger in Blu-ray discs than in DVD.

On the other hand, spherical aberration is not only proportional to the fourth power of the objective lens numerical aperture, but also proportional to the thickness deviation Δt of the recording medium, as shown in equation (1). Therefore, to adopt an objective lens having a high aperture of about 0.85, such as a Blu-ray disc, the recording medium must have a uniform thickness within ± 3 μm. However, it is extremely difficult to manufacture the recording medium within the above thickness deviation range.

Accordingly, it is necessary to efficiently correct the influence of spherical aberration due to thickness variation in the Blu-ray disc.

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and an object thereof is to provide a spherical aberration correction method for effectively correcting the influence of spherical aberration due to thickness variation of the recording medium in an optical disc recording medium.

Another object of the present invention is to provide an optical disk drive suitable for the above-described spherical aberration correction method.

Spherical aberration correction method according to an embodiment of the present invention to achieve the above object

In the method for correcting the spherical aberration according to the thickness deviation of the optical disk,

Dividing the optical disc into a plurality of zones in a radial direction and measuring spherical aberration correction values in each zone; And

And correcting spherical aberration at any position of the optical disk by linear interpolation of spherical aberration correction values of adjacent zones.

Here, the size of the zones is preferably uniform.

In addition, the above method

Changing the layer of the optical disc; And

Measuring spherical aberration correction value for the zones of the changed layer;

The correction process preferably corrects spherical aberration for each layer / zone.

An optical disk drive according to an embodiment of the present invention to achieve the above another object

An optical pickup detecting an electrical signal corresponding to the light beam reflected from the optical disc;

A spherical aberration correcting unit for correcting spherical aberration due to thickness variation of the optical disk;

A sled motor for moving the optical pickup in the radial direction of the disk;

An optical signal processor for generating an electrical signal corresponding to spherical aberration by using the signal detected by the optical pickup; And

The optical signal processor generates the optical pickup by moving the optical pickup to one of a plurality of zones divided in the radial direction of the optical disk, and changing a spherical aberration correction value applied to the spherical aberration corrector within a predetermined range. Obtain spherical aberration correction values in the plurality of zones by measuring a spherical aberration correction value at which an electrical signal is maximum or minimum, and interpolate using spherical aberration correction values in adjacent zones at any position of the optical disc. And a control unit for calculating a spherical aberration correction value and providing the corrected spherical aberration correction unit.

Hereinafter, the configuration and operation of the present invention will be described in detail with reference to the accompanying drawings.

1 is a flowchart showing a method of correcting spherical aberration of an optical disk according to a preferred embodiment of the present invention.

First, a first layer (initial layer) is set. (S102) In the multi-layer optical disc, there may be a thickness variation for each layer, so it is preferable to correct spherical aberration for each layer.

It moves to the first zone (initial zone). (S104) In the embodiment of the present invention, the optical disc is divided into a plurality of zones in the radial direction, and one sample point exists in each zone. That is, the innermost and outermost circumferences of the optical disc are divided into a plurality of zones, and sample points are set for each zone. The size of the zones, that is, the size in the radial direction of the optical disc, is preferably uniform.

The spherical aberration correction value is measured. (S106) Spherical aberration correction values are measured at sample points of each zone, where the spherical aberration correction value is preferably obtained by a three-point measurement method. The three-point measuring method will be described later with reference to FIG. 3.

Move to next zone (s108)

It is checked whether the measurement of the spherical aberration correction value for all the zones is completed (s110).

If the measurement of the spherical aberration correction value for all the zones is not completed, the process returns to s106.

If it is determined in step S110 that the measurement of the spherical aberration correction value is completed for all the zones, it is checked whether the measurement of the spherical aberration correction value for all the layers is completed (s112).

If the measurement of the spherical aberration correction value for all the layers is not completed, the next layer is set (s114) and the process returns to step s104.

If the measurement of the spherical aberration correction value for all the layers is completed, the spherical aberration correction values for each layer / zone are stored (s116).

Correcting the spherical aberration at an arbitrary position on the optical disc by using the spherical aberration correction values for each layer / zone obtained through the processes s102 to s116 is performed as follows.

Spherical aberration correction values are obtained at arbitrary positions and layers of the optical disc by interpolation using spherical aberration correction values in adjacent zones, that is, sample points (s118).

The spherical aberration caused by the thickness deviation of the optical disc is corrected by using the spherical aberration correction value obtained in step s118.

In the spherical aberration correction method according to the preferred embodiment of the present invention as shown in Fig. 1, the spherical aberration correction values are measured at a plurality of sample points on the optical disc, and the spherical surface at adjacent sample points at an arbitrary position on the optical disc. Spherical aberration correction values are obtained by interpolation using aberration correction values.

2A and 2B schematically show an interpolation method using spherical aberration correction values for each zone in the method shown in FIG. 1. Referring to FIGS. 2A and 2B, an optical disc is divided into a plurality of zones, for example, five zones (zones 1 to 5) in the radial direction from the innermost circumference to the outermost circumference, and one sample point (for each zone) d1 to d5) are set.

The thickness of the optical disc is not uniform and varied as shown by the dotted lines in FIG. 2A. The spherical aberration correction value for the optical disk having a thickness distribution as shown in FIG. 2A may be assumed to have a trajectory as shown by the dotted line in FIG. 2B.

According to a preferred embodiment of the present invention, the optical disc is divided into a plurality of zones in the radial direction, spherical aberration correction values at sample points of each zone are measured, and spherical aberration correction values at positions between sample points are Obtained by interpolation. Therefore, referring to FIG. 2B, it can be seen that more accurate spherical aberration correction can be performed as the number of sample points, that is, the number of zones or the number of sample points for each zone increases.

FIG. 3 schematically shows the principle of a three-point measuring method for measuring spherical aberration correction values in each zone in FIG. 1. The three-point measurement method assumes that the spherical aberration has a symmetrical parabolic trajectory according to the quadratic equation with respect to the spherical aberration correction value and estimates the optimal spherical aberration correction value by measuring only three points, that is, three spherical aberration correction values. Way.

Although there is a method of measuring spherical aberration while gradually changing the spherical aberration correction value over a certain range, and obtaining an optimal spherical aberration correction value by using the measured trajectory, this is a large number of samples, which requires a lot of measurement time. The three-point method compensates for these shortcomings and makes it possible to estimate the optimal spherical aberration correction in a short time.

Spherical aberration is known to have a parabolic trajectory represented by a quadratic equation centered on an optimal spherical aberration correction value. Thus, by measuring such a tracking error signal (TE) for any of the three spherical aberration correction values _{(X 0, X x, X} -x) of the interval, the quadratic equation, as shown in Figure 3 using these The parabola to be expressed and the inflection point of the parabola are estimated, and the amounts of spherical aberration at the positions (TE _{+ α} , TE _-α ) separated by a constant distance (+ α, _-α ) from the estimated inflection point (TE ₀ ) By verifying the same, the optimum spherical aberration correction value can be estimated simply.

If, by a predetermined distance from the estimated inflection points (TE ₀₎ -, the spherical aberration at (+ α, α) to a position away (TE _{+ α, -α} TE) not the same, some of the estimated inflection points (TE ₀₎ As you move through them, you search for the best spherical aberration correction.

In one embodiment of the present invention, the amount of spherical aberration is measured as the magnitude (TE) of the tracking error signal. Since the tracking error signal TE is represented as a difference signal between photodetection signals generated by a quadrature or eighth split photodetector, the tracking error signal TE can represent spherical aberration caused by a focal difference between light in the center and the periphery of the objective lens. However, the amount of spherical aberration can be determined not only by the tracking signal but also by an electrical signal corresponding to the spherical aberration, for example, an RF signal or jitter used for data reproduction. Note that the jitter amount with respect to the spherical aberration correction value is opposite to the graph showing the relationship between the tracking error signal and the spherical aberration shown in FIG. 3, that is, the direction of the parabola is reversed.

4 is a block diagram showing the configuration of an optical disk drive according to a preferred embodiment of the present invention. Referring to FIG. 4, the optical disk 402, the optical pickup 404, the tracking error signal generator 406, the spherical aberration corrector 408, the sled motor 410, the spindle motor 412, and the controller 414. ) Is shown. Optical pickup 404 includes a well-known photodetector (not shown) for detecting light beams reflected from optical disk 402.

The tracking error signal generator 406 generates the tracking error signal TE by using the photodetection signal generated by the photodetector of the optical pickup 404. The spherical aberration correcting unit 408 is for correcting spherical aberration due to the thickness variation of the optical disc 402, and may have a configuration as shown in FIG.

The sled motor 410 is for moving the optical pickup 404 in the radial direction of the optical disk, and the spindle motor 412 is for rotating the optical disk 402.

The controller 414 measures and stores spherical aberration correction values for each layer / zone for spherical aberration correction, and performs spherical aberration correction at an arbitrary position of the optical disc 402 using the stored spherical aberration correction values for each layer / zone. .

Measurement of spherical aberration correction values for each layer / zone by the controller 414 is performed as follows.

The controller 414 controls the sled motor 410 to move the optical pickup 404 to one of the plurality of zones (zones 1 to 5 of FIGS. 2A and 2B) that exist in the radial direction of the optical disc 402. Let's do it.

Then, the control unit 414 changes the spherical aberration correction value applied to the spherical aberration correction unit 408 within a predetermined range, while the tracking error signal TE generated by the tracking error signal generation unit 406 becomes the maximum. Measure the aberration correction value. For example, the controller 414 estimates the spherical aberration correction value in the zone by the three point measurement method as described with reference to FIG. 3.

By performing the same process for the other zones and layers, spherical aberration correction values for each layer / zone are obtained. The controller 414 stores the obtained spherical aberration correction values for each layer / zone.

On the other hand, spherical aberration correction at an arbitrary position of the optical disc by the controller 414 is performed as follows.

The controller 414 calculates the spherical aberration correction value SA at the corresponding position by interpolation using the spherical aberration correction values at the sample points adjacent to the position at an arbitrary position of the optical disc 402. The controller 414 provides the calculated spherical aberration correction value SA to the spherical aberration correction unit 408. The spherical aberration correction unit 408 performs spherical aberration correction according to the spherical aberration correction value SA provided from the control unit 414.

In one embodiment of the present invention, the amount of spherical aberration is measured as the tracking error signal TE generated by the tracking error signal generator 406. However, the amount of spherical aberration can be determined not only by the tracking signal but also by an electrical signal corresponding to the spherical aberration, for example, the amount of RF signal or jitter used for data reproduction. Thus, instead of the tracking error signal generator 406, an RF signal generator for generating an RF signal or a jitter signal generator for generating an electrical signal corresponding to the amount of jitter may be used. Note, however, that when jitter is used, there is an inverse relationship between the amount of jitter and spherical aberration.

In one embodiment of the present invention, the tracking error signal generator 406 is adopted, but is not necessarily limited thereto. Accordingly, the tracking error signal generator 406 in the embodiment shown in FIG. 4 corresponds to the optical signal processor in the summary of the present invention.

5A and 5B show an example and operation of the spherical aberration corrector shown in FIG. 4.

A simple example of spherical aberration correction is to install a concave lens 506 behind the collimator lens 504 and to control the distance between them. The collimator lens 504 has a function of varying the diameter of the light beam incident on the objective lens 502. Referring to FIGS. 5A and 5B, it is disclosed that the distance between the collimator lens 504 and the concave lens 506 is increased when the optical disk is thick (FIG. 5A), and when it is thin (FIG. 5B). . That is, by adjusting the distance between the collimator lens 504 and the concave lens 506, the spherical aberration is corrected by adjusting the refractive index of the light beam incident to the center portion of the objective lens 502 and the light beam incident to the peripheral portion.

The spherical aberration corrector 408 adjusts the distance between the objective lens 502 and the collimator lens 504 by moving the collimator lens 504 according to the spherical aberration correction value SA applied from the controller 414. As a result, spherical aberration according to the thickness deviation of the optical disc is corrected.

In the embodiment of the present invention, the tracking error signal TE is used to measure spherical aberration, but is not necessarily limited thereto. For example, a reproduction signal (ie, an RF signal) or jitter amount may be used instead of the tracking error signal TE. Note that the jitter amount with respect to the spherical aberration correction value is reversed from that shown in FIG. 3, that is, the direction of the parabola is reversed.

As described above, the spherical aberration correction method according to the present invention measures the spherical aberration correction value by dividing the optical disc into a plurality of regions, and corrects the spherical aberration correction by interpolation using the measured spherical aberration correction values at arbitrary positions on the optical disc. This makes it possible to effectively cope with the thickness variation of the optical disc.

Claims (9)

In the method for correcting the spherical aberration according to the thickness deviation of the optical disk, Dividing the optical disc into a plurality of zones in a radial direction and measuring spherical aberration correction values in each zone; And And correcting spherical aberration at any position of the optical disk by linear interpolation of spherical aberration correction values of adjacent zones. The spherical aberration correction method according to claim 1, wherein the zones have a uniform size in the radial direction of the optical disc. The method of claim 1, Changing the layer of the optical disc; And Measuring spherical aberration correction value for the zones of the changed layer; The correcting process corrects spherical aberration for each layer / zone. The method of claim 1, wherein the measuring of the spherical aberration correction value Detecting a change in magnitude of an electrical signal corresponding to spherical aberration while changing the spherical aberration correction value; And And determining an optimal spherical aberration correction value by referring to the magnitude change of the electrical signal. The method of claim 4, wherein the electrical signal is one of a tracking error signal, an RF signal, and a jitter signal. An optical pickup detecting an electrical signal corresponding to the light beam reflected from the optical disc; A spherical aberration correcting unit for correcting spherical aberration due to thickness variation of the optical disk; A sled motor for moving the optical pickup in the radial direction of the disk; An optical signal processor for generating an electrical signal corresponding to spherical aberration by using the signal detected by the optical pickup; And The optical signal processor generates the optical pickup by moving the optical pickup to one of a plurality of zones divided in the radial direction of the optical disk, and changing a spherical aberration correction value applied to the spherical aberration corrector within a predetermined range. Obtain spherical aberration correction values in the plurality of zones by measuring a spherical aberration correction value at which an electrical signal is maximum or minimum, and interpolate using spherical aberration correction values in adjacent zones at any position of the optical disc. And a control unit for calculating a spherical aberration correction value and providing the corrected spherical aberration correction unit. The optical disc drive of claim 6, wherein the optical signal processor is a tracking error signal generator. The optical disc drive of claim 6, wherein the optical signal processor is an RF signal generator. 7. The optical disc drive of claim 6, wherein the optical signal processor is a jitter signal generator that generates a jitter signal corresponding to the amount of jitter.

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