JP2008192310A - Optical information recording device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To automatically adjust an optical system to a correct optimal point irrespective of positional shifting of a reproduced signal detector or a residual aberration of the optical system in a rewritable optical disk device or an optical information recording/reproducing device. <P>SOLUTION: A spherical aberration and a focal depth are roughly adjusted simultaneously by using tracking error signal amplitude (PP amplitude) and finely adjusted by using reproduced signal amplitude (RF amplitude). The spherical aberration is adjusted to its correct optimal point. Thus, reliability of a signal to be reproduced is improved. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to an optical disk device, an optical disk medium, and information recording / recording on a recording medium using light.
This is an optical information recording apparatus to be reproduced, and particularly relates to an optical information recording apparatus having a spherical aberration correction function.

As the density of optical discs and optical recording media is increased, the numerical aperture of the optical system is increased, and light having a shorter wavelength is used. Therefore, the problem of aberration due to manufacturing tolerances of lenses and recording media is increasing. For example, even for light of the same wavelength, the spherical aberration due to the tolerance of the cover layer thickness of the recording medium increases rapidly in proportion to the fourth power of the numerical aperture. In addition, by using light having a shorter wavelength, the influence of aberration increases in inverse proportion to the wavelength λ even with the same manufacturing tolerance.

Due to these factors, the optical head of a recent high-density optical information recording apparatus is required to have a spherical aberration correction function. In this specification, an apparatus for recording or reproducing information on a recording medium by means for irradiating light to the recording medium and means for receiving light from the recording medium is generally referred to as optical information recording. Let's call the device.

In the optical information recording apparatus, it is necessary to automatically adjust the spherical aberration at the same time as the focal point of the lens is automatically adjusted. Adjusting the amount of spherical aberration makes the lens apparent focus (optimal focal length)
Slightly changes and shifts, and in order to obtain an optimal adjustment state, it is necessary to adjust the spherical aberration amount and the focal depth (defocus) while simultaneously changing them.

Even if either the spherical aberration amount or the depth of focus does not correctly match the optimum point, the light spot cannot be reduced to a sufficiently small size necessary for high-density recording. In addition, both the spherical aberration and the depth of focus, due to manufacturing tolerances, will cause the zero point of the detection signal to shift if there is lens astigmatism or a photodetector misalignment. become unable. Therefore, it is necessary to search for the optimum point two-dimensionally while simultaneously changing the spherical aberration amount and the focal depth.

As a two-dimensional method of spherical aberration and depth of focus, a method of two-dimensional search of each value in four directions and eight directions has been proposed as disclosed in JP-A-2002-324328. For example, there is a problem that a long waiting time is required from when a medium is inserted into an optical disk device (drive) until it can be used.

The first object of the present invention is to overcome this problem. For example, after inserting an optical disk (medium) into an optical disk apparatus (drive), the spherical aberration and the depth of focus can be adjusted as fast as possible, and the waiting time can be reduced. The object is to provide a short optical disk device (optical information recording device).

Also, in the previously proposed method, when an unrecorded disc (medium) is inserted, there is no recorded portion of the mark, so that the reproduction signal amplitude (RF amplitude) does not affect the manufacturing tolerance. However, there was a problem that adjustment to the correct optimum point was impossible.

The second object of the present invention is to overcome the above-mentioned problems, and even when an unrecorded disk (medium) is inserted, the above-mentioned spherical aberration correction and the depth of focus can be adjusted simultaneously to the optimum point correctly. Information recording).

They also ease manufacturing tolerance limits and record large amounts of information at a lower cost.
It is an object to provide an inexpensive optical disk apparatus (optical information recording apparatus) that can reproduce information with high reliability.

JP 2002-324328 A

In the present invention, the spherical aberration and the depth of focus are coarsely adjusted simultaneously using the tracking error signal amplitude (PP amplitude) and finely adjusted using the reproduction signal amplitude (RF amplitude). At this time, since the position of the focal depth at which the tracking error signal amplitude becomes the maximum value changes when the amount of spherical aberration is changed, the amount of spherical aberration and the amount of spherical aberration are determined in advance according to the ratio of the amount of change in focal depth to this amount of spherical aberration. By changing the depth of focus simultaneously at a constant ratio, the time required for the two-dimensional search is shortened.

In addition, when the unrecorded optical disk (optical recording medium) is used, the adjustment of the spherical aberration amount and the focal depth does not have the reproduction signal amplitude, so when the tracking error signal amplitude can be adjusted to the maximum value. Once the mark is written on the medium, the spherical aberration and the depth of focus are finely adjusted to the correct optimum point using the reproduction signal obtained from the written mark.

Specifically, the optical information recording apparatus includes an amplitude detection unit for a reproduction signal, an amplitude detection unit for a tracking error signal, a variable correction unit for a spherical aberration amount, and a variable control unit for the focal depth of an objective lens. In the search for the maximum value of the tracking error signal amplitude, the focal depth and the spherical aberration correction amount are both changed before and after the tracking error signal amplitude detection with a constant ratio (formula <range) determined by the characteristics of the optical system. Automatically adjust aberration and depth of focus. Ideally, the ratio value is

A value within ± 60% of the value of the ratio of Δt and Δz obtained is used. Here, n is the refractive index of the transparent layer of the recording medium, NA is the numerical aperture of the objective lens, Δt is the correction amount of spherical aberration, and Δz is the shift amount (defocus amount) of the focal depth of the objective lens.

In the adjustment of the spherical aberration and the depth of focus, on the two-dimensional plot of the depth of focus and the spherical aberration correction amount, the search is performed in an oblique direction by searching for the maximum value of the tracking error signal amplitude, and the vertical and horizontal directions are performed by searching for the maximum value of the reproduction signal amplitude. To explore.

For a rewritable optical recording medium, after adjusting so as to increase the amplitude of the tracking error signal, a mark is recorded, and then adjusting to maximize the amplitude of the reproduction signal, thereby adjusting the spherical aberration.

At this time, as a mark pattern to be recorded, a mark repetitive pattern having a mark interval of 2 to 4 times the track interval of the data area is used.

Further, the mark recorded for the adjustment is erased after the adjustment for maximizing the amplitude of the reproduction signal.

Also, depending on the position of the information to be recorded / reproduced on the medium, spherical aberration is measured in advance at the inner and outer circumferences or both ends of the medium and calculated by linear interpolation to obtain a suitable depth of focus and the amount of spherical aberration. Set the correction control amount. Specifically, when a non-rotating recording medium is used, means for storing the optimum value of the correction control amount of the spherical aberration amount at the four corners of the medium (and the optimum value of the focal depth of the objective lens) is stored. The optimum values at both ends are interpolated according to the ratio of the distances from the four corners of the information to be recorded / reproduced to obtain the depth of focus and the correction control amount of the spherical aberration amount.

In the case of using a rotary recording medium, it has means for storing the optimum value of the correction control amount of the spherical aberration amount (and the optimum value of the focal depth of the objective lens) on the inner and outer circumferences of the medium, Depending on the track position of the information to be recorded / reproduced, the optimum values of the inner and outer circumferences are interpolated to obtain the depth of focus and the control amount for correcting the spherical aberration amount.

When a multilayer recording medium is used as the recording medium, the spherical aberration of each layer is measured in advance at the inner and outer circumferences or at both ends of the medium according to the position of information to be recorded and reproduced on the medium, and linear interpolation is performed. Calculate and add the offset just before the jump. (The interpolated value of the inner and outer circumferences is used during the interlayer jump.)
Specifically, it has means for storing an optimum value of the correction control amount of the spherical aberration amount in the uppermost layer and the lowermost layer, and as a correction control amount of the spherical aberration amount set when moving between a plurality of recording layers, Using the interpolation value of the optimum value of the spherical aberration amount at the position of the destination layer, as a correction control amount of the spherical aberration amount set when moving between a plurality of recording layers, the inner circumference of the destination layer and An interpolation value of the optimum value of the spherical aberration amount at the outer periphery is used, and the value is changed to the interpolation value before the jump.

Also, in these cases, when an initialized (recorded / formatted) disc (recording medium) is inserted, the reproduction signal amplitude starts with optimization, and an uninitialized recording medium is inserted. Start with optimization adjustment of tracking error signal amplitude.

Even if there is assembly tolerance or aberration of optical parts, it can be adjusted to the optimal point of correct spherical aberration,
The reliability of the signal to be reproduced can be improved. In the present invention, unrecorded (uninitialized)
Therefore, a wide variety of recording media can be recorded and reproduced because it can be adjusted to the correct optimum point. Further, in the present invention, when adjusting the spherical aberration, it is possible to adjust in advance that the optimum point of the focal depth is deviated, so that the adjustment waiting time after inserting the medium can be shortened and the operation can be performed immediately.

As a result, an optical disc apparatus with high recording density, high reliability, many types of compatible recording media, and good operability can be provided at low cost.

Hereinafter, embodiments of the present invention will be described with reference to FIGS. In order to facilitate understanding, the same reference numerals are given to the portions showing the same action in each drawing.

Spherical Aberration / Focal Depth Adjustment Method for Rewritable Optical Disc An example of the overall configuration of an optical disc apparatus (optical information recording apparatus) having a spherical aberration correction function according to the present invention will be described with reference to FIGS.

First, FIG. 2 shows an example of the overall configuration of an optical disc apparatus (optical information recording apparatus) having a spherical aberration correction function according to the present invention.

(Overall configuration of optical system)
An optical disk 8 as a recording medium is mounted on a motor 10 whose rotation speed is controlled by a rotation servo circuit 9. The medium is irradiated with light from the semiconductor laser 12 driven by the laser drive circuit 11. The light of the semiconductor laser 12 is emitted from a collimating lens 13
After passing through the beam shaping prism 14, the direction is changed by the reflecting mirror 15 and introduced toward the disk 8. The light reflected by the reflecting mirror 15 passes through the deflection beam splitter 16, the liquid crystal aberration correction element 17, and the λ / 4 plate 18, and is condensed and irradiated onto the disk 8 by the objective lens 19. The objective lens 19 is mounted on the actuator 20 so that the focal position can be driven in the track direction by the signal of the tracking servo circuit 21 and in the focal depth direction (focus direction) by the signal of the focus servo circuit 22. ing.
At this time, the liquid crystal aberration correction element 17 causes a substrate thickness error of the disk 8 and the objective lens 1.
The spherical aberration caused by 9 is corrected. The spherical aberration correction element is a spherical aberration correction drive circuit 2.
In accordance with the control voltage 3, the refractive index distribution is different between the inner periphery and the outer periphery of the light beam, and the advance and delay of the wavefront are compensated to compensate for spherical aberration. By correcting the spherical aberration, the focused light spot can be narrowed down sufficiently. With this light, a fine mark pattern recorded on the disk 8 is read or a mark pattern is recorded. A part of the light irradiated by the disk 8 is reflected, passes through the objective lens 19, the λ / 4 plate 18 and the liquid crystal aberration correction element 17 again, and this time by the deflecting beam splitter 16, this time the cylindrical lens 2.
4 directions are separated. The separated light passes through the cylindrical lens 24 and the condenser lens 25, is detected by the quadrant photodetector 26, and is converted into an electric signal. This electrical signal is amplified by a photocurrent amplifier 27, and added and subtracted based on this signal to obtain a tracking error signal generation circuit 28.
The focus error signal generation circuit 29 generates a focus error signal, and the reproduction signal generation circuit 30 generates a reproduction signal. The tracking error signal is detected and output by the tracking error signal amplitude detection circuit 32. The reproduction signal amplitude is detected by a reproduction signal amplitude detection circuit 33 and output. Based on these signal amplitude signals, the correction amount generation circuit 34 detects them. The above configuration is the same as the configuration of a general optical disc apparatus except for the portion related to spherical aberration correction (liquid crystal aberration correction element 17, spherical aberration correction drive circuit 23, correction amount generation circuit 34).

On the other hand, the obtained tracking error signal is also supplied to the tracking servo circuit 21 to control the position of the objective lens 19 in the track direction. The focus error signal is supplied to the focus servo circuit 22 after the defocus signal (focus depth correction amount signal) is added by the defocus amount addition circuit 31, and the focus depth of the objective lens 19 is controlled. The reproduced signal is converted into the original digital signal recorded by the decoding circuit 38 through the equivalent circuit 35, the level detection circuit 36, and the synchronous clock generation circuit 37. These series of circuits are controlled by the main control circuit 39 in an integrated manner.

The correction amount generation circuit 34 detects the tracking error signal amplitude and the reproduction signal amplitude, and generates a spherical aberration correction amount signal and a defocus signal. Next, the operation of the correction amount generation circuit 34 will be described.

(Spherical aberration correction amount generation circuit)
The correction amount generation circuit 34 functions to generate a correct spherical aberration correction amount and a defocus amount from the behavior of the tracking error signal amplitude and the reproduction signal amplitude. The defocus amount is a depth of focus correction amount, which is a focus depth offset amount indicating how much the focus is shifted from the point where the focus error signal becomes zero. Below,
This offset of the focal depth is referred to as defocus.

FIGS. 3 to 4 show the behavior of the tracking error signal amplitude and the reproduction signal amplitude when spherical aberration occurs. These are the ideal states obtained by optical calculation.

FIG. 3 shows changes in the tracking error signal amplitude with respect to the spherical aberration amount and the focal depth. The distribution is a mountainous distribution with slender peaks in the diagonal direction. This indicates that when the focal depth is not correct, the tracking error signal peaks at a position different from the correct focal position where the spherical aberration is corrected. Therefore, in order to adjust to the correct in-focus position, it is necessary to adjust the spherical aberration amount and the depth of focus toward the peak of the slender and gentle peak (the maximum value of the tracking error signal amplitude) while simultaneously adjusting both the spherical aberration amount and the focal depth. It is shown that. However, since the tracking error signal amplitude is likely to be uneven depending on the location due to the rotation of the disk, there are many cases where sufficient adjustment cannot be made by this adjustment alone. In addition, the peak peak position may deviate from the correct in-focus position due to other aberrations (such as astigmatism) other than the spherical aberration of the optical system.

On the other hand, FIG. 4 shows changes in the reproduction signal amplitude with respect to the spherical aberration amount and the focal depth. The distribution has a slightly sharp peak in the center and many small false peaks around it.
Since the central peak is not diagonal, it is easy to find the correct in-focus position near the center of the peak. Therefore, in order to adjust to the correct in-focus position, it is only necessary to adjust toward the peak peak (maximum value of the reproduction signal amplitude) while alternately adjusting the spherical aberration amount and the focal depth. The peak peak position is stable at a relatively correct in-focus position even with other aberrations (such as astigmatism). However, in the case of an unrecorded disc (uninitialized / unformatted disc), the mark has not yet been written, so that the reproduction signal amplitude cannot be detected.

Therefore, in order to adjust the spherical aberration correctly even on an unrecorded disc, first, the maximum value of the tracking error signal amplitude in FIG. 3 is searched, and both the spherical aberration amount and the focal depth are adjusted at the same time. This is a two-stage adjustment that writes the mark that is the source of the reproduction signal, uses the reproduction signal of that mark, finds the maximum value of the reproduction signal amplitude in FIG. 4, and adjusts the spherical aberration amount and the depth of focus. Necessary. This procedure is shown in FIG.

Based on the signal from the main control circuit 39, the correction amount generation circuit 34 performs the two-stage adjustment in the above procedure. A defocus signal is output as the amount of change in depth of focus, and a spherical aberration correction amount signal is output to the spherical aberration correction drive circuit 23. The spherical aberration correction amount signal and the defocus signal are adjusted simultaneously by the above procedure so as to maximize the tracking error signal amplitude, and then, after the mark is recorded, the reproduction signal amplitude is maximized. By alternately adjusting, the optical system is adjusted to the correct in-focus position where the spherical aberration is corrected, and the spherical aberration is correctly corrected and controlled as a whole.

As a method for adjusting the spherical aberration correction amount signal and the defocus signal, for example, a two-dimensional search method may be used. An example of a two-dimensional search procedure in this adjustment will be described in the following examples.

(Effect / Supplement)
In this method, a mark (or pit) is recorded in an unrecorded state as a recording medium (optical disc 8).
Therefore, there is an advantage that the formation of recording marks (pits) is unnecessary and the cost is low.

Also, with this method, the configuration of the optical system other than spherical aberration correction is the same as that of the conventional one. Therefore, in these optical heads, the same parts and circuits as those of the conventional optical system can be used as they are, so that the cost is low. There is.

In addition, by roughly adjusting the tracking error signal amplitude, it is possible to adjust to the vicinity of the center peak of the reproduction signal amplitude in advance, so that it is possible to prevent convergence to a false peak when searching for the maximum value of the reproduction signal amplitude. Therefore, there is an advantage that adjustment can be made highly reliable.

Even if there are other aberrations than spherical aberration, the optical signal is adjusted to the correct in-focus position even if there is a misalignment of the peak peak of the tracking error signal amplitude due to other aberrations because of readjustment with the reproduction signal amplitude. There is an advantage that the system can be adjusted automatically and the adjustment can be made highly reliable.

That is, for a rewritable optical recording medium, the adjustment is made in a two-step procedure in which the tracking error signal amplitude is adjusted to be maximized and then the mark is recorded and the reproduction signal amplitude of the mark is adjusted to be maximized. By doing so, highly reliable automatic adjustment can be performed at low cost.

In addition, this method can also be used by the differential push pull system which added the photodetector surface for tracking error signal detection to said quadrant photodetector 26. FIG. In the differential push-pull method, instead of the tracking error signal, a differential push-pull signal generated by the sum difference of the tracking error signal and the signal on the additional photodetector surface is used. The characteristics of the tracking error signal described so far are the same for the differential push-pull signal. Therefore, this method can be used similarly in the differential push-pull method.

The mark recorded for adjustment may be overwritten or erased after the adjustment. This procedure is shown in FIG. 6 (flow chart). By doing so, it is possible to eliminate the problem of information rewriting due to temporary writing of marks during adjustment.

In addition, the example using a rotation type recording medium assuming an optical disk has been described above. However, the above method and effect can be applied to the case of information recording / reproduction with respect to a non-rotation type recording medium such as a card type. Is the same. In the case of a non-rotating recording medium, the tracking error signal is a signal for obtaining a deviation amount from the center of the aligned line when data is recorded / reproduced aligned on the line (on the recording medium). And it is sufficient. If a groove structure is formed on the recording film on the card-type medium in the same manner as the optical disk, a tracking error signal similar to that on the rotating optical disk can be obtained. The configuration of the head and circuit shown in the figure can be applied as it is.

Further, although an example using the liquid crystal aberration correction element 17 as the spherical aberration correction means has been described above, a combination of lenses can be used instead of the liquid crystal correction element. FIG. 7 shows a configuration example in the case of using a combination of the movable convex lens 6 and the concave lens 7 as spherical aberration correcting means. In this case, by moving the movable convex lens 6 in proportion to the output of the spherical aberration correction drive circuit 23, the spherical aberration caused by the difference in the substrate thickness is changed to the effective focal length change caused by the change in the inter-lens distance. This can be compensated by correcting the focal position. Even in this case, the spherical aberration and focal depth adjustment procedures described above can be applied without change.

In the above description, the spherical aberration correction procedure for cutting an unrecorded disc is shown. However, when performing spherical aberration adjustment on a disc that has already been recorded (initialized), a mark that has already been recorded. Therefore, it is possible to directly start adjustment of the reproduction signal amplitude. Therefore, as in the procedure of FIG. 1 (flow chart), at the beginning of the adjustment, the reproduction signal is detected and it is determined whether it is recorded or unrecorded. By starting from the adjustment of the signal amplitude or by allocating the processing, the adjustment time for the recorded disk can be shortened, and correct spherical aberration adjustment can be performed for both disks. This method has an advantage that the spherical aberration adjustment time for the disk used for the second time and thereafter can be shortened.

Method for Two-Dimensional Search Next, an example of a procedure for a two-dimensional search for spherical aberration / focus depth adjustment according to the present invention will be described with reference to FIG.
Description will be made with reference to FIG.
(Two-dimensional search method for tracking error signal amplitude)
Hereinafter, the procedure of the search for maximizing the tracking error signal amplitude will be described with reference to FIGS.

First, FIG. 8 shows a contour map obtained by enlarging the vicinity of the center of the distribution of the tracking error signal amplitude shown in FIG. In addition, since the positive / negative of the axis | shaft of spherical aberration amount is reversed with FIG. 3 shown previously, the apparent inclination is reverse.

As described in the first embodiment, the distribution of the tracking error signal amplitude is a mountain-shaped distribution having an elongated peak in an oblique direction with respect to the spherical aberration amount and the focal depth.
The distribution is a mountainous distribution with slender peaks in the diagonal direction. Therefore, the depth of focus at which the peak takes a maximum value varies depending on the amount of spherical aberration. For this reason, when searching for a peak, every time the amount of spherical aberration is changed, the depth of focus must be changed to find and compare the maximum point in the oblique direction.

As an example, if the position of the white circle (a) in the figure is the starting point of the search, the spherical aberration amount is first changed to search for the point (b) where the tracking error signal amplitude is maximum. Since (b) is already on the peak of the mountain range, if only the depth of focus is adjusted from here, the tracking error signal amplitude will be smaller than (b) regardless of whether it changes to left or right (b1) or (b2). . Accordingly, in order to find a point where the tracking error signal amplitude is larger than that in (b), it is necessary to move in an oblique direction as in (c) and (c ′). The amplitude further increases from (c) (d), (d) to (e
) To find the peak peak with the maximum amplitude.
As described above, in order to search correctly in the two-dimensional search of the tracking error signal amplitude, a procedure for searching for the larger signal amplitude in the two-dimensional oblique direction with respect to the substrate thickness error and the focal depth is included. Is required. In this search, as shown by the arrows in FIG. 8, on the two-dimensional plot, the trajectory moves in an oblique direction as (b) → (c), (d) → (e). this,
This is called searching in an oblique direction.

When detecting the tracking error signal amplitude, it is usually difficult to match the in-focus part due to the disk's warping, etc., depending on the rotation angle within one rotation of the disk. Since the signal amplitude is often uneven, it is often necessary to wait for the rotation of the disc for one rotation so that the entire amplitude can be detected correctly. For this reason, the search (adjustment) takes time as the number of detection points increases. Therefore, as described above, by searching directly in an oblique direction with one detection, the effect of shortening the search time is great.

Note that the above-described maximization of the tracking error signal amplitude may not be a completely maximum value. The intensity of the central peak in FIG. 8 (intensity at the center of the cross) is 0.626 (arbitrary intensity). However, as can be seen from FIG. The residual spherical aberration amount is within 8 μm (substrate thickness conversion) and the defocus error is within ± 0.7 μm. If the error can be kept within this range by adjusting the tracking error signal amplitude, it will be in the bottom of the central peak in the distribution of the playback signal amplitude later and converge to the correct peak peak by searching for the maximum value of the playback signal amplitude. it can. That is, 96% of the maximum value even if it is not completely maximum
If the adjustment can be made as described above, the expected effect described in the present specification can be obtained. Including this,
Adjustment to increase the amplitude will be referred to herein as “maximization”.

If the inclination in the oblique direction deviates from the ideal inclination during the search, the convergence speed is a four-way search if the inclination ratio value is within ± 60% of the correct ratio value from FIG. More than twice. Also, if it is within ± 25% of the ideal slope, the convergence speed is the fastest (± 0%).
I can keep more than half of it. Therefore, it is desirable that the inclination in the oblique direction be within these ranges from the correct ratio value.

  Ideally, the inclination in the oblique direction can be obtained from the following proportional expression, for example.

Where Δz is the defocus amount, Δt is the substrate thickness error, n is the refractive index of the substrate, and NA is the numerical aperture of the lens. This is the difference between the paraxial image point (Gauss image point) and the ideal image point, Δz, assuming a uniform light distribution up to the pupil radius corresponding to the numerical aperture NA due to the spherical aberration that causes the substrate thickness error Δt. Is what we asked for. This is when n = 1.6 and NA = 0.85.

Thus, a constant ratio relationship proportional to a constant coefficient is obtained. For substrate thickness error of 14.5μm
If the corresponding spherical aberration amount and the defocus amount are changed at the same time at the ratio of the focal depth of 1 μm and the correction driving is performed, the movement can be made without departing from the mountain-shaped peak where the tracking error signal amplitude is maximum. However, the above formula is established when the light quantity distribution of the light beam incident on the lens is uniform. When the distribution is non-uniform, the substantial numerical aperture (NA) value is (mainly). The value changes to be smaller. It is also affected by the ratio between the track spacing and the light spot resolution. Therefore, for example, in an actual optical head, the ratio value (1
4.5) may actually change to a value close to 25 and nearly half the value. Therefore, the value obtained from the above formula is a reference value, and the value obtained by actual measurement with respect to the individually designed optical head is used as the actual inclination ratio value.

Next, FIG. 10 to FIG. 11 show contour maps of the distribution of the tracking error signal amplitude when aberrations other than spherical aberration are caused by component errors or position adjustment errors of the optical system. FIG. 10 shows the distribution when astigmatism occurs, and FIG. 11 shows the distribution when coma occurs. When astigmatism occurs, the center of the peak of the distribution is shifted to the left side, and the peak peak (tracking error signal) It can be seen that even if the amplitude is adjusted to the maximum point, it may not be adjusted to the correct in-focus position. Therefore, it can be seen that adjustment based on the reproduction signal amplitude as described below is required.

In this method, the search for the optimum point of the tracking error signal amplitude, which is the first adjustment of the spherical aberration adjustment, can be speeded up, so that the waiting time immediately after loading or at the time of initialization can be shortened. is there.
(2D search method for playback signal amplitude)
Next, a procedure for maximizing the tracking error signal amplitude will be described with reference to FIGS.

First, FIG. 12 shows a contour map obtained by enlarging the vicinity of the center of the reproduction signal amplitude distribution shown in FIG.

As described in the first embodiment, the reproduction signal amplitude distribution has a slightly sharp peak in the center with respect to the spherical aberration amount and the depth of focus, and a large number of small false peaks in the periphery. Since the central peak is not oblique, the correct focal point position (the top of the central peak) can be found by adjusting the spherical aberration amount and the focal depth independently and alternately.

As an example, when searching with the position of the white circle (e) in the figure as the starting point, the spherical aberration amount is first changed to search for the point (f) where the reproduction signal amplitude is maximum. If only the depth of focus is adjusted from here, the point (g) closer to the peak top is found as a point having a larger reproduction signal amplitude. Thus, if the starting point of the search is in the vicinity of the central peak, the spherical aberration amount and the focal depth are alternately changed so that the reproduction signal amplitude becomes larger, so that the peak at which the amplitude becomes maximum is reached. Can be adjusted. Therefore, in order to adjust to the correct in-focus position, it is only necessary to adjust toward the peak peak (maximum value of the reproduction signal amplitude) while alternately adjusting the spherical aberration amount and the focal depth. Thus, in the two-dimensional search of the reproduction signal amplitude, the fastest search can be performed by simply alternately adjusting the substrate thickness error and the focal depth. Such alternate adjustment becomes a trajectory that moves vertically and horizontally on the two-dimensional plot, as indicated by the arrows in FIG. This is called searching in the vertical and horizontal directions.

Next, FIG. 13 to FIG. 14 show contour maps of the reproduction signal amplitude distribution in the case where aberrations other than spherical aberration occur due to component errors or position adjustment errors of the optical system. FIG. 13 shows the distribution when astigmatism occurs, and FIG. 14 shows the distribution when coma aberration occurs. Now, even with these aberrations, the center of the peak of the distribution almost coincides with the center of the graph. It can be seen that adjustment to the peak peak (the maximum point of the reproduction signal amplitude) enables adjustment to the correct in-focus position. Accordingly, it can be seen that if the fine adjustment is performed with the reproduction signal amplitude, the error caused by the coarse adjustment by the tracking error signal amplitude can be corrected correctly.

Next, when changing the period of the mark pattern to be written to obtain this playback signal,
Contour diagrams of the distribution of the reproduction signal amplitude are shown in FIGS. In these figures, the ratio of the length of the mark portion and the space portion (the portion where no mark is recorded) is 1: 1, and the amplitude of the reproduction signal when recorded as a repetitive pattern indicates the mark period (the mark portion and the space portion). Sum of length)
15 (a) (b) (c) (d), 1.5 times, 2 times, 4 times, 6 times the track interval.
This is the distribution when changed by a factor of two. In general, the track interval is set to a value smaller by 10 to 20% than the diameter of the light spot. Therefore, in a general optical disc apparatus or optical recording medium, the track interval in the data area is a value reflecting the resolution of the light spot.

In FIG. 15A with a short mark period, since the distribution is slightly inclined, the spherical aberration amount and the depth of focus are adjusted alternately for the same reason as the two-dimensional search of the tracking error signal amplitude. In this procedure, the search speed is slightly reduced. On the other hand, in FIG. 15D with a long mark period, the distribution peak center (top: maximum point) is slightly shifted to the lower right side of the graph center (shifted from the correct in-focus position). I understand that. Therefore, when searching for the maximum value of the reproduction signal amplitude to find the correct in-focus position, the length of the mark to be recorded includes 2 of the track interval.
It can be seen that about 4 times is suitable. Also, in this vicinity, the density of the line around the peak is high, and the change in the reproduction signal amplitude with respect to the change in the spherical aberration amount and the depth of focus is large.
It can be seen that the adjustment sensitivity is high and adjustment is easy. The best was around 3 times, halfway between 2 times and 4 times.

Therefore, by setting the period of the mark to be recorded to an appropriate length and using a repeated pattern of marks having a mark interval twice to four times the track interval of the data area as a pattern of the mark to be recorded, It can be easily adjusted to the correct in-focus position by searching for the maximum amplitude.
As a result, the adjustment sensitivity becomes high and is less susceptible to noise and the like, so that there is an advantage that the cost of the control mechanism for adjustment can be reduced.

In the above, the track interval is considered as a reference for the length of the mark, because the track interval usually reflects the diameter of the light spot. Depending on what you can see.

As described above, in the adjustment of the spherical aberration and the depth of focus, in the two-dimensional plot of the depth of focus and the spherical aberration correction amount as shown in FIGS. In the search for the maximum value of the reproduction signal amplitude, the search time is switched to the vertical and horizontal directions, so that the search time can be kept short and the adjustment reliability can be ensured.

(Effect / Supplement)
As described above, since there is a difference in the shape of the tracking error signal amplitude distribution and the reproduction signal amplitude distribution, switching the search method in the maximum value search of both leads to an increase in the speed of adjustment. In the adjustment of the spherical aberration and the depth of focus, on the two-dimensional plot of the depth of focus and the spherical aberration correction amount, a search is performed in an oblique direction (direction oblique to the two axes) by searching for the maximum value of the tracking error signal amplitude. By searching for the maximum value of the reproduction signal amplitude in the vertical and horizontal directions (directions perpendicular / parallel to the two axes), the entire optical system can be adjusted reliably and at high speed.

According to this method, it is possible to cope with an unrecorded recording medium, and to increase the speed of the adjustment as a whole while making the spherical aberration adjustment highly reliable. As a result, the amount of spherical aberration and the depth of focus can be adjusted efficiently, and the time required for adjusting the optical axis can be greatly reduced. This also has the advantage that the waiting time immediately after loading or initialization can be shortened. )
Note that in addition to spherical aberration and depth of focus, tilt (relative tilt between the optical head and the recording medium) may be adjusted. In this case, three-dimensional / four-dimensional adjustment with tilt (two degrees of freedom) is added. A search configuration is possible, but in that case, for example, when two degrees of freedom of spherical aberration and depth of focus are extracted from the four degrees of freedom to obtain a two-dimensional plot, the amount of spherical aberration and the focus are the same as above. The depth may be searched in the diagonal direction and the vertical and horizontal directions.

In addition, in this method, spherical aberration can be adjusted to the correct optimum point regardless of the astigmatism of the disk optical system, so that a medium having a thick plastic layer (cover layer, substrate layer) that easily causes aberration can be used. . Since a stable light spot can be obtained regardless of aberration, there is an advantage that recording can be performed with higher density.
(Example 3: spherical aberration adjustment by interpolation value)
Next, with reference to FIG. 2 and FIGS. 16 to 21, a configuration example of an optical information recording apparatus provided with spherical aberration correction when the thickness of the transparent layer of the medium changes depending on the information recording location of the recording medium will be described. To do.

(Correction in only one recording layer or in the same recording layer)
First, a configuration example of an optical information recording apparatus that corrects spherical aberration due to thickness unevenness of a transparent layer of a recording medium in one recording layer or in the same recording layer will be described with reference to FIGS.

FIG. 16 shows a case where a rotary recording medium having only one recording layer is used as the recording medium.
This is a method for adjusting spherical aberration. FIG. 17 (flow chart) shows the adjustment procedure. The spherical aberration amount and the depth of focus at the points on the inner peripheral side (A) and the outer peripheral side (B) are measured by the methods described in Examples 1-2. Ideally, the points A and B should be near the innermost circumference and the outermost circumference of the data recording area of the disc. The amount of spherical aberration obtained at point A is SA1, the depth of focus is DF1, and similarly, the amount of spherical aberration obtained at point B is SA2, and the depth of focus is DF2.

  At this time, at an arbitrary position Px on the recording medium (disk). Spherical aberration amount SAx

In the above equation, Px1, Px2, and Px are radii at arbitrary positions on each disk. The specific configuration will be described with reference to the configuration example of FIG. The main control circuit 39 determines the radius Px of the position on the disk of the data to be recorded / reproduced, the inner peripheral point (A) already measured,
The radii P1 and P2 of B) are given to the correction amount generation circuit 34. The correction amount generation circuit 34 calculates the spherical aberration amount SAx at the position of the recording / reproduction data on the radius Px and the focal depth DFx according to the above formula, and sends them to the spherical aberration correction drive circuit 23 and the defocus amount addition circuit 31, respectively. Output. Thereby, the spherical aberration at an arbitrary position on the recording medium (disk) is corrected in a first order approximation.

Whether the recording medium is a non-rotating recording medium such as a card type or a multi-layer medium having a plurality of recording layers, the XY position and the radial direction (number of tracks) are the same. By interpolating according to the coordinates in each direction, such as the stacking direction of layers and layers, the spherical aberration amount and the depth of focus value are calculated and corrected, so that recording media having different shapes and storing information in a multidimensional manner can be obtained. Even when it is used, the spherical aberration can be corrected at an arbitrary position in a first-order approximation, and data can be recorded and reproduced.

That is, in this configuration, the optimum value of the correction control amount of the spherical aberration amount (and the optimum value of the depth of focus of the objective lens) is measured on the inner and outer circumferences of the medium, and the information is recorded and reproduced according to the track position. The optimum values of the inner and outer circumferences are interpolated to obtain the correction control amount for the depth of focus and the spherical aberration amount.

  For example, when the recording medium is a multilayer optical disk, the following configuration is adopted.

This is a method for adjusting spherical aberration when the rotary multilayer recording medium 1 as shown in FIG. 18 is used. FIG.
Reference numeral 9 (flow chart) shows the adjustment procedure. Assuming that the spacing between the layers is the same, when recording / reproducing the recording layer of the Pz layer with N layers in the stacking direction 5, the uppermost layer (first layer)
The amount of spherical aberration and the depth of focus at the inner and outer peripheral points of the data recording area of the lowermost layer (Nth layer) are measured by the method described in Examples 1-2. These are SA1T, SA2T and S respectively.
A1B, SA2B, DF1T, DF2T, DF1B, and DF2B are assumed.

At this time, in arbitrary positions Px and Pz layers on the recording medium. The spherical aberration amount SAxz and the depth of focus DFxz are obtained by interpolation as follows.

The specific configuration will be described with reference to the configuration example of FIG. The main control circuit 39 records and reproduces data positions Px and Py on the recording medium, the already measured upper and lower spherical aberration amounts and focal depths, SA1T, SA2T, SA1B, SA2B, DF1T, DF2T, and DF1B. ,
DF2B is stored, and these values are given to the correction amount generation circuit 34. The correction amount generation circuit 34, according to the above formula, has the spherical aberration amount SAxz at the position Px, the position of the recording / reproduction data on the Pz layer. Are calculated and output to the spherical aberration correction drive circuit 23 and the defocus amount addition circuit 31, respectively. Thereby, the spherical aberration at an arbitrary position on the recording medium is corrected in a first order approximation.

That is, in this configuration, there is means for storing the optimum value of the correction amount of the spherical aberration amount at the inner and outer circumferences of the medium (and the optimum value of the focal depth of the objective lens), and the information to be recorded / reproduced is recorded. Depending on the track position, the optimum values of the inner and outer circumferences are interpolated to obtain correction control amounts for the depth of focus and the spherical aberration amount.

Further, in this configuration, with respect to the overlapping direction of the layers, there is means for storing an optimum value of the correction control amount of the spherical aberration amount in the uppermost layer and the lowermost layer, and when moving between a plurality of recording layers As the correction control amount of the spherical aberration amount to be set, the interpolation value of the optimum value of the spherical aberration amount at the position of the movement destination layer is used.

  Further, for example, in the case of a non-rotating type multi-layer recording medium, it is configured as follows.

FIG. 20 is an example of a spherical aberration adjustment method when the card type multilayer recording medium 2 is used. FIG. 21 (flow chart) shows the adjustment procedure. If the spacing between layers is the same, X
When recording / reproducing the recording layer of the Pz layer when the number of layers is N in the stacking direction 5, the uppermost layer (first layer) and the lowermost layer (first layer) Points (Px1, Py1) (Px2, Py1) (Px1, Py2) (Px2) at the four corners (both ends) of the data recording area of the Nth layer)
, Py2), the amount of spherical aberration and the depth of focus are measured by the method described in Examples 1-2. This is respectively SA1T, SA2T, SA3T, SA4T, DF1T, DF2T, D
F3T, DF4T, SA1B, SA2B, SA3B, SA4B, DF1B, DF2B, D
Let F3B and DF4B.

At this time, the spherical aberration amount SAxy at an arbitrary position Px, Py, Pz layer on the recording medium.
z is obtained by the interpolation value as follows, and the depth of focus DFxyz.

The specific configuration will be described with reference to the configuration example of FIG. The main control circuit 39 corrects the position Px, Py, the number of layers Pz on the recording medium of the data to be recorded / reproduced, and the positions Px1, Px2, Py1, Py2, and the number N of stacked points at the four corners (both ends) already measured. According to the above formula, the correction amount generation circuit 34 calculates the spherical aberration amount SAxyz at the position of the recording / reproduction data on the positions Px and Py and the number of layers Pz and the focal depth DFxyz according to the above formula, This is output to the aberration correction drive circuit 23 and the defocus amount addition circuit 31. Thereby, the spherical aberration at an arbitrary position on the recording medium is corrected in a first order approximation.

That is, in this configuration, for one recording layer, there is means for storing the optimum value of the correction control amount of the spherical aberration amount at the four corners of the medium (and the optimum value of the focal depth of the objective lens). ,
According to the ratio of the distance from the four corners of the information to be recorded / reproduced, the values of the optimum values at both ends are interpolated to obtain the correction control amount for the depth of focus and the spherical aberration amount.

Further, in this configuration, with respect to the overlapping direction of the layers, there is means for storing an optimum value of the correction control amount of the spherical aberration amount in the uppermost layer and the lowermost layer, and when moving between a plurality of recording layers As the correction control amount of the spherical aberration amount to be set, the interpolation value of the optimum value of the spherical aberration amount at the position of the movement destination layer is used.
(effect)
In this manner, the spherical aberration can be corrected in a first order approximation at an arbitrary position in this way. There is an advantage that the spherical aberration at an arbitrary track radius can be adjusted to a correct value, and the spherical aberration can be adjusted correctly even in the jump between multiple layers of the multilayer disk. In these recording media, the spherical aberration can be correctly adjusted, so that there is an advantage that good signal recording / reproducing can be performed.

(Overall effect)
As described above, according to the present invention, when the spherical aberration correction is adjusted in the optical information recording apparatus, the spherical aberration correction can be adjusted more accurately at an arbitrary position in a shorter time with higher reliability.

A number of configurations have been proposed for the optical head of such an optical information recording apparatus having a spherical aberration correction function, but this method is applicable to almost all optical heads having a general tracking error signal detection function. It can be used as it is, and accurate spherical aberration correction adjustment is possible, which is advantageous because of low cost.

In addition, since it is not necessary to mount a large number of photodetectors and photoamplifiers as compared with a method of performing dynamic spherical aberration detection / correction driving by splitting a light beam as in JP-A-2002-358877,
The entire circuit can be reduced in noise.

Therefore, a more reliable optical disc device (optical information recording device) having spherical aberration correction can be provided at low cost.

It is an example of the adjustment procedure of spherical aberration and a focal depth by this invention. It is an example of a structure of the optical information recording device provided with spherical aberration correction by this invention. It is a figure which shows the example of distribution of a tracking error signal amplitude. It is a figure which shows the example of distribution of reproduction signal amplitude. It is an example of the adjustment procedure of spherical aberration and a focal depth by this invention. It is an example of the adjustment procedure of spherical aberration and a focal depth by this invention. It is an example of composition of an optical system provided with spherical aberration correction which can apply the present invention. It is an enlarged view of a distribution example of tracking error signal amplitude, and is a contour map. It is an enlarged view of a distribution example of tracking error signal amplitude, and is a contour map. It is an example of distribution of tracking error signal amplitude when astigmatism exists. It is an example of distribution of the tracking error signal amplitude when coma is present. It is an enlarged view of the example of distribution of reproduction signal amplitude, and is a contour map. It is an example of distribution of the reproduction signal amplitude when astigmatism exists. It is an example of distribution of reproduction signal amplitude when coma is present. It is an example of the change of distribution of reproduction signal amplitude with respect to the change of a recording mark pattern period. It is a figure which shows coordinate arrangement | positioning by description of the correction method in a single layer disc. It is an example of the correction | amendment procedure in a single layer disc. It is a figure which shows coordinate arrangement | positioning by description of the correction method in a multilayer disk. It is an example of the correction | amendment procedure in a multilayer disk. It is a figure which shows coordinate arrangement | positioning by description of the correction method in a multilayer card type recording medium. It is an example of the correction | amendment procedure in a multilayer card type recording medium.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Rotation type multilayer recording medium 2 ... Card type multilayer recording medium 3 ... X-axis direction 4 ... Y-axis direction 5 ... Lamination direction (Z-axis direction)
6 ... Convex lens 7 ... Concave lens 8 ... Optical disk 9 ... Rotary servo circuit 10 ... Motor 11 ... Laser drive circuit 12 ... Semiconductor laser 13 ... Collimator lens 14 ... Beam shaping prism 15 ... Reflecting mirror 16 ... Deflection beam splitter 17 ... Liquid crystal aberration correction element 18 ... λ / 4 plate 19 ... objective lens 20 ... actuator 21 ... tracking servo circuit 22 ... focus servo circuit 23 ... spherical aberration correction drive circuit 24 ... cylindrical lens 25 ... condensing lens 26 ... quadrant photodetector 27 ... photocurrent Amplifier 28 ... Tracking error signal generation circuit 29 ... Focus error signal generation circuit 30 ... Reproduction signal generation circuit 31 ... Defocus amount addition circuit 32 ... Tracking error signal amplitude detection circuit 33 ... Reproduction signal amplitude detection circuit 34 ... Correction amount generation circuit 35 ... Equalization circuit 36 ... Level detection circuit 37 ... Synchronous clock Generating circuit 38 ... decoding circuit 39 ... main control circuit.

Claims (8)

An optical information recording apparatus for optically reading and writing information on a recording medium,
A reproduction signal amplitude detection means, a tracking error signal amplitude detection means, a spherical aberration variable correction means, and a variable depth control means of the objective lens,
In the adjustment of the spherical aberration and the depth of focus, on the two-dimensional plot of the depth of focus and the spherical aberration correction amount, the search is performed in an oblique direction by searching for the maximum value of the tracking error signal amplitude, and the vertical and horizontal directions are performed in the search of the maximum value of the reproduction signal amplitude. The optical information recording apparatus is characterized by switching to search. An optical information recording apparatus for optically reading and writing information on a recording medium,
A reproduction signal amplitude detection means, a tracking error signal amplitude detection means, a spherical aberration variable correction means, and a variable depth control means of the objective lens,
For a rewritable optical recording medium, after adjusting the spherical aberration amount and depth of focus to increase the amplitude of the tracking error signal, the mark is recorded and then the spherical aberration amount and depth of focus so as to maximize the amplitude of the reproduced signal. An optical information recording apparatus characterized by adjusting the frequency. An optical information recording apparatus for optically reading and writing information on a recording medium,
A reproduction signal amplitude detection means, a tracking error signal amplitude detection means, a spherical aberration variable correction means, and a variable depth control means of the objective lens,
After adjusting to increase the amplitude of the tracking error signal, the mark is recorded, the amplitude of the reproduction signal is maximized, and then the spherical aberration is adjusted by the procedure of overwriting (erasing) the recorded mark. Optical information recording device. In the optical information recording device according to any one of claims 2 and 3,
2. An optical information recording apparatus according to claim 1, wherein a mark repetitive pattern having a mark interval twice to four times the track interval of the data area is used as the mark pattern to be recorded. The optical information recording apparatus according to any one of claims 1 to 4, wherein the optical information recording apparatus uses a non-rotating recording medium.
According to the ratio of the distance from the four corners of information to be recorded / reproduced, there is a means for storing the optimum value of the correction control amount of the spherical aberration amount at the four corners of the medium (and the optimum value of the focal depth of the objective lens). ,
An optical information recording apparatus characterized by interpolating optimum values at both ends to obtain a correction control amount for the depth of focus and the spherical aberration amount. The optical information recording apparatus according to claim 1, wherein the optical information recording apparatus uses a rotary recording medium.
According to the track position of the information to be recorded / reproduced, there is a means for storing the optimum value of the correction amount of the spherical aberration correction amount (and the optimum value of the focal depth of the objective lens) on the inner and outer circumferences of the medium.
An optical information recording apparatus characterized by interpolating the optimum values of the inner circumference and outer circumference to obtain a correction control amount for the depth of focus and the spherical aberration amount. The optical information recording apparatus according to claim 1, wherein a multilayer recording medium is used as a recording medium.
Means for storing an optimum value of the correction control amount of the spherical aberration amount in the uppermost layer and the lowermost layer, and as a correction control amount of the spherical aberration amount set when moving between a plurality of recording layers, An optical information recording apparatus using the optimum interpolation value of the spherical aberration amount at a position. In the optical information recording device according to any one of claims 1 to 7,
When an initialized recording medium is inserted, the reproduction signal amplitude is optimized, and when an uninitialized recording medium is inserted, the tracking error signal amplitude is optimized and adjusted. Optical information recording device.

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