JP2006221705A - Optical disk device and its adjusting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical disk device which determines whether a spherical aberration is to be corrected, restrains the adjustment of a spherical aberration to a minimum, shortens time required for adjusting a spherical aberration correction and is excellent in comfortableness, and also provide its adjusting method. <P>SOLUTION: The optical disk device has a focus offset adjusting mechanism and a spherical aberration adjusting mechanism. When learning how to adjust a spherical aberration and a focus offset, the optical disk device measures focus offset dependency by using a prescribed evaluation indicator while keeping an initial value (previous state) of a spherical aberration correction value, determines the focus offset dependency of the evaluation indicator, and skips the adjustment of the spherical aberration, when the dependency is at most a prescribed value, to shorten the time required for learning. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an adjustment method during operation of an optical disc apparatus and an optical disc apparatus, and more particularly to whether or not to determine a spherical aberration correction state in an optical disc apparatus having a spherical aberration correction mechanism, and further to an adjustment method and a focus offset of a light beam. is there.

  In recent years, it has been required to increase the recording density of an optical disc as the amount of information increases. Therefore, the recording density of the optical disk has been increased by increasing the linear recording density in the information recording layer of the optical disk or by reducing the track pitch. In order to cope with the higher recording density of the optical disc, it is necessary to reduce the beam diameter of the light beam condensed on the information recording layer of the optical disc.

  As a method of reducing the beam diameter of the light beam, increasing the numerical aperture (NA: Numerical Aperture) of the light beam emitted from the objective lens as the condensing optical system of the optical pickup device for recording and reproducing the optical disk, It is conceivable to shorten the wavelength of the light beam. The shortening of the wavelength of the light beam can be realized by changing the light source from a red semiconductor laser to a blue-violet semiconductor laser that has been opened for practical use.

  On the other hand, as a technique for realizing an objective lens with a high numerical aperture, a technique for realizing a high numerical aperture by combining an objective lens with a hemispherical lens and forming the objective lens with two lenses (two group lenses), or Has been proposed and developed to increase the NA of a single lens.

Generally, in an optical disc, the information recording layer is covered with a cover layer in order to protect the information recording layer from dust and scratches. Therefore, the light beam that has passed through the objective lens of the optical pickup device passes through the cover layer, and is condensed on the information recording layer underneath to be focused. When the light beam passes through the cover layer in this way, spherical aberration occurs. The spherical aberration is expressed by (spherical aberration ∝t * NA ⁴ , t: thickness of the cover layer, NA: numerical aperture of the objective lens), and is proportional to the fourth power of the thickness t of the cover layer and the numerical aperture NA of the objective lens. To do. Usually, the objective lens is designed to cancel out this spherical aberration, so that the spherical aberration of the light beam that has passed through the objective lens and the cover layer is sufficiently small.

  However, if the thickness of the cover glass deviates from a predetermined value, the light beam collected on the information recording layer has a spherical aberration and the beam diameter increases, so that information can be read and written correctly. The problem that it becomes impossible to occur.

  The spherical aberration error caused by the cover glass thickness error Δt is proportional to the cover glass thickness error Δt. That is, as the thickness error Δt of the cover glass increases, the spherical aberration error increases. Furthermore, since it is proportional to the fourth power of NA, the generation of spherical aberration with respect to the cover glass thickness error Δt becomes larger due to the increase in NA. As a result, information may not be correctly read / written.

In a conventional optical disc, for example, a DVD (Digital
As in Versatile Disc), the numerical aperture NA of the objective lens in the optical pickup device used is about 0.6. Accordingly, the error of the spherical aberration caused by the cover glass thickness error Δt is small, and the light beam can be condensed sufficiently small for each information recording layer.

  On the other hand, in order to increase the density of recorded information in the thickness direction of the optical disc, for example, a DVD having two information recording layers has already been commercialized as a multilayer optical disc formed by laminating information recording layers. Such an optical pickup device for recording / reproducing a multilayer optical disc needs to focus the light beam sufficiently small for each information recording layer of the optical disc.

  However, in the multilayer optical disc as described above, the thickness from the surface of the optical disc (cover glass surface) to each information recording layer differs for each laminated information recording layer. As a result, the spherical aberration that occurs when the light beam passes through the cover glass of the optical disc is different in each information recording layer. In this case, for example, the difference in spherical aberration generated in the adjacent information recording layers is proportional to the interlayer distance t (corresponding to the thickness t) of the adjacent information recording layers.

  Further, development of technology for further increasing the density of DVD is being promoted by various companies, and the wavelength of the light source is being advanced at about 405 nm and the NA of the objective lens is being advanced at 0.85. As described above, even when the thickness error Δt of the cover glass is the same, a larger spherical aberration occurs as the numerical aperture NA increases. As described above, since the spherical aberration value is proportional to the fourth power of NA, for example, when NA = 0.85, the spherical aberration is about four times as large as NA = 0.6. Therefore, it can be seen that the higher the numerical aperture, such as NA = 0.85, the greater the spherical aberration generated by the cover glass thickness error Δt.

  The same can be said for an optical disc having multiple recording layers. Even if the interlayer distance t between adjacent information recording layers is equal, a larger spherical aberration difference occurs as the NA of the objective lens of the optical pickup device increases. For example, as described above, even with the same thickness error Δt, the difference in spherical aberration is about four times greater at NA = 0.85 than at NA = 0.6. Therefore, it can be seen that the higher the numerical aperture, such as NA = 0.85, the greater the difference in spherical aberration of each information recording layer.

  Therefore, in the objective lens with a high numerical aperture, the influence of the error of spherical aberration cannot be ignored, causing a problem that the accuracy of reading information is lowered. Therefore, in order to achieve high recording density using an objective lens having a high numerical aperture, it is necessary to correct spherical aberration, and a spherical aberration correction mechanism and correction means have been developed and studied.

  Further, at the time of information recording / reproduction in the optical disk apparatus, the optical head apparatus always forms a minute beam spot along the recording track on the disk. For this purpose, the optical head device performs focus servo and tracking servo. The focus servo controls the objective lens to follow the direction perpendicular to the disk and mainly controls the beam spot diameter to be minimum. Further, the tracking servo controls the direction perpendicular to the track extending direction in the disk surface so that the beam spot having the minimum beam diameter follows the data track.

The focal depth of the focused light irradiated on the information recording surface of the optical disc is proportional to the wavelength λ and inversely proportional to the square of the NA of the objective lens (focus depth ∝λ / NA ² ).

  Therefore, it can be seen that in the optical system in which the laser light wavelength is shortened and the NA of the objective lens is increased in order to improve the recording density, the above-mentioned depth of focus is significantly shorter than that of the current DVD or the like. For this reason, high follow-up performance is required for the focus servo.

  Thus, in the next generation optical disc system, it is considered to introduce a mechanism for correcting spherical aberration due to the influence of the optical system described above. In the recording / reproducing apparatus, some adjustment control of the spherical aberration correction mechanism is required.

  In addition, the change in the shape of the light spot due to spherical aberration has a complementary relationship with the change in the shape of the light spot due to the focus servo offset described above. It is necessary to find the optimal point.

  As a method of optimizing adjustment of the focus servo offset and optimizing adjustment of the spherical aberration correction mechanism in the optical disk system using such a high NA objective lens, there is a method disclosed in Patent Document 1.

  Here, multiple spherical aberration correction states are set by the spherical aberration correction mechanism, and in each state where the spherical aberration correction state is set, the focus offset is changed within a predetermined range by the focus offset adjustment mechanism, and the focus offset is changed. In this case, each characteristic of the information reproduction signal on the information recording surface is detected, the symmetry of the curve of each characteristic is detected, and the curve having the best symmetry is discriminated.

JP 2003-196856 A

  However, in the optical disc apparatus disclosed in Patent Document 1, it is necessary to repeatedly drive the spherical aberration correction mechanism within a predetermined range. Here, the spherical aberration correction mechanism performs spherical aberration correction by moving some optical components of the lens group of the optical pickup in the optical axis direction, and generally uses a stepping motor to drive this lens. The operation of the spherical aberration correction mechanism driven by this motor has a response speed that is orders of magnitude slower than the operation speed of focus and tracking. When adjusting the spherical aberration correction by operating the spherical aberration correction mechanism, focus adjustment is required. A lot of adjustment time is required compared to the above.

  In the short wavelength (ex. Λ: 405) and high NA (NA: 0.85) optical disk drive apparatus as described above, the optimum adjustment of various parameters related to recording and reproduction is an indispensable condition when inserting the disk. I must. For this reason, in this adjustment, if the spherical aberration adjustment mechanism is driven several times to optimize the spherical aberration correction, the startup time for inserting the disk is lengthened and the comfort in the optical disk apparatus is impaired. .

  The present invention has been made in view of the above problems, and its purpose is to determine whether or not to correct spherical aberration, minimize the adjustment of spherical aberration correction, and shorten the time required for adjustment of spherical aberration correction. It is another object of the present invention to provide a more comfortable optical disc apparatus and an adjustment method thereof.

  In order to achieve the above object, the present invention provides a focus offset adjustment mechanism for adjusting a focus offset of a light beam by driving an objective lens with respect to an information recording surface of an optical disc, and a light beam irradiated on the information recording surface. A spherical aberration correction mechanism for correcting the generated spherical aberration, irradiating the information recording surface of the optical disc with the light beam through the objective lens, and reproducing the information on the information recording surface using the reflected light beam As an adjustment method of the optical disc apparatus for adjusting the spherical aberration correction mechanism and the focus offset mechanism within an allowable range in the optical disc apparatus, the spherical aberration correction mechanism is held at a value at the start of adjustment, and the focus offset adjustment mechanism The offset is changed within a predetermined range, and the information is re-recorded on the information recording surface at this time. The characteristic of the signal is detected using a predetermined evaluation index, the dependency of the evaluation index on the focus offset change is detected, and when the evaluation index value and the dependency are equal to or less than a predetermined specified value, the spherical aberration adjustment mechanism Spherical aberration adjustment is omitted.

The present invention also provides a focus offset adjustment mechanism that adjusts a focus offset of a light beam by driving an objective lens with respect to an information recording surface of an optical disc, and a spherical aberration that occurs in the light beam irradiated on the information recording surface. An optical disc apparatus having a spherical aberration correction mechanism for correcting, irradiating the information recording surface of the optical disc with a light beam through the objective lens, and reproducing the information on the information recording surface using the reflected light beam;
The adjustment state of the spherical aberration correction mechanism is held at a predetermined value, and the focus offset is changed within a predetermined range by the focus offset adjustment mechanism, and the characteristic of the information reproduction signal on the information recording surface at this time is evaluated in a predetermined manner A means for detecting using an index, and a means for analyzing the dependence of the evaluation index on the focus offset change. When the dependence is below a predetermined value, the spherical aberration adjustment by the spherical aberration adjustment mechanism is omitted. If the predetermined prescribed value is not satisfied, the adjustment direction of the spherical aberration correction is detected from the focus offset dependency analysis, the spherical aberration adjustment mechanism is driven in the direction to perform the spherical aberration correction, and the determination is repeated. Features.

  According to the present invention, it is possible to omit the driving of the spherical aberration correcting mechanism or reduce the number of driving without impairing the adjustment accuracy of the focus offset and the spherical aberration correcting system, and the time required for adjusting the spherical aberration correction. Can be provided, and an optical disc apparatus that does not impair comfort can be provided.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 2 shows an example of a cross-sectional view of the optical disc 1 in the present invention.

  An information recording layer 3 including, for example, a phase change recording film is formed on a substrate 2 made of polycarbonate. When the optical disc 1 is a read-only disc, an information recording layer 3 made of a metal reflection film is formed instead of the phase change recording film. Next, a light transmission layer (cover layer) 4 having a thickness t is formed on the information recording layer 3. The cover layer 4 is a sheet having a thickness t made of, for example, a plastic material, and is adhered to the information recording layer 3 formed on the substrate 2 via an adhesive or an ultraviolet curable resin.

  FIG. 3 shows how information is recorded on the optical disc 1.

  The information recording layer 3 of the optical disc 1 is formed on a spiral or concentric information recording track 5. An information recording track 5 is formed on the optical disc 1 by a guide groove formed by physical unevenness, and information is recorded in a concave portion and / or a convex portion, for example, by a mark due to a phase change. When the optical disk 1 is a reproduction-only disk, the information recording track 5 is formed in advance by a prepit arrangement.

  FIG. 1 is a block diagram showing an electrical configuration of an optical pickup device according to an embodiment of the present invention.

  The pickup 6 irradiates the optical disk 1 that is an optical recording medium that is rotationally driven by the spindle motor 7 to record and reproduce information. During the recording and reproducing operation, the pickup 6 receives reflected light when the optical disk 1 is irradiated with the read beam light, and converts the reflected light into an electric signal to the focus / tracking processing circuit 8 and the RF signal generation circuit 9. Supply each.

  The pickup 6 includes a semiconductor laser 61, a collimator lens 62, a beam splitter 63, a λ / 4 plate 64, a spherical aberration correction optical system 650, a spherical aberration correction optical system drive mechanism 651, an objective lens 660, a focus / tracking actuator 661, An optical lens 67 and a photodetector 68 are included.

  The semiconductor laser 61 generates laser beam light with a predetermined optical power. This laser beam light is incident on a spherical aberration correction optical system 650 that corrects spherical aberration associated with the thickness error of the transmission substrate of the optical disc 1.

  The spherical aberration correction optical system 650 is a beam expansion type relay lens configured by, for example, a pair of a concave lens 650a and a convex lens 650b, and normally emits parallel light with an expanded beam diameter with respect to incident parallel light. It is configured as follows. Then, by driving the spherical aberration correction optical system drive mechanism 651 that changes the lens interval between the concave lens 650a and the convex lens 650b, the light incident on the objective lens 661 is converted into divergent light or convergent light, and the objective lens. 661 can generate and adjust spherical aberration.

  Therefore, the spherical aberration correcting optical system 650 can be made to function as correcting means for correcting the spherical aberration due to the variation in the cover layer thickness of the optical disc 1 by such an operation.

  The objective lens 660 focuses the laser beam light supplied from the spherical aberration correction optical system 650 on the information track 5 formed on the recording surface of the optical disc 1 as a read beam light. The focus is realized by the focus / tracking actuator 661 moving the objective lens 660 in a direction perpendicular to the information track surface of the optical disc 1, that is, on a so-called focus adjustment trajectory, based on the focus drive signal FES. The tracking is realized by the focus / tracking actuator 661 displacing the optical axis of the objective lens 660 in the disc radial direction of the optical disc 4 based on the tracking drive signal TES.

  An additional explanation of the servo system operation will be given. In the optical head 6, a focus error signal (FES) and a tracking error signal (TES) are generated and output by reflected light from the optical disk 1. The focus error signal (FES) is obtained by detecting the deviation of the beam spot in the direction perpendicular to the information recording layer 3 and converting it into an electric signal.

  As a focus error detection method, a known astigmatism method, knife edge method, spot size detection method, or the like is used. Which method is used for focus error detection is not related to the essence of the present invention, and any method may be used. The tracking error signal (TES) is obtained by detecting the deviation of the beam spot from the center of the information recording track 5 and converting it into an electric signal. As a tracking error detection method, a known push-pull method, DPP (Differential Push-Pull) method, DPD (Differential Phase Detection) method, or the like is used. Which method is used for tracking error detection is not related to the essence of the present invention, and any method may be used.

  When the optical disk 1 is loaded in the optical disk apparatus, the optical disk 1 is rotated by the spindle motor 7 by constant linear velocity or constant rotation speed control. The focus error signal is input to the focus / tracking driving circuit 10 after appropriate signal processing such as phase compensation is performed by the focus processing circuit 8.

  The controller 12 inputs a focus-on signal to the focus drive circuit 10 after the completion of pre-processing such as disk rotation and light source laser lighting, and outputs a drive signal from the focus drive circuit 10 to the focus coil of the objective lens actuator 661. Apply focus control.

  Next, the tracking error signal is input to the focus / tracking driving circuit 10 after appropriate signal processing such as phase compensation is performed by the tracking processing circuit 8.

  After confirming the focus lock, the controller 12 inputs a tracking on signal to the tracking drive circuit 10 and outputs a drive signal to the tracking coil of the objective lens actuator 661 to perform tracking control.

  As described above, the spherical aberration correcting optical system 651 is a beam expansion type relay lens composed of a pair of a concave lens 650a and a convex lens 650b, and is usually a parallel beam whose beam diameter is expanded with respect to incident parallel light. It is configured to emit light. Then, the spherical aberration correction optical system drive mechanism 651 that changes the lens interval between the concave lens 650a and the convex lens 650b is driven by the spherical aberration correction drive circuit 11, whereby the light incident on the objective lens 660 is diverged or converged. It is converted into light, and spherical aberration can be generated and adjusted by the objective lens 660.

  Further, the controller 12 can adjust the offset of the focus control by inputting a signal to the offset adding circuit 13. This is called focus offset adjustment. By intentionally adding an offset to the servo control loop, the focus state of the beam spot can be adjusted up and down (in a direction perpendicular to the optical disc 1) on the optical disc 1. .

  On the other hand, a reproduction signal from the information recording layer 3 of the optical disc 1 is output from the optical head 6, processed by the RF signal processing circuit 9, and sent to the controller 12.

The controller 12 has various functions, and also has a function of calculating and determining an evaluation index of a reproduction signal. As an evaluation index of a reproduction signal, for example,
1. 1. reproduction signal amplitude; 2. Timing jitter measurement, 3. Statistical processing value (SAAM) of likelihood difference at the time of joining predetermined paths in Viterbi decoding Error rate measurement, etc.

  1. Examples of the reproduction signal amplitude include reproduction signal maximum amplitude detection, and MTF detection based on amplitude ratios between different mark lengths.

  2. Examples of the timing jitter measurement include timing jitter measurement by interpolation processing of a sampling level value of a reproduction signal, timing jitter measurement using PLL phase error information, and the like.

  3. The statistical processing value (SAM) of the likelihood difference at the time of joining a predetermined path in Viterbi decoding is the likelihood difference between paths to be selected when a predetermined path is selected when maximum likelihood decoding such as Viterbi decoding is used for reproduction signal processing. And the signal quality is evaluated by the statistical value of this value. This evaluation index has been highly researched in recent years because it has a high correlation with the error rate.

  4). In this error rate measurement, known recording information and reproduction information are compared to measure the bit error rate.

  In the configuration described above, an adjustment method related to the determination of spherical aberration correction, spherical aberration correction, and focus offset adjustment according to the present invention will be described.

  In the present embodiment, an example in which a reproduction signal amplitude and timing jitter are combinedly used as an evaluation index will be described. It should be noted that the correlation between the evaluation index using the path likelihood at the time of Viterbi decoding and the error rate, and the correlation between the timing jitter and the error rate have a good correlation as shown in FIGS. The evaluation index of the reproduction signal is not limited to the timing jitter shown in this example.

  FIG. 6 shows a procedure for adjusting the focus offset and the spherical aberration correction system. At the start of adjustment, the spherical aberration correction mechanism is set to an initial value (S1).

  As the position state of the spherical aberration correction mechanism at the start of adjustment, the following state is assumed in the drive device.

  First, an initial position unique to the drive, for example, reset when a previously used disk is ejected, may be considered. It is also conceivable to keep the position of the spherical aberration mechanism employed in the disk used before, and the position of the spherical aberration correction mechanism that is statistically determined based on past information.

  In any case, there is no particular problem when the information layer is a single layer, but when the information layer takes a multilayer configuration, the information layer to start adjustment from now is which layer of the multilayer configuration, and the state before the adjustment is It is necessary to identify which layer of the multi-layer configuration was targeted.

  As described above, when the adjustment is started, the spherical aberration correction mechanism maintains the position at that time. However, this means that the spherical aberration correction mechanism retains the initial value of the information layer to be adjusted at least according to these situations.

  Next, the focus offset value is set as an initial value (S2), and the process proceeds to a process of evaluating the evaluation index value while changing the focus offset amount by a predetermined step amount.

  To do this, it is first necessary to determine whether or not to record for each focus offset.

  According to the results examined by the present inventor, when the recording power is in an optimum state, there is no major problem with the right detection point of the spherical aberration correction value and the optimum detection point of the focus offset value. Can be judged as not an essential problem.

  However, changing the focus offset both changes the energy density of the recording spot. Therefore, changing the focus offset during the recording operation substantially changes the recording power, and the recording power as well as the focus offset dependency. Dependencies will be included.

  For this reason, when the recording power is not optimal, the energy density of the recording spot changes with the focus offset, so the recording power is substantially included in the recording power, and the focus offset dependency during playback appears as a pure focus offset dependency. There may not be.

  For this reason, in the present invention, recording that does not cause a change in focus offset is employed so as not to cause a substantial change in recording power during recording. In this case, there is a concern that the dependence of the focus offset at the time of reproduction may change depending on the right or wrong of the recording state, but according to the study of the present inventor, although the change appears in the absolute location of the evaluation index, the dependence itself It has been confirmed that there will be no changes that would interfere with

  Therefore, in the present embodiment, a method that does not change the focus offset at the time of recording is selected, and the following description will be continued.

  First, when changing the focus offset, it is conceivable to change on the basis of a recording information unit such as a sector unit in which one round of the disk is divided. The number of divisions must be set in consideration of the control constraints such as the response speed of focus control, maximum swing width, step amount, etc., and the required data amount of the evaluation index. Recording / reproduction over a plurality of tracks is also conceivable.

  When recording, recording is performed in the first round and playback is performed in the second round. As described above, changing the focus offset value at the time of recording is accompanied by a change in recording power. Therefore, the recording is performed at the initial value of the focus offset without changing the focus offset value at the time of recording. For the selection of the recording power, the recommended value described in the disc information may be adopted. When using recorded information or when using a read-only disc, there is no need to consider anything.

  In the present embodiment, as an example, a case where the measurement range of the focus offset value is changed from the end (Fo_set1) to the other end (Fo_set2) will be described as an example.

  First, recording is performed with the recording power set to a recommended value recorded as disk information. The focus offset value at this time is an initial value of the focus offset, in other words, the center value of the focus offset change width is given as a representative example (S3).

  Following the recording, the recorded information is reproduced in the second round, and the reproduced signal is evaluated using a predetermined evaluation index (S4).

  As described above, as an example, the focus offset value has an end (−) of the swing width as an initial value, and is a method of giving a change that becomes the final value of the other end (+) in one round. The focus offset value is reproduced while changing the focus offset value step by step for each divided block.

  If the change time of the focus offset value is concerned, it is naturally conceivable to provide time for changing the focus offset value stepwise before the initial value or after the end value. Needless to say, this is not the only way to change the focus offset.

  Next, regarding the reproduction signal evaluation, here, a case where the reproduction signal is evaluated using a combination of the reproduction signal amplitude and the jitter value of the time interval measurement will be described.

  Here, a description will be added regarding combining the reproduction signal amplitude with another evaluation index as an evaluation index of the reproduction signal.

  According to the inventor's study, when the spherical aberration correction is in an appropriate state, the change in the evaluation index value other than the reproduction signal amplitude value due to the change in the focus offset is extremely small. The determination of the best value becomes difficult, and the necessity of determining in advance the absolute range: ± Fo_range to be evaluated for focus offset increases.

  However, the best point of the focus offset often does not necessarily exist at the “zero” point on the focus error due to device component errors and assembly adjustment errors. In addition, it is known that when the spherical aberration deviates to some extent from the optimum point, the best point is indicated by a focus offset value different from the original best focus offset point. If it is determined, there is a high possibility of causing an erroneous determination.

  On the other hand, the change in the reproduction signal amplitude appears in a state where the maximum value can be determined with respect to the change in the focus offset even when the spherical aberration is in an appropriate state.

  Further, the change in the reproduction signal amplitude is not greatly influenced by the state of the spherical aberration, and the change appears in a state where the maximum value can be determined with respect to the change in the focus offset.

  However, this also means that in a certain spherical aberration correction state, it is impossible to determine whether the state of the spherical aberration is right or wrong from the change state of only the reproduction signal amplitude, and the absolute value of the reproduction signal amplitude is used. If an attempt is made to do so, the absolute signal amplitude changes due to the effect of changes in reflectivity between disks, variations in the disk, reproduction power error, etc., and therefore cannot be used alone.

  On the other hand, it has been found that the evaluation index such as jitter mentioned above changes greatly with respect to the focus offset when the spherical aberration state is not appropriate.

  In the present embodiment, focusing on this feature, attention is paid to a change amount of the second evaluation index such as jitter within a predetermined focus offset range with respect to a focus offset value at which the reproduction signal amplitude takes a maximum value. Thus, it is intended to determine whether the spherical aberration correction state is right or wrong.

  Here, examples of the reproduction signal amplitude measurement include measurement by peak detection and bottom detection. As for jitter measurement, examples include a method of obtaining a time interval by interpolation calculation from a data sample value by a PLL clock, a method of obtaining from a phase error signal of a PLL clock, and the like.

  The flow of spherical aberration determination, spherical aberration and focus offset adjustment will be described.

Set focus offset range (Fo_set1
~ Fo_set2), measure the evaluation index and determine whether or not the spherical aberration is corrected. Hereinafter, the determination will be described.

  First, with respect to the measured reproduction signal amplitude, a focus offset value Fo_Vmax that maximizes the reproduction signal amplitude is calculated (S5).

  If this focus offset value Fo_Vmax is not within the specified range of the focus offset value (Fo_set1 + Fo_range to Fo_set2-Fo_range: Fo_set1 <Fo_set1), this is a case where the amount of correction of spherical aberration differs greatly, and spherical aberration The correction state is determined to be inappropriate, and the process proceeds to a spherical aberration correction adjustment routine (S6).

When Fo_Vmax is within the specified range of the focus offset value, the focus offset value that maximizes the playback signal amplitude
With respect to Fo_Vmax, the amount of change in the jitter value in a predetermined offset range before and after: ± Fo_range is calculated. Here, the amount of change in jitter is the focus offset: Fo_Vmax
Difference between maximum jitter value and minimum jitter value between two points in the ± Fo_range range: means Δ jitter (S7).

  Here, if the predetermined value: Δ jitter_Limit is set to a value at which it is possible to determine that the deviation of the spherical aberration correction can be sufficiently corrected by the focus offset setting, the Δ jitter value is equal to or less than Δ jitter_Limit. In this case, the spherical aberration correction value is almost in an optimum state, and it can be determined that the deviation of the spherical aberration correction can be sufficiently corrected by the focus offset setting. In addition, the absolute value of the jitter best value may be determined together.

  Therefore, if Δjitter is equal to or less than a predetermined value, it is determined that it is not necessary to adjust the spherical aberration correction any more, and the spherical aberration correction is not adjusted, and the focus offset: fo_opt at which the evaluation index takes the best value is calculated. (S9).

  Thus, the determination of whether or not to correct the spherical aberration is completed, and the focus offset value: fo_opt at which the evaluation index jitter takes the minimum value is adopted in the subsequent information recording / reproduction (S9).

  On the other hand, if the Δ jitter value is not less than or equal to the predetermined value, it is determined that the spherical aberration correction value is not within the allowable range, and the process proceeds to a spherical aberration correction adjustment routine (S10).

  The state of the spherical aberration correction adjustment routine (S8) and the spherical aberration correction adjustment routine (S9) will be described with reference to FIG.

  In the figure, in the optical system with a wavelength of 405 nm and NA: 0.85, the spherical aberration correction is appropriate and good, and the spherical aberration correction is inappropriate and there is spherical aberration equivalent to ≈7 μm in terms of the cover layer thickness. This shows the focus offset dependency of the reproduction signal amplitude and the timing jitter in the case where the signal is reproduced. Further, the focus offset error amount on the horizontal axis in the drawing is expressed by adding a correction value to the focus offset value so that the focus offset value giving the maximum reproduction signal amplitude value becomes “0”.

  As described above, in the present embodiment, the timing jitter that is the second evaluation index in the predetermined focus offset range with respect to the focus offset value that gives the maximum value to the reproduction signal amplitude that is the first evaluation index. The amount of change is detected to determine whether the spherical aberration correction amount is right or wrong. When the focus offset range (Fo_range) is ± 0.15 μm, the change in jitter when spherical aberration correction is good is 6.7% + 0.3 points in terms of jitter bottom + Δjitter. On the other hand, when the spherical aberration correction is inappropriate, it appears as 7.3% + 4.7 points.

  Further, although only 0.5 point is seen in the bottom jitter, it can be seen at the same time that the focus offset dependency is greatly shown.

  As described above, in the present invention, whether or not the spherical aberration is corrected is determined based on the change amount of the evaluation index in the focus offset dependency. It is desirable that the evaluation index value Δjitter threshold at this time be statistically determined in a plurality of actual drives.

  If the focus offset value that gives the maximum amplitude of the playback signal is not within the specified range of the focus offset value (Fo_set1 + Fo_range to Fo_set2-Fo_range: Fo_set1 <Fo_set1), the spherical aberration correction state is determined to be inappropriate and the spherical When the process proceeds to the aberration correction adjustment routine (S6) and when the evaluation index value Δ jitter does not satisfy the threshold value and the process proceeds to the spherical aberration correction adjustment routine (S10), the spherical aberration correction direction is determined and the spherical aberration correction is performed. Then, the above-described determination operation for the spherical aberration correction state is repeated.

  First, when the maximum value of the reproduction signal amplitude is not within the predetermined range of the focus offset value (S6), the reproduction signal amplitude takes the maximum value in consideration of the complementary relationship between the spherical aberration and the focus offset. The adjustment direction of the spherical aberration correction can be determined according to the polarity of the focus offset. By determining this polarity, it is possible to determine the direction in which the spherical aberration correction should be adjusted, and the spherical aberration correction mechanism is driven in a predetermined step in this direction. For example, when the reproduction signal amplitude takes the maximum value on the “+” side of the focus offset value, the spherical aberration correction is changed to the “−” side. Conversely, when the reproduction signal amplitude takes the maximum value on the “−” side, the spherical aberration is corrected. The spherical aberration correction mechanism may be operated corresponding to the polarity relationship in the apparatus design, such as changing the correction to the “+” side.

  Here, it is desirable that the change amount of the spherical aberration correction mechanism is set to be large with respect to the adjustment routine (S9) described below.

  Next, when proceeding to the adjustment routine (S9), according to the study of the present inventor, as shown in FIG. 7, when the spherical aberration correction value is inappropriate, the focus offset value that takes the maximum value of the amplitude characteristic is obtained. And a difference in the minimum focus offset value of the jitter characteristic appears. Further, it was confirmed that when the spherical aberration correction value is inappropriate on the opposite side, the focus offset state of the maximum value of the amplitude characteristic and the minimum value of the jitter characteristic appears in the reverse direction. Therefore, by determining the polarity of this deviation, the direction in which the spherical aberration correction should be adjusted can be determined, and the spherical aberration correction mechanism is driven in this direction by a predetermined step, and the above-described determination operation of the spherical aberration correction state is repeated. .

  In addition, when proceeding to the routines (S6) and (S10), since the recording state is expected to be incomplete, re-recording may be considered.

  By performing the operations described above, it is possible to quickly determine whether the apparatus is in a spherical aberration state.

  In the present embodiment, the jitter has been described as an example of the second evaluation index. However, as described in the text, other evaluations such as statistical values of likelihood differences between paths in Viterbi decoding, error rates, and the like. Needless to say, it is possible to determine whether or not to correct spherical aberration in the same manner using the index.

<Embodiment 2>
In the first embodiment, as the evaluation index of the reproduction signal, whether or not to correct the spherical aberration is determined by paying attention to the reproduction signal amplitude and jitter which is another evaluation index. However, in the present embodiment, the embodiment is not limited. As described in 1 above, a method for determining whether or not spherical aberration correction is appropriate for a single evaluation index using the fact that another evaluation index such as jitter has a strong correlation with an error rate will be described.

  Since the configuration of the apparatus and the like is the same as that of the first embodiment, it is omitted.

  Even in this embodiment, the correction of spherical aberration is performed by measuring the focus offset dependency.

  In this embodiment, in the initial spherical aberration correction state, the focus offset dependency is measured, and the center value in the range below the predetermined reference value of the evaluation index is set as Fo_ref. Evaluation in a predetermined focus offset range: ± Fo_range with respect to this value The change amount of the index is measured, and the measured change amount determines whether or not the Δ evaluation index value is equal to or less than a predetermined value, and determines whether or not the spherical aberration correction is appropriate.

  In the present embodiment, a jitter value is taken as an example as an evaluation index of a reproduction signal and will be described below.

  FIG. 8 shows a determination procedure of the focus offset and spherical aberration correction system. Since the procedure from the determination procedure to S3 in the first embodiment is the same, the description thereof is omitted.

  Following the recording, the recorded information is reproduced in the second round, and the reproduced signal is evaluated using a predetermined evaluation index (S4).

  As described above, as an example, the focus offset value has an end (−) of the swing width as an initial value, and is a method of giving a change that becomes the final value of the other end (+) in one round. The focus offset value is reproduced while changing the focus offset value step by step for each divided block.

  If the change time of the focus offset value is concerned, it is naturally conceivable to provide time for changing the focus offset value stepwise before the initial value or after the end value.

  Next, regarding the reproduction signal evaluation, here, a case where the jitter value of the time interval measurement is used alone will be described. In the present embodiment, the jitter value is taken as an example, but it is needless to say that the present invention is not limited to this.

Set focus offset range (Fo_set1
~ Fo_set2), the jitter value of the evaluation index is measured, and the spherical aberration correction state is determined. The setting range of the focus offset may be determined from the limit point on the apparatus. Hereinafter, the determination will be described.

  First, a focus offset range lower than the predetermined jitter criterion 1 is calculated for the measured jitter value, and a center value Fo_ref of the focus offset range is obtained (S5).

  When the measured jitter offset is less than the predetermined jitter criterion 1, the focus offset value Fo_opt giving the best point of the evaluation index is obtained, and the spherical aberration correction value is judged to be good. The determination of whether or not to correct is terminated (S6).

  In the case of S5, the change amount of the jitter value in the predetermined offset range before and after: Fo_range is calculated with respect to Fo_ref. Here, the amount of change in jitter means the difference between the maximum jitter value and the minimum jitter value between two points of the focus offset: Fo_ref ± Fo_range: Δ jitter (S7).

  Here, if the predetermined value: Δ jitter_Limit is set to a value at which it is possible to determine that the deviation of the spherical aberration correction can be sufficiently corrected by the focus offset setting, the Δ jitter value is equal to or less than Δ jitter_Limit. In this case, it can be determined that the spherical aberration correction value is in an almost optimal state, and the deviation of the spherical aberration correction can be sufficiently corrected by the focus offset setting (S8).

  Accordingly, when Δjitter is equal to or smaller than a predetermined value, it is determined that it is not necessary to adjust the spherical aberration correction any more, and the spherical aberration correction is not adjusted, and the focus offset: fo_opt at which the evaluation index has the best value is calculated. .

  Thus, the determination of whether or not to correct the spherical aberration is completed, and the focus offset value: fo_opt at which the evaluation index jitter takes the minimum value is adopted in the subsequent information recording / reproduction (S9).

  On the other hand, if the Δ jitter value is not less than or equal to the predetermined value, it is determined that the spherical aberration correction value is not within the allowable range, and the process proceeds to a spherical aberration correction adjustment routine (S10).

  In the present invention, whether the spherical aberration correction state is right or wrong is determined based on the amount of change in the evaluation index in dependence on the focus offset, and the evaluation index value Δjitter threshold at this time is statistically determined in a plurality of actual drives. Is desirable.

  In the present embodiment, whether or not the spherical aberration is in the initial state is determined, and it is determined whether or not further spherical aberration correction is necessary. When the spherical aberration is inappropriate and the spherical aberration correction is necessary, for example, it is conceivable to adjust the spherical aberration correction by the spherical aberration correction mechanism and repeat the determination of the spherical aberration state.

  By performing the operations described above, it is possible to quickly determine whether the apparatus is in a spherical aberration state.

  In the present embodiment, the jitter is described as an example of the second evaluation index. However, as described in the text, other evaluation indices such as a statistical value of likelihood difference between paths in Viterbi decoding, an error rate, and the like. Needless to say, it is possible to determine whether or not to correct spherical aberration in the same manner.

1 is a configuration diagram of an optical pickup device according to an embodiment of the present invention. It is a block diagram of an optical disk. It is a block diagram of an optical disk. FIG. 5 is a correlation diagram of jitter and error rate in optical disc characteristics. It is a likelihood difference statistical value in an optical disc characteristic, and an error rate correlation diagram. It is a flowchart of the spherical aberration determination process in Embodiment 1 of this invention. FIG. 6 is a focus offset characteristic diagram of a reproduction signal amplitude and jitter when the spherical aberration is good or bad. It is a flowchart of the spherical aberration determination process in Embodiment 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical disk 6 Optical head 61 Semiconductor laser 650 Spherical aberration correction optical system 651 Spherical aberration correction mechanism 660 Objective lens 661 Focus / tracking actuator 10 Focus / tracking drive circuit 11 Spherical aberration correction mechanism drive circuit 12 Controller

Claims (12)

A focus offset adjustment mechanism for adjusting the focus offset of the light beam by driving the objective lens with respect to the information recording surface of the optical disc, and a spherical aberration correction mechanism for correcting the spherical aberration generated in the light beam irradiated on the information recording surface The spherical aberration correction mechanism and the focus in the optical disc apparatus that irradiates the information recording surface of the optical disc through the objective lens and reproduces the information on the information recording surface using the reflected light beam. An adjustment method of an optical disc device for adjusting an offset mechanism to an allowable range,
The spherical aberration correction mechanism is held at the value at the start of adjustment, and the focus offset is changed within a predetermined range by the focus offset adjustment mechanism, and the characteristics of the information reproduction signal on the information recording surface at this time are evaluated in a predetermined manner. Detecting by using an index, detecting the dependency of the evaluation index on the focus offset change, and omitting the spherical aberration adjustment by the spherical aberration adjusting mechanism when the evaluation index value and the dependency are equal to or less than a predetermined specified value. A method of adjusting an optical disk device characterized by the above.   If the evaluation index characteristic does not satisfy the predetermined specified value, the adjustment direction of the spherical aberration correction is detected from the focus offset dependency, the spherical aberration adjustment mechanism is driven in the direction to correct the spherical aberration, and the determination is performed. 2. The method of adjusting an optical disc apparatus according to claim 1, wherein the adjustment is repeated.   The holding of the adjustment state of the spherical aberration correction mechanism to a predetermined value is an initial state uniquely determined by the optical disc apparatus. When the information recording layer of the optical disc has a multilayer structure, the optical disc apparatus corresponds to each layer. 2. The method of adjusting an optical disc apparatus according to claim 1, wherein the initial state is uniquely determined.   The adjustment state of the spherical aberration correction mechanism held at a predetermined value is the adjustment position averaged from the state in which the optical disc device was last used or the past use state, and the information recording layer of the optical disc has a multilayer structure. When the optical disk apparatus is used, the optical disk apparatus is in the last used state having the layer information used last time, or the adjustment position averaged from the past usage state for each layer. The method of adjusting an optical disk device according to claim 1.   3. The method of adjusting an optical disc apparatus according to claim 1, wherein the predetermined evaluation index is a signal amplitude value of an information reproduction signal.   3. The method of adjusting an optical disc apparatus according to claim 1, wherein the predetermined evaluation index is a timing jitter value in an information reproduction signal.   3. The method of adjusting an optical disk device according to claim 1, wherein the predetermined evaluation index is an error rate in information reproduction.   The optical disk apparatus according to claim 1 or 2, wherein the optical disk apparatus employs Viterbi decoding, and the predetermined evaluation index uses a statistical value of likelihood difference at the time of predetermined path merging in Viterbi decoding. Method.   3. The method of adjusting an optical disk apparatus according to claim 1, wherein the predetermined evaluation index is determined by using the evaluation index of claims 5 to 8 in combination.   3. The method of adjusting an optical disk device according to claim 1, wherein the predetermined prescribed value is defined by a best value and a change amount of an evaluation index value with respect to a focus error amount calculated from a focus error signal.   The predetermined prescribed value is a second value in a range in which a reproduction signal amplitude is used as a first evaluation index, a focus offset value at the maximum amplitude of the reproduction signal amplitude value is a reference point, and a predetermined focus offset is given from the reference point. 3. The method of adjusting an optical disk apparatus according to claim 1, wherein the determination is made with a change amount of the evaluation index value of the optical disk apparatus. A focus offset adjustment mechanism for adjusting the focus offset of the light beam by driving the objective lens with respect to the information recording surface of the optical disc, and a spherical aberration correction mechanism for correcting the spherical aberration generated in the light beam irradiated on the information recording surface In the optical disc apparatus for irradiating the information recording surface of the optical disc with the light beam through the objective lens and reproducing the information on the information recording surface using the reflected light beam,
The adjustment state of the spherical aberration correction mechanism is held at a predetermined value, and the focus offset is changed within a predetermined range by the focus offset adjustment mechanism, and the characteristic of the information reproduction signal on the information recording surface at this time is evaluated in a predetermined manner A means for detecting using an index, and a means for analyzing the dependence of the evaluation index on the focus offset change. When the dependence is below a predetermined value, the spherical aberration adjustment by the spherical aberration adjustment mechanism is omitted. If the predetermined prescribed value is not satisfied, the adjustment direction of the spherical aberration correction is detected from the focus offset dependency analysis, the spherical aberration adjustment mechanism is driven in the direction to perform the spherical aberration correction, and the determination is repeated. An optical disc device characterized.

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