JP3692072B2 - Optical disk apparatus adjustment method and optical disk apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for adjusting an optical disk device and an optical disk device. In particular, the present invention relates to a method for adjusting a focus offset of a light beam and a spherical aberration correction system for a high-density optical disc.
[0002]
[Prior art]
At the time of information recording in the optical disk device, the optical head device 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. On the other hand, the tracking servo performs control in a 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.
[0003]
The focus servo needs to satisfy the follow-up performance so that the beam spot diameter is always substantially constant, and this needs to be controlled within a range sufficiently smaller than an amount called a depth of focus. As an approximation, the depth of focus is proportional to the wavelength of the light source and inversely proportional to the square of the numerical aperture (NA) of the objective lens.
[0004]
The spot size of the focused light irradiated on the information recording surface of the optical disc is proportional to the wavelength and inversely proportional to NA indicating the aperture angle of the objective lens for focusing the light. Therefore, in order to reduce the spot size of the focused light in order to improve the recording density, it is necessary to shorten the wavelength and increase the NA of the objective lens.
[0005]
In the case of a DVD (Digital Versatile Disc), which is an optical disc currently in practical use, the wavelength of the light source is 650 nm, and the NA of the objective lens is 0.6. On the other hand, development of technology for further increasing the density of DVD is being promoted by various companies. The wavelength of the light source is assumed to be about 405 nm, and the NA of the objective lens is assumed to be 0.85. Therefore, it can be seen that in the next generation optical disc, the above-mentioned depth of focus is significantly shorter than the current DVD due to its nature. For this reason, high follow-up performance is required for the focus servo.
[0006]
On the other hand, when the disc is tilted due to the warp of the disc or the like, asymmetry of the optical path passing through the substrate occurs. Due to this asymmetry, coma aberration occurs in the focused light on the recording surface. Since the coma aberration amount is approximately proportional to the third power of the NA value, if the NA value is increased to increase the density, a very large coma aberration is generated with a slight change in the characteristics of the disk.
[0007]
Further, when the thickness of the light transmission layer of the disc is different from the specification value, spherical aberration occurs. Since the amount of spherical aberration is approximately proportional to the fourth power of NA, when the NA value is increased to increase the density, the amount of spherical aberration due to the disc thickness error becomes significantly larger.
[0008]
For this reason, in the next generation optical disc system, it is considered to introduce a mechanism for correcting spherical aberration. Naturally, the recording / reproducing apparatus requires fine adjustment control of the spherical aberration correction mechanism. Since this fine adjustment control has the same effect as the above-described focus servo offset adjustment, it is necessary to find an optimum point between the two adjustment points.
[0009]
As an optimization adjustment of the focus servo offset and an optimization adjustment of the spherical aberration correction mechanism in an optical disk system using a high NA objective lens, there is a method disclosed in Japanese Patent Laid-Open No. 10-188301.
[0010]
In this method, the focus offset is first optimized by moving the second group objective lens in an integrated manner, and then the spherical aberration correction mechanism is optimized by moving the distance between the lenses of the second group objective lens. It is.
[0011]
Another known example is an adjustment method disclosed in K. Takahashi et al., ISOM (International Symposium on Optical Memory) 2001, We-B-02. This is a method for effectively adjusting the spherical aberration correction mechanism by adjusting the focus offset and adjusting the position of the beam magnifying lens.
[0012]
[Problems to be solved by the invention]
In all of the above known examples, the amplitude of the RF signal reproduced from the optical disk is detected, and the focus offset or the spherical aberration correction system is adjusted. However, when the point at which the amplitude of the RF signal is maximized is adjusted as the optimum point, it may not always be optimum from the viewpoint of the system margin.
[0013]
That is, when the adjustment of the focus servo offset and the spherical aberration correction system is optimized so as to obtain the maximum value of the amplitude of the RF signal, the bit error rate (bER) after PRML (Partial Response Maximum Likelihood) signal processing is set. It has been found that the problem that the focus offset margin becomes narrow may occur. For this reason, particularly when PRML is used for signal processing, it is no longer appropriate to use the peak value of the RF signal as a reference.
[0014]
Accordingly, an object of the present invention is to provide an optical disc adjustment method and an optical disc apparatus capable of realizing the adjustment of the focus offset and the spherical aberration correction system with high accuracy in order to solve the above problems.
[0015]
[Means for Solving the Problems]
The present invention provides a focus offset adjustment mechanism that adjusts a focus offset by driving an objective lens in a direction perpendicular to an information recording surface of an optical disc, and a spherical surface that corrects spherical aberration that occurs in a light beam irradiated on the information recording surface. In the optical disc apparatus having an aberration correction mechanism, irradiating the information recording surface of the optical disc through the objective lens with a light beam, and reproducing the information on the information recording surface using the reflected light beam, the spherical aberration An optical disk apparatus adjustment method for obtaining an optimal adjustment state of a correction mechanism and a focus offset mechanism, wherein a plurality of spherical aberration correction states are set by the spherical aberration correction mechanism, and each state in which the spherical aberration correction state is set The focus offset is changed within a predetermined range by the focus offset adjustment mechanism. As the characteristics of the information reproduction signal on the information recording surface when the focus offset is changed, the horizontal axis is the focus offset amount and the maximum value of the variable frequency oscillator (VFO) signal amplitude (or jitter) is the center. The characteristic that is expressed as a curve in which the amplitude (or jitter) of the VFO signal changes is detected, and the symmetry of each characteristic curve centered on the local maximum is ± F0 around the local maximum. A difference (A0-A1) between the decrease (or increase) A0 and A1 from the maximum value at a deviated focus offset point is detected, and a curve with the smallest difference is the best in symmetry. It is discriminated as a certain curve, and this spherical aberration correction state is set to obtain this best curve. The focus offset amount is set to give the maximum value of the curve that is the best. It is characterized by that.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0017]
First, the point considered so that the capability of the system of this invention can be extended is demonstrated.
[0018]
The aforementioned coma aberration is proportional to the thickness of the light transmission layer of the disk. For this reason, in the next-generation optical discs that aim to increase the density, it has been studied to reduce the thickness of the light transmission layer in order to ensure a margin for the tilt of the disc. Specifically, it is considered to reduce the light transmission layer thickness of the next generation optical disc from 0.6 mm of the current DVD to 0.1 mm.
[0019]
As described above, in the next generation optical disc, it is considered that an increase in coma aberration accompanying the increase in NA is compensated by making the light transmission layer thinner. On the other hand, as the NA increases, the thickness of the light transmission layer is considered. An increase in spherical aberration due to errors also becomes a problem. This is because the spherical aberration is approximately proportional to the fourth power of the NA value. Variations in thickness of the light transmission layer are inevitable in manufacturing. In addition, a technique of forming the recording layer into two layers in the thickness direction is also considered. In this case, for example, the middle of the two layers must be the specification value of the thickness, and a thickness error occurs in each layer. Become. Since the aberration due to the thickness error cannot be compensated for by reducing the thickness of the light transmission layer, the next generation optical disc is considering introducing a new mechanism for correcting the spherical aberration into the optical system. This is not introduced at all in the conventional DVD or CD system, and there is a difference from the conventional system.
[0020]
Of course, the present invention can sufficiently realize the focus offset and spherical aberration correction of the light beam with high accuracy even if the thickness of the light transmission layer is 0.6 mm.
[0021]
This will be specifically described below.
[0022]
FIG. 1 shows an example of a cross-sectional view of an optical disc 1 according to 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 bonded to the information recording layer 3 formed on the substrate 2 via an adhesive or an ultraviolet curable resin.
[0023]
FIG. 2 shows a state of information recording on the optical disc 1. A spiral or concentric information recording track 5 is formed on the information recording layer 3 of the optical disc 1. An information recording track 5 is formed on the optical disc 1 by a guide groove by physical unevenness, and information is recorded in a concave portion or a convex portion, or both by, for example, a mark by phase change. When the optical disc 1 is a read-only disc, the information recording track 5 is formed in advance by a prepit arrangement. In the configuration of the information recording track 5, a header area 6 in which address information and the like are recorded in advance and a user area 7 in which user information is recorded are alternately arranged.
[0024]
FIG. 3 shows an example of a data layout. The contents of each component of the header area 6 are as follows.
[0025]
The VFO field is a field for providing synchronization to the variable frequency oscillator in the phase-locked loop for phase-synchronizing the read channel bits. VFO is an abbreviation for Variable Frequency Oscillator. The AM field is a field for providing byte synchronization to the optical disk apparatus for the next PID field. AM is an abbreviation for 1 Address Marak (address mark), and PID is an abbreviation for Physical Identification Data. The PID field is a field that stores data including a spare area, a PID number, a sector type, a layer number, a sector number, and the like. An IED (ID Error Detection code) field is a field for detecting an error occurring in the data of the PID field. The PA (Postamble) field is a field composed of data for completing the last byte of the preceding IED field based on the modulation method. The TM (Track-center Mark) field is a field for recording a signal for detecting the physical center of the track.
[0026]
On the other hand, the contents of each component of the user area 7 are as follows.
[0027]
The GAP1 field is a field that gives a time margin from the reproduction of the header area to the subsequent writing of the GUARD (guard) field. The GUARD2 field is a field for recording data for preventing deterioration of the start end of the PS field and the DATA field following the repetitive overwriting, and for providing synchronization to the variable frequency oscillator of the phase locked loop of the read channel bit. The PS field is a field for providing byte synchronization for the following data field. The DATA field is a field for recording user data. The PA field is a field including data for completing a byte based on the modulation method following the preceding DATA field. The GUARD2 field is a field for recording data for preventing the deterioration of the termination of the DATA field, and for compensating for a deviation of the actual recording data length from the ideal value. The GAP2 field is a field for compensating variation in actual data length due to rotation unevenness.
[0028]
Next, a configuration example of the optical head of the optical disc apparatus for recording / reproducing the disc will be described with reference to FIG.
[0029]
A short wavelength semiconductor laser 20 is used as the light source. The wavelength of the emitted light is, for example, in the violet wavelength band in the range of 395 nm to 415 nm. The emitted light 100 from the semiconductor laser light source 20 becomes parallel light by the collimating lens 21 and passes through the polarization beam splitter 22 and the λ / 4 plate 23. Then, after passing through the relay lens system 24, the light enters the objective lens 25.
[0030]
Thereafter, the light emitted from the objective lens 25 passes through the cover layer 4 of the optical disc 1 and is condensed on the information recording layer 3. The reflected light 101 from the information recording layer 3 of the optical disk 1 is transmitted again through the cover layer 4 of the optical disk 1, transmitted through the objective lens 25, the relay lens system 24, and the λ / 4 plate 23, and reflected by the polarization beam splitter 22. Thereafter, the light passes through the light detection system 26 and enters the light detector 27.
[0031]
The light receiving part of the photodetector 27 is usually divided into a plurality of parts, and a current corresponding to the light intensity is output from each light receiving part. The output current is converted into a voltage by an unillustrated I / V amplifier, then processed by the arithmetic circuit 11, and output as an HF signal, a focus error signal, a track error signal, and the like. A focus error signal, a track error signal, and an adjustment signal, which will be described later, obtained by the arithmetic circuit 11 are supplied to the servo driver 12.
[0032]
The objective lens 25 is movable in the optical axis direction and is focus controlled. The movement of the objective lens 25 is controlled by the drive unit 29.
[0033]
Here, the relay lens system 24 includes a bottom lens 24a and a top lens 24b, and the top lens 24b is movable in the optical axis direction. The top lens is moved by the drive unit 28.
[0034]
The relay lens system 24 is designed to be incident on the objective lens 25 as substantially parallel light when the thickness of the cover layer 4 is a specified value (for example, 100 [μm]). However, when the thickness of the cover layer 4 deviates from the specified value, spherical aberration due to the thickness error of the cover layer 4 occurs. At this time, the shape of the focused spot on the information recording layer 3 of the optical disc 1 is distorted, so that stable and accurate recording / reproduction becomes difficult. On the other hand, spherical light is generated by making the incident light to the objective lens 25 into convergent light or divergent light. Further, by moving the top lens 24b of the relay lens system 24 in the optical axis direction, the incident light to the objective lens 25 can be made into convergent light or divergent light.
[0035]
For this reason, the top lens 24b of the relay lens system 24 is moved in the optical axis direction according to the thickness error amount of the cover layer 4, and the incident light to the objective lens 25 is converted into convergent light or divergent light, whereby the cover layer 4 The spherical aberration caused by the thickness error can be corrected.
[0036]
Specifically, when the thickness of the cover layer 4 is thicker than a predetermined value, the top lens 24b of the relay lens system 24 is such that incident light to the objective lens 25 becomes divergent light according to the thickness error amount of the cover layer 4. May be moved in the optical axis direction. Further, when the thickness of the cover layer 4 is thinner than the predetermined value, the top lens 24b of the relay lens system 24 is placed on the optical axis so that incident light to the objective lens 25 becomes convergent light according to the thickness error amount of the cover layer 4. Move in the direction.
[0037]
As described above, it is assumed that the next-generation optical disc apparatus is provided with means for correcting the spherical aberration accompanying the thickness error from the specified value of the cover layer 4 of the optical disc 1.
[0038]
FIG. 5 is a block diagram of the control system in the optical disk apparatus of the present invention, and the operation of the servo system will be described using this. In the optical head 30, a focus error signal (FES) and a tracking error signal (TES) are generated and output by reflected light from the optical disc 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.
[0039]
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.
[0040]
When the optical disk 1 is loaded in the optical disk apparatus, the optical disk 1 is rotated by a spindle motor (not shown) by constant linear velocity or constant rotation speed control. The focus error signal is appropriately amplified by the amplifier 32 via the phase compensation circuit 31 and then input to the focus drive circuit 33.
[0041]
The CPU 34 inputs a focus-on signal to the focus driving circuit 33 via the bus 40 after completion of pre-processing such as disk rotation and light source laser lighting, and the driving signal from the focus driving circuit 33 to the focus coil of the objective lens actuator 35. And apply focus control. Next, the tracking error signal is input to the tracking drive circuit 38 after being appropriately amplified by the amplifier 37 via the phase compensation circuit 36.
[0042]
After confirming the focus lock, the CPU 34 inputs a tracking-on signal to the tracking drive circuit 38 via the bus 40 and outputs a drive signal to the tracking coil of the objective lens actuator 35 to perform tracking control. In the relay lens system 24 that corrects spherical aberration, the top lens 24 b is driven in the optical axis direction by the actuator 41. The CPU 34 inputs a spherical aberration adjustment signal to the relay lens driving circuit 42 via the bus 40 according to a method described later, and drives the actuator 41 to adjust the spherical aberration correction amount.
[0043]
Further, the CPU 34 can adjust the offset of the focus control by inputting a signal to the offset adding circuit 43. This is called focus offset adjustment. By intentionally adding an offset to the servo control loop, the beam spot position can be adjusted up and down on the optical disc 1 (in a direction perpendicular to the optical disc 1).
[0044]
On the other hand, a reproduction signal (HF signal) from the information recording layer 3 of the optical disc 1 is output from the optical head 30 and sent to the CPU 34 through the bus 40. The HF signal is also input to the envelope detection circuit 44, the signal amplitude is detected, and sent to the CPU 34 via the bus 40.
[0045]
Next, a method for optimizing the focus offset adjustment and the spherical aberration correction system according to the present invention will be described.
[0046]
When the optical disc 1 is loaded in the optical disc apparatus, the above-described focus and tracking control is performed. The optical disc 1 has a structure as shown in FIGS. 2 and 3, and the adjustment of the focus offset and the spherical aberration correction system is optimized using the reproduction signal in the header area 6. Since the header area 6 is a data area previously recorded as pre-pits on the optical disc 1, there is an advantage that it is not necessary to record data again for these adjustments.
[0047]
Among the reproduction signals of the header area 6, it is convenient to use the signal amplitude of the VFO field described above. This is because the VFO field has 1) a data length that is usually longer than the other fields of the header area 6, and 2) the signal amplitude is constant because it is composed of repeated data of a single frequency signal. It can be said that it is easy to use as an adjustment signal.
[0048]
FIG. 6 shows a procedure for adjusting the focus offset and spherical aberration correction system using the signal amplitude of the VFO field in the header area 6. First, the position of the top lens 24b of the relay lens system 24, which is a spherical aberration correction system, is moved to the initial position (ST1). Next, the focus offset value is set to an initial value (ST2). Here, the header area is reproduced (ST3), and the signal amplitude of the VFO field is measured (ST4). Next, the final value of the focus offset amount is determined (ST5). If it is the final value, the process proceeds to step ST6. If it is not the final value, the focus offset amount is increased by one step and the process returns to step ST3.
[0049]
When the focus offset amount has been changed within the target range at one relay lens position, the final position of the relay lens is determined (ST6). ST7 If it is not the final position, the relay lens position is increased by one step and the process returns to ST3.
[0050]
When the VFO field signal amplitude is measured within the set relay lens position range using the focus offset amount as a parameter, the process proceeds to optimum value determination. First, a focus offset amount vs. VFO signal amplitude characteristic curve is created for each relay lens position (ST7). Thereby, a plurality of characteristic curves as shown in FIG. 7 are obtained. Although not shown, the plurality of characteristic curves are curves having different peak positions and different curve slopes.
[0051]
Next, the amount of decrease A0, A1 from the peak value of the VFO signal amplitude at a point shifted by ± Fo around the peak value of each characteristic curve is calculated (ST8) (see FIG. 7). In the example of one characteristic curve of FIG. 7, the peak value of the amplitude is 203 mV, the amplitude at the offset position + Fo is A0, and the amplitude at the offset position −Fo is A1.
[0052]
Based on such an agreement, | AO-A1 | of each characteristic curve of all relay lens positions is obtained. Then, the minimum | AO-A1 | is detected among the plurality of | AO-A1 | obtained. The relay lens position that gives a characteristic curve that minimizes | AO-A1 | is set as the optimum position (ST9).
[0053]
The optimum value of the focus offset amount is the focus offset amount that gives the maximum VFO signal amplitude at the optimum relay lens position obtained by the above processing (ST10).
[0054]
By the above procedure, the optimum values for focus offset adjustment and spherical aberration correction system (relay lens system) adjustment are obtained. Thus, instead of simply setting the relay lens position that gives the peak value of the VFO signal amplitude and the focus offset amount to the optimum value, the optimum value is set in terms of keeping the symmetry of the focus offset amount versus the VFO signal amplitude characteristic high. Ask. This concept makes it possible to widen the focus offset margin of the bit error rate (bER) after PRML (Partial Response Maximum Likelihood) signal processing.
[0055]
Next, as another embodiment of the present invention, a spherical aberration correction system using a reproduction signal jitter as a reference and a focus offset adjustment method will be described. As the reproduction signal to be measured, the reproduction signal in the header area 6 is used as in the above embodiment. However, since the VFO field is composed of a single frequency signal, it is considered that the jitter change is poor. In this case, the jitter of the entire header area 6 is used. When jitter measurement is performed, a jitter detection circuit is provided instead of the envelope detection circuit 44 shown in FIG.
[0056]
FIG. 8 shows a spherical aberration correction system and a focus offset adjustment procedure according to this embodiment. First, the position of the top lens 24b of the relay lens system 24, which is a spherical aberration correction system, is moved to the initial position (ST1). Next, the focus offset value is set to an initial value (ST2). Here, the header area is reproduced (ST3), and the jitter value of the header area is measured (ST4).
[0057]
Next, the final value of the focus offset amount is determined (ST5). If it is the final value, the process proceeds to step ST6. If it is not the final value, the focus offset amount is increased by one step and the process returns to step ST3. When the focus offset amount is changed within the target range at one relay lens position, the final position of the relay lens is determined (ST6). When the final position is reached, the process proceeds to the next step (a), and is not the final position. In this case, the relay lens position is increased by one step and the process returns to step ST3.
[0058]
When the jitter value in the header area is measured using the focus offset amount as a parameter within the set relay lens position range, the process proceeds to optimum value determination.
[0059]
First, a focus offset amount vs. jitter value characteristic curve is created for each relay lens position (ST7). Thereby, a plurality of specific curves as shown in FIG. 9 are obtained.
[0060]
A jitter value at a point shifted by ± Fo around the bottom value of each characteristic curve is determined. Next, increase amounts J0 and J1 in which each jitter value increases from the bottom value are calculated (ST8) (see FIG. 9).
[0061]
Based on such an agreement, the characteristic curve | JO-J1 | of all relay lens positions is obtained. The smallest | JO-J1 | is detected from the plurality of | JO-J1 | Then, the relay lens position giving the characteristic curve that minimizes | JO-J1 | is set as the optimum position (ST9). The optimum value of the focus offset amount is the focus offset amount that gives the minimum jitter value at this optimum relay lens position (ST10). By the above procedure, the optimum values for focus offset adjustment and spherical aberration correction system (relay lens system) adjustment are obtained.
[0062]
FIG. 10 further shows another embodiment of the present invention. In this example, the adjustment procedure of the focus offset and spherical aberration correction system using the signal amplitude of the VFO field in the header area 6 is shown. In this example, the envelope detection circuit 44 of FIG. 5 is used as it is.
[0063]
First, the position of the top lens 24b of the relay lens system 24, which is a spherical aberration correction system, is moved to the initial position (ST1). Next, the focus offset value is set to an initial value (ST2).
[0064]
Here, the header area is reproduced (ST3), and the signal amplitude of the VFO field is measured (ST4). Next, the final value of the focus offset amount is determined (ST5). If it is the final value, the process proceeds to ST6. If it is not the final value, the focus offset amount is increased by one step and the process returns to ST3. When the focus offset amount is changed within the target range at one relay lens position, the final position of the relay lens is determined (ST6). When the final position is reached, the process proceeds to the next step (a), and is not the final position. In this case, the relay lens position is increased by one step and the process returns to step ST3.
[0065]
When the VFO field signal amplitude is measured within the set relay lens position range using the focus offset amount as a parameter, the process proceeds to optimum value determination.
[0066]
First, a focus offset amount vs. VFO signal amplitude characteristic curve is created for each relay lens position (ST7). Thereby, a plurality of characteristic curves as shown in FIG. 11 are obtained. Here, the slopes S0 and S1 of the tangent line of the characteristic curve at the point shifted by ± Fo around the peak value of each characteristic curve are calculated (ST8) (see FIG. 11). The calculation of the slopes S0 and S1 is executed by the CPU 34.
[0067]
Based on the above agreement, the characteristic curve of | SO + S1 | at all relay lens positions is obtained. The minimum | SO + S1 | is detected from the plurality of | SO + S1 | Then, the relay lens position giving a characteristic curve that minimizes | SO + S1 | is set as the optimum position (ST9). The optimum value of the focus offset amount is the focus offset amount that gives the maximum VFO signal amplitude at this optimum relay lens position (ST10).
[0068]
By the above procedure, the optimum values for focus offset adjustment and spherical aberration correction system (relay lens system) adjustment are obtained. Also in this embodiment, the optimum value can be obtained from the viewpoint of keeping the symmetry of the focus offset amount versus the VFO signal amplitude characteristic high, and the focus of the bit error rate (bER) after the PRML (Partial Response Maximum Likelihood) signal processing is performed. It becomes possible to widen the offset margin
In the above embodiment, a relay lens system is considered as the spherical aberration correction system, and the position adjustment of the top lens 24b is assumed. However, the adjustment method of the present invention does not depend on the type of the spherical aberration correction system, and is known, for example, The same effect can be expected by using the spherical aberration correction means, such as adjusting the distance between the lenses of the second group objective lens, or correcting the spherical aberration by the liquid crystal element provided in the optical system before the objective lens. In the above description, the signal obtained by reproducing the prepit is used as the reproduction signal to be measured. However, in the case of an optical disk having no prepit, the reproduction signal based on the mark sequence recorded by the optical disk apparatus is used. It is clear that the invention is effective.
[0069]
In the embodiments shown in FIGS. 6, 8, and 10, after setting the relay lens position to the initial position, the focus offset is changed within a predetermined range to obtain the first characteristic, After setting the relay lens position to the second position, the focus offset was changed within a predetermined range to obtain the second characteristic, and this measurement was repeated to detect a plurality of characteristics. . In other words, this is a technique for obtaining a curve with one characteristic by changing the focus offset while the relay lens position is fixed. However, the present invention need not be such a procedure.
[0070]
That is, the initial state of the focus offset is set first, then the relay lens position is changed within a predetermined range to obtain the first characteristic, and then the second state of the focus offset is set, and then the relay Alternatively, the second position may be obtained by changing the lens position within a predetermined range, and a plurality of characteristics may be detected by repeating such measurement.
[0071]
Moreover, although embodiment shown in FIG.6, FIG.8, FIG.10 was demonstrated as independent, embodiment which combined arbitrary things may be sufficient. Then, when the relay lens position determined from the symmetry of the characteristic curve, the relay lens position determined based on less jitter, and the relay lens position determined based on the small inclination of the characteristic curve are found, The final relay lens position may be determined based on the majority decision, or the average relay lens position may be determined.
[0072]
As described above, in the present invention, in the optical disc apparatus for reproducing the information on the information recording surface by irradiating the information recording surface of the optical disc with the light beam through the objective lens, the objective lens is placed on the information recording surface of the optical disc. Thus, the mechanism for adjusting the focus offset by driving in the vertical direction and the spherical aberration correcting mechanism for correcting the spherical aberration generated in the light beam irradiated on the information recording surface are optimized. In this adjustment method, particularly in the present invention, the characteristic of the information reproduction signal on the information recording surface when the focus offset is changed within a predetermined range is measured, and the symmetry of the characteristic curve of the reproduction signal is detected. Is.
[0073]
In this way, the focus offset and the spherical aberration correction system can be optimized so as to widen the focus offset margin by paying attention to the symmetry of the reproduction signal characteristics.
[0074]
In the present invention, the reproduction signal amplitude of the VFO signal in the prepit header area of the optical disk is used as the characteristic of the reproduction signal. This is because relatively long data is recorded in the VFO signal, and since the signal amplitude is constant, it can be easily used as an adjustment signal.
[0075]
Furthermore, in the above embodiment, the reproduction signal jitter in the prepit header area of the optical disc is used as the characteristic of the reproduction signal.
[0076]
Further, PRML signal processing may be used for reproducing information on the information recording surface of the optical disc. This is because the present invention can be applied to an optical disc apparatus that reproduces user data using PRML signal processing. In this case, it is possible to secure a focus offset margin of an error rate especially after PRML signal processing.
[0077]
Further, in an optical disc apparatus that reproduces information on the information recording surface by irradiating an information recording surface of the optical disc through an objective lens, the objective lens is driven in a direction perpendicular to the information recording surface of the optical disc. A mechanism for adjusting a focus offset, and a spherical aberration correction mechanism for correcting a spherical aberration generated in a light beam irradiated on the information recording surface. The focus offset is changed within a predetermined range, and the information is recorded on the information recording surface. Means for measuring a characteristic of a reproduction signal of information and detecting symmetry of a characteristic curve of the reproduction signal.
[0078]
【The invention's effect】
As described above, according to the adjustment method and apparatus of the present invention, the adjustment of the focus offset and the spherical aberration correction system can be realized with high accuracy.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of an optical disk according to an embodiment of the present invention.
FIG. 2 is a diagram showing an example of an information recording form on an optical disc according to the present invention.
FIG. 3 is a diagram showing an example of a data layout on an optical disc according to the present invention.
FIG. 4 is a diagram showing a configuration example of an optical head of an optical disc apparatus according to the present invention.
FIG. 5 is a block diagram showing an example of a control system of the optical disc apparatus of the present invention.
FIG. 6 is a flowchart for explaining an example of the adjustment method of the optical disc apparatus of the present invention.
7 is a diagram showing an example of a characteristic curve shown for explaining the adjustment method of FIG. 6; FIG.
FIG. 8 is a flowchart for explaining another example of the adjustment method of the optical disc apparatus of the present invention.
FIG. 9 is a diagram showing an example of a characteristic curve shown for explaining the adjustment method of FIG. 8;
FIG. 10 is a flowchart for explaining still another example of the adjustment method of the optical disc apparatus of the present invention.
11 is a view showing an example of a characteristic curve shown for explaining the adjustment method of FIG. 10; FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Optical disk, 2 ... Board | substrate, 3 ... Information recording layer, 4 ... Cover layer, 5 ... Information recording track, 6 ... Header area, 7 ... User area, 11 ... Arithmetic circuit, 12 ... Servo driver, 20 ... Semiconductor laser , 21 ... collimating lens, 22 ... beam splitter, 23 ... λ / 4 plate, 24 ... relay lens system, 25 ... objective lens, 26 ... photodetection system, 27 ... photodetector, 30 ... optical head, 31 ... phase compensation Circuit, 36 ... Phase compensation circuit, 32, 37 ... Amplifier, 33, 38, 42 ... Drive circuit, 34 ... CPU, 44 ... Envelope detection circuit.

Claims (4)

A focus offset adjusting mechanism for adjusting the focus offset by driving the objective lens in a direction perpendicular to the information recording surface of the optical disc; and a spherical aberration correcting mechanism for correcting a spherical aberration generated in the light beam irradiated on the information recording surface; An optical disc apparatus that irradiates an information recording surface of the optical disc through the objective lens and reproduces information on the information recording surface using the reflected light beam.
An optical disk apparatus adjustment method for obtaining an optimal adjustment state of the spherical aberration correction mechanism and the focus offset mechanism,
A plurality of spherical aberration correction states are set by the spherical aberration correction mechanism,
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,
As the characteristics of the information reproduction signal on the information recording surface when the focus offset is changed, the horizontal axis is the focus offset amount and the maximum value of the variable frequency oscillator (VFO) signal amplitude (or jitter) is the center. And detecting a characteristic expressed as a curve in which the amplitude (or jitter) of the VFO signal changes,
The symmetry of each characteristic curve centered on the maximum value is the amount of decrease (or increase) from the maximum value at the focus offset point deviated by ± F0 (a constant value) about the maximum value. A difference between A0 and A1 (A0-A1) is detected, and a curve having the smallest difference is determined as a curve having the best symmetry;
An adjustment method for an optical disc apparatus, wherein the best curve is obtained in the spherical aberration correction state, and the focus offset amount is set in a state giving the maximum value of the best curve . 2. The method of adjusting an optical disk apparatus according to claim 1, wherein PRML signal processing is used for reproducing information on the information recording surface of the optical disk. A focus offset adjusting mechanism for adjusting the focus offset by driving the objective lens in a direction perpendicular to the information recording surface of the optical disc; and a spherical aberration correcting mechanism for correcting a spherical aberration generated in the light beam irradiated on the information recording surface; When the information recording surface of the optical disc is irradiated with a light beam through the objective lens and the information on the information recording surface is reproduced using the reflected light beam,
An optical disc apparatus having an adjustment means for obtaining an optimal adjustment state of the spherical aberration correction mechanism and the focus offset mechanism,
Means for setting a plurality of spherical aberration correction states by the spherical aberration correction mechanism;
Means for changing the focus offset within a predetermined range by the focus offset adjustment mechanism in each state in which the spherical aberration correction state is set;
As the characteristics of the information reproduction signal on the information recording surface when the focus offset is changed, the horizontal axis is the focus offset amount and the maximum value of the variable frequency oscillator (VFO) signal amplitude (or jitter) is the center. Means for detecting a characteristic expressed as a curve in which the amplitude (or jitter) of the VFO signal changes;
The symmetry of each characteristic curve centered on the maximum value is the amount of decrease (or increase) from the maximum value at the focus offset point deviated by ± F0 (a constant value) about the maximum value. Means for detecting a difference (A0-A1) between A0 and A1, and determining a curve having the smallest difference as a curve having the best symmetry;
Means for setting the best curve to obtain the spherical aberration correction state, and setting the focus offset amount to a state giving the maximum value of the best curve;
An optical disc apparatus comprising: Spherical aberration correction mechanism for correcting a focus offset adjustment mechanism for adjusting the focus offsets is driven in the vertical direction of the objective lens to the information recording surface of the optical disk, the spherical aberration occurring in the light beam irradiated onto the information recording surface When the information recording surface of the optical disc is irradiated with a light beam through the objective lens and the information on the information recording surface is reproduced using the reflected light beam,
An optical disc apparatus having an adjustment means for obtaining an optimal adjustment state of the spherical aberration correction mechanism and the focus offset mechanism,
Means for setting a plurality of spherical aberration correction states by the spherical aberration correction mechanism;
Means for changing the focus offset within a predetermined range by the focus offset adjustment mechanism in each state in which the spherical aberration correction state is set;
As the characteristics of the information reproduction signal on the information recording surface when the focus offset is changed, the horizontal axis is the focus offset amount, and the maximum value of the variable frequency oscillator (VFO) signal amplitude (or jitter) is the center. Means for detecting a characteristic expressed as a curve in which the amplitude (or jitter) of the VFO signal changes;
The symmetry of each characteristic curve centered on the maximum value is the sum of slopes S0 and S1 of tangents to the curve at the focus offset point shifted by ± F0 (a constant value) around the maximum value ( Means for detecting S0 + S1) and determining the curve with the smallest sum as the curve with the best symmetry;
Means for setting the best curve to obtain the spherical aberration correction state, and setting the focus offset amount to a state giving the maximum value of the best curve;
An optical disc apparatus comprising:

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