JP2005129231A - Device for recording and reproducing optical disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical disk recording and reproducing device having an optical head in which the thickness dispersion of a substrate forming the optical disk can be absorbed and compensated for. <P>SOLUTION: In the optical disk recording and reproducing device having an optical head 4 converging a laser beam on the optical disk by an objective lens for the purpose of performing recording/reproducing of information for an the optical disk D; the device is provided with a substrate thickness compensating mechanism 22 for compensating the thickness dispersion of the substrate of the optical disk at the midst of an optical path of the laser beam of the optical head, and a substrate thickness compensating mechanism control part 24 for compensating and adjusting, by making the substrate thickness compensating mechanism operate, as necessary. Thereby, the thickness dispersion of the substrate forming the optical disk can be absorbed and compensated for. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical disc recording / reproducing apparatus, and more particularly, to an optical disc recording / reproducing apparatus having an optical head that performs compensation using the characteristics of the thickness distribution of a substrate of a high-density optical disc. In the present application, the recording / reproducing apparatus is used as including a recording apparatus, a reproducing apparatus, and both of these apparatuses.

  As represented by CDs (compact discs) and DVDs (digital versatile discs), optical discs record information by imprinting minute irregularities on the surface of a transparent substrate. This uneven shape is generally made by injection molding or the like by mounting a mold called a stamper, which becomes a mother mold of an uneven shape, in a plastic molding die. Then, a metal such as aluminum is formed on the concavo-convex shape on the surface of the molded substrate and used as a reflective film. On this reflective film, a thin resin layer called a protective film is formed, or a substrate called a dummy substrate is bonded to form an optical disk.

Here, a general manufacturing method of an optical disc will be described.
First, a resist is applied to a predetermined thickness on a transparent substrate such as a glass board having a smooth surface. Thereafter, the solvent in the resist is removed to cure the resist. Information is spirally recorded on the resist disk with a predetermined laser beam mounted on a cutting apparatus while rotating a glass disk (referred to as a resist disk) coated with the resist. At this time, the laser light is intermittently interrupted according to the content of information, is a continuous light beam, or the laser light is slightly shaken from side to side. The resist on the resist board is exposed by the laser light, and information is recorded on the resist.

After such cutting, the resist is developed to deposit information that was a latent image as a groove or pit having a concavo-convex shape of the resist. After this development, the resist board is dried and placed in a vacuum apparatus, and a thin nickel conductive film is formed on the resist by vacuum film formation. After this film formation, the resist board is taken out from the vacuum apparatus, and this is put into an electric nickel plating tank to deposit nickel on the nickel film formed on the resist. In order to form a nickel film having a uniform thickness, the resist board is rotated in a nickel plating tank. When a nickel film having a predetermined thickness is formed, the resist board is taken out of the nickel plating tank, and the resist board is washed with pure water. After this cleaning, the nickel-plated board is peeled off from the resist board.
On this nickel disk, irregularities are formed by inverting the shape of the resist imprinted with laser light. This nickel disk is washed with a solvent to remove the remaining resist.

  After that, one method is to make a mother by copying directly from this nickel board (master). This is called a mother process and has the same uneven shape as the cut resist board. Furthermore, a stamper is made by taking a duplicate from this mother. When removing the mother and stamper, the nickel plating is deposited while rotating in the plating tank. In this way, many copies (stampers) of the same shape as the master can be taken from the mother. The stamper replicated in large quantities is used as a mold for injection molding, which enables mass production of optical discs in a short time.

  As another method, the master is used as it is as a mold for injection molding. These masters or stampers (hereinafter referred to as metal master discs) are polished flat on the back surface of the disc with a polishing machine. This back surface polishing is generally performed by rotating a metal master. After the backside polishing, the metal master is cut into a size that can be mounted on a molding die to become a mother die.

  Next, the mother die is carried to the disk forming process. A mold is attached to the injection molding machine in the opposite direction, and a mother mold is attached to one of the molds. Resin is supplied to the injection molding machine and the disc is molded in the mold. Then, the mold is opened for each molding, and the disk molded in the mold is taken out. A reflective film is formed on the information signal surface of the disc that has been taken out. A protective film is formed on the reflective film in the case of a CD, and another substrate having the same shape and called a dummy disk in the case of a DVD. Bonded inside. The next generation optical disc is produced in the same manner.

  By the way, when reproducing this disk, a reflective film formed along the concavo-convex shape by irradiating a reproducing laser beam from the opposite surface on which the concavo-convex shape has been transferred and the concavo-convex shape is not transferred. More reflected light is detected, thereby reproducing information.

Here, a conventional optical disk reproducing apparatus will be described.
FIG. 11 shows an example of a conventional optical disk reproducing apparatus. In the illustrated example, the optical disk D is mounted on the spindle motor 2, and the optical disk D is rotated by the rotation of the spindle motor 2. The optical head 4 for reading a signal is connected to a moving feed motor 6 so as to be movable in the radial direction of the optical disc D, and the laser beam L is emitted toward the optical disc D from this. Then, in response to a reproduction operation command from the control circuit 8, the optical head 4 first focuses on the optical disc D. When a predetermined amount of reflected light is obtained, the spindle motor 2 rotates. The optical head 4 is continuously focused by the built-in objective lens 12 so that the amount of light reflected on the rotating optical disk D is constant, and a tracking control circuit (not shown) in the control circuit 8 is used for tracking. ) Is operated, tracking is performed along the information signal sequence in the optical disc D, and the information signal S1 in the optical disc D is read as a variation in the amount of reflected light. The obtained information signal S1 is guided to the signal processing circuit 10. When it is desired to reproduce the desired track, a signal to that effect is sent from the outside to the control circuit 8 and the vicinity of the desired track is reproduced using the feed motor 6. The address obtained from the reproduction is signal-processed, it is determined whether or not it is a desired track, and the feed motor 6 is further operated so that the desired track can be reproduced. The speed at which the optical head 4 moves on the disk radius by the feed motor is several centimeters per second. The information signal on the optical disc D is reproduced by a series of such operations.

  The recording capacity of the optical disk is determined by the wavelength of the laser beam L to be reproduced and the numerical aperture of the objective lens of the read optical head 4 used for reproduction. On the other hand, how correctly information can be read is determined by the amount of optical aberration, and roughly relates to the focal depth of the objective lens of the optical head of the system. In general, as the recording capacity increases, the depth of focus becomes shallower. Therefore, it is necessary to reduce the thickness deviation of the substrate so that information can be read correctly.

  Incidentally, in the optical disc, the information recording density is determined by the wavelength of the laser beam L used for reproduction and the numerical aperture of the objective lens 12 of the optical head 4 used for reproduction as described above. When the same laser beam is used, information recorded at a higher density can be reproduced by increasing the numerical aperture of the objective lens 12 of the optical head 4. However, when the numerical aperture of the objective lens 12 is increased, the light aberration due to the substrate thickness unevenness caused by the difference in the optical path length of the light increases by the fourth power of the numerical aperture.

  For example, in a CD reproducing apparatus in which the wavelength of the laser beam is 780 nm and the numerical aperture is 0.45, it is necessary to suppress the substrate thickness unevenness to be within ± 100 μm. Next, in the developed DVD reproducing apparatus having a wavelength of 635 nm and a numerical aperture of 0.6, it is necessary to suppress the substrate thickness unevenness within ± 30 μm. Thus, as the density of the disk becomes higher, the manufacturing accuracy of the disk becomes increasingly severe. On the other hand, in the case of an optical disk reproducing apparatus using a laser beam having a wavelength of 400 nm, which is said to be the next generation, even if the numerical aperture of the objective lens used at the time of reproduction is the same as that of the current DVD, the substrate is 0.6. The thickness unevenness of the optical disk becomes ± 20 μm, and it is considered that the thickness unevenness of the substrate must be suppressed to about ± 3 μm in an optical disk reproducing apparatus using a numerical aperture of 0.8. Also, in the case of a double-layer disc adopted from DVD as a standard, this thickness variation must be satisfied even in the two layers, and it is very difficult to establish if the current extension line technology is used. Had the disadvantages. The occurrence of the uneven thickness of the substrate cannot be avoided by the current disk manufacturing method as described above, and the development of an optical head capable of absorbing and compensating for the uneven thickness has been desired. .

  The present invention has been developed in order to effectively solve the above-mentioned problems, and an object of the present invention is to absorb and compensate for the uneven thickness of the substrate on which the optical disk is formed. It is an object of the present invention to provide an optical disc recording / reproducing apparatus having an optical head capable of performing the above.

In order to solve the above problems, the present invention provides an optical disc recording / reproducing apparatus having the following configurations (1) to (6).
(1) In an optical disc recording / reproducing apparatus having an optical head for focusing laser light on the optical disc by an objective lens in order to record / reproduce information with respect to the optical disc,
In the middle of the optical path of the laser beam of the optical head and on the side opposite to the optical disk of the objective lens, in order to compensate for the thickness unevenness of the substrate of the optical disk, by allowing movement along the optical axis, A substrate thickness compensation mechanism comprising an auxiliary lens having a variable distance from the objective lens is provided, and a substrate thickness compensation mechanism control unit that performs compensation adjustment by operating the substrate thickness compensation mechanism when necessary is provided. An optical disc recording / reproducing apparatus.
(2) In an optical disc recording / reproducing apparatus having an optical head for focusing laser light on the optical disc by an objective lens in order to record / reproduce information with respect to the optical disc,
In the middle of the optical path of the laser beam of the optical head, on the opposite side of the objective lens from the optical disk, between two transparent electrodes for changing the optical path length in order to compensate for the uneven thickness of the substrate of the optical disk A substrate thickness compensation mechanism comprising a substrate thickness compensation cell enclosing a liquid crystal is provided, and a substrate thickness compensation mechanism control unit that performs compensation adjustment by operating the substrate thickness compensation mechanism when necessary is provided. Optical disc recording / reproducing apparatus.
(3) In an optical disc recording / reproducing apparatus having an optical head for focusing laser light on the optical disc by an objective lens in order to record / reproduce information with respect to the optical disc,
In the middle of the optical path of the laser beam of the optical head and on the side opposite to the optical disk of the objective lens, in order to compensate for the thickness unevenness of the substrate of the optical disk, by allowing movement along the optical axis, A substrate thickness compensation mechanism comprising a collimator lens having a variable distance from the objective lens is provided, and a substrate thickness compensation mechanism control unit is provided to perform compensation adjustment by operating the substrate thickness compensation mechanism when necessary. An optical disc recording / reproducing apparatus.
(4) In an optical disc recording / reproducing apparatus having an optical head for focusing laser light on the optical disc by an objective lens in order to record / reproduce information with respect to the optical disc,
In the middle of the optical path of the laser beam of the optical head and on the opposite side of the objective lens from the optical disc, the mutual distance along the optical axis is made variable in order to compensate for the thickness unevenness of the substrate of the optical disc. A substrate thickness compensation mechanism comprising a beam expander including two convex lenses is provided, and a substrate thickness compensation mechanism control unit is provided for adjusting compensation by operating the substrate thickness compensation mechanism when necessary. Optical disc recording / reproducing apparatus.
(5) The substrate thickness compensation mechanism control unit optimizes the substrate thickness compensation mechanism based on a signal quality judgment circuit for judging the quality of a reproduction signal read from the optical head and the output of the signal quality judgment circuit. The optical disk recording / reproducing apparatus according to any one of (1) to (4), characterized in that the optical disk recording / reproducing apparatus comprises a compensation mechanism drive control circuit for controlling the state to a certain state.
(6) The substrate thickness compensation mechanism control unit stores a state before and after the best point of the reproduction signal when performing inspection of the quality of the reproduction signal, and determines an intermediate position before and after that as an adjustment position. The optical disc recording / reproducing apparatus according to any one of (1) to (5) above.

  According to the optical disk recording / reproducing apparatus of the present invention, the following excellent operational effects can be exhibited. That is, by utilizing the fact that the thickness variation (unevenness) of the substrate constituting the optical disk is small in the circumferential direction of the disk, even if a circuit for compensating the substrate thickness whose operation speed is relatively slow is used, a good substrate thickness Compensation can be performed, deterioration of the reproduction signal due to substrate thickness unevenness is small, and the quality of the reproduction signal can be maintained well.

Hereinafter, an embodiment of an optical disk recording / reproducing apparatus according to the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a graph showing an example of substrate thickness unevenness in the circumferential direction of the optical disc, FIG. 2 is a graph showing an example of substrate thickness variation (same phase position on the optical disc) for each optical disc, and FIG. It is a graph which shows an example of the thickness nonuniformity of the board | substrate in the radial direction.

  First, before explaining the apparatus of the present invention, the thickness distribution of the optical disk substrate such as CD and DVD was investigated by the optical disk manufacturing method as described above. The investigation result of distribution (unevenness) will be described. Here, as an example, the uneven thickness of the substrate of the CD disk and the uneven thickness of the substrate of the DVD disk are shown. For example, in a CD disk substrate, the thickness variation on the substrate circumference is about 10 μm (the CD disk substrate in FIG. 1), but the average thickness variation for each substrate or the same radius of the disk substrate The thickness variation at the same phase position was about 70 μm (CD disk substrate in FIG. 2), and the thickness unevenness in the radial direction of the disk substrate was about 20 μm (CD disk substrate in FIG. 3). Further, for example, in the DVD disk substrate, the thickness variation on the substrate circumference is about 5 μm (DVD disk substrate in FIG. 1), but the average thickness variation for each substrate or the same disk substrate. The variation in thickness at the same phase in the radius was about 20 μm (DVD disc substrate in FIG. 2), and the thickness variation in the disc radial direction was about 15 μm (DVD disc substrate in FIG. 3).

  Thus, it has been found that the reason why the uneven thickness of the disk substrate has a characteristic distribution in the substrate surface is that the disk is produced through a specific process in manufacturing the optical disk.

  In other words, one of the causes is the plating process for producing the metal master. That is, the plating is performed while rotating in the plating tank, and the backside of the metal master is also polished by the rotation. It has been found that the fact that this metal master is manufactured while being rotated indicates that the thickness unevenness in the rotating direction of the finished metal master is reduced.

  Another cause is injection molding with a mold fitted with a mother die. In the plating process, plating is performed by a rotating operation, so that the thickness unevenness of the metal master is small in the circumferential direction and large in the diameter direction. In addition, if the metal master to be used is different, the average thickness of the metal master or the thickness at the same radius and the same phase will be different. When a metal master having such characteristics is used as a matrix for the molding process, the flatness in the mold is generally very good, so the molded substrate inherits the uneven thickness distribution of the metal master. It becomes like this. Furthermore, in molding, the amount of resin used for each substrate varies slightly due to variations in the amount of resin injected during molding, and this is found to occur as variations in the thickness of the molded substrate. It was.

  That is, it was found that the variation in the substrate thickness is small in the circumferential direction of the substrate, large in the diameter direction of the substrate, and larger in each substrate, for convenience of the production process. Further, in the DVD disc, a double-layer disc having two information recording layers at different thicknesses in the substrate from one side has appeared. This indicates that there is a thing with different substrate thickness due to the convenience of the disk configuration, in addition to the characteristics of the current manufacturing process. Such a double-layer disc structure is surely followed by the next generation optical disc.

  However, the information signal of the optical disk is imprinted on the substrate in the circumferential direction. This is common to CD, DVD, and the next generation. That is, when information is reproduced from the disc, as described above, the information is reproduced in a direction in which the thickness unevenness in one round is small. It has been found that, when reproducing, fast-forwarding, track jumping, or reproducing different discs, the thickness unevenness of the substrate changes greatly only when different layers are reproduced in a two-layer disc.

  Therefore, a substrate thickness compensation mechanism having a relatively slow operation speed is provided in the optical head, and as described above, when fast-forwarding, track jumping, or when reproducing a different disk, when reproducing between layers of a two-layer disk. In addition, it has been found that if the substrate thickness compensation mechanism is operated only when a portion having a relatively different substrate thickness is reproduced, the optical aberration due to the substrate thickness is sufficiently corrected.

  For example, when reproducing information signals normally, even if it is a high-density disk, there is little influence on aberrations because there is little fluctuation in the substrate thickness, and fast feed, track jump, disk Even when switching or reproducing the different layers, the aberration due to the variation of the substrate thickness tends to increase even when the optical head does not move. By utilizing such a tendency and providing a mechanism for compensating the substrate thickness in the optical head, it is possible to reduce the aberration caused by the substrate thickness when the disk has a high density.

  In this case, a sufficient effect can be obtained by correcting the aberration of the optical head at a period much slower than the alternating period of the signal obtained when reproducing information on the disk circumference. Due to the uneven thickness of the substrate, the optical head does not correct aberrations when reproducing information along the circumferential direction of the disk. Aberration correction is performed at the time of interlayer reproduction on a two-layer disc. In such an operation, a response time as a circuit for correcting aberrations is sufficient even at a slow speed of 0.1 seconds to 0.5 seconds or less, and the thickness of the substrate for compensating the aberration is also about 5 to 50 μm. A range of is sufficient.

  From this point of view, a high-density optical disk reproducing apparatus using blue laser light called the next generation is provided by providing a mechanism for removing (compensating) optical aberration due to a thickness variation of about 100 μm of the substrate in the optical head. And it has the merit that it can be produced without strict disc manufacturing conditions, and the dual-layer disc introduced in DVD can also produce multi-layer discs with 3 layers and 4 layers for the next generation Has the advantage of being possible.

  As described above, since the present invention corrects the substrate thickness variation, the substrate thickness variation of 0.1 mm or less can exhibit a good effect.

  The present invention is effective not only for the next generation but also for current DVD double-layer discs. For example, when there is a reproducing apparatus using an optical head that minimizes optical aberration when the substrate thickness, which is the minimum substrate thickness of the DVD standard, is 0.57 mm, the substrate thickness, which is the maximum substrate thickness of the DVD standard. When information is reproduced from an optical disk having a substrate with a thickness of 0.63 mm, it is possible to suppress a 0.9% deterioration in signal jitter during DVD signal reproduction.

  In a reproducing apparatus having a numerical aperture (NA) 0.6 of the objective lens of an optical head whose wavelength of the reproducing laser beam is 635 nm, the signal degradation amount is about this level. Therefore, in the next generation reproducing apparatus having the wavelength of the blue laser beam. If there is a substrate thickness unevenness similar to that of a DVD, the signal deterioration amount is considered to exceed 3%. Therefore, especially in the next generation of blue laser light wavelength optical disk, the degradation of the reproduction signal due to the increase in optical aberration due to the uneven thickness of the substrate is large, and the substrate thickness can be controlled without using the mechanism of the present invention. It must be controlled much more strictly than DVD.

  However, as described in the present invention, the possibility of realizing the next generation disk will be dramatically improved by using the substrate thickness compensation mechanism in the optical head by utilizing the property of the substrate thickness unevenness. . In addition, the substrate thickness compensation mechanism can be realized at a low cost because it is possible even when the response speed is relatively slow as described above.

Such a substrate thickness compensation mechanism may have the following mechanism or structure.
(1) A plate thickness compensation plate having different thicknesses in a taper shape or a step shape is mounted between the objective lens of the optical head and the optical disc, and the thickness of the substrate is adjusted by continuously moving the plate thickness compensation plate. Compensate. The plate thickness compensation plate operates only when the disk enters the reproducing operation, when the optical head itself moves, and when the layer of two or more multilayer disks jumps and moves to another layer. .

(2) The objective lens of the optical head is made into a set of two, and the distance between both objective lenses is continuously changed to compensate for the substrate thickness. When the objective lens performs the compensation operation, it is the same as that described in (1) above.

(3) A small cell is placed between the objective lens of the optical head and the optical disk, a material having a refractive index anisotropy in the molecular structure is inserted into the cell, and the direction of the molecule is changed by changing the electric field. The apparent substrate thickness is corrected by changing the inner optical path length. A typical example is a liquid crystal material. The molecular structure of this liquid crystal includes a Schiff base type, an ester type, a pyrimidine type, and the like, and functionally includes a nematic liquid crystal, a ferroelectric liquid crystal, a multiplex drive, and an active matrix. As a general material, for example, a cell having a thickness of 1 mm is formed, and a material having a high polarizability such as chlorobenzene and a large optical anisotropy such as a benzene ring is enclosed therein, and an electric field is applied to the cell. Thus, the orientation of chlorobenzene molecules in the cell can be made constant, and the optical length in the cell can be changed. A change of 0.1 in the refractive index in the cell is equivalent to a change in optical length of 100 μm. When this cell performs the compensation operation, it is the same as that described in (1) above.

  As another method, the same effect can be obtained by installing one or more auxiliary lenses behind the objective lens and changing the distance between the objective lens and the auxiliary lens. As such an auxiliary lens, use of a collimator lens, use of a beam expander, or the like can be considered.

  By using such an optical head, with respect to one optical disk, the variation in the substrate thickness is determined in terms of the circumferential direction of the substrate, the diameter direction of the substrate, and the thickness average value for each substrate. Thus, the productivity of the optical disk is dramatically improved, and the quality of the reproduction signal is ensured. For example, in a commercially available DVD, the thickness unevenness in the circumferential direction of the substrate thickness is 3 μm PP, the thickness variation in the circumferential direction of the substrate is 100 μm PP (PP: peak-to-peak), and the average thickness for each disk. If the unevenness is set to 100 μm PP, coupled with the performance of the optical head for compensating the substrate thickness, even if a mature CD production facility is used at present, the jitter degradation resulting from the substrate thickness will jump to 0.2% or less. Will be improved. Regarding the above thickness unevenness, when CD production equipment is used, there are molds that show a bad value of thickness unevenness in the circumferential direction of about 50 μm, so even using a mature CD equipment is sufficiently satisfactory. Therefore, it is necessary to confirm that the flatness on the circumference of the mold is several μm.

  For example, in a reproducing apparatus using a next-generation blue laser beam, the information layer that can be reproduced from the reproducing surface side is one layer in a system having a laser beam wavelength of about 400 nm and an optical head objective lens numerical aperture of 0.6. When the playback optical transmission film thickness is 0.6 mm, the thickness variation of the substrate used is ± 5 μm to ± 3 μm in the disk circumferential direction, the disk diameter direction and the thickness change between the disks. If the range is ± 30 μm to ± 20 μm, this is a numerical value that is highly likely to be realized in the next generation. In the case of a two-layer disc, the thickness unevenness in the disc circumferential direction is ± 4 μm, and the range where the average thickness of the two intermediate layers is 40 μm to 20 μm is a highly feasible numerical value as in the case of a single-layer disc.

  In this case, the substrate thickness change in the single-layer disc is, for example, when the thickness unevenness in the disc circumferential direction is ± 4 μm, and the thickness change between the disc diameter direction and the disc is 20 μm, the maximum thickness is 44 μm. Similarly, in the case of a two-layer disc, when the average thickness of the intermediate layer is 30 μm and the thickness unevenness in the circumferential direction is ± 4 μm, the thickness change is 68 μm at maximum, and the jitter deterioration of the single layer disc is The jitter degradation of 2% and 2 layer board is estimated to be 4%. If the next-generation signal uses the same signal system as DVD, the jitter must be 8% or less, which is the same as the DVD standard. For this purpose, laser light such as reduction in recording capacity or warping of the disk is required. However, it is possible to eliminate the disadvantage that means for reducing the amount of signal deterioration caused by not being perpendicular to the information recording surface, that is, means for reducing the warp angle of the disk, etc. must be taken. As described above, the effect of compensating for the variation in the substrate thickness with the optical head can improve the efficiency of disk production, and can record high-capacity information with peace of mind. In this explanation, the operation of the present invention has been described to obtain the best operating point of the device of the present invention while measuring the reproduction jitter. However, the use of the reproduction jitter is one example, for example, signal processing is performed. This can be done by measuring the error rate thereafter, or by measuring the period fluctuation obtained from the shortest pit length. This will be described in more detail with reference to examples.

(First embodiment)
4 is a block diagram showing an optical disk recording / reproducing apparatus according to an embodiment of the present invention, FIG. 5 is a partially enlarged view showing a first example of the optical head in FIG. 4, and FIG. 6 is a plan view showing a plate thickness compensation plate. It is. The same components as those in the conventional apparatus shown in FIG.

  As shown in the figure, in this optical disk recording / reproducing apparatus 20, 2 is a spindle motor for rotating the optical disk D, 4 is an optical head having an objective lens 12 therein, and this optical head 4 is moved by a feed motor 6 for movement. It is engaged with a long screw 14 that is rotated forward and backward so that it can move in the radial direction of the optical disk D. A signal processing circuit 10 applies predetermined processing to the information signal S1 read from the optical head 4. A control circuit 8 controls the optical head 4 and the moving feed motor 6 based on a part of the signals obtained by the signal processing circuit 10. The control circuit 10 also controls the rotational speed of the spindle motor 2 and the like.

  The optical head 4 is provided with a substrate thickness compensation mechanism 22 which is a feature of the present invention and compensates for thickness variations (unevenness) of the substrate of the optical disk D in the middle of the optical path of the laser beam. Reference numeral 24 denotes a substrate thickness compensation mechanism control unit that operates the substrate thickness compensation mechanism 22 when necessary to perform compensation adjustment. The substrate thickness compensation mechanism control unit 24 determines the quality of the reproduction signal read by the optical head 4 and the substrate thickness compensation based on the output of the signal quality determination circuit 26. A compensation mechanism drive control circuit 28 that specifically controls the mechanism 22 to an optimum state is constituted.

  The substrate thickness compensation mechanism 22 is provided on the tip side of the optical head 4 in this embodiment. Specifically, the substrate thickness compensation mechanism 22 has a transparent disc-shaped thickness compensation plate 30 that is rotatably arranged in the optical path between the objective lens 12 and the optical disc D. The plate thickness compensation plate 30 is rotatably provided by a compensation rotation motor 32 that can control the rotation speed and the stop position (rotation angle) such as a step motor.

  As shown in FIG. 6, the thickness compensation plate 30 is gradually changed in thickness in the circumferential direction step by step, and in the illustrated example, there are six fan-like shapes around the rotation center of the thickness compensation plate 30. Area 30A-30F. The thickness of each area is different by, for example, 10 μm. For example, the area 30A is 100 μm, the area 30B is 110 μm, the area 30C is 120 μm, the area 30D is 130 μm, the area 30E is 140 μm, and the area 30F is 150 μm. Has been.

The number of plate thickness areas and the difference in thickness between adjacent areas are not limited to the numerical examples described above, but are arbitrarily determined depending on the thickness unevenness to be compensated for the disk substrate.
In addition, the plate thickness may be changed in a tapered manner along the circumferential direction, instead of changing the plate thickness stepwise.

  In FIG. 5, the objective lens 12 is provided with a voice coil 16 that magnetically interacts with a focus coil (not shown). As is well known, the objective lens 12 is moved closer to and away from the optical disc D to focus. It has become. The laser beam L emitted toward the optical disc D is incident from the substrate 18 side of the optical disc D, and the information is read out.

  Next, the operation of the device of the present invention configured as described above will be described.

  First, the optical disk D is mounted on the spindle motor 2, and the optical disk D is rotated by the rotation of the spindle motor 2. The optical head 4 for reading the information signal is connected to a moving feed motor 6 so as to be movable in the radial direction of the optical disk D, and is movable in the radial direction of the disk. In response to a reproduction operation command from the control circuit 8, the optical head 4 first focuses on the optical disk D. When a predetermined amount of reflected light is obtained, the spindle motor 2 rotates. The optical head 4 keeps focusing so that the amount of reflected light on the rotating optical disk D is constant, and a tracking control circuit (not shown) in the control circuit 8 operates to track the information signal in the disk. Tracking is performed along the column, and the information signal in the disk is read as a variation in the amount of reflected light. The obtained information signal S1 is guided to the signal processing circuit 10. The signal obtained by the signal processing circuit 10 is sent to the signal quality judgment circuit 26.

  The signal quality judgment circuit 26 sends a command for operating the substrate thickness compensation mechanism 22 to the compensation mechanism drive control circuit 28 in order to check whether the signal quality is optimum. By this command, the compensation rotation motor 32 shown in FIG. 5 is driven to rotate the plate thickness compensation plate 30. Thereby, since the laser beam L passes through the plate thickness compensation plate 30, the optical path length is substantially set according to the thickness of each area 30A-30F of the plate thickness compensation plate 30 through which the laser beam L passes. It will change little by little. The reproduced signal obtained together with it is determined by the signal quality determination circuit 26 whether or not the signal quality is improved as compared with that before the plate thickness compensator 30 is operated. Further, a command to rotate the plate thickness compensation plate 30 is sent out, and similarly the reproduction signal quality is determined. This determination operation may be performed for each of the areas 30A to 30F to obtain the highest quality area, or the signal quality may be determined for each area as follows. For example, if the reproduction signal quality has been improved earlier, the compensation rotation motor 32 is operated again to determine the reproduction signal quality in order to obtain the optimum point.

  If the reproduction signal quality is further lowered, the area is returned to the previous position, and the series of operations is completed. Further, when it is desired to reproduce a desired track, a signal to that effect is sent to the control circuit 8, and the feed motor 6 is used to move the optical head 4 to the vicinity of the desired track for reproduction. The address obtained by reproduction is signal-processed, it is determined whether or not it is a desired track, and the feed motor 6 is further operated so that the desired track can be reproduced. When the desired address is obtained, the substrate thickness compensation mechanism 22 is operated again as described above, and the same operation as before is performed. At this time, the speed at which the optical head 4 moves on the disk radius by the feed motor 6 is about several centimeters per second. The information signal on the optical disc can be reproduced by a series of such operations. In FIG. 4, of course, the reproduction signal is sent from the signal processing circuit 10 to a normal reproduction system (not shown) in the subsequent stage.

  As described above, since the plate thickness compensation plate 30 is stopped at a position (area) where the quality of the reproduction signal is good, even if there is unevenness in the thickness of the disc substrate, this is compensated and absorbed. Can do. The timing for performing compensation adjustment for such substrate thickness unevenness is, for example, the following three items.

(1) After the turntable that clamps the optical disk rotates and the optical head starts an operation for focusing, in order to start playback after the optical disk is mounted on the playback device.
(2) After the optical disk is being played and the optical head is moved by random access or the like.
(3) At the time of reproducing a multi-layer disc, when an instruction for moving the information layer for reproduction is issued.

  After the above three operations, the reproduction signal quality is inspected to compensate for thickness unevenness compensation. That is, the quality of the reproduction signal is inspected, and if it is determined that the quality is not appropriate, the reproduction signal obtained is inspected while rotating the plate thickness adjusting plate 30 by a predetermined angle (corresponding to the opening angle of the area) The states before and after the best point are stored, and the plate thickness compensation plate 30 is fixed at an intermediate position.

  By operating the plate thickness compensation plate 30 in this way, the quality of the reproduction signal of the optical disc could be greatly improved regardless of the thickness unevenness of the substrate. Here, since an optical disk was actually created and evaluated using a conventional reproducing apparatus and the apparatus of the present invention, the evaluation result will be described.

First, the manufacturing process of the optical disk used for the evaluation will be described.
First, a stamper (track pitch is 0.36 μm, shortest pit length is 0.24 μm) engraved with information for blue laser light was mounted on a DVD molding die, and many next-generation optical discs were produced by injection molding. . Different types of metal masters (track pitch and shortest pit length are the same) were also used. All the thickness irregularities during one round of the metal master were 3 μm PP. However, the average thickness unevenness of the master was 10 μm. When this was mounted on a mold and molded, the thickness of the molded substrate was 0.6 mm, and the thickness variation across the entire surface of the substrate was 30 μm. However, the thickness unevenness during one round when measuring one round was 3 μmpp or less. An aluminum reflective film was formed on the signal information surface of this substrate, a dummy substrate having a thickness of 0.6 mm was adhered on the aluminum reflective film, and a single-layer bonded optical disk was prototyped.

  A next-generation reproducing apparatus (without a substrate thickness compensation mechanism) equipped with an optical head having such an optical disk having a reproduction wavelength of 400 nm and a numerical aperture of 0.6 from the opposite substrate surface on which the signal surface is molded. When reproduced, jitter, which is an indicator of signal quality, deteriorated by 2% depending on the optical disk. Similarly, a silver translucent film is formed on one signal surface of a substrate molded in the same manner, an aluminum reflective film is formed on the signal surface of the other substrate, and the signal surfaces of each other are formed. A two-layer optical disc was prepared by bonding the inner side using an ultraviolet curable resin. The thickness of the two adhesive layers formed of the ultraviolet curable resin was 40 μm. In this two-layer optical disc, the thickness of the first layer (first layer) viewed from the reading surface side is 0.6 mm on average, but the second layer (second layer) viewed from the reading surface side. ) From the reading surface on average was 0.64 mm. The jitter of the reproduction signal of the second layer having a thickness of 40 μm deteriorated by 5%. As described above, in the reproducing apparatus without the substrate thickness compensation mechanism 22, the quality of the reproduced signal is greatly deteriorated.

  On the other hand, when the information of the optical disc was reproduced using the above-described apparatus of the present invention, the jitter degradation of the single-layer optical disc was improved to 0.3%, and the jitter degradation of the double-layer optical disc was also reduced to 0. It was as good as 3%.

  As shown in FIG. 6, the thickness compensation plate 30 has a stepwise thickness on the circumference with a thickness of 100 μm (area 30A) at the thinnest thickness and 150 μm (area 30F) at the thickest thickness, for example. However, the thickness compensation plate 30 is not limited to this shape, and may be, for example, a strip shape that is displaced in the left-right direction. Further, the thickness distribution of the plate thickness compensation plate 30 may be one in which the thickness changes continuously, or the thickness changes discontinuously in units of 5 μm, for example. It doesn't matter. In the first example, the plate thickness compensation plate 30 is used as a part of the substrate thickness compensation mechanism 22. However, the present invention is not limited to this, and is configured as shown in the second to second examples shown below. Also good.

(Example 2)
FIG. 7 is a partially enlarged view showing a second example of the optical head.
Here, instead of the thickness compensation plate 30, an auxiliary objective lens 40 is provided in parallel with the objective lens 12, an auxiliary voice coil 42 is coupled to the auxiliary objective lens 40, and the distance between the lenses 12 and 40 is changed. I can do it. The auxiliary voice coil 42 is operated by a control command from the compensation mechanism drive control circuit 28 in FIG. In this case, a control current is supplied to the auxiliary voice coil 42 to stop the auxiliary objective lens 40 at a position where the reproduction signal is best. Also in this case, the compensation adjustment operation may be performed in the three modes (1) to (3) as described in the first example.

  In this second example, when the reproduction signal quality is inspected and it is determined that the quality is not appropriate, a current is passed through the auxiliary voice coil 42 holding the auxiliary objective lens 40 to perform the substrate thickness compensation operation. . Then, the obtained reproduction signal was inspected, the states before and after the best point were stored, and the position of the auxiliary objective lens 40 was fixed at an intermediate position.

  By manipulating the position of the auxiliary objective lens 40 in this way, the jitter deterioration of the single-layer optical disk is improved to 0.3% with respect to the optical disk previously used for evaluation, and the jitter deterioration of the double-layer optical disk is similarly 0. It was as good as 3%.

(Example 3)
FIG. 8 is a partially enlarged view showing a third example of the optical head. Here, instead of the plate thickness compensation plate 30, a substrate thickness compensation cell 46 is inserted in the middle of the optical path in front of the objective lens 12 (on the side opposite to the position of the optical disk). The compensation cell 46 has a shape having two transparent electrodes 48 and 50 parallel to each other, and the thickness between the transparent electrodes 48 and 50 is about 0.1 mm. A liquid crystal 52 having a refractive index change of about 0.2 is filled between the transparent electrodes 48 and 50. By changing the voltage V applied to the transparent electrodes 48 and 50, the molecular arrangement of the liquid crystal 52 is changed, the optical path length is changed, and a plate thickness change corresponding to a maximum disc plate thickness of 20 μm can be corrected. Also in this case, the voltage applied to the transparent electrodes 48 and 50 is controlled by a command signal from the drive control circuit 28. Then, the applied voltage is fixed at a position where the reproduction signal is good. Also in this case, the compensation adjustment operation may be performed in the three modes (1) to (3) as described in the first example.

  In this third example, when the reproduction signal quality is inspected and it is determined that the quality is not appropriate, a voltage is applied to the transparent electrodes 48 and 50, and the applied voltage of the substrate thickness compensation cell 46 is changed to obtain. The reproduction signal was inspected, the states before and after the best point were stored, and the applied voltage V of the substrate thickness compensation cell 46 was fixed at an intermediate position.

  By operating the substrate thickness compensation cell 46 in this way, with respect to the optical disk used for the previous evaluation, the jitter deterioration of the single-layer optical disk is improved to 0.3%, and the jitter deterioration of the double-layer optical disk is also the same. It was as good as 0.3%.

Example 4
FIG. 9 is a schematic configuration diagram showing a fourth example of the optical head. Here, only main components necessary for explaining the present invention of the optical head are shown, and other components such as a beam splitter and a photodetector are described. Is omitted.

  In the fourth example, the plate thickness compensation plate 30 is replaced by a collimator lens 58 that aligns the laser beam L emitted from the laser beam element 56 with parallel light. Specifically, an auxiliary voice coil 60 is attached to the collimator lens 58 so that it can be moved by a minute distance in the optical path direction, and a control signal from the compensation mechanism drive control circuit 28 (see FIG. 4) is passed through the coil 60. The collimator lens 58 is adjusted to move back and forth in the optical path direction. The control signal S2 is used to control the collimator lens 58 to stop at a position where the signal reproduction signal is best. Also in this case, the compensation adjustment operation may be performed in the three modes (1) to (3) as described in the first example.

  In the fourth example, when the reproduction signal quality is inspected and it is determined that the quality is not appropriate, a current flows through the auxiliary voice coil 60 holding the collimator lens 58, and the substrate thickness compensation operation is performed. Then, the obtained reproduction signal was inspected, the states before and after the best point were stored, and the position of the collimator lens 58 was fixed at an intermediate position.

  By manipulating the position of the collimator lens 58 in this way, the jitter degradation of the single-layer optical disk of the optical disk used for the previous evaluation is improved to 0.3%, and the jitter degradation of the double-layer optical disk is also zero. It was as good as 3%.

(Example 5)
FIG. 10 is a schematic diagram showing a fifth embodiment of the optical head. Here, only the main parts necessary for the description of the present invention of the optical head are shown, and other parts such as a beam splitter and a photodetector are shown. The description is omitted.

  In this fifth example, instead of the plate thickness compensation plate 30, the beam expander is an optical path of the laser beam L emitted from the laser beam element 56, and is composed of two convex lenses 62 and 64 at the rear stage of the collimator lens 58. An auxiliary voice coil 68 is attached to one of the two convex lenses 62 and 64, for example, the convex lens 64, so that it can be moved by a minute distance in the optical path direction. As a result, the distance d between the biconvex lenses 62 and 64 is variable to change the parallelism of the laser light.

  Then, a control signal from the compensation mechanism drive control circuit 28 (see FIG. 4) is supplied to the coil 68, so that the convex lens 64 is moved and adjusted in the optical path direction. Then, the control lens S2 is controlled to stop the convex lens 64 at a position where the reproduction signal of the signal is the best. Also in this case, the compensation adjustment operation may be performed in the three modes (1) to (3) as described in the first example.

In this fifth example, when the reproduction signal quality is inspected and it is determined that the quality is not appropriate, a current flows through the auxiliary voice coil 68 holding the convex lens 64 of the beam expander 66, and the substrate thickness compensation operation is performed. Went. Then, the obtained reproduction signal is inspected, the states before and after the best point are stored, and the convex lens 64 is located at an intermediate position.
The position of was fixed.

By manipulating the position of the convex lens 64 in this way, the jitter deterioration of the single-layer optical disk is improved to 0.3% in the optical disk used for the previous evaluation, and the jitter deterioration of the double-layer optical disk is similarly reduced to 0.3%. It was as good as 3%.
In the structure using the beam expander 66 as in the fifth example, for example, when this operation is performed using a recording optical head, the recording optical head generally performs beam shaping of the laser light L. Therefore, this is particularly effective when the means using the collimator lens 58 as in the fourth embodiment cannot be used.

  Although the above embodiments have been described mainly using the reproducing apparatus as an example, it goes without saying that the apparatus of the present invention can also be applied to a recording apparatus. Here, the operation of the recording apparatus will be described with an example.

  There are two main types of substrate compensation operations in the recording apparatus. One is the time of recording, and address information, recording timing information, and the like necessary for recording are input as information from the disk information surface to the optical head. The effect of the present invention can be obtained by performing the substrate compensation operation of the optical head so that the signal quality of the input information is good. As another method, there is a recording method in which a verify operation for confirming whether or not a signal has been recorded satisfactorily during recording on an optical disc is performed intermittently during recording. The effect of the present invention can be obtained by performing the substrate compensation operation of the present invention during the intermittently performed recording information quality confirmation operation.

It is a graph which shows an example of the thickness nonuniformity of the board | substrate in the circumferential direction of an optical disk. It is a graph which shows an example of the thickness variation (same phase position on an optical disk) of the board | substrate for every optical disk. It is a graph which shows an example of the thickness nonuniformity of the board | substrate in the radial direction of an optical disk. It is a block block diagram which shows one Example of the optical disk recording / reproducing apparatus of this invention. FIG. 5 is a partially enlarged view showing a first example of the optical head in FIG. 4. It is a top view which shows a plate thickness compensation board. It is the elements on larger scale which show the 2nd example of an optical head. It is the elements on larger scale which show the 3rd example of an optical head. It is a schematic block diagram which shows the 4th example of an optical head. It is a schematic block diagram which shows the 5th example of an optical head. It is a figure which shows an example of the conventional optical disk reproducing | regenerating apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 2 ... Spindle motor, 4 ... Optical head, 6 ... Movement feed motor, 8 ... Control circuit, 10 ... Signal processing circuit, 12 ... Objective lens, 20 ... Optical disk recording / reproducing apparatus, 22 ... Substrate thickness compensation mechanism, 24 ... Substrate thickness compensation mechanism control unit 26 ... Signal quality judgment circuit 28 ... Compensation mechanism drive control circuit 30 ... Plate thickness compensation plate 32 ... Compensation rotation motor 40 ... Compensation objective lens 46 ... Substrate thickness compensation cell 58 ... Collimator lens, 66 ... Beam expander, D ... Optical disc.

Claims (6)

In an optical disc recording / reproducing apparatus having an optical head for focusing laser light on the optical disc by an objective lens in order to record / reproduce information with respect to the optical disc,
In the middle of the optical path of the laser beam of the optical head and on the side opposite to the optical disk of the objective lens, in order to compensate for the thickness unevenness of the substrate of the optical disk, by allowing movement along the optical axis, A substrate thickness compensation mechanism comprising an auxiliary lens having a variable distance from the objective lens is provided, and a substrate thickness compensation mechanism control unit that performs compensation adjustment by operating the substrate thickness compensation mechanism when necessary is provided. An optical disc recording / reproducing apparatus. In an optical disc recording / reproducing apparatus having an optical head for focusing laser light on the optical disc by an objective lens in order to record / reproduce information with respect to the optical disc,
In the middle of the optical path of the laser beam of the optical head, on the opposite side of the objective lens from the optical disk, between two transparent electrodes for changing the optical path length in order to compensate for the uneven thickness of the substrate of the optical disk A substrate thickness compensation mechanism comprising a substrate thickness compensation cell enclosing a liquid crystal is provided, and a substrate thickness compensation mechanism control unit that performs compensation adjustment by operating the substrate thickness compensation mechanism when necessary is provided. Optical disc recording / reproducing apparatus. In an optical disc recording / reproducing apparatus having an optical head for focusing laser light on the optical disc by an objective lens in order to record / reproduce information with respect to the optical disc,
In the middle of the optical path of the laser beam of the optical head and on the side opposite to the optical disk of the objective lens, in order to compensate for the thickness unevenness of the substrate of the optical disk, by allowing movement along the optical axis, A substrate thickness compensation mechanism comprising a collimator lens having a variable distance from the objective lens is provided, and a substrate thickness compensation mechanism control unit is provided to perform compensation adjustment by operating the substrate thickness compensation mechanism when necessary. An optical disc recording / reproducing apparatus. In an optical disc recording / reproducing apparatus having an optical head for focusing laser light on the optical disc by an objective lens in order to record / reproduce information with respect to the optical disc,
In the middle of the optical path of the laser beam of the optical head and on the opposite side of the objective lens from the optical disc, the mutual distance along the optical axis is made variable in order to compensate for the thickness unevenness of the substrate of the optical disc. A substrate thickness compensation mechanism comprising a beam expander including two convex lenses is provided, and a substrate thickness compensation mechanism control unit is provided for adjusting compensation by operating the substrate thickness compensation mechanism when necessary. Optical disc recording / reproducing apparatus.   The substrate thickness compensation mechanism control unit optimizes the substrate thickness compensation mechanism based on a signal quality determination circuit that determines the quality of a reproduction signal read from the optical head and an output of the signal quality determination circuit. 5. The optical disc recording / reproducing apparatus according to claim 1, further comprising a compensation mechanism drive control circuit for controlling the optical disc. The substrate thickness compensation mechanism control unit stores a state before and after the best point of the reproduction signal when inspecting the quality of the reproduction signal, and determines an intermediate position before and after that as an adjustment position. Item 6. The optical disc recording / reproducing apparatus according to any one of Items 1 to 5.

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