The present invention belongs to the technical fields of an optical pickup, an aberration correcting method, an optical pickup program, an information recording device and method, an information recording program, an information reproducing device and method, an information reproducing program, and an information recording medium. More particularly, the invention belongs to the technical fields of an optical pickup, an aberration correction method, and an optical pickup program having at least the function of correcting astigmatism which occurs due to a manufacture error of an optical part or the like in a light beam emitted to an optical recording medium such as an optical disk, an information recording device including the optical pickup and the like, an information recording method, and an information recording program, an information reproducing device including the optical pickup and the like, an information reproducing method, and an information reproducing program, and an information recording medium on which the program is recorded.
In the case of optically recording/reproducing information by emitting a light beam to an optical recording medium such as an optical disk, generally, it is necessary to perform a control of making an information recording position in an information recording face of the optical recording medium and a focus position of the light beam coincide with each other. As the control, there are mainly two kinds of controls; focus servo of controlling a light condensing position in a direction perpendicular to the information recording face, and tracking servo of controlling a light condensing position (in other words, a light emission position in the information recording face of the light beam) in the direction parallel with the information recording face.
One of the methods in the focus servo is focus servo of the astigmatism method. The general focus servo of the astigmatism method will be described with reference to
In the focus servo of the astigmatism method, a linearly polarized light beam emitted from a light source such as a semiconductor laser passes through a polarization beam splitter and is converted to a circularly polarized light beam by a λ/4 plate. The light beam further passes through an objective lens and forms a beam spot on an optical disk. Reflection light of the light beam from the optical disk passes again through the objective lens and is converted to a linearly polarized beam in the direction perpendicular to that of the incident light beam. The linearly polarized beam is guided by the polarization beam splitter to a condenser optical system. In the condenser optical system, a lens for condensing the reflection light and, simultaneously, giving astigmatism is disposed in the direction tilted by 45° with respect to a recording track of the optical disk. By reflection light which has passed through the lens, a circle C of least confusion is formed on the light reception face of a detector D divided in four parts as shown in
When the distance between the objective lens and the optical disk is ideal, the circle C of least confusion on the detector D is almost completely round. The value of a focus error signal FES output as the difference of sum signals of divided detectors in the positions facing each other on the detector D (in the case of
On the other hand, when the distance between the objective lens and the optical disk is not ideal, the shape of the circle C of least confusion on the detector D is an ellipse. According to the distance between the objective lens and the optical disk, the tilt of the ellipse changes as shown in
As described above, in the focus servo of the astigmatism method, the distance between the objective lens and the optical disk is determined using the value of the focus error signal and, on the basis of the value, the objective lens is moved in the direction perpendicular to the optical disk. Consequently, it is necessary to minimize occurrence of an error in the focus error signal due to, for example, noise which occurs in the focus error signal itself.
One of noises found to be added from the outside to the focus error signal is so-called track crossing noise which occurs when a light beam is emitted to an optical disk having the land/groove structure. The track crossing noise is noise added to the focus error signal when a beam spot on an optical disk is moved across the land track and the groove track in the radial direction at the time of, for example, a so-called track search.
It has been known that one of causes of the track crossing noise is a manufacture error of an optical system including an objective lens.
Specifically, in the case where astigmatism in the direction of 45° with respect to each of the tracks parallel to each other remains due to the manufacture error in an optical system in an outgoing path of a light beam from a light source to an optical disk, when the intensity distribution of reflection light of a light beam reflected/diffracted by the optical disk is observed on an objective lens, generally, the intensity distribution on the land track and that on the groove track formed on the optical disk as shown in
Some methods of reducing the track crossing noise caused by the difference in the intensity distributions have been proposed. One of them is disclosed in Japanese Patent Application Laid-Open (JP-A) No. 2000-40249.
In the method disclosed in JP-A No. 2000-40249, a liquid crystal panel is inserted between an objective lens and a light source. Pseudo astigmatism is generated by the liquid crystal panel to cancel out astigmatism caused by a manufacture error in an optical system, thereby reducing track crossing noise caused by an aberration in an outgoing path.
On the other hand, in recent years, an optical disk with improved recording density (hereinbelow, called a high-recording-density optical disk) is being developed, by shortening the wavelength of a light beam for recording/reproduction of a CD (Compact Disc) or a DVD (Digital Versatile Disc) generally used at present. In the high-recording-density optical disk, the interval between tracks is narrower than that in the DVD and the distance between the surface of an optical disk and a recording layer is shorter than that of the DVD. Consequently, the capture range (see
However, in studies in recent years of the inventors of the present invention, it was found that when the capture range in an optical disk having the land/groove structure is made narrower than the capture range at present, track crossing noise which cannot be reduced or eliminated even by the method disclosed in JP-A No. 2000-40249 occurs. Due to the track crossing noise, noise in the focus error signal in the high-recording-density optical disk increases. As a result, a problem occurs such that the operation such as a track search cannot be performed accurately.
The present invention has been achieved in consideration of the problem, and an object of the invention is to provide an optical pickup capable of performing a track search operation accurately by reducing noise occurring in a focus servo system during the track search operation and also accurately recording/reproducing information to/from an optical disk, an aberration correcting method, an optical pickup program, an information recording device including the optical pickup, an information recording method, an information recording program, an information reproducing device including the optical pickup, an information reproducing method, an information reproducing program, and an information recording medium on which the program is recorded.
To achieve the object, the invention of claim 1 provides an optical pickup for emitting a light beam to an optical recording medium in which recording tracks having a land/groove structure are formed and receiving reflection light from the optical recording medium of the emitted light beam, including: first correcting means such as a liquid crystal panel for correcting astigmatism included at least in the reflection light caused by a cause peculiar to an optical system as a component of the optical pickup in a state where tracking servo is on, the tracking servo for controlling a position on the optical recording medium, of a light spot formed on the recording track by the emission of the light beam and a position of the recording track; second correcting means such as a liquid crystal panel, when the tracking servo is off, for correcting the astigmatism and cancelling out noise included in the reflection light and received caused by the difference between a phase distribution in the light spot on the land and the phase distribution on the groove when the light spot continuously moves across the land and the groove; and control means such as a liquid crystal panel control unit for operating the first and second correcting means while making a switch between the first and second correcting means in accordance with the state of the tracking servo.
To achieve the object, the invention of claim 6 provides an information recording device for optically recording information on the optical recording medium in any of claims 1 to 5, including: the optical pickup according to any one of claims 1 to 5; servo control means such as a tracking control unit for turning on the tracking servo; and modulating means such as a recording processing unit for modulating the light beam in the on state in correspondence with the recording information and emitting the modulated light beam to the light recording medium.
To achieve the object, the invention of claim 7 provides an information reproducing device for optically reproducing reproduction information recorded on the optical recording medium in any of claims 1 to 5, including: the optical pickup according to any one of claims 1 to 5; servo control means such as a tracking control unit for turning on the tracking servo; and reproducing means such as a reproduction processing unit for receiving the reflection light of the light beam in the on state emitted to the optical recording medium and reproducing the reproduction information.
To achieve the object, the invention of claim 8 provides an aberration correcting method executed in an optical pickup of emitting a light beam to an optical recording medium such as an optical disk in which recording tracks having a land/groove structure are formed and receiving reflection light from the optical recording medium of the emitted light beam, including: a first correcting step of correcting astigmatism included at least in the reflection light caused by a cause peculiar to an optical system as a component of the optical pickup in a state where tracking servo is on, the tracking servo for controlling a position on the optical recording medium, of a light spot formed on the recording track by the emission of the light beam and a position of the recording track; and a second correcting step of correcting the astigmatism when the tracking servo is off, and cancelling out noise included in the reflection light and received due to the difference between a phase distribution in the light spot on the land and a phase distribution on the groove when the light spot continuously moves across the land and the groove.
To achieve the object, the invention of claim 9 provides an information recording method for optically recording information on the optical recording medium in claim 8, wherein in the case of recording the recording information onto the optical recording medium, a servo-on control step of turning on the tracking servo, the first correcting step in claim 8, and a modulating step of modulating the light beam in the on state in correspondence with the recording information and emitting the modulated light beam to the optical recording medium are executed, and in the case of executing a track search for retrieving the recording track on the optical recording medium, a servo-off control step of turning off the tracking servo, the second correcting step in claim 8, and a search step of executing the track search during execution of the second correcting step are executed.
To achieve the object, the invention of claim 10 provides an information reproducing method for optically reproducing reproduction information recorded on the optical recording medium in claim 8, wherein in the case of reproducing the reproduction information from the optical recording medium, a servo-on control step of turning on the tracking servo, the first correcting step in claim 8, and a reproducing step of receiving the reflection light of the light beam in the on state reflected by the optical recording medium and reproducing the reproduction information are executed, and in the case of executing a track search for retrieving the recording track on the optical recording medium, a servo-off control step of turning off the tracking servo, the second correcting step in claim 8, and a search step of executing the track search during execution of the second correcting step are executed.
To achieve the object, the invention of claim 11 makes a control computer included in the optical pickup according to any one of claims 1 to 5 function as the control means in any of claims 1 to 5.
To achieve the object, the invention of claim 12 makes a recording computer included in the information recording device in claim 6 function as: the control means as a component of the optical pickup of claim 7; the servo control means; and the modulating means.
To achieve the object, the invention of claim 13 makes a reproduction computer included in the information reproducing device in claim 7 function as: the control means as a component of the optical pickup of claim 7; the servo control means; and the reproducing means.
To achieve the object, in the invention of claim 14, the optical pickup program of claim 11 is recorded so that it can be read by the control computer.
To achieve the object, in the invention of claim 15, the information recording program of claim 12 is recorded so that it can be read by the recording computer.
To achieve the object, in the invention of claim 16, the information reproduction program of claim 13 is recorded so that it can be read by the reproduction computer.
Best modes for carrying out the invention will now be described with reference to the drawings. The following embodiments relate to the case of applying the present invention to an optical pickup for recording/reproducing information to/from both of the DVD and the high-recording-density optical disk, or an information recording device or an information reproducing device including the optical pickup.
Prior to concrete description of an embodiment of the present invention, first, the principle of the invention will be described with reference to
As described above, the inventors of the present invention found out that by making the capture range of a focus error signal in an optical disk having a land/groove structure narrower than that for a DVD, track crossing noise which cannot be reduced or prevented even by the method disclosed in JP-A No. 2000-40249 (hereinbelow, the newly found track crossing noise will be called fundamental track crossing noise).
As obvious from
Therefore, when the beam spot on the optical disk is moved in the radial direction in, for example, a track search or the like, due to the difference between the intensity distributions shown in the right and left lower graphs of
The phase distribution on the objective lens shown in the center in the left part of
As obvious from
The inventors of the present invention who found existence of the fundamental track crossing noise separately from track crossing noise caused by a manufacture error described with reference to
(II) Next, embodiments of the invention based on the principle will be described concretely with reference to
As shown in
The light source 1, the polarization beam splitter 2, the λ/4 plate 4, the objective lens 6, and the multi-lens 9 are optical parts. The tracking control unit 7, the liquid crystal panel control unit 8, the optical disk determining circuit 11, and the focus control unit 12 are mainly constructed by electronic circuits.
The general operation of the optical pickup PU will now be described.
In the case of optically reproducing information recorded on an optical disk DK (such as a DVD-RAM or DVD-RW having the land/groove structure) fixed to a spindle motor 10 and rotated, or in the case of optical recording the information to the optical disk DK, the light source 1 in the optical pickup PU emits a light beam B having preset intensity in a linearly polarized state. The light beam B passes through the polarization beam splitter 2 and is applied on the liquid crystal panel 3.
The liquid crystal panel 3 has a configuration in which an alignment layer, a transparent electrode, a protection layer, and the like are stacked in order from the position close to the liquid crystal on both sides of a liquid crystal while sandwiching the liquid crystal. Each of the transparent electrode, as a transparent electrode 30 shown in the plan view of
Referring again to
Next, the reflected light beam B in a state where the direction of the circular polarization becomes opposite passes through the objective lens 6, and the circularly polarization state is reset to the linear polarization state by the λ/4 plate 4. The reset orientation of the linear polarization is turned from the direction of the linear polarization of the light beam B emitted from the light source 1 by 90°.
The light beam B in the linear polarization state passes again through the liquid crystal panel 3 so that phase differences are added again to the areas corresponding to the partial electrodes 30A to 30E. The resultant light beam is reflected by the polarization beam splitter 2 and enters the multi-lens 9. The reason why the light beam B is reflected by the polarization beam splitter 2 is that, as described above, the polarization direction in the circular polarization becomes opposite by the reflection in the information recording surface of the optical disk DK and, further, the orientation of the linear polarization is turned from that emitted from the light source 1 by 90°.
Next, the multi-lens 9 adds astigmatism for focus servo by the astigmatism method to the incident light beam B and condenses the light beam B onto the detector D. A circle C of least confusion generated on the detector D by the condensing is as shown in
Consequently, from the detector D, the focus error signal Sfes (see
On the other hand, the tracking control unit 7 drives the tracking actuator 5 by using a drive signal Scd, thereby executing necessary tracking at the time of recording/reproducing information, and outputs a servo state signal Sco indicating that a servo loop in the tracking servo is in a closed state (in other words, a state of recording/reproducing information to/from the optical disk DK) or an open state (in other words, a track search state) to the liquid crystal panel control unit 8.
On the other hand, the optical disk determining circuit 11 determines, for example, the kind of the optical disk DK (more concretely, for example, a DVD-RAM, a DVD-RW, or a DVD-ROM) by a conventional method using, for example, an optical detector. The optical disk determining circuit 11 generates a kind signal Sj indicative of the determined kind and outputs it to the liquid crystal panel control unit 8.
On the basis of the servo state signal Sco and the kind signal Sj, the liquid crystal panel control unit 8 generates the control signal Sdv and drives each of the partial electrodes 30A to 30E in the liquid crystal panel 3 to control the drive voltage in the liquid crystal panel 3 at the time of recording/reproducing information to/from the optical disk DK and at the time of a track search.
Next, the drive modes of the liquid crystal panel 3 by the liquid crystal panel control unit 8 will be described more concretely with reference to
First, drive modes of the liquid crystal panel 3 at the time of recording/reproducing information to/from the optical disk DK (that is, when the tracking servo loop is closed) will be described.
At the time of recording/reproducing the information, the liquid crystal pane 3 displays the function of giving the pseudo astigmatism for cancelling out the astigmatism caused by the manufacture error of the optical system.
Consequently, as shown in the upper and intermediate parts of
As concrete values of the drive voltages Va to Vc, as shown in
The drive mode of the liquid crystal panel 3 shown in
On the other hand, at the time of performing a track search on the optical disk DK (that is, when the tracking servo loop is open), the liquid crystal panel 3 displays the function of giving the pseudo astigmatism for cancelling off the two track crossing noises each other to the light beam B.
With respect to the drive voltages Va to Vc applied to the partial electrodes 30A to 30E, as shown in
Specifically, as shown in
In the example of
Next, the operation for eliminating the track crossing noise executed in the optical pickup PU having the configuration described by referring to
As shown in
Next, while applying the drive voltages, the focus servo loop is set in the close state (step S3) and, further, whether the track search operation is performed or not is checked on the basis of an instruction operation from the user or the like (step S4). When the track search operation is not performed (NO in step S4), the tracking servo loop is closed on assumption that information on the optical disk DK loaded at that time is reproduced (step S5). As the drive voltages applied to the partial electrodes 30A to 30D, the drive voltages at the time of recording/reproducing information (in the case of
During reproduction of information, whether the reproducing operation is stopped or not is always monitored (step S8). When the reproduction operation is stopped (YES in step S8), the operation is stopped as it is. On the other hand, when the operation is continued (NO in step S8), the program returns to the step S4 and the subsequent processes are repeated.
On the other hand, when it is determined in step S4 that the track search operation is performed (YES in step S4), if the determination in the step S4 is executed immediately after the operation in the step S3 or executed after the operations in steps S9 to S11 which will be described later and the tracking servo loop is continuously in the open state, the liquid crystal panel 3 is driven with the drive voltages (as described in step S2) (step S9). Further, the tracking servo loop remains in the open state (step S10) and a necessary track search is performed (step S1). The program returns again to the step S4, and the subsequent processes are repeated.
On the other hand, when the determination in the step S4 is executed after the operations in the steps S5 to S8 are performed at least once and the tracking servo loop remains in the closed state by the operation in the step S5, the drive voltages applied to the partial electrodes 30A to 30D are set as drive voltages applied when the tracking servo loop is open (in the case shown in
Finally, the process for determining the values of the drive voltages shown in
Concrete values of the drive voltages are determined, for example, at the time of shipment from a manufacturing factor of the optical pickup PU or turn-on of the power of a product including the optical pickup PU, using a jitter included in an output signal output from the detector D, error rate, or the like.
Specifically, as shown in
On the other hand, when it is determined in step S22 that the measurement value at that time is not the upper limit value (NO in step S22), the drive voltage is increased only by a preset unit amount (step S23), the program returns again to step S21, and repeats the following processes.
By performing the operation shown in
Next, in the case of determining the drive voltage (Va_open or Vb_open in
On the other hand, when it is determined in step S33 that the drive voltage at that time is not the upper limit value (NO in step S33), the drive voltage is increased only by a preset unit amount (step S34), and the program returns again to step S32 and repeats the following processes.
By performing the operations shown in
In the case where the optical pickup PU of the embodiment is assembled in the information recording apparatus, as shown in
In the case where the optical pickup PU is assembled in the information reproducing apparatus, as shown in
As described above, by the operation of the optical pickup PU of the embodiment, the state of the tracking servo is switched so as to correct the astigmatism caused by the manufacture error to improve the recording/reproducing characteristic when the tracking servo loop is closed and so as to correct the track crossing noise caused when the tracking servo loop is open. In particular, the track crossing noise which occurs in the case where the tracking servo loop is open is effectively corrected as a whole, so that so-called track search operation can be performed accurately.
When the tracking servo loop is closed, that is, when information is recorded/reproduced to/from the optical disk DK, the astigmatism by a cause peculiar to the optical system is corrected. Thus, the information can be recorded/reproduced accurately.
Further, the track crossing noise is corrected generally by generation of cancellation aberration, and the correction can be easily and effectively performed.
Further, by sharing the single liquid crystal panel 3 and generating pseudo astigmatisms, the optical pickup PU can be miniaturized as a whole.
Since the amount of the pseudo astigmatism generated in the light beam B is changed by switching the pre-stored drive voltage in accordance with the kind of the optical disk DK, the track crossing noise of the amount which varies among the kinds of the optical disk DK can be corrected with simple configuration and control.
Further, information can be recorded/reproduced accurately, and occurrence of the track crossing noise in the track search operation executed in a state where the tracking servo is executed in the open state an be also effectively corrected.
By recording the program corresponding to the flowchart shown in
Number | Date | Country | Kind |
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2005-123694 | Apr 2005 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2006/306130 | 3/27/2006 | WO | 00 | 10/19/2007 |