JP2004178685A - Estimating device of double refraction of optical disk, and optical disk drive - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To estimate the amount of double refraction caused by a stress applied to an optical disk during rotation. <P>SOLUTION: An information processing device 47 estimates the double refractivity (X) of the optical disk from a peak level of an HF signal obtained from the optical pickup when the optical pickup(OPU) is positioned at an inner periphery position of the optical disk (DISC) as a reference level (I-TOP(in)), and from a peak level (I-TOP(out)) of the HF signal measured when the optical pickup is positioned at the prescribed position where it is estimated that the stress of the optical disk is the highest (in the case of a CD disk of a diameter of 12cm, the position corresponding to time range of 60-70 minutes). <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical disk birefringence amount estimation device and an optical disk drive.
[0002]
[Prior art]
Recently, electronic devices such as personal computers are often equipped with optical disk drives (optical disk devices). As recording media usable for the optical disk drive, a compact disc-recordable (CD-R) and a compact disc-rewritable (CD-RW) are known.
[0003]
CD-R is a recordable recording medium. With a CD-R, data can be written only once, and what has been written cannot be erased or rewritten.
[0004]
The CD-RW is a rewritable recording medium, but is compatible with a CD-ROM and an audio CD (CD-DA). Unlike CD-R, CD-RW uses a phase-change material for the recording layer. In a CD-RW, an erased state (crystalline phase) and a recorded state (amorphous phase) are recorded by laser light irradiation, and data is read based on the difference in reflectance. A CD-RW has a lower reflectance of light from a medium than a press-type CD-ROM or a CD-R using a dye.
[0005]
Writing information (data) to a CD-R or CD-RW requires a dedicated device and a writing application. On the other hand, reading of information (data) from a CD-R or CD-RW can be executed by a normal CD-ROM drive. The CD-R, CD-RW, CD-ROM, audio CD, DVD-ROM, DVD-R, DVD-RAM, DVD + RW, DVD-RW, and the like are collectively referred to herein as "optical disks".
[0006]
Now, in order to write information (data) to and read information (data) from or to such an optical disk, the optical disk drive is provided with a recording / reproducing optical pickup for irradiating a laser beam onto the optical disk. .
[0007]
Generally, this type of optical pickup includes a laser light source that emits a laser beam, and an optical system that guides the emitted laser beam to an optical disk. As described above, the CD-R can perform not only reading of information but also writing of information. In an optical pickup for a CD-R, the output of a laser beam emitted from a laser light source needs to be switched between when reading information and when writing information.
The reason is that writing of information is performed by forming pits in the recording layer of the optical disk by irradiating a laser beam. The output of the laser beam emitted from the laser light source at the time of writing information is larger than the output at the time of reading information, for example, about 10 to 20 times.
[0008]
Now, in such an optical pickup, a laser beam emitted from the laser light source passes through an optical system, and is condensed on a signal recording surface of an optical disk by an objective lens constituting the optical system, thereby recording information ( Write) and erase. On the other hand, the optical pickup reproduces information by detecting reflected light (return light) from the signal recording surface with a photodetector (photodetector) as light detecting means. Note that there are two types of optical systems for optical pickups, a polarizing optical system and a non-polarizing optical system. Here, “polarizing optical system” refers to an optical system that can change the polarization direction of a laser beam, and “non-polarizing optical system” refers to an optical system that does not change the polarization direction of a laser beam. Say.
[0009]
As described above, in the optical disk drive, recording and reproduction of the optical disk are performed using the laser beam emitted from the optical pickup, so that focusing control and tracking control are indispensable. Here, “focusing control” refers to controlling the distance between the optical disc and the objective lens to be constant, and “tracking control” refers to following a beam spot of a laser beam on a track of the optical disc. It means to control to make it. In order to perform the focusing control and the tracking control, the optical pickup includes an optical pickup actuator for displacing the objective lens in a vertical direction (focus direction) and a horizontal direction (tracking direction).
[0010]
By the way, an optical disc has an optical defect called “birefringence”. Here, "birefringence" refers to a phenomenon in which two refracted lights appear when light is refracted at the boundary surface. In other words, birefringence means that when light passes through a substance, the speed at which the light travels varies depending on the direction of the vibrating surface of the light. is called. An azimuth in which light travels fast (phase advances) is called a “fast axis” of the retarder, and an azimuth that is slow (phase lags) is called a “slow axis”. The fast axis and the slow axis are collectively referred to as the "principal axis" of birefringence.
[0011]
A polymer alignment film, a liquid crystal polymer, an optical crystal and the like exhibit birefringence. Also, it is known that when an isotropic substance (medium) is applied with stress, an electric field, a magnetic field, or the like from the outside, it temporarily exhibits anisotropy and generates birefringence (photoelastic effect, Kerr effect, Magnetic birefringence). The "photoelastic effect" is a phenomenon in which, when a mechanical force is applied to an optically isotropic elastic body, strain or stress causes optical distortion, that is, optically anisotropic and birefringence. Say. The “Kerr effect” is one of the electro-optic effects, and refers to a birefringence induced by the square of the electric field E among phenomena in which the refractive index of a substance is changed by an electric field. “Magnetic birefringence” is a phenomenon in which an optically transparent substance or a transparent magnetic substance in a magnetic field causes optical birefringence, and is also called “Cotton-Mouton effect”.
[0012]
[Problems to be solved by the invention]
In an optical disk drive using an optical pickup of a polarization optical system, a reflection signal from an optical disk is reduced due to the birefringence phenomenon.
[0013]
Further, in the case of a writable optical disk, a phenomenon that writing characteristics are deteriorated also occurs. This occurs because optical distortion occurs in the optical disk due to birefringence. Therefore, it is unclear how much the spot is distorted, and the quality degradation of the signal written on the optical disc cannot be predicted.
[0014]
Further, the value of the birefringence of the optical disc differs for each optical disc (that is, depending on molding conditions, materials, and the like). The value of the birefringence also differs depending on the position (location) of the optical disk due to the stress applied to the optical disk due to the increase in the number of rotations of the optical disk.
[0015]
Conventionally, measurement (detection) of the amount of birefringence of an optical disk is performed while the optical disk is stationary.
[0016]
In general, when measuring and predicting a change in state occurring on the outer peripheral side of an optical disk in advance, a point to be measured is set as close to the outermost peripheral of the optical disk as possible, and the signal level, shape, frequency, etc. from an optical pickup or the like is determined. Measurement is often performed.
[0017]
However, birefringence that occurs when the optical disk is rotated at a high speed occurs because stress generated by rotating the optical disk at a high speed is distributed on the optical disk. Therefore, the degree of birefringence tends to decrease rather at the outermost periphery of the optical disk. This is because the outermost periphery of the optical disk does not have an optical disk outside the outermost region, so that the stress is reduced.
[0018]
Therefore, an object of the present invention is to provide an optical disk birefringence amount estimating apparatus and an optical disk drive capable of reliably estimating the amount of birefringence caused by the effect of stress applied to a rotating optical disk.
[0019]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided an apparatus for estimating the amount of birefringence of an optical disk in an optical disk drive for picking up a signal from a rotating optical disk (DISC) by a polarization optical system optical pickup (OPU). Means (S111) for rotating at a desired rotation speed, means (S202) for moving the polarization optical system optical pickup to the inner circumference of the optical disk to be measured, and a predetermined signal obtained from the polarization optical system optical pickup are measured. Means (S203, S204) for storing as a signal (I_TOP (in)); means (S205) for moving the polarization optical system optical pickup to a predetermined position where the stress of the optical disk to be measured is estimated to be the highest; Means (S206, S207) for measuring a predetermined signal obtained from the system optical pickup; And the resulting signal (I_TOP (out)) as a reference signal from the means for estimating the amount of birefringence of the optical disc (S208), the birefringence amount estimation apparatus of an optical disc with obtained.
[0020]
In the apparatus for estimating the amount of birefringence of an optical disk according to the first aspect of the present invention, the predetermined signal may be any one of a peak level of an HF signal, an amplitude of an HF signal, a TE signal, and an FE signal. When the optical disk to be measured is an optical disk having a diameter of 12 cm, the predetermined position is in a range of 50 to 55 mm in radius. When the optical disk to be measured is a CD disk having a diameter of 12 cm, the predetermined position is a position corresponding to a time range of 60 to 70 minutes.
[0021]
According to the second aspect of the present invention, in an optical disk drive for picking up a signal from a rotating optical disk (DISC) by an optical pickup (OPU), the optical disk is read before writing / reading data to / from the optical disk. (S111), a means for moving the optical pickup to the inner circumference of the optical disk (S202), and a peak level of the HF signal obtained from the optical pickup is measured to obtain a reference level (I_TOP (in)). ), Means for moving the optical pickup to a predetermined position where the optical disk is estimated to have the highest stress (S205), and the peak level of the HF signal obtained from the optical pickup is measured. Means (S206, S207) and the peak level of the measured HF signal I_TOP and (out)) as a reference level and a means for estimating the amount of birefringence of the optical disc (S208), the optical disc drive is obtained which is characterized by having a.
[0022]
Note that the amplitude of the HF signal may be used instead of the peak level of the HF signal.
[0023]
In the optical disk drive according to the second aspect of the present invention, when the optical disk is an optical disk having a diameter of 12 cm, the predetermined position is in a range of 50 to 55 mm in radius. When the optical disk is a CD disk having a diameter of 12 cm, the predetermined position is a position corresponding to a time range of 60 to 70 minutes.
[0024]
It should be noted that the reference numerals in the parentheses are provided for easy understanding, are merely examples, and are not limited to these.
[0025]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0026]
First, an optical disk drive to which an apparatus for estimating the amount of birefringence of an optical disk according to the present invention will be described with reference to FIGS. FIG. 1 shows a state when the optical pickup OPU moves to the inner periphery, and FIG. 2 shows a state when the optical pickup OPU moves to the outer periphery. 1 (a) and 2 (a) are plan views, and FIGS. 1 (b) and 2 (b) are left side views.
[0027]
On the chassis 11, a spindle motor 13 and a feed motor 15 are mounted. The spindle motor 13 rotates a turntable 17 mounted thereon. An optical disk (not shown) is mounted on the turntable 17. Therefore, when the spindle motor 13 rotates, the optical disk mounted on the turntable 17 also rotates.
[0028]
A drive reduction gear 19 is engaged with the drive shaft of the feed motor 15, and the drive reduction gear 19 is engaged with a rack 21 formed on one side of the optical pickup OPU. The optical pickup OPU is guided by a pair of guide shafts 23a and 23b.
Therefore, when the feed motor 15 rotates, the optical pickup OPU is transported along the pair of guide shafts 23a and 23b.
[0029]
Referring to FIG. 3, the optical pickup OPU includes a semiconductor laser (laser diode) LD, a diffraction grating GRT, a collimator lens CL, a polarizing beam splitter PBS, a quarter-wave plate QWP, an objective lens OL, and a sensor. It has a lens SL and a photodetector PD. The illustrated optical pickup OPU includes a front monitor FM for monitoring a part of the laser beam emitted from the semiconductor laser LD, and a laser driver 25 for driving the semiconductor laser LD.
[0030]
The illustrated optical pickup OPU includes a polarization beam splitter PBS and a quarter-wave plate QWP, and is therefore called a polarization optical system optical pickup.
[0031]
Incidentally, one laser beam emitted from the semiconductor laser LD is separated into three laser beams by the diffraction grating GRT. These three laser beams consist of a main beam at the center and sub-beams on both sides of the main beam. The laser beam emitted from the semiconductor laser LD is linearly polarized light.
[0032]
Anyway, the three laser beams emitted from the semiconductor laser LD and separated by the diffraction grating GRT are collimated by the collimator lens CL and then reflected at right angles by the polarization beam splitter PBS. The laser beam reflected by the polarizing beam splitter PBS is circularly polarized by the quarter-wave plate QWP, and then condensed (irradiated) on the signal recording surface (reflection surface) of the optical disc DISC via the objective lens OL. You.
[0033]
FIG. 4 shows a spot of the laser beam applied to the optical disc DISC. As described above, the three laser beams divided by the diffraction grating GRT connect three spots to the track on the pit surface of the optical disc DISC as shown in FIG.
[0034]
Returning to FIG. 3, the reflected light (return light) from the signal recording surface of the optical disc DISC passes through the objective lens OL, is bent 90 ° with respect to the polarization direction of the outward path by the quarter-wave plate QWP, and is polarized by the polarization beam splitter PBS. And is detected by the photodetector PD through the sensor lens SL.
[0035]
The illustrated optical pickup OPU employs a method using three beams formed using a diffraction grating as a tracking error detection method. Among the methods using three beams, the differential push-pull method is particularly used.
[0036]
More specifically, as described above, one laser beam emitted from the laser diode LD as a light source is separated into three laser beams by the diffraction grating GRT. Therefore, the reflected light (return light) from the optical disc DISC also includes three laser beams. Of the three laser beams, the central main beam is used to generate a read signal and a focus error signal, and the two sub beams on both sides are used to generate a tracking error signal.
[0037]
FIG. 5 shows a configuration of a photodetector PD for receiving reflected light (return light). 5A is a front view, and FIG. 5B is a right side view. The photodetector PD has a main light receiving element 31 for receiving a main beam, and a pair of sub light receiving elements 32 and 33 for receiving two sub beams on both sides. The main light receiving element 31 is constituted by a four-division photodiode, and each of the sub light receiving elements 32 and 33 is constituted by a two-division photodiode.
[0038]
Therefore, of the three spots shown in FIG. 4A, the reflected light (main part) from the center spot (the part marked with A, B, C, and D in FIG. 4A). 5) are received by the main light receiving element 31 shown in FIG. 5 as four main electric signals indicated by reference numerals A, B, C, and D in FIG. The reflected light (sub-beam) from the spot on one side (the portion denoted by reference signs E and F in FIG. 4A) is transmitted by one sub-light receiving element 32 shown in FIG. Are received as two sub-electrical signals indicated by symbols E and F. Then, the reflected light (sub-beam) from the other side spot (the part marked with G and H in FIG. 4A) is reflected by the other sub-light receiving element 33 shown in FIG. Are received as two sub-electric signals indicated by G and H symbols.
[0039]
Next, a circuit for detecting the level of a reflection-side signal (hereinafter, referred to as “I-TOP”) of the HF signal will be described with reference to FIG.
[0040]
The illustrated I-TOP level detection circuit includes an addition circuit 41, a peak hold circuit 43, and an A / D conversion circuit 45. The A / D conversion circuit 45 is built in a central processing unit (CPU) 47.
[0041]
The adder circuit 41 includes an operational amplifier 411. The four main electric signals described above are supplied to the non-inverting input terminal + thereof through the resistors 422 to 425, and the HF reference voltage is supplied to the inverting input terminal thereof. It is supplied via a resistor 426, and a resistor 427 is connected between its output terminal and the inverting input terminal-. The output terminal of the adding circuit 41 is connected to the input terminal of the peak hold circuit 43. The peak hold circuit 43 holds the peak of the signal added by the addition circuit 41 and outputs a peak hold signal. An output terminal of the peak hold circuit 43 is connected to an input terminal of the A / D conversion circuit 45. The A / D conversion circuit 45 is also supplied with an HF reference signal. The A / D conversion circuit 45 converts the peak hold signal output from the peak hold circuit 43 into a digital signal. This digital signal indicates the level of the I-TOP.
[0042]
Anyway, the I-TOP level detection circuit detects the level of I-TOP as described above.
[0043]
The present invention estimates the birefringence (actually, “relative birefringence”) of an optical disk by utilizing the correlation between the I-TOP level and the birefringence of the optical disk. Related to the device. That is, the higher the level of I-TOP, the smaller the amount of birefringence, and the lower the level of I-TOP, the larger the amount of birefringence. As described above, if the rotation speed of the optical disk is sufficiently low (for example, 1000 rpm or less), the birefringence does not occur remarkably due to the stress generated by the centrifugal force due to the rotation. Even if the rotation speed of the optical disk is high, no stress is generated on the inner peripheral side of the optical disk, so that no birefringence occurs on the inner peripheral side of the optical disk. Therefore, in the present invention, the level of I-TOP measured by the polarization optical system optical pickup at the position of the optical disk which is not affected by the stress is set as a reference level, and the level of I-TOP from this reference level is determined. The relative birefringence is estimated from the degree of reduction (ratio).
[0044]
FIG. 7 shows a configuration of an optical disk drive to which the apparatus for estimating the amount of birefringence of an optical disk according to one embodiment of the present invention is applied. The illustrated optical disk drive includes a spindle driver 51 for driving the spindle motor 13, a BTL driver 53 for performing feed control of the feed motor 15 and focusing control and tracking control of the polarization optical system optical pickup OPU, and the addition circuit 41. And an analog signal processor (ASP) 55 including the peak hold circuit 43. The analog signal processor 55 controls the laser driver 25 (FIG. 3) to control the amount of laser beam emitted from the semiconductor laser LD.
[0045]
The analog signal processor 55, the BTL driver 53, and the spindle driver 51 are controlled by the central processing unit 47. The central processing unit 47 has a CD-DSP 471, an ENDEC 472, a G / A 473, a microcontroller 474, and a memory such as a dynamic RAM 475 and a flash memory 476.
[0046]
The central processing unit 47 sends a sending command to the BTL driver 53. In response to this feed command, the BTL driver 53 drives the feed motor 15 to move the polarization optical system optical pickup OPU from the inner circumference to the outer circumference of the optical disc DISC.
[0047]
Further, the central processing unit 47 sends a rotation speed command to the spindle driver 51. In response to the rotation speed command, the spindle driver 51 rotates the spindle motor 13 at the rotation speed specified by the rotation speed command, thereby rotating the optical disc DISC at a plurality of different rotation speeds.
[0048]
A signal obtained by being reflected from the optical disc DISC by the polarization optical system optical pickup OPU is taken into the central processing unit 47 via the analog signal processor 55. At this time, the level of the I-TOP is taken into the central processing unit 47 by the peak hold circuit 43 in the analog signal processor 55.
[0049]
In FIG. 8, when the rotation speed (speed) of the optical disc DISC is 40 times speed (CLV (constant linear velocity)), it is obtained when the polarization optical system optical pickup OPU is moved from the inner circumference to the outer circumference of the optical disc DISC. 2 shows the obtained I-TOP ratio. Here, the optical disk is a CD disk having a diameter of 12 cm, and the I-TOP ratio based on a position corresponding to one minute of double speed (CLV) is shown.
[0050]
As is clear from FIG. 8, the I-TOP ratio gradually decreases as the position of the polarization optical system optical pickup OPU moves from the inner circumference to the outer circumference of the optical disc DISC. Then, the I-TOP ratio becomes the smallest at a position where the position of the polarization optical system optical pickup OPU corresponds to a time of 60 to 70 minutes on the optical disc DISC. The position corresponding to the time of 60 to 70 minutes on the optical disk DISC corresponds to a range of 50 to 55 mm in radius. It can be seen that when the polarization optical system optical pickup OPU moves further to the outer periphery of the optical disc DISC than at that position, the I-TOP ratio is rather increased. This is presumed to be because the outermost periphery of the optical disk does not have an optical disk outside of the outermost region, so that the stress is reduced.
[0051]
Taking the above into consideration, the optical disk birefringence amount estimating apparatus according to the embodiment of the present invention estimates the birefringence amount as described below. However, in the embodiment described below, not only the operation of measuring (estimating) the amount of birefringence of the optical disk, but also the operation of reducing the number of rotations is performed.
[0052]
The operation in the case where the amount of birefringence is measured (estimated) before reading / writing in advance and the rotation speed is reduced is described below with reference to FIGS. In this example, a CD disk having a diameter of 12 cm is used as the optical disk to be measured DISC.
[0053]
Referring to FIG. 9, first, information processing device 47 checks whether or not optical disc DISC has been loaded (step S101). When the optical disc DISC is loaded (Yes in step S101), the information processing device 47 performs an optical disc DISC recognition process (step S102). Subsequently, the information processing device 47 rotates the optical disk DISC at double speed by sending a rotation speed command to rotate the optical disk DISC at double speed to the spindle driver 51 (step S103). The information processing device 47 checks whether the optical disc DISC has been correctly recognized (step S104). When the optical disc DISC cannot be correctly recognized (No in step S104), the information processing device 47 determines that an error has occurred and performs an error process (step S105).
[0054]
On the other hand, if the optical disc DISC is correctly recognized (Yes in step S104), the information processing device 47 performs a servo adjustment process (step S106), and then instructs the spindle driver 51 to rotate the optical disc DISC at quadruple speed. To rotate the optical disc DISC at a quadruple speed (step S107). Subsequently, the information processing unit 47 reads information from the optical disk DISC via the optical pickup OPU and the analog signal processor 55 (optical disk initialization) (step S108).
[0055]
The information processing device 47 checks whether information from the optical disc DISC has been correctly acquired (step S109). When the information from the optical disc DISC has not been correctly obtained (No in step S109), the information processing device 47 determines that an error has occurred and performs an error process (step S110).
[0056]
On the other hand, when the information from the optical disc DISC has been correctly acquired (Yes in step S109), the information processing device 47 sends the designated rotation speed to the spindle driver 51, thereby causing the optical disc DISC to have the designated speed ( (For example, 48 times speed) (step S111).
[0057]
Moving to FIG. 10, the information processing device 47 checks whether or not the optical disc DISC has been changed (step S112). That is, it is checked whether the currently loaded optical disc DISC is the same as the optical disc DISC loaded immediately before. To enable this confirmation, the information processing device 47 recognizes an identifier (ID) assigned to each optical disc DISC when loading the optical disc DISC, and stores the ID in the dynamic RAM 475.
[0058]
If the optical disc DISC has been changed (Yes in step S112), the information processing device 47 sets the variables of I_TOP (in) and I_TOP (out) to zero (step S113), stores the variables in the dynamic RAM 475, and then performs birefringence. The measurement is performed (Step S114).
[0059]
Next, the birefringence measurement will be described with reference to FIG.
[0060]
First, the information processing device 47 checks whether or not zero is included in I_TOP (in) (step S201). When zero is included in I_TOP (in) (Yes in step S201), the information processing device 47 sets the target address to 0 min0sec0block on the inner circumference (step S202), and sends a sending command to the BLT driver 53. By driving the feed motor 15, the optical pickup OPU is moved to the inner peripheral position of the optical disc DISC. The I-TOP level of the HF signal detected from the optical disc DISC by the photodetector PD of the optical pickup OPU is detected by the peak hold circuit 43 in the analog signal processor 55. The information processing device 47 measures the level of the I-TOP with the A / D converter 45 (step S203), and stores the measured value in a variable called I_TOP (in) (step S204). This I_TOP (in) indicates a reference level.
[0061]
Next, the information processing device 47 sets the target address to the outer circumference of 65 min0 sec0 block (step S205), drives the feed motor 15 by sending a send command to the BLT driver 53, and moves the optical pickup OPU to a predetermined position on the optical disc DISC. To the outer peripheral position. In the same manner as described above, the information processing device 47 measures the level of the I-TOP detected by the peak hold circuit 43 with the A / D converter 45 (step S206), and outputs the measured value to I_TOP (out). (Step S207).
[0062]
The information processing device 47 calculates the birefringence amount X from I_TOP (in) and I_TOP (out) measured as described above, and the following formula X = (I_TOP (in) −I_TOP (out)) / I_TOP (in)
And the calculated value X is stored in the dynamic RAM 475 as the birefringence amount BI-FEF (step S208).
[0063]
Returning to FIG. 10, the information processing device 47 determines whether the birefringence amount BI-FEF is smaller than a specified value BI-FEF-Limit (step S115). When the amount of birefringence BI-FEF is equal to or larger than the specified value BI-FEF-Limit (No in step S115), the information processing device 47 determines that the birefringence of the optical disc DISC is caused by the rotational stress, and the spindle driver is driven. By controlling the number of revolutions of the spindle motor 13 via the controller 51, a deceleration process of decreasing the number of revolutions (a process of reducing the speed by one step (32 times speed) from the current speed (48 times speed)) is performed (step S116).
[0064]
Returning to step S114, the birefringence measurement is again performed, and the information processing device 47 operates in steps S114 to S116 until the birefringence amount BI-FEF becomes smaller than the specified value BI-FEF-Limit (Yes in step S115). repeat.
[0065]
After that, the information processing device 47 drives the feed motor 15 by sending a send command to the BLT driver 53, and seeks the optical pickup OPU to the target address of read / write (step S117). The information processing device 47 performs read / write processing (including data transfer for each designated block number) via the optical pickup OPU and the analog signal processor 55 (step S118).
The information processing device 47 repeats the read / write processing until the designated END address is reached (step S119).
[0066]
As described above, the rotation speed can be reduced by measuring (estimating) the amount of birefringence before reading / writing.
[0067]
FIG. 12 illustrates the dependence of the amount of returning light to the photodetector PD and the amount of birefringence of the optical disc DISC. In FIG. 12, the vertical axis indicates the amount of return light to the photodetector PD with the maximum value normalized to 1, and the horizontal axis indicates the birefringence [nm] of the optical disc DISC. Here, it is assumed that the light emitted from the quarter-wave plate QWP toward the optical disc DISC is perfectly circularly polarized light, and that the wavelength of the laser beam emitted from the semiconductor laser LD is 785 nm.
[0068]
As is clear from FIG. 12, it can be seen that the birefringence of the optical disc DISC increases as the amount of return light to the photodetector PD decreases. When the amount of light returning to the photodetector PD is zero, the birefringence of the optical disc DISC is 392.5 [nm].
[0069]
Next, the dependence of the return light to the photodetector PD on the birefringence of the optical disc DISC will be described with reference to FIG. It is assumed that light is perpendicularly incident on the quarter-wave plate QWP, the direction of linearly polarized light is parallel to the X (radial) direction, and the optical disc DISC has no birefringence. In this case, light transmitted through the quarter-wave plate QWP becomes circularly polarized light. Here, it is assumed that the circularly polarized light is clockwise. The light reflected by the optical disc DISC is turned into counterclockwise circularly polarized light and enters the quarter-wave plate QWP. The light emitted from the quarter-wave plate QWP becomes linearly polarized light parallel to the Y (tangential) direction, transmits nearly 100% through the polarization beam splitter PBS, and enters the photodetector PD. Hereinafter, this state is set to 1 and standardized for consideration.
[0070]
Next, it is assumed that the phase is advanced by δ radians due to the birefringence of the optical disc DISC. In the following, 4) when (1) 0 <δ <π / 2, (2) when δ = π / 2, (3) when π / 2 <δ <π, and (4) when δ = π A description will be given separately for the following cases.
[0071]
{Circle around (1)} When 0 <δ <π / 2, the light reflected by the optical disk DISC is converted into left-handed elliptically polarized light, enters the quarter-wave plate QWP, and is straightened at a certain position inside the quarter-wave plate QWP. It becomes polarized light. Thereafter, the outgoing light from the quarter-wave plate QWP is emitted as elliptically polarized light in a clockwise direction with a phase advanced by π / 2 from the incident light. Since the amount of light transmitted through the polarization beam splitter PBS is represented by a component in the Y direction of the ellipse, the amount of light incident on the photodetector PD is cos (δ / 2).
[0072]
{Circle around (2)} When δ = π / 2, the light reflected by the optical disc DISC is converted into linearly polarized light parallel to the Y direction, enters the quarter-wave plate QWP, and rotates clockwise from the quarter-wave plate QWP. And emitted. Therefore, the light amount of the incident light on the photodetector PD is also cos (π / 4) ≒ 0.707.
[0073]
{Circle around (3)} When π / 2 <δ <π, the light reflected by the optical disc DISC becomes clockwise elliptically polarized light, enters the quarter-wave plate QWP, and forms a circle at a certain position inside the quarter-wave plate QWP. It becomes polarized light. Thereafter, the outgoing light from the quarter-wave plate QWP is emitted as elliptically polarized light in a clockwise direction with a phase advanced by π / 2 from the incident light. Therefore, the light quantity of the incident light on the photodetector PD is cos (δ / 2).
[0074]
{Circle around (4)} When δ = π, the light reflected by the optical disk DISC is converted into clockwise circularly polarized light, enters the quarter-wave plate QWP, and becomes linearly polarized light parallel to the X direction from the quarter-wave plate QWP. And is emitted. Therefore, the light quantity of the incident light on the photodetector PD is also cos (π / 2) = 0.
[0075]
Tables and graphs that summarize the above are shown in FIGS. 14 and 15, respectively. FIG. 14 is a table showing the relationship between the amount of birefringence of the optical disk, the phase shift, and the amount of incident light on the photodetector. FIG. 15 is a diagram showing the relationship between the amount of incident light on the photodetector and the amount of birefringence on the optical disk.
[0076]
The elliptically polarized light whose major axis is in the Y direction indicates a case where the phase δ advanced by the birefringence of the optical disc DISC is in the range of 0 to π. In this case, the birefringence amount of the optical disc DISC in the graph shown in FIG. 15 corresponds to the portion where the birefringence is from 0 nm to 392.5 nm.
[0077]
On the other hand, the elliptically polarized light whose major axis is in the X direction indicates a case where the phase δ advanced by the birefringence of the optical disc DISC becomes π or more or becomes negative. In this case, the birefringence amount of the optical disc DISC in the graph shown in FIG. 15 corresponds to the portion from 392.5 nm to 785 nm.
[0078]
The present invention is not limited to the above-described embodiment, and needless to say, various changes and modifications can be made without departing from the spirit of the present invention. For example, in the above-described embodiment, the level of the I-TOP is measured. However, an error signal such as a TE (tracking error) signal or an FE (focusing error) signal may be measured instead. It is. Further, the amplitude of the HF signal may be used instead of the peak level of the HF signal. In the above-described embodiment, the HF signal is shaped by the peak hold circuit before being taken into the information processing apparatus. However, the HF signal is directly supplied to the A / D conversion circuit, converted into a digital signal, and then converted into a digital signal. The peak level and amplitude of the signal may be detected. In the above-described embodiment, a position corresponding to a time of 65 minutes is selected as the predetermined position at which the stress of the optical disk is estimated to be the highest, in the case of a CD disk having a diameter of 12 cm. The position may be any position corresponding to the time range of minutes, and in the case of an optical disk having a diameter of 12 cm, the position may be within the range of 50 to 55 mm.
[0079]
【The invention's effect】
As is apparent from the above description, according to the present invention, before reading / writing data to / from the optical disk, the HF signal obtained from the optical pickup when the optical pickup is at the inner peripheral position of the optical disk is read. The peak level (amplitude) is defined as a reference level (reference amplitude), and the reference level (reference amplitude) and the peak level of the HF signal measured by moving the optical pickup to a predetermined position where the optical disk is estimated to have the highest stress. Since the amount of birefringence of the optical disk is estimated from (amplitude), the amount of birefringence of the optical disk can be reliably estimated.
[Brief description of the drawings]
FIG. 1 is a diagram showing a state of an optical disk drive to which an apparatus for estimating the amount of birefringence of an optical disk according to the present invention is applied, when an optical pickup is moved to an inner periphery; FIG. It is a left side view.
FIGS. 2A and 2B are diagrams showing a state of the optical disk drive shown in FIG. 1 when an optical pickup moves to an outer periphery, where FIG. 2A is a plan view and FIG. 2B is a left side view.
FIG. 3 is a block diagram showing a configuration of a polarization optical system optical pickup used in the optical disk drive shown in FIGS. 1 and 2;
4A and 4B are diagrams showing spots of a laser beam applied to an optical disk, wherein FIG. 4A is a plan view and FIG. 4B is a schematic sectional view.
5A and 5B are diagrams illustrating a configuration of a photodetector for receiving reflected light (return light) used in the polarization optical system optical pickup illustrated in FIG. 3, wherein FIG. 5A is a front view and FIG. FIG.
FIG. 6 is a block diagram illustrating a configuration of an I-TOP level detection circuit that detects a level of a reflection side signal (I-TOP) of the HF signal.
FIG. 7 is a block diagram showing a configuration of an optical disc drive including the optical disc birefringence amount estimating apparatus according to one embodiment of the present invention.
FIG. 8 is a diagram showing an I-TOP ratio obtained when the polarization optical system optical pickup is moved from the inner circumference to the outer circumference of the optical disk when the rotation speed (speed) of the optical disk is 49 times speed. is there.
FIG. 9 is a flowchart for explaining an operation in a first half part in which a birefringence is measured (estimated) before reading / writing, and a rotation speed deceleration operation is performed.
FIG. 10 is a flowchart for explaining the latter half operation of measuring (estimating) birefringence before reading / writing and performing a rotation speed deceleration operation.
11 is a flowchart for explaining the operation of the birefringence measurement in FIG.
FIG. 12 is a diagram illustrating a dependence relationship between the amount of returning light to the photodetector and the amount of birefringence of the optical disk.
FIG. 13 is a diagram for explaining dependence of return light to a photodetector on birefringence of an optical disk.
FIG. 14 is a table showing a relationship between a birefringence amount of an optical disc, a phase shift, and an incident light amount of a photodetector.
FIG. 15 is a diagram showing a relationship between an incident light amount of a photodetector and a birefringence amount of an optical disk.
[Explanation of symbols]
OPU polarization optical system optical pickup DISC optical disk 13 spindle motor 15 feed motor 25 laser driver 43 peak hold circuit 45 A / D conversion circuit 47 central processing unit (CPU)
475 Dynamic RAM
51 Spindle driver 53 BTL driver 55 Analog signal processor (ASP)

Claims (12)

An apparatus for estimating the amount of birefringence of an optical disc in an optical disc drive for picking up a signal from a rotating optical disc by a polarization optical system optical pickup,
Means for rotating the optical disk to be measured at a desired rotation speed,
Means for moving the polarization optical system optical pickup to the inner periphery of the optical disk to be measured,
Means for measuring a predetermined signal obtained from the polarization optical system optical pickup, and storing it as a reference signal,
Means for moving the polarization optical system optical pickup to a predetermined position where the stress of the measured optical disk is estimated to be the highest,
Means for measuring the predetermined signal obtained from the polarization optical system optical pickup,
Means for estimating the amount of birefringence of the optical disc from the signal obtained by the measurement and the reference signal,
An apparatus for estimating the amount of birefringence of an optical disc comprising: 2. The apparatus according to claim 1, wherein the predetermined signal is a peak level of an HF signal. The apparatus according to claim 1, wherein the predetermined signal is an amplitude of an HF signal. 2. The apparatus according to claim 1, wherein the predetermined signal is a TE signal. The optical disc birefringence amount estimation apparatus according to claim 1, wherein the predetermined signal is an FE signal. 2. The optical disc birefringence amount estimating apparatus according to claim 1, wherein when the measured optical disc is an optical disc having a diameter of 12 cm, the predetermined position is in a range of 50 to 55 mm in radius. 2. The optical disc birefringence amount estimating apparatus according to claim 1, wherein when the measured optical disc is a CD disc having a diameter of 12 cm, the predetermined position is a position corresponding to a time range of 60 to 70 minutes. In an optical disk drive that picks up a signal from a rotating optical disk by an optical pickup,
Means for previously rotating the optical disc at a desired number of revolutions before reading / writing data to / from the optical disc;
Means for moving the optical pickup to the inner periphery of the optical disc;
Means for measuring a peak level of an HF signal obtained from the optical pickup and storing the measured peak level as a reference level;
Means for moving the optical pickup to a predetermined position where the optical disk is estimated to have the highest stress;
Means for measuring a peak level of the HF signal obtained from the optical pickup;
Means for estimating the birefringence of the optical disk from the measured peak level of the HF signal and the reference level;
An optical disk drive comprising: In an optical disk drive that picks up a signal from a rotating optical disk by an optical pickup,
Means for previously rotating the optical disc at a desired number of revolutions before reading / writing data to / from the optical disc;
Means for moving the optical pickup to the inner periphery of the optical disc;
Means for measuring the amplitude of the HF signal obtained from the optical pickup and storing it as a reference amplitude;
Means for moving the optical pickup to a predetermined position where the optical disk is estimated to have the highest stress;
Means for measuring the amplitude of the HF signal obtained from the optical pickup;
Means for estimating the amount of birefringence of the optical disk from the measured amplitude of the HF signal and the reference amplitude;
An optical disk drive comprising: 10. The optical disk drive according to claim 8, wherein the optical pickup comprises a polarization optical system optical pickup. 10. The optical disk drive according to claim 8, wherein when the optical disk is an optical disk having a diameter of 12 cm, the predetermined position is in a range of 50 to 55 mm in radius. 10. The optical disk drive according to claim 8, wherein when the optical disk is a CD disk having a diameter of 12 cm, the predetermined position is a position corresponding to a time range of 60 to 70 minutes.

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