JP2004185750A - Estimation device of birefringence of optical disk and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To estimate the amount of birefringence of an optical disk in a state of rotating the optical disk. <P>SOLUTION: A CPU 47 and and a host PC 60 measure a signal acquired by reflecting from a reference disk by an optical pickup of a polarized optical system while moving the optical pickup OPU of a polarized optical system toward the circumference from an interior of the reference disk in a state of rotating a reference optical disk at a desired rotation speed to be measured, and store the signal as a reference signal. Then, they measure the signal acquired by reflecting from a measurement object optical disk by an optical pickup of a polarized optical system while moving the optical pickup of a polarized optical system toward the circumference from the interior of the measurement object disk in a state of rotating the measurement object optical disk at a desired rotation speed to be measured. Then, the amount of birefringence of measurement object optical disk is estimated from the drop of the signal acquired by the measurement of the reference signal. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an apparatus and a method for estimating the amount of birefringence of an optical disc.
[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, there is an apparatus for measuring a birefringence amount of a stationary optical disc. However, there is no device that measures birefringence due to the effect of stress applied to an optical disk rotating at high speed.
[0016]
Further, birefringence of the optical disk is remarkably generated by a stress caused by a centrifugal force when the rotation speed of the optical disk is increased. Therefore, it is necessary to measure the birefringence of the optical disk while rotating the optical disk.
[0017]
Therefore, an object of the present invention is to provide a birefringence amount estimation device for an optical disc which can estimate birefringence caused by the effect of stress applied to a rotating optical disc.
[0018]
[Means for Solving the Problems]
According to the present invention, the amount of birefringence of an optical disk under measurement (DISC) in a rotating state is estimated using an optical disk drive (62) equipped with a polarization optical system optical pickup (OPU). In a quantity estimating apparatus, the reference optical disk is rotated at the rotation speed to be measured, and the polarization optical system optical pickup is moved from the inner circumference to the outer circumference of the reference disk while the reference optical disk is being rotated. Measuring means (62, 60) for measuring a signal reflected from the optical disk and storing the signal as a reference signal, and measuring the polarization optical system optical pickup while rotating the optical disk to be measured at the desired rotational speed. While moving from the inner circumference to the outer circumference of the target optical disk, the light is reflected from the target optical disk by the polarization optical system optical pickup. A measuring object measuring means (60, 62) for measuring the obtained signal and an estimating means (60, 62) for estimating the birefringence of the optical disk to be measured from the degree of reduction of the signal obtained by the measurement with respect to the reference signal An apparatus for estimating the amount of birefringence of an optical disc, characterized in that the apparatus has:
[0019]
In the apparatus for estimating the amount of birefringence of an optical disc, the reference optical disc may be an optical disc whose birefringence does not change significantly as compared with a stationary state even when a stress is generated by a rotational force. As such a reference optical disk, for example, a glass optical disk or a selected optical disk can be used.
[0020]
Further, according to the present invention, a method of estimating the amount of birefringence of a rotating optical disk to be measured (DISC) using an optical disk drive (62) equipped with a polarization optical system optical pickup (OPU) is provided. Then, by comparing the signal obtained by picking up the reference optical disk with the polarizing optical system optical pickup and the signal obtained by picking up the measuring object optical disk with the polarizing optical system optical pickup, the duplication of the measuring object optical disk is performed. A method for estimating the amount of birefringence of an optical disc, characterized in that the amount of refraction is estimated (60, 62).
[0021]
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.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0023]
First, an optical disk drive to which an apparatus for estimating the amount of birefringence of an optical disk according to an embodiment of 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.
[0024]
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.
[0025]
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.
[0026]
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.
[0027]
The illustrated optical pickup OPU is called a polarization optical system optical pickup because it includes a polarization beam splitter PBS and a 波長 wavelength plate QWP at the branch of the forward path / return path.
[0028]
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.
[0029]
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.
[0030]
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.
[0031]
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.
[0032]
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.
[0033]
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.
[0034]
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.
[0035]
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.
[0036]
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.
[0037]
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.
[0038]
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.
[0039]
Anyway, the I-TOP level detection circuit detects the level of I-TOP as described above.
[0040]
The present invention utilizes the fact that the level of the I-TOP and the birefringence of the optical disc DISC to be measured are correlated, and the birefringence of the optical disc to be measured (actually, “relative birefringence )). 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. In the present invention, a reference optical disk is used in which birefringence does not significantly change even when stress is generated due to rotational force (centrifugal force) as compared with a stationary state. As such a reference optical disk, for example, a glass optical disk or a selected optical disk can be used. Therefore, in the present invention, the level of the I-TOP measured by the polarization optical system optical pickup OPU from the reference optical disk which is not affected by the stress is set as the reference level, and the optical disk to be measured which is affected by the reference level and the stress is determined. The relative birefringence is estimated from the degree of decrease (ratio) of the I-TOP level measured by the polarization optical system optical pickup OPU from the DISC.
[0041]
As described above, the conventional optical disc birefringence measuring apparatus measures the birefringence of a measured optical disc in a stationary state. On the other hand, the apparatus for estimating the amount of birefringence of an optical disk according to the present invention estimates the amount of birefringence of an optical disk DISC in a rotating state using a reference optical disk. In the present invention, the amount of birefringence of the optical disc DISC to be measured in a rotating state is determined by using a reference optical disc and an optical disc drive (FIGS. 1 and 2) equipped with a polarization optical system optical pickup OPU (FIG. 3). ,presume. That is, the apparatus for estimating the amount of birefringence of an optical disc according to the present invention moves the polarization optical system optical pickup from the inner circumference to the outer circumference of the reference disc while rotating the reference optical disc at the rotation speed to be measured. A reference measuring means for measuring a signal reflected from a reference disk by a polarization optical system optical pickup and storing the signal as a reference signal, and a polarization optical system optical pickup with the target optical disk rotated at a desired rotational speed. Measuring means for measuring a signal obtained by being reflected from the optical disk to be measured by the polarization optical system optical pickup while moving the optical disk from the inner circumference to the outer circumference of the optical disk to be measured, and a signal obtained by the measurement with respect to the reference signal. Estimating means for estimating the amount of birefringence of the optical disk to be measured from the degree of signal decrease.
[0042]
FIG. 7 shows an example of a configuration of a birefringence amount estimation device according to an embodiment of the present invention. The illustrated birefringence amount estimating apparatus 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, An analog signal processor (ASP) 55 including an addition circuit 41 and a peak hold circuit 43 is provided. 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.
[0043]
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.
[0044]
The central processing unit 47 is connected to a host personal computer (PC) 60 via an ATAPI interface (IF) 57. The host PC 60 has a memory (not shown). The combination of the central processing unit 47 and the host PC 60 functions as the above-described reference measurement unit, measurement target measurement unit, and estimation unit.
[0045]
A reading device (optical disk drive) 62 is constituted by the polarization optical system optical pickup OPU, analog signal processor 55, spindle motor 13, feed motor 15, BTL driver 53, spindle motor 51, CPU 47, and ATAPI interface 57. .
[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. The captured I-TOP level is transferred from the central processing unit 47 to the host PC 60 via the ATAPI interface 57.
[0049]
FIG. 8 shows a case where the polarization optical system optical pickup OPU is moved from the inner circumference to the outer circumference of the reference optical disk and the measurement target optical disk when the reference optical disk and the measurement target optical disk are rotated at the rotation speed to be measured. The obtained I-TOP level is shown. The I-TOP level data thus obtained is transferred from the central processing unit 47 to the host PC 60, stored in its memory (not shown) as a log file, and displayed as a screen on a display device (not shown). Is done.
[0050]
If the level of the I-TOP has decreased, the host PC 60 can determine (determine) that it is the influence of the birefringence due to the rotational stress of the optical disc DISC to be measured.
[0051]
As is clear from FIG. 8, when the optical disk is the reference optical disk, the level of the I-TOP obtained from the polarization optical system optical pickup OPU does not change regardless of the position of the polarization optical system optical pickup OPU. In other words, in the reference optical disk, even if stress is generated due to rotational force (centrifugal force), the birefringence does not change significantly compared to the stationary state. Therefore, in the present invention, as described later, the level of the I-TOP obtained at this time is used as a reference signal.
[0052]
On the other hand, when the optical disk is the optical disk to be measured, the level of the I-TOP obtained from the polarization optical system optical pickup OPU changes depending on the position of the polarization optical system optical pickup OPU.
[0053]
In consideration of the above, in the embodiment of the present invention, the amount of birefringence of the optical disc DISC to be measured is measured and estimated as described below.
[0054]
After the reference optical disc is mounted on the turntable 17 of the reading device 62, the central processing unit 47 first sends a rotation speed command to the spindle driver 51, and the rotation speed (for example, 48 × speed) at which the reference optical disc is to be measured is measured. ), The feed command is sent to the BTL driver 53, and the polarization optical system optical pickup OPU is moved from the inner circumference to the outer circumference of the reference optical disc from a predetermined position (address) to the position. , A signal (I-TOP level) obtained by reflection from the reference optical disk by the polarization optical system optical pickup OPU is measured via the peak hold circuit 43, and the I-TOP level for each address is sent to the host PC 60 by the ATAPI. The data is transferred via the interface 57 and stored as a reference signal in a memory (not shown) in the host PC 60. Storage) makes.
[0055]
Next, after the measurement target optical disc DISC is mounted on the turntable 17 of the reading device 62, the central processing unit 47 sends a rotation speed command to the spindle driver 51, and the rotation speed (for example, the rotation speed at which the measurement target optical disc DISC is to be measured) , 48 ×), and sends a feed command to the BTL driver 53 to move the polarization optical system optical pickup OPU from the inner circumference to the outer circumference of the optical disc DISC to be measured to a predetermined position (address). At this position, a signal (I-TOP level) obtained by reflection from the optical disc DISC to be measured by the polarization optical system optical pickup OPU is measured via the peak hold circuit 43, and the level of the I-TOP for each address is measured. To the host PC 60 via the ATAPI interface 57.
[0056]
The host PC compares the level of the stored reference signal and the level of the signal obtained by the measurement at the position of the polarization optical system optical pickup OPU, and determines the amount of birefringence of the optical disc DISC to be measured from the degree of decrease. presume. Since there is a correlation between the decrease in the signal level and the birefringence amount of the optical disc DISC to be measured, it is possible to convert the signal into a measured value of the absolute birefringence of the optical disc DISC to be measured.
[0057]
FIG. 9 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. 9, the vertical axis represents the amount of return light to the photodetector PD with the maximum value normalized to 1, and the horizontal axis represents 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.
[0058]
As is clear from FIG. 9, it is found 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].
[0059]
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.
[0060]
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.
[0061]
{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).
[0062]
{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.
[0063]
{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).
[0064]
{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.
[0065]
Tables and graphs that summarize the above are shown in FIGS. 11 and 12, respectively. FIG. 11 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. 12 is a diagram showing the relationship between the amount of incident light on the photodetector and the amount of birefringence on the optical disk.
[0066]
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 of the optical disc DISC in the graph shown in FIG. 12 corresponds to the portion where the birefringence is from 0 nm to 392.5 nm.
[0067]
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 of the optical disc DISC in the graph shown in FIG. 12 corresponds to the portion from 392.5 nm to 785 nm.
[0068]
In this way, the birefringence amount estimating apparatus according to the present invention can estimate the birefringence amount of the rotating optical disc DISC as viewed from the polarization optical system optical pickup OPU using the reference optical disc. As described above, the optical disk drive 62 used in the birefringence amount estimating apparatus according to the present invention can use an existing optical disk drive as it is or use a slightly modified one. Therefore, the birefringence amount estimation device can be manufactured at very low cost.
[0069]
The present invention is not limited to the above-described embodiment, and it goes without saying that various changes and modifications can be made without departing from the spirit of the present invention. For example, in the above-described embodiment, an example in which the host PC 60 and the reading device 62 are combined to form a birefringence amount estimation device has been described. However, the CPU 47 built in the reading device 62 is controlled by firmware (F / W). The birefringence amount estimating device may be configured by an integrated device that displays all data by controlling all display devices such as a liquid crystal display device (LCD) from the CPU 47 by storing and comparing data. In the above-described embodiment, the I-TOP level detection circuit includes the addition circuit 41 and the peak hold circuit 43. However, the peak hold circuit 43 is omitted and the output of the addition circuit 41 is directly sent to the CPU 47. You may make it supply. In this case, the CPU 47 may detect a peak signal (I-TOP level) from the digital signal converted by the A / D conversion circuit 45. Further, in the above-described embodiment, only the case where the level of the I-TOP is used as the signal obtained by reflection from the reference optical disk and the optical disk to be measured by the polarization optical system optical pickup is described. Of course, the amplitude or the like may be used.
[0070]
【The invention's effect】
As apparent from the above description, according to the present invention, it is possible to estimate the birefringence amount of a rotating optical disc, not a stationary optical disc.
[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 an embodiment of the present invention is applied when an optical pickup moves to an inner periphery; FIG. 3B 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 illustrating a configuration of a birefringence amount estimation device according to an embodiment of the present invention.
FIG. 8 shows the results obtained when the polarizing optical system optical pickup is moved from the inner circumference to the outer circumference of the reference optical disk and the optical disk to be measured when the optical disk for measurement and the optical disk to be measured are rotated at the rotation speed to be measured. It is a figure which shows the level of I-TOP.
FIG. 9 is a diagram showing a dependence relationship between the amount of returning light to the photodetector and the amount of birefringence of the optical disk.
FIG. 10 is a diagram for explaining dependence of return light to a photodetector on birefringence of an optical disk.
FIG. 11 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. 12 is a diagram showing the relationship between the amount of incident light on a photodetector and the amount of birefringence on an optical disk.
[Explanation of symbols]
OPU Polarized optical system optical pickup DISC Optical disk 13 to be measured Spindle motor 15 Feed motor 47 Central processing unit (CPU)
51 Spindle driver 53 BTL driver 55 Analog signal processor (ASP)
60 Host personal computer (PC)
62 Reading device (optical disk drive)

Claims (5)

An apparatus for estimating the birefringence of an optical disc that estimates the amount of birefringence of an optical disc to be measured in a rotating state, using an optical disc drive equipped with a polarization optical system optical pickup,
While the reference optical disk is rotated at the rotation speed to be measured, the polarization optical system optical pickup is moved from the inner circumference to the outer circumference of the reference disk while the polarization optical system optical pickup is moved from the reference disk. Reference measuring means for measuring a signal obtained by reflection and storing the signal as a reference signal;
While the optical disk to be measured is being rotated at the rotation speed to be measured, the polarization optical system optical pickup is moved from the inner periphery to the outer periphery of the optical disk to be measured while the polarization optical system optical pickup is used to measure the measurement object. Measuring object measuring means for measuring a signal obtained by reflection from the optical disc;
Estimating means for estimating the amount of birefringence of the optical disk to be measured from the degree of decrease in the signal obtained by the measurement with respect to the reference signal. The optical disc birefringence amount estimating device according to claim 1, wherein the reference optical disc is an optical disc whose birefringence does not significantly change as compared with a stationary state even when a stress is generated by a rotational force. The optical disc birefringence amount estimation device according to claim 2, wherein the reference optical disc is a glass optical disc. The optical disc birefringence amount estimating apparatus according to claim 2, wherein the reference optical disc is a selected optical disc. A method of estimating the amount of birefringence of an optical disk to be measured in a rotating state using an optical disk drive equipped with a polarization optical system optical pickup,
By comparing a signal obtained by picking up the reference optical disk with the polarization optical system optical pickup and a signal obtained by picking up the measurement target optical disk with the polarization optical system optical pickup, the signal of the measurement target optical disk is compared. A method for estimating a birefringence of an optical disc, comprising estimating a birefringence.

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