JP6081246B2 - Optical disk playback device - Google Patents

Description

  The present invention relates to a technique for correcting spherical aberration in an optical disk reproducing apparatus.

  As a technique for correcting the spherical aberration in the optical disk reproducing apparatus, the optical disk reproducing apparatus is provided with a mechanism for moving a collimator (collimating lens) arranged in the optical path of the beam light used for reading a signal from the optical disk in the optical axis direction. Prior to the start of reproduction, a technique for adjusting the collimator position so that spherical aberration is corrected is known.

  In addition, as a technique for adjusting the position of such a collimator, the tracking servo is out of control due to an excessive balance value of the tracking error signal during the position adjustment of the collimator performed while moving the collimator on a trial basis. In order to suppress this, a technique for correcting a coefficient used for generating a tracking error signal according to the position of the collimator only during the position adjustment of the collimator is known (for example, Patent Document 1).

  Here, in this technique, prior to the start of the position adjustment of the collimator, the collimator is moved to at least two different positions, and a coefficient value that minimizes the balance value of the tracking error signal is calculated for each position. Based on the coefficient value, a correction formula that defines the correction value of the coefficient using the position of the collimator as a variable is obtained. Then, the position adjustment of the collimator performed while moving the collimator on a trial basis is performed while changing the coefficient according to the position of the collimator according to the above correction equation.

JP 2012-256381

  According to the above technique, since it is necessary to calculate the coefficient value that minimizes the balance value of the tracking error signal at least for two different positions of the collimator before the start of the position adjustment of the collimator, the time required for the calculation, There is a problem that the time required to complete the position adjustment of the collimator is prolonged, and as a result, the reproduction start of the optical disk is delayed.

  Therefore, an object of the present invention is to quickly adjust the position of the collimator while suppressing the tracking servo from being detached.

In order to achieve the above object, the present invention provides an optical disk reproducing device for reproducing an optical disk, a pickup for irradiating the optical disk with light, detecting the reflected light of the light from the optical disk, and outputting it as a detection signal, and tracking An error signal generating means, a tracking control means, a coefficient setting means, and a collimator position adjusting means are provided. Here, the pickup includes a light source, an objective lens capable of controlling a radial position of the optical disc, a collimator disposed in an optical path between the light source and the objective lens, and the collimator in the optical axis direction. A moving mechanism that moves; a beam splitting unit that splits the reflected light that has entered the objective lens and passed through the collimator into a main beam and a sub beam; and a main light detection that is an array of a plurality of photoelectric elements that detect the main beam. A unit and a sub light detection unit that is an array of a plurality of photoelectric elements for detecting the sub beam. Further, the tracking error signal generating means is a deviation amount of an image of the main beam on the main light detection unit in a direction corresponding to a radial direction of the optical disk, which is obtained from outputs of a plurality of photoelectric elements of the main light detection unit. The main push-pull MPP, the sub-push-pull SPP is the amount of shift in the direction corresponding to the radial direction of the optical disc of the image by the sub-beam on the sub-light detection unit obtained from the outputs of the plurality of photoelectric elements of the sub-light detection unit The tracking error signal TE expressed as TE = MPP−k (SPP) is generated using the coefficient k. Then, the tracking control means controls tracking of the pickup with respect to the track of the optical disc in accordance with the tracking error signal TE. Further, the coefficient setting means is configured so that a fluctuation range of a balance value of the tracking error signal TE accompanying a fluctuation in a radial position of the optical disc of the objective lens is a predetermined level or less in a state where the position of the collimator is fixed. The coefficient k is calculated as an appropriate k value. The collimator position adjusting means sets the k to a value smaller than the appropriate k value, and moves the collimator by the moving mechanism under the tracking control by the tracking control means. After calculating the appropriate position and calculating the appropriate position, the position of the collimator is set to the appropriate position and the coefficient k is set to the appropriate k value.

  Here, according to such an optical disk reproducing apparatus, when calculating the appropriate position of the collimator, the coefficient k of the SPP is set to be greater than the appropriate k value that is the appropriate value of the coefficient k during tracking servo control during normal reproduction of the optical disk. It is possible to suppress the fluctuation of the balance value of the tracking error signal TE accompanying the change of the collimator position from becoming excessive. Therefore, even when calculating the appropriate position of the collimator while moving the collimator, the tracking servo control means can appropriately perform tracking. Further, such appropriate tracking can be realized by a process that only reduces the coefficient k of the SPP, so that the position of the collimator can be quickly adjusted.

  The optical disc reproducing apparatus as described above is provided with an eccentric amount calculating means for calculating the eccentric amount of the optical disc in the optical disc reproducing apparatus, and the eccentric amount is larger than a predetermined value in the collimator position adjusting means. The k is not set to a value smaller than the appropriate k value, and the collimator is moved by the moving mechanism under the tracking control by the tracking control means in a state where the k is set to the appropriate k value. While moving, the appropriate position of the collimator may be calculated, and the position of the collimator may be set to the calculated appropriate position.

  In the above optical disk reproducing apparatus, the collimator position adjusting means obtains the position of the collimator that minimizes the jitter with respect to a predetermined frequency of the detection signal output from the pickup while moving the collimator by the moving mechanism. The calculated position may be calculated as the appropriate position of the collimator.

In the above optical disk reproducing apparatus, the main light detection unit has a column direction as a direction corresponding to a radial direction of the optical disk of an image on the main light detection unit, and a direction corresponding to a circumferential direction of the optical disk as a row direction. And four photoelectric elements arranged in two columns and two rows, the sub-light detection unit having two columns with a direction corresponding to the radial direction of the optical disc of the image on the sub-light detection unit as a column direction. Comprising two arranged photoelectric elements, in the tracking error signal generating means,
MPP = (SA + SD)-(SB + SC)
SPP = SE-SF
As
TE = {(SA + SD)-(SB + SC)}-k (SE-SF)
Thus, the tracking error signal TE may be generated. However, while the first direction of the radial direction toward the radial direction and the outer toward the inner circumference side of the optical disk, the other as a second direction, the SA and SD are the main light detecting units Of the four photoelectric elements, the outputs of two photoelectric elements arranged on the direction side corresponding to the first direction of the image on the main light detection unit, the SB and SC are the main light detection Out of the four photoelectric elements of the unit, the outputs of two photoelectric elements arranged on the direction side corresponding to the second direction of the image on the main light detection unit, and the SE is the sub light detection Of the two photoelectric elements of the unit, the output of the photoelectric element arranged on the direction side corresponding to the first direction of the image on the sub photodetection unit, and SF is the sub photodetection unit Of the two photoelectric elements, the sub-light The output of which photoelectric elements arranged in direction corresponding to the second direction of the image on the output unit.

  As described above, according to the present invention, the position of the collimator can be adjusted more quickly while suppressing the tracking servo from being removed.

1 is a block diagram showing a configuration of an optical disc drive according to an embodiment of the present invention. It is a figure showing typically composition of a pickup concerning an embodiment of the present invention. It is a flowchart which shows the collimator position adjustment process which concerns on embodiment of this invention. It is a figure which shows the process example of the collimator position adjustment process which concerns on embodiment of this invention.

Hereinafter, embodiments of the present invention will be described.
FIG. 1 shows a configuration of an optical disc drive according to the present embodiment.
As shown in the figure, the optical disk drive 1 includes a clamper 101, a turntable 102, a spindle motor 103, a feed motor 104, a pickup 105, a head amplifier 106, a signal processing unit 107, a servo control unit 108, a system controller 109, and a host device 2. A host interface 110 to be connected is provided.

  In such a configuration, the clamper 101 and the turntable 102 clamp the optical disc 3 such as a BD (Blu-ray Disc) mounted on the optical disc drive 1, and the spindle motor 103 clamps between the turntable 102 and the clamper 101. The optical disk 3 is rotated. The feed motor 104 performs a seek operation for moving the pickup 105 in the radial direction of the optical disc 3.

  Next, as shown in FIG. 2, the pickup 105 includes a laser light source 201, a hologram 202, a collimator 203, a reflecting mirror 204, an objective lens 205, a main light detection unit 206, a sub light detection unit 207, A collimator actuator 208 that moves the collimator 203 in the optical axis direction, a focus actuator 209 that moves the objective lens 205 in the optical axis direction to adjust the focal position, and tracking by moving the objective lens 205 in the radial direction of the optical disc 3. And a tracking actuator 210 that performs adjustment.

  The laser light emitted from the laser light source 201 is incident on the collimator 203 through the hologram 202, converted into parallel light by the collimator 203, reflected by the reflecting mirror 204, and then incident on the objective lens 205. The lens 205 collects light so as to form a light spot on the recording layer of the optical disc 3.

  On the other hand, the reflected light of the spot from the recording layer of the optical disc 3 enters the objective lens 205, is reflected by the reflecting mirror 204, and enters the hologram 202 through the collimator lens. The reflected light incident on the hologram 202 is branched into a main beam and a sub beam by the hologram 202, and a spot image of the recording layer of the optical disc 3 by the main beam is formed on the main light detection unit 206, and the optical disc 3 by the sub beam is formed. An image of the spot on the recording layer is formed on the sub light detection unit 207.

Here, the main light detection unit 206 has a column direction as a direction corresponding to the radial direction of the optical disk 3 of the image of the main beam formed on the main light detection unit 206 and a direction corresponding to the circumferential direction of the optical disk 3 as a row direction. The four photoelectric elements A, B, C, and D arranged in two columns and two rows, the photoelectric element A outputs a detection signal SA obtained by photoelectrically converting the incident main beam portion, and the photoelectric element B is incident Output a detection signal SB obtained by photoelectrically converting the main beam portion, photoelectric element C outputs a detection signal SC obtained by photoelectrically converting the incident main beam portion, and photoelectric device D photoelectrically converts the incident main beam portion. Output the detected signal SD.

Next, the sub light detection unit 207 includes two photoelectric elements E arranged in two rows, with the direction corresponding to the radial direction of the optical disc 3 of the sub beam formed on the sub light detection unit 207 as the column direction. F, the photoelectric element E outputs a detection signal SE obtained by photoelectric conversion of the incident sub-beam portion, and the photoelectric element F outputs a detection signal SF obtained by photoelectric conversion of the incident sub-beam portion.

Incidentally, as one of the positive direction of the radial direction toward the inner circumference side in the radial direction toward the outer peripheral side of the optical disk 3, the photoelectric elements A and D of the main light detecting unit 206, rather than a C photoelectric device B, The light reflected by the portion on the positive direction side of the optical disc 3 is arranged to enter, and the photoelectric element E of the sub light detection unit 207 receives light reflected by the portion on the positive direction side of the optical disc 3 rather than the photoelectric element F. It arrange | positions so that it may inject.

Now, referring back to FIG. 1, the head amplifier 106 generates (SA + SB + SC + SD) as an RF signal from the detection signal output from the pickup 105 and outputs it to the signal processing unit 107 and the servo control unit 108. .
Further, the head amplifier 106 generates (SA + SC) − (SB + SD) as a focus error signal (FE) from the detection signal output from the pickup 105.
Further, the head amplifier 106 generates a tracking error signal (TE) = MPP-k (SPP) from the detection signal output from the pickup 105. Here, MPP is a push-pull signal indicating the amount of deviation of the image by the main beam on the main light detection unit 206 in the direction corresponding to the radial direction of the optical disk 3 calculated using the main light detection unit 206. = (SA + SD)-(SB + SC). SPP is a push-pull signal representing the amount of deviation of the image by the sub beam on the sub light detection unit 207 calculated using the sub light detection unit 207 in the direction corresponding to the radial direction of the optical disc 3, and SPP = ( SE-SF). Therefore, when expanded, the tracking error signal (TE) = {(SA + SD) − (SB + SC)} − k (SE−SF). K is a coefficient of the SPP and is set by the servo control unit 108.

  Next, the signal processing unit 107 performs demodulation of data from the RF signal output from the head amplifier 106, detection of errors generated in the demodulated data, and correction of errors, and the data recorded on the optical disc 3 is processed. The reproduced data is transmitted to the host interface 110.

  In addition, the servo control unit 108 controls the seek operation of the feed motor 104 according to the control of the system controller 109 and the focus error signal (FE so that the objective lens 205 can properly focus the light onto the recording layer of the optical disc 3. ) According to the tracking error signal (TE) so that the focus servo control for controlling the focus actuator 209 in accordance with the tracking error signal (TE) is properly performed on the track of the optical disc 3 by the objective lens 205. Servo control, rotation servo control for controlling the rotation speed of the spindle motor 103 according to the jitter amount of the RF signal so that the RF signal is reproduced at an appropriate reproduction rate, and the like, and before the reproduction of the optical disc 3 are started. Adjusts the position of the collimator 203.

  Then, the system controller 109 controls the above-described units, reproduces the data requested by the host command from the optical disc 3 according to the host command received from the host apparatus 2 via the host interface 110, and performs the host interface 110. A read process for transferring to the host device 2 via the host is performed.

Hereinafter, the position adjustment of the collimator 203 performed by the servo control unit 108 before the reproduction of the optical disk as described above will be described.
FIG. 3 shows a procedure of collimator position adjustment processing performed by the servo control unit 108 for adjusting the position of the collimator 203.
As shown in the figure, in this process, focus servo control is first started (step 302).
Next, an appropriate k value is calculated (step 304).
Here, the appropriate k value is calculated as follows.
That is, in calculating the appropriate k value, first, the tracking actuator 210 is controlled to move the objective lens 205 in the radial direction of the optical disc 3 while the head amplifier 106 generates the tracking error signal (TE). The coefficient k is changed, and the relationship between the radial position (r0-r3) of the objective lens 205, the coefficient k of the SPP and the tracking error signal balance TEBL as shown in FIG. 4a is obtained.

Here, as shown in FIG. 4b, the tracking error signal balance TEBL is v1, the magnitude measured in the positive direction from the predetermined reference value Vref of the upper peak value of the tracking error signal (TE), and the tracking error signal. The magnitude measured in the negative direction from the reference value Vref of the lower peak value of (TE) is v2,
TEBL = (v1-v2) / (v1 + v2)
Calculated by

Then, the coefficient k of the SPP that minimizes the TEBL fluctuation amount or the predetermined value or less with respect to the radial position fluctuation of the objective lens 205 is calculated as an appropriate k value. In the case of FIG. 4a, approximately 3 is a value that minimizes the variation amount of TEBL.
Returning to FIG. 3, next, when the appropriate k value is calculated as described above, the calculated appropriate k value is set in the head amplifier 106 as the coefficient k of the SPP used for generating the tracking error signal (TE). (Step 306).
Next, the eccentricity of the optical disk 3 is calculated (step 308).
Here, the eccentric amount of the optical disk 3 is obtained from the wave number per rotation of the optical disk 3 of the tracking error signal (TE) obtained by rotating the optical disk 3 in a state where the tracking servo control is stopped.
Next, it is examined whether the eccentricity calculated as described above is smaller than a predetermined threshold value Th (for example, Th is a value satisfying 150 μm>Th> 100 μm) (step 310).
If the amount of eccentricity is smaller than the predetermined threshold value Th (step 310), the value of 1 / n of the appropriate k value calculated in step 304 (n is 4 for example) is set to the tracking error signal (TE). The coefficient k used for generation is set in the head amplifier 106 (step 312), the appropriate collimator position is calculated (step 314), the collimator actuator 208 is controlled, and the position of the collimator 203 is set to the calculated appropriate collimator position. Above (step 316), the coefficient k of the SPP used for generating the tracking error signal (TE) is restored to the appropriate k value calculated in step 304 (step 318), and the collimator position adjustment process is terminated.
When the collimator position adjustment process is completed in this way, the optical disc 3 is reproduced under tracking servo control using the SPP coefficient k set to an appropriate k value in step 318.

  On the other hand, when the eccentricity amount is not smaller than the predetermined threshold value Th (step 310), the coefficient k used for generating the tracking error signal (TE) in the head amplifier 106 is maintained at the appropriate k value calculated in step 304. As it is, the appropriate collimator position is calculated (step 322), the collimator actuator 208 is controlled to set the position of the collimator 203 to the calculated appropriate collimator position (step 324), and the collimator position adjustment process is terminated. When the collimator position adjustment process is completed in this manner, the optical disk 3 is reproduced under tracking servo control using the SPP coefficient k set to an appropriate k value in step 306.

Here, the calculation of the proper collimator position in step 314 and step 322 is performed as follows.
That is, first, tracking servo control is started, the collimator actuator 208 is controlled, and the jitter amount of the RF signal with respect to the reference clock representing the appropriate reproduction frequency of the RF signal is minimized while moving the collimator 203 in the optical axis direction. The position of the collimator 203 is calculated as the proper collimator position. That is, when the relationship between the position of the collimator 203 and the jitter amount is as shown in FIG. 4C, P0 having the jitter amount as the minimum value min is calculated as the appropriate collimator position.

The collimator position adjustment process performed by the servo control unit 108 has been described above.
As described above, according to the present embodiment, when the eccentricity amount of the optical disk 3 is smaller than the predetermined threshold value Th, the proper collimator position is calculated while changing the position of the collimator 203 under tracking servo control. When the position of the collimator 203 is fixed, that is, the coefficient k of the tracking error signal (TE) = MPP-k (SPP) is made smaller than the appropriate value during normal reproduction.

  Here, since the position and shape of the spot formed on the recording layer of the optical disc 3 change as the position of the collimator 203 changes, the balance TEBL of the tracking error signal changes as the position of the collimator 203 changes. . In particular, when the position of the collimator 203 is fixed and the MPP and SPP that show the same change change in the opposite direction in accordance with the change in the position of the collimator 203, the tracking error signal balance TEBL increases. Change.

  For example, when the position of the collimator 203 is changed, as shown in FIG. 4d, an example of the relationship between the position of the collimator 203, the coefficient k, and the balance TEBL of the tracking error signal, the coefficient k of the SPP is large. If the balance TEBL fluctuates excessively, tracking may not be performed properly.

  On the other hand, according to this embodiment, when calculating the appropriate collimator position, the coefficient k of the SPP is reduced, so that the fluctuation range of TEBL is suppressed from being excessive, and even if the position of the collimator 203 is changed, the tracking servo Tracking can be performed appropriately by the control. Further, such appropriate tracking can be realized by a process of simply reducing the coefficient k when calculating the appropriate collimator position, so that quick position adjustment of the collimator 203 is realized.

  In the present embodiment, when the amount of eccentricity of the optical disc 3 is equal to or greater than the predetermined threshold Th, the coefficient k is not reduced when calculating the proper collimator position when the amount of eccentricity of the optical disc 3 is large. This is because if the coefficient k is small, there is a high probability that tracking servo control cannot be performed normally.

The embodiment of the present invention has been described above.
In the above embodiment, the reflected light is branched into the main beam and one sub beam, and the sub push-pull SPP represents the deviation of the image on the sub light detection unit 207 of the sub beam in the direction corresponding to the radial direction of the optical disc 3. Although SE-SF is used, other values can be used as the sub push-pull SPP.

For example, the sub push-pull SPP may be generated as follows.
That is, the reflected light is branched into a main beam and two sub beams, and the two sub beams are detected by the two sub light detection units 207, respectively. Here, one of the sub light detection units 207 is arranged in two rows with the direction corresponding to the radial direction of the optical disc 3 of the image of the one sub beam formed on the sub light detection unit 207 as the column direction. The other sub-light detection unit 207 has a direction corresponding to the radial direction of the optical disc 3 of the image of the other sub-beam formed on the sub-light detection unit 207 in the column direction. Assuming that two photoelectric elements G and H arranged in two rows are provided. Then, SE-SF representing a shift in the direction corresponding to the radial direction of the optical disk 3 of the image on one sub light detection unit 207 of the image by one sub beam, and the optical disk of the other sub light detection unit image of the other sub beam. The SPP is calculated by SPP = (SE-SF) + (SG-SH) using SG-SH representing the deviation in the direction corresponding to the radial direction of 3. Where SE is the output of the photoelectric element E, SF is the output of the photoelectric element F, SG is the output of the photoelectric element G, and SH is the output of the photoelectric element H. Further, the photoelectric element E of one sub light detection unit 207 is arranged so that the light reflected by the portion on the positive direction side of the optical disc 3 is incident on the optical element 3 relative to the photoelectric element F, and the photoelectric element of the other sub light detection unit 207 is incident. The element G is arranged so that the light reflected by the portion on the positive direction side of the optical disc 3 from the photoelectric element H is incident.

  DESCRIPTION OF SYMBOLS 1 ... Optical disk drive, 2 ... Host apparatus, 3 ... Optical disk, 101 ... Clamper, 102 ... Turntable, 103 ... Spindle motor, 104 ... Feed motor, 105 ... Pickup, 106 ... Head amplifier, 107 ... Signal processing part, 108 ... Servo controller, 109 ... system controller, 110 ... host interface, 201 ... laser light source, 202 ... hologram, 203 ... collimator, 204 ... reflector, 205 ... objective lens, 206 ... main light detection unit, 207 ... sub light detection unit 208, collimator actuators, 209, focus actuators, 210, tracking actuators.

Claims (4)

An optical disk playback device for playing back an optical disk,
A pickup for irradiating the optical disc with light, detecting the reflected light of the light from the optical disc, and outputting it as a detection signal;
Tracking error signal generating means;
Tracking control means;
Coefficient setting means;
Collimator position adjusting means,
The pickup includes a light source, an objective lens capable of controlling a radial position of the optical disc, a collimator disposed in an optical path between the light source and the objective lens, and a movement for moving the collimator in the optical axis direction. A mechanism, beam splitting means for splitting the reflected light that has entered the objective lens and passed through the collimator into a main beam and a sub beam, and a main light detection unit that is an array of a plurality of photoelectric elements that detect the main beam; A sub-light detection unit that is an array of a plurality of photoelectric elements for detecting the sub-beam,
The tracking error signal generation means calculates an amount of displacement in a direction corresponding to a radial direction of the optical disc of the image of the main beam on the main light detection unit obtained from outputs of a plurality of photoelectric elements of the main light detection unit. The amount of deviation in the direction corresponding to the radial direction of the optical disk of the sub-beam on the sub-light detection unit obtained from the outputs of the plurality of photoelectric elements of the sub-light detection unit is defined as SPP, using the coefficient k,
TE = MPP -k (SPP)
Generates a tracking error signal TE represented as
The tracking control means controls tracking of the track of the optical disc of the pickup according to the tracking error signal TE,
The coefficient setting means is the coefficient k in which the fluctuation range of the balance value of the tracking error signal TE accompanying the fluctuation of the position of the objective lens in the radial direction of the optical disk in a state where the position of the collimator is fixed is equal to or less than a predetermined level. Is calculated as an appropriate k value,
The collimator position adjusting means sets the k to a value smaller than the appropriate k value, and moves the collimator by the moving mechanism under the tracking control by the tracking control means, while adjusting the appropriate position of the collimator. If the appropriate position is calculated, the position of the collimator is set at the appropriate position, and the coefficient k is set to the appropriate k value. An optical disk reproducing apparatus according to claim 1, wherein
An eccentric amount calculating means for calculating an eccentric amount of the optical disc;
In the state where the collimator position adjusting means sets the k to the appropriate k value without setting the k to a value smaller than the appropriate k value when the eccentricity amount is larger than a predetermined value, An optical disk reproduction characterized by calculating an appropriate position of the collimator while moving the collimator by the moving mechanism under tracking control by the tracking control means, and setting the position of the collimator at the calculated appropriate position apparatus. An optical disk reproducing apparatus according to claim 1 or 2, wherein
The collimator position adjusting means obtains a position of the collimator that minimizes jitter with respect to a predetermined frequency of a detection signal output from the pickup while moving the collimator by the moving mechanism, and determines the obtained position as an appropriate value of the collimator. An optical disk reproducing apparatus characterized by calculating as a position. The optical disk reproducing apparatus according to claim 1, 2, or 3,
The main light detection units are arranged in two columns and two rows, with the direction corresponding to the radial direction of the optical disc of the image on the main light detection unit as the column direction and the direction corresponding to the circumferential direction of the optical disc as the row direction. Four photoelectric elements,
The sub-light detection unit includes two photoelectric elements arranged in two rows, with the direction corresponding to the radial direction of the optical disc of the image on the sub-light detection unit as a column direction,
The tracking error signal generating means includes
MPP = (SA + SD)-(SB + SC)
SPP = SE-SF
As
TE = {(SA + SD)-(SB + SC)}-k (SE-SF)
Generates a tracking error signal TE,
While the first direction of the radial direction toward the radial direction and the outer toward the inner circumference side of the optical disk, the other as a second direction,
SA and SD are outputs of two photoelectric elements arranged on the direction side corresponding to the first direction of the image on the main light detection unit among the four photoelectric elements of the main light detection unit. Yes,
The SB and SC are outputs of two photoelectric elements arranged on the direction side corresponding to the second direction of the image on the main light detection unit among the four photoelectric elements of the main light detection unit. Yes,
The SE is an output of a photoelectric element arranged on the direction side corresponding to the first direction of the image on the sub-light detection unit, out of the two photoelectric elements of the sub-light detection unit,
The SF is an output of a photoelectric element arranged on a direction side corresponding to the second direction of an image on the sub light detection unit, out of two photoelectric elements of the sub light detection unit. An optical disk playback device.