JP2001266381A - Tilt detection method and apparatus and optical disc apparatus using the same - Google Patents

Abstract

(57) Abstract: An object of the present invention is to provide a low-cost and simple method capable of mainly detecting a DC tilt amount while focusing on an information surface of an optical disk without requiring a separate tilt sensor. It is to propose a tilt detection method. In a state where a reproducing beam spot is focused on an information surface of an optical disk, reflected light is received by a four-divided light receiving element divided by orthogonal dividing lines, and a light receiving element forming a diagonal of the four divided light receiving element. And outputs the absolute value of the difference between the two addition results obtained by adding the outputs. The tilt amount is obtained based on the amplitude or the minimum value of the absolute value of the output signal obtained when the irradiation light scans in the direction orthogonal to the track.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tilt detecting device for detecting the tilt of an optical head and an optical disk in an apparatus for reproducing information by irradiating a laser beam onto an optical information recording medium such as an optical disk.

[0002]

2. Description of the Related Art In the case of optical disks such as CDs and DVDs, in general, irradiation light emitted from an optical head may be obliquely incident on the optical disk due to warpage or surface deflection of the disk, displacement of an optical system, or the like. As a result, coma aberration occurs and the beam spot diameter of the irradiation light is distorted, so that the quality of the reproduced signal is deteriorated due to deterioration of crosstalk and jitter from an adjacent track. In particular, DVDs and next-generation optical discs require shorter wavelengths and higher NA to achieve higher densities.
There is a problem that the coma aberration increases if it is slightly tilted.

In order to solve such a problem, it has been proposed to provide a tilt servo mechanism for detecting the amount of tilt between the optical disk and the head by using some means and correcting the optical axis of the light emitted from the optical disk and the optical head so as to maintain the optical axis vertically. Have been.

The electrical components of the tilt amount include the warpage of the disk, the state of the clamp, the displacement of the optical system, and the like.
The tilt amount can be broadly divided into a DC tilt amount and an AC tilt amount caused by a disk runout or the like. In particular, for DVDs, DPD (Differential Ph
Although this method employs pit information, it is required that the RF reproduction signal be of high quality.

[0005] In the next generation optical disc of DVD, it is necessary to shorten the wavelength and increase the NA in order to realize a higher density. However, if there is a tilt, the quality of the reproduced signal deteriorates due to coma aberration. , The DPD detection sensitivity is reduced. Therefore, it is necessary to correct DC tilt in a state where the information surface of the optical disc is focused.

As a method of detecting the amount of tilt between the optical disk and the optical head, a method of detecting the amount of tilt between the optical disk and the head using a sensor called a tilt sensor separately from the optical head is well known in the prior art. I have. Further, as a method not using the tilt sensor, a method using a difference signal between left and right signals of a detector divided in the left and right direction of a track disclosed in Japanese Patent Application Laid-Open No. 8-36773, and No. 273113, a method of detecting the amount of tilt using signals from left and right sub-beams using a three-beam optical head, a method of detecting the amplitude of an RF reproduction signal and detecting the amount of tilt from the amplitude Etc. are known.

[0007]

However, in the above-described system using the tilt sensor, a sensor unit as a separate component is required separately, and an extra cost is required. Further, there is a problem that accuracy cannot be obtained because the irradiation position of the irradiation light is different from the measurement position of the sensor.

In the method using the difference signal between the left and right signals of the detector divided in the right and left direction of the track,
Depending on the pit depth allowed by the DVD standard, a sufficient amplitude cannot be obtained, and there is a problem that S / N is poor.

In the system using three beams, an optical system
There is a problem that the electric system becomes complicated and extra cost is required like the tilt sensor. Furthermore, since crosstalk cancellation and tilt detection are performed at the same time, and there is a problem that tilt cannot be detected when the information surface of the optical disc is focused, it is necessary to avoid the above-described problem of detecting the DPD due to tilt. Is difficult.

On the other hand, the method of detecting the amount of tilt based on the amplitude of the RF signal can be realized at low cost, but is weak to noise added to the entire light receiving element due to fluctuations in the amount of reflected light or the like. There is a problem that the detection sensitivity is low, which is low.

Accordingly, an object of the present invention is to provide a low-cost and simple tilt detection method capable of mainly detecting a DC tilt amount while focusing on an information surface of an optical disk without requiring a tilt sensor as a separate component. It is to propose.

[0012]

According to a first aspect of the present invention, there is provided a tilt detecting method for irradiating irradiation light with focusing on an information surface of an optical disk during rotation of the optical disk. The reflected light is received by the light receiving element divided into four by the orthogonal dividing line, the outputs of the light receiving elements forming the diagonal of the four divided light receiving element are added, and the absolute value of the difference between the two added signals is calculated. The tilt amount is obtained based on the amplitude of the absolute value or the minimum value of the absolute value obtained when the irradiation light scans in a direction orthogonal to the track.

Further, according to the present invention, in the tilt detecting method described above, the tilt amount is obtained based on the amplitude or the minimum value of the absolute value obtained when the optical head or the optical disk is tilted in the radial direction.

Further, the tilt detecting method according to the second aspect of the present invention
When the optical disc is rotated, the information surface of the optical disc is focused and irradiated with irradiation light, and the reflected light of the irradiation light is received by a light receiving element divided into four by an orthogonal dividing line. The outputs of the light receiving elements to be formed are added, a mutual phase difference is detected from a binary signal obtained by binarizing the two added signals, and a phase difference pulse having a time width proportional to the phase difference is output. Calculate the sum of the pulse widths of the phase difference pulse,
The tilt amount is obtained based on the minimum value of the total value of the pulse width obtained when the irradiation light scans in a direction orthogonal to the track.

Further, in the above-described tilt detecting method, the tilt amount is obtained based on the minimum value of the sum of the pulse widths obtained when the optical head or the optical disk is tilted in the radial direction.

Further, the optical disk device of the present invention has the above-mentioned 2
A tilt detection device using at least one of the tilt amount detection methods, scans the irradiation light from the inner circumference to the outer circumference of the optical disc, and temporarily stores the tilt amount of the optical head and the optical disc with respect to the radial position of the optical disc in the temporary storage means. The apparatus further comprises means for storing and correcting the tilt of the optical head and the optical disk based on tilt amount information for the radial position of the optical head and the radial position stored in the temporary storage means.

[0017]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a first tilt detecting device using the tilt detecting method according to the present invention. The beam emitted from the semiconductor laser 106 passes through the collimator lens 105 and is converted into parallel light.
The light is condensed by the light source 2 and is irradiated with the information surface of the optical disc 101 focused.

The reflected light from the optical disk 101 passes through the beam splitter 104 and the lens 103 and passes through the optical disk 10
4 divided into 4 parts corresponding to the left, right, top and bottom of one information track
The light enters a general photodetector 107 having a split light receiving element.

The outputs A, 4 of the quadrant light receiving element of the photodetector 107
The outputs of the diagonal light receiving elements among B, C and D are added by adders 108a and 108b, respectively, to generate two signals (A + C) and (B + D). The outputs of (A + C) and (B + D) pass through high-frequency emphasizing circuits 109a and 109b, respectively,
Subtraction processing is performed at 0. This difference output passes through the absolute value detection circuit 111 to generate an absolute value signal as | (A + C) − (B + D) |.

The configuration up to the four-divided light receiving element in the above configuration is completely the same as the configuration of a normal optical disk device, and can be used together. The output from the quadrant light receiving element can be used simultaneously for focus, tracking, and generation of a reproduced RF signal. The output of the signal | (A + C)-(B + D) | is in the RF band, and changes in diffracted light due to pits on the information surface of the optical disc 101 are detected in the high-frequency band.

The signal of | (A + C)-(B + D) | is thereafter temporally averaged by a low-pass filter (LPF) 112 to detect the absolute value of the amplitude or the minimum value of the absolute value.
13 and, as a result, a signal corresponding to the amount of tilt is output.

The tilt correction mechanism 114 monitors a signal corresponding to the tilt amount and adjusts the angle between the optical head and the optical disk so that the tilt becomes zero.

A concrete tilt correction method is performed by the following two methods.

The first is that the optical head and the optical disk are tilted by a tilt correction mechanism so that the signal after passing through the low-pass filter of | (A + C)-(B + D) | Adjust the tilt angle between them.

The second is a case where a beam spot is scanned in a direction perpendicular to the track direction while the focus servo is applied (that is, when the track offset changes).
| (A + C)-(B + D) | after passing through the low-pass filter, and adjust the angle of the tilt angle between the optical head and the optical disk by the tilt correction mechanism to maximize the signal amplitude I do.

The operation of tilt amount detection according to the above-described embodiment will be described.

FIG. 2 shows the positional relationship between the beam spot and the information pit when the beam spot 201 irradiates the track center when there is no crosstalk.

If there is no tilt, beam spot 201
Since no coma aberration occurs, the relationship between the information pits 202 of the information track and the spot shape is completely symmetric with respect to the radial direction of the optical disk. As a result, the signals of (A + C) and (B + D) completely match, and the signal of | (A + C)-(B + D) |

In an actual optical disk, the signals (A + C) and (B + D) differ due to crosstalk from adjacent tracks, so that (A + C)-(B + D) does not become 0, The average value of | (A + C)-(B + D) | after passing through the filter (the average value of | (A + C)-(B + D) |) is a constant value.

When a tilt exists, a coma aberration 301 occurs as shown in FIG. 3, and the beam spot has an asymmetric shape with respect to the tilt direction. 302 is an information pit.

For this reason, the reproduced signal itself is distorted, and furthermore, a change in the influence of crosstalk from an adjacent track due to tilt causes a difference between the signals (A + C) and (B + D), and | (A + C) -(B
+ D) | is a value corresponding to the tilt amount.

If there is a track offset, there is a phase difference between the signals (A + C) and (B + D), so that | (A + C)-(B + D) |

That is, when the beam spot is scanned in the direction perpendicular to the track direction with only the focus servo applied, the average value of | (A + C)-(B + D) | is shown in FIG. Become like By detecting the signal amplitude, the tilt amount can be detected in a state where only the focus servo is applied.

In FIG. 5, the horizontal axis indicates the track offset amount, and the vertical axis indicates the average value of | (A + C)-(B + D) |.
When scanning in the direction perpendicular to the track direction (radial method), the amplitude differs according to the amount of radial tilt, and becomes maximum when the tilt becomes zero.

The inventor has performed an optical simulation to confirm the operation of the present invention. FIG. 4 shows a simulation result when a beam spot scans the track center when the radial tilt is changed.

The vertical axis represents the average value of | (A + C)-(B + D) |, and the unit is normalized when the total amount of light incident on the entire light receiving element without a pit is set to 1. Value.

The horizontal axis represents the radial tilt, and shows the calculation results under the following simulation conditions.

Simulation conditions Wavelength: 400 nm NA: 0.62 Track pitch: 0.363 μm Minimum mark length: 0.227 μm Modulation method: 8/12 modulation Substrate thickness: 0.6 mm Reproduction data amount: 3000 CHbit As shown in FIG. , For increased tilt | (A + C)-(B + D)
The average value of | increases almost linearly, and it is possible to detect the amount of tilt with the proposed configuration.

Returning to FIG. FIG. 5 shows | (A + C)
This shows the track offset dependency of the average value of-(B + D) |.
The vertical axis represents the average value of | (A + C)-(B + D) | as in FIG. 4, and the horizontal axis represents the track offset amount. FIG. 5 shows that | (A + C)-(B +) obtained when the track offset is changed (when the beam spot is scanned perpendicular to the track direction).
It can be seen that the amplitude of the average value of D) | increases as the radial tilt decreases.

FIG. 6 is a graph showing the radial tilt on the horizontal axis and the average value of | (A + C)-(B + D) | on the vertical axis. The amplitude of the average value of (A + C)-(B + D) | decreases almost linearly, and the tilt amount can be detected by the configuration of the present invention.

Next, a second tilt detecting apparatus using the tilt detecting method according to the present invention will be described.

FIG. 7 shows an example of a block configuration of a second tilt detecting device using the tilt detecting method according to the present invention.

The beam emitted from the semiconductor laser 706 passes through a collimator lens 705, is converted into parallel light, is condensed by an objective lens 702, and
Irradiation is performed while focusing on the information surface of No. 1.

The reflected light from the optical disk 701 passes through the beam splitter 704 and the lens 703, and passes through the optical disk 70.
4 divided into 4 parts corresponding to the left, right, top and bottom of one information track
The light is incident on a general photodetector 707 having a split light receiving element.

The outputs A, A,
The outputs of the diagonal light receiving elements among B, C, and D are added by adders 708a and 708b, respectively, to generate two signals (A + C) and (B + D). Outputs of (A + C) and (B + D) pass through high-frequency emphasizing circuits 109a and 109b, respectively, and are further converted into binary signals by binarizers 710a and 710b.

The two binarized signals are input to a general phase difference detector 711. The phase difference detector 711 outputs a phase signal when the signal (A + C) is ahead of the signal (B + D). Output a leading phase pulse with a time width equivalent to the
When (A + C) is behind the phase of the signal (B + D), a delayed phase pulse having a time width equivalent to the time during which the phase is delayed is output.

Average pulse width detection circuits 712a, 712b
Detects the time width of the phase difference pulse, and outputs a voltage converted to a voltage value corresponding to the sum of the pulse time widths in a certain fixed time.

The outputs from the two average pulse width detection circuits 712a and 712b corresponding to the leading phase pulse and the lagging phase pulse are signals added by the adder 713, and this is a signal corresponding to the amount of tilt. This signal is input to the minimum value detection circuit 714, and the minimum value detection output is given to the tilt correction function 715. Tilt correction mechanism 715
By adjusting the angle of the tilt angle between the optical head and the optical disk by the tilt correction mechanism so that the signal corresponding to the tilt amount becomes smaller, the tilt can be made closer to zero.

The configuration from the four-segment light receiving element for receiving the reflected light to the phase difference detector uses a DPD (Differential) generally known as a method for detecting a tracking error signal.
This is exactly the same as the tialPhase Detection) method and can be used together, so that the tilt detection method of this configuration can be realized at low cost.

The inventor has performed an optical simulation to confirm the operation of the present invention. FIG. 8 shows a simulation result in the case where the beam center scans the track center when the radial tilt is changed.

In FIG. 8, the vertical axis indicates the ratio of the total sum of the detected phase difference pulse widths to a certain amount of data when a certain amount of data is reproduced.

The horizontal axis represents radial tilt, and the simulation conditions are the same as those described above.

As shown in FIG. 8, according to the configuration of the present invention, the value of the sum of the phase difference pulse widths increases with the increase of the tilt amount, and the tilt amount can be detected with the configuration of the present invention. It is.

Next, an optical disk device using the tilt detecting method according to the present invention will be described.

FIG. 9 is a block diagram of an optical disk apparatus using the tilt detecting method according to the present invention. The optical disc device of the present invention includes the tilt detection device using the above-described first tilt amount detection method or the tilt detection device 908 using the second tilt amount detection method. Parts corresponding to those in the embodiment of FIG. 1 will be described with the same reference numerals.

The system of the memory 909, the control signal generator 911, and the tilt actuator 912 corresponds to the tilt correction mechanism 114 or 715 described above.

First, the tilt of the optical head 913 and the optical disk 101 is changed within a certain range by the tilt actuator 912 in a state where the focus servo is applied, and a point at which the tilt becomes 0 is searched from the tilt amount output by the tilt detecting device 908. At this time, the control signal generator 91
The signal level sent to the tilt actuator 912 through 1 is detected.

At the same time, from the linear motor 910 or the reproduction signal, the optical disk 10 irradiated with the beam spot is irradiated.
1 is calculated, and the radius position and the signal level sent to the tilt actuator 912 are stored as a set of data in the memory 909. Thus, the optical disk 101
This means that the tilt amount on a certain radius is detected, and the correction information is obtained.

The optical head 913 is driven by the linear motor 910.
Is scanned from the inner circumference to the outer circumference of the optical disk 101, and the radial position of the optical head 913 is changed. Each time the tilt position of the optical head 913 becomes zero at the radial position of the optical head 913 by the above-described method.
2 is stored in the memory 909. As a result, the overall tilt correction information of the optical disc 101 in the radial direction is obtained.

At the stage of applying the tracking servo, first, a signal level sent from the memory 909 to the tilt actuator 912 corresponding to the radial position of the optical head 913 is called from the memory 909, and based on the signal,
After correcting the tilt between the optical head 913 and the optical disc 901, a tracking servo is performed to reproduce a signal.

According to the configuration of the present invention, for example, the tilt amount of the optical disk with respect to the radial position of the optical head can be detected in a state where the optical disk is focused when the optical disk is inserted, and the tilt can be corrected before the tracking servo is applied. Can be avoided.

[0063]

As described above, according to the configuration of the present invention, a special tilt sensor and a three-beam optical system are not required, so that the tilt amount can be detected with a low-cost and simple configuration.

Furthermore, the amount of tilt can be detected in a focused state, and the problem of a reduction in DPD detection sensitivity due to tilt can be avoided.

In the tilt detection method of the present invention, since the difference signal between the divided light receiving elements is calculated, for example, a noise that affects the entire light receiving element, such as a change in the total amount of reflected light from the disk, is obtained. , Tilt can be detected with relatively high sensitivity.

[Brief description of the drawings]

FIG. 1 is a block diagram of a first tilt detection device using a tilt detection method according to the present invention.

FIG. 2 is a diagram illustrating a shape relationship between an information pit and a beam spot when there is no tilt.

FIG. 3 is a diagram illustrating a shape relationship between an information pit and a beam spot when there is a tilt;

FIG. 4 is a diagram showing simulation result 1 showing the effect of the present invention.

FIG. 5 is a diagram showing a simulation result 2 showing the effect of the present invention.

FIG. 6 is a diagram showing a simulation result 3 showing the effect of the present invention.

FIG. 7 is a block diagram of a second tilt detection device using the tilt detection method according to the present invention.

FIG. 8 is a diagram showing a simulation result 4 showing the effect of the present invention.

FIG. 9 is a block diagram of an optical disk device using the tilt detection method according to the present invention.

[Explanation of symbols]

101, 701, 901 ... optical disk, 102, 70
2, 902: Objective lens, 103: Collimator lens,
104, 704, 904 ... beam splitter, 105,
705, 905 ... collimator lens, 106, 706,
906: semiconductor laser, 107, 707, 907 ... 4
Split photodetectors, 108, 708... Adders, 109, 70
Reference numeral 9: high-frequency emphasis filter, 110: subtraction circuit, 111: absolute value detection circuit, 112: low-pass filter, 113: amplitude detector, minimum value detector, 114, 715: tilt correction mechanism, 201: reproduction beam spot (tilt) None), 20
2,302: information pit, 301: reproduction beam spot
(With tilt), 710: binarizer, 711: phase difference detector, 712: average pulse width detector, 713: adder, 7
14 ... Minimum value detector, 908 ... Tilt detector, 909
.., Memory, 910, linear motor, 911, control signal generator, 912, tilt actuator, 913, optical head.

Claims (7)

[Claims] 1. A light-receiving element which irradiates an information surface of an optical disk while irradiating the optical surface with focus on the information surface of the optical disk while rotating the optical disk, and divides the reflected light of the irradiation light into four parts by orthogonal division lines. , The outputs of the light receiving elements forming the diagonal of the four divided light receiving elements are added to obtain two added signals, and the absolute value of the difference between the two added signals is calculated. A tilt detection method comprising: obtaining a tilt amount based on an amplitude of the absolute value or a minimum value of the absolute value obtained when scanning is performed in a direction orthogonal to a track of the optical disc. 2. The tilt detecting method according to claim 1, wherein a tilt amount is obtained based on an amplitude or a minimum value of the absolute value obtained when the optical head or the optical disk is tilted in a radial direction. Tilt detection method. 3. An information surface of the optical disk is irradiated with light focused from the optical head when the optical disk is rotating, and the reflected light of the irradiated light is divided into four light beams by orthogonal dividing lines. The light is received by the element, and the outputs of the light receiving elements forming the diagonal of the four-divided light receiving element are added to obtain two added signals. Detecting a phase difference, obtaining a phase difference pulse having a time width proportional to the phase difference, calculating a total value of pulse widths of the phase difference pulse, and scanning the irradiation light in a direction orthogonal to a track. A tilt detection method, wherein a tilt amount is obtained based on a minimum value of the obtained sum of the pulse widths. 4. The tilt detecting method according to claim 3, wherein a tilt amount is obtained based on a minimum value of the sum of the pulse widths obtained when the optical head or the optical disk is tilted in a radial direction. Tilt detection method. 5. A means for rotating an optical disk, a means provided on an optical head for irradiating irradiation light with focusing on an information surface of the optical disk, and a means provided on the optical head for reflecting reflected light of the irradiation light A light receiving element divided into four by an orthogonal dividing line for receiving light, two adders for adding outputs of light receiving elements forming diagonals of the divided light receiving elements, and subtraction using outputs of the two adders A subtracter for processing; a unit for calculating an absolute value of an output of the subtractor; and a unit for tilting the optical head or the optical disk in a radial direction, wherein the irradiation light scans in a direction orthogonal to a track of the optical disk. A tilt detecting device for obtaining an amount of tilt of the optical head with respect to the disk based on the amplitude of the absolute value or the minimum value of the absolute value obtained when the tilting is performed. 6. A means for rotating an optical disc, a means provided on an optical head for irradiating irradiation light while focusing on an information surface of the optical disc, and a means provided on the optical head for receiving reflected light of the irradiation light A light-receiving element divided into four by an orthogonal dividing line, two adders for adding outputs of light-receiving elements that form diagonals of the divided light-receiving elements, and binarizing the outputs of the two adders. A binarizing means for converting the signal into a signal; a means for detecting a phase difference between the two binarized signals and outputting a phase difference pulse having a time width proportional to the phase difference; Means for calculating a sum, and means for tilting the optical head or the optical disc in a radial direction, based on a minimum value of the sum of the pulse widths obtained when the irradiation light is scanned in a direction orthogonal to a track. disk Tilt detection apparatus characterized by obtaining a tilt amount of the optical head against. 7. A tilt detecting device according to claim 5, wherein irradiation light is scanned from the inner circumference to the outer circumference of the optical disk, and an optical head and a tilt amount of the optical disk with respect to a radial position of the optical disk are temporarily stored in a temporary storage means. An optical disc apparatus having means for storing and correcting tilt of an optical head and an optical disc based on a radial position of an optical head and tilt amount information for a radial position stored in the temporary storage means.