JPH02260135A - Measuring method for spot phase difference in light pickup - Google Patents

Abstract

PURPOSE:To raise the precision of the measurement of phase difference between subspots by detecting the phase difference between electric signals based on the reflected lights of one of the subspots for tracking error detection and a main spot, and displaying DC output due to the phase difference on a display device. CONSTITUTION:A laser beam is emitted from a laser diode 1 and passes through a diffraction grating 2, and forms the main spot Sa and the subspots Sb, Sc on an eccentric disk D. Then, a track T is moved in the radial direction of the disk by the rotation of the eccentric disk D, but adjustment is executed so that the center of the amplitude of this movement is irradiated by the main spot Sa. The disk D is rotated in this state, and as observing the level of the DC output to be displayed, the relative position of the spots Sa to Sc on the disk is moved by rotating the diffraction grating 2, and when the output level on the display device becomes a prescribed value, the rotation of the grating 2 is stopped. In this case, the phase difference between Sa and Sb becomes 90 deg., and the phase difference between Sb and Sc becomes 180 deg., and the subspots Sb and Sc are formed at the best phase angle theta.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for measuring the phase difference of sub-spots for tracking error detection, and particularly relates to a method for measuring the phase difference of sub-spots for tracking error detection, and in particular, when an error occurs in the phase difference of the detection output due to the sub-spots. , relates to a spot phase difference measurement method that enables accurate detection of this phase difference.

[Conventional technology]

Fig. 7 is an explanatory diagram showing the structure of a 3-beam optical pickup installed in a compact disc player, etc. Fig. 8 is an explanatory diagram of the photodiode shown in Fig. 7;
Figures A and 9B are explanatory diagrams showing the positional relationship between spots and tracks formed on the disc.

This optical pickup is composed of light receiving elements such as a laser diode 1, a diffraction grating 2, a beam splitter 3, a collimating lens 4, a total reflection prism 5, an objective lens 6, a cylindrical lens 7, and a photodiode 8. The photodiode 8 has a light receiving surface 8c divided into four parts for detecting focusing errors, etc.
, light receiving surfaces 8a and 8b for tracking error detection are formed. The detection beam emitted from the laser diode 1 is made into a parallel beam by the collimating lens 4, reflected in the right angle direction by the total reflection prism 5, and focused on the recording surface of the optical disc D by the objective lens 6.

In this optical pickup, three minute spots S are formed on the recording surface of the optical disc D by the diffraction phenomenon of the diffraction grating 2.
a, Sb, and Sc are formed (see FIGS. 9A and 9B). Furthermore, the beam reflected from the recording surface of the optical disc D is reflected in the right angle direction by the beam splitter 3,
It is detected by a photodiode 8 via a cylindrical lens 7.

In this photodiode 8, reflected light based on the main spot Sa is detected by the light receiving surface 8c, and the light receiving surface 8a
, 8b allows the reflected light based on the sub-spots Sb and Sc to be detected.

As shown in FIG. 9A, on the recording surface of the optical disc D, the pits P on the track T are read by the central main spot Sa of the three beam spots. Further, the sub-spots sb and Sc are spots for tracking error detection, and are arranged at a constant interval in the direction of a constant phase angle θ with respect to the tangential direction of the track T. 9th
In figure A, about half of the sub-spots sb and Sc are covered by the track T, and the light-receiving surfaces 8a and 8b are
The amount of light detected is made to be equal. In this state, the output from the differential amplifier 9 shown in FIG. 8 is zero, and there is no tracking error, that is, the detection beam is accurately irradiated onto the track T.

On the other hand, as shown in FIG. 9B, when the sub-spots sb and Sc have different areas covering the track T (or the mirror surfaces Ml, M2 on which no pit P is formed), the sub-spots sb and Sc have different areas from the optical disc D. The amount of reflected light differs depending on the light receiving surfaces 8a, 8b.
Different amounts of light are detected, and the differential amplifier 9 outputs a tracking error signal TR. Then, tracking correction is performed in accordance with the magnitude of this tracking error signal TR.

In addition, in FIGS. 9A and 9B, the track pitch TP is 1.6 μm, and the track width (pit width) Tw is 0.5 μm.
μm, sub-spot pitch Sp in α and β directions is 0.8
The case of 1 Lm is shown.

In order to detect tracking errors well in the three-beam system, the phase angle θ between the sub-spots sb and Sc formed on the optical disc D and the track must be optimally determined. When shown schematically, the phase angle θ between the sub-spots sb and Sc is such that the sub-spot sb is located at the center of the mirror surface M1, M2, and Sc is located at the center of the track T, as shown in FIG. 9B. In this state, when a tracking error signal is detected by moving the track back and forth in the left-right direction in the figure, the phase difference between the detection outputs of the sub-spots sb and Sc becomes 180°.

Here, using FIG. 1O, we will adjust the formation positions of the sub-spots Sb and Sc in the 3-beam system with respect to the recording surface of the optical disc D. In other words, what phase angles will the sub-spots Sb and Sc have with respect to the track? A conventional method for measuring whether the angle θ is formed will be explained.

For example, an eccentric disk is used for this measurement. The rotation of the eccentric disk causes the main spot Sa to be irradiated onto the center of the amplitude of the track T's fluctuation. In this state, the phase difference between the detection signals of the sub-spots Sb and Sc formed on the recording surface of the eccentric disk is measured.

FIG. 10 shows an apparatus for measuring the phase difference of sub-spots. In FIG. 10, reference numerals 10a and lob indicate low-pass filters. Low pass filter 10
An electric signal Sl (see FIG. 11 (A+)) based on the reflected light of the sub-spot sb formed on the optical disc D is input to a.The low-pass filter 10b receives the reflected light of the sub-spot Sc. An electrical signal S2 (see FB in FIG. 11) based on light is input.

The low-pass filters 10a and 10b are connected to the signal S1. S2
Pass only the low frequency part of with low attenuation, respectively.
It is designed to output to comparators 11a and 11b. When the appropriate phase angle θ is set as shown in Fig. 9A, comparators 11a and 11b produce signals that are 180° out of phase with each other as shown in the output waveforms of Fig. 11 fc) and FD), respectively. Signal S3. S4 is now output. These signals S3. S4
is subjected to phase comparison by the phase comparator 12, and the signal S
5 (see Fig. 11 (see El)) is output. This signal S5 has an output waveform in which linear peaks appear every 180°. Also, reference numeral 13 indicates an integrating circuit. Output signal S5 from the phase comparator 12
is displayed on the display 14 via this integrating circuit 13 as a DC output level. The output from the phase comparator 12 is the first
When the signal S5 in the case of fEl in FIG. 1 is input to the integrating circuit 13, its output becomes zero. Therefore, in the conventional art, the phase angle θ of the sub-spot was adjusted by moving the optical pickup so that the output level displayed on the display 14 became zero.

Note that when the phase angle θ between the signals S1 and 32 is zero, that is, the sub-spots 1-3b, Sc and the main spot Sa
is on a straight line on the track T, the signal output from the phase comparator 12 becomes a signal as shown by S8 in FIG. 11fH).

This S8 signal has the same period and the same level as S3 (S4), and the output from the integrating circuit 13 is ■. A
It becomes x. This output indicates the maximum value that can be output from the integrating circuit 13.

[Problem to be solved by the invention]

In the above conventional example, for example, when spots are formed in a state where the phase angle θ is increased and a state where it is decreased as shown in FIG. 9A, the phase difference between the signals S1 and 82 may be 225° and 135°, respectively. be. At this time, phase comparator 1
The output waveforms from 2 are shown in Figure 11, CFl and fGl, respectively.
S6. As shown in S7, the output from the integrating circuit 13 is ((225-180)/180)
VMAx ((180-1351/180)
ViiAx, and its value is (VMAX
I/4). That is, when the phase difference is around 180°, the same level of DC output may be displayed on the display 141, and when the phase difference is around 180°, the phase difference and the DC output value displayed on the display 14 may be different. does not change linearly.

Therefore, it becomes impossible to determine whether the phase is positive or negative before or after the phase difference of 180°, and there is a problem that it takes time to adjust the phase angle θ.

Moreover, especially within the range of phase difference 18[1'' ±lO°, the output voltage from the integrating circuit 13 hardly changes due to the influence of disk eccentricity.Therefore,
In measuring the phase difference between sub-spots sb and Sc,
It is necessary to take measures such as assuming that the phase difference is 180° in the middle of the portion that does not change, which is disadvantageous in that the measurement work takes a long time. Furthermore, it is difficult to accurately measure the phase difference. In particular, since the output level from the integrating circuit 13 does not increase linearly, it is difficult to eliminate the influence of disk eccentricity in phase difference measurements, resulting in a problem in which errors in phase difference measurements become large.

The present invention is based on the above iiiE! The purpose of this study is to develop a method for measuring the spot phase difference in an optical pickup that allows the sub-spot phase difference to be easily measured without being adversely affected by the eccentricity of the disk. The purpose is to provide.

[Means to solve the problem]

A method for measuring a spot phase difference in an optical pickup according to the present invention is to measure a spot phase difference between a pair of spots for detecting a tracking error by sandwiching a main spot for reading pits on a track of a disk and at a predetermined interval in the tangential direction of the track. Sub-spots are formed on the recording surface of the disk, a phase difference between electrical signals based on the reflected light between one of the pair of sub-spots and the main spot is detected, and a DC output based on this phase difference is sent to a display. It is characterized by displaying the spot and measuring the phase difference of the spot.

[Function] According to the above means, the phase difference between the sub-spots is measured by measuring the phase difference between either one of the pair of sub-spots and the main spot. Therefore, when adjusting to form sub-spots on the disk so that the phase difference between the sub-spots is 180°, it is sufficient to set the phase difference between the sub-spots and the main spot to 90°. Before and after this phase difference of 90°, the output level displayed on the display changes linearly based on the phase difference. Therefore, the phase difference of the sub-spots can be easily measured without being adversely affected by the eccentricity of the disk.

[Example] The present invention will be described in detail below based on the drawings.

Figure 1 [A] is a waveform diagram of an electrical signal based on the reflected light from the main spot Sa, Figure 1 [B] is a waveform diagram of an electrical signal based on the reflected light from the sub spot sb, and Figure 1 [C] Also, FIG. 2(A) is a waveform diagram of the signal S12 output from converter lla, FIG. 1(D), FIG. 2(B), and FIG.
Figure (A), Figure 4 [A] and Figure 5 fA) are waveform diagrams of the signal 313 that can be output from the comparator llb.
Figure (E), Section 2 (C), Figure 3 (B), Figure 4 (C)
, FIG. 5 (El) is a diagram showing the waveform of the signal output from the phase comparator 12 and the level of the DC output displayed on the display 14, and FIG. 7 is a graph showing the relationship between the phase difference and the DC output level displayed on the display 14. FIG.

The apparatus used in the spot detection method of the sub-spots sb and Sc for tracking error detection according to the present invention is the same as that shown in FIG.

In this embodiment, a signal 510 (first
Figure fAl 8) is input.

On the other hand, the low-pass filter 10b includes a subsubbot Sb,
Alternatively, an electrical signal based on Sc is input. Note that the waveforms shown in FIG. 1 (Al and FIG. 2 FBl) are such that, due to the rotation of the eccentric disk, the track T moves in the α direction centering on the position where the main spot Sa is formed (the position shown in FIG. 9A). (the state shown in FIG. 9B) and then in the β direction.

In this embodiment, an electric signal Sll based on the reflected light of the sub-spot sb is input to the low-pass filter 11b. In addition, Fig. 1 fAl and Fig. 1 f
At Bl, the phase difference between the signals SIO and Sll is 906
The case of is shown. This is a state where the phase angle θ of the sub-spot shown in FIG. 9A is optimal, and the sub-spot sb
When the phase difference between the outputs of and Sc is 180° (Fig. 11 (
The measurement of the phase angle θ of sub-spots sb and Sc in this example, which corresponds to the state of Al, FB+, is based on the electric signal SIO based on the reflected light of the main spot Sa and the reflected light of the sub-spot sb. It is measured based on the phase difference of electrical signals. As shown in FIG. 9A, the phase difference between the sub spots sb and Sc is 180°, and when the phase difference is in the best condition, the main spot S
The phase difference between a and sub-spot sb is half of that, 90°.

Therefore, in this embodiment, when the phase difference between the sub spot sb and the main spot Sa is 90°, the phase angle θ between the sub spots sb and Sc is considered to be the best (the phase difference is 180°), and the sub spot Sb is selected.

The phase angle of Sc is adjusted.

Hereinafter, the DC output level displayed on the display 14 will be examined using the sub-spot phase difference measuring device shown in FIG. 11 and the waveform diagrams shown in FIG. 1fAl to FIG. 5(B).

As shown in Figure 1 fAl and (B), the signals SIO and S
When the signals are manually input to the low-pass filters 10a and 10b at timings in which the phase of the signal lla is shifted by 90 degrees (the phase of the signal Sll is delayed by 90' from the phase of the signal SIO), the comparator lla outputs the signal shown in FIG. 1 (C1). A square wave signal S12 as shown in FIG.
A square wave signal S13 whose phase is delayed by 90 degrees from the signal S12 is output from the signal lb. These signals S12. S1
3 is manually input to the phase comparator 12, and the phase comparator 12 outputs a signal 514 (a square wave signal shown by a solid line in FIG. 1(E)) based on the phase difference. This signal 5
14 is determined by the integrating circuit 13 (1/2
) and displayed on the display 14. For example, when VMAX is IOV, the DC output is 5V, which is indicated by point A on the graph of FIG. When the display 14 shows 5■, the phase difference between the main spot Sa and the sub spot sb is 90°.
, that is, the phase difference between sub-spots sb and Sc is 180
', and this state is the state in which the phase angle θ between the sub-spots sb and Sc is the best.

Next, when the signals SIO and Sll are inputted to the low-pass filters 10a and 10b with a zero phase difference (phase angle e shown in FIG. 9A is zero), the outputs from the comparators 11a and 11b are , respectively in Figure 2 fAl
A square wave signal S with zero phase difference as shown in , fB)
12. It becomes S13. Further, the output from the phase comparator 12 becomes a square wave signal S15 as shown in FIG. 2 FC+. This signal S15 has the same waveform as the signals 512 and S13, and when the signal S15 is inputted to the integrating circuit 13, its output reaches the level MAX (10 ■) It is assumed that the DC output is
will be displayed. This corresponds to point B in the graph of FIG. 6, and this shows the case where the phase difference between sub-spots sb and Sc in the conventional measurement method is zero.

Further, when the signal Sll is delayed by 45 degrees in phase from the signal SIG, the comparator llb outputs a signal S13 which is delayed by 456 degrees from the signal S12, as shown in FIG. 3(B). Further, the phase comparator 12 outputs a signal S16 as shown by the solid line in FIG. 3 fB). Then, the display 14 shows the DC output level (f180-45+/1801 XV, Ax=3/
4 V, A, (=7.5 V) is displayed. This corresponds to point C in the graph of FIG.
The case where the phase difference is 90° is shown.

In addition, the output from comparator llb when signal Sll is delayed by 135° in phase than signal SIO is shown in Figure 4 (B
), it becomes a square wave with a phase delay of 135° from the signal S12. Furthermore, the waveforms of the signal S17 output from the phase comparator 12 and the integrating circuit 13 are
It looks like the solid line shown in Figure FC+. Therefore, the level of DC output displayed on the display 14 is ((180-1351/1801 x V, A)
It becomes 1/4 V 1iAx, which becomes 2.5■. This corresponds to the dot in the graph of Figure 6,
The phase difference between sub-spots sb and Sc in the conventional measurement method corresponds to 270°.

Furthermore, when the signal Sll leads the signal S10 by 180° in phase, the output signal S13 from the comparator llb is 180° more advanced than the signal 512 as shown in FIG.
It becomes a square wave with a delayed phase. Further, the waveform output from the phase comparator 12 is a waveform in which peaks on a line are expressed every 180° as shown in FIG. 5 fB).

Also, the output level output from the integrating circuit 13 is (f180-180) / 1801 XV,A
x becomes 0■. This is shown in the graph of Figure 6.
This corresponds to point E, where the phase difference between sub-spots sb and Sc in the conventional measurement method is 360°.

The above measured values (theoretical values) are summarized in the table below.

(Left below) In the above table, the left column of phase difference is the signal SIO and Sll based on the reflected light from the main spot Sa and sub spot sb.
Which phase difference is shown and the middle column shows the sub-spot s
The phase difference between b and the sub-spot is shown. The DC output in the table indicates the level of the DC voltage output from the integrating circuit in the method of the present invention.

Figure 6 is a graph drawn based on this table. The horizontal axis of this graph is the phase difference between the signals SIO and Sll,
Below that, the axis of the phase difference between the sub-spots is also written. Also, the output of the integrating circuit 13 is plotted on the vertical axis. In addition, the straight line in Figure 6 is V = 10- (Viax /1.80) X l
It is represented by O. However, θ indicates the phase difference between the main spot Sa and the sub spot sb. Moreover, the points indicated by white circles in FIG. 6 show the results of actual measurement.

Next, a method for measuring the phase difference between sub-spots sb and Sc will be explained.

First, the laser diode l emits light, and the diffraction grating 2 (
7) to form a main spot Sa and sub spots Sb and Sc on the eccentric disk D. In this case, as the eccentric disk D rotates, the track T moves in the radial direction of the disk, and adjustment is made so that the main spot Sa is irradiated at the center of the amplitude of this movement. Then, in this adjusted state, the eccentric disk D is rotated, and while observing the DC output level displayed on the display 14, the diffraction grating 2 is rotated, and the (by adjusting the phase angle θ shown in FIG. 9A). Here, when the output level displayed on the display 14 reaches 5■, the rotation of the diffraction grating 2 is stopped. In this state, as is clear from the graph in Figure 6, the phase difference between the main spot Sa and the sub spot sb is 90°, that is, the phase difference between the sub spots sb and Sc is 180°. , sub-spots sb and Sc are formed on the disk at the best phase angle θ.

In the conventional example, the phase difference between sub-spots sb and Sc is 180°±45°, which is 225° (in the case of this example, it is 112°).
5°) and 135° (675° in this example)
), the DC output level displayed on the display 14 was the same, and it was not possible to immediately determine whether the phase angle θ was shifted in the positive direction or in the negative direction. As is clear from the graph, the DC output levels at these phase differences are displayed on the display 14 as levels that differ from 5V (90° phase difference between the main spot Sa and the sub spot). Become so. In calculation, sub-spots sb and Sc
When the phase difference is 225°, it is 1[1-1[]/180
X (225/21・3.75(V) When 135°, 10-10/180X (135/2)・6.25(V
). Therefore, the display on the display 14 is 375
When V, in the direction of setting the output level to 5■, that is,
The phase difference between main spot Sa and sub spot sb is 1
By moving from 125° to 90°, the phase difference can be changed to 67.5° at 6.25V.
By moving the sub-spots 1-Sb and Sc by 90° from 90°, that is, in the opposite direction to the above case, the phase difference between sub-spots 1-Sb and Sc can be easily brought to the best state.

Although the invention made by the present inventor has been specifically explained based on Examples above, it is not limited thereto. That is, in the above embodiment, the phase difference between the sub spot sb and the main spot Sa is compared, but the phase difference between the sub spot Sc and the main spot Sa is compared, and the phase difference between the sub spots Sb and Sc is compared. You may also ask for

[Effects] As described above, according to the present invention, the phase angle between the sub-spot and the track can be easily measured.

Further, according to the present invention, it becomes possible to display a phase using a main spot and sub-spots, and the phase difference between the sub-spots progresses around 180°, making it possible to display a delayed phase. Therefore, it becomes possible to absorb measurement errors due to the adjustment and the eccentric disk, and it is possible to obtain the effect that the accuracy of adjustment and measurement of the phase difference between sub-spots is improved.

[Brief explanation of drawings]

Fig. 1 fA) is a waveform diagram of an electrical signal based on the reflected light of the main spot Sa, Fig. 1 FB+ is a waveform diagram of an electrical signal based on the reflected light of the sub spot sb, Fig. 1 (C), 2 Figure (A), Figure 4 fA+ are waveform diagrams of the signals output from comparator lla, Figure 1 (D), Figure 2 (B),
Figure 3 (A), Figure 4 + B) and Figure 5 (Kari is a waveform diagram of the signal output from comparator lake Ilb, Figure 1 (
E), Figure 2 (C), Figure 3 (B), Figure 4 (C), Figure 5 (Bl is the waveform diagram of the signal output from the phase comparator 12 and displayed on the display 14. FIG. 6 is a graph showing the relationship between the phase difference between the main spot Sa and the sub spot sb and the DC output level displayed on the display 14, and FIG. 7 is a graph showing the relationship between the DC output level displayed on the compact disc player An explanatory diagram showing the structure of a 3-beam optical pickup installed in a disc, etc., Figure 8 is an explanatory diagram of the photodiode in Figure 7, and Figures 9A and 9B are the spots formed on the disc. An explanatory diagram showing the positional relationship with the track, FIG. 10 is a block diagram of a device that measures the phase difference between sub-spots, and FIGS. 11(C) and 11CD) are diagrams showing the waveforms of the signals output from the comparators 11a and 11b, respectively, and FIG. 11(E) to FIG. 11 The solid line in CD) is a diagram showing the waveform of the signal output from the phase comparator, and the dotted line is a diagram showing the level of the DC output from the integrating circuit. 10 a, 10 b--o-pass filter, 11
a. 11b... Comparator, 12... Phase comparator, 1
3...Integrator circuit, 14...Display device.綜区綜υ】 ward

Claims (1)

[Claims] 1. A pair of sub-spots for detecting tracking errors are formed on the recording surface of the disc, sandwiching a main spot for reading pits on the track of the disc and at a predetermined interval in the tangential direction of the track. The phase difference between the spots is measured by detecting a phase difference between electrical signals based on reflected light between one of the spots and the main spot, and displaying a DC output based on this phase difference on a display. Method for measuring spot phase difference in optical pickup