JPH056564A - Tracking error detecting system in optical disk reader - Google Patents

Abstract

PURPOSE:To provide a tracking error (TE) detecting system in an optical disk reader which detects TE signals with a high sensitivity during the detection of TE signals by a push-pull method and prevents the generation of a direct current offset caused by a displacement of an objective lens and a tilt of the optical disk. CONSTITUTION:TE detecting light sensors (c) and (d) are placed within regions S1 and S2, in which zero th-order diffracted light beams and first-order diffracted light beams of reflected far field pattern are superimposed, when an objective lens displacement against the light receiving surface of a tracking servo light detector 1 is generated. Furthermore, position adjusting light sensors (a) and (b)are placed in the center portion between the sensors (c) and (d) along the orthogonal direction of these sensors and make a position adjustment of the light detector 1 so that the output error amplifiers 2 and 3, which amplify the output difference of the sensors (c) and (d) and the sensors (a) and (b) becomes zero then, drive the tracking servo with the output of the error amplifier 2 as TE signals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tracking error detection method in an optical disk reading apparatus, and in an optical disk apparatus for detecting a tracking error (TE) signal by a push-pull method using a single beam, the TE signal is detected with high sensitivity. It is an object of the present invention to provide a method that does not generate a DC offset.

[0002]

2. Description of the Related Art In an optical disk reader, a tracking servo (TS) system is incorporated in order to keep a frame error rate (FER) characteristic of a reproduced signal due to a track following error of a laser beam below a predetermined level. Even when operated in this state, the laser beam of the optical pickup is accurately traced along the track (1.6 μm interval). There are single beam method and three beam method as the TE signal detection method, and there are various signal processing methods in each method, but the push-pull method is the simplest method for checking the presence of pre-groove and light utilization efficiency. It can be said to be a method with a simple configuration.

The optical disc reading device to which the push-pull method is applied may have an optical configuration as shown in FIG. 4, for example. In the figure, a laser beam emitted from a light source (laser diode) 51 passes through a beam splitter (BS) 52 and collimator lens 53
Then, it becomes parallel light at the optical disc 56, which is focused by the objective lens 55 after passing through the quarter-wave plate 54.
Connect the beam spot to the reflective surface of the. Meanwhile, the optical disc 56
The reflected light from the reverse returns from the objective lens 55 to the BS52 via the 1/4 wavelength plate 54 and the collimator lens 53, and the BS52 changes the angle of the returning light by 90 ° and makes it incident on the adjacent BS57,
In BS57, a part of the incident light is directly incident on the reproduction signal detecting photodetector 58 to form an image, but for the other part of the incident light, the angle is further changed by 90 ° and incident on the TS photodetector 59. Let

In the push-pull method, the photodetector 59 described above is used.
Is a two-division photo detector (PD). The output difference of each photodiode C, D is amplified by the error amplifier 60 and T
You are getting an E signal. Here, the principle of this method will be described in detail with reference to FIGS. The reflected light from the optical disc 56 is passed through the optical system from the objective lens 54 to the photodetector 59.
Far field pattern 61 is formed on the light receiving surface of
Since the groove (or pit) 62a is formed on the surface of the optical disc 56, the 0th-order diffracted light 63 directly reflected by the groove (or pit) 62a and the land portion 62b are incident on the far field pattern 61 to form a wavefront. Overlapping areas (hatched areas) S1 and S2 with the curved first-order diffracted lights 64 and 65 are formed.
Then, since the light amount distribution of the overlapping areas S1 and S2 largely changes due to the interference effect of light due to the presence of the groove (or pit) 62a, the photodiodes C and D are arranged in the respective areas S1 and S2. TE can be detected. That is, the light amount distribution on the light receiving surface of the photodetector 59 has a beam spot at the center position of the groove (or pit) 62a (or at the center of the land portion 62b) as shown in (1) of FIG. Shows a symmetrical distribution curve 66 and the TE signal becomes 0V, while
When the beam spot is at a position displaced from the groove (or pit) 62a as shown in (2) of FIG. 6, the TE signal becomes EV (E ≠ 0) due to asymmetry as shown by the distribution curve 67. As a result, as shown in FIG. 7, as the optical pickup moves,
The TE signal changes around 0V, and the position where the TE signal becomes 0V alternately indicates on-track and off-track.

[0005]

The above principle is established on the assumption that the optical axes of the image forming optical system and the error detecting optical system in FIG. 4 are completely coincident with each other, and they are not coincident with each other. If there is, DC offset occurs in the TE signal. For example, as shown in FIG. 8, when the objective lens 55 is displaced to the left or right (displacement amount: ω) from the neutral state (state in which the optical system is in the normal position), the photodetector 59 receives light. The far field pattern 61 is displaced on the surface, and a DC offset appears in the TE signal. Further, as shown in FIG. 9, the disk 56 is tilted from the plane orthogonal to the optical axis of the objective lens 55.
If it is (tilt angle: θ), the optical axis of the reflected light is shifted and the same result is brought about. That is, the TE signal changes around the offset voltage Vos as shown in FIG. 10, and the irradiation beam is not located at the center of the track even if the signal indicates 0V.

Further, in order to increase the sensitivity of the TE signal, it is necessary to align the center of the two-divided PD (the midpoint of the dividing line of the photodiodes C and D) with the center of the far field pattern. The method of adjusting while referring to the output of each photodiode C, D of is adopted. According to this method, it is easy to align the center of the far field pattern with the dividing line. It is difficult to locate to a point. That is, if the center of the far-field pattern is on the dividing line, the photodiodes C and D always have the same output, and therefore the midpoint of the dividing line cannot be obtained, and the optical axis of the reflected light on the dividing line. And the midpoint of the dividing line do not match, the sensitivity of the photodetector 59 is reduced.

Therefore, the present invention employs a push-pull system for TE.
It was created for the purpose of providing a TE detection method in which a TS photodetector always detects a TE signal with high sensitivity and a DC offset does not occur in the TE signal in an optical disk reader for detecting a signal.

[0008]

According to a first aspect of the present invention, in an optical disc reading apparatus for detecting a tracking error signal by a push-pull method, an imaging optical system and an error detection are performed on a light receiving surface of a tracking servo photodetector. Even if the optical axes do not match with each other between the optical systems, the tracking error detecting optical sensors are respectively provided in two areas where the 0th-order diffracted light and the 1st-order diffracted light are supposed to overlap in the reflected light far field pattern from the optical disk. Along with the arrangement, two optical sensors for position detection, which are divided by a line segment connecting the centers of the optical sensors, are arranged in the central region between the optical sensors, and the optical sensor for tracking error detection is arranged. And the light amount detection signals of the position detection optical sensor to refer to the tracking server to match the midpoint of the line segment with the center of the reflected light far field pattern. The position of use photodetector adjusted fixed, according to the tracking error detection method in the optical disc reading apparatus and detecting a tracking error by using the light quantity detection signal of the tracking error detecting optical sensor.

A second aspect of the present invention relates to the first condition regarding the arrangement condition of the TE detecting photosensor with respect to the light receiving surface of the TS photodetector.
The same as the invention of the above, but the position detecting photosensors divided into three or more parts are arranged in the central region between the TE detecting photosensors, and the light amount detection signals of the position detecting photosensors are detected. Referring to the position of the TS photodetector, adjust and fix the position of the TS photodetector so that the midpoint of the line connecting the centers of the TE detection photosensors matches the center of the reflected light far-field pattern. The present invention relates to a TE detection method in an optical disk reading device, which is characterized by detecting TE using a detection signal.

[0010]

In the first aspect of the present invention, when adjusting the position of the TS photodetector, the light detection signal of each TE detection photosensor is used to determine the midpoint in the direction in which the sensor is arranged for position detection. The midpoint in the direction orthogonal to the above-mentioned arrangement direction can be found by referring to each light amount detection signal of the photosensor, and the highest sensitivity position of the photodetector for TS (the center of symmetry of both TE detection photosensors (The position corresponding to) can be aligned with the center of the far field pattern.

In the second aspect of the invention, when the position is adjusted, the TE detecting optical sensor is not used, and only the position detecting optical sensor is used to adjust the center of the far field pattern to the maximum sensitivity position. That is, by using each light amount detection signal of the position detecting optical sensor of three or more divisions, it becomes possible to specify the highest sensitivity position on the plane, and the position can be adjusted without using the TE detecting optical sensor.

In both inventions, in consideration of the case where the far field pattern is displaced or the optical axis of the reflected light is shifted due to the displacement of the objective lens or the inclination of the optical disk, the TE detection sensor is used as the reflected light far field. Since the 0th-order diffracted light and the 1st-order diffracted light are assumed to overlap in the two regions in the pattern, the signal from the TE detection optical sensor is processed by the push-pull method to always detect only the TE component. Will be possible. That is, it is possible to prevent a DC offset from occurring in the TE signal.

[0013]

Embodiments of the present invention will be described below with reference to FIGS. FIG. 1 shows a plan view of a TS photodetector and a signal detection circuit in an optical disk reading apparatus according to the first embodiment. In the figure, 1 is a photodetector for TS, and a photodetector c for TE detection, which is a photodiode, on its light-receiving surface.
d and position adjusting optical sensors a and b are provided, the output of each TE detecting optical sensor c and d is to the error amplifier 2, and the output of each position adjusting optical sensor a and b is to the error amplifier 3. It is connected. Further, in FIG. 1, the XX direction indicates the track crossing direction and the YY direction indicates the track direction due to the optical relationship with the optical disk plane.

In the photodetector 1 for TS, each optical sensor
The arrangement relationship of c, d, a and b is as follows. First, TS
Assuming the displacement range of the objective lens and the tilt range of the optical disc with the photodetector 1 attached to the regular position, the optical system of the optical disc reader is analyzed to show the above range on the light receiving surface. Even if there is a displacement or inclination of the optical disc, there are two areas in which the 0th-order diffracted light and the 1st-order diffracted light overlap in the reflected light from the optical disc.
Although S1 and S2 can be assumed, the TE detecting optical sensors c and d are arranged in the two regions S1 and S2, respectively. In FIG. 1, 4 and 5 and 6 respectively indicate the patterns of the 0th-order diffracted light and the 1st-order diffracted light.

On the other hand, the position adjusting photosensors a and b have the centers of the TE detecting photosensors c and d in the central portion of the region formed between the TE detecting photosensors c and d. They are arranged in a manner of being divided by connecting line segments.

Therefore, in the optical disk reading apparatus shown in FIG. 4, the TS photodetector 1 of FIG. 1 is temporarily fixed in place of the conventional TS photodetector 59 to read an adjustment optical disk having no track. Output of error amplifiers 2 and 3 is 0
If the position of the photodetector 1 for TS is adjusted to V, each TE
The center of the reflected light far-field pattern can be aligned with the midpoint of the line segment connecting the centers of the detection optical sensors c and d, and TE detection can be performed with the highest sensitivity. That is, the output of the error amplifier 2 can be used as the adjustment signal in the X-axis direction, and the output of the error amplifier 3 can be used as the adjustment signal in the Y-axis direction. Since the light amount is such that it is attenuated as it goes away from the center on the surrounding concentric circles, the maximum sensitivity is obtained at the position where each output of the error amplifiers 2 and 3 is 0V. As a specific adjusting means, while finely adjusting the position of the TS photodetector 1 using a position adjusting jig while measuring the output voltage of the error amplifiers 2 and 3 with a voltmeter or an oscilloscope or the like. Become.

When the position adjustment of the TS photodetector 1 is completed as described above, the TS photodetector 1 in that state is completely fixed to the assembly mechanism of the optical pickup, and a normal optical disk is read. , The TE detecting optical sensors c and d are arranged in the respective areas S1 and S2, respectively, so that when the objective lens 55 is displaced from the neutral position (N) to the left and right (L) as shown in FIG. Also in (R), the TE detection optical sensors c and d are always present at positions where the 0th-order diffracted light and the 1st-order diffracted light overlap in the reflected light far-field pattern, and the error amplifier 2 always TE signal without DC offset can be obtained. This is also the case when the optical disc 56 is tilted as shown in FIG. 9, and enables accurate tracking control by a TE signal having no DC offset.

Next, FIG. 2 shows a plan view of a TS photodetector and a signal detection circuit according to the second embodiment. In the figure,
Reference numeral 11 is a photodetector for TS, and on its light-receiving surface are photodetectors c and d for TE detection, which are photodiodes, and a photosensor for position adjustment.
e, f, g, h are arranged. The output of each TE detecting optical sensor c, d is connected to the error amplifier 12, but the output of each position adjusting optical sensor e, f, g, h is the sensor e, f.
Output of the sensor g, h to the adder circuit 13
The outputs of the sensors e and g are connected to the adder circuit 15 and the outputs of the sensors f and h are connected to the adder circuit 16, and the outputs of the adder circuits 13 and 14 are further connected to the error amplifier 17 and the adder circuits 15 and 16 respectively. The circuit configuration has an output connected to the error amplifier 18.

Further, the arrangement relationship of the optical sensors c, d, e, f, g, h in the photodetector 11 for TS is the same as in the first embodiment for the photosensors c, d for TE detection. Same as the above, but for position adjustment optical sensors e, f, g, h, TE detection optical sensors c, d
Is arranged in a region divided into four by a line segment connecting the centers of the lines and a line segment orthogonal to the midpoint of the line segment.

In this embodiment, the TS photodetector 11 is adjusted to the highest sensitivity position only by the position adjusting photosensors e, f, g, and h. Do not use c and d. That is, as in the first embodiment, the photodetector 11 for TS is used.
When the output of each position adjustment optical sensor e, f, g, h is Ve, Vf, Vg, Vh in the state where is temporarily stopped, Vx = (Ve + Vf) from the error amplifier 17 as the adjustment signal in the X-axis direction. -(Vg + Vh) is Vy = (Ve + Vg) − as the adjustment signal in the Y-axis direction from the error amplifier 18.
Although (Vf + Vh) is obtained, the position of the TS photodetector 11 is adjusted so that both of these adjustment signals Vx and Vy become zero.
Since the reflected light far-field pattern of the adjustment optical disk exhibits the light amount distribution having the above-mentioned symmetry, the centers of the TE detection optical sensors c and d are connected in the state of Vx = Vy = 0. The center of the reflected light far-field pattern can be aligned with the midpoint of the line segment, and by fixing the TS photodetector 11 at that position, TE at the maximum sensitivity can be obtained.
It becomes possible to detect. In this embodiment, the TS photodetector 11
Although it means that a 4-division PD is used for the above, in principle, the above-mentioned adjustment can be performed by using a 3-division PD or more.

Further, even when the ordinary optical disk 56 is read in this embodiment, the TE detecting optical sensors c and d take into consideration the displacement of the objective lens 55 and the inclination of the optical disk 56, and the 1st order diffracted light and the 1st order diffracted light. DC offset does not always exist because it is arranged in the areas S1 and S2 where the second-order diffracted light overlaps.
The TE signal can be detected.

[0022]

The tracking error detection method in the optical disk reading apparatus of the present invention has the above-mentioned configuration, and thus the TS photodetector for setting the TE signal detection sensitivity by the push-pull method to the maximum is provided. In addition to facilitating the position adjustment, the TE detection sensor allows the 0th-order diffracted light and the 1st-order diffracted light in the far-field pattern reflected from the optical disk even when the optical axes of the imaging optical system and the error detection optical system do not match.
Since it is provided in two areas where the second-order diffracted light is supposed to overlap, DC offset can be prevented from occurring in the TE signal even if the objective lens is displaced or the optical disc is tilted, and accurate tracking control for the optical pickup is performed. To enable.

[Brief description of drawings]

FIG. 1 is a plan view and a signal detection circuit of a TS photodetector corresponding to a first embodiment of a tracking error detection method in an optical disc reading apparatus of the present invention.

FIG. 2 is a plan view and a signal detection circuit of a TS photodetector corresponding to the second embodiment.

FIG. 3 shows a reflected light far-field pattern and TE formed on the light receiving surface of the photodetector for TS when the objective lens is displaced.
It is a figure which shows the positional relationship of the optical sensor for signal detection.

FIG. 4 is a diagram showing an optical configuration of an optical disc reading apparatus when a push-pull method is applied to detect a TE signal.

FIG. 5 is a diagram showing a TE signal detection principle by a push-pull method.

FIG. 6 is a diagram showing a TE signal detection principle by a push-pull method.

FIG. 7: Change in TE signal corresponding to movement of optical pickup
8 is a graph showing (a state in which no DC offset occurs).

FIG. 8 is a diagram showing how the reflected light far-field pattern formed on the light receiving surface of the TS photodetector changes when the objective lens is displaced.

FIG. 9 is a diagram showing how the reflected light far-field pattern formed on the light receiving surface of the TS photodetector changes when the optical disc is tilted.

FIG. 10 is a graph showing changes in the TE signal (DC offset occurrence state) corresponding to movement of the optical pickup.

[Explanation of symbols]

1,11 ... TS photo detector, 2,3,12,17,18 ... Error amplifier, 4 ...
0th-order diffracted light pattern, 5,6 ... 1st-order diffracted light pattern, 13,1
4,15,16 ... Adder circuit, a, b, e, f, g, h ... Position adjustment optical sensor, c, d ... TE detection optical sensor, S1, S2 ... 0th-order diffracted light and 1st-order diffracted light are always Overlapping areas.

Claims (2)

[Claims] 1. An optical disc reading apparatus for detecting a tracking error signal by a push-pull method, wherein an optical axis mismatch between an imaging optical system and an error detecting optical system with respect to a light receiving surface of a tracking servo photodetector. Even if it occurs, the tracking error detecting optical sensors are arranged in the two regions where the 0th-order diffracted light and the 1st-order diffracted light are supposed to overlap in the reflected light far-field pattern from the optical disk, and the optical sensors described above are also provided. Two position detecting photosensors divided by a line segment connecting the centers of those photosensors are arranged in the central area between them, and each light amount detection of the tracking error detecting photosensor and the position detecting photosensor is performed. Referring to the signal, adjust the position of the tracking servo photodetector so that the midpoint of the line segment matches the center of the reflected light far-field pattern. A tracking error detection method in an optical disk reading apparatus, characterized in that a tracking error is detected by using each light amount detection signal of a tracking error detection optical sensor. 2. In an optical disk reading apparatus for detecting a tracking error signal by a push-pull method, there is a discrepancy in the optical axis between the imaging optical system and the error detecting optical system with respect to the light receiving surface of the tracking servo photodetector. Even if it occurs, the tracking error detecting optical sensors are arranged in the two regions where the 0th-order diffracted light and the 1st-order diffracted light are supposed to overlap in the reflected light far-field pattern from the optical disk, and the optical sensors described above are also provided. An optical sensor for position detection, which is multi-divided into three or more parts, is arranged in the central region between
The position of the tracking servo photodetector to match the midpoint of the line segment connecting the centers of the tracking error detection photosensors with the center of the reflected light far-field pattern by referring to the light amount detection signal of each position detection photosensor. Adjust and fix,
A tracking error detection method in an optical disk reading device, characterized in that a tracking error is detected by using each light amount detection signal of a tracking error detection optical sensor.