JPH08315377A - Optical recording medium reader - Google Patents

Abstract

PURPOSE: To embody an exact tracking control by detecting the light in which the zero-order diffracted light and first-order diffracted light interfere with each other among the reflected light rays from a beam spot and detecting the intensity of the reflected light rays of this beam spot. CONSTITUTION: In the reflected light rays of sub-spots 302, 303, the diffracted light of high order are distributed. A tracking signal photodetector 101 detects the region where the zero-order diffracted light and the +1st-order diffracted light interfere and, therefore, if the sub-spots 302, 303 exist on pits, the intensity of the reflected light rays thereof is minimized. The intensity increases gradually as going further from the pits and becomes the max. value when the subs-spots deviate completely from the pits and, therefore, there is no disorder in the tracking error signal obtd. by subtraction with a subtractor 304. The exact control of the tracking position of a main spot 301 is thus made possible.

Description

Detailed Description of the Invention

[0001]

[0001]

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photodetector used for tracking control of a pickup of an optical recording medium reading device for reading information on an optical recording medium such as an optical disk or an optical card.

[0003]

[0002]

[0004]

2. Description of the Related Art Conventionally, a compact disc (hereinafter referred to as a CD) is known as an optical disc.

In a CD, pits for recording information bits are spirally arranged on one side, and a reproducing device of the CD is a disc in which a pickup for reading the pits scans at a relatively constant speed in the disc rotation direction. While the laser is controlled to rotate at a constant linear velocity (CLV), the laser beam light of the pickup is tracking-controlled to optically read information.

A three-beam tracking method is known as a method used for tracking control.

[0007]

FIG. 6 shows a method of detecting a tracking error signal using the 3-beam tracking method.

3 with a diffraction grating (not shown) of the pickup
The split beam connects three spots on the disc. The central spot 601 is a main spot by a main beam for reading recorded information, and two spots 602 and 603 on both sides of the central spot are sub-beams for tracking control by a sub-beam.

Sub-spot 60 for tracking control
2, 603 are symmetrical with respect to the main spot 601 and the alignment direction is a small constant angle a with respect to the scanning track direction of the pit read by the main spot 601.
It is only displaced.

The photodiodes 604 and 605 receive the reflected light from the sub-spots 602 and 603, respectively, and output tracking signals.

When the sub-spot is on the track row, the intensity of the reflected light is minimum, and gradually increases as the sub-spot deviates from the pit, and reaches the maximum value when completely displaced from the pit. Subspots 602, 6
Since 03 is symmetrical with respect to the main spot, when the main spot 601 is on the scanning track of the pit to be read, these two photodiodes 60
The difference between the tracking outputs of Nos. 4 and 605 is 0, but if they are deviated to either one, the output of one becomes large and the tracking error signal of the main spot 601 is detected.

[0012]

Here, the intensity distribution of the reflected light of the sub-spot 602 will be described.

Beam diameter d of pickup for reading CD
Is calculated by the following equation (1).

D = k · λ / NA (1) λ: wavelength of laser light NA: numerical aperture of objective lens k: constant For CD, λ = 780 (nm), NA = 0.46, k
= 0.8, d = 1.36 (μm).

The track pitch of the pits of a normal CD is about 1.6 μm, and the pit width is about 0.5 μm.

When the track pitch is constant, the pit train can be regarded as a diffraction grating. That is, as shown in FIG. 7, high-order diffracted lights are generated on both sides of the reflected light (0th-order light) and interfere with each other, so that the intensity distribution of the reflected light is not uniform. In FIG. 7, the high-order diffracted light is represented only by the + 1st-order diffracted light and the −1st-order diffracted light, but in reality, the higher-order diffracted light is distributed further outside.

[0017]

FIG. 8 shows how the sub-spots 602 are generated and distributed by high-order diffracted light due to CD pits having a track pitch P. When the pit 801 is irradiated with the sub-spot 602, high-order light is distributed symmetrically on both sides of the reflected light (zero-order light) at a constant pitch X.
802 is the + 1st order diffracted light, 803 is the -1st order diffracted light, 8
Reference numeral 04 is the + 2nd order diffracted light, and 805 is the −2nd order diffracted light. Here, up to the second-order diffracted light is shown, but actually higher-order diffracted light is distributed.

Here, the pitch X of the adjacent diffracted light is calculated by the following equation (2).

X = n · λ / NA · P (2) n: Order of diffraction (0, 1, 2, 3, ...) λ: Wavelength of laser light NA: Numerical aperture of objective lens P: Track pitch

[0020]

In the reflection optical system from the pit, since the reflected light outside the sub-spot 602 does not pass through the objective lens, the light received by the photodiode 604 is within the reflected light area 901 (hatched portion) in FIG. And the 0th-order light, and the 0th-order light and the + 1st-order diffracted light that interfere with each other,
It receives light in which 0th-order light and −1st-order diffracted light interfere with each other. The photodiode 605 is also the photodiode 6
As with 04, since the reflected light outside the sub-spot 603 does not pass through the objective lens, the 0th order light, the 0th order light and the +
It receives light in which the 1st-order diffracted light interferes with each other and light in which the 0th-order light and the −1st-order diffracted light interfere with each other.

[0021]

FIG. 10 is a diagram showing the amplitude characteristic of the tracking error signal obtained by the reflected light of the sub-spot 602 and the sub-spot 603 irradiated on the pit in the three-beam tracking method. The tracking error signal 1001 is the sub-spot 602 in FIG.
And 0 of the reflected light of the sub-spot 603.
The amplitude of the tracking error signal 1001 is obtained by the output difference of the signals obtained from the overlapping portion of the secondary light and the primary light, and is 0 when the main spot 601 is located on the scanning track of the pit or in the center between the tracks. Draw an S-curve so that

[0022]

In the conventional CD reproducing pickup, the 3-beam type tracking error signal was detected as described above. In recent years, a high density optical disc having a narrow pit track pitch has been developed with the increase in information density. However, accurate reproduction is also required. In order to reproduce this disc, it is necessary to reduce the size of the beam spot obtained by irradiating the disc with a laser beam. This can be realized by setting the wavelength λ of the laser light to a shorter wavelength than that used in the conventional CD reproducing pickup according to the formula (1).

[0023]

FIG. 11 shows how the sub-spots of the high-density optical disk reproducing pickup using the three-beam tracking system generate and distribute high-order diffracted light by the pits of the high-density optical disk.

In the figure, 1101 is a pit of a high density optical disc. 1102 is the 0th order diffracted light, and 1103 is +
The 1st-order diffracted light, 1104 is the -1st-order diffracted light, 1105 is the + 2nd-order diffracted light, and 1106 is the -2nd-order diffracted light. Here, up to the second-order diffracted light is shown, but as in FIG. 8, actually higher-order diffracted light is distributed.

The reflected light is affected by the pits as described above, and the high-order diffracted light is distributed symmetrically at a constant pitch X1. However, the photodiode does not receive the diffracted light of the second or higher order. Are set and formed.

[0026]

However, a conventional CD is used in a pickup for reproducing a high-density optical disk using the 3-beam tracking method.
In accordance with the equation (2), the pitch of the diffracted light of the sub-spot becomes small and the 0-th order diffraction is performed in the light receiving region of the photodiode receiving the reflected light of the sub-spot. The light is received in the area where the light interferes with the diffracted light of the second or higher order, or the area where the light of two or more different diffracted higher orders interferes. Therefore, harmonics are generated in the tracking error signal obtained from the photodiode, and the amplitude of the tracking error is disturbed.

Therefore, when a conventional CD is reproduced by a pickup for reproducing a high-density optical disk using the 3-beam tracking system, there is a drawback that accurate tracking control cannot be performed.

[0028]

FIG. 12 shows how the sub-spots of a pickup for reproducing a high-density optical disk using the 3-beam tracking system are distributed by generating high-order diffracted light by CD pits.

When the pits 1201 of the CD are irradiated with the sub-spots 1202 of the pickup for reproducing the high density optical disk using the laser light of the short wavelength, the high-order light is symmetrically distributed on both sides of the reflected light (0th-order light) at the constant pitch X2. To be done.
Reference numeral 1203 is a + 1st order diffracted light, 1204 is a −1st order diffracted light, 1205 is a + 2nd order diffracted light, and 1206 is a −2nd order diffracted light. Here, up to the second-order diffracted light is shown, but actually higher-order diffracted light is distributed as in the case of FIG.

Pitch X2 as calculated from equation (2)
Is smaller than that of a conventional CD reproducing pickup because the wavelength of the laser light is shortened. Therefore, it can be seen that the second-order diffracted light interferes with the reflected light of the sub-spot 1202.

[0031]

FIG. 13 shows a tracking error signal obtained from a CD by the three-beam tracking method, which is obtained by using a tracking error signal 1301 obtained by using a conventional CD reproducing pickup and a high density optical disc reproducing pickup. Tracking error signal 13
No. 02 is shown by comparison. As can be seen from this figure, when a pickup for reproducing a high-density optical disc is used, the tracking error signal is disturbed, so that accurate tracking control cannot be performed.

[0032]

[0013]

[0033]

SUMMARY OF THE INVENTION The present invention has been made in view of the above drawbacks, and is a light receiving device for tracking control of a pickup for reproducing a high density optical disk of a three-beam tracking system capable of accurately controlling CD tracking. To provide a container.

[0034]

[0014]

[0035]

According to the first aspect of the present invention,
A pit recorded on an optical recording medium is irradiated with convergent laser beam light to obtain reflected light accompanied by a plurality of diffracted lights, and a pickup for receiving the reflected light is provided, and the pit and the pickup are mutually scanned. In an optical recording medium reading device for reading information, the pickup is configured so that only 0th-order diffracted light and + 1st-order diffracted light of reflected light from a pit interfere with each other, and 0th-order diffracted light and -1st-order diffracted light only. A light receiving device for detecting light beams that interfere with each other is provided, and a tracking error detecting means for detecting a tracking error signal of a pit from an output signal of the light receiving device is provided.

[0036]

[0015]

[0037]

Since the present invention is configured as described above, it is preferable that
According to the invention described above, when the reflected light from the beam spot obtained by irradiating the CD with the high-density optical disk reproducing pickup is received to obtain the tracking signal, the 0th order of the reflected light from the beam spot is obtained. Diffracted light and one in one
Since the light beams in which the second-order diffracted lights interfere with each other are detected, the intensity of the reflected light becomes minimum when the beam spot is on the pit of the CD, and gradually increases as the beam spot deviates from the pit to completely disappear from the pit. If it deviates, it becomes the maximum value, so that accurate tracking control can be realized.

When a CD is tracked by a pickup for reproducing a high-density optical disc using the 3-beam tracking method, the 0th order diffracted light and the 1st order diffracted light of the reflected light from the tracking control sub-spots. Since the lights that interfere with each other are detected, the tracking error signal is not disturbed, so that accurate tracking control can be realized.

[0039]

[0016]

[0040]

EXAMPLE An example of the present invention will be described below with reference to FIG. FIG. 1 is a diagram showing a main part of a tracking signal light receiver of a pickup for reproducing an optical disk of a three-beam tracking system in an embodiment of the present invention.

Reference numeral 101 is a tracking signal light receiver for receiving the reflected light from the sub-spot on one side. The light receiving area of the tracking signal light receiver 101 includes a light receiving portion 101a and a light receiving portion 101b. An adder 102 adds the output signals of the tracking signal light receiver 101 to obtain a tracking signal.

[0042]

FIG. 2 shows a portion of the distribution of the diffracted light in FIG. 12 where the 0th-order diffracted light and the 1st-order diffracted light interfere with each other, and 201 indicates the 0th-order diffracted light and the + 1st-order diffracted light. This is the area of interference. Reference numeral 202 is a region where the 0th-order diffracted light and the -1st-order diffracted light interfere with each other.

The light receiving unit 101a is shaped so that the reflected light from the region 201 and the reflected light from the region 202 are received by the light receiving unit 101b.

[0044]

FIG. 3 shows a tracking signal light receiver 101 of the present invention when a CD is reproduced by a pickup for reproducing a high density optical disk using the three-beam tracking system.
3 shows a method of detecting a 3-beam tracking error signal by using. In the figure, 301 is a main spot, and 302 and 303 are sub-spots. Again 30
4 is a subtractor.

Diffraction grating of the pickup (not shown)
The beam divided into three is irradiated onto the disc so as to connect the main spot 301 and the two sub-spots 302 and 303.

The reflected light from the sub-spots 302 and 303 has high-order diffracted light distributed as shown in FIG.
Since the tracking signal light receiver 101 receives a region where the 0th-order diffracted light and the + 1st-order diffracted light interfere with each other and a region where the 0th-order diffracted light and the −1st-order diffracted light interfere with each other, the sub-spot 30
2, 303 has the minimum intensity of the reflected light when it is on the pit, and gradually increases as it deviates from the pit, and reaches the maximum value when completely deviated from the pit. The tracking error signal obtained by the subtraction is not disturbed, and the main spot 301
The tracking position of can be controlled accurately.

[0047]

FIG. 4 is a diagram showing a tracking error signal obtained from a CD by using the tracking signal light receiver 101 of the present invention as a light receiver of reflected light from a sub-spot in the three-beam tracking system.

Reference numeral 401 is a tracking error signal obtained by the tracking signal light receiver 101 of the present invention, and reference numeral 402 is a tracking error signal when a conventional high-density optical disk reproducing pickup is used.

As can be seen from the figure, the tracking error signal 402 has a signal disturbance, but the 401 eliminates the signal disturbance.

[0050]

In the present embodiment, as shown in FIG. 1, the tracking signal photodetector 101 has a region where the 0th-order diffracted light and the + 1st-order diffracted light interfere with each other in the reflected light from the pit, and the 0th-order diffracted light. Although only the area where the 1st-order diffracted light interferes with is received, the tracking signal photodetector 10 defines the areas 101c and 101d where only the 0th-order diffracted light is distributed in the figure.
The signal obtained by receiving light at 1 becomes a DC component of the output of the tracking error signal and does not affect the shape of the S-order curve of the tracking error signal. Therefore, the tracking signal light receiver 101 includes the regions 101c and 101c in addition to the above light receiving region.
Even if the reflected light of d is received, the main spot 301
The tracking position of can be controlled accurately.

[0051]

In this embodiment, the tracking signal light receiver 101 according to the present invention is used as a light receiver for the reflected light from the sub-spot in the three-beam tracking method, but the tracking signal light receiver in the one-beam push-pull method is used. Similarly, the tracking position of the reading beam can be accurately controlled.

When it is used as a tracking signal light receiver in the one-beam push-pull system, the tracking error signal is obtained by subtracting the outputs of the light receiving units 101a and 101b. The tracking error signal in this case is as shown in FIG.

Also in this case, since the signals obtained from the regions 101c and 101d of the tracking signal photodetector 101 become the DC component of the output of the tracking error signal, the regions 101c and 101b are simultaneously added to the regions 101c and 101b. Even if the reflected light of the area 101d is received, it does not affect the shape of the S-order curve of the tracking error signal. Therefore, even if these light receiving portions and regions are used as a tracking signal light receiver of the one-beam push-pull method and a tracking error signal is obtained from these light reception outputs, the tracking position of the reading beam can be controlled accurately.

[0054]

FIG. 5 is a diagram showing a tracking error signal obtained from a CD by using the tracking signal light receiver 101 of the present invention as a light receiver of the reflected light from the beam spot in the one-beam tracking system.

Reference numeral 501 is a tracking error signal obtained by the tracking signal light receiver 101 of the present invention, and 502 is a tracking error signal when a conventional high-density optical disk reproducing pickup is used.

As can be seen from this figure, the tracking error signal 502 has signal disturbance, but 501 eliminates the signal disturbance.

[0057]

The present invention is not limited to the embodiments described above, and various applications are possible. For example, the optical recording medium may be not only a rotating optical disk but also an optical card that moves at a predetermined speed. Further, the tracks of the optical recording medium may not be formed in a spiral shape, but may be formed by concentric circles or a pit array of a plurality of substantially parallel loci.

The present invention includes all such application examples without departing from the scope of the claims.

[0059]

[0024]

[0060]

Since the present invention is configured as described above, when a reflected light from a beam spot obtained by irradiating a CD with a high-density optical disk reproducing pickup is received to obtain a tracking signal, the beam spot is emitted from the beam spot. Since the 0th-order diffracted light and the 1st-order 1st-order diffracted light of the reflected light are detected, the intensity of the reflected light becomes minimum when the beam spot is on the pit of the CD, As the value gradually increases as it deviates from the pit and completely deviates from the pit, the maximum value is reached, so that accurate tracking control can be realized.

Further, when the CD is subjected to tracking control by the high-density optical disk reproducing pickup using the three-beam tracking system, the 0th-order diffracted light and the 1st-order 1st-order diffracted light of the reflected light from the tracking control sub-spot are Since the lights that interfere with each other are detected, the tracking error signal is not disturbed, so that accurate tracking control can be realized.

Further, since it is possible to control the tracking of the optical discs having different pitches by using one pickup, it is possible to realize the optical recording medium reading device capable of controlling the tracking compatibility with a simple structure.

[Brief description of drawings]

FIG. 1 is a diagram showing a main part of a tracking signal light receiver of an optical disk reproducing pickup of a three-beam tracking system in an embodiment of the present invention.

FIG. 2 shows the distribution of sub-spots of a pickup for reproducing a high-density optical disc using a three-beam tracking system, in which high-order diffracted light is generated and distributed by CD pits, and the zero-order diffracted light is distributed. It is a figure which shows the part which diffracted light and 1st-order diffracted light interfere.

FIG. 3 shows a case where a tracking signal light receiver 101 of the present invention is used to reproduce a CD when a CD is reproduced by a pickup for reproducing a high density optical disc using a 3-beam tracking system.
It is a figure which shows the method of detecting a beam tracking error signal.

FIG. 4 is a tracking signal light receiver 101 according to the present invention.
FIG. 3 is a diagram showing a tracking error signal obtained from a CD by using the above as a light receiver for reflected light from a sub-spot in a three-beam tracking system.

FIG. 5 is a tracking signal light receiver 101 according to the present invention.
FIG. 3 is a diagram showing a tracking error signal obtained from a CD by using the above as a light receiver for reflected light from a sub-spot in the one-beam tracking system.

FIG. 6 is a diagram showing a tracking error signal detection method using a three-beam tracking method.

FIG. 7 is a diagram showing a state of intensity distribution of reflected light from a beam spot located on a pit of a CD.

FIG. 8 is a diagram showing a manner in which sub-spots of a CD reproducing pickup using the 3-beam tracking method are generated and distributed by high-order diffracted light generated by CD pits.

FIG. 9 is a diagram showing a reflected light region from a sub-spot received by a photodiode of a CD reproducing pickup using the 3-beam tracking method.

FIG. 10 is a diagram showing an amplitude characteristic of a tracking error signal of a CD reproducing pickup using a 3-beam tracking method.

FIG. 11 is a diagram showing a manner in which sub-spots of a pickup for reproducing a high-density optical disc using the 3-beam tracking method are generated and distributed by high-order diffracted light by pits of the high-density optical disc.

FIG. 12 is a diagram showing a manner in which sub-spots of a pickup for reproducing a high-density optical disc using the three-beam tracking method are distributed because high-order diffracted light is generated by CD pits.

FIG. 13 is a diagram showing a tracking error signal obtained from a CD by a 3-beam tracking method.

[Explanation of symbols]

 101 ... Tracking signal light receiver 101a ... Light receiving part 101b ... Light receiving part 101c ... Region 101d ... Region 102 ... Adder 201 ... Region 202 ... Region 301 ... ・ Main spot 302 ・ ・ ・ ・ Sub spot 303 ・ ・ ・ ・ Sub spot 304 ・ ・ ・ ・ Subtractor 401 ・ ・ ・ ・ Tracking error signal 402 ・ ・ ・ ・ ・ ・ Tracking error signal 501 ・ ・ ・ Tracking error Signal 502 ... Tracking error signal 601 ... Main spot 602 ... Sub spot 603 ... Sub spot 604 ... Photo diode 605 ... Photo diode 701 ... Zero order Light 702 ... + 1st order diffracted light 703 ... -1st order diffracted light 704 ... 0th order light and +1 Area where the diffracted light of 705 ... interferes with the 0th-order light and the minus first-order diffracted light 801 ... Pit 802 .... + 1st-order diffracted light 803 ... Diffracted light 804 ... + 2nd-order diffracted light 805 ...-- 2nd-order diffracted light 901 ...- Reflected light region 1001 ... Tracking error signal 1101 ... Pit 1102 ... Sub-spot 1103 ... + 1st-order diffracted light 1104 ...- first-order diffracted light 1105 ... + second-order diffracted light 1106 ...- second-order diffracted light 1201 ... pit 1202 ... sub-spot 1203 ... + 1st-order diffracted light 1204 ...- first-order diffracted light 1205 ... + second-order diffracted light 1206 ...- second-order diffracted light 1301 ... tracking error signal 1302 ... tracking error Belief

Claims (1)

[Claims] 1. A pickup for irradiating a pit recorded on an optical recording medium with convergent laser beam light to obtain reflected light accompanied by diffracted light of a plurality of orders, and for receiving the reflected light, the pit and the pit In an optical recording medium reader for reading information by mutually scanning a pickup, the pickup is configured to
Light in which only the 1st-order diffracted light and the + 1st-order diffracted light interfere with each other,
It is provided with a photodetector for detecting a 0th-order diffracted light and a light in which only the -1st-order diffracted light interferes with each other, and a tracking error detecting means for detecting a tracking error signal of the pit from an output signal of the photodetector. Optical recording medium reader.