JP2001126273A - Focus error signal detection method and optical disk head device for land/groove recording/reproduction - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a leakage amount into a focus error signal due to track cross and to improve bit error rate characteristics between both of lands/grooves while holding the advantages of a usual astigmatic method that temperature characteristics is excellent and secular deterioration is less. SOLUTION: The land/groove is irradiated by a main beam 20, and the adjacent land/groove is irradiated simultaneously by a sub-beam 30, and the focus error signal are obtained from both of the lands/grooves. Since they are operated electrically, even when the main beam exists on a which track of the land/ groove, the leakage of the track cross into the focus error signal is canceled. Further, the difference of focus servo between the land/groove and the difference of a focus offset in land/groove recording are eliminated in recording/ reproducing bit error rate characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head device used for an optical disk device for recording and reproducing data on both lands and grooves, and a method for detecting a focus error signal.

[0002]

2. Description of the Related Art In order to perform high-density recording / reproducing on an optical disk, a land / groove recording / reproducing method for recording not only on a land portion and a groove portion of a recording track but also on both of them has been adopted. The servo mechanism for constantly focusing the recording / reproducing beam of the optical head on a specific track of the optical disc is a tracking servo and a focus servo. Among the focus error detection methods in the focus servo, an astigmatism method, a knife edge method, and an improvement thereof have been developed. The method is a typical example.

FIG. 6 shows the principle of a conventional focus error detecting optical system based on the astigmatism method. The optical disk substrate 100, the objective lens 110, the focusing lens 120, and the like are shown in FIG.
It comprises a cylindrical lens 130 and a four-division optical sensor 140. In the figure, both cases where the recording / reproducing beam to the optical disk substrate is in focus (b), where the disk substrate is closer (a) and farther (c) than the in-focus position, correspond to each state. 4 shows an intensity distribution of light on a four-division optical sensor. Difference of sum of photoelectric conversion outputs of diagonal elements of sensor divided into four in ABCD = (A + C)-(B +
The focus error signal is detected from D).

When comparing the length of the astigmatism method and the length of the double knife edge method, firstly, there is an increase in the margin for alignment, and in particular, the sensitivity to the positional shift of the focus sensor. The astigmatism method is more stable against the shift of the focus sensor than the double knife edge method. This means that the astigmatism method is superior to the double knife edge method in terms of temperature stability and deterioration over time.

However, an optical head for detecting a focus error signal by the conventional astigmatism method uses a land / land track.
When groove recording is performed, if the leakage into the focus error signal due to track cross is called "modulation" here, in the conventional astigmatism method, the "modulation" of the focus offset is compared with the double knife edge method. large. This makes tracking pull-in unstable and hinders stable recording and reproduction. Further, from the viewpoint of the bit error rate characteristic with respect to the focus offset, the focus offset point at which the bit error rate of the land and the groove becomes minimum differs in the conventional astigmatism method, and the minimum bit error rate itself also differs from the land. There is a drawback that it is different from a groove.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to maintain the characteristics of the conventional astigmatism method that the temperature characteristics are excellent and the deterioration over time is small, and at the same time, the amount of leakage into the focus error signal due to track crossing. (Modulation) and the difference in recording / reproducing characteristics between both lands / grooves, especially the improvement in bit error rate characteristics in digital recording.

The inventor of the present invention has found that such a focus offset leaks into a focus error signal due to track crossing ("modulation") and that the bit error rate characteristics do not match between lands / grooves. It was found that the change was caused by the change of the diffraction pattern from the land / groove and the focus error signal detecting means. That is, when the focus error signal detection beam reaching the four-split sensor of the conventional astigmatism method is closely observed, the zero-order light reflected by the land or groove of the optical disk includes the reflection of the land or groove by the objective lens plus the first-order light. Origami and reflection-1
When the focus error signal is differentially detected by crossing of the sensor element of the four-divided sensor, these diffracted lights mainly appear as a wraparound of the track cross signal in the photoelectric conversion signal. Responsible. FIG. 5 shows modulation to a focus error signal. In the conventional astigmatism method, “modulation” is 3% of the focus error signal amplitude.
0%, which causes instability of the focus servo, or instability of the recording / reproducing characteristics. It is necessary to reduce "modulation" to the focus error signal as shown by the arrow in the figure. Further, the difference in recording / reproducing characteristics between the land and the groove is caused not only by the instability of the focus servo due to the above-mentioned cause, but also by the difference in the minute reflection / diffraction characteristics of the land / groove of the manufactured optical disk medium itself. Is also caused. In any case, it is an object to improve a focus error signal detection method for performing focus servo in the astigmatism method.

[0008]

According to a first aspect of the present invention, there is provided a method for detecting a focus error signal in an optical disc head for recording / reproducing data on a land / groove recording / reproducing laser beam, wherein a laser beam for recording / reproducing a sub-beam light amount to a main beam light amount. The beam splits into a main beam and a sub-beam having a light amount ratio of 1 or less, and each of the two beams is irradiated on either a land track or a groove track of an optical disk and simultaneously, and reflected light of the two beams from the optical disk Each focus error signal is detected independently by the astigmatism method,
A focus error signal of the main beam and a signal obtained by multiplying a focus error signal of the sub beam by a reciprocal of the light amount ratio are added. According to a second aspect of the present invention, there is provided a land / groove recording / reproducing optical disc head device, comprising: a laser; a condensing optical system for condensing light emitted from the laser onto the optical disc; and a tracking error caused by reflected light from the optical disc. A land / groove recording / reproducing optical disk head device comprising: a light detecting optical system including a unit for detecting an error, a unit for detecting a focus error, and a unit for detecting an RF signal; Means for splitting the light into a main beam and a sub-beam having a light intensity ratio of the sub-beam light amount to the main beam light amount of 1 or less, and simultaneously irradiating each of the two beams to either a land track or a groove track of the optical disc and simultaneously. The focus error detecting means included in the light receiving optical system is configured to detect reflected light of the two beams from the optical disc. It detected independently of each focus error signal by astigmatic method, characterized in that it comprises a focusing error signal detecting means having means for generating a focus servo feedback signals from the two focus error signal detected in the independent.
According to a third aspect of the present invention, there is provided an optical disk head device for land / groove recording / reproduction according to the second aspect of the present invention, wherein the laser light of the condensing optical system according to the second aspect of the invention is obtained by dividing the amount of sub-beam light / main beam light. The means for splitting the laser beam into a main beam and a sub-beam having a light amount ratio of 1 or less, and simultaneously irradiating each of the two beams to either a land track or a groove track of the optical disk, and simultaneously irradiating the laser and the light of the laser A collimator lens for forming a light beam, a wedge plate having a small wedge angle for transmitting a parallel light beam by the collimator lens, and an objective lens for condensing laser light transmitted through the wedge plate onto the optical disc, I do. The land / groove recording / reproducing optical disk head device according to the invention according to claim 4 of the present invention is the optical disk head device according to the invention according to claim 3, wherein
The means for generating a focus servo feedback signal from the two focus error signals is means for adding a signal obtained by multiplying a focus error signal of the main beam and a focus error signal of the sub beam by a reciprocal of the light amount ratio. And According to a fifth aspect of the present invention, there is provided an optical disk head device for land / groove recording / reproducing, wherein the means for detecting the tracking error according to the second aspect of the present invention is configured to reflect the two beams from the optical disk. A tracking error signal detecting means is provided which has a means for independently detecting each tracking error signal from light by a push-pull method and generating a track servo feedback signal from the two independently detected tracking error signals. The land / groove recording / reproducing optical disk head device according to the invention according to claim 6 of the present invention, wherein the track servo feedback signal is generated from the two independently detected tracking error signals according to the invention according to claim 5. Is means for subtracting a signal obtained by multiplying the tracking error signal of the sub beam by the reciprocal of the light amount ratio from the tracking error signal of the main beam.

[0009]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an optical configuration of an optical disk head according to an embodiment of the present invention. It comprises a condensing system and a light receiving system including a focus / track error detection system and an RF signal detection system. In the focusing system, the light emitted from the semiconductor laser 1 becomes parallel light via the collimator lens 2 and enters the wedge plate 3 having a small wedge angle. From the wedge plate 3 having a small wedge angle, multiple reflected light is emitted in addition to directly transmitted light as shown in FIG. The intensity of the multiple reflection light of each order forms a geometric series determined by the reflectance of the wedge plate 3 having a small wedge angle. When the transmittance of the directly transmitted light is high, the intensity of the higher-order repeatedly reflected transmitted light is low, and the main beam 20, which is the directly transmitted light, and the sub-beam light 30 which is reflected once and emitted from the wedge plate, and Emerges from the wedge plate having a small wedge angle as a main beam. Main beam 20, sub beam 3
0 is converted from an elliptical cross-sectional intensity distribution to a circular cross-sectional intensity distribution by a beam shaping prism 4, passes through a polarizing beam splitter 5 and a １ ／ wavelength plate 6, and is condensed on an optical disc 50 by an objective lens 7.

The main beam 2 reflected from the optical disk 50
0, the reflected light of the sub-beam 30 reverses the same optical path as above, is deflected by 90 degrees in the optical path by the polarizing beam splitter 5, and is guided to the light receiving system. The reflected light from the optical disk guided to the light receiving system is first transmitted to the condenser lens 17 for adjusting the size of the light spot on the optical disk to the size of the subsequent photodetector according to the focal length ratio with the objective lens 7. Is done.
After that, the light amount to the tracking error detection sensor 11 for detecting the tracking error is separated by the first half mirror 8, given astigmatism by the cylindrical lens 9, and sent to the focus error detection sensor 12 for detecting the focus error Is separated by the second half mirror 10 and reaches the RF sensor 13 for reading a recording signal recorded on the optical disk. Two sensors are provided so that the RF signal detection can be extracted from the two main and sub light beams. The light receiving system shown here has been described with a configuration in which two error detection systems and an RF signal detection system are serially arranged for easy understanding. However, use of a functional composite optical component such as a hologram element, Techniques such as the use of a multi-segment optical sensor and separation of an error signal and an RF signal by an analog / digital operation circuit can be used as appropriate.

Next, an embodiment of a component characterizing an embodiment of the present invention will be described.

FIG. 3 also shows the plane configuration of the land / groove recording / reproducing optical disk medium and the positional relationship between the main beam and the sub beam with respect to the land / groove. As an optical disk medium, as an example, the track width of a land and a groove is 0.6 μm, and the track pitch (Tp) is 1.2.
μm is shown. The positional relationship between the beam and the land / groove shows a case where the main beam 20 irradiates the groove and the sub beam irradiates the land. The light intensity ratio (K) between the main beam and the sub beam is set to about 10: 1 (K = 10) so that recording is performed only with the main beam, and the center-to-center distance between two light spots on the optical disk is in the track tangential direction. Is set to about 10 μm, and 0.6 μm which is １ ／ of the track pitch (Tp) in the track orthogonal direction. This is determined by the wedge plate 3 having a small wedge angle. For reproduction, as described for the RF signal detection sensor of the light receiving system, the sensor for the sub beam is also provided, and the signal can be detected even with the sub beam.

The wedge plate 3 having a small wedge angle shown in FIG. 2 generates the main beam and the sub beam on the optical disk. The vertex angle of the wedge is set to about 0.2 degrees between the collimated light beams so that the objective lens 7 has a focal length of 3 mm, so that the above-mentioned main-sub beam distance of 10 μm is formed on the optical disk. It is set to be incident. In addition, the wedge has a slight angle with the beam shaping prism or polarizing beam splitter in the optical axis cross section so that the main and sub beams are irradiated on the adjacent lands and grooves, and are shifted by 0.6 μm in the direction perpendicular to the track of the disk. It is installed to have. Also, a dielectric film is provided on the light transmitting / reflecting surface of the wedge so that the light intensity ratio between the main and sub beams is about 10: 1.

Next, regarding the focus error detection system,
FIG. 4 shows the configuration of the focus error signal detection sensor. The focus error signal detection sensor 12 receives the main beam reflected light 200 from the optical disk, and detects the focus error of the main beam by the four-split sensor 12a and the sub beam reflected light 30.
It is provided with two quadrant sensors, namely a quadrant sensor 12b that receives 0 and detects a focus error of the sub beam. Each is labeled ABCD and EFGH. 2
The distance between the split centers of the four split sensors 12a and 12b is set to a length obtained by multiplying the image forming magnification determined by the ratio of the focal length of the condenser lens 17 and the focal length of the objective lens 7 to the interval between the main and sub beam spots on the optical disk. I have. The focus error signal of each of the main beam and the sub beam is such that FEa = (A
+ C)-(B + D), and the sub beam is FEb = (E + G)
− (F + H). Each of the individually extracted photoelectric conversion signals has an S-shaped curve as shown in FIG. 5 (a), and leaks from a track cross as described in the section of the problem to be solved by the invention. The "modulation" referred to here is superimposed.

It is known that the phase of the above-mentioned "modulation" is inverted when the beam moves from the groove to the land on the optical disk and when the beam moves from the groove to the land. Therefore, when one is condensed on the land, the other is based on the positional relationship of the main and sub beams of the present invention, which are always located in the groove, on the track, so that the "modulation" superimposed on the focus error signal FEa of the main beam. The phase and the “modulation” phase superimposed on the focus error signal FEb of the sub beam are opposite phases. On the other hand, since the S-shaped waveform as the main waveform has the same phase, in the present invention, the levels of the electric signals of the error signal of the sub beam and the error signal of the main beam are equalized and added. That is, the focus error signal FE of the present invention is calculated as FE = ((A + C)-(B + D))) + K
((E + G)-(F + H)), only "modulation" is canceled at the electric signal level from the above-described phase relationship. Since the S-shaped curves are in phase, a smooth S-shaped curve focus error signal as shown in FIG. 5B is secured.

The focus error signal obtained by adding the error signal of the sub beam and the error signal of the main beam is fed back to the focus actuator, whereby the focus servo is performed. Therefore, regardless of whether the main beam runs on the land or on the groove, the focus zero cross point where the S-shaped curve crosses zero does not change depending on the land / groove. Therefore, the signal reproduction characteristics,
In particular, the focus offset that gives the minimum bit error rate does not change land or groove.
The minimum value is also the same, and there is no difference between the land / groove in the bit error rate characteristic.

Next, for the track error signal detection system, a method adopted in a single-beam push-pull method or a three-beam method using a normal two-split sensor can be used. ing. The focus error signal detection sensor 12 is connected to the track error signal detection sensor 11.
In the same manner as described above, two push sensors are used to detect both the main beam and the sub beam using two quadrant sensors, and the detection signal from the sub beam is multiplied by K to extract the difference from the detection signal from the main beam. . That is, the track error signal TE is used, and TE =
((A + D)-(B + C))-K ((E + H)-(F +
G)), it is possible to cancel the low-frequency undulation of the envelope appearing in the track cross signal, which is an important signal at the time of track jump, which is caused by the eccentric rotation and undulation of the optical disk. Therefore, a stable track jump can be realized, and a stable track servo is applied. The reason is that the track error signals of the lands and the grooves are in opposite phases, but the phase of the waving of the envelope is the same phase. Therefore, the difference between the track error signals of the main and sub beams is canceled out. Because it is done.

[0018]

According to the present invention, the land / groove is irradiated with either the main beam or the sub-beam at the same time, the focus error signal is obtained from both the land / groove, and the calculation is performed electrically. Regardless of which track, land or groove, the tracking servo is applied, leakage of the track cross into the focus error signal, that is, "modulation" is canceled. As a result, there is no difference in the bit error rate characteristics of recording / reproducing of each land / groove.

[Brief description of the drawings]

FIG. 1 is a diagram showing an optical configuration of an optical head according to an embodiment of the present invention.

FIG. 2 is a view showing an example of a “wedge” plate having a small wedge angle which constitutes an embodiment of the present invention.

FIG. 3 is a diagram showing an arrangement configuration of light spots on an optical disk by the optical head according to the embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of a focus error detection sensor constituting an embodiment of the present invention.

FIG. 5 is a diagram showing a waveform with respect to a focus offset of a focus error detection signal by an astigmatism method;
(A) shows a conventional detection signal waveform, and (B) shows a desirable detection signal waveform.

FIG. 6 is a diagram showing the principle of a conventional focus error detection optical system based on the astigmatism method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 Collimator lens 3 Wedge plate with small wedge angle 20 Main beam 30 Sub beam 4 Beam shaping prism 5 Polarization beam splitter 6 1/4 wavelength plate 7 Objective lens 8 First half mirror 9 Cylindrical lens 10 Second half Mirror 11 Tracking error detection sensor 12 Focus error detection sensor 12a Quadrant sensor 12b Quadrant sensor 13 RF sensor 17 Condensing lens 50 Optical disc 100 Optical disc substrate 110 Objective lens 120 Converging lens 130 Cylindrical lens 140 Quadrant optical sensor 200 Main beam reflected light 300 Sub beam reflected light

Claims (6)

[Claims] In a land / groove recording / reproducing optical disk head, a recording / reproducing laser beam is split into a main beam and a sub-beam having a light intensity ratio of a sub-beam light amount to a main beam light amount of 1 or less. To the land track or the groove track of the optical disk, and simultaneously irradiate the two beams from the optical disk, and independently detect each focus error signal by the astigmatism method from the reflected light of the two beams. A focus error signal detection method, comprising adding a focus error signal and a signal obtained by multiplying a focus error signal of the sub-beam by a reciprocal of the light amount ratio. 2. A laser, a condensing optical system for condensing light emitted from the laser onto an optical disk, a means for detecting a tracking error from light reflected from the optical disk, a means for detecting a focus error, and detecting an RF signal. A land / groove recording / reproducing optical disk head device comprising: a light receiving optical system including a means for performing a light-emitting operation. Means for splitting the beam into a main beam and a sub beam, and irradiating each of the two beams to either a land track or a groove track of an optical disc, and simultaneously;
The focus error detecting means included in the light receiving optical system independently detects each focus error signal from reflected light of the two beams from the optical disc by an astigmatism method, and detects the two focus errors detected independently. An optical disc head device for land / groove recording / reproduction, comprising a focus error signal detection means having means for generating a focus servo feedback signal from a signal. 3. The laser beam of the condensing optical system is split into a main beam and a sub-beam having a sub-beam light amount / main beam light amount ratio of 1 or less, and each of the two beams is land track of an optical disk. Or means for simultaneously irradiating the groove track with the laser, the laser and a collimator lens that converts the laser light into a parallel light beam, a wedge plate having a small wedge angle that transmits the parallel light beam by the collimator lens, and the wedge plate. 3. The optical disk head device for land / groove recording / reproduction according to claim 2, further comprising an objective lens for condensing the transmitted laser light on said optical disk. 4. A means for generating a focus servo feedback signal from the two independently detected focus error signals is obtained by multiplying the focus error signal of the main beam and the focus error signal of the sub beam by the reciprocal of the light amount ratio. 4. The optical disk head device for land / groove recording / reproduction according to claim 3, wherein said optical disk head device is means for adding a signal. 5. The tracking error detecting means independently detects respective tracking error signals from reflected light of the two beams from the optical disk by a push-pull method, and the two tracking error signals detected independently. 3. The optical disk head device for land / groove recording / reproduction according to claim 2, further comprising a tracking error signal detecting means having a means for generating a track servo feedback signal from the head. 6. A means for generating a track servo feedback signal from the two independently detected tracking error signals, wherein the tracking error signal of the sub beam is multiplied by the reciprocal of the light amount ratio from the tracking error signal of the main beam. 6. The optical disk head device for land / groove recording and reproduction according to claim 5, wherein the device is a means for subtracting a signal.