JPH11120607A - Optical head device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical head device which is not affected by the track offset induced by the offset component included in an off-track signal and lens shift control. SOLUTION: This optical head device is provided with photodetecting regions 24a, 24b for offset component detection for removing the output of the offset component included in the off-track signal in part of the photodetecting regions 23a, 23b of a photodetector 23 which detects the off-track signal, by which the light of the part superposed with all of the zero order diffracted light, first order diffracted light and minus first order diffracted light of the reflected light reflected from an optical disk is used to eliminate the influence of the offset component included in the off-track signal, i.e., lens shift, on the track error signal. Then, the stable tracking control is made possible. The header signal by using the output of the two detection regions on the outer side of the photodetector 23 is exactly readable and the dealing with even the optical disk of a land and groove recording system is possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an optical head device for recording information on an optical disk as a recording medium and reproducing information from the optical disk.

[0002]

2. Description of the Related Art An optical disk device includes an optical head device having an objective lens for irradiating a recording surface of an optical disk as a recording medium with a light beam having a cross-sectional beam diameter set to a predetermined size. By irradiating the beam, reflected light corresponding to the information recorded on the optical disk is taken out to reproduce the information.

The above-described optical head device has a semiconductor laser device (hereinafter simply referred to as a laser device) as a light source for generating a light beam and a light beam radiated from the laser device on a recording surface of an optical disk as a recording medium. An objective lens for converging and extracting a reflected light beam reflected by the recording surface, a photodetector for photoelectrically converting the reflected light beam extracted by the objective lens and outputting a reproduction signal corresponding to information recorded on the optical disc; Each element is formed by a plurality of optical members or the like constituting an optical path of a light beam. The optical head device has an objective lens mounted on an actuator (movable part) in order to enable high-speed access, and a laser element, a photodetector, and an optical member forming an optical path are fixed units separated from the actuator. (Fixed part) is widely used.

On the recording surface of the optical disk, a guide groove called a groove is provided so that the condensed spot of the light beam condensed by the objective lens can always follow a predetermined radial position. I have.

In order to always match the center of the condensed spot converged by the objective lens with the center of the groove,
The objective lens is moved in the radial direction of the optical disk by the well-known tracking control.

In this case, the amount by which the objective lens should be moved, that is, the tracking control amount, is set based on a track error signal obtained using, for example, a known push-pull method. In the push-pull method, a light beam reflected / diffracted by a groove is received by a photodetector having a light sensing unit divided into two parts, and photoelectrically converted. A difference between the photoelectrically converted signals is determined by a track error. This method is used as a signal. For example, "optical disk technology" (Noboru Murayama et al., 19
1989, Radio Technology Co., Ltd., pp. 86-88 and FIG.

On the medium of an optical disk, for example,
As described in “Basics and Application of Optical Disk Storage” (Masahiro Ojima et al., Institute of Electronics, Information and Communication Engineers, 1995, pages 140 to 141), an ID section for providing address information and a SYNC for providing a synchronization signal Departments,
There is a header part formed as a pre-pit. The header portions are arranged at predetermined positions of the groove at predetermined intervals. The header portion is usually formed as a pit row of predetermined various lengths without shifting in the direction in which the groove extends when viewed in the circumferential direction.

In recent years, in response to a demand for higher density of an optical disk, a method of recording information not only between grooves but also between grooves, that is, a land (land / groove recording method) has been proposed. .

More details are described in, for example, pages 59 to 74 of "Next Generation Optical Disc Technology" (Takuto Fujiwara et al., Triceps 1995).

As one of the methods of forming the header portion in the land / groove recording method, for example, as shown in “C-287 of the 1995 IEICE General Conference Proceedings,” the header portion has a groove pitch. In some cases, a total of four sets are formed, each two sets being shifted from the inner circumferential side and the outer circumferential side by a quarter. According to this proposal,
From all the information recorded in the four headers,
The track position and the like are detected.

In the above-mentioned land / groove recording method, data is recorded on both the land and the groove (recorded data exists). In other words, the condensed spot is formed on each of the land and the groove. Must be traced.

In this case, it is necessary to determine whether the focused spot traces the land or the groove based on the information recorded in the header portion. Detection is performed by extracting an output as a difference signal of a light receiving pattern using a photodetector formed along the direction. That is,
Each time the focused spot passes through the pits constituting the header, the reproduced signal waveform having a certain amplitude, for example, if the header is shifted to the inner circumference side of the groove, for example, a + When the header portion is shifted to the outer peripheral side of the groove, the output includes a negative deviation component, so that each is output, so by specifying the polarity of this deviation component, Lands and grooves are identified.

[0013]

By the way, when it is necessary to read information at a position (groove) different from the current groove (track) on the optical disk, or to newly record information in another groove, It is necessary to move the light-converged spot from the groove currently hit by the light-converged spot to a predetermined target groove.

In many cases, for example, the actuator is driven in the radial direction by a linear motor, and the objective lens on the actuator is deflected in the tracking direction (hereinafter, referred to as lens shift). This is done by doing

At this time, from the viewpoint of realizing fast reading or writing of information, if the focused spot reaches a desired track, the focused spot can follow the track center as quickly as possible by tracking control. desired. In order to realize this, generally, first, the entire actuator is coarsely moved to the vicinity of a target track, for example, 5 to 10 tracks before by a linear motor, and the movement of the remaining few tracks is controlled by lens shift. Further, a method is adopted in which the amount of lens shift is reduced by finely moving the linear motor as the vehicle approaches or reaches the target track.

However, if the above-described lens shift is used when the objective lens is tracked to the target track, an offset component is superimposed on the phase difference signal, and the center of the condensed spot is shifted from the center of the target track. There is a problem that a track offset occurs in which the tracked state is regarded as a track center and tracking control becomes unstable.

In the detection of a track shift signal by the push-pull method, an undesired track shift such as a track shift occurs even though the center of the track coincides with the center of the focused spot. A signal (fake track shift signal) is output, and the tracking control becomes similarly unstable. If the fake track deviation signal and the track offset have the same polarity, the tracking control may cause the track to go off.

Separately from this, in the land / groove recording method, a signal from the header portion contains a deviation component, that is, a component which may be discriminated as any of the above-described track offset or fake track deviation signal. Therefore, it is necessary to clearly separate the original deviation components. That is, in land / groove recording, unless the original deviation component is separated, the reproduced signal from the header on either the inner circumference or the outer circumference is buried in the track offset or the fake track shift signal described above, and However, there is a problem in that the reproduction accuracy of the information recorded in the unit is reduced, and in the worst case, a reading error occurs or reading becomes impossible.

[0019]

SUMMARY OF THE INVENTION The present invention has been made based on the above-described problems, and includes a light emitting means for supplying a light beam to an information recording medium, and a light emitting means for emitting the light beam from the light emitting means. The information recording medium according to claim 1, wherein the optical recording medium includes at least a condensing unit for condensing the light on the information recording medium, and a photoelectric conversion unit for converting light reflected and diffracted from the information recording medium into an electric signal. Has a groove-shaped groove for guiding a condensed spot obtained by condensing the light beam by the condensing means in a circumferential direction of the information recording medium, and the groove is provided at a break of the groove. Has a header portion composed of a bripit row that is deviated with respect to, the photoelectric conversion means comprises a plurality of light-sensitive regions that receive reflected light from the information recording medium, and At least one of the dividing lines that divides the light-sensitive area and at least one of the dividing lines, when the condensed spot obtained by being converged by the objective lens moves in the radial direction of the information recording medium, reflects the reflected light on the photoelectric conversion unit. All or a part of the light diffracted by the information recording medium, in which only the 0th-order light component and the 1st-order light component overlap, is a direction substantially perpendicular to the moving direction, and The light beam to be received is received in the light receiving area and photoelectrically converted to generate a first header auxiliary signal, and only the 0th-order light component and the -1st-order light component of the light diffracted by the information recording medium are reduced. All or part of the overlapping portion, or a light beam whose main component is a part thereof, is received in the light-sensitive region and photoelectrically converted to generate a second header auxiliary signal, and the first header auxiliary signal. The second header Generates a difference signal between the auxiliary signal, is intended to provide an optical head device which is characterized in that the this header signal.

The present invention also provides a light emitting means for supplying a light beam to the information recording medium, a light collecting means for condensing the light beam emitted from the light emitting means on the information recording medium, An optical head device having at least photoelectric conversion means for converting light reflected and diffracted from the information recording medium into an electric signal, wherein the information recording medium is obtained by condensing the light beam by the condensing means. The grooved groove for guiding the condensed light spot in the circumferential direction of the information recording medium, and a header portion composed of a prepit row that is deviated from the groove at a break of the groove. And the photoelectric conversion unit includes a plurality of light sensitive areas that receive the reflected light, and at least one of the dividing lines that divides the light sensitive area,
When the condensed spot obtained by being converged by the objective lens moves in the radial direction of the information recording medium, the direction is substantially perpendicular to the direction in which the reflected light moves on the photoelectric conversion means, Of the light diffracted by the information recording medium, at least a part of a portion where the zero-order light component, the first-order light component, and the first-order light component all overlap, and a part including at least a part of the zero-order light component A first light-sensitive region having a rectangular shape longer than the beam diameter of the reflected light in a direction parallel to the dividing line and receiving light, and located on both sides of the dividing line; Of the light diffracted by the medium, the light receiving part of the light protruding from the first light receiving area, and having a second light receiving area located on both sides of the dividing line, the first light Two areas separated by the dividing line of the sensitive area A first difference signal that is a difference signal between the obtained photoelectric conversion signals and a second difference that is a difference signal between the photoelectric conversion signals obtained from the two regions separated by the dividing line of the second light-sensitive region. An optical head device characterized in that a difference signal obtained by subtracting the first difference signal from a sum signal with a signal is used as a header signal.

Further, the present invention provides a light emitting means for supplying a light beam to an information recording medium, a light collecting means for condensing the light beam emitted from the light emitting means on the information recording medium, An optical head device having at least photoelectric conversion means for converting light reflected and diffracted from the information recording medium into an electric signal, wherein the information recording medium is obtained by condensing the light beam by the condensing means. The grooved groove for guiding the condensed light spot in the circumferential direction of the information recording medium, and a header portion composed of a prepit row that is deviated from the groove at a break of the groove. And the photoelectric conversion unit includes a plurality of light sensitive areas that receive the reflected light, and at least one of the dividing lines that divides the light sensitive area,
When the condensed spot obtained by being converged by the objective lens moves in the radial direction of the information recording medium, the direction is substantially perpendicular to the direction in which the reflected light moves on the photoelectric conversion means, Of the light diffracted by the information recording medium, at least a part of a portion where all of the 0th-order light component, the 1st-order light component, and the -1st-order light component overlap, and a portion including at least a part of the 0th-order light component A first light-sensitive region having a rectangular shape longer than the beam diameter of the reflected light in a direction parallel to the dividing line and receiving light, and located on both sides of the dividing line; Of the light diffracted by the medium, the light receiving part of the light protruding from the first light receiving area, and having a second light receiving area located on both sides of the dividing line, the first light Two areas separated by the dividing line of the sensitive area A first difference signal that is a difference signal between the obtained photoelectric conversion signals and a second difference that is a difference signal between the photoelectric conversion signals obtained from the two regions separated by the dividing line of the second light-sensitive region. An optical head device characterized in that a difference signal obtained by subtracting a signal obtained by amplifying or reducing the first difference signal by a predetermined value from a sum signal with a signal is used as a header signal.

Also, the present invention provides a light emitting means for supplying a light beam to the information recording medium, a light collecting means for condensing the light beam emitted from the light emitting means on the information recording medium, An optical head device having at least photoelectric conversion means for converting light reflected and diffracted from the information recording medium into an electric signal, wherein the information recording medium is obtained by condensing the light beam by the condensing means. A converging spot having a groove-like groove for guiding the information recording medium in a circumferential direction of the information recording medium, and a header portion formed of a prepit row that is deviated from the groove at a break of the groove. And the photoelectric conversion unit includes a plurality of light sensitive areas that receive the reflected light, and at least one of the dividing lines that divides the light sensitive area,
When the condensed spot obtained by being converged by the objective lens moves in the radial direction of the information recording medium, the direction is substantially perpendicular to the direction in which the reflected light moves on the photoelectric conversion means, Of the light diffracted by the information recording medium, at least a part of a portion where all of the 0th-order light component, the 1st-order light component, and the -1st-order light component overlap, and a portion including at least a part of the 0th-order light component A first light-sensitive region having a rectangular shape longer than the beam diameter of the reflected light in a direction parallel to the dividing line and receiving light, and located on both sides of the dividing line; Of the light diffracted by the medium, the light receiving part of the light protruding from the first light receiving area, and having a second light receiving area located on both sides of the dividing line, the first light Two areas separated by the dividing line of the sensitive area A signal obtained by amplifying or reducing one of the obtained photoelectric conversion signals by a predetermined value is divided by a first difference signal, which is a difference signal obtained by subtracting the other signal from the other signal, and the division line of the second light-sensitive region. An optical head characterized in that a difference signal obtained by subtracting the first difference signal from a sum signal of a photoelectric conversion signal obtained from two regions to be applied and a second difference signal is a header signal. An apparatus is provided.

Further, the present invention provides a light emitting means for supplying a light beam to the information recording medium, a light collecting means for condensing the light beam emitted from the light emitting means on the information recording medium, An optical head device having at least photoelectric conversion means for converting light reflected and diffracted from the information recording medium into an electric signal, wherein the information recording medium is obtained by condensing the light beam by the condensing means. A converging spot having a groove-like groove for guiding the information recording medium in a circumferential direction of the information recording medium, and a header portion formed of a prepit row that is deviated from the groove at a break of the groove. And the photoelectric conversion unit includes a plurality of light sensitive areas that receive the reflected light, and at least one of the dividing lines that divides the light sensitive area,
When the condensed spot obtained by being converged by the objective lens moves in the radial direction of the information recording medium, the direction is substantially perpendicular to the direction in which the reflected light moves on the photoelectric conversion means, Of the light diffracted by the information recording medium, at least a part of a portion where all of the 0th-order light component, the 1st-order light component, and the -1st-order light component overlap, and a portion including at least a part of the 0th-order light component A first light-sensitive region having a rectangular shape longer than the beam diameter of the reflected light in a direction parallel to the dividing line and receiving light, and located on both sides of the dividing line; Of the light diffracted by the medium, the light receiving part of the light protruding from the first light receiving area, and having a second light receiving area located on both sides of the dividing line, the first light Two areas separated by the dividing line of the sensitive area A signal obtained by amplifying or reducing one of the obtained photoelectric conversion signals by a predetermined value is divided by a first difference signal, which is a difference signal obtained by subtracting the other signal from the other signal, and the division line of the second light-sensitive region. The difference signal obtained by subtracting the signal obtained by amplifying or reducing the first difference signal by a predetermined value from the sum signal of the second difference signal, which is the difference signal between the photoelectric conversion signals obtained from the two regions, is obtained. It is an object to provide an optical head device characterized in that it is a signal.

Further, in the optical head device according to the present invention, the header signal has the signal levels L1 and L2 output from the two areas separated by the dividing line of the first light sensitive area, (L1−L2) pp indicates the maximum value of the amplitude of the difference signal between the first signal and the second signal as (L1 + L
2) Let a denote the sum signal of the first signal and the second signal for the reflected light beam reflected from the area of the recording surface where the information is not recorded and the area where the guide groove is not formed, respectively. 0.35 ≦ [(L1−L2) pp / (L1 + L2)
a], [(L1-L2) pp / (L1 + L2) a] ≦ 1.05, and [(L1-L2) / (L1 + L)
2)] pp, regardless of the presence or absence of information on the recording surface
The instantaneous value of the signal level (L1-L2) is converted to the signal level (L
1.10 ≦ [(L1−L2) / (L1 + L2)] pp, [(L1−L2) / (L1 + L2)] pp ≦ 1.65 and [(L1-L2) / (L1 + L2)]
[(L1-L2) / (L1 + L) indicating the maximum value of pp
2)] ppmax and [(L1-L2) / (L1 + L
2)] The minimum value of pp [(L1−L2) / (L1 +
L2)] ppmin, [(L1-L2) / (L1 + L2)] ppmin /
[(L1-L2) / (L1 + L2)] ppmax ≧ 0.
70, the difference signal between the output signals from the two regions is condensed by a condensing means for matching the center of the guide groove formed in advance on the recording surface of the recording medium with the center of the light beam passing through the condensing means. Is used as a track error signal that can be used for tracking control for moving in a direction crossing the guide groove.

Further, in the optical head device according to the present invention, the header portion is provided two each in the inner circumferential direction and the outer circumferential direction of the information recording medium with respect to the center of the groove.
The first header, the second header, the third header, and the fourth header are unevenly distributed, and the header signal indicates the _LVFO and the _VFO of the pre-pits constituting the header. Signal amplitude in the part, L _0
Let L _VFO / L ₀ ≧ 0.25 and L _{VFO be the} signal level in the mirror section where the information on the recording surface of the optical disc is not recorded, and L _{hmax be} the maximum value of the signal amplitude in the header section. / L _hmax ≧ 0.50, L _AMHD1 is the maximum value of the signal amplitude from the first header portion, L _AMHD2 is the maximum value of the signal amplitude from the second header portion, L _AMHD3 is The maximum value of the signal amplitude from the third header, and L
_{When AMHD4} is the maximum value of the signal amplitude from the fourth header portion, 0.9 ≦ _LAMHD2 / _LAMHD1 ≦ 1.1 0.9 ≦ _LAMHD4 / _LAMHD3 ≦ _1.10.8 ≦ L _AM13 / _LAMHD1 and 0.8 ≦ _LAM31 / _LAMHD3 and _LαHD1 are set to VF (not shown) when the condensed spot is on the groove with respect to the signal of the first header portion.
The level of the difference between the upper limit value of the signal from the O section and the upper limit value of the entire header signal, and when the condensing spot is on the land, the lower limit value of the signal from the VFO section not shown and the lower limit value of the entire header signal When the focused spot is on the groove with respect to the signal of the second header section, the difference level between the upper limit value of the signal from the VFO section (not shown) and the upper limit value of the entire header signal is _defined as L _αHD2. When the _focused spot is on the land, the level of the difference between the lower limit of the signal from the VFO unit (not shown) and the lower limit of the entire header signal, _LαHD3, is _set with respect to the signal of the third header unit. When the focused spot is on the groove, the level of the difference between the upper limit value of the signal from the VFO unit (not shown) and the upper limit value of the entire header signal, and when the focused spot is on the land, V is not shown. The lower limit of the signal from the O portion and the difference between the level of the lower limit value of the entire header signal, the L _ArufaHD4,
Regarding the signal of the fourth header portion, when the focused spot is on the groove, the level of the difference between the upper limit value of the signal from the VFO unit (not shown) and the upper limit value of the entire header signal, and the focused spot is located on the land , A VFO (not shown)
The level of the difference between the lower limit value of the signal from the unit and the lower limit value of the entire header signal, _LβHD1 , is determined from the VFO unit (not shown) when the focused spot is on the groove with respect to the signal from the first header unit. The level of the difference between the lower limit value of the signal of FIG. 1 and the lower limit value of the entire header signal, and when the light-collecting spot is on the land, the difference between the upper limit value of the signal from the VFO unit (not shown) and the upper limit value of the entire header signal Level, L
_βHD2 is set to a VFO (not shown) when the focused spot is on the groove with respect to the signal from the second header section.
Level of the difference between the lower limit of the signal from the unit and the lower limit of the entire header signal.
The level of the difference between the upper limit value of the signal from the VFO unit (not shown) and the upper limit value of the entire header signal, _LβHD3 , is not shown when the focused spot is on the groove with respect to the signal from the third header unit. The level of the difference between the lower limit value of the signal from the VFO unit and the lower limit value of the entire header signal. When the light-collecting spot is on the land, the upper limit value of the signal from the VFO unit (not shown) and the upper limit value of the entire header signal When the focused spot is on the groove with respect to the signal from the fourth header portion, the difference level L _βHD4 between the lower limit value of the signal from the VFO portion (not shown) and the lower limit value of the entire header signal is determined. The difference level, that is, the difference level between the upper limit value of the signal from the VFO unit (not shown) and the upper limit value of the entire header signal when the condensed spot is on the land, −0.1 ≦ (L _{βHD1 −LαHD1} ) / 2L _AMHD1 ≦ _0.1−0.1 ≦ ( _{LβHD2− LαHD2} ) _{/2LAMHD1≦0.1−0.1≦} ( _{LβHD3− LαHD3} ) / 2L _AMHD1 ≦ 0.1 and _{-0.1 ≦ (L βHD4 -L αHD4)} / 2L AMHD1 ≦ 0.1 is _satisfied, obtain a _{L HD1,} the light beam incident to the optical detector relative to the first header section by photoelectrically converting For the signal, the lower limit level of the amplitude, L _HD2, is set, and for the signal obtained by photoelectrically converting the light beam incident on the photodetector with respect to the second header portion, the lower limit level of the amplitude, L _{HD3, is set. For the} signal obtained by photoelectrically converting the light beam incident on the photodetector with respect to the third header portion, the lower limit level of the amplitude, L _{HD4, is} transmitted to the photodetector with respect to the fourth header portion. Entering For the signal obtained by photoelectrically converting the emitted light beam, the lower limit level of its amplitude,
| [(L _HD1 + L _HD2 ) − (L _HD3 +
L _HD4 )] / 2L ₀ | ≦ 0.05, and when the focused spot is offset by 0.1 μm from the center of the groove in the radial direction of the information recording medium, 0.15 ≦ | [(L _HD1 + L _HD2 ) − (L _HD3 +
L _HD4 )] / 2L ₀ |.

Further, according to the present invention, the wavelength is approximately 650.
A light source that emits a light beam of nm and a numerical aperture of approximately 0.6
In, a lens means for condensing a light beam emitted from the light source on a recording surface of a recording medium, and a photoelectric conversion means for converting a reflected light beam reflected and diffracted on the recording surface of the recording medium into an electric signal, The recording medium includes a spiral or a plurality of concentric guide grooves having a center-to-center distance defined to be approximately 1.48 μm, and information is provided approximately at the center of the guide grooves or between the guide grooves. Can be recorded, and when the condensed spot obtained by being converged by the lens unit moves in the radial direction of the recording medium, the photoelectric conversion unit reflects the reflected light reflected by the recording medium on the condensed spot. A photoelectric conversion area divided into a plurality of light receiving areas by at least one division line defined in a direction substantially orthogonal to a direction in which a beam is projected onto the photoelectric conversion means and moves. Wherein the light beam reflected and diffracted by the recording medium is subjected to photoelectric conversion by converting a light beam mainly or partly or entirely of a light beam in which only the zero-order light component and the first-order light component overlap. 1 of the light beam reflected and diffracted by the recording medium, and the light beam mainly composed of a part or all of the light beam in which only the 0th-order light component and the -1st-order light component overlap. The second signal is converted to generate a second signal, and the difference signal between the first signal and the second signal passes through the center of the guide groove formed in advance on the recording surface of the recording medium and the light condensing means. The present invention provides an optical head device characterized by using a track error signal that can be used for tracking control for moving the light condensing means in a direction crossing a guide groove so that the center of the light beam matches.

Further, the present invention provides a light source for emitting a light beam, a polarizing beam splitter for guiding the light beam emitted from the light source toward a recording medium, and a light beam passing through the polarizing beam splitter. An objective lens for giving a predetermined imaging characteristic to the recording medium and converging it on a recording surface of the recording medium; and a track control coil for generating a propulsive force for moving the objective lens in a direction orthogonal to a guide groove specific to the recording medium. The light beam converged on the recording surface of the recording medium by the objective lens, reflected on the recording surface, and passed again through the objective lens is separated from the light beam reflected by the polarizing beam splitter and traveling toward the objective lens. A non-polarizing beam splitter functioning as a half mirror for splitting the split light beam into two light beams having substantially equal light intensities, and a recording medium First and second two light receiving regions divided by a dividing line extending along a direction in which the shadow of the unique guide groove is projected, and the dividing line is provided in the first and second light receiving regions. And a first and a second linear light receiving area divided by a linear outer dividing line defined symmetrically with respect to the axis of symmetry. The light beam split by the beam splitter is received and photoelectrically converted to generate a track error signal indicating the degree of deviation between the center of the guide groove unique to the recording medium and the center of the light beam converged by the objective lens. A light beam irradiated by the first and second linear light receiving areas to a region where the 0th-order diffraction light, the 1st-order diffraction light, and the -1st-order diffraction light of the light beam reflected by the recording surface of the recording medium overlap each other. Receiving A photodetector that generates a signal corresponding to an offset component in a track error signal indicating a degree of deviation between the center of the guide groove specific to the recording medium and the center of the light beam converged by the objective lens. The first of this photodetector
Difference between two signals obtained by adding the outputs output from the first and second linear light receiving regions to the outputs output from the respective second light receiving regions based on a predetermined combination. The difference signal between the output signals output from each of the first and second linear light receiving regions is subtracted from the signal, and the center of the guide groove unique to the recording medium and the light beam converged by the objective lens are reduced. Based on a track shift and offset detection circuit for determining the actual degree of shift from the center and a track shift signal obtained by the track shift and offset detection circuit,
A tracking control circuit for supplying a current in a predetermined direction to the track control coil.

[0028]

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

FIG. 1 is a block diagram schematically illustrating an optical disk device in which an optical head device according to an embodiment of the present invention is incorporated.

As shown in FIG. 1, the optical disk device 1
Is an optical head device 3 for recording information on a recording surface of an optical disk D as a recording medium or reading information already recorded on the recording surface, and a signal corresponding to information to be recorded on the optical head device 3. And a control unit 9 that controls a motor 7 that rotates the optical head device 3 and the optical disc D at a predetermined speed. Have. An external device 99 such as a host computer is connected to the signal processing unit 5 via an interface (not shown).

In FIG. 1, the optical head device 3 transmits and receives electric signals to and from the signal processing unit 5 while controlling the irradiation position of the laser beam irradiating the optical disc D by the control signal from the control unit 9. A laser beam is exchanged with the optical disk D.

The signal processing unit 5 converts the information read from the optical disk D by the optical head device 3 into an electric signal based on an instruction from the external device 99, and reproduces the information as recorded information. A recording signal is generated to make the information to be recorded correspond to the change in the light intensity of the laser beam emitted from the optical head device 3.

The controller 9 controls the light intensity of the laser beam emitted from the optical head device 3 to the optical disk D, the position of the laser beam on the optical disk, the rotation speed of the optical disk D rotated by the motor 7, and the like.

Hereinafter, the operation of the optical disk device 1 shown in FIG. 1 will be briefly described.

First, the signal processing unit 5 receives a command signal for reproducing or recording information on the optical disk D from the external device 99.

Based on this command signal, the signal processing unit 5
Exchanges electrical signals with the optical head device 3 and transmits control signals to the control unit 9.

On the basis of the transmitted control signal, the control unit 9 controls the optical disk D irradiated by the optical head device 3.
And the rotation speed of the motor 7 are controlled.

As described above, the optical head device 3 transmits and receives a laser beam to and from the optical disc D based on the electric signal exchanged with the signal processing unit 5 under the control of the control unit 9. To reproduce or record information.

When the information is reproduced or recorded, the optical head device 3 obtains an electric signal corresponding to the information recorded on the optical disk D and the information on the laser beam irradiation position, and converts the electric signal into a signal processing unit. 5 is transmitted.

The signal processing section 5 sends a control signal for changing the position of the optical head device 3 to the control section 9 based on the electric signal corresponding to the information on the laser beam irradiation position from the electric signal, and sends the control signal to the optical disk D. After performing processing such as decoding on the electric signal corresponding to the recorded information,
The processed electric signal (reproduced signal) is transmitted to an external device 99.
Transmit to

The external device 99 that has received the reproduction signal from the signal processing unit 5 refers to the reproduction signal and refers to the optical disk device 1.
Then, the instruction signal as the next instruction is transmitted to the signal processing unit 5 again.

The optical disc apparatus 1 reproduces information recorded on the optical disc D or records information on the optical disc D by repeating a series of operations as described above.

Next, the structure of the optical head device 3 will be described with reference to FIGS.

As shown in FIG. 2, the optical head device 3
Are a laser light emitting / receiving unit (hereinafter, referred to as a fixed optical system) 3a fixed on the base 31 and a fixed optical system 3a
And an actuator 3b for irradiating the recording surface of the optical disk D with the laser beam from the optical disk D and guiding the reflected laser beam reflected on the recording surface of the optical disk D again to the fixed optical system 3a. The actuator 3b includes, as shown in FIG. 3, a carriage 33 movably formed on a pair of guide rails 32, 32 extending in the radial direction of the optical disc D, and is integrally formed with the carriage 33. The guide rails 32, 34 are formed by a pair of radial drive coils 34, 34 and a magnetic field supplied from a magnetic field supply mechanism (not shown).
32 is formed so as to be movable in the radial direction of the optical disc D.

The fixed optical system 3a has a housing 10 made of, for example, aluminum, as shown in FIG.

A predetermined wavelength,
For example, a laser device (semiconductor laser) 1 that generates a laser beam of approximately 650 nanometers (hereinafter, referred to as nm)
1 is fixed.

The divergent laser beam Rf is emitted in the direction in which the laser beam Rf emitted from the semiconductor laser 11 travels.
A collimator lens 12 for collimating f is arranged.

In the direction in which the laser beam Rf collimated by the collimator lens 12 is guided, the cross-sectional beam shape of the laser beam Rf emitted in an ellipse is changed from an ellipse to a circle in relation to an aspect ratio specific to the laser beam Rf. The elliptical correction prism 13 to be corrected and the laser beam Rf formed integrally with the elliptical correction prism 13 and having a substantially circular cross-sectional shape are passed toward the actuator 3b, that is, the optical disk D, and are reflected by a recording surface (not shown) of the optical disk D. A beam splitter 14 for separating the reflected laser beam Rr from the laser beam Rf heading toward the optical disk D and a direction of the polarization plane of the laser beam Rf passed through the beam splitter 14 and directed to the actuator 3b from linear to circular polarization. And reflected on the optical disc D Direction of polarization direction of the polarization plane of the reflected laser beam Rr which the circular polarization to the direction of the plane of polarization of the laser beam Rf directed to actuator 3b is 90
A λ / 4 plate (phase delay plate) 15 for converting into linearly polarized light rotated by ° is arranged in order. Note that the beam splitter 14 is a polarization beam splitter.

The optical disk D is controlled by the beam splitter 14.
In the direction in which the reflected laser beam Rr separated from the laser beam Rr traveling toward
With two further reflected laser beams Rra and Rrb
Half-mirror type beam splitter 16
Is arranged.

In the direction in which one of the two reflected laser beams Rra split by the beam splitter 16 is guided, a converging lens 17 for providing the reflected laser beam Rra with predetermined imaging characteristics and convergence is arranged. I have.

In the direction in which the reflected laser beam Rra given convergence and predetermined imaging characteristics by the converging lens 17 travels, the reflected laser beam Rra
Lens 1 for improving aberration due to convergence given to lens
8. Reflected laser beam Rra passed through concave lens 18
Next, a cylindrical lens 19 for providing a predetermined imaging characteristic for detecting a focus shift described later, a reflected laser beam Rra given a predetermined imaging characteristic by the cylindrical lens 19, and the reflected laser beam Rra The photodetectors 20 that output output signals corresponding to the light intensities are arranged in order.

In the direction in which the reflected laser beam Rrb split into two by the beam splitter 16 is guided, a mirror 21 for guiding the reflected laser beam Rrb reflected on the optical disk D in a predetermined direction is arranged.

In the direction in which the reflected laser beam Rrb bent by the mirror 21 travels, a converging lens 22 for giving a predetermined convergence to the reflected laser beam Rrb is arranged.

In the direction in which the reflected laser beam Rrb having a predetermined convergence given by the converging lens 22 is guided, a photodetector 23 used for detecting a track shift and an offset amount described later is arranged. I have.

The carriage 33 of the actuator 3b has
As shown in FIG. 5, the laser beam Rf emitted from the fixed optical system 3a after passing through the beam splitter 14 and the λ / 4 plate 15 of the fixed optical system 3a is bent so as to be incident on an objective lens described below. A rising mirror 35 is provided.

The predetermined direction of the recording surface of the optical disk D is set between the direction in which the laser beam Rf guided by the rising mirror 35 and bent by approximately 90 ° by the rising mirror 35 is directed, that is, between the rising mirror 35 and the optical disk D. An objective lens 36, which is bent by the rising mirror 35 to converge the laser beam Rf and takes out the reflected laser beam Rr reflected by the recording layer of the optical disc D, is arranged on the recording layer (not shown).

The objective lens 36 is moved in a direction parallel to the recording surface of the optical disk D described in detail later with reference to FIG. The optical disc D is held so as to be movable in a tracking direction substantially orthogonal to a guide groove or groove g formed in advance and a focus direction orthogonal to a recording surface of the optical disc D.

The objective lens 36 is a semiconductor laser 1
For the wavelength 650 nm of the laser beam emitted by 1,
An aperture ratio of approximately 0.6 is given, and the focal length Fo
Is Fo = 3.3 mm, the effective diameter is about 4 mm, and provides a focused beam spot diameter of about 0.0XX mm on the recording surface of the optical disc D. The size of a recording mark, ie, a pit, formed on the optical disc D is 0.4 to 0.44 μm in pit width (in the direction perpendicular to the groove).
m, pit length (in the direction along the groove) 0.63 μm or 0.84 μm, pit depth approximately 0.7 μm,
The interval between the pits in the groove direction is approximately 0.74 μm. As the optical disk D, a substrate having a thickness of 0.6 mm is used. The usable wavelength of the laser beam is, for example, 635 to 685 nm.

As shown in FIG. 5, the lens holder 37
Has a bearing portion 37a substantially at the center, and a lens holding surface 37b holding the objective lens 36 on a circumference of a concentric circle having a predetermined radius centered on the bearing portion 37a, and a direction perpendicular to the lens holding surface 37b. A bearing portion 37a is provided on a shaft 39 having a cylindrical surface 37c formed in a partially cut-out cylindrical shape, and extending substantially from the center of a lens holder base 38 fixed at a predetermined position of the carriage 33. By being engaged, it is formed to be rotatable around the shaft 39.

The two sets of coils 4 are provided on the cylindrical surface 37c of the lens holder 37 at positions defined so as to divide the outer periphery of the cylindrical surface 37c into approximately four equal parts along the axis passing through the bearing 37a.
0, 40 and 41, 41 are provided.

The lens holder base 38 has a cylindrical shape at an arbitrary radius whose radius is increased compared to the cylindrical surface 37c of the lens holder 37 with the axis 39 as the center axis and corresponding to the circumference of the concentric circle. A yoke 42 having a notched portion is formed. At a predetermined position on the inner wall of the yoke 42, two sets of magnets 43, 43 and 44, which provide a magnetic field in a predetermined direction toward the cylindrical surface 37c of the lens holder 37,
44 are provided. The magnets 43, 43 are magnetized to have N and S poles in a form that is divided into two by a plane orthogonal to the optical axis of the objective lens 36. The N and S poles are magnetized in such a manner that the N and S poles are divided into two parts by a plane parallel to.

Next, the flow of the laser beam in the optical head device 3 described with reference to FIGS. 2 to 5 will be described.

The laser beam Rf emitted from the semiconductor laser 11 is converted into a parallel light beam by the collimator lens 12, the cross-sectional shape is corrected to a substantially circular shape by the elliptical correction prism 13, and the laser beam Rf passes through the beam splitter 14.

The laser beam Rf transmitted through the beam splitter 14 passes through the quarter-wave plate 15 so that the polarization direction is changed from linearly polarized light to circularly polarized light, and is emitted toward the rising mirror 35 of the actuator 3b. Is done.

The laser beam Rf guided to the rising mirror 35 is bent by approximately 90 ° by the rising mirror 35 and guided to the objective lens 36 held by the lens holder 37.

The laser beam Rf is guided to the objective lens 36 and converged, and then radiated to the optical disc D as a spot.

The laser beam R applied to the optical disc D
f is a guide groove on the recording surface of the optical disc D, that is, a groove g.
The reflected laser beam Rr reflected by the objective lens 36
Then, the rising mirror 35 is sequentially returned, and the polarization state is converted from circularly polarized light to linearly polarized light again by the １ ／ wavelength plate 15 and guided to the beam splitter 14. The polarization direction of the reflected laser beam Rr is exactly 90 degrees with respect to the polarization direction of the initial laser beam Rf emitted from the semiconductor laser 11.
か ら Since the laser beam is rotated in different directions, the reflected laser beam Rr is reflected by the polarization plane of the beam splitter 14 this time.

The reflected laser beam Rr separated from the laser beam Rf from the semiconductor laser 11 toward the objective lens 36 by the beam splitter 14 is converted into two reflected laser beams Rra and Rrb having substantially equal light intensities by the beam splitter 16. Is divided.

The reflected laser beam Rra transmitted through the beam splitter 16 is given a predetermined image forming characteristic and convergence by the converging lens 17, then the aberration characteristic is improved by the concave lens 18, and the defocus is detected by the cylindrical lens 19. The photodetector 20 is irradiated with astigmatism for

The reflected laser beam Rra applied to the photodetector 20 is converted by the photodetector 20 into an electric signal having a magnitude corresponding to the light intensity, and is used as a focus error signal and a reproduction signal. In this example, the detection of the focus error signal is a well-known astigmatism method, and a detailed description thereof will be omitted.

On the basis of the focus error signal generated by the photodetector 20, focus control, ie, focusing, is performed to eliminate a deviation between the focal point of the spot converged by the objective lens 36 and the recording surface of the optical disk D in the optical axis direction. You. In focusing, the coils 40, 40 are controlled based on the focus error signal.
Is supplied with a current in a predetermined direction, so that the magnets 43, 4
As a result of the attraction or repulsion due to the electromagnetic interaction with the magnetic field provided by 3, the lens holder 37 (objective lens 36) is moved either in a direction toward or away from the recording surface of the optical disc D.

The remaining reflected laser beam Rrb reflected by the beam splitter 16 passes through the optical path 9
It is bent by 0 °, given a predetermined convergence by the converging lens 22, and guided to a photodetector 23 used for detecting a track shift and an offset amount. In addition,
The photodetector 23 includes two light receiving regions 24a and 24b and two more light receiving regions 23a and 23b surrounding the outside as shown in FIG.

The two light receiving areas 2 of the photo detector 23
Each of the signals photoelectrically converted by 3a and 23b is used for generating a track shift signal by applying a well-known push-pull method, as will be described later in detail with reference to FIG. Each signal photoelectrically converted by the other two light receiving regions 24a and 24b is similarly applied to a well-known push-pull method, and is used to generate a signal indicating the degree of an offset component included in the track shift signal. .

A track error signal is generated by the signal processing unit shown in FIG. 8 based on the track shift signal and the offset signal generated by the photodetector 23.
Track control, that is, tracking, is performed to eliminate a deviation between the focus of the spot converged by the objective lens 36 and the center of the groove g on the recording surface of the optical disc D. In the tracking, current is supplied to the coils 41, 41 in a predetermined direction based on a track shift signal, which is a difference between outputs of the light receiving areas 23a and 23b of the photodetector 23, so that the magnets 44, 44 provide the tracking. As a result of attraction or repulsion due to electromagnetic field interaction with the applied magnetic field, the lens holder 37 (objective lens 36) is shifted toward the center of the optical disc D in the radial direction in the direction orthogonal to the groove g along the recording surface of the optical disc D or the outer periphery. Moved closer to one. Also, the magnitude of the current supplied to the coils 41, 41 is corrected based on the offset signal, which is the difference between the outputs of the two light receiving regions 24a and 24b.

By the way, an optical disk (DVD) for high-density digital recording, which has a higher recording density than the conventionally used music optical disk (CD) and also records video information, has been put into practical use. A DV capable of writing and reproducing information at the same recording density as DVD
A D-RAM (having a groove g and a distance between grooves of about 1.48 micrometers (hereinafter referred to as μm) is being put to practical use, and the distance between adjacent grooves g has been reduced. , The occurrence of the offset,
Since the crosstalk between the adjacent groove g is increased, the offset component included in the track shift signal must be reliably removed. The two light receiving areas 24a and 24 near the center of the photodetector 23
Since b corresponds to the high intensity portion of the 0th-order diffracted light component, it is useful for correcting the offset component included in the track shift signal obtained by the photodetector 23.

More specifically, the 0th-order diffracted light of the reflected laser beam Rrb applied to the photodetector 23 has an outer peripheral portion blurred by the objective lens 36, but as described below with reference to FIG. Since the laser beam substantially corresponds to the center of the laser beam, it has a sufficient light intensity.

That is, although the light receiving areas of the two light receiving areas 24a and 24b near the center of the photodetector 23 are smaller than the light receiving areas of the light receiving areas 23a and 23b, for example, the light receiving areas 24a and 24b near the center respectively.
Is obtained even if the center of the groove g is slightly deviated from the reflected laser beam Rrb passing through the center of the objective lens 36.
This is reflected as a sharp increase or decrease in one of the outputs 4a and 24b. Here, the width of the light receiving area, which defines the area of the light receiving areas 24a and 24b, that is, the distance from the division line, depends on the specifications of the optical disk D, the wavelength of the laser beam Rf emitted from the semiconductor laser 11, the aperture ratio of the objective lens 36, and the result. It is easily obtained from the image characteristics and the optical design specifications of the fixed optical system 3a. As an example, when the center-to-center (inter-interval) distance of the grooves g formed on the recording surface of the optical disk D is approximately 1.48 μm, the beam spot diameter of the reflected laser beam reflected by the optical disk D (0 (Original light component). Note that this setting enables information to be recorded either between the grooves g or at the center of the groove g when information is recorded on the recording surface of the optical disc D.

The offset signal obtained in this manner is applied to the light receiving areas 23a and 23a of the photodetector 23.
Correcting the position of the objective lens 36 by subtracting from the track shift signal output by b to generate a corrected track shift signal, that is, a track error signal, enables proper track control.

As a result, the reflected laser beam Rrb passing through the center of the objective lens 36 and the groove g of the optical disc D
Can be matched exactly.

FIG. 6 shows, for example, that the 0th-order diffraction light, 1st-order diffraction light and -1st-order diffraction light of the reflected laser beam Rr reflected on the recording surface of the high-density optical disk D represented by a DVD-RAM disk are objective lenses. It is a schematic diagram which roughly explains the state guide | guided to 36.

As shown in FIG. 6, the reflected laser beam Rr reflected by the groove g on the recording surface of the optical disc D
Are the 0th-order diffracted light that passes through substantially the entire area of the objective lens 36, the 1st-order diffracted light that partially overlaps the 0th-order diffracted light, and −
The light is incident on the objective lens 36 as an aggregate of the first-order diffracted light, the high-order diffracted light including the second-order not shown, and the high-order diffracted light including the second-order.

As is apparent from FIG. 6, each of the first-order diffracted light and the −1st-order diffracted light has a portion that overlaps with the zero-order diffracted light. That is, as described above, the DVD-R
In a high-density optical disc for AM, a well-known music C
Since the distance between adjacent grooves g is smaller than that of D and the like, each of the first-order diffracted light and the -1st-order diffracted light partially overlaps with the 0th-order diffracted light, and furthermore, a part of each other overlap. In a region where the 0th-order diffracted light, the 1st-order diffracted light, and the -1st-order diffracted light each overlap, the 0th-order diffracted light is a laser beam substantially corresponding to the center of the reflected laser beam Rr as described above. Since there is intensity, when the lens shift occurs, a sharp change in light intensity in each of the region where the 0th-order diffraction light and the 1st-order diffraction light overlap and the region where the 0th-order diffraction light and the -1st-order diffraction light overlap each other. Can be provided.

More specifically, since each of the 0th-order diffracted light, the 1st-order diffracted light, and the -1st-order diffracted light is partially blocked by the opening of the objective lens 36, only a part of the reflected laser beam Rr is Through the fixed optical system 3a.

That is, the zero-order diffracted light is guided to the two light receiving areas 23a and 23b of the photodetector 23 shown in FIG. On the other hand, the first-order diffracted light and the -1st-order diffracted light respectively enter the two light receiving regions 23a and 23b of the photodetector 23 while overlapping with the 0th-order diffracted light. That is, a difference between the photoelectric conversion signals from the two light receiving regions 23a and 23b is a track shift signal.

Accordingly, if there is a condensed spot at a position where the center of the condensed spot of the laser beam converged on the optical disc D by the objective lens 36 and the center of the groove g, the radial direction of the groove g Since a symmetrical diffracted light is generated, the difference signal between the output signals from the two light receiving areas is at the 0 level, and if they do not match, the intensity of one of the diffracted lights increases, and the difference signal level becomes 0 Will shift.

FIG. 7 is a plan view showing the light receiving surface of the photodetector 23.

As shown in FIG. 7, the photodetector 23
Are used for generating the track error signal of the present embodiment, and the two light-receiving regions 23a and 23b divided by the dividing line 23c and the linear dividing line 23d set with the dividing line 23c as the axis of symmetry. Strip-like light receiving areas 2 arranged symmetrically with respect to the dividing line 23c by the lines 23e and 23e
4a and 24b. Note that the band-shaped light receiving region 24
The division lines 23d and 23e defined on the opposite sides of the division lines 23a and 23b of the reflection laser beams a and 24b are the reflection laser beams in the region where all of the 0th-order diffraction light, the 1st-order diffraction light, and the -1st-order diffraction light of the reflection laser beam Rr overlap. Part or all are formed so as to be capable of photoelectric conversion. Also, the dividing line 23c is
Are arranged so as to be substantially parallel to the direction in which the shadow of the groove g is projected.

FIG. 8 is a schematic block diagram showing an example of a signal processing unit and a control unit which can be used for the signal processing unit 5 and the control unit 9 of the optical disk device 1 shown in FIG.

As shown in FIG. 8, the signal processing section 5 is connected to the main control circuit 50, and reproduces information recorded on the optical disk D based on outputs from four light receiving areas (not shown) of the photo detector 20. The information reproducing circuit 51 is provided. The information reproducing circuit 51 includes, for example, a threshold circuit (not shown), a binarizing circuit, a data expanding circuit, a buffer memory, and the like. The information reproducing circuit 51 includes a current-voltage converting circuit, a differential amplifier, and an adder described in detail later. The information corresponding to the output from each light receiving area converted into a signal is output to the external device 99 via the main control circuit 50.

On the other hand, the control section 9 comprises a linear motor control circuit 61 for supplying a current in a predetermined direction to the radial drive coil 34 for moving the actuator 3b in the radial direction of the optical disc D, and an objective lens 36 for controlling the recording surface of the optical disc D. A focus error detection circuit 62 for setting a current value to be supplied to the two coils 40, 40 on the cylindrical surface of the lens holder 37 in order to move in a direction perpendicular to the direction of movement of the lens holder 37, and removing a focus error detected by the focus error detection circuit 62. And a focus control circuit 63 for supplying a focus control current to the coils 40 and 40, and the cylindrical surface of the lens holder 37 for moving the objective lens 36 in a direction intersecting the tangent to the groove g on the recording surface of the optical disc D. Track offset and offset for setting the current value to be supplied to the two coils 41, 41 The detection circuit 64, a coil in order to remove the outputted track deviation and offset from the track deviation and offset detection circuit 64 41,
It has a track control circuit 65 for supplying a track control current and a laser drive circuit 66 for setting the light intensity of the laser beam emitted from the semiconductor laser 11 to a predetermined intensity. Each circuit is connected to the main control circuit 50.

The information reproducing circuit 51 is connected to each of the four light receiving areas (not shown) of the photodetector 20 and converts the output current output from each light receiving area into a voltage. The added output of the adder 72 for obtaining the sum of the voltage signals output from each of 71a to 71d is input.

The focus error detection circuit 62 includes the first
And first and second differential amplifiers 73a and 73a for obtaining a differential output between two predetermined outputs among the output voltages output from the fourth to fourth current-voltage converters 71a to 71d.
An output obtained by adding each output of 73b by an adder 74 is input.

Track deviation and offset detection circuit 6
4 and the linear motor control circuit 61 respectively have light receiving areas 23a, 24a and 2a of the photodetector 23.
A signal obtained by subjecting the current output from each of 3b and 24b to current-to-voltage conversion by each of the fifth to eighth current-to-voltage converters 81a to 81d, and processing the resulting signal by a predetermined combination. A signal is input. As shown in the figure, an example of the combination is the output from the light receiving area 23a of the photodetector 23, that is, the fifth output.
Of the current-to-voltage converter 81a, the output from the linear light receiving region 24a, that is, the sixth current-to-voltage converter 81a
b is added to the output of adder 82a and light receiving area 2
3b, that is, the seventh current-voltage converter 81c
The output from the linear light receiving region 24b, that is, the output obtained by adding the output of the eighth current-voltage converter 81d to the output of the eighth current-voltage converter 81d by the adder 82b is subtracted by the differential amplifier 83 to generate a first difference signal. , The difference between the outputs of the two linear light receiving regions 24a and 24b by the differential amplifier 84, ie, the sixth and seventh outputs.
Of the outputs of the current-voltage converters 81b and 81c of
The first amplifier generated by the differential amplifier 83 by the differential amplifier 85
, And a second difference signal obtained by calculating the difference between the difference signal and the output of the differential amplifier 84 is input.

As described above, according to the optical head device 3 shown in FIGS. 2 to 7, the track deviation of the objective lens 36 is different from the output from the light receiving area 23a of the photodetector 23 added by the adder 82b. A differential amplifier 84 is obtained from a first difference signal obtained by subtracting the output from the light receiving region 23b of the photodetector 23 added by the adder 82a from the output from the linear light receiving region 24a and the output from the linear light receiving region 24b. The difference between the outputs of the two linear light receiving regions 24a and 24b near the center of the photodetector 23 obtained by the above is displayed by a second difference signal obtained by subtraction by the differential amplifier 85.

Since the above-described embodiment can be applied to the optical disk for DVD-RAM as described above, the first difference signal is obtained from the output of the adder 82b and the output of the adder 82a. The output level of the differential amplifier 83 is L1, the output level of the second difference signal output from the differential amplifier 84 is L2, and the maximum value of the amplitude of the first difference signal and the second difference signal is (L1 -L2) pp, the sum signal of the first difference signal and the second difference signal with respect to the reflected light beam reflected from the area where the information on the recording surface of the optical disc D is not recorded and the area where the groove g is not formed; (L1 + L
2) Assuming a, 0.35 ≦ [(L1−L2) pp / (L1 + L2)
a], [(L1−L2) pp / (L1 + L2) a] ≦ 1.05.

The maximum value of the amplitude obtained by dividing the instantaneous value of the signal level (L1−L2) by the instantaneous value of the signal level (L1 + L2) regardless of the presence or absence of information on the recording surface of the optical disc D is [ (L1-L2) / (L1 + L
2)] pp, 1.10 ≦ [(L1−L2) / (L1 + L2)] pp, [(L1−L2) / (L1 + L2)] pp ≦ 1.65. Further, [(L1-L2) / (L1 + L
2)] indicates the maximum value of pp [(L1-L2) / (L1 +
L2)] ppmax and [(L1-L2) / (L1 + L
2)] The minimum value of pp [(L1−L2) / (L1 +
L2)] ppmin, [(L1-L2) / (L1 + L2)] ppmin /
[(L1-L2) / (L1 + L2)] ppmax ≧ 0.
70 are satisfied.

As described above, the track shift amount obtained by the differential amplifier 83 and the offset amount detected by the differential amplifier 84 are calculated by the track shift and offset detection circuit 64, so that the objective lens 36
Due to the lens shift described above, it is possible to compensate for the offset amount that behaves as a track error, that is, the influence of the offset component included in the track shift signal.
Therefore, crosstalk in a high-density optical disk represented by an optical disk for DVD and DVD-RAM can be significantly reduced. The combination of the outputs of the adder and the differential amplifier described above is obtained, for example, by adding the outputs of the fifth and eighth current-voltage conversion circuits 81a and 81d by the differential amplifier 86 as shown in FIG. The output of the differential amplifier 84 may be removed again by the differential amplifier 85 from the signal obtained by adding the output signal obtained and the output signal obtained by the differential amplifier 84 by the adder 87.

FIGS. 10 and 11 are graphs showing an output from the photodetector shown in FIG. 7 and a track error signal provided from the signal processing unit and the control unit shown in FIG. 8, respectively.

As is clear from FIG. 11, the offset component included in the track shift signal output from the light receiving regions 23a and 23b of the photodetector 23 using the outputs of the linear light receiving regions 24a and 24b of the photodetector 23. , Track shift and offset detection circuit 64
As a result, the center value of the track shift signal input to the track control circuit 65 approaches 0 as compared with the conventional track error signal including the influence of the lens shift indicated by the dotted line in FIG. Is recognized.

FIG. 12 is a schematic block diagram showing another example of the signal processing unit and the control unit shown in FIG.

As shown in FIG. 12, between the differential amplifier 84 and the differential amplifier 85, a gain controller 88 for matching the output signal level between the output of the differential amplifier 83 and the differential amplifier 84 is provided. The magnitude of the offset component included in the track shift signal is as if the offset was caused by the difference between the output signal levels of the central light receiving areas 24a and 24b of the photodetector 23 and the output signal levels of the outer light receiving areas 23a and 23b. It is possible to prevent an output that is generated or not present from being output.

FIG. 13 is a schematic block diagram showing another example of the signal processing unit and the control unit shown in FIG.

As shown in FIG. 13, a gain controller 89 is provided for either the output of the sixth or seventh current-voltage conversion circuit 81b or 81c for converting the output of each of the light receiving regions 24a and 24b from current to voltage. By connecting, it is possible to correct a difference in output level caused by an area difference between the light receiving regions 24a and 24b or an assembly error inherent to the optical head device 3.

By using the signal processing unit and the control unit shown in FIG. 13, the offset component contained in the track error signal
It is as if an offset is generated or present due to a difference between the areas generated when the 4a and 24b are manufactured or a difference between the output signals of the respective light receiving regions due to an error in assembling inherent to the optical head device 3. It is possible to prevent the output that does not occur from being output.

FIG. 14 is a schematic block diagram showing another example of the signal processing unit and the control unit shown in FIG.

As shown in FIG. 14, a gain controller 88 for matching the output signal level between the output of the differential amplifier 83 and the differential amplifier 84 is provided between the differential amplifier 84 and the differential amplifier 85. , And light receiving areas 24a and 2
By connecting a gain controller 89 to either the output of the sixth or seventh current-voltage conversion circuit 81b or 81c for current-voltage conversion of each output of the light-receiving regions 24a and 24b, It is possible to correct a difference in output level caused by a difference in area or an error during assembly peculiar to the optical head device 3. That is, the magnitude of the offset component included in the track error signal depends on the output signal level of the photodetector 23,
The output as if an offset has occurred or does not exist is output, and the offset component included in the track error signal is
It is as if an offset is present or present as a result of a difference in area between the two light receiving regions due to manufacturing reasons or a difference in output signals of the respective light receiving regions due to an assembly error inherent to the optical head device 3. It is possible to prevent the output that does not occur from being output.

FIGS. 15 and 16 are graphs showing an output from the photodetector shown in FIG. 7 and a track error signal provided by the signal processing unit and the control unit shown in FIG. 14, respectively.

As is apparent from FIG. 16, the offset components included in the track shift signals output from the light receiving regions 23a and 23b of the photodetector 23 using the outputs of the linear light receiving regions 24a and 24b of the photodetector 23. , Track shift and offset detection circuit 64
Further, the difference between one area and the other area of the light receiving regions 23a and 23b of the photodetector 23, the deviation of the output level inherent to the optical head device 3, and the light receiving regions 23a and 23b and the linear light receiving region 2
Eliminating the output associated with an element that apparently changes the magnitude of the output level, such as due to the difference in output level between 4a and 24b, includes the effect of lens shift shown by the dotted line in FIG. Compared with the conventional track error signal, the center value of the track shift signal input to the track control circuit 65 can be approximated to almost zero.
In FIG. 16, the vertical axis represents the level of the tracking error signal, and the levels of 1.0 and −1.0 indicate that all the light incident on the optical disc D
This corresponds to the case where all light is incident on one of the two light-sensitive regions of the photodetector when reflected by the light detector. As is apparent from this figure, when a conventionally used photodetector is used, it can be reconfirmed that a large track offset occurs due to the addition of a lens shift.

Next, the application of the photodetector having the divided areas shown in FIG. 7 and the signal processing system shown in FIG. 14 to the land / groove recording method will be described in detail.

In the land / groove recording method, in the pit row on the optical disk D, as shown schematically in FIG. 17, the header portion is shifted to the inner peripheral side and the outer peripheral side by a quarter of the groove pitch. In this state, two sets each are formed, for a total of four sets.

From this, as described above, since a deviation component caused by a lens shift, that is, a component which may be discriminated as any of the above-described track offset and fake track shift signal is included,
The original deviation components must be clearly separated.

That is, in the optical disk D on which information is recorded by the land / groove recording method, if the condensed spot is, for example, on the groove, the first and second header portions shown in FIG. , ID2) appear as a waveform having a positive polarity, for example, and the third and fourth header portions (ID3, ID3, respectively)
(Referred to as ID4) appears as a waveform having a negative polarity. If the focused spot is on the land, the reproduced signals from IDI and ID2 appear as waveforms having a negative polarity, and the reproduced signals from ID3 and ID4 appear as waveforms having a positive polarity.

Therefore, when a track shift signal is obtained by a well-known four- or two-part photodetector in a state where a lens shift is added, a reflected laser beam is incident in an asymmetrical positional relationship with respect to the division line of the photodetector. Thus, a large difference occurs between the two signal levels obtained. The amplitude of the header signal is
Curves a and b in FIG. 18 show the results of a simulation of how this changes as the lens shift increases.
In FIG. 18, the curve a indicates that the pit length is 0.64.
The curve b shows the case where the pit length is 0.83 μm. The curves a and b in FIG.
Indicates either ID1 or ID2 or ID3 or ID4. If the header portion is the opposite, the output is a graph symmetrically moved with respect to the vertical axis in FIG. The calculation conditions used for the simulation are as follows: wavelength λ of the laser beam from the semiconductor laser = 660 nm, numerical aperture of the objective lens 0.60, groove pitch of the optical disk 1.48 μm.
m, pit width (average value) 0.74 μm, pit depth 70
nm and the thickness of the optical disc are set to 0.6 mm. The interval between pits is the same as the length of the pit.

On the other hand, by using the four-divided photodetector shown in FIG. 7 and the signal processing system shown in FIG. 14, the change in the amplitude of the header signal as shown by the curves A and B in FIG. It recognized. Note that curve A
Indicates a case where the pit length is 0.64 μm, and a curve B indicates a case where the pit length is 0.83 μm.

As is apparent from FIG. 18, even though a lens shift is added to achieve a high-speed seek, the change in the relative amplitude is 1 compared to curves a and b.
/ 2 or less.

Hereinafter, the reason why the change in the relative amplitude can be improved as shown in FIG. 18 will be described.

When the pit rows of the groove and the header portion of the optical disc D are arranged as shown in FIG. 17, the pits are unevenly distributed toward the inner or outer circumference when viewed from the center of the groove. , The majority of the AC component in the header signal is obtained as a change in the intensity of the diffracted light due to a substantially half on the inner circumference side or a substantially half on the outer circumference side of the focused spot.

When the lens shift is added, as described above, the reflected laser beam from the optical disk D guided to the detection surface of the photodetector is applied to the photodetector 2.
On 3, the center of the light intensity of the zero-order diffracted light is deviated.

However, as described with reference to FIG. 14 (FIG. 8), the output of the area where all of the 0th-order diffracted light, the 1st-order diffracted light, and the -1st-order diffracted light are not used for detecting the track shift. Even if the center of the light intensity of the 0th-order diffracted light of the reflected laser beam incident on the photodetector 23 is displaced due to the addition of the lens shift, the amount of displacement is two light receiving regions 24a from the center. , 24b, there is almost no influence of the lens shift on the header signal. The two light receiving areas 2
4a, 24b, that is, the distance between the dividing lines 23d and 23e is preferably about 1/3 of the diameter of the focused spot circle provided by the 0th-order diffracted light, as described above, for example, about 0.001 mm. Is set. The header signal is obtained, for example, from the output of the adder 85 of the signal processing unit shown in FIG. 14 or FIG.

FIG. 19 shows, for comparison, a well-known two-segment photodetector (not shown) divided in a direction perpendicular to and parallel to the shadow of the groove projected on the photodetector, and the magnitude of the lens shift is indicated by “ 0 "
Is a graph showing the result of calculating the variation of the header signal, where curve h represents the output of the header signal and curve r represents the output from the two detection areas located on the right side with respect to the groove shadow projected on the photodetector as the axis of symmetry. The curve l represents the sum or signal of the outputs from the two detection areas located on the left side with respect to the symmetry axis of the groove shadow projected on the photodetector, and the curve s represents the output or signal of all the detection areas. The sum is shown. The horizontal axis represents the position of the light spot when the light spot traces some pits, and the vertical axis represents the level of the reproduced signal as a relative value. 21 and 23.
Are obtained by adding, to the conditions shown in FIG. 19, the condition that the magnitude of the lens shift is 10% of the aperture ratio of the objective lens and that the lens shift is located on the inner circumferential side and the outer circumferential side of the groove. 6 is a graph showing a calculated value obtained by calculating the magnitude of the variation of the header signal of FIG.

FIG. 20 shows a lens shift using outputs of two detection areas outside the photodetector divided into four parts parallel to the shadow of the groove projected on the photodetector according to the embodiment of the present invention shown in FIG. The size of "0"
7 is a graph showing a result of calculating a fluctuation of a header signal as a result. The conditions indicated by each curve are as follows: curve h is the output of the header signal; curve r is the output signal from the detection area 23b located on the right side with the shadow of the groove projected on the photodetector 23 as the axis of symmetry; The output signal from the detection region 23a located on the left side with the shadow of the groove projected on the photodetector 23 as the axis of symmetry, and the curve s represents the sum of the outputs of the detection regions 23a and 23b. Other conditions are the same as those in FIG.

FIG. 20 shows that the magnitude of the fluctuation of the curve s is reduced by about 40% as compared with FIG.

FIG. 22 shows the result of calculating the variation of the header signal when a lens shift of 10% of the aperture ratio of the objective lens is given toward the inner peripheral side of the groove under the conditions shown in FIG. FIG. Note that the conditions indicated by each curve are indicated by the same reference numerals in FIG.

FIG. 24 is a graph showing the result of calculating the variation of the header signal when a lens shift of 10% of the aperture ratio of the objective lens is given toward the outer periphery of the groove under the conditions shown in FIG. It is a graph shown. Note that the conditions indicated by each curve are indicated by the same reference numerals in FIG.

As shown in FIGS. 19 to 24, when FIG. 19 (conventional example) corresponding to FIG. 20 (this embodiment), that is, when the lens shift is “0”, the two are compared, the shadow of the groove is reduced. Although the magnitude of the output fluctuation (curve l) from the photodetection region on the left side as the axis of symmetry increases, the magnitude of the fluctuation of the reproduction signal (curve s) is greatly reduced. 21 corresponding to FIG. 22 (this embodiment).
When the two are compared (conventional example), that is, when the lens shift occurs on the inner peripheral side, the magnitude of the fluctuation (curve s) of the reproduction signal is greatly reduced as shown in FIG. . On the other hand, FIG. 2 corresponding to FIG. 24 (this embodiment)
3 (conventional example), ie, when the lens shift occurs on the outer peripheral side, when the two are compared, it is possible to prevent the header signal from being buried and to reduce the variation in the magnitude of the reproduction signal. According to the present embodiment, it can be seen from FIGS. 22 and 24 that even when a lens shift is added, the variation of the header signal is smaller than that of the example using the well-known two-segment photodetector shown in FIG. It is confirmed that a header signal that can be approximated (that is, does not require special correction) is obtained when the lens shift shown in FIG. 22 is “0”.

The calculation results shown in FIG. 20, FIG. 22, and FIG. 24 are a total of four calculation results, two each in the inner circumferential direction and the outer circumferential direction of the optical disk with respect to the center of the groove as shown in FIG. In a state where the first header section, the second header section, the third header section, and the fourth header section are unevenly distributed, the L _{VFO is changed} to the signal amplitude in the VFO portion of the prepits constituting the header section, L
_{When 0} is a signal level in a mirror portion where information on the recording surface of the optical disk is not recorded, and L _hmax is a maximum value of a signal amplitude in a header portion, L _VFO / L ₀ ≧ 0.25 and L _{In addition} to satisfying _VFO / L _hmax ≧ 0.50, L _{AMHD1 represents} the maximum value of the signal amplitude from the first header portion, L _{AMHD2 represents} the maximum value of the signal amplitude from the second header portion, and L _{AMHD3 represents} the maximum value of the signal amplitude from the second header portion. , The maximum value of the signal amplitude from the third header part, and L
_{When AMHD4} is the maximum value of the signal amplitude from the fourth header portion, 0.9 ≦ _LAMHD2 / _LAMHD1 ≦ 1.1 0.9 ≦ _LAMHD4 / _LAMHD3 ≦ _1.10.8 ≦ L _AM13 / _LAMHD1 and 0.8 ≦ _LAM31 / _LAMHD3 and _LαHD1 are set to VF (not shown) when the condensed spot is on the groove with respect to the signal of the first header portion.
The level of the difference between the upper limit value of the signal from the O section and the upper limit value of the entire header signal, and when the condensing spot is on the land, the lower limit value of the signal from the VFO section not shown and the lower limit value of the entire header signal When the focused spot is on the groove with respect to the signal of the second header section, the difference level between the upper limit value of the signal from the VFO section (not shown) and the upper limit value of the entire header signal is _defined as L _αHD2. When the _focused spot is on the land, the level of the difference between the lower limit of the signal from the VFO unit (not shown) and the lower limit of the entire header signal, _LαHD3, is _set with respect to the signal of the third header unit. When the focused spot is on the groove, the level of the difference between the upper limit value of the signal from the VFO unit (not shown) and the upper limit value of the entire header signal, and when the focused spot is on the land, V is not shown. The lower limit of the signal from the O portion and the difference between the level of the lower limit value of the entire header signal, the L _ArufaHD4,
Regarding the signal of the fourth header portion, when the focused spot is on the groove, the level of the difference between the upper limit value of the signal from the VFO unit (not shown) and the upper limit value of the entire header signal, and the focused spot is located on the land , A VFO (not shown)
The level of the difference between the lower limit value of the signal from the unit and the lower limit value of the entire header signal, _LβHD1 , is determined from the VFO unit (not shown) when the focused spot is on the groove with respect to the signal from the first header unit. The level of the difference between the lower limit value of the signal of FIG. 1 and the lower limit value of the entire header signal, and when the light-collecting spot is on the land, the difference between the upper limit value of the signal from the VFO unit (not shown) and the upper limit value of the entire header signal Level, L
_βHD2 is set to a VFO (not shown) when the focused spot is on the groove with respect to the signal from the second header section.
Level of the difference between the lower limit of the signal from the unit and the lower limit of the entire header signal.
The level of the difference between the upper limit value of the signal from the VFO unit (not shown) and the upper limit value of the entire header signal, _LβHD3 , is not shown when the focused spot is on the groove with respect to the signal from the third header unit. The level of the difference between the lower limit value of the signal from the VFO unit and the lower limit value of the entire header signal. When the light-collecting spot is on the land, the upper limit value of the signal from the VFO unit (not shown) and the upper limit value of the entire header signal When the focused spot is on the groove with respect to the signal from the fourth header portion, the difference level L _βHD4 between the lower limit value of the signal from the VFO portion (not shown) and the lower limit value of the entire header signal is determined. The difference level, that is, the difference level between the upper limit value of the signal from the VFO unit (not shown) and the upper limit value of the entire header signal when the condensed spot is on the land, −0.1 ≦ (L _{βHD1 −LαHD1} ) / 2L _AMHD1 ≦ _0.1−0.1 ≦ ( _{LβHD2− LαHD2} ) _{/2LAMHD1≦0.1−0.1≦} ( _{LβHD3− LαHD3} ) / 2L _AMHD1 ≦ 0.1 and _{-0.1 ≦ (L βHD4 -L αHD4)} / 2L AMHD1 ≦ 0.1 is _satisfied, obtain a _{L HD1,} the light beam incident to the optical detector relative to the first header section by photoelectrically converting For the signal, the lower limit level of the amplitude, L _HD2, is set, and for the signal obtained by photoelectrically converting the light beam incident on the photodetector with respect to the second header portion, the lower limit level of the amplitude, L _HD3, is set. For the signal obtained by photoelectrically converting the light beam incident on the photodetector with respect to the third header portion, the lower limit level of the amplitude, L _HD4, is transmitted to the photodetector with respect to the fourth header portion. Entering For the signal obtained by photoelectrically converting the emitted light beam, the lower limit level of its amplitude,
| [(L _HD1 + L _HD2 ) − (L _HD3 +
L _HD4 )] / 2L _{0 |} ≦ 0.05, and when the converging spot is offset from the center of the groove by 0.1 μm in the radial direction of the information recording medium, 0.15 ≦ | [(L _HD1 + L _HD2 ) − (L _HD3 +
L _HD4 )] / 2L ₀ |.

As described above, the generation of the header signal and the reproduction signal from the unevenly distributed prepits can be detected well. This makes it possible to extract a signal for realizing recording and reproduction on a DVD-RAM disk, for example.

[0128]

As described above, according to the optical head device of the present invention, the output of the offset component contained in the track error signal is removed from a part of the light receiving area of the photodetector for detecting the track error signal. By providing the light receiving area for detecting the offset component, the light of the 0th-order diffracted light, the 1st-order diffracted light, and the -1st-order diffracted light of the reflected light reflected from the optical disk can be used to generate the track error signal. , The influence of the lens shift on the track error signal can be removed, and stable tracking control can be performed.

Further, according to the optical head device of the present invention,
The respective outputs of the linear light receiving area for detecting the offset component and the light receiving area for detecting the track shift are set to appropriate magnitudes by the gain controller. Therefore, a photodetector capable of detecting the offset component can be provided at low cost, and the offset component is not detected or its size is prevented from being changed due to the output of the photodetector.

Further, according to the optical head device of the present invention, there is a possibility that the difference occurs between the area difference between the two light receiving regions used for detecting the offset component, the component accuracy of the elements of the optical head device, or the assembly of the optical head device. Is set to an appropriate magnitude by the gain controller. Therefore, there is no increase in assembly cost and component cost for detecting the offset component.

Further, by devising a method for reading the header signal, it is possible to read the header information in the land / groove recording type optical disk.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an optical disk device having an optical head device according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a configuration of an optical head device incorporated in the optical disk device shown in FIG.

FIG. 3 is a schematic diagram showing an example of an actuator of the optical head device shown in FIG. 2;

FIG. 4 is a schematic diagram showing an example of a fixed optical system of the optical head device shown in FIG.

FIG. 5 is a schematic diagram illustrating a lens holder of the actuator shown in FIG. 3 and its vicinity.

FIG. 6 is a schematic diagram illustrating a state of a reflected laser beam from the optical disc returned to the objective lens of the actuator shown in FIGS. 3 and 5;

FIG. 7 is a schematic plan view showing a detection area of a photodetector used for track shift detection capable of detecting an offset component included in the reflected laser beam shown in FIG. 6;

FIG. 8 is a schematic block diagram illustrating an example of a signal processing unit and a control unit that can be used in the signal processing unit and the control unit of the optical disc device illustrated in FIG. 1;

FIG. 9 is a schematic block diagram showing a modified example of the signal processing unit and the control unit shown in FIG. 8;

FIG. 10 is a graph showing an offset amount obtained by the photodetector shown in FIG. 7;

11 is a graph showing an output from the photodetector shown in FIG. 7 and a track shift signal provided by the signal processing unit and the control unit shown in FIG. 8;

FIG. 12 is a schematic block diagram illustrating another example of the signal processing unit and the control unit illustrated in FIG. 8;

FIG. 13 is a schematic block diagram showing still another example of the signal processing unit and the control unit shown in FIG. 8;

FIG. 14 is a schematic block diagram showing still another example of the signal processing unit and the control unit shown in FIG. 8;

FIG. 15 is a graph showing an offset amount obtained by the photodetector shown in FIG. 7 and the signal processing unit and the control unit shown in FIG. 14;

16 is a graph showing an output from the photodetector shown in FIG. 7 and a track shift signal provided by the signal processing unit and the control unit shown in FIG. 14;

FIG. 17 is a schematic diagram schematically showing a relationship between a groove and a pit in a header portion of an optical disc used for land / groove recording.

FIG. 18 is a graph showing a simulation result of how the amplitude of a header signal obtained by reproducing a header portion of an optical disk on which land / groove recording is performed changes as the lens shift increases.

FIG. 19 is a graph showing a result of calculating a change in a header signal using a conventionally used two-segment photodetector and setting a lens shift amount to “0”.

FIG. 20 is a graph showing a result of calculating a change in a header signal using the four-segment photodetector shown in FIG. 7 and setting the lens shift amount to “0”.

FIG. 21 shows a case where a conventionally used two-segment photodetector is used, the lens shift is set to a size of 10% of the aperture ratio of the objective lens, and a condition that the lens shift is located on the inner circumferential side of the groove is added. 9 is a graph showing a result of calculating a change in a header signal.

22 shows a case where a lens shift having a size of 10% of the aperture ratio of the objective lens is given using the four-segment photodetector shown in FIG. 7, and a condition that the lens shift is located on the inner circumferential side of the groove is added. 9 is a graph showing a result of calculating a change in a header signal.

FIG. 23 shows a header in a case where a conventionally used two-segment photodetector is used, a lens shift is set to a size of 10% of an aperture ratio of an objective lens, and a condition that the lens shift is located on the outer peripheral side of the groove is added. 7 is a graph showing a result of calculating a signal fluctuation.

24 shows a header in which a condition that a lens shift having a size of 10% of the aperture ratio of an objective lens is given using the four-segment photodetector shown in FIG. 7 and the lens shift is located on the outer peripheral side of the groove is added. 7 is a graph showing a result of calculating a signal fluctuation.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Optical disk apparatus, 3 ... Optical head apparatus, 3a ... Fixed optical system, 3b ... Actuator, 5 ... Signal processing part, 7 ... Motor, 9 ... Control part, 10 ... Housing, 11 ... Semiconductor laser, 12 ... Collimator lens, 13: Elliptical correction prism, 14: Beam splitter (polarization), 15: λ / 4 plate (phase delay element), 16: Beam splitter (half mirror), 17: Convergent lens, 18: Concave lens, 19: Cylindrical lens, 20 photodetector, 21 mirror, 22 convergent lens, 23 photodetector, 23a first detection area, 23b radial division line, 23c radial division line, 24 tangential division line, 24a second detection Area, 24b: third detection area, 25: tangential division line, 25a: fourth detection Area, 25b: fifth detection area, 31: base, 32: guide rail, 33: carriage, 34: radial drive coil, 35: rising mirror, 36: objective lens, 37: lens holder 38: lens holder base, 39: axis, 40: coil, 41: coil, 42: yoke, 43: magnet, 44: magnet, 50: main control circuit, 51: information reproduction circuit, 61: linear motor control circuit, 62: focus error detection circuit, 63: Focus control circuit, 64: Track shift and offset detection circuit, 65: Track control circuit, 66: Laser drive circuit, 71a: Current-voltage conversion circuit, 71b: Current-voltage conversion circuit, 71c: Current-voltage conversion circuit 71d: current-voltage conversion circuit, 72: adder, 73a: differential amplifier, 73b: differential amplifier 74 ... adder, 81a ... current-voltage conversion circuit, 81b ... current-voltage conversion circuit, 81c ... current-voltage conversion circuit, 81d ... current-voltage conversion circuit, 82a ... adder, 82b ... adder, 83 ... difference Dynamic amplifier, 84: Differential amplifier, 85: Differential amplifier, 86: Differential amplifier, 87: Differential amplifier, 88: Gain controller, 89: Gain controller, D: Optical disk, g: Groove.

Claims (15)

[Claims] 1. A light emitting means for supplying a light beam to an information recording medium, a light condensing means for condensing the light beam emitted from the light emitting means on the information recording medium, and the information recording medium An optical head device having at least photoelectric conversion means for converting light reflected and diffracted from the light into an electric signal, wherein the information recording medium is formed by condensing the light beam by the light condensing means. It has a groove-shaped groove for guiding the spot in the circumferential direction of the information recording medium, and has a header portion composed of a bripit row positioned offset from the groove at a break of the groove, The photoelectric conversion unit includes a plurality of light-sensitive areas that receive reflected light from the information recording medium, and one of the dividing lines that divides the light-sensitive area is at least connected to the objective lens. When the converged spot obtained by converging moves in the radial direction of the information recording medium, the direction is substantially orthogonal to the direction in which the reflected light moves on the photoelectric conversion means, and A light beam whose main component is all or a part of the light diffracted by the medium in which only the 0th-order light component and the 1st-order light component are overlapped is received in the light-sensitive region and photoelectrically converted. A first header auxiliary signal is generated, and all of the portions of the light diffracted by the information recording medium, in which only the 0th-order light component and the -1st-order light component overlap,
Or, a light beam having a part as its main component is received in the light-sensitive region and photoelectrically converted to generate a second header auxiliary signal, and the first header auxiliary signal and the second header auxiliary signal. An optical head device which generates a difference signal from the header signal and uses the signal as a header signal. 2. A light emitting means for supplying a light beam to an information recording medium, a light condensing means for condensing the light beam emitted from the light emitting means on the information recording medium, and the information recording medium. An optical head device having at least photoelectric conversion means for converting light reflected and diffracted from the light into an electric signal, wherein the information recording medium is formed by condensing the light beam by the light condensing means. It has a groove-shaped groove for guiding the spot in the circumferential direction of the information recording medium, and has a header portion composed of a pre-pit row that is positioned offset from the groove at a break of the groove, The photoelectric conversion means includes a plurality of light-sensitive areas that receive the reflected light, and divides the light-sensitive area into one of the dividing lines.
At least, when the condensed spot obtained by being converged by the objective lens moves in the radial direction of the information recording medium, the direction is substantially perpendicular to the direction in which the reflected light moves on the photoelectric conversion means. And a zero-order light component and a first-order light component of the light diffracted by the information recording medium.
At least a part of a portion where all of the first-order light components overlap, and a light of a portion including at least a part of the zero-order light component, and are positioned on both sides of the dividing line and are parallel to the dividing line. In the direction has a first light-sensitive region having a rectangular shape longer than the beam diameter of the reflected light, of the light diffracted by the information recording medium, of the portion protruding from the first light-sensitive region Receiving light, and having a second light-sensitive region located on both sides of the dividing line, of a photoelectric conversion signal obtained from two regions separated by the dividing line in the first light-sensitive region From a sum signal of a first difference signal that is a difference signal and a second difference signal that is a difference signal of a photoelectric conversion signal obtained from two regions separated by the dividing line of the second light sensitive region. A difference signal obtained by subtracting the first difference signal is used as a header signal. Optical head device. 3. A light emitting means for supplying a light beam to the information recording medium, a light condensing means for condensing the light beam emitted from the light emitting means on the information recording medium, and the information recording medium. An optical head device having at least photoelectric conversion means for converting light reflected and diffracted from the light into an electric signal, wherein the information recording medium is formed by condensing the light beam by the light condensing means. It has a groove-shaped groove for guiding the spot in the circumferential direction of the information recording medium, and has a header portion composed of a pre-pit row that is positioned offset from the groove at a break of the groove, The photoelectric conversion means includes a plurality of light-sensitive areas that receive the reflected light, and divides the light-sensitive area into one of the dividing lines.
At least, when the condensed spot obtained by being converged by the objective lens moves in the radial direction of the information recording medium, the direction is substantially perpendicular to the direction in which the reflected light moves on the photoelectric conversion means. Out of the light diffracted by the information recording medium,
At least a part of a portion where all of the first-order light components overlap, and a light of a portion including at least a part of the zero-order light component, and are positioned on both sides of the dividing line and are parallel to the dividing line. In the direction has a first light-sensitive region having a rectangular shape longer than the beam diameter of the reflected light, of the light diffracted by the information recording medium, of the portion protruding from the first light-sensitive region Receiving light, and having a second light-sensitive region located on both sides of the dividing line, of a photoelectric conversion signal obtained from two regions separated by the dividing line in the first light-sensitive region From a sum signal of a first difference signal that is a difference signal and a second difference signal that is a difference signal of a photoelectric conversion signal obtained from two regions separated by the dividing line of the second light sensitive region. A difference obtained by subtracting a signal obtained by amplifying or reducing the first difference signal by a predetermined value. An optical head device wherein a signal is used as a header signal. 4. A light emitting means for supplying a light beam to an information recording medium, a light condensing means for condensing the light beam emitted from the light emitting means on the information recording medium, and the information recording medium. An optical head device having at least photoelectric conversion means for converting light reflected and diffracted from the light into an electric signal, wherein the information recording medium is formed by condensing the light beam by the light condensing means. It has a groove-shaped groove for guiding the spot in the circumferential direction of the information recording medium, and has a header portion composed of a pre-pit row that is positioned offset from the groove at a break of the groove, The photoelectric conversion means includes a plurality of light-sensitive areas that receive the reflected light, and divides the light-sensitive area into one of the dividing lines.
At least, when the condensed spot obtained by being converged by the objective lens moves in the radial direction of the information recording medium, the direction is substantially perpendicular to the direction in which the reflected light moves on the photoelectric conversion means. Out of the light diffracted by the information recording medium,
At least a part of a portion where all of the first-order light components overlap, and a light of a portion including at least a part of the zero-order light component, and are positioned on both sides of the dividing line and are parallel to the dividing line. In the direction has a first light-sensitive region having a rectangular shape longer than the beam diameter of the reflected light, of the light diffracted by the information recording medium, of the portion protruding from the first light-sensitive region Receiving light, and having a second light-sensitive region located on both sides of the dividing line, of a photoelectric conversion signal obtained from two regions separated by the dividing line in the first light-sensitive region A signal obtained by amplifying or reducing one of the signals by a predetermined value, and two regions separated by the first difference signal, which is a difference signal obtained by subtracting the other signal from the other signal, and the dividing line of the second light-sensitive region. Sum signal with the second difference signal which is the difference signal of the photoelectric conversion signal obtained from An optical head device, wherein a difference signal obtained by subtracting the first difference signal from the first signal is used as a header signal. 5. A light emitting means for supplying a light beam to an information recording medium, a light condensing means for converging the light beam emitted from the light emitting means on the information recording medium, and the information recording medium. An optical head device having at least photoelectric conversion means for converting light reflected and diffracted from the light into an electric signal, wherein the information recording medium is formed by condensing the light beam by the light condensing means. It has a groove-shaped groove for guiding the spot in the circumferential direction of the information recording medium, and has a header portion composed of a pre-pit row that is positioned offset from the groove at a break of the groove, The photoelectric conversion means includes a plurality of light-sensitive areas that receive the reflected light, and divides the light-sensitive area into one of the dividing lines.
At least, when the condensed spot obtained by being converged by the objective lens moves in the radial direction of the information recording medium, the direction is substantially perpendicular to the direction in which the reflected light moves on the photoelectric conversion means. Out of the light diffracted by the information recording medium,
At least a part of a portion where all of the first-order light components overlap, and a light of a portion including at least a part of the zero-order light component, and are positioned on both sides of the dividing line and are parallel to the dividing line. In the direction has a first light-sensitive region having a rectangular shape longer than the beam diameter of the reflected light, of the light diffracted by the information recording medium, of the portion protruding from the first light-sensitive region Receiving light, and having a second light-sensitive region located on both sides of the dividing line, of a photoelectric conversion signal obtained from two regions separated by the dividing line in the first light-sensitive region A signal obtained by amplifying or reducing one of the signals by a predetermined value, and two regions separated by the first difference signal, which is a difference signal obtained by subtracting the other signal from the other signal, and the dividing line of the second light-sensitive region. Sum signal with the second difference signal which is the difference signal of the photoelectric conversion signal obtained from An optical head device, wherein a difference signal obtained by subtracting a signal obtained by amplifying or reducing the first difference signal by a predetermined value from the difference signal is used as a header signal. 6. The header signal includes signals L1 and L2 output from two regions separated by the dividing line in the first light sensitive area.
Where (L1−L2) pp is the first signal and the second signal
(L1 + L2) a is the first signal for the reflected light beam reflected from the area of the recording surface where the information is not recorded and the area where the guide groove is not formed. And the sum signal of the second signal are expressed as follows: 0.35 ≦ [(L1−L2) pp / (L1 + L2)
a], [(L1-L2) pp / (L1 + L2) a] ≦ 1.05, and [(L1-L2) / (L1 + L)
2)] When pp is the maximum value of the amplitude obtained by dividing the instantaneous value of the signal level (L1−L2) by the instantaneous value of the signal level (L1 + L2) regardless of the presence or absence of information on the recording surface. 1.10 ≦ [(L1−L2) / (L1 + L2)] pp, [(L1−L2) / (L1 + L2)] pp ≦ 1.65, and [(L1−L2) / (L1 + L2) ]
[(L1-L2) / (L1 + L) indicating the maximum value of pp
2)] ppmax and [(L1-L2) / (L1 + L
2)] The minimum value of pp [(L1−L2) / (L1 +
L2)] ppmin, [(L1-L2) / (L1 + L2)] ppmin /
[(L1-L2) / (L1 + L2)] ppmax ≧ 0.
70, in order to match the difference signal between the output signals from the two areas with the center of the guide groove formed in advance on the recording surface of the recording medium and the center of the light beam passing through the light collecting means. 6. The optical head device according to claim 2, wherein a track error signal usable for tracking control for moving the light condensing means in a direction crossing the guide groove is used. 7. The information processing apparatus according to claim 1, wherein the header portion comprises a first header portion, a second header portion, two in each of an inner circumferential direction and an outer circumferential direction of the information recording medium with respect to the center of the groove. The third header portion and the fourth header portion are unevenly distributed, and the header signal is obtained by _converting the L _VFO into the V of the pre-pits constituting the header portion.
When the signal amplitude in the FO portion, L ₀ , is the signal level in the mirror portion where information on the recording surface of the optical disc is not recorded, and L _hmax is the maximum value of the signal amplitude in the header portion, L _VFO / L ₀ ≧ 0.25 and L _VFO / L _hmax ≧ 0.50, L _AMHD1 is the maximum value of the signal amplitude from the first header portion, L _AMHD2 is the signal amplitude from the second header portion. When L _AMHD3 is the maximum value of the signal amplitude from the third header portion and L _AMHD4 is the maximum value of the signal amplitude from the fourth header portion, 0.9 ≦ L _AMHD2 / L _AMHD1 ≦ 1.1 0.9 ≦ L _AMHD4 / L _AMHD3 ≦ 1.1 0.8 ≦ _LAM13 / _LAMHD1 and 0.8 ≦ _LAM31 / _LAMHD3 And L _αHD1 is the level of the difference between the upper limit of the signal from the VFO unit (not shown) and the upper limit of the entire header signal when the focused spot is on the groove with respect to the signal of the first header. When the focused spot is on the land, the level of the difference between the lower limit value of the signal from the VFO unit (not shown) and the lower limit value of the entire header signal, _LαHD2, is set as the focused spot for the signal of the second header portion. Is on the groove, the level of the difference between the upper limit value of the signal from the VFO unit (not shown) and the upper limit value of the entire header signal, and when the light spot is on the land, the signal from the VFO unit (not shown) level difference between the lower limit value and the lower limit value of the entire header signal, the L _ArufaHD3, relates to a signal of the third header portion, when the focused spot is on a groove, or receive from the VFO portion, not shown And the level of the difference between the lower limit of the signal from the VFO unit (not shown) and the lower limit of the entire header signal when the condensing spot is on the land. , L _αHD4 is the level of the difference between the upper limit of the signal from the VFO unit (not shown) and the upper limit of the entire header signal when the focused spot is on the groove with respect to the signal of the fourth header. When the light spot is on the land, the level of the difference between the lower limit value of the signal from the VFO unit (not shown) and the lower limit value of the entire header signal, _LβHD1, is _set to the focused spot for the signal from the first header unit. Is on the groove, VF (not shown)
The level of the difference between the lower limit value of the signal from the O section and the lower limit value of the entire header signal, and when the light-collecting spot is on the land, the upper limit value of the signal from the VFO section (not shown) and the upper limit value of the entire header signal L _LHD2 is _set to VF (not shown) when the focused spot is on the groove with respect to the signal from the second header.
The level of the difference between the lower limit value of the signal from the O section and the lower limit value of the entire header signal, and when the light-collecting spot is on the land, the upper limit value of the signal from the VFO section (not shown) and the upper limit value of the entire header signal When the focused spot is on the groove with respect to the signal from the third header portion, the level of the difference L _βHD3 is
The level of the difference between the lower limit value of the signal from the O section and the lower limit value of the entire header signal, and when the light-collecting spot is on the land, the upper limit value of the signal from the VFO section (not shown) and the upper limit value of the entire header signal When the focused spot is on the groove with respect to the signal from the fourth header portion, the level of the difference L _βHD4 is
The level of the difference between the lower limit value of the signal from the O section and the lower limit value of the entire header signal, and when the light-collecting spot is on the land, the upper limit value of the signal from the VFO section (not shown) and the upper limit value of the entire header signal −0.1 ≦ (L _βHD1 −L _αHD1 ) / 2L _AMHD1 ≦ 0.1 −0.1 ≦ (L _βHD2 −L _αHD2 ) / 2L _AMHD1 ≦ 0.1 −0.1 ≦ (L _βHD3 −L _αHD3 ) / 2L _AMHD1 ≦ 0.1 and −0.1 ≦ (L _βHD4 −L _αHD4 ) / 2L _AMHD1 ≦ 0.1, and L _HD1 with _respect to the first header portion A signal obtained by photoelectrically converting the light beam incident on the photodetector, the lower limit level of the amplitude, L _HD2, is obtained by photoelectrically converting the light beam incident on the photodetector with respect to the second header portion. Obtained With respect to the signal, the lower limit level of the amplitude, the L _HD3, with respect to the signal obtained by a light beam incident to the light detector with respect to the third header portion photoelectrically converting the lower limit level of the amplitude, the L _HD4 , [ _LHD1 + _LHD2 )-( _{LHD3] where} the lower limit level of the amplitude of the signal obtained by photoelectrically converting the light beam incident on the photodetector with respect to the fourth header portion is +
L _HD4 )] / 2L ₀ | ≦ 0.05 and 0.15 ≦ 0.15 when the focused spot is offset by 0.1 μm from the center of the groove in the radial direction of the information recording medium. | [(L _HD1 + L _HD2 ) − (L _HD3 +
L _{HD4)] /} 2L ₀ | claims 2, characterized by satisfying that the to optical head device according to either of the 5. 8. A light source for emitting a light beam having a wavelength of about 650 nm, lens means having a numerical aperture of about 0.6, and condensing the light beam emitted from the light source on a recording surface of a recording medium; A photoelectric conversion means for converting a reflected light beam reflected and diffracted on the recording surface of the recording medium into an electric signal, wherein the recording medium has a center-to-center distance of approximately 1.48 μm. A guide groove having a shape of a circle or a plurality of concentric circles, and information can be recorded substantially at the center of the guide groove or between the guide grooves, and the photoelectric conversion means is a condensed spot obtained by being converged by the lens means. When the recording medium moves in the radial direction of the recording medium, a direction substantially perpendicular to the direction in which the reflected light beam reflected by the recording medium on the condensing spot is projected onto the photoelectric conversion unit and moves. At least one defined for
A part of a light beam having a photoelectric conversion region divided into a plurality of light receiving regions by one dividing line, and in which only the zero-order light component and the primary light component of the light beam reflected and diffracted by the recording medium overlap; Alternatively, a first signal is generated by photoelectrically converting a light beam including all of the light as a main component, and a light in which only the 0th-order light component and the -1st-order light component of the light beam reflected and diffracted by the recording medium overlaps A second signal is generated by photoelectrically converting a light beam mainly or partially of the beam, and a difference signal between the first signal and the second signal is previously recorded on a recording surface of the recording medium. A track error signal that can be used for tracking control for moving the light condensing means in a direction crossing the guide groove so that the center of the formed guide groove matches the center of the light beam that has passed through the light condensing means. Optical head characterized by Location. 9. The track error signal, wherein the level of each of the first signal and the second signal is L1, L2, and (L1-L2) pp is the first signal.
And the maximum value of the amplitude of the difference signal between the second signal and
(L1 + L2) a is the sum of the first signal and the second signal for the reflected light beam reflected from the area of the recording surface where the information is not recorded and the area where the guide groove is not formed, respectively. As shown, 0.35 ≦ [(L1−L2) pp / (L1 + L2)
a], [(L1-L2) pp / (L1 + L2) a] ≦ 1.05, and [(L1-L2) / (L1 + L)
2)] When pp is the maximum value of the amplitude obtained by dividing the instantaneous value of the signal level (L1−L2) by the instantaneous value of the signal level (L1 + L2) regardless of the presence or absence of information on the recording surface. 1.10 ≦ [(L1−L2) / (L1 + L2)] pp, [(L1−L2) / (L1 + L2)] pp ≦ 1.65, and [(L1−L2) / (L1 + L2) ]
[(L1-L2) / (L1 + L) indicating the maximum value of pp
2)] ppmax and [(L1-L2) / (L1 + L
2)] The minimum value of pp [(L1−L2) / (L1 +
L2)] ppmin, [(L1-L2) / (L1 + L2)] ppmin /
[(L1-L2) / (L1 + L2)] ppmax ≧ 0.
70, and the difference signal between the output signals from the first and second regions is
Used for tracking control in which the light condensing means is moved in a direction crossing the guide groove so that the center of the guide groove formed in advance on the recording surface of the recording medium coincides with the center of the light beam passing through the light condensing means. 9. The optical head device according to claim 8, wherein the signal is a possible track error signal. 10. A plurality of light receiving areas of said photoelectric conversion means,
First and second light receiving regions divided only by the dividing line, and two light receiving regions which are arranged line-symmetrically with the dividing line as a symmetry axis and divide respective predetermined regions of the first and second light receiving regions. 9. The optical head device according to claim 8, further comprising third and fourth light receiving areas further divided by the linear dividing lines. 11. The linear dividing line according to claim 1, wherein the primary light component and the −1st light component are respectively coincident with a tangent of a contour defined by a region where the primary light component and the −1st light component overlap each other. The optical head device according to claim 10. 12. The optical head device according to claim 10, wherein said first light receiving area and said third light receiving area are respectively located on the same side divided by said dividing line. 13. A light source that emits a light beam, a polarizing beam splitter that guides the light beam emitted from the light source toward a recording medium, and a light beam that has passed through the polarizing beam splitter has a predetermined shape. An objective lens for giving image characteristics to converge on a recording surface of a recording medium; a track control coil for generating a propulsive force for moving the objective lens in a direction orthogonal to a guide groove specific to the recording medium; The light beam converged on the recording surface of the recording medium, reflected by the recording surface, and passed again through the objective lens is reflected by the polarizing beam splitter and separated from the light beam traveling toward the objective lens. A non-polarizing beam splitter that functions as a half mirror that splits the light beam into two light beams of approximately equal light intensity, and a guide groove that is unique to the recording medium. First and second 2 but divided by dividing lines extending along the direction to be projected
A first light receiving area and two first and second linear light receiving areas divided by a linear outer dividing line symmetrically defined with the dividing line as an axis of symmetry in the first and second light receiving areas; A light beam split by the non-polarizing beam splitter is received by the first and second light receiving regions, photoelectrically converted, and converged by the center of a guide groove unique to a recording medium and the objective lens. A track error signal indicating the degree of deviation from the center of the light beam to be generated, and the first and second linear light receiving regions generate a zero-order diffracted light of the light beam reflected on the recording surface of the recording medium. A light beam applied to an area where the first-order diffracted light and the -1st-order diffracted light overlap each other is received and photoelectrically converted, and the center of the guide groove unique to the recording medium and the center of the light beam converged by the objective lens are determined. of A photodetector for generating a signal corresponding to the offset component of the track error signal in indicating the degree of Les, the first output which is output from each of said first and second light receiving regions of the photodetector
From the difference signal between the two signals obtained by adding the outputs output from each of the first and second linear light receiving regions based on a predetermined combination, the first and second linear light receiving regions Track shift and offset detection for subtracting the difference signal between the output signals to determine the actual shift between the center of the guide groove unique to the recording medium and the center of the light beam converged by the objective lens. An optical head device comprising: a circuit; and a tracking control circuit that supplies a current in a predetermined direction to the track control coil based on a track shift signal obtained by the track shift and offset detection circuit. 14. A light beam emitted from the light source has a wavelength of 635 to 685 nm, a numerical aperture of the objective lens is approximately 0.6, and a minimum length of 0.40 is provided on a recording surface of the recording medium. 14. The optical head device according to claim 13, wherein recording pits having a recording pitch of about 0.74 [mu] m in a radial direction of the recording medium are formed at a recording pitch of about 0.44 [mu] m. 15. The level of two signals output from each of the first and second light receiving regions of the photodetector is represented by L1 and L2, (L1-L2) pp, and the amplitude of a difference signal between the two signals. When (L1 + L2) a is the level of the sum signal of the two signals when the converging spot from the objective lens is irradiated on the mirror area where the information is not written on the recording medium. 35 ≦ [(L1−L2) pp / (L1 + L2)
a], [(L1−L2) pp / (L1 + L2) a] ≦ 1.05 is satisfied, and [(L1−L2) / (L1 + L2)] pp indicates that information is written on the recording medium. Regardless of (L
1-L2) is changed to the signal level (L1
+ (L2) / (L1 + L2)] ppmin, the minimum value of the same amplitude value, [(L1-L2) / (L1 + L2)] ppmax, the same amplitude value obtained by dividing by the instantaneous value of (+ L2). 1.10 ≦ [(L1−L2) / (L1 + L2)] pp ≦
1.65 and {[(L1-L2) / (L1 + L2)] pp @ min /} [(L1-L2) / (L1 + L2)] pp @ max
The optical head device according to claim 14, wherein? 0.70 is satisfied.