JP4212572B2 - Optical head device and optical information processing method - Google Patents

Description

  The present invention relates to an optical head device that records, reproduces, or erases information on an information storage medium such as an optical disk or an optical card, an optical information processing device, and a beam and information storage focused by a condensing optical system in the device. The present invention relates to an inclination detection device that detects an angle formed by a medium.

  An optical disk or an optical card is used as a high-density and large-capacity information storage medium. In the optical memory technology using an optical disk or an optical card, its applications such as a digital audio disk, a video disk, a document file disk, and a data file are expanding. In this optical memory technology, information is recorded / reproduced with high accuracy and reliability on an optical disc through a finely focused light beam. This recording / reproducing operation depends solely on the optical system.

The basic function of the optical head device, which is the main part of the optical system, is
(1) Condensation that forms a diffraction-limited microspot,
(2) Focus control and tracking control of the optical system, and information signal reproduction,
(3) It is roughly classified into erasing and writing of information signals by concentration of light.

  These functions are realized by a combination of various optical systems and photoelectric conversion detection photodetectors according to the purpose and application.

  As a first conventional example, an example of a conventional optical head device is shown.

  As a conventional example of the optical head device, the configuration and operation in the case where the focus is the astigmatism method and the tracking is the push-pull method and the phase difference method will be described. FIG. 42 shows a schematic diagram of an optical system of the optical head device.

  FIG. 42 schematically illustrates an optical system of the optical head device according to the first embodiment.

  Light emitted from the semiconductor laser 101 as the light source is reflected by the parallel plate beam splitter 102 and becomes parallel light by the collimator lens 103 which is a part of the condensing optical system. This light is further condensed by the objective lens 104 which is a part of the condensing optical system, and is condensed on the information layer 108 of the optical disk 105 which is an information storage medium. The actuator 107 moves the objective lens 104 and the holding means 106 following the surface deflection and eccentricity of the optical disk 105.

  The reflected light 108 a diffracted and reflected by the information layer 108 of the optical disc 105 passes through the objective lens 104 again and becomes parallel light. The reflected light 108 a that has become the parallel light again becomes convergent light by the collimator lens 103. Astigmatism is given when the reflected light 108a which has become the convergent light passes through the parallel plate beam splitter 102. The convergent light given astigmatism is received by the photodetector 150. When the condensing point F0 of the light emitted from the objective lens 104 coincides with the information layer 108 of the optical disc 105, the detection surface of the photodetector 150 comes to the position of the minimum confusion circle of the convergent light to which astigmatism is given. As such, the optical system is arranged.

FIG. 43 a shows a pattern of a conventional example of the detection region of the photodetector 150 and a cross-sectional shape of the reflected light 108 a by the photodetector 150. The photodetector 150 includes four detection areas 251 to 254. Signals obtained according to the amounts of light received from the detection regions 251 to 254 are denoted by s1 to s4, respectively. Although the arithmetic circuit as the tracking error signal generating means is not shown, the following equation TE1 = (s1 + s4) − (s2 + s3) (Equation 1) is used as the tracking error signal TE1.
To generate a tracking error signal.

  The phase difference tracking error signal TE2 is obtained by comparing the phases of the sum signal of s1 and s3 and the sum signal of s2 and s4.

The focus error signal FE of the astigmatism method is
FE = (s1 + s3)-(s2 + s4) (Formula 2)
Obtained from.

  When the information layer 108 of the optical disc 105 moves away from the objective lens 104 from the condensing point F0 of the light emitted from the objective lens 104, the cross-sectional shape of the reflected light 108a by the photodetector 150 is as shown in FIG. . Conversely, when the information layer 108 of the optical disk 105 approaches the objective lens 104 from the focal point F0 of the objective lens 104, the cross-sectional shape of the reflected light 108a by the photodetector 150 is as shown in FIG. 43c.

The RF signal that is the information reproduction signal is a sum of signals obtained from all regions,
RF = s1 + s2 + s3 + s4 (Equation 3)
Obtained from.

In the conventional optical head device shown in the first conventional example,
(1) The tracking error signal is generated by a differential signal in a region simply divided into two by a dividing line passing through a point corresponding to the center of the aperture. In this configuration, when aberration occurs due to the tilt of the objective lens and the optical disc (when tilt occurs), or when the objective lens moves in the direction perpendicular to the track with respect to the optical axis following the eccentricity of the optical disc (objective lens). When a shift occurs), there are problems that off-tracking occurs and tracking control does not operate stably.
(2) Further, when the position where the condensing point of the light emitted from the objective lens is shifted from the track on which the information to be reproduced is scanned, it is divided into two by a dividing line passing through a point corresponding to the center of the aperture. When a reproduction signal is generated using a differential signal in a region, there is a problem that a margin for disturbance or the like cannot be sufficiently obtained.

  In addition, there are various configurations of tilt detection devices that detect the relative tilt amount between the beam condensed by the condensing optical system in the optical information device and the information storage medium in order to accurately read and write information on the information storage medium. Has been proposed.

  Next, an example of a tilt detection apparatus will be shown as a second conventional example.

FIG. 44 is a block diagram showing an example of a conventional tilt detection apparatus.
A linearly polarized divergent beam 70 emitted from a semiconductor laser 101 as a light source is converted into parallel light by a collimator lens 103 and then enters a polarization beam splitter 130. All the beams 70 incident on the polarization beam splitter 130 pass through the polarization beam splitter 130, pass through the quarter-wave plate 122, are converted into circularly polarized beams, and are condensed on the information storage medium 105 by the objective lens 104. Is done.

  FIG. 45 shows the configuration of the information storage medium 105. Gn-1, Gn, Gn + 1,... Are guide grooves. Information is recorded as a mark or space on the guide groove. Therefore, the tracks Tn−1, Tn, Tn + 1,... For recording information coincide with the guide grooves. Gp is an interval between adjacent guide grooves, tp is an interval between adjacent tracks, and Gp and tp are equal. The beam 70 reflected and diffracted by the information storage medium 105 passes through the objective lens 104 again, then passes through the quarter-wave plate 122, and is a linearly polarized beam having a direction different by 90 degrees from that emitted from the light source 101. Is converted to The beam 70 transmitted through the quarter-wave plate 122 is totally reflected by the polarization beam splitter 130 and then converted to a convergent beam by the detection lens 133. The convergent beam 70 converted by the detection lens 133 is transmitted by the parallel plate 134 and then received by the photodetector 158. As the beam 70 passes through the parallel plate 134, astigmatism is applied to the beam 70 in order to detect a focus error signal. The beam 70 received by the photodetector 158 is converted into an electrical signal corresponding to the amount of light.

  In the present specification, when the optical disk is a ROM disk, the mark means a pit, the space means a plane part, and when the optical disk is a phase change storage medium, the mark means an amorphous part, and the space means It means a crystal part, or conversely, a mark means a crystal part, and a space means an amorphous part. Alternatively, when the optical disk is a magnetic storage medium, the mark may mean upward magnetization and the space may mean downward magnetization, or conversely, the mark may mean downward magnetization and the space may mean upward magnetization. Further, when the optical disc is a magnetic storage medium, the mark may mean the right direction of magnetization and the space may mean the left direction of magnetization, or conversely, the mark may mean the left direction of magnetization and the space may mean the right direction of magnetization. When the optical disk is a write-once such as a CD-R, the mark means a dye-modified region and the space means a non-modified region.

  The focus error signal and the tracking error signal are applied to the focus control actuator 107 and the tracking control actuator 107, respectively, so that the beam 70 emitted from the light source 101 is focused at a desired position on the information storage medium 105. Control the position of the. Since the method of generating the focus error signal and the tracking error signal is a well-known method, description thereof is omitted here.

  An electrical signal output from the photodetector 158 is input to the signal processing unit 703.

  FIG. 46 shows the configuration of the signal processing unit 703. The photodetector 158 includes four light receiving units 158A, 158B, 158C, and 158D. Signals output from the light receiving units 158A to 158D are current / voltage converted by current / voltage conversion units 855 to 858, respectively. Signals output from the current-voltage conversion units 855 to 858 are differentially calculated by the calculation unit 871. A signal output from the arithmetic unit 871 is output from the terminal 814. A signal output from the terminal 814 is an inclination detection signal.

  When the tilt is detected by utilizing the fact that the beam reflected by the information storage medium is scattered at the aperture of the objective lens 104 in the conventional tilt detector as shown in the second conventional example, the aperture of the objective lens 104 is detected. The greater the number, the lower the detection sensitivity. Recently, in order to record a large amount of information on an information storage medium, a configuration in which the numerical aperture of the condensing optical system is 0.6 and the thickness of the substrate of the information storage medium is 0.6 mm has been proposed. The jitter characteristic of the read information changes greatly only by changing the angle formed between the beam condensed by the objective lens and the information storage medium by about 0.5 degrees. Therefore, when an inclination servo that corrects a change in the angle between the beam condensed by the objective lens and the information storage medium is introduced, the inclination detection device needs to detect with an accuracy of 0.5 degrees or less. However, in the conventional tilt detection apparatus, when the numerical aperture of the objective lens is 0.6, for example, even if the tilt occurs by 0.5 degrees, the change in the signal is only about 2%, and the tilt is 0.5 degrees or less. There is a problem that it is difficult to accurately detect.

  Furthermore, another example of the optical head device is shown as a third conventional example.

  FIG. 47 is a block diagram showing an example of a conventional optical head device.

  A linearly polarized divergent beam 70 emitted from a semiconductor laser 101 as a light source is converted into parallel light by a collimator lens 103 and then enters a polarization beam splitter 130. All the beams 70 incident on the polarization beam splitter 130 pass through the polarization beam splitter 130, pass through the quarter-wave plate 122, are converted into circularly polarized beams, and are condensed on the information storage medium 105 by the objective lens 104. Is done. The beam 70 reflected and diffracted by the information storage medium 105 passes through the objective lens 104 again, then passes through the quarter-wave plate 122, and is a linearly polarized beam having a direction different by 90 degrees from that emitted from the light source 101. Is converted to The beam 70 transmitted through the quarter-wave plate 122 is totally reflected by the polarization beam splitter 130 and then converted to a convergent beam by the detection lens 133. The convergent beam 70 converted by the detection lens 133 is transmitted by the parallel plate 134 and then received by the photodetector 158. As the beam 70 passes through the parallel plate 134, astigmatism is imparted to the beam 70 so that a focus error signal can be detected. The beam 70 received by the photodetector 158 is converted into an electrical signal corresponding to the amount of light.

  The electrical signal output from the photodetector 158 is input to the signal processing unit 705. FIG. 48 shows the configuration of the signal processing unit 705. The photodetector 158 includes four light receiving units 158A, 158B, 158C, and 158D. Signals output from the light receiving units 158A to 158D are current / voltage converted by current / voltage conversion units 851 to 854, respectively. Signals output from the current / voltage converters 851 and 854 are added by an adder 891, signals output from the current / voltage converters 852 and 853 are added by an adder 892, and signals output from the current / voltage converters 851 and 853 are added. The signal output from the current / voltage converters 852 and 854 is added by the adder 894 in the unit 893. Signals output from the addition units 891 and 892 are differentially calculated by the calculation unit 871, and signals output from the addition units 893 and 894 are differentially calculated by the calculation unit 872. A signal output from the calculation unit 871 is output from the terminal 811, and a signal output from the calculation unit 872 is output from the terminal 812. A signal output from the terminal 811 is a tracking error signal, and a signal output from the terminal 812 is a focus error signal. A method for generating a focus error signal is a well-known method for astigmatism, and a method for generating a tracking error signal is a method well known as a push-pull method. The focus error signal and the tracking error signal are respectively applied to the focus control actuator 107 and the tracking control actuator 107 so that the beam 70 emitted from the light source 101 is focused on a desired position on the information storage medium 105. Control the position of the.

  FIG. 49 shows a configuration on the information storage medium 105. Gn−1, Gn, Gn + 1,... Are guide grooves that enable detection of tracking error signals. Information is recorded as marks or spaces on and between guide grooves. When the interval between adjacent guide grooves is Gp and the interval between adjacent tracks is tp, the relationship is Gp = 2 · tp.

The optical head device of the present invention includes a laser light source that emits a beam, an optical element that receives the beam emitted from the laser light source, and divides the received beam into a first beam and a second beam, and the first A condensing optical system that receives the beam and the second beam and focuses the first beam and the second beam onto a small spot on the information storage medium; and the first beam reflected and diffracted by the information storage medium And a beam including the second beam, a first beam branching element for branching the received beam, a beam branched by the first beam branching element, and the received beam received by the first beam And a second beam branching element that branches into the second beam, and the first beam and the second beam branched by the second beam branching element are received by different light receiving sections. A photodetector that outputs a signal corresponding to the light quantity of each of the received first beam and the second beam, and a signal that receives the signal output from the photodetector and calculates the received signal A processing unit, and a drive unit that performs relative positioning of the condensing optical system and the information storage medium based on a signal calculated by the signal processing unit,
The first beam is different from the second beam in terms of effective numerical aperture when condensed by the condensing optical system, and the first beam and the second beam divided by the optical element are different. Are formed coaxially with each other, and the signal processing unit has a smaller effective numerical aperture at the time of being condensed by the condensing optical system among the first beam and the second beam. The apparatus further includes tracking error signal generation means for generating a tracking error signal using a signal from the beam, thereby achieving the above object.

The information storage medium has a mark or a predetermined groove that makes it possible to detect a tracking error signal, and a period of the mark or the predetermined groove that makes it possible to detect a tracking error signal on the information storage medium is Gp. When the wavelength of the beam emitted from the light source is λ and the numerical aperture on the information storage medium side of the condensing optical system is NA, the first beam generated by the optical element is Gp> λ / NA The second beam generated by the optical element has a relationship of Gp <λ / NA, and the tracking error signal generating means generates a tracking error signal from the second beam. Also good.

The optical element may be a polarizing filter.

The optical element may be integrated with the condensing optical system.

An optical information processing method of the present invention includes an emission step of emitting a beam from a laser light source, a division step of receiving the beam emitted in the emission step, and dividing the received beam into a first beam and a second beam, A condensing step of receiving the first beam and the second beam, and condensing the first beam and the second beam onto a small spot on the information storage medium, and reflecting on the information storage medium; Receiving a beam including the diffracted first beam and the second beam, and branching the received beam; and receiving and receiving the beam branched in the first beam branching step; A second beam branching step for branching the beam into the first beam and the second beam, and each of the first beam and the second beam branched in the second beam branching step Photodetection process for outputting signals in accordance with the respective light amounts of the first beam and the second beam received by different light receiving units, and signals received in the photodetection process and received signals A signal processing step for calculating the first beam, and a positioning step for determining a relative position between the condensing optical system and the information storage medium based on the signal calculated by the signal processing step. Is different in effective numerical aperture when being focused by the focusing optical system, and the first beam and the second beam divided by the optical element are coaxial with each other. The signal processing step is formed on the first beam and the second beam using a signal having a smaller effective numerical aperture when being focused by the focusing optical system. Tracking error signal Further includes a tracking error signal generating step of generating, by the above-described object is achieved.

  As described above, according to the optical head device of the present invention, the following effects are mainly obtained.

  (1) Even when an objective lens shift or radial tilt occurs, the value TE0 of the tracking error signal obtained when light is irradiated to the center of the track and the maximum value of the tracking error signal obtained when crossing the track The difference between the absolute values | TEmax−TE0 | and | TEmin−TE0 | of each difference between TEmax and the minimum value TEmin can be reduced. At this time, even if the off-track amount is corrected to 0, a shift in symmetry of the tracking error signal can be suppressed, so that stable tracking control can be realized.

  (2) Even if the position shifted from the track is scanned with the condensing point, the information recorded on the track can be stably reproduced with a low error rate.

  (3) Since fluctuation in the gain of the focus error signal can be suppressed, stable focus control can be realized.

  As described above, the error rate can be kept small during information reproduction, and writing and erasing operations can be stably performed during information writing and erasing, so that different optical information processing apparatuses and information storage media can be used. The optical information processing apparatus increases compatibility.

  Further, according to the tilt detection apparatus of the present invention, it is possible to detect the tilt signal with high accuracy even when the tilt angle of the beam condensed by the information storage medium and the focusing optical system is 1 degree or less.

  In addition, by using the optical information processing apparatus of the present invention, information can be stably recorded and reproduced even on an information storage medium having a large amount of warpage.

  Embodiments of the present invention will be described below with reference to the drawings. The configurations indicated by the same reference numerals in the drawings perform the same functions.

(Embodiment 1)
FIG. 1 schematically shows an optical system of the optical head device according to the first embodiment.

  Light emitted from the semiconductor laser 101 as the light source is reflected by the parallel plate beam splitter 102 and becomes parallel light by the collimator lens 103 which is a part of the condensing optical system. This light is further condensed by the objective lens 104 which is a part of the condensing optical system, and is condensed on the information layer 108 of the optical disk 105 which is an information storage medium. The actuator 107 moves the objective lens 104 and the holding means 106 that holds the objective lens 104 following the surface deflection and eccentricity of the optical disc 105.

  The reflected light 108 a diffracted and reflected by the information layer 108 of the optical disc 105 passes through the objective lens 104 again and becomes parallel light. The reflected light 108 a that has become the parallel light again becomes convergent light by the collimator lens 103. Astigmatism is given when the reflected light 108a which has become the convergent light passes through the parallel plate beam splitter 102. The convergent light given astigmatism is received by the photodetector 150. When the condensing point F0 of the light emitted from the objective lens 104 coincides with the information layer 108 of the optical disc 105, the detection surface of the photodetector 150 comes to the position of the minimum confusion circle of the convergent light to which astigmatism is given. As such, the optical system is arranged.

  Let Gp be the distance from the center of a groove in the optical disk 105 as the information storage medium to the center of the adjacent groove. Information is recorded either on or between the grooves, or both on and between the grooves. In this embodiment, a series in which these pieces of information are recorded is called a track. Also, NA is the numerical aperture of the objective lens 104 as the condensing optical system of the optical head device, and λ is the wavelength of the light emitted from the semiconductor laser 101.

In the first embodiment,
λ / (NA · Gp) <1 (Formula 4)
A case where the above condition is satisfied will be described.

  FIG. 2 shows a circuit configuration as the detection regions 201 to 208, the information reproduction signal generation unit 450, and the tracking error signal generation unit 451 of the photodetector 150 according to the first embodiment.

The photodetector 150 is divided into eight regions of detection regions 201 to 208 by dividing lines 301 to 304. Under the condition of Expression 4, the + 1st order diffracted light and the −1st order diffracted light diffracted by the groove of the optical disc 105 have portions that overlap each other. In FIG. 2, the overlapping area 200 that is the overlapping portion is indicated by hatching. The maximum width W in the radial direction of the overlapping area 200 is
W = 2 × (1−λ / (NA × Gp)) (Equation 5)
It becomes. However, the opening is a circle with a radius of 1.

  The dividing lines 301 to 303 are straight lines parallel to the tangent line of the groove of the optical disc 105. The dividing line 304 is a straight line perpendicular to the tangent to the groove of the optical disc 105. Here, the direction of the tangent to the groove is the direction optically projected on the photodetector.

  When the astigmatism method is used as the focus error signal detection method, when astigmatism is given about the groove of the optical disk 105 and the direction of 45 degrees, the direction of the groove projected on the photodetector is rotated by 90 degrees. To do. Therefore, even if the direction of the actual dividing line is perpendicular to the tangential direction of the groove of the optical disk 105, if the direction is parallel to the direction of the tangential line of the groove projected on the photodetector, the "division parallel to the tangent line of the groove" "Line". Hereinafter, the same expression is used.

  The dividing line 302 passes through the center of projection of the aperture of the optical system onto the photodetector 150. The dividing line 301 and the dividing line 303 are arranged so as to sandwich the overlapping area 200. The distance d between the dividing line 301 and the dividing line 302 and the distance d between the dividing line 302 and the dividing line 303 are set to be substantially the same as W / 2. With this arrangement, as shown in FIG. 2, the overlapping region 200 of the + 1st order diffracted light and the −1st order diffracted light due to the groove of the optical disc 105 enters the detection regions 202, 203, 206, 207 of the photodetector 150. . Signals obtained according to the amounts of light received from the detection areas 201 to 208 are denoted by s1 to s8, respectively.

Here, the focus error signal FE is
FE = (s1 + s2 + s5 + s6) − (s3 + s4 + s7 + s8) (Expression 6)
Can be obtained by calculating. Note that FIG. 2 does not show an arithmetic circuit for obtaining the focus error signal FE.

  Hereinafter, a circuit system of the information reproduction signal generation unit 450 will be described. The information reproduction signal generation means 450 includes an adder 401 to an adder 405. The information reproduction signal generation unit 450 generates an RF signal which is an information reproduction signal. An RF signal, which is an information reproduction signal, is obtained from the sum of signals obtained from all regions. As shown in FIG. 2, the adder 401 outputs a sum signal of “signal s1 + signal s8”, the adder 402 outputs a sum signal of “signal s2 + signal s7”, and the adder 403 outputs “signal s3 + signal s6”. Is output, and the adder 404 outputs a sum signal of “signal s4 + signal s5”.

The adder 405 receives the output signals of the adders 401 to 404 and outputs a sum signal that is the sum of the respective output signals. An information reproduction signal raw (RF signal) that is an output signal output from the adder 405 is:
RF = s1 + s2 + s3 + s4 + s5 + s6 + s7 + s8 (Expression 7)
Can be obtained.

Hereinafter, a circuit system of the tracking error signal generation unit 451 will be described. The tracking error signal generation unit 451 includes an adder 401, an adder 404, and a differential operation circuit 406. The differential operation circuit 406 receives the output signals of the adder 401 and the adder 404 and outputs the differential signal. The output signal output from the differential arithmetic circuit 406 is
TE1 = (s1 + s8) − (s4 + s5) (Equation 8)
Can be obtained. The output signal output from the differential operation circuit 406 is a tracking error signal TE1.

  When the tilt of the optical disk 105 occurs in a direction (radial direction) perpendicular to the tangent of the groove of the optical disk 105, the conventional optical head device has the following inconvenience in tracking control.

  The reflected light detected when the tilt occurs shifts in the tilted direction. When the tilt of the disk is θ, the reflected light is shifted by 2θ. For example, if the numerical aperture NA is 0.6, the tilt θ is 0.8 degrees, and the aperture is a substantially circle having a radius of 1, (sin 2θ) /NA=0.047, and the detected reflected light is tilted. It is shifted 0.047 in the direction.

  When the tilt occurs, the tracking error signal value TE0 obtained when the focal point F0 of the light emitted from the objective lens 104 coincides with the center of the groove and the maximum of the tracking error signal obtained when crossing the groove. The difference between the absolute values | TEmax−TE0 | and | TEmin−TE0 | of the difference between the value TEmax and the minimum value TEmin increases.

  FIG. 3 shows the relationship between the tracking error signal and the off-track amount. The off-track amount means the distance from the track center to the condensing point F0.

A signal indicated by a black square is a tracking error signal when there is no aberration. A signal indicated by an unmarked solid line is a tracking error signal when a tilt occurs. In the tracking error signal indicated by the unmarked solid line, TE0 = 0.0.20 with respect to TEmax = 0.38 and TEmin = −0.42,
| TEmax−TE0 | = 0.58, | TEmin−TE0 | = 0.22,
Thus, a big difference occurs.

  When tracking control is performed in this state, the condensing point F0 of the light emitted from the objective lens 104 is positioned away from the track center, and information cannot be recorded or reproduced accurately.

  A case where an offset voltage is applied to the tracking error signal so that the condensing point F0 is located at the track center in this state will be described.

  The signal indicated by the white triangle in FIG. 3 is a tracking error signal after correction so that the off-track amount becomes zero. An offset voltage is applied so that the track center and the zero cross point of the tracking error signal coincide. At this time, the upper amplitude and the lower amplitude with respect to the zero level of the tracking error signal are asymmetric.

  When this asymmetry increases, the tracking control operation becomes unstable, and information cannot be recorded or reproduced accurately. Thus, as the difference between | TEmax−TE0 | and | TEmin−TE0 | increases, the off-track amount increases. Even if an offset voltage is added to reduce the off-track amount, the deviation of the symmetry of the tracking error signal becomes large. This degree can be expressed as a shift in symmetry of the tracking error signal when the off-track amount is corrected to zero.

  The result of comparison between the first embodiment and the conventional optical head device will be described below regarding the deviation in symmetry of the tracking error signal.

  When reproducing an optical disk having an objective lens numerical aperture NA = 0.6 and a light wavelength λ = 0.66 μm and a groove interval Gp = 1.48 μm, if the aperture is a circle with a radius of 1, the + 1st order diffracted light The −1st order diffracted light has an overlapping region with a width of W = 0.51 at the center.

  Assuming that the substrate thickness of the optical disk is 0.6 mm and a tilt occurs in the radial direction of 0.4 degrees, the conventional optical head device causes an off-track of about 0.07 μm with respect to the track center. Further, when the off-track amount is corrected to 0 by adding an offset voltage, a deviation of 31% occurs in the TE symmetry.

  Here, the symmetry of the tracking error signal is defined as (A + B) / (A−B), where A is the upper end value of the tracking error signal and B is the lower end value.

  In the case of the first embodiment, by taking the tracking error signal TE1 only from the outside of the overlapping region of the + 1st order and −1st order diffracted light, the off-track amount with respect to the track center when a 0.4 ° radial tilt occurs is , About 0.045 μm. Further, when the off-track amount is corrected to 0, the deviation in symmetry of the tracking error signal is 19%, which is suppressed to about 2/3 of the conventional example.

  Further, in the conventional optical head device, when the objective lens shift occurs, the detection spot moves on the detector, and when the off-track amount is corrected to 0, the symmetry of the tracking error signal is shifted. With an objective lens shift of 150 μm, if the off-track amount is corrected to 0, the deviation in symmetry of the tracking error signal becomes 16%.

  On the other hand, in the first embodiment, when the off-track amount is corrected to 0 with an objective lens shift of 150 μm, the deviation in symmetry of the tracking error signal can be suppressed to 3%.

  As described above, in the first embodiment, stable tracking control can be realized while maintaining a small off-track amount even when the optical disk 105 is tilted or the like. For this reason, Embodiment 1 can realize information recording / reproduction with a low error rate.

  Hereinafter, another example that provides the same effect as the above-described optical head device will be described with reference to FIG.

  FIG. 4 shows the detection areas 201, 204, 205, 208, and 209 of the photodetector 151, and the circuit configuration as the information reproduction signal generation means 450 and the tracking error signal generation means 451. The difference from the optical head device described above is that a photodetector 151 is used instead of the photodetector 150. The optical arrangement is the same as that shown in FIG.

  The photodetector 151 is divided into five detection areas 201, 204, 205, 208, and 209 by dividing lines 301, 303, 305, and 306. The dividing line 301 and the dividing line 303 are arranged so as to sandwich the overlapping area 200 of the + 1st order diffracted light and the −1st order diffracted light, and the detection area 209 is defined by the dividing line 301 and the dividing line 303. The light of the overlapping area 200 enters.

  The detection areas 201, 204, 205, 208, and 209 generate signals s1, s2, s3, s4, and s5 according to the amount of light received by them.

  A circuit system as the information reproduction signal generation means 450 will be described. The information reproduction signal generation means 450 includes adders 401, 404 and 405. An RF signal, which is an information reproduction signal, is obtained from the sum of signals s1, s2, s3, s4, and s5 output from all regions 201, 204, 205, 208, and 209. As shown in FIG. 4, the adder 401 outputs a sum signal of “signal s1 + signal s4”, and the adder 404 outputs a sum signal of “signal s2 + signal s3”. The adder 405 receives the output signal of the adder 401, the output signal of the adder 404, and the signal s5 output from the detection region 209, and outputs a sum signal of the received signals.

An RF signal that is an output signal output from the adder 405 is:
RF = s1 + s2 + s3 + s4 + s5 (Equation 9)
Can be obtained.

Hereinafter, a circuit system as the tracking error signal generation unit 451 will be described. The tracking error signal generation unit 451 includes adders 401 and 404 and a differential operation circuit 406. The differential arithmetic circuit 406 receives output signals from the adder 401 and the adder 404 and outputs a differential signal that is a difference between the output signals. The output signal output from the differential arithmetic circuit 406 is
TE1 = (s1 + s4) − (s2 + s3) (Equation 10)
Can be obtained.

  In this example, the same effects as in the example of FIG. 2 can be obtained with a configuration in which the number of detection regions and the number of head amplifiers are smaller than in the example shown in FIG.

  Hereinafter, still another example that provides the same effect as the optical head device having the configuration shown in FIG. 2 will be described with reference to FIG.

  FIG. 5 shows the photodetector 152. The photodetector 152 is divided into eight regions by dividing lines 306 to 309. The dividing lines 307 and 309 perpendicular to the tangent line of the groove are arranged so as to sandwich the overlapping region 200 of the + 1st order diffracted light from the groove and the −1st order diffracted light from the groove. The detection areas 210 to 213 outside the two dividing lines 307 and 309 and not including the center of the circle receive light, and the signals s1 to s4 are generated according to the amounts of light received by the detection areas 210 to 213, respectively.

The tracking error signal TE1 is
TE1 = (s1 + s4) − (s2 + s3) (Equation 11)
Can be obtained.

  The optical head device of this example can also receive the diffracted light except for most of the overlapping region 200 of the + 1st order diffracted light and the −1st order diffracted light, and has the configuration shown in FIGS. In almost the same manner as the optical head device, the characteristics of the tracking error signal can be improved. Since the optical head device having the configuration shown in FIG. 5 can perform stable tracking control with a small amount of off-track, information can be recorded and reproduced with a low error rate.

  Hereinafter, still another example that provides the same effect as the optical head device having the configuration shown in FIG. 2 will be described with reference to FIG.

  FIG. 6 shows the photodetector 153. The photodetector 153 is divided into eight regions by dividing lines 310 to 313. The dividing lines 310 and 312 parallel to the tangent of the groove are located toward the end of the cross section of the reflected light 108a on the photodetector 153. The regions 214 to 217 outside the dividing lines 310 and 312 and not including the center of the circle receive light, and the signals s1 to s4 are generated according to the amounts of light received by the regions 214 to 217, respectively.

  The tracking error signal TE1 is obtained by the same calculation as that in Equation 11 above.

  In this example, the overlapping area 200 of the + 1st order diffracted light and the −1st order diffracted light can be largely removed to receive the diffracted light, which is almost the same as the optical head device having the configuration shown in FIGS. In addition, the characteristics of the tracking error signal can be improved. Since the optical head device having the configuration shown in FIG. 6 can perform stable tracking control with a small amount of off-track, information can be recorded and reproduced with a low error rate.

  In the first embodiment, the dividing line is an example of a straight line. However, the overlapping region 200 of the + 1st order diffracted light and the −1st order diffracted light by the groove of the optical disc 105 is an area surrounded by a curve. Therefore, the dividing line may be formed with a curve matched to this.

(Embodiment 2)
In the second embodiment, as in the first embodiment, a case where the condition of Expression 4 is satisfied will be described.

  In the second embodiment, a configuration and a method for correcting a tracking error signal from a signal obtained from an overlapping region of a + 1st order diffracted light and a −1st order diffracted light by a groove of the optical disc 105 will be described.

  The schematic diagram of the optical system of the optical head device of Embodiment 2 is the same as that shown in FIG. For this reason, the configuration and operation of the optical system of the optical head device of the second embodiment are the same as the configuration and operation of the first embodiment, and thus the description of the configuration and operation is omitted.

  FIG. 7 shows the configuration of the detection areas 201 to 208 of the photodetector 150 according to the second embodiment and the circuit as the tracking error signal generation means 451. The photodetector 150 is divided into eight regions of detection regions 201 to 208 by dividing lines 301 to 304. The arrangement of the dividing lines is the same as in the first embodiment. The detection areas 201 to 208 receive light, and the detection areas 201 to 208 generate signals s1 to s8 according to the amount of light received. Since the method of generating the focus error signal FE and the information reproduction signal is the same as that in the first embodiment, a description thereof will be omitted.

  A circuit system as the tracking error signal generation means 451 will be described. The tracking error signal generation unit 451 includes adders 401 to 404, 407 and 408 and a dynamic operation circuit 406.

  As shown in FIG. 7, the adder 401 outputs a sum signal of “signal s1 + signal s8”, the adder 402 outputs a sum signal of “signal s2 + signal s7”, and the adder 403 outputs “signal s3 + signal”. The sum signal of “s6” is output, and the adder 404 outputs the sum signal of “signal s4 + signal s5”. The adder 407 receives the output of the adder 401 and the output signal of the adder 403, and outputs a sum signal of these output signals. The adder 408 receives the output signal of the adder 402 and the output signal of the adder 404 and outputs a sum signal of these output signals. The differential operation circuit 406 receives the output signal of the adder 407 and the output signal of the adder 408, and outputs a differential signal of these output signals.

The output signal of the differential arithmetic circuit 406 is
TE1 = (s1 + s3 + s6 + s8) − (s2 + s4 + s5 + s7) (Equation 12)
Given in.

  The method of processing the signal generated by the detection region that receives the light in the overlapping region 200 of the central + 1st order diffracted light and the −1st order diffracted light in the second embodiment is different from the normal push-pull method. In the second embodiment, the polarity of a part of the signal generated by the detection area that receives the light in the overlapping area 200 is inverted, and the polarity of the signal is inverted, and the remaining part of the signal generated by the detection area Are added to correct the tracking error signal.

  According to the second embodiment, when the tilt occurs in the radial direction under the same conditions as in the first embodiment, if the off-track amount is corrected to 0, the tracking error signal shifts in symmetry by 14%. This is about ½ of the conventional optical head device, and the effect of suppressing the radial tilt is particularly great.

  As described above, the optical head according to the second embodiment can realize stable tracking control while maintaining a small off-track amount even when the apparatus optical disk 105 is tilted. As a result, information recording / reproduction can be realized with a low error rate.

  Hereinafter, still another example that provides the same effect as that of the optical head device having the configuration shown in FIG. 7 will be described with reference to FIG.

  FIG. 8 shows the photodetector 153. The photodetector 153 is divided into 12 detection areas 218 to 229 by dividing lines 315 to 320. The dividing line 315 and the dividing line 319 are parallel to the tangent line of the groove of the optical disc, and are arranged so as to sandwich the overlapping region of the + 1st order diffracted light and the −1st order diffracted light from the groove. The distance between the dividing line 315 and the dividing line 319 is approximately the same as W in Expression 5 above. The dividing lines 316 to 318 are arranged at equal intervals between the dividing line 315 and the dividing line 319. The detection areas 218 to 229 generate signals s1 to s12 according to the amount of received light, respectively.

  A circuit system as the tracking error signal generation means 451 will be described. The tracking error signal generation unit 451 includes adders 401 to 404 and 409 to 412 and a differential operation circuit 406.

The adder 401 outputs the sum signal of the signals s1 and s12, the adder 402 outputs the sum signal of the signals s2 and s11, the adder 403 outputs the sum signal of the signals s3 and s10, and the adder 404 outputs the sum signal of the signals s4 and s9, the adder 409 outputs the sum signal of the signals s5 and s8, and the adder 410 outputs the sum signal of the signals s6 and s7. The adder 411 receives the output signals output from the adders 401, 403, and 409, and outputs a sum signal of these output signals. The adder 412 receives the output signals output from the adders 402, 404, and 410, and outputs a sum signal of these output signals. The differential operation circuit 406 receives the output signal of the adder 411 and the output signal of the adder 412 and outputs a differential signal that is the difference between these output signals. The output signal of the differential arithmetic circuit 406 is
TE1 = (s1 + s3 + s5 + s8 + s10 + s12)
− (S2 + s4 + s6 + s7 + s9 + s11) (Equation 13)
Given by.

  In the optical head device having the configuration shown in FIG. 8, even if the radial tilt is 0.4 degrees, the off-track amount is 0.042 μm.

  When the off-track amount is corrected to 0, in the optical head device having the configuration shown in FIG. 8, the symmetry deviation of the tracking error signal is 18%. On the other hand, in the conventional optical head device, the deviation in symmetry of the tracking error signal is 31%, and the optical head device having the configuration shown in FIG. It has better tracking error signal symmetry than the optical head device.

  In addition, when the objective lens shift is 150 μm and the off-track amount is corrected to 0, in the optical head device having the configuration shown in FIG. 8, the deviation in symmetry of the tracking error signal becomes 8%. In the head device, the deviation in symmetry of the tracking error signal is 16%. The optical head device having the configuration shown in FIG. 8 can reduce the poor symmetry of the tracking error signal by about half compared to the conventional optical head device.

  As described above, the optical head device according to the second embodiment can realize stable tracking control while maintaining a small off-track amount even when the optical disk 105 is tilted or the like. In the optical head device of the second embodiment, information recording / reproduction can be realized with a low error rate.

  In this embodiment, the overlapping region of the + 1st order and −1st order diffracted light by the track is divided into four in the direction perpendicular to the tangent to the groove of the optical disk 105, but it may be further finely divided. The same effect as this embodiment can be obtained.

  Further, considering the astigmatism method as a focusing method, a dividing line 320 perpendicular to the tangent line of the groove is provided, but when there is no dividing line, the adders 401 to 404, 409, and 410 are not necessary. become. Even in such a case, the effect can be obtained in the same manner as the embodiment shown here.

(Embodiment 3)
In the third embodiment, as in the first and second embodiments, a case where the condition of Expression 4 is satisfied will be described.

  In the third embodiment, a correction signal corresponding to a disturbance is generated from a signal obtained from the overlapping region 200 of the + 1st order diffracted light and the −1st order diffracted light by the groove, and the tracking error signal is corrected.

  The schematic diagram of the optical system of the optical head device of Embodiment 3 is the same as that shown in FIG. For this reason, the configuration and operation of the optical system of the optical head device according to Embodiment 3 are the same as the configuration and operation of Embodiment 1, and therefore the description of the configuration and operation is omitted.

  FIG. 9 shows the detection areas 201 to 208 of the photodetector 150 of the third embodiment and the configuration of the circuit as the tracking error signal generation means 451.

  The photodetector 150 is divided into eight regions of detection regions 201 to 208 by dividing lines 301 to 304. The arrangement of the dividing lines is the same as in the first embodiment. The detection areas 201 to 208 generate signals s1 to s8 according to the amount of received light, respectively.

  Since the method of generating the focus error signal FE and the information reproduction signal is the same as that in the first embodiment, a description thereof will be omitted. The input signals input to the adders 401 to 404 and the method by which the adders 401 to 404 calculate those input signals are the same as in the first embodiment.

  A circuit system as the tracking error signal generation unit 451 according to the third embodiment will be described. The tracking error signal generation means 451 includes adders 401 to 404, variable gain amplification circuits 413 and 414, and differential operation circuits 406, 415 and 416.

  The variable gain amplifier circuit 414 receives the output signal from the adder 402 and outputs a signal obtained by multiplying this signal by α1. Here, α1 is a predetermined value. The variable gain amplifier circuit 413 receives the output signal from the adder 403 and outputs a signal obtained by multiplying this signal by α2. Here, α2 is a predetermined value.

  The differential operation circuit 406 receives the output signal of the adder 401 and the output signal of the adder 404, and outputs a differential signal obtained by subtracting the output signal of the adder 404 from the output signal of the adder 401.

  The differential arithmetic circuit 415 receives the output signal of the variable gain amplifier circuit 413 and the output signal of the variable gain amplifier circuit 414, and outputs a differential signal that is the difference between these output signals.

  The differential arithmetic circuit 416 receives the output signal of the differential arithmetic circuit 406 and the output signal of the differential arithmetic circuit 415, and outputs a differential signal that is the difference between these output signals.

The output signal of the differential arithmetic circuit 416 is
TE1 = (s1 + s8) − (s4 + s5)
− {Α1 · (s2 + s7) −α2 · (s3 + s6)} (Equation 14)
Given in.

  The gain α1 of the variable gain amplifier circuit 414 and the gain α2 of the variable gain amplifier circuit 413 are determined in consideration of the generation amount and polarity of the radial tilt and the generation amount and polarity of the objective lens shift. By changing the gains α1 and α2, the difference between | TEmax−TE0 | and | TEmin−TE0 | can be reduced. In other words, since the correction amount can be adjusted by adjusting the gain, Embodiment 3 has a significant improvement effect that the difference can be reduced compared to Embodiment 2.

  Therefore, in the third embodiment, stable tracking control can be realized while maintaining a small off-track amount even when the optical disk 105 is tilted, etc., and information recording / reproduction can be realized with a low error rate. it can.

  In the third embodiment, the overlapping region 200 of the + 1st order and −1st order diffracted light by the track is divided into two in the direction perpendicular to the tangent to the groove of the optical disc 105, but it may be further finely divided. Even in such a case, such an optical head device can obtain the same effects as those of the third embodiment described above.

(Embodiment 4)
In the fourth embodiment, as in the first, second, and third, a case where the condition of Expression 4 is satisfied will be described.

  In the fourth embodiment, the optical transmittance of the region including the overlapping region of the + 1st order diffracted light and the −1st order diffracted light by the groove is reduced, and the characteristics of the tracking error signal are improved.

  FIG. 10 a shows a schematic diagram of an optical system of the optical head device of the fourth embodiment. The configuration of the optical system in FIG. 10 a is the same as the configuration of the optical system in FIG. 1 except for the objective lens 109. For this reason, detailed description of components other than the objective lens 109 is omitted.

  Hereinafter, the objective lens 109 in FIG. 10A will be described with reference to FIG. 10B.

  FIG. 10 b shows a front view of the objective lens 109 that is a part of the condensing optical system of the fourth embodiment. As dimming means, a hologram is provided in the shaded portion 110 of the objective lens 109. The light diffracted by the hologram becomes unnecessary light, does not contribute to signal reproduction, and only the 0th-order light that has not been diffracted is effectively collected on the information layer 108 of the optical disc 105.

  The detection regions 251 to 254 of the photodetector 150 of the fourth embodiment may be arranged as shown in FIG. 43a. When the detection areas 251 to 254 are arranged as shown in FIG. 43a, the tracking error signal TE1, the focus error signal FE, and the information reproduction signal RF are obtained by the above-described Expression 1, Expression 2, and Expression 3.

  The result of comparison between the fourth embodiment and the conventional optical head device will be described below regarding the deviation in symmetry of the tracking error signal.

  The radial tilt is set to 0.4 degrees and the off-track amount is set to 0 under the same conditions as in the first embodiment, where the transmittance T of the region 110 is 55% and the ratio of the radius of the region 110 to the radius of the objective lens 109 is 0.72. When corrected, in Embodiment 4, the tracking error signal symmetry shift is suppressed to 17%, but in the conventional optical head device, the tracking error signal symmetry shift is 31%. The fourth embodiment can reduce the deviation of the symmetry of the tracking error signal by about ½ as compared with the conventional optical head device.

  In the fourth embodiment, stable tracking control can be realized while maintaining a small off-track amount even when the optical disk 105 is tilted or the like. Thus, the fourth embodiment can realize information recording / reproduction with a low error rate.

  In this embodiment, another spot may be formed by diffracted light of a hologram provided on the objective lens 109. In this case, the 0th-order diffracted light can be used as a DVD spot having a substrate thickness of 0.6 mm, and the 1st-order diffracted light can be used as a CD spot having a substrate thickness of 1.2 mm. By forming another spot with the diffracted light of the hologram, the function of the bifocal lens can be achieved.

  In this embodiment, the hologram is provided as the dimming means, but the same effect can be obtained even if a reflection film having an appropriate transmittance or an absorption film is attached to the objective lens.

  In addition, as shown in FIG. 11, instead of directly attaching the dimming means to the objective lens, a similar hologram element or filter 111 with a film is held by the holding means 106 so as not to move relative to the objective lens. May be. In these cases, the same effects as those shown in this embodiment can be obtained.

  The dimming means shown in FIG. 11 covers the surface of the objective lens 104 farther from the information storage medium, but may cover the surface closer to the information storage medium. Similarly, the dimming means in FIG. 10a may cover the surface of the objective lens 109 closer to the information storage medium.

  In this embodiment, the dimming means is provided integrally with the condensing optical system, but may be provided separately on the fixed optical system side. FIG. 12 shows an example in which there is a dimming means in the optical path from the light source to the information storage medium. As shown in FIG. 12, the light emitted from the semiconductor laser 101 as the light source passes through the filter 111 as the light reducing means, the light amount near the center is reduced, and is reflected by the parallel plate beam splitter 102. In this case, the 0th order light in the overlapping region of the + 1st order diffracted light and the −1st order diffracted light from the track of the optical disk 105 is reduced, and the influence of the overlapping region can be reduced.

  FIG. 13 shows an example in which there is a dimming means in the optical system from the information storage medium to the photodetector. As shown in FIG. 13, a method of providing a light reduction region 113 below the parallel plate prism 112 may be used. Even if it arrange | positions in this way, the influence of the overlapping area | region of a + 1st order diffracted light and a -1st order diffracted light can be reduced, and the substantially same effect is acquired.

  In the first to fourth embodiments, the astigmatism method is used as a method for obtaining the focus error signal. However, the effect of the present invention is not limited to this, and the focus method may be a Foucault method or a spot size method. This method can be combined with the above method, and is not limited to the focus method.

(Embodiment 5)
In the fifth embodiment, a case where the condition of Expression 4 is satisfied will be described as in the first to fourth embodiments.

  In the fifth embodiment, a hologram element or a step prism is used as the dividing means. A spot size method is used as a method for obtaining a focus error signal.

  FIG. 14 is a schematic diagram of an optical system of the optical head device according to the fifth embodiment.

  Hereinafter, the configuration and operation of the fifth embodiment will be described with reference to FIG.

  Light emitted from the semiconductor laser 101 as a light source is converted into parallel light by the collimator lens 103 and reflected by the beam splitter 115. This light becomes convergent light by the objective lens 104 which is a part of the condensing optical system. The convergent light is collected on the information layer 108 of the optical disc 105 as an information storage medium. The reflected light 108a reflected by the information layer 108 passes through the objective lens 104 again and becomes parallel light. The reflected light 108 a that has become parallel light passes through the beam splitter 115 and becomes convergent light at the detection lens 116. The 108a that has become the converged light is diffracted by the hologram element 117, which is a dividing means. The −1st order diffracted light 108 b and the + 1st order diffracted light 108 c diffracted by the hologram element 117 are received by the photodetector 154.

  FIG. 15 shows a pattern of area division of the hologram element 117, a detection area of the photodetector 154, and cross-sectional shapes of the −1st order diffracted light 108 b and the + 1st order diffracted light 108 c on the photodetector 154.

  The hologram element 117 is divided into a plurality of strip-shaped regions. Symbols attached to the respective regions correspond to symbols attached to the cross sections of the −1st order diffracted light 108b and the + 1st order diffracted light 108c on the photodetector 154 in FIG. The −1st order diffracted light 108b generated from the region represented by the uppercase letters A to D is condensed on the side farther from the detection lens 116 than the −1st order diffracted light 108b generated from the area represented by the lowercase letters a to d.

  When the condensing point F0 of the light emitted from the objective lens 104 coincides with the information layer 108 of the optical disc 105, the cross section of the diffracted light and the small letter a on the photodetector 154 marked with capital letters AD. The optical system and the hologram element 117 are designed so that the cross section of the diffracted light marked with -d has the same size.

  The detection areas 230 to 232 output signals f1 to f3 according to the received light quantity.

The focus error signal FE is
FE = f1 + f3-f2 (Equation 15)
Sought by.

  When the information layer 108 of the optical disc 105 is moved away from the objective lens 104 from the condensing point F0 of the light emitted from the objective lens 104, the cross section of the −1st order diffracted light 108b with the symbols A to D is made smaller and lowercase. The cross section of the −1st order diffracted light 108b with symbols a to d is enlarged. Therefore, the signals f1 and f3 decrease, the signal f2 increases, and the focus error signal FE decreases.

  When the information layer 108 of the optical disk 105 is closer to the objective lens 104 than the condensing point F0 of the light emitted from the objective lens 104, the cross section of the −1st order diffracted light 108b with the symbols of capital letters A to D becomes larger and lowercase letters. The cross section of the −1st order diffracted light 108b marked with “a” to “d” becomes smaller. Therefore, the signals f1 and f3 increase, the signal f2 decreases, and the focus error signal FE increases.

  As a result, focus control for maintaining the condensing point F0 on the information layer 108 is realized.

  Signals obtained according to the amount of light received from the detection regions 233 to 236 of the photodetector 154 are denoted by t1 to t4. An arithmetic circuit (not shown) as a tracking error signal generating means generates a tracking error signal TE1.

The tracking error signal TE1 is
TE1 = (t1 + t4) − (t2 + t3) (Equation 16)
Sought by.

  This substantially gives a difference in the amount of light between the non-hatched area and the hatched area in the hologram element 117 of FIG.

  A phase difference tracking error signal TE2 is obtained by comparing the phases of (signal t1 + signal t3) and (signal t2 + signal t4).

The RF signal for reproducing information is given by RFf in Expression 17 or RFt in Expression 18 or the sum of both RFf and RFt.
RFf is
RFf = f1 + f2 + f3 (Equation 17)
Sought by.
RFt is
RFt = t1 + t2 + t3 + t4 (Equation 18)
Sought by.

  A feature of the fifth embodiment is that several regions on both sides of a dividing line passing through the center of the opening and parallel to the track are interchanged diagonally. In FIG. 15, a total of eight of A and D, B and C, a and d, and b and c are interchanged. Thereby, the effect similar to Embodiment 2 can be acquired. In the fifth embodiment, when the off-track amount is corrected to 0 when the tilt occurs in the radial direction at 0.4 degrees, the deviation in the symmetry of the tracking error signal becomes 14%. This deviation in symmetry of the tracking error signal is about ½ of the deviation in symmetry of the tracking error signal of the conventional optical head device. The fifth embodiment particularly suppresses radial tilt.

  In the fifth embodiment, stable tracking control can be realized while maintaining a small off-track amount even when the optical disk 105 is tilted or the like. Thus, the fifth embodiment can realize information recording / reproduction with a low error rate.

  Further, as another region pattern, an example in which the photodetector 153 shown in FIG. 8 of the second embodiment is used if only a part of the central region is diagonally replaced like the hologram element 118 shown in FIG. The same effect can be obtained. In this case, when the radial tilt is 0.4 degrees, the off-track amount is 0.042 μm. When the off-track amount is corrected to 0, the deviation in symmetry of the tracking error signal becomes 18%. When the radial tilt is 0.4 degrees, when the off-track amount is corrected to 0, in the conventional optical head device, the deviation of symmetry of the tracking error signal is 31%. That is, the fifth embodiment using the hologram element 118 shown in FIG. 16 can greatly reduce the deviation of the symmetry of the tracking error signal as compared with the conventional optical head device.

  Further, in the fifth embodiment using the hologram element 118 shown in FIG. 16, if the off-track amount is corrected to 0 when the objective lens shift is 150 μm, the deviation in symmetry of the tracking error signal becomes 8%. On the other hand, in the conventional optical head device, when the off-track amount is corrected to 0 when the objective lens shift is 150 μm, the deviation in symmetry of the tracking error signal is 16%. That is, the fifth embodiment using the hologram element 118 shown in FIG. 16 can reduce the deviation of the symmetry of the tracking error signal to about half compared to the conventional optical head device.

  In the fifth embodiment using the hologram element 118 shown in FIG. 16, it is possible to realize stable tracking control while maintaining a small off-track amount with respect to the tilt of the optical disk 105 or the like. Accordingly, the fifth embodiment using the hologram element 118 shown in FIG. 16 can realize information recording / reproduction with a low error rate.

  As described above, in the fifth embodiment, by using the hologram element as the dividing unit, a great effect can be realized without increasing the detection area of the photodetector from the conventional example. For this reason, it is not necessary to increase the head amplifier for obtaining the RF signal, and the circuit load is small.

  Further, in the fifth embodiment, a lower-case symbol a that divides a region by a dividing line that passes through the center of the opening and is perpendicular to the tangent of the track and generates a spherical wave having a condensing point on the side close to the collimator lens 103 is used. The region represented by ~ d and the region represented by uppercase symbols A to D that create a spherical wave having a condensing point on the far side are arranged so as to contact each other across this dividing line. In addition, these two types of regions are alternately arranged outside the opening that is not normally irradiated with light.

  In the case where the dividing line is not provided in the direction perpendicular to the track and the elongated region reaches the end of the opening in the direction parallel to the track, if the center of the opening of the hologram element 117 and the objective lens 104 is shifted, the photodetector 154 The balance between the amount of light entering the region represented by lowercase symbols a to d and the amount of light entering the region represented by uppercase symbols A to D is lost. Further, when the condensing point F0 of the light emitted from the objective lens 104 is shifted from the intelligence layer 108 of the optical disk 105 and defocusing occurs, ± first-order diffracted light and zero-order light by the track of the optical disk 105 are generated. In the overlapping portion, a light and dark stripe pattern parallel to the track is generated. Depending on how the stripe pattern and the area of the hologram element 117 are overlapped, the balance between the amount of light entering the region represented by lowercase symbols a to d and the amount of light entering the region represented by uppercase symbols A to D is balanced. Collapse.

  According to the method of the fifth embodiment, such balance deviation is eliminated in principle.

  In the calculation, in the case of the conventional example in which the dividing line is not perpendicular to the track tangent, the numerical aperture NA of the objective lens is 0.5, the light wavelength λ is 0.795 μm, the diameter of the objective lens is 4 mm, and the hologram element When the width of each region is 0.2 mm and the center of the objective lens and the polarization anisotropic hologram element is shifted by 100 μm, the focus gain changes by 3.4 dB with a defocus of ± 2 μm.

  In the case of the arrangement as in the fifth embodiment, the focus gain changes only by 1.2 dB under the same conditions in calculation. This fluctuation amount is about 1/3 of the conventional example, which is greatly reduced. As a result, stabilization of the focus control can be realized and it becomes strong against disturbance, so that an error rate at the time of information reproduction is lowered.

  Further, if two regions are provided alternately outside the opening without dividing the track in the vertical direction, the focus gain changes only by 1.8 dB under the same conditions in calculation. This variation is about ½ of the conventional example. As a result, stabilization of the focus control can be realized, and the error rate at the time of information reproduction decreases.

  Further, the pattern of the area of the hologram element as the dividing means can be freely set as compared with the pattern of the detection area of the photodetector, and the pattern of the area suitable for the purpose can be easily realized.

  Although the dividing means of the fifth embodiment is simply a hologram element, a polarization anisotropic hologram element and a quarter wavelength plate may be used in combination. In this case, the light utilization efficiency can be increased without impairing the effects of the present invention.

  In the fifth embodiment, the dividing means for simultaneously realizing the invention related to the focus control and the invention related to the tracking control is shown. However, the invention related to the focus control and the invention related to the tracking control are independent, and only one of them is used. If it is set as a structure, the effect according to the invention can be acquired independently, respectively.

  Further, as the dividing means, there is a method using a step prism or the like in addition to the hologram element. FIG. 17 shows a schematic diagram of the optical system in that case. A step prism 119 is used instead of the hologram element 117 of FIG. The light separated by the step prism is received by the photodetector 154. In this case as well, the same effect as when the hologram element is used can be obtained.

(Embodiment 6)
A configuration and method for reproducing information recorded at an off-track position with respect to a groove of an optical disc as an information storage medium will be described below.

  The schematic diagram of the optical system of the optical head device of Embodiment 6 is the same as that shown in FIG. For this reason, the configuration and operation of the optical system of the optical head device according to the fifth embodiment are the same as the configuration and operation of the sixth embodiment, and thus the description of the configuration and operation is omitted.

  FIG. 18 shows a detection region of the photodetector 150 according to the sixth embodiment, and a circuit configuration as the information reproduction signal generation unit 450 and the tracking error signal generation unit 451.

  The photodetector 150 is divided into eight regions of detection regions 201 to 208 by dividing lines 301 to 304. The arrangement of the dividing lines is the same as in the first embodiment. Signals obtained according to the amounts of light received from the detection areas 201 to 208 are denoted by s1 to s8, respectively.

  18 includes adders 401 to 404 and 405 as in the first embodiment. 18 includes adders 417 and 419 and differential operation circuits 418 and 420. The tracking error signal generation means 451 includes adders 401 to 404, 421, and 422 and a differential operation circuit 423.

  Hereinafter, an operation when reading a pit row recorded at an off-track position will be described with reference to FIGS. 19a, 19b, and 19c.

  FIG. 19a shows an optical disc in which grooves 501 and pits 502 are arranged on the optical disc. The grooves 501 and pits 502 are recorded on the information layer 108 in FIG.

  In the first address zone 504, the center of the pit row of the track 508 is off-tracked by a predetermined distance with respect to the zone 503 in which the groove is disposed and the track 507 passing through the groove center of the zone 506. In the second address zone 505, the center of the pit row of the track 509 is off-tracked by a predetermined distance in the direction opposite to the track 508.

  When the focusing point F0 of the light emitted from the objective lens 104 is in the zone 503 or the zone 506, if the tracking control is performed, the focusing point F0 exists on the track 507, for example, the point 510. As the optical disk 105 rotates, the relative position with the optical head device moves, and the condensing point F0 moves on the extension line of the track 507 in the order of point 511, point 512, and point 513. While the focusing point F0 is in the first address zone 504 and the second address zone 505, the tracking error signal is held.

  As in the first embodiment, the focus error signal FE is obtained by calculating FE = (s1 + s2 + s5 + s6) − (s3 + s4 + s7 + s8).

The tracking error signal can be obtained by the calculation of Equation 19 below. In the tracking error signal generation unit 451 in FIG. 18, the adder 421 receives the signal t1 output from the adder 401 and the signal t2 output from the adder 402, and outputs a signal that is the sum of the signal t1 and the signal t2. To do. The adder 422 receives the signal t3 output from the adder 403 and the signal t4 output from the adder 404, and outputs a signal that is the sum of the signal t3 and the signal t4. The differential operation circuit 423 receives the signal output from the adder 421 and the signal output from the adder 422, and outputs these differential signals. That is, the output signal TE of the differential arithmetic circuit 423 is
TE = (t1 + t2) − (t3 + t4) (Equation 19)
Sought by. Tracking control is performed by the tracking error signal TE.

  The information reproduction signal generator 450 in FIG. 18 generates the information reproduction signal RF in the same manner as the information reproduction signal generator 450 in FIG. A method for generating the information reproduction signal will be described below. The information reproduction signal generation unit 450 includes adders 401 to 405.

The adder 401 receives the signal s1 and the signal s8, and outputs a signal t1 that is the sum of the signal s1 and the signal s8. The adder 402 receives the signal s2 and the signal s7, and outputs a signal t2 that is the sum of the signal s2 and the signal s7. The adder 403 receives the signal s3 and the signal s6, and outputs a signal t3 that is the sum of the signal s3 and the signal s6. The adder 404 receives the signal s4 and the signal s5, and outputs a signal t4 that is the sum of the signal s4 and the signal s5. The adder 405 receives the output signals t1 to t4 filed from the adders 401 to 404, and outputs a signal that is the sum of these signals. The information reproduction signal RF output from the adder 405 is
RF = t1 + t2 + t3 + t4 (Equation 20)
Given in.

Adder 417 receives signals t2, t3, and t4 output from adders 402, 403, and 404, and outputs a signal that is the sum of these signals. The differential operation circuit 418 receives the output signal from the adder 401 and the output signal from the adder 417, and outputs these differential signals. The signal RFa1 output from the differential arithmetic circuit 418 is
RFa1 = t1− (t2 + t3 + t4) (Equation 21)
Given in.

The adder 419 receives the signals t1, t2, and t3 output from the adders 401, 402, and 403, and outputs a signal that is the sum of these signals. The differential operation circuit 420 receives the output signal from the adder 419 and the output signal from the adder 404, and outputs those differential signals. The signal RFa2 output from the differential arithmetic circuit 420 is
RFa2 = (t1 + t2 + t3) −t4 (Equation 22)
Given in.

  The address detection circuit 424 receives the tracking error signal TE from the differential arithmetic circuit 423, and determines whether the condensing point F0 of the light emitted from the objective lens 104 is in the grooved zone 503 or the zone 506. It is determined whether it is in the address zone 504 or the second address zone 505, and an identification signal as a result of the determination is output.

  The control circuit 425 receives the identification signal output from the address detection circuit 424 and controls the switch 426 and the switch 427 based on the identification signal.

  The switch 426 receives a signal output from the differential operation circuit 418 and a signal output from the differential operation circuit 420, and outputs one of them.

  The switch 427 receives the signal output from the adder 405 and the signal output from the switch 426 and outputs one of them. A signal output from the switch 427 is used to reproduce information or an address recorded in the information storage medium.

  When the condensing point F0 of the light output from the objective lens 104 is in the grooved zone 503 or the zone 506, the control circuit 425 outputs the output signal RF of the adder 405 from the switch 427. Control the switch. Further, when the focal point F0 is in the first address zone 504, the switch is controlled so that the output signal RFa1 of the differential arithmetic circuit 418 is output from the switch 427. Further, when the focal point F0 is in the second address zone 505, the switch is controlled so that the output signal RFa2 of the differential operation circuit 420 is output from the switch 427.

  That is, when the focal point F0 is on the point 511 of the first address zone 504, as shown in FIG. 19b, from the differential signal that is the difference between the two regions output from the two regions across the dividing line 301. The information recorded as a pit row on the track 507 is reproduced.

  When the condensing point F0 is on the point 512 of the second address zone 505, as shown in FIG. 19c, the track is obtained from the differential signal that is the difference between the two regions sandwiched by the dividing line 303. Information recorded as a pit row on 507 is reproduced.

  Hereinafter, the numerical aperture NA of the objective lens is set to 0.6, the wavelength of light λ is set to 0.660 μm, the gap Gp is set to 1.48 μm, and the track 508 and the track 509 are each 0.37 μm with respect to the track 507. The result of comparing the optical head device of the sixth embodiment and the conventional optical head device with respect to jitter in the optical disk that is off-tracked each time is shown.

  In the conventional optical head device in which the detection area is divided by the dividing line at the center of the opening and information is reproduced from the differential signals output from the divided areas, the calculated jitter is 6.4%. It becomes.

  On the other hand, in the sixth embodiment, the detection area is divided by the dividing line 303 or the dividing line 301 at the position of d = 0.23, where the opening is a circle with a radius of 1 and the distance from the dividing line 302 is d. When information is reproduced from a differential signal that is a difference output from each region, the calculated jitter is 1.8%. The sixth embodiment can improve the jitter by 4% or more as compared with the conventional optical head device.

  If d is 0.1 or more and d is 0.3 or less, the jitter according to the sixth embodiment is 3% or less, and the jitter according to the sixth embodiment is less than half of the jitter caused by the conventional optical head device. become.

  As described above, in the configuration as shown in the present embodiment, the pit row at the off-track position can be reproduced with a small amount of jitter, so the margin for disturbances and the like is increased. It is possible to stabilize the recording and reproduction of information on the optical disk on which information is recorded.

  Hereinafter, an optical head device having a photodetector different from the photodetector shown in FIG. 18 will be described with reference to FIG.

  FIG. 20 shows detection areas 201, 204, 205, 208, and 209 of the photodetector 151, an information reproduction signal generation means 450, and a tracking error signal generation means 451.

  20 includes adders 401, 404, 405, 417, and 419, and differential operation circuits 418 and 420. 20 includes adders 401 and 404 and a differential operation circuit 423. The tracking error signal generation means 451 shown in FIG.

  The adder 405 generates a signal corresponding to the amount of light received by all the detection areas 201, 204, 205, 208, and 209 of the photodetector 151. Further, the differential arithmetic circuit 418 generates a differential signal {signal t1- (signal t2 + signal t3)}. Further, the differential arithmetic circuit 420 generates a differential signal {(signal t1 + signal t2) −signal t3}. Here, the signal t 1 is generated by the adder 401, the signal t 2 is the same signal as the signal s 5 output by the region 209, and the signal t 3 is generated by the adder 404.

  The tracking error signal is a signal t1 obtained by adding the signals output from the two regions on the left side of the dividing line 301, and a signal t3 obtained by adding the signals output by the two regions on the right side of the dividing line 303. The differential signal is the difference between

  With the configuration described above, the optical head device having the photodetector shown in FIG. 20 can stabilize the recording and reproduction of information on and from the optical disk on which information such as addresses is recorded.

  Hereinafter, an optical head device having an information reproduction signal generation unit different from the information reproduction signal generation unit shown in FIG. 18 will be described with reference to FIGS. 21a, 21b, and 21c.

  FIG. 21a shows an optical disc in which grooves 501 and pits 502 are arranged on the optical disc. The grooves 501 and pits 502 are recorded on the information layer 108 in FIG.

  FIGS. 21 b and 21 c schematically show the photodetector 350 and the information reproduction signal generating means 450.

  FIG. 21 b shows a circuit configuration necessary for reproducing the information recorded in the first address zone 504. FIG. 21 c shows a circuit configuration necessary for reproducing the information recorded in the second address zone 505. Information reproduction signal generation means 450 includes adder 430 and differential operation circuit 431 shown in FIG. 21b, and adder 432 and differential operation circuit 433 shown in FIG. 21c.

  The differential operation circuit 431 generates the reproduction signal RFa3 based on the following equation 23, and the differential operation circuit 433 generates the reproduction signal RFa4 based on the following equation 24.

RFa3 = t1- (t3 + t4) (Equation 23)
RFa4 = (t1 + t2) −t4 (Equation 24)
When reproducing the information recorded in the first address zone 504, the reproduction signal RFa3 is used. When reproducing the information recorded in the second address zone 505, the reproduction signal RFa4 is used. The information reproduction signal generation unit 450 may include a selection unit that selects the reproduction signal RFa3 or the reproduction signal RFa4.

  In the following, the numerical aperture of the objective lens is NA = 0.6, the wavelength of light is λ = 0.660 μm, the gap between the grooves is Gp = 1.48 μm, and the track 508 and the track 507 21 shows the result of comparison between the optical head device having the configuration of FIGS. 21b and 21c and the conventional optical head device with respect to the jitter of the optical disk in which 509 is off-tracked by 0.37 μm.

  As described above, in the conventional optical head device in which the detection area is divided by the dividing line at the center of the aperture and information is reproduced from the differential signals that are the respective differences output from the divided areas, Is 6.4%.

  On the other hand, in the optical head device having the configuration of FIGS. 21b and 21c, the opening is a circle with a radius of 1, the distance from the dividing line 302 is d, and the dividing line 303 or the dividing line 301 at the position of d = 0.23 is used. When the detection area is divided and information is reproduced from the differential signal RFa3 or RFa4 obtained by calculating the signal output from the divided area as described above, the calculated jitter is 1.4%. The optical head device having the configuration shown in FIGS. 21b and 21c can improve the jitter by 5% or more as compared with the conventional optical head device.

  As described above, even with the configuration shown in the present embodiment, the pit row at the off-track position can be reproduced with a small amount of jitter, so the margin for disturbances and the like is increased. It is possible to stabilize the recording and reproduction of information on the optical disk on which information is recorded.

  Hereinafter, an optical head device having information reproduction signal generation means different from the information reproduction signal generation means shown in FIGS. 18 and 20 will be described with reference to FIGS. 22a and 22b.

  FIG. 22a shows an optical disc in which grooves 501 and pits 502 are arranged on the optical disc. The grooves 501 and the pits 502 are recorded on the information layer in FIG.

  FIG. 22 b shows an outline of the photodetector 351 and the information reproduction signal generation means 450.

  The information reproduction signal generation unit 450 includes a differential operation circuit 434. The differential operation circuit 434 generates the reproduction signal RFa0 based on the following equation 25.

RFa0 = t1-t4 (Equation 25)
The reproduction signal RFa0 is used as a reproduction signal in the first and second address zones 504 and 505, and information is reproduced.

  In the following, the numerical aperture of the objective lens is NA = 0.6, the wavelength of light is λ = 0.660 μm, the gap between the grooves is Gp = 1.48 μm, and the track 508 and the track 507 Reference numeral 509 shows the result of comparison between the optical head device having the configuration of FIG. 22b and the conventional optical head device with respect to the jitter of the optical disk that is off-tracked by 0.37 μm.

  As described above, in the conventional optical head device, the calculated jitter is 6.4%. The jitter by the optical head device having the configuration of FIG. 22b is 2.6%. The optical head device having the configuration of FIG. 22b can improve the jitter by nearly 4% as compared with the conventional optical head device.

  As described above, even with the configuration shown in the present embodiment, the pit row at the off-track position can be reproduced with a small amount of jitter, so the margin for disturbances and the like is increased. It is possible to stabilize the recording and reproduction of information on the optical disk on which information is recorded.

  In the optical head device having the configuration of FIG. 22b, the information reproduction signal generating means 450 outputs the information being reproduced depending on whether it is located in the first address zone 504 or the second address zone 505. There is no need to select a signal. Therefore, the optical head device having the configuration of FIG. 22b can be realized with a relatively simple circuit system.

  Hereinafter, an optical head device having information reproduction signal generation means different from the information reproduction signal generation means shown in FIGS. 18, 20 and 22 will be described with reference to FIGS. 23a and 23b.

  FIG. 23a shows an optical disc in which grooves 501 and pits 502 are arranged on the optical disc. The grooves 501 and pits 502 are recorded on the information layer 108 in FIG.

  FIG. 23 b shows an outline of the photodetector 352 and the information reproduction signal generation means 450.

  The information reproduction signal generation means 450 includes a differential operation circuit 437 and adders 435 and 436. The differential operation circuit 437 generates a reproduction signal RFa00 based on the following equation (26).

RFa00 = (t1 + t3) − (t2 + t4) (Equation 26)
RFa00 is used as a reproduction signal in the first and second address zones 504 and 505.

  As described above, in the conventional optical head device, the calculated jitter is 6.4%. The jitter by the optical head device having the configuration of FIG. 23b is 1.2%. The optical head device having the configuration of FIG. 23b can improve the jitter close to 5% as compared with the conventional optical head device.

  In the optical head device having the configuration of FIG. 23b, the information reproduction signal generation means 450 outputs the information being reproduced depending on whether it is located in the first address zone 504 or the second address zone 505. There is no need to select a signal. Therefore, the optical head device having the configuration of FIG. 23b can be realized with a relatively simple circuit system.

(Embodiment 7)
In the seventh embodiment, as in the sixth embodiment, a pit string composed of a mark and a space recorded at an off-track position is reproduced with respect to a groove of an optical disk as an information storage medium.

  The optical system of the optical head device of the seventh embodiment is the same as the optical system of the fifth embodiment shown in FIG. 14 except for the following points. In the optical system of the optical head device according to the seventh embodiment, the hologram element 120 is used instead of the hologram element 117 shown in FIG. 14, and the photodetector 155 is used instead of the photodetector 154.

  A region division pattern of the hologram element 120 will be described with reference to FIG. FIG. 24 shows the area division pattern of the hologram element 120, the detection region of the photodetector 155, and the cross-sectional shapes of the 0th-order light 108a, the −1st-order diffracted light 108b, and the + 1st-order diffracted light 108c on the photodetector 155. Yes.

  The hologram element 120 is divided into a plurality of strip-shaped regions. Symbols attached to the respective regions correspond to the symbols of the cross sections of the 0th-order light 108a, the −1st-order diffracted light 108b, and the + 1st-order diffracted light 108c on the photodetector 154 in FIG. The −1st order diffracted light 108b generated from the area of symbols of uppercase letters A to D is focused on the side farther from the detection lens 116 than the −1st order diffracted light 108b generated from the area of symbols of lowercase letters a to d. The light in the region indicated by the symbol X is not diffracted and becomes all 0th-order light 108a.

  The −1st order diffracted light 108b is received by the detection regions 230 to 232, and the + 1st order diffracted light 108c is received by the detection regions 233 to 236. The 0th order light is received by the detection region 237. The focus error signal is generated from a signal obtained according to the amount of light received from the detection areas 230 to 232.

Signals obtained according to the amount of light received in the detection areas 233 to 236 are denoted by t1 to t4, respectively. A signal obtained according to the amount of light received by the detector 237 is set to x0. The tracking error signal TE for the groove 501 of the optical disc 105 is
TE = (t1 + t4) − (t2 + t3) (Equation 27)
Obtained from.

  Let β be the ratio of the diffraction efficiency of the + 1st order diffracted light 108c diffracted in a region other than X to the 0th order light transmitted through the X region of the hologram element 120.

The information reproduction signal RF is
RF = t1 + t2 + t3 + t4 + β · x0 (Equation 28)
Obtained from.

  When reproducing the optical disk 105 having the structure as shown in FIG. 19a, if there is a condensing point F0 on the track 507 in the first address zone 504, the track 508 is obtained by performing an operation so as to obtain the following RFa1. The information recorded as a pit row is reproduced.

RFa1 = (s1 + s4) − (s2 + s3 + β · x0) (Equation 29)
Further, when the focal point F0 is on the track 507 of the second address zone 505, the information recorded as the pit string on the track 509 is reproduced by performing an operation to obtain the following expression RFa2.

RFa2 = (s1 + s4 + β · x0) − (s2 + s3) (Equation 30)
With such a configuration, the same effects as in the sixth embodiment can be obtained in the seventh embodiment. In the seventh embodiment, jitter is reduced when a pit row recorded at a position off-tracked with respect to the focal point F0 is reproduced. Therefore, in the seventh embodiment, it is possible to stabilize the recording / reproducing of information on an optical disc in which information such as an address is recorded in such a format.

(Embodiment 8)
The eighth embodiment shows an example in which the characteristics of the TE signal are improved using a hologram element. The focus uses a spot size method and the tracking uses a push-pull method.

  FIG. 25 is a schematic diagram of an optical system of the optical head device according to the eighth embodiment. Hereinafter, the configuration and operation of the optical system will be described with reference to FIG.

  The linearly polarized light 101a emitted from the semiconductor laser 101 as the light source becomes parallel light by the collimator lens 103 as a part of the condensing optical system. The parallel light 101a enters the polarization anisotropic hologram element 121 as a dividing means. The polarization direction of the light 101a emitted from the semiconductor laser 101 is arranged in a direction that does not generate diffracted light in the polarization anisotropic hologram element 121. The light 101 a that has passed through the polarization anisotropic hologram element 121 passes through the quarter-wave plate 122 and becomes circularly polarized light. The light 101a is further condensed by an objective lens 104 as a part of a condensing optical system, and is condensed on an information layer 108 of an optical disk 105 as an information storage medium.

  The holding means 106 integrally holds the polarization anisotropic hologram element 121, the quarter wavelength plate 122, and the objective lens 104. The actuator 107 moves the holding means 106 following the surface deflection and eccentricity of the optical disk 105.

  The reflected light 108 a diffracted and reflected by the information layer 108 of the optical disc 105 passes through the objective lens 104 again and becomes parallel light. The reflected light 108a that has become the parallel light passes through the quarter-wave plate 122 once again and becomes linearly polarized light that is different from the light 101a by 90 degrees. The linearly polarized light in this direction is diffracted by the polarization anisotropic hologram element 121 to generate −1st order diffracted light 108b and + 1st order diffracted light 108c. The −1st order diffracted light 108b and the + 1st order diffracted light 108c are again converged by the collimator lens 103. The −1st order diffracted light 108 b that has become the convergent light is received by the photodetector 156, and the + 1st order diffracted light 108 c is received by the photodetector 157.

  FIG. 26 shows the pattern of area division of the polarization anisotropic hologram element 121 as the dividing means, the detection areas of the photodetector 156 and the photodetector 157, and the −1st order diffracted light 108b and the + 1st order diffracted light 108c on the photodetector. The cross section of is shown. The polarization anisotropic hologram element 121 is divided into a plurality of strip-shaped regions.

  The −1st order diffracted light 108b generated from the regions represented by uppercase symbols A and B is condensed on the side farther from the collimator lens 103 than the −1st order diffracted light 108b generated from the regions represented by lowercase letters a and b.

  When the condensing point F0 of the light emitted from the objective lens 104 coincides with the information layer 108 of the optical disc 105, the cross section of the −1st order diffracted light 108b marked with capital letters A and B on the photodetector 156 The optical system and the hologram element 121 are designed so that the cross section of the −1st order diffracted light 108b with the symbols of lowercase letters a and b is the same size.

  Signals obtained according to the amounts of light received from the detection regions 238 to 243 are referred to as signals f1 to f6, respectively. The focus error signal FE is obtained by an operation corresponding to Equation 31 or Equation 32.

FE = (f1 + f3 + f5) − (f2 + f4 + f6) (Equation 31)
FE = f5-f2 (Equation 32)
When the information layer 108 of the optical disc 105 moves away from the objective lens 104 from the condensing point F0 of the output light from the objective lens 104, the cross section of the −1st order diffracted light 108b with the symbols A and B becomes smaller and lowercase letters. The cross section of the −1st order diffracted light 108b with the symbols a and b is enlarged. Accordingly, the signals f1, f3, and f5 are decreased, the signals f2, f4, and f6 are increased, and the focus error signal FE is decreased.

  When the information layer 108 of the optical disk 105 is closer to the objective lens 104 than the condensing point F0 of the light emitted from the objective lens 104, the cross section of the −1st order diffracted light 108b with the symbols A and B becomes larger and lowercase. The cross section of the −1st order diffracted light 108b marked with a and b becomes smaller. Therefore, the signals f1, f3, and f5 increase, the signals f2, f4, and f6 decrease, and the focus error signal FE increases.

  Thereby, in the eighth embodiment, it is possible to realize focus control for keeping the focal point F0 on the information layer 108.

  The detection areas 244 and 245 of the photodetector 157 generate signals t1 and t2 according to the received light quantity. The tracking error signal TE1 can be obtained by the following equation 33 by the push-pull method.

TE1 = t1-t2 (Equation 33)
The tracking error signal TE1 substantially means a difference in light amount between the non-shaded area and the shaded area of the polarization anisotropic hologram element 121 in FIG.

  The RF signal for reproducing information is given by RFf derived by the following equation 34, RFt derived by the following equation 35, or the sum of both RFf and RFt.

RFf = f1 + f2 + f3 + f4 + f5 + f6 (formula 34)
RFt = t1 + t2 (Formula 35)
In the following, the result of comparison between the eighth embodiment and a conventional optical head device with respect to the deviation in symmetry of the tracking error signal is shown.

  An optical disc has a track composed of a groove or a pit row, and an interval from the center of one track to the center of an adjacent track is Tp. The numerical aperture of the objective lens 104 is NA, and the wavelength of light is λ.

In this embodiment 8,
λ / (NA · Tp) ≧ 1 (Equation 36)
A case where the above condition is satisfied will be described.

  The feature of the eighth embodiment is that the opening is a circle having a radius of 1, and the region included in a range of about 0.1 width in contact with the dividing line parallel to the track of the optical disc 105 passing through the center of the opening, The calculation is performed by exchanging the areas included in the range of about 0.1 width in contact with the end.

  On the left side of the dividing line 302 of a certain polarization anisotropic hologram element, strip-shaped areas A and strip-shaped areas a are alternately adjacent, and on the right side of the dividing line 302 of a certain polarization anisotropic hologram element, Regions B and strip-like regions b are alternately adjacent. In FIG. 26, the two areas of the strip-shaped area A and the strip-shaped area b are interchanged with each other in the area near the center. Moreover, in the area | region of the edge of opening, the strip-shaped area | region A and the strip-shaped area | region a, the strip-shaped area | region B, and the strip-shaped area | region b are mutually replaced.

  When the replacement as shown in this embodiment is not performed, the numerical aperture NA of the objective lens is 0.5 and the light wavelength λ is 0.795 μm, and the radial light amount distribution is at the end of the objective lens with respect to the center. Assuming that the intensity is 10%, the deviation in symmetry of the tracking error signal generated at an objective lens shift of 500 μm with respect to a pit row having an optical disk substrate thickness of 1.2 mm and a track interval Tp = 1.6 μm is 53 %, The deviation of the symmetry of the tracking error signal generated at a radial tilt of 1.0 degree is 24%.

  On the other hand, in the case of the eighth embodiment, assuming that the width of the opening center and both end regions is 0.1 of the radius of the objective lens, the objective lens shift is 500 μm with respect to the pit row having the track interval Tp = 1.6 μm. The deviation of symmetry of the tracking error signal generated at 1 is 46%, and the deviation of symmetry of the tracking error signal generated at a radial tilt of 1.0 degree is 12%. The tracking error signal symmetry deviation that occurs when the objective lens shift is 500 μm is reduced by 13% compared to the conventional example, and the tracking error signal symmetry deviation that occurs when the radial tilt is 1.0 degree is reduced by 50%. Decrease. For this reason, stabilization of tracking control can be realized, it becomes strong against disturbance and the like, and the error rate at the time of information reproduction or the like is lowered.

  In the simple division, the difference between the focus position where the amplitude of the information reproduction signal is maximum and the focus position where the amplitude of the tracking error signal is maximum is 1.5 to 1.0 μm. Then, it decreases to 1.0 to 0.5 μm. For this reason, the error rate at the time of information reproduction can be kept low while still realizing stable tracking control.

  In the eighth embodiment, the polarization anisotropic hologram element is used as the dividing means. However, the same effect can be obtained by using a normal hologram element having no polarization anisotropy.

  In the eighth embodiment, the polarization anisotropic hologram element as the dividing means is configured to be driven integrally with the objective lens. However, the dividing means is arranged anywhere in the optical path of the photodetector from the condensing optical system. May be. In this case, as the objective lens moves following the eccentricity of the track of the optical disc, the positional relationship between the dividing means and the aperture of the objective lens moves. If the hologram element pattern shown in the eighth embodiment is used, Degradation of the tracking error signal due to this movement can be suppressed.

(Embodiment 9)
A schematic diagram of the optical system of the optical head device according to the ninth embodiment is shown in FIG. 25. Since the configuration and operation are the same as those in the eighth embodiment, description thereof will be omitted. However, the polarization anisotropic hologram element 123 shown in FIG. 27 is used instead of the polarization anisotropic hologram element 121 as the dividing means.

  In the ninth embodiment, a method for correcting a shift in symmetry of a tracking error signal will be described.

  The polarization anisotropic hologram element 123 is as shown in FIG. The aperture is a circle with a radius of 1, and an area with a width of about 0.6 is distributed alternately around the dividing line that passes through the center of the opening and is parallel to the track, and enters the shaded area and the non-hatched area. The difference in light quantity is used as a tracking error signal. In FIG. 27, four regions at the center of the opening are distributed.

  It is assumed that the numerical aperture NA = 0.5, the light wavelength λ = 0.955 μm, the diameter of the objective lens = 4 mm, and the light quantity distribution in the radial direction is 10% intensity at the objective lens end with respect to the center. In the conventional example in which the distribution is not performed, the deviation of the symmetry of the tracking error signal generated by the objective lens shift of 500 μm is 53% and the radial tilt is 1.0 degree with respect to the pit row having the track interval Tp = 1.6 μm. The deviation of symmetry of the generated tracking error signal is 24%.

  On the other hand, in another example of the ninth embodiment, it is assumed that the alternately arranged regions at the center of the opening are regions having a width of 1.2 mm composed of six regions having a width of 0.2 mm. When the objective lens shift is 500 μm, the deviation of the symmetry of the tracking error signal generated is 45%, and the deviation of the symmetry of the tracking error signal generated at a radial tilt of 1.0 degree is 14%. The amount of symmetry deviation of the tracking error signal that occurs when the objective lens shift is 500 μm is about 15% less than that of the conventional example, and the amount of symmetry deviation of the tracking error signal that occurs when the radial tilt is 1.0 degree is about 42% less. There is a significant decrease.

  Regarding the objective lens shift, the effect is slightly larger than the example of the eighth embodiment. In this way, stabilization of tracking control can be realized and it becomes strong against disturbance, so that an error rate at the time of information reproduction or the like decreases.

  In the ninth embodiment, the polarization anisotropic hologram element is used as the dividing means. However, the same effect can be obtained by using a normal hologram element having no polarization anisotropy.

  In the description of Embodiments 1 to 9 shown here, an optical disk is assumed as the information storage medium, but the same effect can be obtained with an optical card or the like.

In the description of Embodiments 1 to 9 shown here, the condensing optical system has an infinite system configuration using a collimator lens and an objective lens. However, the collimator lens is omitted, and the role of the collimator lens is only the objective lens. Even if the configuration of the finite system is provided, the effect of the present invention is not impaired.
(Embodiment 10)
FIG. 28 is a configuration diagram showing an example of the tilt detection apparatus of the present invention. A linearly polarized divergent beam 70 emitted from a semiconductor laser 101 as a light source is converted into parallel light by a collimator lens 103 and then enters a polarization beam splitter 130 as a beam branching element. All of the beam 70 incident on the polarizing beam splitter 130 passes through the polarizing beam splitter 130, then passes through the quarter-wave plate 122, is converted into a circularly polarized beam, and is stored in the objective lens 104 as a condensing optical system. It is condensed on the medium 105. The beam 70 reflected and diffracted by the information storage medium 105 passes through the objective lens 104 again, then passes through the quarter-wave plate 122, and is a linearly polarized beam having a direction different by 90 degrees from that emitted from the light source 101. Is converted to The beam 70 transmitted through the quarter-wave plate 122 is totally reflected by the polarization beam splitter 130 and then enters the beam splitter 132. The beam 70 incident on the beam splitter 132 is divided into two beams 70A and 70B, and the beam 70B is received by the photodetector 159. On the other hand, the beam 70A is converted into a convergent beam by the detection lens 133. The convergent beam 70A converted by the detection lens 133 is transmitted by the parallel plate 134 and then received by the photodetector 158. As the beam 70A passes through the parallel plate 134, astigmatism for detecting a focus error signal is given to the beam 70A. The beam 70A received by the photodetector 158 and the beam 70B received by the photodetector 159 are converted into electrical signals corresponding to the amount of light. The electrical signals output from the photodetectors 158 and 159 are input to the signal processing unit 700 in FIG.

  FIG. 29 shows the configuration of the signal processing unit 700. The photodetector 158 has four light receiving units 158A to 158D, and the photodetector 159 has two light receiving units 159A to 159B. Signals output from the light receiving unit 158A and the light receiving unit 158C are subjected to current-voltage conversion by the current-voltage conversion unit 854, and signals output from the light receiving unit 158B and the light receiving unit 158D are converted from current to voltage by the current-voltage conversion unit 853. The signal output from 159A is current-voltage converted by the current-voltage converter 852, and the signal output from the light-receiving unit 159B is current-voltage converted by the current-voltage converter 851. Signals output from the current-voltage conversion units 853 and 854 are subjected to differential calculation by the calculation unit 874. The signal output from the calculation unit 874 is output from the terminal 811, and the output signal becomes a focus error signal.

  On the other hand, with respect to the signals output from the current-voltage converters 851 and 852, a differential calculation is performed by the calculation unit 871. The signal output from the calculation unit 871 is output from the terminal 812, and the output signal becomes a tracking error signal. This focus error signal detection method is called an astigmatism method, and the tracking error signal detection method is a known technique called a push-pull method, so a detailed description thereof will be omitted.

  The focus error signal and the tracking error signal are respectively applied to an actuator 107 serving as a focus control drive unit and a tracking control drive unit. The relative position between the information storage medium 105 and the optical system is controlled so that the beam 70 emitted from the light source 101 is focused on a desired position on the information storage medium 105.

  Signals output from the current-voltage converters 851 and 852 are further added by an adder 891. A signal output from the adder 891 is input to the sample and hold units 821 and 822. In the sample and hold units 821 and 822, sampling and holding are performed at the timing of the signals Sa1 and Sa2 generated by the trigger signal generation unit 801. The signals output from the sample and hold units 821 and 822 are subjected to differential calculation by the calculation unit 872, and then output from the terminal 813 to become a tilt detection signal.

  FIG. 30 shows the relationship between the pattern on the information storage medium 105 and the timing of the timing signal generated by the trigger signal generation unit 801. In FIG. 30, x represents a direction orthogonal to the track for recording information, y represents a direction parallel to the track for recording information, and z represents a direction orthogonal to x and y, respectively.

  The information storage medium 105 has a first pattern area made up of marks and spaces and a second pattern area made up of guide grooves, and the first pattern area and the second pattern area are in the y direction. Are alternately arranged. In the second pattern region, Gn-1, Gn, and Gn + 1 indicate guide grooves, respectively.

  Gp is an interval between adjacent guide grooves. Data is recorded on or between the guide grooves in the second pattern area. Tn-2,... Tn + 2 indicate tracks on which information is recorded. In order to increase the capacity that can be recorded in the information storage medium 105, information can be recorded not only on the guide grooves but also between the guide grooves. When the interval between adjacent tracks is tp, the intervals Gp and tp have a relationship of Gp = 2 · tp. Here, Gp = 1.48 μm, the wavelength λ of the beam 70 emitted from the light source 101 is 650 nm, and the numerical aperture NA of the objective lens 104 is 0.6.

  In the first pattern area, marks 541 and 542 are formed at positions different from the center position of the guide groove by ± Gp / 4 in the x direction. Timings Sa1 and Sa2 included in the timing signal generated by the trigger signal generation unit 801 correspond to the positions of the marks 541 and 542 formed in the first pattern region, respectively. The tracking error signal is generated using a signal obtained from the photodetector 159 when the beam 70 condensed by the objective lens 104 irradiates the second pattern region. When the signal output from the terminal 812 is a tracking error signal, if the angle formed between the beam 70 condensed by the objective lens 104 and the information storage medium 105 is tilted, the signal is output from the terminal 813 depending on the tilt angle. Signal to be changed.

  FIG. 31a is a diagram schematically showing a part of the track of FIG. A and B in FIG. 31a indicate the locus of the focused beam. When the focused beam passes along the trajectory A, the waveform of the signal output from the adder 891 in FIG. 29 is shown in FIG. 31b, and the waveform of the signal output from the calculator 872 in FIG. 29 is shown in FIG. When the focused beam passes along the locus B, the waveform of the signal output from the adder 891 in FIG. 29 is shown in FIG. 31d, and the waveform of the signal output from the arithmetic unit 872 in FIG. 29 is shown in FIG. Show.

  In FIG. 31b, since the value of the output signal from the adder 891 at the timing Sa1 and the timing Sa2 is equal, the output signal of the arithmetic unit 872 after the timing Sa2 becomes 0 as shown in FIG. 31c. On the other hand, in FIG. 31d, since the value of the output signal from the adder 891 at the timing Sa1 and the timing Sa2 is different, as shown in FIG. 31e, the value of the output signal of the arithmetic unit 872 after the timing Sa2 is 0. Different.

  FIG. 32 shows the relationship between the inclination of the angle formed by the beam 70 condensed by the objective lens 104 and the information storage medium 105 and the inclination detection signal obtained from the terminal 813 when Gp is 1.48 μm and 0.83 μm. Shows about the case. In FIG. 32, the inclination 0 is when the optical axis of the beam 70 condensed by the objective lens 104 is parallel to the z direction, that is, the optical axis of the beam 70 condensed by the objective lens 104 is orthogonal to the information storage medium 105. Corresponds to the state.

  In both cases where Gp is 1.48 μm and 0.83 μm, a tilt signal can be detected in a range where the tilt angle is 1 degree or less, and the sensitivity is more than five times that of a conventional tilt detector. This is because the tilt detection apparatus of the present invention is based on the principle that the pattern in the information storage medium 105 and the phase of the beam diffracted by the guide groove change. The detection sensitivity when Gp is 1.48 μm is higher than the detection sensitivity when Gp is 0.83 μm. This is due to the fact that the principle of the present invention increases the detection sensitivity by overlapping the pattern in the information storage medium 105 and the ± first-order diffracted light beams diffracted by the guide grooves. The condition that the ± first-order diffracted light overlaps is represented by the relationship NA> λ / Gp. That is, when the optical system has a relationship of NA> λ / Gp, the inclination detection sensitivity is high.

  By using the tilt detection apparatus of the present invention, the tilt of the angle formed by the information storage medium and the beam condensed by the focusing optical system can be detected with higher accuracy than the conventional tilt detection apparatus. In addition, tilt detection can be performed by using a photodetector that detects a tracking error signal, that is, it is not necessary to provide a new component as a detector to detect tilt, and an inexpensive and small tilt detection device is obtained. .

  In this embodiment, the signal output from the terminal 812 is the tracking error signal and the signal output from the terminal 813 is the tilt detection signal. However, the signal output from the terminal 813 is the tracking error signal and the terminal. The signal output from 812 can also be used as a tilt detection signal. In particular, even when the information storage medium 105 and the beam 70 focused by the objective lens 104 are tilted, in an optical head device that does not include a drive unit that corrects the tilt, a signal output from the terminal 813 is used as a tracking error signal. Thus, even when the beam 70 condensed by the objective lens 104 and the information storage medium 105 are tilted, the deviation between the position of the guide groove and the position of the track is small, and a plurality of different optical head devices and information storage media are used. The compatibility of the case will be higher.

  As shown in FIG. 28, the tilt detection signal is a control signal for the drive unit 135 that drives the optical system, and is controlled so that the information storage medium 105 and the beam 70 condensed by the objective lens 104 have a desired angle. For example, an optical head device capable of stably reading information from the information storage medium 105 having a large amount of warpage can be realized. Further, by controlling the beam intensity when recording information on the information storage medium 105 according to the tilt detection signal, it is possible to record information satisfactorily even on an information storage medium with a large amount of warpage. Become.

Here, an embodiment is shown in which the photodetector 158 for detecting the focus error signal and the tracking error signal and the photodetector 159 for obtaining the tilt detection signal are separately configured. However, the optical system shown in FIG. Can be used.
(Embodiment 11)
FIG. 33 shows a configuration of a signal processing unit 701 in an inclination detection apparatus that is another embodiment of the present invention. For example, the signal processing unit 701 can be used in place of the signal processing unit 700 shown in FIG. The signal processing unit 701 is different from the signal processing unit 700 in that a sample and hold unit 823, a variable gain amplification unit 831 and a calculation unit 873 are provided and a timing signal output from the trigger signal generation unit 812. The sample and hold unit 823 performs the sample and hold operation with the timing signal having the timing of Sa3 output from the trigger signal generation unit 812. The timing of Sa3 is a position corresponding to a space in the first pattern area of the information storage medium 105 as shown in FIG. The signal sampled by the sample and hold unit 823 is proportional to the offset generated in the tracking error signal when the objective lens moves in an optical system that drives the objective lens for tracking control as shown in FIG. Signal. For example, the signal output from the sample and hold unit is input to the variable gain amplifier 831 and the input signal is adjusted to a desired level. The signal output from the variable gain amplifying unit 831 is subjected to differential calculation with the signal output from the calculating unit 871 in the calculating unit 873. A signal output from the calculation unit 873 is output from the terminal 812. An offset generated in the tracking error signal even if the objective lens is moved by tracking control by differentially calculating the signal output from the variable gain amplifier 831 and the signal output from the calculator 871 by the calculator 873. Is removed, a stable tracking operation can be performed, and a tilt signal can be accurately detected.
Embodiment 12
FIG. 34 shows the configuration of the information storage medium in the tilt detection apparatus according to another embodiment of the present invention, and FIG. 35 shows the configuration of the signal processing unit 702. The configuration of the information storage medium shown in the embodiment of the present invention is different from the configuration of the information storage medium shown in Embodiment 10 in that a plurality of marks 541 and 542 are provided in the first pattern area. Sampling and holding units 824 to 827 in the signal processing unit 702 sample the signals output from the adding unit 891 at timings Sa4 to Sa7, respectively, which correspond to the mirror surfaces between the marks 541 and 542 and the marks, respectively. . A signal having a sampling timing is generated by the trigger signal generation unit 803. Signals output from the sample and hold units 824 and 825 are differentially calculated by the calculation unit 875, and signals output from the sample and hold units 826 and 827 are differentially calculated by the calculation unit 876. Signals output from the calculation units 875 and 876 are differentially calculated by the calculation unit 872. The signal output from the calculation unit 872 is output from the terminal 813 and becomes an inclination detection signal.

The tilt detection apparatus using the information storage medium shown in the present embodiment can obtain a tilt signal with higher sensitivity than the tilt detection apparatus shown in the tenth embodiment.
(Embodiment 13)
FIG. 36 is a block diagram showing an example of the optical head device of the present invention. A semiconductor laser 101 as a light source emits a beam 70 having a wavelength λ of 650 nm. The linearly polarized divergent beam 70 emitted from the semiconductor laser 101 is converted into parallel light by the collimator lens 103 and then enters a beam splitter 136 as a beam branching element. The beam splitter 136 is a half mirror whose optical characteristics do not depend on the polarization direction of the incident beam. Of the beam 70 incident on the beam splitter 136, a beam having a half intensity is transmitted through the beam splitter 136. The beam 70 transmitted through the beam splitter 136 is incident on the polarization filter 137.

  FIG. 37 shows the configuration of the polarizing filter 137. The polarizing filter 137 includes two regions 137A and 137B. The region 137A has a characteristic of transmitting 100% of the beam polarized in the x direction but not transmitting the beam polarized in the y direction. The region 137B has a characteristic of transmitting 100% of the beam polarized in the x direction and the beam polarized in the y direction. Here, the x direction is a radial direction of the information storage medium 105 and is a direction orthogonal to a track on which information is recorded. The y direction is a direction parallel to the track for recording information on the information storage medium 105 and is orthogonal to the radial direction of the information storage medium 105. The z direction is a direction orthogonal to both the radial direction and the track direction of the information storage medium 105, and is a direction parallel to the optical axis of the beam 70. In FIG. 37, 70R is a mapping of the aperture of the objective lens 104. 70S represents the size of the region 137B. 70S is smaller than 70R, and the effective numerical aperture NA of the objective lens 104 for the beam polarized in the y direction is small. Here, the effective numerical aperture NA of the objective lens 104 for the beam polarized in the x direction is 0.6, and the effective numerical aperture NA of the objective lens 104 for the beam polarized in the y direction is 0.4. A beam having an effective numerical aperture of 0.6 of the objective lens 104 is a first beam, and a beam having an effective numerical aperture of the objective lens 104 is 0.4. As the beam polarized in the x direction and the y direction, a laser that oscillates in both the TE and TM modes may be used for the semiconductor laser 101. In the case of a laser that oscillates only in one of the TE and TM modes, a light source is used. This can be realized if the polarization direction 101 is slightly shifted from the x or y direction. Of course, the beam emitted from the light source 101 may be incident on the wave plate to obtain a circular or elliptically polarized beam. In the present embodiment, the polarization direction of the semiconductor laser 101 is slightly shifted from the x direction.

  The beam 70 that has passed through the polarizing filter 137 enters an objective lens 104 as a condensing optical system, and the beam 70 that has entered the objective lens 104 is collected on the information storage medium 105. The beam 70 reflected and diffracted by the information storage medium 105 passes through the objective lens 104 again and then passes through the polarizing filter 137. The beam 70 that has passed through the polarization filter 137 enters the beam splitter 136, and a beam having a half intensity is reflected by the beam splitter 136. The beam 70 reflected by the beam splitter 136 enters the polarization beam splitter 130. The polarization beam splitter 130 has a characteristic of transmitting almost 100% of the beam polarized in the x direction and reflecting almost 100% of the beam polarized in the y direction. In the beam 70 incident on the polarization beam splitter 130, the first beam is transmitted through the polarization beam splitter 130 to become a beam 70A, and the second beam is reflected by the polarization beam splitter 130 to become a beam 70B. The beam 70B is received by the photodetector 159. On the other hand, the beam 70A is converted into a convergent beam by the detection lens 133. The convergent beam 70 converted by the detection lens 133 passes through the parallel plate 134 and is then received by the photodetector 158. As the beam 70A passes through the parallel plate 134, astigmatism is applied to the beam 70A so that a focus error signal can be detected. The beam 70A received by the photodetector 158 and the beam 70B received by the photodetector 159 are converted into electrical signals corresponding to the respective light amounts. Electric signals output from the photodetectors 158 and 159 are input to the signal processing unit 704.

  FIG. 38 shows the configuration of the signal processing unit 704. The light detector 158 includes four light receiving units 158A to 158D, and the light detector 159 includes two light receiving units 159A to 159B. The signals output from the light receiving unit 158A and the light receiving unit 158C are the current / voltage converting unit 854, the signals output from the light receiving unit 158B and the light receiving unit 158D are the current / voltage converting unit 853, and the signal output from the light receiving unit 159A is the current. In the voltage conversion unit 852, the signal output from the light receiving unit 159B is current-voltage converted by the current-voltage conversion unit 851. Signals output from the current-voltage conversion units 853 and 854 are subjected to differential calculation by the calculation unit 872. A signal output from the calculation unit 872 is output from the terminal 812 and becomes a focus error signal. On the other hand, the signals output from the current-voltage conversion units 851 and 852 are subjected to differential calculation by the calculation unit 871. A signal output from the calculation unit 871 is output from the terminal 811 and becomes a tracking error signal. The focus error signal and the tracking error signal are respectively applied to a focus control drive unit and an actuator 107 as a tracking control drive unit, and the beam 70 emitted from the light source 101 is focused on a desired position on the information storage medium 105. The relative positions of the information storage medium 105 and the optical system are controlled so as to connect the two.

  Information recorded in the information storage medium 105 is obtained by adding signals output from the current-voltage converters 853 and 854.

  On the information storage medium 105, a guide groove that can detect a tracking error signal is formed, and its period Gp is 1.48 μm. In the optical head device of the present invention, the effective numerical aperture NA of the objective lens 104 with respect to the first beam for reading the information recorded on the information storage medium 105 is 0.6, and the second detecting the tracking error signal. By setting the effective numerical aperture NA of the objective lens 104 with respect to the beam to 0.4, even if the beam 70 condensed by the objective lens 104 and the information storage medium 105 are tilted from a normal angle, the tracking error signal is generated. Little phase shift occurs. Therefore, almost no off-track occurs. By applying the optical head device of the present invention, compatibility with different optical head devices and information storage media can be improved. A phenomenon in which a phase shift occurs in the tracking error signal when the beam 70 collected by the objective lens 104 and the information storage medium 105 are tilted from a normal angle is remarkable when the relationship Gp> λ / NA is satisfied. Become. Therefore, in the optical head device of the present invention, the effective numerical aperture NA of the objective lens 104 with respect to the second beam for detecting the tracking error signal has a relationship of Gp <λ / NA, so that a good tracking error can be obtained. A signal is obtained.

  In the optical head device of the present invention, two beams having effectively different numerical apertures NA of the objective lens 104 are generated so as to have exactly the same optical axis under any conditions by utilizing the difference in polarization. . Therefore, in the optical head device of the present invention, the information storage medium 105 is irradiated with two beams, but adjustment when assembling the optical head device is not complicated as compared with the conventional optical head device.

  Note that the optical head device of the present invention is not subject to any restrictions on the method of detecting the focus error signal, and for example, the focus error signal may be detected using the second beam. In that case, a wavefront that enables detection of a focus error signal such as astigmatism may be given to the second beam. At this time, since the effective numerical aperture NA of the objective lens 21 is smaller in the second beam than in the first beam, the wavefront aberration is also reduced. Therefore, when the focus error signal is detected using the second beam, the beam condensed by the objective lens 43 is more on the information storage medium 43 than when the focus error signal is detected using the first beam. Since the noise mixed in the focus error signal when crossing the track is reduced, more stable focus control can be realized.

  In this embodiment, the beam splitter 136 is a half mirror. However, the optical head device of the present invention is not affected by the reflectance and transmittance characteristics of the beam splitter 136. 90% and the reflectance may be 30 to 10%. When the beam splitter 136 is a half mirror, the signals output from the photodetectors 158 and 159 are maximized, which is suitable for a read-only optical head device. On the other hand, when the transmittance of the beam splitter 136 is 70 to 90%, the amount of light on the forward path from the semiconductor laser 101 to the information storage medium 105 increases, which is suitable for an optical head device for recording and reproduction.

In this embodiment, a continuous guide groove is formed on the information storage medium 105 as a pattern that enables detection of the tracking error signal. However, as a pattern that enables detection of the tracking error signal, discrete marks or A guide groove may be formed. In the case of an information storage medium in which discrete marks or guide grooves are formed, a sample and hold unit may be provided on the input side of the calculation unit 871 of the signal processing unit 704.
(Embodiment 14)
FIG. 39 shows the configuration of an optical head device according to another embodiment of the present invention. In the present embodiment, focus and tracking control is performed by driving the objective lens 104 with an actuator as a drive unit. Reference numeral 107 denotes an actuator for focus control and tracking control. Further, the objective lens 104 and the polarizing filter 137 are integrally driven by an actuator 107. The beam 70 reflected and diffracted by the information storage medium 105 and then reflected by the beam splitter 136 is collected by the detection lens 133. The beam 70 converted into a convergent beam by the detection lens 133 enters the hologram element 138. A zero-order diffracted light 70C and two first-order diffracted lights 70D and 70E are generated from the hologram element 138, and the beams 70C to 70E are received by the photodetector 160.

  FIG. 40 schematically shows a pattern formed on the hologram element 138. The hologram element 138 is formed with an off-axis Fresnel zone plate as a pattern. When the beam 70 collected by the objective lens 104 is focused on the information storage medium 105, the first-order diffracted light 70D generated from the hologram element 138 is on the near side of the photodetector 160, and the first-order diffracted light 70E is light. It has a focal point behind the detector 160. In addition, the hologram element 138 has polarization dependency on the diffraction efficiency. For a beam polarized in the x direction, the diffraction efficiency of the 0th-order diffracted light is 0%, and the diffraction efficiency of the ± 1st-order diffracted light is 40%. The diffraction efficiency of 0th-order diffracted light is designed to be 100% and the diffraction efficiency of ± 1st-order diffracted light is 0% for a beam polarized in the y direction. The pattern on the hologram element 138 is produced by proton exchange of lithium niobate.

  FIG. 41 shows the relationship between the light receiving unit of the photodetector 160 and the beams 70C to 70E. The photodetector 160 has light receiving portions 160A to 160H. The beam 70C is received by the light receiving units 160A to 160B, the beam 70D is received by the light receiving units 160C to 160E, and the beam 70E is received by the light receiving units 160F to 160H, respectively. In the optical head device of the present embodiment, the signal processing unit can use the signal processing unit 704 shown in the thirteenth embodiment as it is. A signal output from the light receiving unit 160A is output to the current / voltage conversion unit 852, a signal output from the light receiving unit 160B is input to the current / voltage conversion unit 851, and signals output from the light receiving units 160D, 160F, and 160H are output to the current / voltage conversion unit 854. In addition, the signals output from the light receiving units 160C, 160E, and 160G may be input to the current-voltage conversion unit 853, respectively. The focus error signal detection method shown in the present embodiment is a method called a spot size detection method, and this method is well known as well as the astigmatism method.

  In the embodiment of the present invention, the center of the objective lens 104 and the center of the polarizing filter 137 can always be matched by driving the objective lens 104 and the polarizing filter 137 integrally with an actuator. At this time, the second beam is condensed on the information storage medium 105 with little aberration, and even if the beam 70 collected by the objective lens 104 and the information storage medium 105 are tilted, the phase shift or offset is not generated. A small tracking error signal can be obtained.

  Further, by using the hologram element 138, a focus error signal, a tracking error signal, and an information signal recorded on the information storage medium 105 can be detected from one photodetector 160, and an inexpensive optical head device is obtained.

It is the schematic of the optical system of the optical head apparatus which shows one Embodiment of this invention. It is a block diagram of a circuit as a detection region, an information reproduction signal generation unit, and a tracking error signal generation unit of a photodetector showing an embodiment of the present invention. It is a figure which shows the tracking error signal when the tracking error signal when radial tilt exists and the positional relationship between the tracks and the off-track amount are corrected to zero. It is a block diagram of the circuit as another detection area | region of the photodetector which shows one Embodiment of this invention, an information reproduction signal production | generation means, and a tracking error signal production | generation means. It is a top view which shows another detection area of the photodetector which shows one Embodiment of this invention. It is a top view which shows another detection area of the photodetector which shows one Embodiment of this invention. It is a block diagram of a circuit as a detection area and tracking error signal generation means of a photodetector showing an embodiment of the present invention. It is a block diagram of a circuit as a detection area and tracking error signal generation means of a photodetector showing an embodiment of the present invention. It is a block diagram of a circuit as a detection area and tracking error signal generation means of a photodetector showing an embodiment of the present invention. It is the schematic of the optical system of the optical head apparatus which shows one Embodiment of this invention. It is a front view of the objective lens which shows one Embodiment of this invention. It is the schematic of the optical system using another light reduction means of the optical head apparatus which shows one Embodiment of this invention. It is the schematic of the optical system using the optical head apparatus which shows one Embodiment of this invention, and another light reduction means. It is the schematic of the optical system using another light reduction means of the optical head apparatus which shows one Embodiment of this invention. It is the schematic of the optical system of the optical head apparatus which shows one Embodiment of this invention. It is a top view which shows the area arrangement | positioning of the hologram element which shows one Embodiment of this invention, the area division | segmentation of a photodetector, and the relationship of the cross section of the diffracted light on a photodetector. It is a front view which shows another area | region arrangement | positioning of the hologram element which shows one Embodiment of this invention. It is the schematic of the example of another optical system of the optical head apparatus which shows one Embodiment of this invention. It is a block diagram of the detection area of the photodetector which shows one Embodiment of this invention, the circuit as a tracking error signal production | generation means, and the circuit as an information reproduction signal production | generation means. FIG. 3 is a layout diagram of tracks on an optical disc. It is the schematic of the circuit as an information reproduction signal production | generation means at the time of reproducing | regenerating the off-track information which shows one Embodiment of this invention. It is the schematic of the circuit as an information reproduction signal production | generation means at the time of reproducing | regenerating the off-track information which shows one Embodiment of this invention. FIG. 5 is a configuration diagram of a detection area of another photodetector, a circuit as a tracking error signal generation unit, and a circuit as an information reproduction signal generation unit showing an embodiment of the present invention. FIG. 3 is a layout diagram of tracks on an optical disc. It is the schematic of another example of the circuit as an information reproduction signal production | generation means at the time of reproducing | regenerating the off-track information which shows one Embodiment of this invention. It is the schematic of another example of the circuit as an information reproduction signal production | generation means at the time of reproducing | regenerating the off-track information which shows one Embodiment of this invention. FIG. 3 is a layout diagram of tracks on an optical disc. It is the schematic of another example of the circuit as an information reproduction signal production | generation means at the time of reproducing | regenerating the off-track information which shows one Embodiment of this invention. FIG. 3 is a layout diagram of tracks on an optical disc. It is the schematic of another example of the circuit as an information reproduction signal production | generation means at the time of reproducing | regenerating the off-track information. It is a top view which shows the area arrangement | positioning of the hologram element which shows one Embodiment of this invention, the area division | segmentation of a photodetector, and the relationship of the cross section of the diffracted light on a photodetector. It is the schematic of the optical system of the optical head apparatus which shows one Embodiment of this invention. It is a top view which shows the area arrangement | positioning of the hologram element which shows one Embodiment of this invention, the area division | segmentation of a photodetector, and the relationship of the cross section of the diffracted light on a photodetector. It is a front view which shows another area | region arrangement | positioning of the hologram element which shows one Embodiment of this invention. It is a block diagram of the inclination detection apparatus which shows one Embodiment of this invention. It is a block diagram of the signal processing part in the inclination detection apparatus which shows one Embodiment of this invention. It is a block diagram of the information storage medium used for the inclination detection apparatus which shows one Embodiment of this invention. It is the figure which showed a part of track | truck of FIG. 30 typically. It is a figure which shows the waveform of the signal output from the addition part 891 of FIG. 29 when the condensed beam passes the locus | trajectory A of FIG. 31a. It is a figure which shows the waveform of the signal output from the calculating part 872 of FIG. 29 when the condensed beam passes the locus | trajectory A of FIG. 31a. It is a figure which shows the waveform of the signal output from the addition part 891 of FIG. 29, when the condensed beam passes the locus | trajectory B of FIG. 31a. It is a figure which shows the waveform of the signal output from the calculating part 872 of FIG. 29, when the condensed beam passes the locus | trajectory B of FIG. 31a. It is a figure which shows the characteristic of the inclination detection signal obtained from the inclination detection apparatus which shows one Embodiment of this invention. It is a block diagram of the signal processing part in the inclination detection apparatus which shows one Embodiment of this invention. It is a block diagram of the information storage medium used for the inclination detection apparatus which shows one Embodiment of this invention. It is a block diagram of the signal processing part in the inclination detection apparatus which shows one Embodiment of this invention. It is a block diagram of the optical head apparatus which shows one Embodiment of this invention. It is a block diagram of the polarizing filter in the optical head apparatus which shows one Embodiment of this invention. It is a block diagram of the signal processing part in the optical head apparatus which shows one Embodiment of this invention. It is a block diagram of the optical head apparatus which shows one Embodiment of this invention. It is a block diagram of the hologram element in the optical head apparatus which shows one Embodiment of this invention. FIG. 3 is a diagram showing the relationship between a photodetector and a beam in an optical head device showing an embodiment of the present invention. It is the schematic of the optical system of the optical head apparatus which shows a prior art example. The reflected light from the information layer on the photodetector when the detection region of the photodetector showing the embodiment of the present invention and the conventional example and the condensing point of the light emitted from the objective lens coincide with the information layer It is a top view which shows a cross section. The reflected light from the information layer on the photodetector when the information layer moves away from the detection area of the photodetector and the condensing point of the light emitted from the objective lens according to the embodiment of the present invention and the conventional example It is a top view which shows a cross section. An embodiment of the present invention and a conventional example, a detection region of a photodetector and reflected light from the information layer on the photodetector when approaching the information layer from a condensing point of light emitted from the objective lens It is a top view which shows a cross section. It is a block diagram of the conventional inclination detection apparatus. It is a block diagram of the information storage medium used for the conventional inclination detection apparatus. It is a block diagram of the signal processing part in the conventional inclination detection apparatus. It is a block diagram of the conventional optical head apparatus. It is a block diagram of the signal processing part in the conventional optical head apparatus. It is a block diagram of the information storage medium used for the conventional optical head apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Semiconductor laser 102 Parallel plate beam splitter 103 Collimator lens 104 Objective lens 105 Optical disk 106 Holding means 107 Actuator 108 Information layer 108a Reflected light

Claims (5)

And a laser light source that emits a bi-over-time,
An optical element that receives the beam emitted from the laser light source and divides the received beam into a first beam and a second beam;
A condensing optical system that receives the first beam and the second beam, and converges the first beam and the second beam onto an information storage medium into a minute spot;
A first beam branching element for receiving the beam including the first beam and the second beam reflected and diffracted by the information storage medium and branching the received beam;
A second beam branching element that receives the beam branched by the first beam branching element and branches the received beam into the first beam and the second beam;
Receiving each of said branched by the beam splitter of the second first beam and said second beam in different light receiving unit, according to the respective light intensity of the first beam and the second beam received A photodetector that outputs the detected signal;
A signal processing unit that receives a signal output from the photodetector and calculates the received signal;
And a drive section based on the calculated signal by the signal processing unit performs the relative positioning of the light converging optical system and the information storage medium,
It said first beam and said second beam have different effective numerical aperture when light is collected by the condensing optical system,
The first beam and the second beam divided by the optical element are formed coaxially with each other;
The signal processing unit generates a tracking error signal using a signal of a beam having a smaller effective numerical aperture when the light is condensed by the condensing optical system among the first beam and the second beam. An optical head device further comprising tracking error signal generation means for generating. The information storage medium has a mark or predetermined groove allows detecting a tracking error signal, the period of the marks or predetermined groove allows detecting a tracking error signal on the information storage medium and Gp, the laser a wavelength included in the beam emitted from the light source and lambda, when a numerical aperture of the information storage medium side of the converging optical system has a NA, first beam generated by the optical element Gp> lambda / NA The second beam generated by the optical element has a relationship of Gp <λ / NA,
The optical head device according to claim 1, wherein the tracking error signal generation unit generates a tracking error signal from the second beam. The optical head device according to claim 1 or 2 optical element is a polarization filter. The optical head device according to claim 1 , wherein the optical element is integrated with the condensing optical system. An emission step of emitting a laser light source Calabi over arm,
A splitting step of receiving the beam emitted in the emission step and dividing the received beam into a first beam and a second beam;
A condensing step of receiving the first beam and the second beam, and condensing the first beam and the second beam onto an information storage medium into a minute spot;
A first beam branching step of receiving a beam including the first beam and the second beam reflected and diffracted by the information storage medium, and branching the received beam;
Receiving a beam branched in the first beam branching step and branching the received beam into the first beam and the second beam;
Receiving each of said branched by the second beam splitting step first beam and said second beam in different light receiving unit, according to the respective light intensity of the first beam and the second beam received A light detection process for outputting the detected signal;
A signal processing step of receiving a signal output in the light detection step and calculating the received signal;
Includes a positioning step for determining the relative position between the light condensing optical system and the information storage medium based on the calculated signal by the signal processing step,
It said first beam and said second beam have different effective numerical aperture when light is collected by the condensing optical system,
The first beam and the second beam divided by the optical element are formed coaxially with each other;
In the signal processing step, a tracking error signal is generated using a signal of a beam having a smaller effective numerical aperture when the light is condensed by the condensing optical system of the first beam and the second beam. further comprising, an optical information processing method a tracking error signal generating step to generate.

Images