JP4372126B2 - Optical pickup device - Google Patents

Description

  The present invention relates to an optical pickup device, and is particularly suitable when a DPP (Differential Push-Pull) method is used as a tracking error signal generation method.

  Conventionally, a push-pull method is known as a method for generating a tracking error signal, and is used in an optical pickup device used for a recording type CD (Compact Disc), a DVD (Digital Versatile Disc), or the like. However, in this method, a DC offset is generated in the tracking error signal due to the optical axis shift of the objective lens, thereby causing a problem that the tracking error signal is deteriorated. Therefore, as a technique for avoiding this problem, the DPP method has been proposed and has already been adopted in an optical pickup device used for a recording type DVD.

  However, even in this DPP method, when a lens shift occurs in the objective lens during tracking servo or the like, the amplitude appears in the sub-beam push-pull signal (side push-pull signal), which causes a problem that the tracking error signal deteriorates. Arise.

As a method for avoiding this problem, for example, a technique described in Patent Document 1 below has been proposed. In this method, a phase structure having a constant period is given to a grating that divides laser light from a semiconductor laser into a main beam and a sub beam, thereby suppressing generation of amplitude in the side push-pull signal. Specifically, the period D of the phase structure of the grating is set to be 2/3 of the moving distance of the diffracted light by the disk (track) on the pupil of the objective lens. As a result, the phase patterns of the 0th order light and the ± 1st order light from the disk (track) are inverted at the overlapping portion of these lights, and as a result, the amplitude of the push-pull signal at this overlapping portion is suppressed to substantially zero. .
JP 2005-100550 A

  However, since the moving distance of the diffracted light by the disk (track) depends on the track width, for example, a DVD-RAM with a track pitch of 1.23 μm and a DVD-R with a track pitch of 0.74 μm are shown in FIG. As described above, the moving distance of the ± first-order light and the overlapping state of the zero-order light and the ± first-order light are different.

  On the other hand, in the method of Patent Document 1, as described above, the period D of the phase structure of the grating is set based on the moving distance of the ± first-order light. It is impossible to set the period D of the phase structure of the grating so as to satisfy the above-mentioned conditions simultaneously for the kind of disk. Therefore, the method of Patent Document 1 is difficult to exhibit sufficient effects for an optical pickup device used for different types of disks having different track pitches.

  The present invention solves such problems, and an optical pickup capable of smoothly suppressing the amplitude of a sub-beam push-pull signal (side push-pull signal) even when dealing with different types of discs having different track pitches. It is an object to provide an apparatus.

According to the first aspect of the present invention, a light source that emits laser light, the laser light is divided into a main beam and a sub beam, the sub beam is divided into a plurality of diffracted lights, and the optical axis of the laser light of the grating is A grating having a phase structure configured such that the sum of signal components of the side push-pull signal based on each split light becomes zero by adjusting a rotational direction position as an axis, and a disk of the main beam and the sub beam In an optical pickup device comprising a photodetector having a sensor pattern for receiving reflected light from the main beam and generating a side push-pull signal and a side push-pull according to the intensity of the main beam and sub-beam,
In the grating, two types of phase structures that cause a phase difference in the laser beam are alternately arranged at a constant period, and these two types of phase structures adjust the position of the grating in the rotational direction. Thus, the phase difference and the interval between the basic vectors are set such that the sum of the signal components of the side push-pull signal based on each split light becomes zero.

  The invention of claim 1 is an optical pickup device, wherein a light source that emits laser light, a grating that divides the laser light into a main beam and a sub beam, reflected light from a disk of the main beam and the sub beam, And a photodetector having a main push-pull signal corresponding to the intensity of the main beam and the sub beam and a sensor pattern for generating a side push pull, and the grating divides the sub beam into a plurality of diffracted lights. And a phase structure configured such that the sum of the signal components of the side push-pull signal based on each split light becomes zero by adjusting the position of the grating in the rotational direction about the optical axis of the laser beam. It is characterized by having.

  According to a second aspect of the present invention, in the optical pickup device according to the first aspect, two types of phase structures that cause a phase difference in the laser beam are alternately arranged in the grating at a constant period. These two types of phase structures adjust the rotational direction position of the grating so that the sum of the signal components of the side push-pull signal based on each split light becomes zero, and the basic vector An interval is set.

  According to a second aspect of the present invention, in the optical pickup device according to the first aspect, two types of rhombus-shaped phase structures are arranged in the grating so as to be alternately arranged at a constant period. To do.

  According to a third aspect of the present invention, in the optical pickup device according to the second aspect, the phase difference based on the two types of phase structures is set so that the sub beam is composed of zero-order light and four ± first-order lights. It is characterized by.

According to a fourth aspect of the present invention, in the optical pickup device according to the second aspect, the phase difference based on the two types of phase structures is set so that the sub beam is composed of four ± first-order lights. Features.

  According to a fifth aspect of the present invention, in the optical pickup device according to the first aspect, two types of strip-like phase structures are arranged in the grating so as to be alternately arranged at a constant period. .

  According to a sixth aspect of the present invention, in the optical pickup device according to the fifth aspect, the phase difference based on the two types of phase structures is set so that the sub-beam is composed of zero-order light and two ± first-order lights. It is characterized by.

  According to the present invention, since the phase structure is set so that the sum of the signal components of the side push-pull signal based on each split light becomes zero, for example, the track pitch changes as in DVD-RAM and DVD-R. A push-pull signal (side push-pull signal) can be generated smoothly and satisfactorily even when dealing with such different types of discs. Therefore, according to the present invention, a tracking error signal can be generated smoothly and satisfactorily based on the DPP method even when dealing with different types of disks.

  The features of the present invention will become more apparent from the following description of embodiments. It should be noted that the phase structure setting method and its effect in the present invention will be clearly understood based on the simulation examples shown in the embodiments.

  However, the following embodiment is merely one specific example of the present invention, and the meaning of the terms of the present invention or each constituent element is limited to those described in the following embodiment. is not.

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

  First, FIG. 1 shows an optical system of an optical pickup device according to the embodiment. As shown in the figure, this optical system includes a semiconductor laser 101, a grating 102, a polarization beam splitter 103, a collimating lens 104, a linkage mirror 105, a rising mirror 106, a λ / 4 plate 107, and an objective lens 108. An anamorphic lens 109, a photodetector 110, and an FMD (front monitor diode) 110.

  The semiconductor laser 101 emits laser light having a predetermined wavelength. The grating 102 divides the laser light from the semiconductor laser 101 into a main beam and two sub beam groups. These two sub-beam groups are each composed of zero-order light and ± first-order light. The configuration of the grating 102 and the formation state of the sub-beam group will be described later with reference to FIGS.

  The polarization beam splitter 103 transmits the laser beam from the grating 102 substantially entirely. The collimating lens 104 converts the laser light transmitted through the polarization beam splitter 103 into parallel light. The linkage mirror 105 is a mirror with a film that transmits a part (approximately several percent) of the laser light from the collimator lens 104. The laser beam that has passed through the linkage mirror 105 is received by the FMD 110. The output of the FMD 110 is used for power control of the semiconductor laser 101.

  The raising mirror 106 raises the laser beam reflected by the linkage mirror 105 in the direction of the objective lens 108. The λ / 4 plate 107 converts the laser light from the rising mirror 106 into circularly polarized light, and converts the reflected light from the disk into linearly polarized light that is orthogonal to the polarization direction of the laser light incident from the rising mirror 106 side. To do. Thereby, the reflected light from the disk is substantially totally reflected by the polarization beam splitter 103.

  The objective lens 108 converges the laser light from the λ / 4 plate 107 on the disk. The anamorphic lens 109 converges the laser light (reflected light from the disk) reflected by the polarization beam splitter 103 on the photodetector 110. The anamorphic lens 109 includes a condenser lens and a cylindrical lens, and introduces astigmatism into the reflected light from the disk.

  The photodetector 110 has a sensor pattern for deriving a reproduction RF signal, a focus error signal, and a tracking error signal from the intensity distribution of the received laser beam. A signal from each sensor is output to the reproduction circuit and the servo circuit on the optical disk apparatus side.

  FIG. 2A shows the configuration of the grating 102.

  As shown in the figure, the grating 102 is provided with two kinds of rhombus-shaped phase structures at a constant period. There is a phase difference in the laser light after passing through the phase structure of the shaded portion and when passing through the phase structure of the white portion. Due to this phase difference, the laser beam is divided into a main beam and two sub beam groups. In the phase structure shown in FIG. 2A, the sub-beam group is divided into five beams of zero-order light and ± first-order light as shown in FIG.

  Here, the intensity ratio between the ± 1st order light and the 0th order light is determined by the phase difference when the laser light passes through the two types of phase structures. When this phase difference is 180 degrees, the intensity of the 0th-order light becomes zero. That is, when the phase difference is 180 degrees, each of the two sub beam groups includes four ± first-order lights. Further, the interval between the ± first-order light and the zero-order light is inversely proportional to the interval between the basic vectors of the grating 102 shown in FIG. Therefore, by adjusting the interval between the phase difference due to the phase structure and the basic vector, it is possible to change the intensity ratio and interval between the 0th order light and the 1st order light constituting the sub beam group.

Note that the intensity ratio I ₀ / I _{± 1} and the interval s between the 0th-order light and the primary light constituting the sub-beam group are given by the following equations.

a and b are basic vector unit vectors, and L is a unit vector having a size of 1 parallel to the optical axis.

FIG. 3 shows the irradiation state of the laser beam on the disk and the configuration of the photodetector 110.

  As shown in FIG. 5A, the main beam and the two sub beam groups divided by the grating 102 are irradiated onto the disk so as to be aligned in the track direction. The rotation position of the grating 102 is adjusted so that the main beam and the two sub beam groups are arranged on the disk in this way.

  As shown in FIG. 2B, the photodetector 110 includes a main beam sensor 110a and sub beam sensors 110b and 110c. Each sensor has a region divided into four by two orthogonal straight lines. When the main beam is in an on-track state, each of the two sub-beam groups has sub-beam sensors 110b and 110c such that the optical axis of the zero-order light passes through the center points (intersections of the dividing lines) of the sub-beam sensors 110b and 110c. Is irradiated. At this time, the main beam is irradiated to the main beam sensor 110a so that its optical axis passes through the center point (intersection of the dividing lines) of the main beam sensor 110a.

  FIG. 4 shows a configuration of a signal generation circuit for generating a tracking error signal.

  As illustrated, the signal generation circuit includes arithmetic circuits 201 to 204, 206 and an amplifier circuit 205.

  The operational amplifier circuit 201 describes signals output from the sensor areas A to D of the main beam sensor 101a (hereinafter, each signal output from the sensor areas A, B, C, and D is described as A, B, C, and D). (A + B)-(C + D) signal calculation is executed based on the above, and the main push-pull signal MPP is generated.

  The operational amplifier circuit 202 describes signals output from the sensor areas E to H of the sub-beam sensor 101b (hereinafter, signals output from the sensor areas E, F, G, and H are referred to as E, F, G, and H). ), (E + F) − (G + H) signal calculation is executed, and the calculation result is input to the calculation circuit 204.

  The operational amplifier circuit 203 describes signals output from the sensor areas I to L of the sub-beam sensor 101c (hereinafter, signals output from the sensor areas I, J, K, and L are referred to as I, J, K, and L). ), A signal calculation of (I + J) − (K + L) is executed, and the calculation result is input to the calculation circuit 204.

  The arithmetic circuit 204 adds the arithmetic results input from the arithmetic circuits 202 and 203 to generate a sub push-pull signal SPP. The amplifier circuit 205 amplifies the side push-pull signal SPP generated by the arithmetic circuit 204 at a preset magnification.

  The arithmetic circuit 206 subtracts the signal generated by the amplifier circuit 205 from the main push-pull signal MPP generated by the arithmetic circuit 201 to generate a tracking error signal TE. The generated tracking error signal TE is input to a servo circuit (not shown).

  FIG. 5 shows a configuration of a signal generation circuit for generating a focus error signal.

  As illustrated, the signal generation circuit includes arithmetic circuits 211 to 214, 216 and an amplifier circuit 215.

  The operational amplification circuit 211 performs a signal calculation of (A + C) − (B + D) based on signals output from the sensor areas A to D of the main beam sensor 101a, and generates a main focus error signal MFE.

  The operational amplification circuit 212 performs signal computation of (E + G) − (F + H) based on signals output from the sensor areas E to H of the sub-beam sensor 101 b and inputs the computation result to the computation circuit 214. The operational amplifier circuit 213 performs signal computation of (I + K) − (J + L) based on the signals output from the sensor regions I to L of the sub-beam sensor 101 c and inputs the computation result to the computation circuit 214.

  The arithmetic circuit 214 adds the arithmetic results input from the arithmetic circuits 212 and 213 and generates a side focus error signal SFE. The amplifier circuit 215 amplifies the side focus error signal SFE generated by the arithmetic circuit 214 at a preset magnification.

  The arithmetic circuit 216 subtracts the signal generated by the amplifier circuit 215 from the main focus error signal MFE generated by the arithmetic circuit 211 to generate a focus error error signal FE. The generated focus error error signal FE is input to a servo circuit (not shown).

  Next, a design method of the grating 102 will be described with reference to FIG.

  As described above, the intensity ratio and interval between the 0th-order light and the ± 1st-order light constituting the sub-beam group can be adjusted by appropriately changing the phase structure shown in FIG. That is, between the two types of phase structures shown in FIG. 2 (a), between the phase of the laser light when passing through the phase structure of the shaded portion and the phase of the laser light when passing through the phase structure of the white portion By appropriately changing the phase difference based on these two types of phase structures, it is possible to adjust the intensity ratio between the zero-order light and the first-order light. Further, by appropriately changing the interval between the basic vectors (see FIG. 2A) based on these phase structures, the interval between the 0th order light and the 1st order light can be adjusted.

  FIG. 6 shows that the 0th order light and the 1st order light so that the sum of the push pull signal generated by the 0th order light and the push pull signal generated by the four ± 1st order lights is always zero regardless of the displacement of the sub beam group in the tracking direction. It is a figure which shows the example of a simulation when the intensity ratio and space | interval of a next light are adjusted.

  Note that the amplitude waveform shown in FIG. 6 shows the change of the push-pull signal when the sub-beam group (0th order light and 4 ± 1st order light) is displaced in the tracking direction, and the 0th order light and 4 ± 1st order light. Are individually displayed, and these are superimposed and displayed. In the figure, the horizontal axis represents the amount of displacement of the sub-beam group in the tracking direction, and the vertical axis represents the amplitude of the push-pull signal. The amplitude at the position “T” in the figure is the amplitude of the push-pull signal based on the 0th-order light and the four ± first-order lights when the 0th-order light is positioned at the center of the groove. When the sub-beam group is displaced from this position in the tracking direction, the push-pull signals based on the 0th order light and the four ± 1st order lights change as shown in FIG.

  FIG. 4A is a simulation example when the sub beam group is displaced in the tracking direction on a DVD-RAM (track pitch = 1.23 μm), and FIG. 4B shows the sub beam group. It is a simulation example when it is displaced in the tracking direction on DVD-R (track pitch = 0.74 μm). In the simulation example of FIG. 5B, the amplitude waveforms of the two inner ± first-order lights approaching the zero-order light overlap the amplitude waveforms of the two outer ± first-order lights.

In these simulation examples, among the four ± first-order lights, the interval in the tracking direction between the two ± first-order lights on the inner side approaching the zero-order light and the zero-order light is set to about 0.2 μm, An interval in the tracking direction between the two outer ± first-order lights and zero-order light is set to about 0.52 μm. The intensity ratio I ₀ / I _{± 1} between the 0th order light and the ± 1st order light is set to I ₀ / I _{± 1} ≈0.72.

  By adjusting the intensity ratio and interval between the 0th-order light and the 1st-order light in this way, the sum of the push-pull signals generated by the 0th-order light and the four ± 1st-order lights is, as shown, the sub-beam group in the tracking direction. Always zero regardless of displacement. Therefore, as shown in the figure, for example, a good push-pull signal (side push-pull signal) can be obtained even when dealing with different types of discs with different track pitches such as DVD-RAM and DVD-R. Can be generated.

In the present embodiment, as shown in FIG. 6, the phase structure of the grating 102 is such that the sum of the push-pull signals generated by the zero-order light and the four ± first-order lights is always zero regardless of the displacement of the sub-beam group in the tracking direction. It is set to become. Note that the amplitude characteristics shown in FIG. 6 are such that the phase structure of the diffraction grating has the following parameter values on the pupil of the objective lens when the wavelength λ = 660 nm and the focal length f = 2.5 mm of the objective lens, for example. It is realized when.

  Note that θa and θb are angles formed by the disctangential direction and basic vectors (unit vectors a and b) as shown in FIG. Here, θa and θb are values set by a rotational coordinate axis in which the rotational direction from the tangential direction to the left is positive in FIG.

  As described above, according to the present embodiment, the phase of the grating 102 is set so that the sum of the push-pull signals generated by the zero-order light and the four ± first-order lights is always zero regardless of the displacement of the sub-beam group in the tracking direction. Since the structure is set, the push-pull signal (side push-pull signal) can be transmitted smoothly and satisfactorily even when dealing with different types of discs with different track pitches, such as DVD-RAM and DVD-R. Can be generated.

  Further, according to the present embodiment, as shown in FIG. 2, since the phase structure is generated at a fine pitch, even if a lens shift occurs in the objective lens 108, the incident pupil is on the entrance pupil as compared with the case where there is no lens shift. Thus, the phase state of the laser beam at the laser beam does not change greatly, and hence the intensity of distortion in the beam spot on the disk does not occur. Therefore, according to the present embodiment, even if a lens shift occurs in the objective lens 108 during a tracking servo operation or the like, no unnecessary amplitude is generated in the push-pull signal (side push-pull signal) based on the sub beam group.

  Thus, according to the present embodiment, it is possible to generate a tracking error signal smoothly and satisfactorily based on the DPP method even when dealing with different types of disks.

  In addition, this invention is not limited to the said embodiment, In addition to the above, various changes are possible for embodiment concerning this invention.

  FIG. 7 shows an example when the phase structure of the grating 102 is changed.

  As shown in FIG. 5A, in this configuration example, two types of band-like phase structures are arranged on the grating 102 at a constant period. Similar to the case of FIG. 2A, a phase difference occurs in the laser beam after passing through the phase structure of the shaded portion and when passing through the phase structure of the white portion. Due to this phase difference, the laser beam is divided into a main beam and two sub beam groups. In the phase structure shown in FIG. 6A, the sub beam group is divided into three beams of 0th order light and ± 1st order light, as shown in FIG.

  Here, the intensity ratio of the ± first-order light and the zero-order light is determined by the phase difference when the laser light passes through the two types of phase structures as described above. When this phase difference is 180 degrees, the intensity of the 0th-order light becomes zero. That is, when the phase difference is 180 degrees, each of the two sub beam groups includes two ± first-order lights. Further, the interval between the ± first-order light and the zero-order light is inversely proportional to the interval between the basic vectors (solid lines) of the grating 102 shown in FIG. Therefore, by adjusting the interval between the phase difference due to the phase structure and the basic vector, it is possible to change the intensity ratio and interval between the 0th order light and the 1st order light constituting the sub beam group.

  Note that the intensity ratio and interval between the 0th-order light and the 1st-order light constituting the sub-beam group are given by the equation shown in Equation 1 above.

  FIG. 8 shows the irradiation state of the laser beam on the disk and the configuration of the photodetector 110.

  As shown in FIG. 5A, the main beam and the two sub beam groups divided by the grating 102 are irradiated onto the disk so as to be aligned in the track direction. The rotation position of the grating 102 is adjusted so that the main beam and the two sub beam groups are arranged on the disk in this way.

  As shown in FIG. 2B, the photodetector 110 includes a main beam sensor 110a and sub beam sensors 110b and 110c. The configuration of the photodetector 110 is the same as that in FIG. The configuration of the arithmetic circuit that generates the tracking error signal and the focus error signal is the same as that in the case of FIGS.

  FIG. 9 is a diagram for explaining a design method of the grating 102 in this configuration example.

  As described above, the intensity ratio and interval between the 0th order light and the ± 1st order light constituting the sub beam group can be adjusted by appropriately changing the phase structure shown in FIG.

  FIG. 9 shows that in this configuration example, the sum of the push-pull signal generated by the zero-order light and the push-pull signal generated by the two ± first-order lights is always zero regardless of the displacement of the sub-beam group in the tracking direction. It is a figure which shows the example of a simulation when the intensity ratio and space | interval of 0th-order light and primary light are adjusted.

  9, the amplitude waveform shown in FIG. 9 represents the change of the push-pull signal when the sub-beam group (zero order light and two ± first order lights) is displaced in the tracking direction, as in FIG. Two ± first-order lights are individually simulated and displayed in an overlapping manner. In the figure, the horizontal axis represents the amount of displacement of the sub-beam group in the tracking direction, and the vertical axis represents the amplitude of the push-pull signal. The amplitude at the position “T” in the figure is the amplitude of the push-pull signal based on the 0th-order light and the two ± 1st-order lights when the 0th-order light is positioned at the center of the groove. When the sub beam group is displaced from this position in the tracking direction, the push-pull signals based on the 0th order light and the two ± 1st order lights change as shown in FIG.

  FIG. 4A is a simulation example when the sub beam group is displaced in the tracking direction on a DVD-RAM (track pitch = 1.23 μm), and FIG. 4B shows the sub beam group. It is a simulation example when it is displaced in the tracking direction on DVD-R (track pitch = 0.74 μm).

In these simulation examples, the interval in the tracking direction between the two ± first-order lights and the zero-order light is set to about 0.46 μm. Further, the intensity ratio I ₀ / I _{± 1} between the 0th order light and the ± 1st order light is set to I ₀ / I _{± 1} ≈2.0.

  By adjusting the intensity ratio and the interval between the 0th-order light and the 1st-order light in this way, the sum of the push-pull signals generated by the 0th-order light and the two ± 1st-order lights can be obtained as shown in FIG. Always zero regardless of displacement. Therefore, as shown in the figure, for example, a good push-pull signal (side push-pull signal) can be obtained even when dealing with different types of discs with different track pitches such as DVD-RAM and DVD-R. Can be generated.

  In this configuration example, as shown in FIG. 9, the phase structure of the grating 102 is always zero regardless of the displacement of the sub-beam group in the tracking direction, as the sum of the push-pull signals generated by the zero-order light and the four ± first-order lights. It is set to be. Note that the amplitude characteristics shown in FIG. 9 are such that the phase structure of the diffraction grating has the following parameter values on the pupil of the objective lens when the wavelength λ = 660 nm and the focal length f = 2.5 mm of the objective lens, for example. It is realized when.

  Note that θa and θb are angles formed by the disctangential direction and basic vectors (unit vectors a and b) as shown in FIG. Here, θa and θb are values set by a rotational coordinate axis in which the rotational direction from the tangential direction to the left is positive in FIG. Further, in this configuration example, the phase structure has a band shape, and there is no periodicity of the phase structure in the direction of the basic vector b, so that the unit vector b is assumed to be b = ∞.

  According to this configuration, the phase structure of the grating 102 is set so that the sum of the push-pull signals generated by the zero-order light and the two ± first-order lights is always zero regardless of the displacement of the sub-beam group in the tracking direction. As in the case of FIG. 2, the push-pull signal (side push) can be smoothly and satisfactorily applied to different types of discs with different track pitches, such as DVD-RAM and DVD-R. Pull signal) can be generated.

  Further, according to the present configuration example, as shown in FIG. 7, since the phase structure is generated at a fine pitch, even when a lens shift occurs in the objective lens 108, compared with the case where there is no lens shift, the incident lens 108 is on the entrance pupil. The phase state of the laser beam does not change greatly, and therefore, no distortion in intensity occurs in the beam spot on the disk. Therefore, according to this configuration example, even if a lens shift occurs in the objective lens 108 during a tracking servo operation or the like, no unnecessary amplitude is generated in the push-pull signal (side push-pull signal) based on the sub beam group.

  As described above, according to the present configuration example, the tracking error signal can be generated smoothly and satisfactorily based on the DPP method even when dealing with different types of discs as in the case of the above embodiment. it can.

  Note that the simulation example of FIG. 6 is a case where the sub-beam group is configured by 0th order light and four ± 1st order lights in the grating 102 shown in FIG. 2, but as shown in FIG. The sub-beam group can also be configured with four ± first-order lights.

  As described above, the intensity ratio between ± 1st order light and 0th order light is determined by the phase difference when the laser light passes through the two types of phase structures shown in FIG. 2, and when this phase difference is 180 degrees, The intensity of the 0th order light becomes zero. That is, when the phase difference is 180 degrees, the two sub-beam groups are composed of four ± first-order lights as shown in FIG.

  In the case shown in FIG. 10, as in the simulation example shown in FIG. 6, the grating is set so that the sum of the push-pull signals generated by the four ± first-order lights is always zero regardless of the displacement of the sub beam group in the tracking direction. 102 phase structures (interval between phase difference and basic vector) are set. Thus, as in the case of FIG. 2 described above, the push-pull signal (smoothly and satisfactorily, for example, in the case of dealing with different types of discs with different track pitches such as DVD-RAM and DVD-R. Side push-pull signal).

  FIG. 11 is a modification example of the sensor pattern and the signal generation circuit of the photodetector 110.

  In this configuration example, the sub-beam sensors 110b and 110c are configured by two-divided sensors. When the main beam is in an on-track state, the two sub-beam groups are irradiated to the sub-beam sensors 110b and 110c so that the optical axis of the zero-order light passes through the center point of the dividing line of the sub-beam sensors 110b and 110c, respectively. The

  In the signal generation circuit, the arithmetic circuits 207 and 208 are changed in accordance with the change of the sub-beam sensors 110b and 110c. Other circuit configurations are the same as those in FIG.

  The operational amplifier circuit 207 performs E-F signal calculation based on signals output from the sensor regions E and F of the sub-beam sensor 101 b and inputs the calculation result to the calculation circuit 204. The operational amplifier circuit 208 performs GH signal computation based on the signals output from the sensor regions G and H of the sub-beam sensor 101 c and inputs the computation result to the computation circuit 204.

  The arithmetic circuit 204 adds the arithmetic results input from the arithmetic circuits 202 and 203 to generate a sub push-pull signal SPP. The amplifier circuit 205 amplifies the side push-pull signal SPP generated by the arithmetic circuit 204 at a preset magnification.

  The arithmetic circuit 206 subtracts the signal generated by the amplifier circuit 205 from the main push-pull signal MPP generated by the arithmetic circuit 201 to generate a tracking error signal TE. The generated tracking error signal TE is input to a servo circuit (not shown).

  FIG. 12 is a diagram illustrating a modification example of the optical system of the optical pickup device.

  This optical system is divided into two types: an optical system for irradiating laser light of infrared / red wavelengths to CD / DVD, and an optical system for irradiating laser light of blue wavelengths to next-generation DVDs. It has an optical system.

  The optical system for the next-generation DVD includes a semiconductor laser 301, a λ / 2 plate 302, a polarization beam splitter 303, a rising mirror 304, a collimator lens 305, a λ / 4 plate 306, an objective lens 307, An anamorphic lens 308, a photodetector 309, and an FMD 310 are provided.

  The semiconductor laser 301 emits blue laser light having a wavelength of about 400 nm. The λ / 2 plate 302 is used for adjusting the polarization direction of the laser light with respect to the polarization beam splitter 303. That is, the position of the λ / 2 plate 302 is adjusted so that the ratio of transmission and reflection of the laser beam to the polarization beam splitter 303 becomes a constant value.

  The polarization beam splitter 303 transmits and reflects the laser light from the λ / 2 plate 302 at a constant rate. The raising mirror 304 raises the laser beam transmitted through the polarization beam splitter 303 in the direction of the objective lens 307. The collimating lens 305 converts the laser light from the rising mirror 304 into parallel light.

  The λ / 4 plate 306 converts the laser light from the collimating lens 305 into circularly polarized light, and converts the reflected light from the disk into linearly polarized light orthogonal to the polarization direction of the laser light incident from the collimating lens 305 side. The objective lens 307 converges the laser light from the λ / 4 plate 306 on the disk. The anamorphic lens 308 converges the reflected light from the disk reflected by the polarization beam splitter 303 on the photodetector 309. The anamorphic lens 308 includes a condenser lens and a cylindrical lens, and introduces astigmatism into the reflected light from the disk.

  The photodetector 309 has a sensor pattern for deriving a reproduction RF signal, a focus error signal, and a tracking error signal from the intensity distribution of the received laser beam. A signal from each sensor is output to the reproduction circuit and the servo circuit on the optical disk apparatus side. The FMD 310 receives the laser beam reflected by the polarization beam splitter 303 and outputs a signal corresponding to the amount of received light. A signal from the FMD 310 is used for power control of the semiconductor laser 301.

  In the next-generation DVD optical system, a one-beam push-pull method is used as a tracking error signal generation method. The sensor pattern of the photodetector 310 and the configuration of the arithmetic circuit for generating the tracking error signal are in accordance with the one-beam push-pull method.

  The optical system for CD / DVD includes a semiconductor laser 321, a grating 322 with a λ / 4 plate, a half mirror 323, a rising mirror 324, a collimator lens 325, an objective lens 326, and a photodetector 327. ing.

  The semiconductor laser 321 emits infrared laser light having a wavelength of about 780 nm and red laser light having a wavelength of about 450 nm in the same direction with a certain gap.

  The grating 322 with a λ / 4 plate is a combination of the λ / 4 plate that converts laser light of each wavelength into circularly polarized light and the grating described in the above embodiment. Laser light of each wavelength is converted into circularly polarized light by passing through the λ / 4 plate of the λ / 4 plate and the grating, and is divided into a main beam and two sub beam groups by passing through the grating. . As described above, the two sub-beam groups are each composed of zero-order light and ± first-order light.

  The half mirror 323 raises half of the laser light from the grating 322 with a λ / 4 plate and reflects it in the direction of the rising mirror 324. The raising mirror 324 raises the laser light from the half mirror 323 toward the objective lens 326. The collimating lens 325 converts the laser light from the rising mirror 324 into parallel light. The objective lens 326 converges the laser light from the collimating lens 325 on the disk.

  The reflected light from the disk travels backward along the optical path when the disk is incident, and half of the light passes through the half mirror 323. At this time, since the half mirror 323 is arranged in an inclined state with respect to the optical axis of the reflected light, astigmatism is introduced into the reflected light by the half mirror 323. The reflected light into which the astigmatism is introduced enters the photodetector 327.

  The photodetector 327 has a sensor pattern for deriving a reproduction RF signal, a focus error signal, and a tracking error signal from the intensity distribution of the received laser beam. The photodetector 327 is individually provided with a sensor pattern for receiving the CD laser beam and the DVD laser beam. A signal from each sensor is output to the reproduction circuit and the servo circuit on the optical disk apparatus side.

  The grating of the λ / 4 plate-equipped grating 322 has, for example, a phase structure so that only the DVD laser light out of the CD laser light and the DVD laser light has the amplitude characteristics shown in FIG. Is configured. When the amplitude characteristics shown in FIG. 6 or 9 are applied not only to the DVD laser beam but also to the CD laser beam, the phase structure having a wavelength selectivity corresponding to the wavelength band of the DVD laser beam is used. And a wavelength-selective phase structure corresponding to the wavelength band of the laser beam for CD may be arranged in the grating.

  In the configuration example shown in FIG. 12, the one-beam push-pull method is applied as a tracking error signal generation method to the optical system of the next-generation DVD laser light. When the DPP method is applied also to the optical system, for example, the grating shown in FIG. 2 or FIG. 7 may be arranged between the semiconductor laser 301 and the λ / 2 plate 302.

  As mentioned above, although various embodiments of the present invention have been illustrated and described, the present invention is not limited to these embodiments. The embodiments of the present invention can be appropriately modified in various ways within the scope of the technical idea shown in the claims.

The figure which shows the optical system of the optical pick-up apparatus which concerns on embodiment The figure explaining the structure of the grating which concerns on embodiment The figure which shows the irradiation state of the sub beam group which concerns on embodiment, and the structure of a photodetector The figure which shows the structure of the signal generation circuit which concerns on embodiment The figure which shows the structure of the signal generation circuit which concerns on embodiment The figure explaining the setting method of the phase structure of the grating concerning an embodiment The figure explaining the setting method of the phase structure of the grating concerning an embodiment The figure explaining the structure of the grating which concerns on the example of a change of embodiment The figure explaining the setting method of the phase structure of the grating which concerns on the example of a change of embodiment The figure explaining the structure of the grating which concerns on the example of a change of embodiment The figure which shows the structure of the photodetector and signal generation circuit which concern on the example of a change of embodiment The figure which shows the optical system of the optical pick-up apparatus which concerns on the example of a change of embodiment Diagram explaining the problems of the conventional example

Explanation of symbols

101 Semiconductor laser (light source)
102 Grating 110 Photodetector 110a Main beam sensor 110b Sub beam sensor 110c Sub beam sensor 321 Semiconductor laser (light source)
322 grating with λ / 4 plate 327 photodetector

Claims (6)

A light source that emits laser light, the laser light is divided into a main beam and a sub beam, the sub beam is divided into a plurality of diffracted lights, and a rotational direction position about the optical axis of the laser light of the grating is defined. By adjusting, a grating having a phase structure configured such that the sum of the signal components of the side push-pull signal based on each split light becomes zero, and the reflected light from the disk of the main beam and the sub beam are received. And in an optical pickup device comprising a main push-pull signal according to the intensity of the main beam and sub beam and a photodetector having a sensor pattern for generating a side push pull,
In the grating, two types of phase structures that cause a phase difference in the laser beam are alternately arranged at a constant period, and these two types of phase structures adjust the position of the grating in the rotational direction. By doing so, the interval between the phase difference and the basic vector is set so that the sum of the signal components of the side push-pull signal based on each split light becomes zero.
An optical pickup device characterized by that. In claim 1 ,
In the grating, two types of phase structures of rhombus are arranged so as to be alternately arranged at a constant period,
An optical pickup device characterized by that. In claim 2 ,
A phase difference based on the two types of phase structures is set so that the sub-beam is composed of zero-order light and four ± first-order lights.
An optical pickup device characterized by that. In claim 2 ,
A phase difference based on the two types of phase structures is set so that the sub-beam is composed of four ± first-order lights.
An optical pickup device characterized by that. In claim 1 ,
In the grating, two kinds of phase structures in the form of strips are arranged so as to be alternately arranged at a constant period.
An optical pickup device characterized by that. In claim 5 ,
A phase difference based on the two types of phase structures is set so that the sub-beam is composed of zero-order light and two ± first-order lights.
An optical pickup device characterized by that.

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